On 20/07/2023 04:29, VSim wrote:
> On Thursday, July 20, 2023 at 4:01:31 AM UTC+3, Hamish Laws wrote:
>> On Wednesday, July 19, 2023 at 11:34:20 PM UTC+10, VSim wrote:
>>> On Wednesday, July 19, 2023 at 4:27:42 PM UTC+3, Hamish Laws wrote:
>>>> On Wednesday, July 19, 2023 at 10:20:37 PM UTC+10, VSim wrote:
>>>>> On Wednesday, July 19, 2023 at 3:18:02 PM UTC+3, pete...@gmail.com wrote:
>>>>>> On Tuesday, July 18, 2023 at 9:46:09 AM UTC-4, VSim wrote:
>>>>>>> Increase the orbit of the Earth by a few million kilometers.
>>>>>>> How do we do that ? By means of the gravity attraction of a big enough flyby object.
>>>>>>>
>>>>>>> From the start it should be noted that this is by no means new. See
>>>>>>>
>>>>>>> https://www.scientificamerican.com/article/a-modest-proposal-lets-change-earths-orbit
>>>>>>>
>>>>>>> there are few other pages out there on the same subject, with more or less similar conclusions.
>>>>>>> Which are that it is not possible with current technology. While I don't necessarily dispute this, they don't convince me on this point.
>>>>>>>
>>>>>>> So let's see. From the page above I understand that an object with a mass of around 1% of that of the Earth (which is similar to the Moon) would be enough. If it passed some 1 million km away from us, with the right trajectory and speed, it would do the trick. Without altering the Moon's orbit too much, we don't want that, let alone losing it completely in the process. Also, the distance to the Earth is big enough so that we don't risk hitting the Earth itself by some error.
>>>>>>> Of course, these things should be confirmed by specialists, but judging from the page above they seem right to me. Correct me if I'm wrong.
>>>>>>>
>>>>>>> Now the big question, where do we get that object from ? The page above and other similar ones reach the conclusion that it doesn't exist in the solar system. Which IMO is where they're wrong. There are a few moons of Jupiter and one of Saturn which are just big enough. Maybe we could borrow one of them ? Hit it with an asteroid big enough so it leaves the orbit around its planet, then steer it towards Earth on the right trajectory. And, after the job is done, I'm pretty sure we could even put it back into its orbit (more or less).
>>>>>>>
>>>>>>> One more observation, it doesn't have to be done in one shot. It probably would even be better to do it in 2 or even 3 steps. One, because the distance would be bigger and the risk of an accident considerably smaller (it would be practically non-existent anyway but the safer the better). Two, because we could wait a few year to see the effects of a smaller increase first before moving further.
>>>>>>>
>>>>>>> So, I welcome any observations. You can thank me for saving the planet later.
>>>>>>> V. Sim.
>>>>>>>
>>>>>>> (And even if it can't be done today, maybe in 100 years it will be possible. As we know, global warming won't end with 0-emission energy, if we're ever capable of doing that. That is, if in 100 years there's still something worth saving.)
>>>>>>>
>>>>>> The idea of a 'gravity tug' isn't new. Its been around for at least 50 years. I just finished rereading Niven's 'A World Out Of Time', where one is a major plot point,
>>>>>> and I don't think it was new in 1976. Most practical versions envisage hundreds or thousands of passes by a much smaller tug.
>>>>>>
>>>>> But that would take centuries. We need a quicker solution.
>>>> Compared to the time it'll take for us to come up with a way of moving a moon out of orbit of a gas giant, moving it for there to close enough to earth to affect the orbit and controlling it accurately enough to get the desired new orbit centuries seems a more likely bet
>>> I strongly doubt that. But then of course I'm no expert. Are you ?
>> Jupiter's orbital speed is 13 km/s
>> Saturn's is 9.7 km/s
>>
>> We'd need to accelerate one of their moons to Earth's 29.8 km/s
>>
>> 1% of earth's mass is 5.972 × 10^22 kg
>>
>> You figure out the energy involved in doing that
>
> As I said I'm not an expert. I'd like somebody who is to look at it properly.
> And just throwing out big numbers won't change anything. We know we're dealing with pretty big things here, and the tools and actions needed to do them will need to be correspondingly big.
>

"Throwing out big numbers" is exactly the point. The laws of physics and
thermodynamics say what is possible to do and what it would take to do
it, and it seems you don't have an appreciation for what it would take
to do what you're saying - on a pure resource consumption level, let
alone developing the infrastructure and political will to achieve
something so unlike anything any human society has ever done before.

It seems like your mental image of this problem is that we need to nudge
these huge foam balls floating in space in our direction. Like a small
tugboat pulling a huge ship, it seems manageable because there is no
friction, right. Even if you can't move it a lot, a small amount of
acceleration in the right direction is enough to make it move in the
right direction and then it kind of takes care of itself.

The two issues are 1) these aren't huge foam balls or a large ship,
they're planetary bodies within two order of magnitudes of our own
planet in size. It's hard to picture how big that is because we can't
even picture how big *our* planet is BECAUSE IT'S SO BIG, but it's big.
And 2) while there is no friction in space to oppose movement, all those
planetary bodies are subject to gravitational forces that do.

Now, it's been too long since I've done maths and physics to actually do
the maths for you but I can try and find numbers that can help our
intuitions. First, in terms of mass it seems that Europa or Io are the
only ones of Jupiter's moons that are in our ballpark, with about
9x10^22 kg to the Moon's 7 for Io and 4x10^22 for Europa. Io is about
420 000 km from Jupiter, only a bit more than the 380 000 km the Moon is
from the Earth, and Europa is further at 670 000 km from Jupiter. All
the other moons are bigger (Callisto and Ganymede) or so many orders of
magnitudes smaller that you'd need millions to get the mass you want.

(already things are starting pretty badly because I can already say the
political will for destroying Io or Europa, of all moons in the Solar
System, will be nil).

Anyway, the distance from Jupiter tells you how much energy they'll need
to get out of Jupiter's orbit. Earth's mass is about 6x10^24 kg while
Jupiter's is about 500x that. While I can no longer do the math, I
*think* it should mean that at from an equal starting distance it should
take about 500x more energy to leave Jupiter's orbit than Earth's (I
checked equations, yes it seems energy should scale linearly with mass
and inversely with distance).

In other words, it would take 500 times more energy to pull Io from
Jupiter's orbit than it would take to pull the Moon from Earth's orbit,
and with smaller, further Europe it would merely take a modest 100 times
more energy to achieve that goal.

OK so pulling the Moon from Earth's orbit is also pretty hard to
picture, but unlike Io and Europa we have some concrete examples of
interacting with it. So here are some questions for you:

* By how much did the Apollo landers push the Moon when they landed on
it, do you think? Did they appreciably impact its orbit or was their
impact about as negligeable as that of you jumping on the couch ?

* For that matter, would you say that the total number of spaceships
that crashed into the Moon since the dawn of the space age had a
noticeable impact on its orbit or nah?

* While we're at it, what impact do you think atom bomb explosions had
on Earth's orbit?

* With that calibration out of the way, how much mass in terms of
spaceships or energy in terms of atom bombs do you think we'd have to
slam into the Moon to significantly impact its orbit?

* How much more do you think it would take to make it leave Earth's
orbit entirely and hurtle down towards Venus?

* If that mass is supposed to come from Earth, what fraction of that
mass would you say is carried in a typical Artemis launch - the most
powerful rocket launched so far ? 2 ? 10 ? 1000 ? 1 000 000 ? A number
too big to usefully picture?

* How many Artemis launches could humanity make a year if we *really*
tried do you think - considering right now we've done 1 and the next is
in a couple of years? And that adding it all other rockets (even though
many are doing things like launching satellites that we might want to
continue doing) increases that number by maybe two orders of magnitude
at most?

And that's ignoring the distance issue. Currently a probe takes 4-6
years to get to Jupiter (if they're actually going there; flybys can get
there in a year but this wouldn't be a flyby. And of course it takes
waaaaaaay longer than a year to organize a mission to Jupiter from
scratch). But Io or Europa are something like 10^20 more massive than a
probe, so accelerating them to a similar velocity is, well, I don't
know, maybe way harder than getting them to escape velocity; certainly
not much easier. So either we're adding yet more orders of magnitudes to
the energy we don't have, or the trip will be too long for a "quick"
solution. If it can even happen within a generation, again I haven't
done the math.

That's not even considering the fact that in space everything actually
depends on where the orbits are at any given time - you can definitely
reduce the amount of energy required, not to a possible amount but still
reduced, by picking the impulses and trajectories so as to use
gravitational forces as much as possible, as we currently do with
gravitational slingshots. I don't know what combination would be
required for the best results but apparently Earth and Jupiter have
close approaches about once a year. Add Europa/Io's orbits and I'd guess
we'd have several years between windows. And if you want to use
asteroids or other moons to push them instead of mass coming from Earth
then you also need to calculate those orbits - I wonder if that starts
hitting the limits of what we can even do computationally tbh.

>>>> although both of them seem much less practical than eliminating fossil fuel usage.
>>> Going carbon-neutral won't solve the problem.
>> It does stop further ocean acidification, limits the increase in temperature etc and over time afterwards natural processes will reduce the atmospheric CO2 levels (and we can do carbon extraction, although how practical it is to do is still unknown)
>
> I'm not arguing in any way against 0-emissions. Please do (though it looks like it's easier said than done). But it doesn't solve the problem of natural global warming. It will have to be addressed at some point, my guess is it will be pretty soon.

The catastrophe of anthropogenic global warming isn't so much that it's
happening (which is a problem, but not necessarily a catastrophe), but
that it's happening too fast for even our societies to smoothly adapt,
let alone evolved ecosystems. Natural climate fluctuations are much less
of an issue on that front; even insofar as it's true that we're adapted
to an unusually stable Holocene period and that natural fluctuations
could take us into unprecedented territory, we're also very adaptable
critters and there's no reason to think we couldn't make such a change
work if it happened over millenia or more. At those scales global
warming could even be beneficial, insofar as it causes the Earth to
support higher productivity.

I'm not sure what natural global warming you're talking about, if it's
linked to the Milankovich cycles or what, but do you have a cite on the
rate of change that's expected from it?

Either way I don't really see how moving the Earth's orbit would protect
us from climate fluctuations. It would make for a slightly colder
baseline, but *natural* climate change is capable of fluctuations around
that baseline that are massively larger than anything humanity's ever
experienced. If we're considering the human future over geological time
frames then dealing with significantly different climates (or forces
threatening to cause such) will be a must. Unless you think we should
keep adjusting the Earth's orbit like a dial marked "RACISM".