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arts / rec.arts.sf.written / Hard science question: How do G forces work???

SubjectAuthor
* Hard science question: How do G forces work???David Brown
+* Re: Hard science question: How do G forces work???Michael F. Stemper
|+- Re: Hard science question: How do G forces work???Quadibloc
|+* Re: Hard science question: How do G forces work???peterwezeman@hotmail.com
||+- Re: Hard science question: How do G forces work???Quadibloc
||`* Re: Hard science question: How do G forces work???Hamish Laws
|| +* Re: Hard science question: How do G forces work???Jibini Kula Tumbili Kujisalimisha
|| |`* Re: Hard science question: How do G forces work???peterwezeman@hotmail.com
|| | +* Re: Hard science question: How do G forces work???Dimensional Traveler
|| | |`- Re: Hard science question: How do G forces work???peterwezeman@hotmail.com
|| | `- Re: Hard science question: How do G forces work???Ninapenda Jibini
|| `- Re: Hard science question: How do G forces work???Gary R. Schmidt
|`* Re: Hard science question: How do G forces work???David Brown
| +* Re: Hard science question: How do G forces work???James Nicoll
| |+- Re: Hard science question: How do G forces work???Wolffan
| |`* Re: Hard science question: How do G forces work???David Johnston
| | `- Re: Hard science question: How do G forces work???Quadibloc
| +- Re: Hard science question: How do G forces work???Alan
| +* Re: Hard science question: How do G forces work???peterwezeman@hotmail.com
| |+- Re: Hard science question: How do G forces work???Quadibloc
| |+* Re: Hard science question: How do G forces work???rkshullat
| ||`* Re: Hard science question: How do G forces work???Lynn McGuire
| || +* Re: Hard science question: How do G forces work???Michael F. Stemper
| || |`* Re: Hard science question: How do G forces work???Lynn McGuire
| || | +- Re: Hard science question: How do G forces work???Wolffan
| || | +* Re: Hard science question: How do G forces work???Hamish Laws
| || | |+* Re: Hard science question: How do G forces work???Quadibloc
| || | ||`* Re: Hard science question: How do G forces work???Lynn McGuire
| || | || `* Re: Hard science question: How do G forces work???Quadibloc
| || | ||  `- Re: Hard science question: How do G forces work???Lynn McGuire
| || | |`* Re: Hard science question: How do G forces work???Lynn McGuire
| || | | `- Re: Hard science question: How do G forces work???Hamish Laws
| || | +* Re: Hard science question: How do G forces work???Paul S Person
| || | |`* Re: Hard science question: How do G forces work???Lynn McGuire
| || | | `* Re: Hard science question: How do G forces work???Hamish Laws
| || | |  `* Re: Hard science question: How do G forces work???Lynn McGuire
| || | |   `* Re: Hard science question: How do G forces work???Thomas Koenig
| || | |    +* Re: Hard science question: How do G forces work???Paul S Person
| || | |    |+* Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    ||`* Re: Hard science question: How do G forces work???Thomas Koenig
| || | |    || +* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    || |`- Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    || `* Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    ||  `* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||   +* Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    ||   |`* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||   | `- Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    ||   `* Re: Hard science question: How do G forces work???Thomas Koenig
| || | |    ||    +- Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||    `* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||     +* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||     |`* Re: Hard science question: How do G forces work???Dimensional Traveler
| || | |    ||     | +- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||     | +* Re: Hard science question: How do G forces work???Kevrob
| || | |    ||     | |`- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||     | +* Re: Hard science question: How do G forces work???Thomas Koenig
| || | |    ||     | |+- Re: Hard science question: How do G forces work???Ninapenda Jibini
| || | |    ||     | |`* Re: Hard science question: How do G forces work???Dimensional Traveler
| || | |    ||     | | `* Re: Hard science question: How do G forces work???David Brown
| || | |    ||     | |  `* Re: Hard science question: How do G forces work???Ninapenda Jibini
| || | |    ||     | |   `* Re: Hard science question: How do G forces work???David Brown
| || | |    ||     | |    +- Re: Hard science question: How do G forces work???Jibini Kula Tumbili Kujisalimisha
| || | |    ||     | |    `- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||     | `- Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    ||     `* Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    ||      +* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||      |`* Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    ||      | `- Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||      `* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       +* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       |`* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | +* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | |+* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       | ||+* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | |||`- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||+- Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||       | ||+* Re: Hard science question: How do G forces work???Titus G
| || | |    ||       | |||`- Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       | ||+* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | |||`* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | ||| `* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       | |||  `- Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | ||`* Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    ||       | || `* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||  `* Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||       | ||   +* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | ||   |`* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||   | `* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | ||   |  +- Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||       | ||   |  `* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||   |   `* Re: Hard science question: How do G forces work???Scott Lurndal
| || | |    ||       | ||   |    `- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||   `* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       | ||    +- Re: Hard science question: How do G forces work???Titus G
| || | |    ||       | ||    +- Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||       | ||    +* Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||    |+* Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    ||       | ||    ||`- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||    |+* Re: Hard science question: How do G forces work???Michael F. Stemper
| || | |    ||       | ||    ||`- Re: Hard science question: How do G forces work???Paul S Person
| || | |    ||       | ||    |`* Re: Hard science question: How do G forces work???pete...@gmail.com
| || | |    ||       | ||    `* Re: Hard science question: How do G forces work???rkshullat
| || | |    ||       | |`* Let's Keep the Dimensions Straight (was Re: Hard science question: How do G forcRobert Woodward
| || | |    ||       | `- Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    ||       `- Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | |    |`* Re: Hard science question: How do G forces work???Thomas Koenig
| || | |    +- Re: Hard science question: How do G forces work???Lynn McGuire
| || | |    `* Re: Hard science question: How do G forces work???Dorothy J Heydt
| || | `* Re: Hard science question: How do G forces work???Quadibloc
| || +* Re: Hard science question: How do G forces work???rkshullat
| || `* Re: Hard science question: How do G forces work???Dorothy J Heydt
| |`* Re: Hard science question: How do G forces work???William Hyde
| `- Re: Hard science question: How do G forces work???Wolffan
+- Re: Hard science question: How do G forces work???Alan
+* Re: Hard science question: How do G forces work???Wolffan
+* Re: Hard science question: How do G forces work???pyotr filipivich
`- Re: Hard science question: How do G forces work???Lynn McGuire

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Hard science question: How do G forces work???

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Subject: Hard science question: How do G forces work???
From: davidnbr...@gmail.com (David Brown)
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 by: David Brown - Wed, 9 Nov 2022 16:21 UTC

Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???

David N. Brown
Mesa, Arizona

Re: Hard science question: How do G forces work???

<tkgl89$8vn9$1@dont-email.me>

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From: michael....@gmail.com (Michael F. Stemper)
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Subject: Re: Hard science question: How do G forces work???
Date: Wed, 9 Nov 2022 10:41:45 -0600
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 by: Michael F. Stemper - Wed, 9 Nov 2022 16:41 UTC

On 09/11/2022 10.21, David Brown wrote:
> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???

If you're going to try to do hard science, you need to start by understanding
units of measure. One accelerates to a velocity (speed). You have your ship
accelerating to a distance -- 250000 miles. That means that after it has gone
that far it stops accelerating.

I think that you probably want it to accelerate up to some speed, such as:
- 250000 miles/year
- 250000 miles/month
- 250000 miles/day
- 250000 miles/hour
Something like one of those.

For instance, let's take a look at your car example. When you discuss a car
accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
two speeds. That change in speed, if spread out evenly over a ten-second
interval, would not be one mile per second (as you stated), but six miles per
hour per second.

I think that you need to sit down with pencil and paper and work through all
of this, making the units explicit throughout your work.

Getting to your last question, the units are correct here (although I have
no idea whether it's consistent with anything that went before).

5040 miles per hour per day works out to 210 miles per hour per hour, which
means that over a period of one hour, you've sped up by 210 miles per hour.
If you think about it, a commercial airliner speeds up from stopped on the
tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
or so, which is an acceleration of about 3000 miles per hour per hour, or
much greater than what is mentioned here.

By the way, this would be much less subject to error if you did your work
exclusively in meters and seconds.

--
Michael F. Stemper
Economists have correctly predicted seven of the last three recessions.

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
From: jsav...@ecn.ab.ca (Quadibloc)
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 by: Quadibloc - Wed, 9 Nov 2022 18:44 UTC

On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:

> For instance, let's take a look at your car example. When you discuss a car
> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> two speeds. That change in speed, if spread out evenly over a ten-second
> interval, would not be one mile per second (as you stated), but six miles per
> hour per second.

Making use of this important insight about keeping units straight, let's take
the next step, and perform the arithmetic:

A mile is 5280 feet.
An hour is 3600 seconds.
One gravity is approximately 32 feet per second squared.

Six miles per hour per second is, therefore, (6 * 5280 / 3600) feet per second squared,
which is 8.8 feet per second squared. That is a bit over 1/4 g, not 10g.

Thus, you don't need to be fit enough to be an astronaut in order to drive a car.

John Savard

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
From: peterwez...@hotmail.com (peterwezeman@hotmail.com)
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 by: peterwezeman@hotmail - Wed, 9 Nov 2022 19:35 UTC

On Wednesday, November 9, 2022 at 10:41:50 AM UTC-6, Michael F. Stemper wrote:
> On 09/11/2022 10.21, David Brown wrote:
> > Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
> If you're going to try to do hard science, you need to start by understanding
> units of measure. One accelerates to a velocity (speed). You have your ship
> accelerating to a distance -- 250000 miles. That means that after it has gone
> that far it stops accelerating.
>
> I think that you probably want it to accelerate up to some speed, such as:
> - 250000 miles/year
> - 250000 miles/month
> - 250000 miles/day
> - 250000 miles/hour
> Something like one of those.
>
> For instance, let's take a look at your car example. When you discuss a car
> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> two speeds. That change in speed, if spread out evenly over a ten-second
> interval, would not be one mile per second (as you stated), but six miles per
> hour per second.
>
> I think that you need to sit down with pencil and paper and work through all
> of this, making the units explicit throughout your work.
>
> Getting to your last question, the units are correct here (although I have
> no idea whether it's consistent with anything that went before).
>
> 5040 miles per hour per day works out to 210 miles per hour per hour, which
> means that over a period of one hour, you've sped up by 210 miles per hour.
> If you think about it, a commercial airliner speeds up from stopped on the
> tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
> or so, which is an acceleration of about 3000 miles per hour per hour, or
> much greater than what is mentioned here.
>
> By the way, this would be much less subject to error if you did your work
> exclusively in meters and seconds.

This reminds me of a story. Someone bought a high-performance Italian
sports car, and was showing it to her friend, another enthusiast, for the
first time. After riding as a passenger over some challenging roads it
was his turn to drive. Taking the driver's seat, he listened attentively to
her pointers. Before they started off she said, "And remember, the
speedometer is calibrated in metric units."

He let in the clutch and accelerated cautiously to 60, getting the feel of
the car. After a short time he asked, "Have you checked the speedometer
with a stopwatch? I've driven in Europe, and it sure seems to me that
we're going faster than sixty kilometers per hour."

She replied, "We are. That's meters per second."

Peter Wezeman
anti-social Darwinist

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
From: davidnbr...@gmail.com (David Brown)
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 by: David Brown - Wed, 9 Nov 2022 20:21 UTC

On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
> On 09/11/2022 10.21, David Brown wrote:
> > Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
> If you're going to try to do hard science, you need to start by understanding
> units of measure. One accelerates to a velocity (speed). You have your ship
> accelerating to a distance -- 250000 miles. That means that after it has gone
> that far it stops accelerating.
>
> I think that you probably want it to accelerate up to some speed, such as:
> - 250000 miles/year
> - 250000 miles/month
> - 250000 miles/day
> - 250000 miles/hour
> Something like one of those.
>
> For instance, let's take a look at your car example. When you discuss a car
> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> two speeds. That change in speed, if spread out evenly over a ten-second
> interval, would not be one mile per second (as you stated), but six miles per
> hour per second.
>
> I think that you need to sit down with pencil and paper and work through all
> of this, making the units explicit throughout your work.
>
> Getting to your last question, the units are correct here (although I have
> no idea whether it's consistent with anything that went before).
>
> 5040 miles per hour per day works out to 210 miles per hour per hour, which
> means that over a period of one hour, you've sped up by 210 miles per hour.
> If you think about it, a commercial airliner speeds up from stopped on the
> tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
> or so, which is an acceleration of about 3000 miles per hour per hour, or
> much greater than what is mentioned here.
>
> By the way, this would be much less subject to error if you did your work
> exclusively in meters and seconds.
>
> --
> Michael F. Stemper
> Economists have correctly predicted seven of the last three recessions.
Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
Date: Wed, 9 Nov 2022 21:00:23 -0000 (UTC)
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 by: James Nicoll - Wed, 9 Nov 2022 21:00 UTC

In article <6b70c77f-74e0-4315-9fb2-db8bbb37205cn@googlegroups.com>,
David Brown <davidnbrown80@gmail.com> wrote:
>Thanks for this. For further context, my core parameters are a
>ship that could make a trip from Mars to Neptune in 20 months,
>assuming the former to be partly colonized by the late 20th/
>early 21st century.

These target dates are very ambitious.

> I would assume I'm missing something
>about how horizontal acceleration converts to normally vertical
>gravitational force, but I'm not sure what the details would be.

I say this supportively: your issue with units and the phrasing
above suggest you need to have a look at the very basics of
physics. Atomic Rockets may be useful:

http://www.projectrho.com/public_html/rocket/index.php

In the old days, there were primers like Clarke's Interplanetary
Flight. Not sure what the modern analogs are.
--
My reviews can be found at http://jamesdavisnicoll.com/
My tor pieces at https://www.tor.com/author/james-davis-nicoll/
My Dreamwidth at https://james-davis-nicoll.dreamwidth.org/
My patreon is at https://www.patreon.com/jamesdnicoll

Re: Hard science question: How do G forces work???

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From: nuh...@nope.com (Alan)
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Subject: Re: Hard science question: How do G forces work???
Date: Wed, 9 Nov 2022 15:05:23 -0800
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 by: Alan - Wed, 9 Nov 2022 23:05 UTC

On 2022-11-09 08:21, David Brown wrote:
> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???

What you're missing is basic understanding that 15 minutes of searching
the web cold have given you.

If you want to have a sensible conversation about anything, you need to
start by agree on terminology.

Distances can be measured in miles.

Speeds in miles per something (e.e miles per hour)

Accelerations in miles per something per something

Nothing can accelerate to a distance, so I'm assuming you meant "250,000
miles" as a velocity, but 250,000 per WHAT?

Second, 0-60 miles per hour in 10 seconds means an average acceleration
of SIX miles per hour per second, not 1 mile per second.

So in 24 hours, that acceleration would take it to 518,400 miles per hour.

5040 miles per hour per day is an acceleration of only 0.0583... miles
per hour per second.

Acceleration due to gravity (1g) is 9.8 metres per second per second.

9.8 meters per second is 21.77... miles per hour per second, or a little
more than double the acceleration of a car that goes from 0-60mph in 10
seconds.

Re: Hard science question: How do G forces work???

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 by: Alan - Wed, 9 Nov 2022 23:07 UTC

On 2022-11-09 12:21, David Brown wrote:
> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
>> On 09/11/2022 10.21, David Brown wrote:
>>> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>> If you're going to try to do hard science, you need to start by understanding
>> units of measure. One accelerates to a velocity (speed). You have your ship
>> accelerating to a distance -- 250000 miles. That means that after it has gone
>> that far it stops accelerating.
>>
>> I think that you probably want it to accelerate up to some speed, such as:
>> - 250000 miles/year
>> - 250000 miles/month
>> - 250000 miles/day
>> - 250000 miles/hour
>> Something like one of those.
>>
>> For instance, let's take a look at your car example. When you discuss a car
>> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
>> two speeds. That change in speed, if spread out evenly over a ten-second
>> interval, would not be one mile per second (as you stated), but six miles per
>> hour per second.
>>
>> I think that you need to sit down with pencil and paper and work through all
>> of this, making the units explicit throughout your work.
>>
>> Getting to your last question, the units are correct here (although I have
>> no idea whether it's consistent with anything that went before).
>>
>> 5040 miles per hour per day works out to 210 miles per hour per hour, which
>> means that over a period of one hour, you've sped up by 210 miles per hour.
>> If you think about it, a commercial airliner speeds up from stopped on the
>> tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
>> or so, which is an acceleration of about 3000 miles per hour per hour, or
>> much greater than what is mentioned here.
>>
>> By the way, this would be much less subject to error if you did your work
>> exclusively in meters and seconds.
>>
>> --
>> Michael F. Stemper
>> Economists have correctly predicted seven of the last three recessions.
> Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.

You're missing basic understanding of the linked concepts of distance,
time, velocity and acceleration.

Re: Hard science question: How do G forces work???

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 by: peterwezeman@hotmail - Wed, 9 Nov 2022 23:16 UTC

On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
> > On 09/11/2022 10.21, David Brown wrote:
> > > Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
> > If you're going to try to do hard science, you need to start by understanding
> > units of measure. One accelerates to a velocity (speed). You have your ship
> > accelerating to a distance -- 250000 miles. That means that after it has gone
> > that far it stops accelerating.
> >
> > I think that you probably want it to accelerate up to some speed, such as:
> > - 250000 miles/year
> > - 250000 miles/month
> > - 250000 miles/day
> > - 250000 miles/hour
> > Something like one of those.
> >
> > For instance, let's take a look at your car example. When you discuss a car
> > accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> > two speeds. That change in speed, if spread out evenly over a ten-second
> > interval, would not be one mile per second (as you stated), but six miles per
> > hour per second.
> >
> > I think that you need to sit down with pencil and paper and work through all
> > of this, making the units explicit throughout your work.
> >
> > Getting to your last question, the units are correct here (although I have
> > no idea whether it's consistent with anything that went before).
> >
> > 5040 miles per hour per day works out to 210 miles per hour per hour, which
> > means that over a period of one hour, you've sped up by 210 miles per hour.
> > If you think about it, a commercial airliner speeds up from stopped on the
> > tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
> > or so, which is an acceleration of about 3000 miles per hour per hour, or
> > much greater than what is mentioned here.
> >
> > By the way, this would be much less subject to error if you did your work
> > exclusively in meters and seconds.
> >
> > --
> > Michael F. Stemper
> > Economists have correctly predicted seven of the last three recessions.
> Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.

I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.

One possible source of confusion is that horizontal speeds are often given in miles per hour or kilometers
hour whereas accelerations are given in feet per second per second or meters per second per second.
As Michael Stemper suggests, try keeping the units consistent.

Peter Wezeman
anti-social Darwinist

Re: Hard science question: How do G forces work???

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 by: Wolffan - Wed, 9 Nov 2022 23:21 UTC

On 09 Nov 2022, David Brown wrote
(in article<d672798f-3b06-4d93-b740-3ee7981aba17n@googlegroups.com>):

> Here's something I've been working on for a retro future project with hard
> sci fi elements. It calls for a gigantic 300+ meter ship

that’s aircraft carrier size. I hope that you’re starting from orbit, or
there’s likely to be a problem.

Also, that’s one dimension. What shape is it? It’s one thing if it’s a
300 metre long cylinder, with a diameter of, oh, 30 metres. It’s something
else if it’s a 30-metre thick disk with a diameter of 300 metres. It’s a
whole other thing if it’s a 300-metre radius sphere.
> to accelerate to
> 250,000 miles

250,000 miles per what?
> for a trip to the outer solar system, which I arm waved to
> maybe +12,000 miles of acceleration per day.

you don’t do acceleration in miles per day. Personally, I work best in SI
units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
thing. The acceleration due to gravity, one gee, is approximately 9.81 metres
per second per second. (that last ‘per second’ is kind of important) One
gee is a rather significant acceleration. I usually just round up to a nice
even 10 m/s/s, it’s easier to work with.

Some basic concepts:

delta-vee is the total mission change in velocity. It’s rather significant.

the mission delta-vee for a rocket-propelled vehicle is equal to the rocket's
exhaust velocity times the natural log of the mass ratio, where the mass
ratio is the total mass of rocket, payload, reaction mass, and everything
else at the start of the flight (m1) divided my the mass of whatever is left
at the end of the flight (m2). Note that that’s for the _total_ mission,
you usually need to get there and back.

v = u + at. That is, the final velocity equals the intial velocity plus the
acceleration times the time spent under acceleration.

s = ut + 0.5at^2. That is, the displacement equals the inital velocity times
the time under acceleration plus half the acceleration times the square of
the time.

So let’s do an example: we want to go to the Moon. We want to do it at one
gee continuous accel. We want to get back.

So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See below)

Ok... problem. We need to arrive at the Moon with velocity of zero relative
to the Moon. We need to get back to Earth, or at least Earth orbit, with
velocity zero. (well, we have to make lunar orbit and Earth orbit, but we can
worry about that later.) This means that we can’t just boost all the way,
we must boost half way, turn around, slow down. We must do this twice to make
the round trip. As we need to fiddle around a little, let’s say that it’s
400,000 km to the Moon. Our total displacement is now 800,000 km.

Ok, so the displacement we have to calculate is one quarter of 800,000 km, or
200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8 m.

We simplify where possible, and set u to zero. As will be seen later, actual
values of u won’t make much difference.

So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.

Now, a =10. (keep things simple...) which means that

10t^2 = 4 x 10^8

so... t^2 = 4 x 10 ^7.

hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes, 1.76
hours) approximately. Hmm, We must do this four times (once accel going to
the Moon, once delec to zero, once accel going back to Earth, once decel to
zero) so that’s 25300 seconds, approximately.

hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
delta vee is... 253,000 metres per second, 253 km/s. So... how much reaction
mass are you going to need? delta-vee = ve x ln mr. The best chemical rockets
have a ve on the order of 4 km/s. The natural log of the mass ratio is going
to be... 63.25. You’re gonna need a who lot of go-juice. And now you know
why NASA didn’t try to use continuous accel in the Apollo moonships. Either
you’re going to need something hotter than a chemical rocket, or you
can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
ve... that at least gives a managable mr. Still not good, though. You need
better. Fusion rockets would be a lot better. Photon rockets would be nice.
Neither one is likely to be available for the near future, if at all.
You’re gonna need to think carefully about what kind of trajectories you
want to use, continuous accel is off the table. It’d be nice; 3.5 hours to
the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at most,
for anywhere in the system... Not happening without magic tech.

Jerry Pournelle went into great detail about this kind of thing in his A Step
Further Out columns in Galaxy, some of which were collected into a nice big
paperback. Look it up.
> Here's the weird thing. Regular
> terrestrial cars can accelerate 0-60

that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
Moon. That’s 4000 hours, assuming that the car could achieve escape
velocity, which it can’t. (it’s worse than that, you have to flip and
decel, so it’s gonna take longer)
> in 10 seconds without even being
> considered that fast, which comes out at 1 mile per second

one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
could hit 2000 to 2400 mph before atmospheric friction would heat it up and
destroy it.
> . That means if all
> conventional limitations were removed (friction, cooling, controllability,
> fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours

nope.
> . The
> monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or
> 21 miles per hour,

no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
second. At the end of the first second, that’s 10 metres per second, 36000
metres per hour, a.k.a. 360 km/s. At the end of the second second, that’s
20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> and people aren't supposed to be able survive 10 G of
> acceleration for more than a few seconds.

it ain’t the people you should be concerned about, it’s the structure of
your vehicle. Very few vehicles can take 10 gees.
> Therefore, a manned vehicle
> accelerating at +5040 miles per hour every 24 hours would already kill the
> crew many times over. What am I missing here???

yes. You accel at, say, 1 gee, and you get to anywhere in the system in under
a month and a half. One gee. You’re mixing up velocity and acceleration.

May I suggest a basic course on statics and dynamics?
>
>
> David N. Brown
> Mesa, Arizona

Re: Hard science question: How do G forces work???

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 by: Wolffan - Wed, 9 Nov 2022 23:34 UTC

On 09 Nov 2022, David Brown wrote
(in article<6b70c77f-74e0-4315-9fb2-db8bbb37205cn@googlegroups.com>):

> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
> > On 09/11/2022 10.21, David Brown wrote:
> > > Here's something I've been working on for a retro future project with hard
> > > sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to
> > > 250,000 miles for a trip to the outer solar system, which I arm waved to
> > > maybe +12,000 miles of acceleration per day. Here's the weird thing.
> > > Regular terrestrial cars can accelerate 0-60 in 10 seconds without even
> > > being considered that fast, which comes out at 1 mile per second. That
> > > means if all conventional limitations were removed (friction, cooling,
> > > controllability, fuel supply, etc), the car could accelerate to 86,400 mph
> > > in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change
> > > of only 35 kph or 21 miles per hour, and people aren't supposed to be able
> > > survive 10 G of acceleration for more than a few seconds. Therefore, a
> > > manned vehicle accelerating at +5040 miles per hour every 24 hours would
> > > already kill the crew many times over. What am I missing here???
> > If you're going to try to do hard science, you need to start by
> > understanding
> > units of measure. One accelerates to a velocity (speed). You have your ship
> > accelerating to a distance -- 250000 miles. That means that after it has
> > gone
> > that far it stops accelerating.
> >
> > I think that you probably want it to accelerate up to some speed, such as:
> > - 250000 miles/year
> > - 250000 miles/month
> > - 250000 miles/day
> > - 250000 miles/hour
> > Something like one of those.
> >
> > For instance, let's take a look at your car example. When you discuss a car
> > accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> > two speeds. That change in speed, if spread out evenly over a ten-second
> > interval, would not be one mile per second (as you stated), but six miles
> > per
> > hour per second.
> >
> > I think that you need to sit down with pencil and paper and work through all
> > of this, making the units explicit throughout your work.
> >
> > Getting to your last question, the units are correct here (although I have
> > no idea whether it's consistent with anything that went before).
> >
> > 5040 miles per hour per day works out to 210 miles per hour per hour, which
> > means that over a period of one hour, you've sped up by 210 miles per hour.
> > If you think about it, a commercial airliner speeds up from stopped on the
> > tarmac to a speed speed of over 500 miles per hour in a matter of ten
> > minutes
> > or so, which is an acceleration of about 3000 miles per hour per hour, or
> > much greater than what is mentioned here.
> >
> > By the way, this would be much less subject to error if you did your work
> > exclusively in meters and seconds.
> >
> > --
> > Michael F. Stemper
> > Economists have correctly predicted seven of the last three recessions.
> Thanks for this. For further context, my core parameters are a ship that
> could make a trip from Mars to Neptune in 20 months,

You’re going to need excellent rockets. Chemicals need not apply. Low-end
hot jet nuclear need not apply. Probably some variant on nuclear electric.
You will not be launching from Mars’ surface with most practical nuclear
electric systems.
> assuming the former to
> be partly colonized by the late 20th/ early 21st century.

errr.. we’re already in the early 21st. To get Mars colonized by the late
20th would require some pretty impressive handwaving.
> Outside of some
> shorthand, I'd say this confirms my numbers are "realistic", to the extent
> they describe how manned vehicles behave. I would assume I'm missing
> something about how horizontal acceleration converts to normally vertical
> gravitational force, but I'm not sure what the details would be.

There is no ‘horizontal’ accel. Acceleration, like velocity, is a vector.
It has magnitude and direction, and the direction is in three dimensions. (x,
y, and z, usually. As an undergrad I once tried to write a program, in
FORTRAN, describing the motion of objects under acceleration in space. It got
very complicated very quickly.) Speed is not velocity. Speed is not a vector.
It has magnitude, but not direction.

Re: Hard science question: How do G forces work???

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 by: Wolffan - Wed, 9 Nov 2022 23:42 UTC

On 09 Nov 2022, James Nicoll wrote
(in article <tkh4d7$rm1$1@reader2.panix.com>):

> In article<6b70c77f-74e0-4315-9fb2-db8bbb37205cn@googlegroups.com>,
> David Brown <davidnbrown80@gmail.com> wrote:
> > Thanks for this. For further context, my core parameters are a
> > ship that could make a trip from Mars to Neptune in 20 months,
> > assuming the former to be partly colonized by the late 20th/
> > early 21st century.
>
> These target dates are very ambitious.

no kidding.
>
>
> > I would assume I'm missing something
> > about how horizontal acceleration converts to normally vertical
> > gravitational force, but I'm not sure what the details would be.
>
> I say this supportively: your issue with units and the phrasing
> above suggest you need to have a look at the very basics of
> physics. Atomic Rockets may be useful:
>
> http://www.projectrho.com/public_html/rocket/index.php

he needs a lot of work before he goes there.
>
>
> In the old days, there were primers like Clarke's Interplanetary
> Flight. Not sure what the modern analogs are.

A good high school or freshman college level physics text should have a few
chapters on statics and dynamics. Newton’s laws, that kind of thing. Way
back at Ye Dawne of Time, my GCE ‘O’ and ‘A’ Level physics texts
would have been good. But that was then, long ago and far away.

Re: Hard science question: How do G forces work???

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 by: Quadibloc - Wed, 9 Nov 2022 23:42 UTC

On Wednesday, November 9, 2022 at 12:35:42 PM UTC-7, peterwezeman@hotmail.com wrote:

> Before they started off she said, "And remember, the
> speedometer is calibrated in metric units."

> He let in the clutch and accelerated cautiously to 60, getting the feel of
> the car. After a short time he asked, "Have you checked the speedometer
> with a stopwatch? I've driven in Europe, and it sure seems to me that
> we're going faster than sixty kilometers per hour."

> She replied, "We are. That's meters per second."

LOL. Of course, though, it's her fault. She used ambiguous terminology in
describing the speedometer. Kilometers per hour _is_ a metric unit. What
it isn't is an SI unit.

John Savard

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 by: Quadibloc - Wed, 9 Nov 2022 23:44 UTC

On Wednesday, November 9, 2022 at 4:16:40 PM UTC-7, peterwezeman@hotmail.com wrote:

> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.

My first year physics textbook was Fundamentals of Physics by Halliday and Resnick.

John Savard

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 by: James Nicoll - Thu, 10 Nov 2022 00:05 UTC

In article <0001HW.291C6D8F024FF16E7000027B338F@news.supernews.com>,
Wolffan <akwolffan@zoho.com> wrote:
>On 09 Nov 2022, David Brown wrote
>(in article<d672798f-3b06-4d93-b740-3ee7981aba17n@googlegroups.com>):
>
>> Here's something I've been working on for a retro future
>project with hard
>> sci fi elements. It calls for a gigantic 300+ meter ship
>
>that’s aircraft carrier size. I hope that you’re starting
>from orbit, or
>there’s likely to be a problem.
>
>Also, that’s one dimension. What shape is it? It’s one thing
>if it’s a
>300 metre long cylinder, with a diameter of, oh, 30 metres.
>It’s something
>else if it’s a 30-metre thick disk with a diameter of 300
>metres. It’s a
>whole other thing if it’s a 300-metre radius sphere.
>> to accelerate to
>> 250,000 miles
>
>250,000 miles per what?
>> for a trip to the outer solar system, which I arm waved to
>> maybe +12,000 miles of acceleration per day.
>
>you don’t do acceleration in miles per day. Personally, I work
>best in SI
>units: metres, kilogrammes, seconds, joules, watts, newtons, that
>kind of
>thing. The acceleration due to gravity, one gee, is approximately
>9.81 metres
>per second per second. (that last ‘per second’ is kind of
>important) One
>gee is a rather significant acceleration. I usually just round up
>to a nice
>even 10 m/s/s, it’s easier to work with.
>
>Some basic concepts:
>
>delta-vee is the total mission change in velocity. It’s rather
>significant.
>
>the mission delta-vee for a rocket-propelled vehicle is equal to
>the rocket's
>exhaust velocity times the natural log of the mass ratio, where the mass
>ratio is the total mass of rocket, payload, reaction mass, and
>everything
>else at the start of the flight (m1) divided my the mass of
>whatever is left
>at the end of the flight (m2). Note that that’s for the _total_
>mission,
>you usually need to get there and back.
>
>v = u + at. That is, the final velocity equals the intial
>velocity plus the
>acceleration times the time spent under acceleration.
>
>s = ut + 0.5at^2. That is, the displacement equals the inital
>velocity times
>the time under acceleration plus half the acceleration times the
>square of
>the time.
>
>So let’s do an example: we want to go to the Moon. We want to
>do it at one
>gee continuous accel. We want to get back.
>
>So... the distance from the Earth to the Moon is 380,000
>kilomtres, or 380
>million mtres. That’s 3.8 x 10^8 metres. We have to get there
>and back.
>That’s 7.6 x 10^8 metres. (It’s not really 380 million
>metres. See below)
>
>Ok... problem. We need to arrive at the Moon with velocity of
>zero relative
>to the Moon. We need to get back to Earth, or at least Earth orbit, with
>velocity zero. (well, we have to make lunar orbit and Earth
>orbit, but we can
>worry about that later.) This means that we can’t just boost
>all the way,
>we must boost half way, turn around, slow down. We must do this
>twice to make
>the round trip. As we need to fiddle around a little, let’s say
>that it’s
>400,000 km to the Moon. Our total displacement is now 800,000 km.
>
>Ok, so the displacement we have to calculate is one quarter of
>800,000 km, or
>200,000 km (there’s a reason why I picked 400,000 km...) So s =
>2 x 10^8 m.
>
>We simplify where possible, and set u to zero. As will be seen
>later, actual
>values of u won’t make much difference.
>
>So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
>
>Now, a =10. (keep things simple...) which means that
>
>10t^2 = 4 x 10^8
>
>so... t^2 = 4 x 10 ^7.
>
>hmm. My calculator says that t must equal 6325 seconds, (105.4
>minutes, 1.76
>hours) approximately. Hmm, We must do this four times (once accel
>going to
>the Moon, once delec to zero, once accel going back to Earth,
>once decel to
>zero) so that’s 25300 seconds, approximately.
>
>hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your
>total mission
>delta vee is... 253,000 metres per second, 253 km/s. So... how
>much reaction
>mass are you going to need? delta-vee = ve x ln mr. The best
>chemical rockets
>have a ve on the order of 4 km/s. The natural log of the mass
>ratio is going
>to be... 63.25. You’re gonna need a who lot of go-juice. And
>now you know
>why NASA didn’t try to use continuous accel in the Apollo
>moonships. Either
>you’re going to need something hotter than a chemical rocket, or you
>can’t accel all the way. Hot-jet nukes might, in theory, get to
>100 km/s
>ve... that at least gives a managable mr. Still not good, though.
>You need
>better. Fusion rockets would be a lot better. Photon rockets
>would be nice.
>Neither one is likely to be available for the near future, if at all.
>You’re gonna need to think carefully about what kind of
>trajectories you
>want to use, continuous accel is off the table. It’d be nice;
>3.5 hours to
>the Moon, 7 hours for a round trip, a few days to Mars, a few
>weeks, at most,
>for anywhere in the system... Not happening without magic tech.
>
>Jerry Pournelle went into great detail about this kind of thing
>in his A Step
>Further Out columns in Galaxy, some of which were collected into
>a nice big
>paperback. Look it up.
>> Here's the weird thing. Regular
>> terrestrial cars can accelerate 0-60
>
>that’s miles per hour. Call it 100 km per hour. It’s 400,000
>km to the
>Moon. That’s 4000 hours, assuming that the car could achieve escape
>velocity, which it can’t. (it’s worse than that, you have to
>flip and
>decel, so it’s gonna take longer)
>> in 10 seconds without even being
>> considered that fast, which comes out at 1 mile per second
>
>one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
>could hit 2000 to 2400 mph before atmospheric friction would heat
>it up and
>destroy it.
>> . That means if all
>> conventional limitations were removed (friction, cooling,
>controllability,
>> fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
>
>nope.
>> . The
>> monkey wrench is, 1 G of acceleration amounts to a change of
>only 35 kph or
>> 21 miles per hour,
>
>no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
>second. At the end of the first second, that’s 10 metres per
>second, 36000
>metres per hour, a.k.a. 360 km/s. At the end of the second
>second, that’s
>20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
>> and people aren't supposed to be able survive 10 G of
>> acceleration for more than a few seconds.
>
>it ain’t the people you should be concerned about, it’s the
>structure of
>your vehicle. Very few vehicles can take 10 gees.
>> Therefore, a manned vehicle
>> accelerating at +5040 miles per hour every 24 hours would
>already kill the
>> crew many times over. What am I missing here???
>
>yes. You accel at, say, 1 gee, and you get to anywhere in the
>system in under
>a month and a half. One gee. You’re mixing up velocity and
>acceleration.
>
>May I suggest a basic course on statics and dynamics?
>>
>>
>> David N. Brown
>> Mesa, Arizona
>
>

--
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Re: Hard science question: How do G forces work???

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 by: pyotr filipivich - Thu, 10 Nov 2022 00:35 UTC

David Brown <davidnbrown80@gmail.com> on Wed, 9 Nov 2022 08:21:29
-0800 (PST) typed in rec.arts.sf.written the following:
>Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>
>David N. Brown
>Mesa, Arizona

"It's complicated." But basically, you are mistaking
"acceleration" and "speed". Short form, speed is the change of
location over time. Acceleration is the change of speed over time. It
is an exponent, so you can start off with a slow speed but add to that
with a modest acceleration and eventually you will reach some really
high speed.

For starters, You are here ===> +
This is your location.
+ <=== You were here, now you are here ===> +
This change in location is "distance", e.g., "a furlong"
Change of Distance over time is Rate. E.g furlongs per fortnight
Changes of Rate over time are Acceleration, (Rate over time or
R/T, or D/T^2) which is where G (gravity) is figured. Furlongs per
fortnight per fortnight. In customary units that works out to about
32 ft/s^2.
[I'm not sure if there is a term for change in acceleration over
time, but it is there. I was really bored one night.]

Now, engineering: 1 g acceleration is what you feel on the surface
of the earth. "Free Fall" or "zero-g" is when you and your
surroundings are both falling at the same rater (accelerating) (32
ft/s^2). Human beings can handle "high" acceleration for some values
of "high". But there is a limit above which system and structural
failure sets in. That is to say, the heart cannot pump blood "up"
that far, or the bones of your body cannot bear the stress and break.

So, to your question "accelerating at +5040 miles per hour" is
how many feet per second?
5040 mph is 84 /miles per minute, 1.4 miles per second or 7392
feet per second. Divide by 32 and you have 231 gs of acceleration.

Now, you might be able to reach 5040 miles per hour at 1 G in
about 308 days. I'd have to look up formula for the distance covered,
but it's not far.

--
pyotr filipivich
This Week's Panel: Us & Them - Eliminating Them.
Next Month's Panel: Having eliminated the old Them(tm)
Selecting who insufficiently Woke(tm) as to serve as the new Them(tm)

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
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 by: David Brown - Thu, 10 Nov 2022 06:42 UTC

On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> On 09 Nov 2022, David Brown wrote
> (in article<d672798f-3b06-4d93...@googlegroups.com>):
> > Here's something I've been working on for a retro future project with hard
> > sci fi elements. It calls for a gigantic 300+ meter ship
> that’s aircraft carrier size. I hope that you’re starting from orbit, or
> there’s likely to be a problem.
>
> Also, that’s one dimension. What shape is it? It’s one thing if it’s a
> 300 metre long cylinder, with a diameter of, oh, 30 metres. It’s something
> else if it’s a 30-metre thick disk with a diameter of 300 metres. It’s a
> whole other thing if it’s a 300-metre radius sphere.
> > to accelerate to
> > 250,000 miles
> 250,000 miles per what?
> > for a trip to the outer solar system, which I arm waved to
> > maybe +12,000 miles of acceleration per day.
> you don’t do acceleration in miles per day. Personally, I work best in SI
> units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
> thing. The acceleration due to gravity, one gee, is approximately 9.81 metres
> per second per second. (that last ‘per second’ is kind of important) One
> gee is a rather significant acceleration. I usually just round up to a nice
> even 10 m/s/s, it’s easier to work with.
>
> Some basic concepts:
>
> delta-vee is the total mission change in velocity. It’s rather significant.
>
> the mission delta-vee for a rocket-propelled vehicle is equal to the rocket's
> exhaust velocity times the natural log of the mass ratio, where the mass
> ratio is the total mass of rocket, payload, reaction mass, and everything
> else at the start of the flight (m1) divided my the mass of whatever is left
> at the end of the flight (m2). Note that that’s for the _total_ mission,
> you usually need to get there and back.
>
> v = u + at. That is, the final velocity equals the intial velocity plus the
> acceleration times the time spent under acceleration.
>
> s = ut + 0.5at^2. That is, the displacement equals the inital velocity times
> the time under acceleration plus half the acceleration times the square of
> the time.
>
> So let’s do an example: we want to go to the Moon. We want to do it at one
> gee continuous accel. We want to get back.
>
> So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
> million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
> That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See below)
>
> Ok... problem. We need to arrive at the Moon with velocity of zero relative
> to the Moon. We need to get back to Earth, or at least Earth orbit, with
> velocity zero. (well, we have to make lunar orbit and Earth orbit, but we can
> worry about that later.) This means that we can’t just boost all the way,
> we must boost half way, turn around, slow down. We must do this twice to make
> the round trip. As we need to fiddle around a little, let’s say that it’s
> 400,000 km to the Moon. Our total displacement is now 800,000 km.
>
> Ok, so the displacement we have to calculate is one quarter of 800,000 km, or
> 200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8 m.
>
> We simplify where possible, and set u to zero. As will be seen later, actual
> values of u won’t make much difference.
>
> So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
>
> Now, a =10. (keep things simple...) which means that
>
> 10t^2 = 4 x 10^8
>
> so... t^2 = 4 x 10 ^7.
>
> hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes, 1..76
> hours) approximately. Hmm, We must do this four times (once accel going to
> the Moon, once delec to zero, once accel going back to Earth, once decel to
> zero) so that’s 25300 seconds, approximately.
>
> hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
> delta vee is... 253,000 metres per second, 253 km/s. So... how much reaction
> mass are you going to need? delta-vee = ve x ln mr. The best chemical rockets
> have a ve on the order of 4 km/s. The natural log of the mass ratio is going
> to be... 63.25. You’re gonna need a who lot of go-juice. And now you know
> why NASA didn’t try to use continuous accel in the Apollo moonships. Either
> you’re going to need something hotter than a chemical rocket, or you
> can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
> ve... that at least gives a managable mr. Still not good, though. You need
> better. Fusion rockets would be a lot better. Photon rockets would be nice.
> Neither one is likely to be available for the near future, if at all.
> You’re gonna need to think carefully about what kind of trajectories you
> want to use, continuous accel is off the table. It’d be nice; 3.5 hours to
> the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at most,
> for anywhere in the system... Not happening without magic tech.
>
> Jerry Pournelle went into great detail about this kind of thing in his A Step
> Further Out columns in Galaxy, some of which were collected into a nice big
> paperback. Look it up.
> > Here's the weird thing. Regular
> > terrestrial cars can accelerate 0-60
> that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
> Moon. That’s 4000 hours, assuming that the car could achieve escape
> velocity, which it can’t. (it’s worse than that, you have to flip and
> decel, so it’s gonna take longer)
> > in 10 seconds without even being
> > considered that fast, which comes out at 1 mile per second
> one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
> could hit 2000 to 2400 mph before atmospheric friction would heat it up and
> destroy it.
> > . That means if all
> > conventional limitations were removed (friction, cooling, controllability,
> > fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
> nope.
> > . The
> > monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or
> > 21 miles per hour,
> no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
> second. At the end of the first second, that’s 10 metres per second, 36000
> metres per hour, a.k.a. 360 km/s. At the end of the second second, that’s
> 20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> > and people aren't supposed to be able survive 10 G of
> > acceleration for more than a few seconds.
> it ain’t the people you should be concerned about, it’s the structure of
> your vehicle. Very few vehicles can take 10 gees.
> > Therefore, a manned vehicle
> > accelerating at +5040 miles per hour every 24 hours would already kill the
> > crew many times over. What am I missing here???
> yes. You accel at, say, 1 gee, and you get to anywhere in the system in under
> a month and a half. One gee. You’re mixing up velocity and acceleration.
>
> May I suggest a basic course on statics and dynamics?
> >
> >
> > David N. Brown
> > Mesa, Arizona
I have ridiculously detailed and probably incoherent specs for the ship in chapters posted on my blog. It's called the Janus, and my head description is Tinker Toy ship. My specs have been 360 m long (cut down from my very first ideas) and 40-60 meters wide at one or two places including a Von Braun style ring for artificial gravity. There's also supposed to be a fusion reactor and a space shuttle-sized landing craft up front. The general idea was always something long and skinny that could be simply lined with fuel. After putting things down and getting feedback here, I recalculated the speed as 400,000 kph, to be reached with acceleration of +800 kph per hour. I now believe the G count would come out as something like 0.022, which would be completely pitiful for anything that wasn't in the size range of the Empire State Building. It really would be a "different" approach to spaceship design. It could be called the Space Yugo, except the timeline would diverge before communist Yugoslavia existed. Hope this makes a little more sense; I might put up a link or so tomorrow.

Re: Hard science question: How do G forces work???

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 by: Scott Lurndal - Thu, 10 Nov 2022 14:31 UTC

David Brown <davidnbrown80@gmail.com> writes:
>On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:

<snip long physics lesson>

>> > crew many times over. What am I missing here???
>> yes. You accel at, say, 1 gee, and you get to anywhere in the system in u=
>nder=20
>> a month and a half. One gee. You=E2=80=99re mixing up velocity and accele=
>ration.=20
>>=20
>> May I suggest a basic course on statics and dynamics?
>> >=20
>> >=20
>> > David N. Brown=20
>> > Mesa, Arizona
>I have ridiculously detailed and probably incoherent specs for the ship in =
>chapters posted on my blog. It's called the Janus, and my head description =
>is Tinker Toy ship. My specs have been 360 m long (cut down from my very fi=
>rst ideas) and 40-60 meters wide at one or two places including a Von Braun=
> style ring for artificial gravity.

So many 'spaceship' designs follow terrestrial characteristics (i.e. typically
cylindrical, or in the case of Star Wars, et. al., space-born aircraft carriers).

For spaceships that never intend to fly -in- atmosphere, it would seem that the sphere
is the optimal form factor (given structural loading from internal atomspheric pressure),
and the movie form (e.g. star wars) would be far from optimal.

The enterprise is pretty, but not particularly optimal, particularly the
saucer section.

Re: Hard science question: How do G forces work???

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 by: Wolffan - Thu, 10 Nov 2022 14:38 UTC

On 10 Nov 2022, David Brown wrote
(in article<657e2ac8-4184-43f2-86ed-15a4d44c912dn@googlegroups.com>):

> On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> > On 09 Nov 2022, David Brown wrote
> > (in article<d672798f-3b06-4d93...@googlegroups.com>):
> > > Here's something I've been working on for a retro future project with hard
> > > sci fi elements. It calls for a gigantic 300+ meter ship
> > that’s aircraft carrier size. I hope that you’re starting from orbit, or
> > there’s likely to be a problem.
> >
> > Also, that’s one dimension. What shape is it? It’s one thing if it’s a
> > 300 metre long cylinder, with a diameter of, oh, 30 metres. It’s something
> > else if it’s a 30-metre thick disk with a diameter of 300 metres. It’s a
> > whole other thing if it’s a 300-metre radius sphere.
> > > to accelerate to
> > > 250,000 miles
> > 250,000 miles per what?
> > > for a trip to the outer solar system, which I arm waved to
> > > maybe +12,000 miles of acceleration per day.
> > you don’t do acceleration in miles per day. Personally, I work best in SI
> > units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
> > thing. The acceleration due to gravity, one gee, is approximately 9.81
> > metres
> > per second per second. (that last ‘per second’ is kind of important) One
> > gee is a rather significant acceleration. I usually just round up to a nice
> > even 10 m/s/s, it’s easier to work with.
> >
> > Some basic concepts:
> >
> > delta-vee is the total mission change in velocity. It’s rather
> > significant.
> >
> > the mission delta-vee for a rocket-propelled vehicle is equal to the
> > rocket's
> > exhaust velocity times the natural log of the mass ratio, where the mass
> > ratio is the total mass of rocket, payload, reaction mass, and everything
> > else at the start of the flight (m1) divided my the mass of whatever is left
> > at the end of the flight (m2). Note that that’s for the _total_ mission,
> > you usually need to get there and back.
> >
> > v = u + at. That is, the final velocity equals the intial velocity plus the
> > acceleration times the time spent under acceleration.
> >
> > s = ut + 0.5at^2. That is, the displacement equals the inital velocity times
> > the time under acceleration plus half the acceleration times the square of
> > the time.
> >
> > So let’s do an example: we want to go to the Moon. We want to do it at one
> > gee continuous accel. We want to get back.
> >
> > So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
> > million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
> > That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See
> > below)
> >
> > Ok... problem. We need to arrive at the Moon with velocity of zero relative
> > to the Moon. We need to get back to Earth, or at least Earth orbit, with
> > velocity zero. (well, we have to make lunar orbit and Earth orbit, but we
> > can
> > worry about that later.) This means that we can’t just boost all the way,
> > we must boost half way, turn around, slow down. We must do this twice to
> > make
> > the round trip. As we need to fiddle around a little, let’s say that
> > it’s
> > 400,000 km to the Moon. Our total displacement is now 800,000 km.
> >
> > Ok, so the displacement we have to calculate is one quarter of 800,000 km,
> > or
> > 200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8
> > m.
> >
> > We simplify where possible, and set u to zero. As will be seen later, actual
> > values of u won’t make much difference.
> >
> > So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
> >
> > Now, a =10. (keep things simple...) which means that
> >
> > 10t^2 = 4 x 10^8
> >
> > so... t^2 = 4 x 10 ^7.
> >
> > hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes, 1.76
> > hours) approximately. Hmm, We must do this four times (once accel going to
> > the Moon, once delec to zero, once accel going back to Earth, once decel to
> > zero) so that’s 25300 seconds, approximately.
> >
> > hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
> > delta vee is... 253,000 metres per second, 253 km/s. So... how much reaction
> > mass are you going to need? delta-vee = ve x ln mr. The best chemical
> > rockets
> > have a ve on the order of 4 km/s. The natural log of the mass ratio is going
> > to be... 63.25. You’re gonna need a who lot of go-juice. And now you know
> > why NASA didn’t try to use continuous accel in the Apollo moonships.
> > Either
> > you’re going to need something hotter than a chemical rocket, or you
> > can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
> > ve... that at least gives a managable mr. Still not good, though. You need
> > better. Fusion rockets would be a lot better. Photon rockets would be nice.
> > Neither one is likely to be available for the near future, if at all.
> > You’re gonna need to think carefully about what kind of trajectories you
> > want to use, continuous accel is off the table. It’d be nice; 3.5 hours to
> > the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at
> > most,
> > for anywhere in the system... Not happening without magic tech.
> >
> > Jerry Pournelle went into great detail about this kind of thing in his A
> > Step
> > Further Out columns in Galaxy, some of which were collected into a nice big
> > paperback. Look it up.
> > > Here's the weird thing. Regular
> > > terrestrial cars can accelerate 0-60
> > that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
> > Moon. That’s 4000 hours, assuming that the car could achieve escape
> > velocity, which it can’t. (it’s worse than that, you have to flip and
> > decel, so it’s gonna take longer)
> > > in 10 seconds without even being
> > > considered that fast, which comes out at 1 mile per second
> > one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
> > could hit 2000 to 2400 mph before atmospheric friction would heat it up and
> > destroy it.
> > > . That means if all
> > > conventional limitations were removed (friction, cooling, controllability,
> > > fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
> > nope.
> > > . The
> > > monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or
> > > 21 miles per hour,
> > no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
> > second. At the end of the first second, that’s 10 metres per second, 36000
> > metres per hour, a.k.a. 360 km/s. At the end of the second second, that’s
> > 20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> > > and people aren't supposed to be able survive 10 G of
> > > acceleration for more than a few seconds.
> > it ain’t the people you should be concerned about, it’s the structure of
> > your vehicle. Very few vehicles can take 10 gees.
> > > Therefore, a manned vehicle
> > > accelerating at +5040 miles per hour every 24 hours would already kill the
> > > crew many times over. What am I missing here???
> > yes. You accel at, say, 1 gee, and you get to anywhere in the system in
> > under
> > a month and a half. One gee. You’re mixing up velocity and acceleration.
> >
> > May I suggest a basic course on statics and dynamics?
> > >
> > >
> > > David N. Brown
> > > Mesa, Arizona
> I have ridiculously detailed and probably incoherent specs for the ship in
> chapters posted on my blog. It's called the Janus, and my head description is
> Tinker Toy ship. My specs have been 360 m long (cut down from my very first
> ideas) and 40-60 meters wide at one or two places including a Von Braun style
> ring for artificial gravity. There's also supposed to be a fusion reactor and
> a space shuttle-sized landing craft up front. The general idea was always
> something long and skinny that could be simply lined with fuel. After putting
> things down and getting feedback here, I recalculated the speed as 400,000
> kph, to be reached with acceleration of +800 kph per hour. I now believe the
> G count would come out as something like 0.022, which would be completely
> pitiful for anything that wasn't in the size range of the Empire State
> Building. It really would be a "different" approach to spaceship design. It
> could be called the Space Yugo, except the timeline would diverge before
> communist Yugoslavia existed. Hope this makes a little more sense; I might
> put up a link or so tomorrow.


Click here to read the complete article
Re: Hard science question: How do G forces work???

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From: jdnic...@panix.com (James Nicoll)
Newsgroups: rec.arts.sf.written
Subject: Re: Hard science question: How do G forces work???
Date: Thu, 10 Nov 2022 14:57:09 -0000 (UTC)
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 by: James Nicoll - Thu, 10 Nov 2022 14:57 UTC

In article <657e2ac8-4184-43f2-86ed-15a4d44c912dn@googlegroups.com>,
David Brown <davidnbrown80@gmail.com> wrote:
>>
>I have ridiculously detailed and probably incoherent specs for
>the ship in chapters posted on my blog. It's called the Janus,
>and my head description is Tinker Toy ship. My specs have been
>360 m long (cut down from my very first ideas) and 40-60 meters
>wide at one or two places including a Von Braun style ring for
>artificial gravity. There's also supposed to be a fusion reactor
>and a space shuttle-sized landing craft up front. The general
>idea was always something long and skinny that could be simply
>lined with fuel. After putting things down and getting feedback
>here, I recalculated the speed as 400,000 kph, to be reached with
>acceleration of +800 kph per hour. I now believe the G count
>would come out as something like 0.022, which would be completely
>pitiful for anything that wasn't in the size range of the Empire
>State Building. It really would be a "different" approach to
>spaceship design. It could be called the Space Yugo, except the
>timeline would diverge before communist Yugoslavia existed. Hope
>this makes a little more sense; I might put up a link or so
>tomorrow.

Your choice of units makes the Baby Jesus cry.

One gee adds about 10 m/s each second. Over an hour (or
3600 seconds), that adds up to 36000 m/s or 36 km/s.
36 kilometers per second equals about 130,000 km/hr.
800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01.

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 800/130,000 is 0.006. Call it 0.01 gee (or .1 m/s/s)

But the thing about sustained acceleration is that it adds
up faster than you may expect. One day (or 86400 seconds)
at 0.1 m/s/s gets you to 8640 (roughly orbital velocity
around Earth). A few days will get you to Hohmann transfer
orbit speeds. Two months will get you to Saturn (if you
don't want to stop), three months if you do. 40 years
will get you to Alpha Centauri.

(With a peak velocity of about 1/5th the speed of light,
which is, uh, ambitious for a fusion rocket)
--
My reviews can be found at http://jamesdavisnicoll.com/
My tor pieces at https://www.tor.com/author/james-davis-nicoll/
My Dreamwidth at https://james-davis-nicoll.dreamwidth.org/
My patreon is at https://www.patreon.com/jamesdnicoll

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
From: jack.boh...@gmail.com (Jack Bohn)
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 by: Jack Bohn - Thu, 10 Nov 2022 15:51 UTC

On Thursday, November 10, 2022 at 1:42:36 AM UTC-5, David Brown wrote:

> My specs have been 360 m long (cut down from my very first ideas) and 40-60 meters wide at one or two places including a Von Braun style ring for artificial gravity. There's also supposed to be a fusion reactor and a space shuttle-sized landing craft up front.

Landing craft. Space Shuttle-sized, about 37m, OK, about 10% of the ship's length... Well, with its external fuel tank, 56 m. Maybe something like the VentureStar, 45m long with internal tank. I suspect there is less difference between VTOHL and HLVTO than there would be between VTOL and VLTO.

--
-Jack

Re: Hard science question: How do G forces work???

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 by: rkshul...@rosettacondot.com - Thu, 10 Nov 2022 16:07 UTC

peterwezeman@hotmail.com <peterwezeman@hotmail.com> wrote:
> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
>> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
>> > On 09/11/2022 10.21, David Brown wrote:
>> > > Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>> > If you're going to try to do hard science, you need to start by understanding
>> > units of measure. One accelerates to a velocity (speed). You have your ship
>> > accelerating to a distance -- 250000 miles. That means that after it has gone
>> > that far it stops accelerating.
>> >
>> > I think that you probably want it to accelerate up to some speed, such as:
>> > - 250000 miles/year
>> > - 250000 miles/month
>> > - 250000 miles/day
>> > - 250000 miles/hour
>> > Something like one of those.
>> >
>> > For instance, let's take a look at your car example. When you discuss a car
>> > accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
>> > two speeds. That change in speed, if spread out evenly over a ten-second
>> > interval, would not be one mile per second (as you stated), but six miles per
>> > hour per second.
>> >
>> > I think that you need to sit down with pencil and paper and work through all
>> > of this, making the units explicit throughout your work.
>> >
>> > Getting to your last question, the units are correct here (although I have
>> > no idea whether it's consistent with anything that went before).
>> >
>> > 5040 miles per hour per day works out to 210 miles per hour per hour, which
>> > means that over a period of one hour, you've sped up by 210 miles per hour.
>> > If you think about it, a commercial airliner speeds up from stopped on the
>> > tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
>> > or so, which is an acceleration of about 3000 miles per hour per hour, or
>> > much greater than what is mentioned here.
>> >
>> > By the way, this would be much less subject to error if you did your work
>> > exclusively in meters and seconds.
>> >
>> > --
>> > Michael F. Stemper
>> > Economists have correctly predicted seven of the last three recessions.
>> Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.
>
> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.
>
> One possible source of confusion is that horizontal speeds are often given in miles per hour or kilometers
> hour whereas accelerations are given in feet per second per second or meters per second per second.
> As Michael Stemper suggests, try keeping the units consistent.

When my wife and I were in college our physics professors put a lot of
emphasis on dimensional analysis:
<https://en.wikipedia.org/wiki/Dimensional_analysis>
She's continued the tradition with her students.
Getting the units right isn't a guarantee that you're correct but getting them
wrong pretty much ensures that you're incorrect.
My into physics professor loved to give problems in unusual units with the
answer in a different set (start with meters and hours and calculate velocity
in furlongs per fortnight). You learned very quickly to convert to consistent
units and carry those all the way through.

Robert
--
Robert K. Shull Email: rkshull at rosettacon dot com

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Subject: Re: Hard science question: How do G forces work???
From: davidnbr...@gmail.com (David Brown)
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 by: David Brown - Thu, 10 Nov 2022 18:23 UTC

On Thursday, November 10, 2022 at 7:31:10 AM UTC-7, Scott Lurndal wrote:
> David Brown <davidn...@gmail.com> writes:
> >On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> <snip long physics lesson>
> >> > crew many times over. What am I missing here???
> >> yes. You accel at, say, 1 gee, and you get to anywhere in the system in u=
> >nder=20
> >> a month and a half. One gee. You=E2=80=99re mixing up velocity and accele=
> >ration.=20
> >>=20
> >> May I suggest a basic course on statics and dynamics?
> >> >=20
> >> >=20
> >> > David N. Brown=20
> >> > Mesa, Arizona
> >I have ridiculously detailed and probably incoherent specs for the ship in =
> >chapters posted on my blog. It's called the Janus, and my head description =
> >is Tinker Toy ship. My specs have been 360 m long (cut down from my very fi=
> >rst ideas) and 40-60 meters wide at one or two places including a Von Braun> > style ring for artificial gravity.
> So many 'spaceship' designs follow terrestrial characteristics (i.e. typically
> cylindrical, or in the case of Star Wars, et. al., space-born aircraft carriers).
>
> For spaceships that never intend to fly -in- atmosphere, it would seem that the sphere
> is the optimal form factor (given structural loading from internal atomspheric pressure),
> and the movie form (e.g. star wars) would be far from optimal.
>
> The enterprise is pretty, but not particularly optimal, particularly the
> saucer section.
I've been a defender of the old-fashioned flying saucer, at least in its truly radial variations. It lets you keep the command center and vital systems in a small area, while still allowing you to spread the engines, sensors and weapons (if any) across a 360 arc. Also, if there's incoming debris or actual weapons fire, there's still one axis that's mostly flat. Ironically, the Millennium Falcon is the one cinematic ship to be shown taking advantage of these characteristics, and it still had some terrible design features (partly because the life-sized sets had been created for a completely different ship).

Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
From: davidnbr...@gmail.com (David Brown)
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 by: David Brown - Thu, 10 Nov 2022 19:06 UTC

On Thursday, November 10, 2022 at 7:38:11 AM UTC-7, Wolffan wrote:
> On 10 Nov 2022, David Brown wrote
> (in article<657e2ac8-4184-43f2...@googlegroups.com>):
> > On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> > > On 09 Nov 2022, David Brown wrote
> > > (in article<d672798f-3b06-4d93...@googlegroups.com>):
> > > > Here's something I've been working on for a retro future project with hard
> > > > sci fi elements. It calls for a gigantic 300+ meter ship
> > > that’s aircraft carrier size. I hope that you’re starting from orbit, or
> > > there’s likely to be a problem.
> > >
> > > Also, that’s one dimension. What shape is it? It’s one thing if it’s a
> > > 300 metre long cylinder, with a diameter of, oh, 30 metres. It’s something
> > > else if it’s a 30-metre thick disk with a diameter of 300 metres. It’s a
> > > whole other thing if it’s a 300-metre radius sphere.
> > > > to accelerate to
> > > > 250,000 miles
> > > 250,000 miles per what?
> > > > for a trip to the outer solar system, which I arm waved to
> > > > maybe +12,000 miles of acceleration per day.
> > > you don’t do acceleration in miles per day. Personally, I work best in SI
> > > units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
> > > thing. The acceleration due to gravity, one gee, is approximately 9.81
> > > metres
> > > per second per second. (that last ‘per second’ is kind of important) One
> > > gee is a rather significant acceleration. I usually just round up to a nice
> > > even 10 m/s/s, it’s easier to work with.
> > >
> > > Some basic concepts:
> > >
> > > delta-vee is the total mission change in velocity. It’s rather
> > > significant.
> > >
> > > the mission delta-vee for a rocket-propelled vehicle is equal to the
> > > rocket's
> > > exhaust velocity times the natural log of the mass ratio, where the mass
> > > ratio is the total mass of rocket, payload, reaction mass, and everything
> > > else at the start of the flight (m1) divided my the mass of whatever is left
> > > at the end of the flight (m2). Note that that’s for the _total_ mission,
> > > you usually need to get there and back.
> > >
> > > v = u + at. That is, the final velocity equals the intial velocity plus the
> > > acceleration times the time spent under acceleration.
> > >
> > > s = ut + 0.5at^2. That is, the displacement equals the inital velocity times
> > > the time under acceleration plus half the acceleration times the square of
> > > the time.
> > >
> > > So let’s do an example: we want to go to the Moon. We want to do it at one
> > > gee continuous accel. We want to get back.
> > >
> > > So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
> > > million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
> > > That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See
> > > below)
> > >
> > > Ok... problem. We need to arrive at the Moon with velocity of zero relative
> > > to the Moon. We need to get back to Earth, or at least Earth orbit, with
> > > velocity zero. (well, we have to make lunar orbit and Earth orbit, but we
> > > can
> > > worry about that later.) This means that we can’t just boost all the way,
> > > we must boost half way, turn around, slow down. We must do this twice to
> > > make
> > > the round trip. As we need to fiddle around a little, let’s say that
> > > it’s
> > > 400,000 km to the Moon. Our total displacement is now 800,000 km.
> > >
> > > Ok, so the displacement we have to calculate is one quarter of 800,000 km,
> > > or
> > > 200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8
> > > m.
> > >
> > > We simplify where possible, and set u to zero. As will be seen later, actual
> > > values of u won’t make much difference.
> > >
> > > So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
> > >
> > > Now, a =10. (keep things simple...) which means that
> > >
> > > 10t^2 = 4 x 10^8
> > >
> > > so... t^2 = 4 x 10 ^7.
> > >
> > > hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes, 1.76
> > > hours) approximately. Hmm, We must do this four times (once accel going to
> > > the Moon, once delec to zero, once accel going back to Earth, once decel to
> > > zero) so that’s 25300 seconds, approximately.
> > >
> > > hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
> > > delta vee is... 253,000 metres per second, 253 km/s. So... how much reaction
> > > mass are you going to need? delta-vee = ve x ln mr. The best chemical
> > > rockets
> > > have a ve on the order of 4 km/s. The natural log of the mass ratio is going
> > > to be... 63.25. You’re gonna need a who lot of go-juice. And now you know
> > > why NASA didn’t try to use continuous accel in the Apollo moonships.
> > > Either
> > > you’re going to need something hotter than a chemical rocket, or you
> > > can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
> > > ve... that at least gives a managable mr. Still not good, though. You need
> > > better. Fusion rockets would be a lot better. Photon rockets would be nice.
> > > Neither one is likely to be available for the near future, if at all.
> > > You’re gonna need to think carefully about what kind of trajectories you
> > > want to use, continuous accel is off the table. It’d be nice; 3.5 hours to
> > > the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at
> > > most,
> > > for anywhere in the system... Not happening without magic tech.
> > >
> > > Jerry Pournelle went into great detail about this kind of thing in his A
> > > Step
> > > Further Out columns in Galaxy, some of which were collected into a nice big
> > > paperback. Look it up.
> > > > Here's the weird thing. Regular
> > > > terrestrial cars can accelerate 0-60
> > > that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
> > > Moon. That’s 4000 hours, assuming that the car could achieve escape
> > > velocity, which it can’t. (it’s worse than that, you have to flip and
> > > decel, so it’s gonna take longer)
> > > > in 10 seconds without even being
> > > > considered that fast, which comes out at 1 mile per second
> > > one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
> > > could hit 2000 to 2400 mph before atmospheric friction would heat it up and
> > > destroy it.
> > > > . That means if all
> > > > conventional limitations were removed (friction, cooling, controllability,
> > > > fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
> > > nope.
> > > > . The
> > > > monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or
> > > > 21 miles per hour,
> > > no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
> > > second. At the end of the first second, that’s 10 metres per second, 36000
> > > metres per hour, a.k.a. 360 km/s. At the end of the second second, that’s
> > > 20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> > > > and people aren't supposed to be able survive 10 G of
> > > > acceleration for more than a few seconds.
> > > it ain’t the people you should be concerned about, it’s the structure of
> > > your vehicle. Very few vehicles can take 10 gees.
> > > > Therefore, a manned vehicle
> > > > accelerating at +5040 miles per hour every 24 hours would already kill the
> > > > crew many times over. What am I missing here???
> > > yes. You accel at, say, 1 gee, and you get to anywhere in the system in
> > > under
> > > a month and a half. One gee. You’re mixing up velocity and acceleration.
> > >
> > > May I suggest a basic course on statics and dynamics?
> > > >
> > > >
> > > > David N. Brown
> > > > Mesa, Arizona
> > I have ridiculously detailed and probably incoherent specs for the ship in
> > chapters posted on my blog. It's called the Janus, and my head description is
> > Tinker Toy ship. My specs have been 360 m long (cut down from my very first
> > ideas) and 40-60 meters wide at one or two places including a Von Braun style
> > ring for artificial gravity. There's also supposed to be a fusion reactor and
> > a space shuttle-sized landing craft up front. The general idea was always
> > something long and skinny that could be simply lined with fuel. After putting
> > things down and getting feedback here, I recalculated the speed as 400,000
> > kph, to be reached with acceleration of +800 kph per hour. I now believe the
> > G count would come out as something like 0.022, which would be completely
> > pitiful for anything that wasn't in the size range of the Empire State
> > Building. It really would be a "different" approach to spaceship design.. It
> > could be called the Space Yugo, except the timeline would diverge before
> > communist Yugoslavia existed. Hope this makes a little more sense; I might
> > put up a link or so tomorrow.
> You still have a problem with ‘acceleration’ and ‘velocity’. I
> suspect that you’re making the Star Trek/Wars Error and have the decks
> parallel to the thrust. Won’t work. When under accel, down is aft.. When
> spinning, down is out. Spinning while under accel is a Bad Idea(™), as it
> will tend to induce nausea.
>


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Re: Hard science question: How do G forces work???

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Subject: Re: Hard science question: How do G forces work???
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 by: Scott Lurndal - Thu, 10 Nov 2022 19:24 UTC

David Brown <davidnbrown80@gmail.com> writes:
>On Thursday, November 10, 2022 at 7:31:10 AM UTC-7, Scott Lurndal wrote:
>> David Brown <davidn...@gmail.com> writes:=20
>> >On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
>> <snip long physics lesson>
>> >> > crew many times over. What am I missing here???
>> >> yes. You accel at, say, 1 gee, and you get to anywhere in the system i=
>n u=3D=20
>> >nder=3D20=20
>> >> a month and a half. One gee. You=3DE2=3D80=3D99re mixing up velocity a=
>nd accele=3D=20
>> >ration.=3D20=20
>> >>=3D20
>> >> May I suggest a basic course on statics and dynamics?
>> >> >=3D20=20
>> >> >=3D20=20
>> >> > David N. Brown=3D20=20
>> >> > Mesa, Arizona=20
>> >I have ridiculously detailed and probably incoherent specs for the ship =
>in =3D=20
>> >chapters posted on my blog. It's called the Janus, and my head descripti=
>on =3D=20
>> >is Tinker Toy ship. My specs have been 360 m long (cut down from my very=
> fi=3D=20
>> >rst ideas) and 40-60 meters wide at one or two places including a Von Br=
>aun=3D
>> > style ring for artificial gravity.
>> So many 'spaceship' designs follow terrestrial characteristics (i.e. typi=
>cally=20
>> cylindrical, or in the case of Star Wars, et. al., space-born aircraft ca=
>rriers).=20
>>=20
>> For spaceships that never intend to fly -in- atmosphere, it would seem th=
>at the sphere=20
>> is the optimal form factor (given structural loading from internal atomsp=
>heric pressure),=20
>> and the movie form (e.g. star wars) would be far from optimal.=20
>>=20
>> The enterprise is pretty, but not particularly optimal, particularly the=
>=20
>> saucer section.
>I've been a defender of the old-fashioned flying saucer, at least in its tr=
>uly radial variations. It lets you keep the command center and vital system=
>s in a small area, while still allowing you to spread the engines, sensors =
>and weapons (if any) across a 360 arc. Also, if there's incoming debris or =
>actual weapons fire, there's still one axis that's mostly flat. Ironically,=
> the Millennium Falcon is the one cinematic ship to be shown taking advanta=
>ge of these characteristics, and it still had some terrible design features=
> (partly because the life-sized sets had been created for a completely diff=
>erent ship).

Your typical tube airliner (e.g. 737) has an internal pressure of 11psi
at a cruising altitude of 35,000 feet where the external pressure is
less than 4psi. That's over 7 pounds per square inch of pressure
on the internal cabin area
that needs to be designed for; the rear bulkhead, for instance is
dome shaped, rather than flat.

https://aviation.stackexchange.com/questions/31292/why-do-airliners-have-pressure-bulkheads

"The shape of the final aft section is not well suited to resist
pressurization stresses: the best shape is a sphere; the cylinder
(with spherical terminations) comes a close second. The conical
shape would require serious stiffeners to survive pressurization
cycles for the whole life of the aircraft; the bulkhead solves
this problem by using a shape that is naturally more resistant
to stresses - and thus can be built with less material - leading
to less weight, and hence fuel savings (in addition to the increased safety)."

"It's worth making a rough estimate of just how big the force on
such a bulkhead is. At sea level, atmospheric pressure of 14.7 psi
is roughly the same as 1 ton per square foot. The difference between
the internal and external pressure at cruising altitude is about half
that value. The fuselage diameter of a B777 is about 20 feet, so the
area of the bulkhead is about 300 square feet. So the total force on
the bulkhead is about 150 tons. Compare that with the max takeoff weight
of the plane, which is about 250 tons - it's a seriously large number."

While a ship designed to remain in space permenently won't be subjected
to pressurization cycles, a spherical shape will continue to be
optimal to deal with stresses.

Question: What affect does acceleration have on the atmosphere within
the spaceship?

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