On Tuesday, June 27, 2023 at 7:15:06 AM UTC-6, Jack Bohn wrote:

> I think Time Travel is on the list of impossible things that are proverbially limited to one per story, like FTL

That's a general rule for SF. Of course, Star Trek breaks it, as well as many
stories that validly show time travel as a consequence of FTL.

This is about stories that qualify as hard SF. Stories that basically include
_no_ impossible things, but instead include advanced technologies only
where based on real science.

John Savard

On Sunday, June 25, 2023 at 6:51:33 PM UTC-6, Lynn McGuire wrote:

> Dan says "I’m considering hard SF to mean a few different things:

> As with all my lists, I play pretty loose with the rules
> because I think it’s more important to get people reading good books
> than sticking to some arbitrary sub-genre definitions."

I do *not* approve.

It's certainly good to get people reading good books. If you can't
put those books on one list, put them on another list.

But if you don't use the generally-accepted definition of "Hard SF"
for the works on a list of "the best Hard SF books", then

a) the list is less useful, and

b) you're getting people to read the books under false pretenses.

John Savard

On Wednesday, July 5, 2023 at 2:02:58 AM UTC-4, Hamish Laws wrote:
> On Wednesday, July 5, 2023 at 3:45:23 PM UTC+10, Lynn McGuire wrote:
> > On 7/4/2023 8:50 AM, Hamish Laws wrote:
> > > On Tuesday, July 4, 2023 at 9:32:08 AM UTC+10, Dorothy J Heydt wrote:
> > >> In article <1598c45c-d412-43ee...@googlegroups.com>,
> > >> Hamish Laws <hamis...@gmail.com> wrote:
> > >>> I read it in hardback when it was released, my recollection is that
> > >>> there's a lot of actually scientifically impossible stuff in the series
> > >>> A simple example is the idea of a stealth ship in space. It doesn't work.
> > >> (Hal Heydt)
> > >> Take it up with E. E. "Doc" Smith. Lensman universe doesn't seem
> > >> to have developed IR detection systems.
> > >
> > > Would anybody ever have described Lensmen as hard science fiction?
> > > I've read several of the Darkship series and I enjoyed them but I don't think they qualify as hard science fiction, admittedly I'm not sure how many of the ones Livingston lists would either
> > The Darkship books are 300+ years in the future. Things can and will
> > radically change by then. Unless, we end up radiating the entire planet..
> >
> > First, we had the stone age. Then we had the bronze age. Then we had
> > the iron age. Then we had the steel age. Now we are in the carbon
> > fiber age. Who knows what magic materials will be created next in these
> > fast moving times ?
> >
> https://www.forbes.com/sites/chadorzel/2015/12/22/the-expanse-and-the-physics-of-stealth-in-space/?sh=6af1cc7c6482
> has a bit of a breakdown on the problems of stealth in space

....and cites our own James Nicoll!

Seriously, you can't make a ship that's stealthy from every direction. But if you know where the observer is, you can do better.
You make a ice cream cone shaped shield, covered with radar absorbing material, and actively cooled down the level of the CRB. (~3K).
This is hard, but shouldn't be impossible, since some parts of the JWST run at just 6K. Most of the cold side of the JWST is
passively cooled to ~40k, which I suspect is enough to imitate a shaded asteroid.

Point the cooled shield at the observer - the shape and RAM protect against radar, and the cooled surface prevents you from standing
out in IR. You can radiate on the backside, away from the observer.

Note that maneuvering while shielded is a lot tougher. You don't want a hot gas plume. In LEO, some movement can perhaps be accomplished using
magnetic torque.

pt

On Wed, 5 Jul 2023 03:34:44 -0700 (PDT), Quadibloc <jsavard@ecn.ab.ca>
wrote:

>On Sunday, June 25, 2023 at 6:51:33?PM UTC-6, Lynn McGuire wrote:
>
>> Dan says "I’m considering hard SF to mean a few different things:
>
>> As with all my lists, I play pretty loose with the rules
>> because I think it’s more important to get people reading good books
>> than sticking to some arbitrary sub-genre definitions."
>
>I do *not* approve.
>
>It's certainly good to get people reading good books. If you can't
>put those books on one list, put them on another list.
>
>But if you don't use the generally-accepted definition of "Hard SF"
>for the works on a list of "the best Hard SF books", then
>
>a) the list is less useful, and
>
>b) you're getting people to read the books under false pretenses.

And he is giving them a false understanding of, in this case, what
"hard science fiction" refers to. Whether they read the books or
merely examine them on (say) Wikipedia.
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."

On 7/5/2023 1:02 AM, Hamish Laws wrote:
> On Wednesday, July 5, 2023 at 3:45:23 PM UTC+10, Lynn McGuire wrote:
>> On 7/4/2023 8:50 AM, Hamish Laws wrote:
>>> On Tuesday, July 4, 2023 at 9:32:08 AM UTC+10, Dorothy J Heydt wrote:
>>>> In article <1598c45c-d412-43ee...@googlegroups.com>,
>>>> Hamish Laws <hamis...@gmail.com> wrote:
>>>>> I read it in hardback when it was released, my recollection is that
>>>>> there's a lot of actually scientifically impossible stuff in the series
>>>>> A simple example is the idea of a stealth ship in space. It doesn't work.
>>>> (Hal Heydt)
>>>> Take it up with E. E. "Doc" Smith. Lensman universe doesn't seem
>>>> to have developed IR detection systems.
>>>
>>> Would anybody ever have described Lensmen as hard science fiction?
>>> I've read several of the Darkship series and I enjoyed them but I don't think they qualify as hard science fiction, admittedly I'm not sure how many of the ones Livingston lists would either
>> The Darkship books are 300+ years in the future. Things can and will
>> radically change by then. Unless, we end up radiating the entire planet.
>>
>> First, we had the stone age. Then we had the bronze age. Then we had
>> the iron age. Then we had the steel age. Now we are in the carbon
>> fiber age. Who knows what magic materials will be created next in these
>> fast moving times ?
>>
> https://www.forbes.com/sites/chadorzel/2015/12/22/the-expanse-and-the-physics-of-stealth-in-space/?sh=6af1cc7c6482
> has a bit of a breakdown on the problems of stealth in space

I got paywalled.

Lynn

On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
> On 2023-07-04, Scott Lurndal <scott@slp53.sl.home> wrote:
>
>> Modern designs for thermal detection prevention focus on placing
>> the heat producing elements on the top of the fuselage, to shield the thermal
>> emissions from ground-based detectors. They also pump fuel through
>> the leading edge surfaces to cool them.
>
> Stupid question: Aren't you trailing a plume of hot exhaust?

If the plume is very hot, you are not running very efficiently on modern
jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
are running 11:1 on the combustion air versus the fanned air. The old
days of 900 F exhaust are gone except for old planes like the B-52s and
the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
bypass jet engines are probably running 200 F exhaust (SWAG) assuming
good mixing between the combustion air and the fanned air.

I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
is. Probably at least 5:1 though since they have an afterburner also
that probably complicates bypassing.

Lynn

On Wednesday, July 5, 2023 at 11:59:57 PM UTC+1, Lynn McGuire wrote:
> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
> > On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:
> >
> >> Modern designs for thermal detection prevention focus on placing
> >> the heat producing elements on the top of the fuselage, to shield the thermal
> >> emissions from ground-based detectors. They also pump fuel through
> >> the leading edge surfaces to cool them.
> >
> > Stupid question: Aren't you trailing a plume of hot exhaust?
> If the plume is very hot, you are not running very efficiently on modern
> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
> are running 11:1 on the combustion air versus the fanned air. The old
> days of 900 F exhaust are gone except for old planes like the B-52s and
> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
> bypass jet engines are probably running 200 F exhaust (SWAG) assuming
> good mixing between the combustion air and the fanned air.
>
> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
> is. Probably at least 5:1 though since they have an afterburner also
> that probably complicates bypassing.
>
> Lynn
Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to damage the ground (or deck) under it (which curiously was not such a problem with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-heating-problems/

The newly released document, hosted on a government building-design resource
site, outlines what base-construction engineers need to do to ensure that
the F-35B’s exhaust does not turn the surface it lands on into an
area-denial weapon. And it’s not trivial. Vertical-landing “pads will be
exposed to 1700 deg. F and high velocity (Mach 1) exhaust,” the report says.
The exhaust will melt asphalt and “is likely to spall the surface of
standard airfield concrete pavements on the first VL.” (The report leaves to
the imagination what jagged chunks of spalled concrete will do in a
supersonic blast field.)

Andrew McDowell <mcdowell_ag@sky.com> writes:
>On Wednesday, July 5, 2023 at 11:59:57=E2=80=AFPM UTC+1, Lynn McGuire wrote=
>:
>> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:=20
>> > On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:=20
>> >=20
>> >> Modern designs for thermal detection prevention focus on placing=20
>> >> the heat producing elements on the top of the fuselage, to shield the =
>thermal=20
>> >> emissions from ground-based detectors. They also pump fuel through=20
>> >> the leading edge surfaces to cool them.=20
>> >=20
>> > Stupid question: Aren't you trailing a plume of hot exhaust?
>> If the plume is very hot, you are not running very efficiently on modern=
>=20
>> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX=20
>> are running 11:1 on the combustion air versus the fanned air. The old=20
>> days of 900 F exhaust are gone except for old planes like the B-52s and=
>=20
>> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high=20
>> bypass jet engines are probably running 200 F exhaust (SWAG) assuming=20
>> good mixing between the combustion air and the fanned air.=20
>>=20
>> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2=20
>> is. Probably at least 5:1 though since they have an afterburner also=20
>> that probably complicates bypassing.=20
>>=20
>> Lynn
>Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to d=
>amage the ground (or deck) under it (which curiously was not such a problem=
> with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-he=
>ating-problems/
>
>The newly released document,

For some value of "newly released" that includes 13 years ago.....

On 7/5/2023 11:41 PM, Andrew McDowell wrote:
> On Wednesday, July 5, 2023 at 11:59:57 PM UTC+1, Lynn McGuire wrote:
>> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
>>> On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:
>>>
>>>> Modern designs for thermal detection prevention focus on placing
>>>> the heat producing elements on the top of the fuselage, to shield the thermal
>>>> emissions from ground-based detectors. They also pump fuel through
>>>> the leading edge surfaces to cool them.
>>>
>>> Stupid question: Aren't you trailing a plume of hot exhaust?
>> If the plume is very hot, you are not running very efficiently on modern
>> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
>> are running 11:1 on the combustion air versus the fanned air. The old
>> days of 900 F exhaust are gone except for old planes like the B-52s and
>> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
>> bypass jet engines are probably running 200 F exhaust (SWAG) assuming
>> good mixing between the combustion air and the fanned air.
>>
>> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
>> is. Probably at least 5:1 though since they have an afterburner also
>> that probably complicates bypassing.
>>
>> Lynn
> Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to damage the ground (or deck) under it (which curiously was not such a problem with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-heating-problems/
>
> The newly released document, hosted on a government building-design resource
> site, outlines what base-construction engineers need to do to ensure that
> the F-35B’s exhaust does not turn the surface it lands on into an
> area-denial weapon. And it’s not trivial. Vertical-landing “pads will be
> exposed to 1700 deg. F and high velocity (Mach 1) exhaust,” the report says.
> The exhaust will melt asphalt and “is likely to spall the surface of
> standard airfield concrete pavements on the first VL.” (The report leaves to
> the imagination what jagged chunks of spalled concrete will do in a
> supersonic blast field.)

I found it. I was hopelessly optimistic at 5:1. The bypass ratio for
the F-35 engine is 0.57:1. That means the exhaust is probably 500 F to
600 F.
https://en.wikipedia.org/wiki/Pratt_%26_Whitney_F135

Lynn

On Friday, July 7, 2023 at 6:40:21 AM UTC+1, Lynn McGuire wrote:
> On 7/5/2023 11:41 PM, Andrew McDowell wrote:
> > On Wednesday, July 5, 2023 at 11:59:57 PM UTC+1, Lynn McGuire wrote:
> >> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
> >>> On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:
> >>>
> >>>> Modern designs for thermal detection prevention focus on placing
> >>>> the heat producing elements on the top of the fuselage, to shield the thermal
> >>>> emissions from ground-based detectors. They also pump fuel through
> >>>> the leading edge surfaces to cool them.
> >>>
> >>> Stupid question: Aren't you trailing a plume of hot exhaust?
> >> If the plume is very hot, you are not running very efficiently on modern
> >> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
> >> are running 11:1 on the combustion air versus the fanned air. The old
> >> days of 900 F exhaust are gone except for old planes like the B-52s and
> >> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
> >> bypass jet engines are probably running 200 F exhaust (SWAG) assuming
> >> good mixing between the combustion air and the fanned air.
> >>
> >> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
> >> is. Probably at least 5:1 though since they have an afterburner also
> >> that probably complicates bypassing.
> >>
> >> Lynn
> > Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to damage the ground (or deck) under it (which curiously was not such a problem with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-heating-problems/
> >
> > The newly released document, hosted on a government building-design resource
> > site, outlines what base-construction engineers need to do to ensure that
> > the F-35B’s exhaust does not turn the surface it lands on into an
> > area-denial weapon. And it’s not trivial. Vertical-landing “pads will be
> > exposed to 1700 deg. F and high velocity (Mach 1) exhaust,” the report says.
> > The exhaust will melt asphalt and “is likely to spall the surface of
> > standard airfield concrete pavements on the first VL.” (The report leaves to
> > the imagination what jagged chunks of spalled concrete will do in a
> > supersonic blast field.)
> I found it. I was hopelessly optimistic at 5:1. The bypass ratio for
> the F-35 engine is 0.57:1. That means the exhaust is probably 500 F to
> 600 F.
> https://en.wikipedia.org/wiki/Pratt_%26_Whitney_F135
>
> Lynn
Well spotted. I have the impression that military requirements for supersonic speed and stealth (not letting radars see the fan blades) make high bypass ratios tricky, although https://en.wikipedia.org/wiki/Adaptive_Versatile_Engine_Technology might perhaps reach higher bypass ratios at times.

On 7/7/2023 11:31 AM, Andrew McDowell wrote:
> On Friday, July 7, 2023 at 6:40:21 AM UTC+1, Lynn McGuire wrote:
>> On 7/5/2023 11:41 PM, Andrew McDowell wrote:
>>> On Wednesday, July 5, 2023 at 11:59:57 PM UTC+1, Lynn McGuire wrote:
>>>> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
>>>>> On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:
>>>>>
>>>>>> Modern designs for thermal detection prevention focus on placing
>>>>>> the heat producing elements on the top of the fuselage, to shield the thermal
>>>>>> emissions from ground-based detectors. They also pump fuel through
>>>>>> the leading edge surfaces to cool them.
>>>>>
>>>>> Stupid question: Aren't you trailing a plume of hot exhaust?
>>>> If the plume is very hot, you are not running very efficiently on modern
>>>> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
>>>> are running 11:1 on the combustion air versus the fanned air. The old
>>>> days of 900 F exhaust are gone except for old planes like the B-52s and
>>>> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
>>>> bypass jet engines are probably running 200 F exhaust (SWAG) assuming
>>>> good mixing between the combustion air and the fanned air.
>>>>
>>>> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
>>>> is. Probably at least 5:1 though since they have an afterburner also
>>>> that probably complicates bypassing.
>>>>
>>>> Lynn
>>> Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to damage the ground (or deck) under it (which curiously was not such a problem with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-heating-problems/
>>>
>>> The newly released document, hosted on a government building-design resource
>>> site, outlines what base-construction engineers need to do to ensure that
>>> the F-35B’s exhaust does not turn the surface it lands on into an
>>> area-denial weapon. And it’s not trivial. Vertical-landing “pads will be
>>> exposed to 1700 deg. F and high velocity (Mach 1) exhaust,” the report says.
>>> The exhaust will melt asphalt and “is likely to spall the surface of
>>> standard airfield concrete pavements on the first VL.” (The report leaves to
>>> the imagination what jagged chunks of spalled concrete will do in a
>>> supersonic blast field.)
>> I found it. I was hopelessly optimistic at 5:1. The bypass ratio for
>> the F-35 engine is 0.57:1. That means the exhaust is probably 500 F to
>> 600 F.
>> https://en.wikipedia.org/wiki/Pratt_%26_Whitney_F135
>>
>> Lynn
> Well spotted. I have the impression that military requirements for supersonic speed and stealth (not letting radars see the fan blades) make high bypass ratios tricky, although https://en.wikipedia.org/wiki/Adaptive_Versatile_Engine_Technology might perhaps reach higher bypass ratios at times.

Modern high bypass jet engines have huge first stage blades. That does
seem to be a limit for stealthiness. Plus the afterburners might
require a high inlet temperature.

Lynn

Lynn McGuire <lynnmcguire5@gmail.com> writes:
>On 7/7/2023 11:31 AM, Andrew McDowell wrote:
>> On Friday, July 7, 2023 at 6:40:21 AM UTC+1, Lynn McGuire wrote:
>>> On 7/5/2023 11:41 PM, Andrew McDowell wrote:
>>>> On Wednesday, July 5, 2023 at 11:59:57 PM UTC+1, Lynn McGuire wrote:
>>>>> On 7/4/2023 10:06 AM, Christian Weisgerber wrote:
>>>>>> On 2023-07-04, Scott Lurndal <sc...@slp53.sl.home> wrote:
>>>>>>
>>>>>>> Modern designs for thermal detection prevention focus on placing
>>>>>>> the heat producing elements on the top of the fuselage, to shield the thermal
>>>>>>> emissions from ground-based detectors. They also pump fuel through
>>>>>>> the leading edge surfaces to cool them.
>>>>>>
>>>>>> Stupid question: Aren't you trailing a plume of hot exhaust?
>>>>> If the plume is very hot, you are not running very efficiently on modern
>>>>> jet engines. The latest ultra lean fire engines on the Boeing 737 MAX
>>>>> are running 11:1 on the combustion air versus the fanned air. The old
>>>>> days of 900 F exhaust are gone except for old planes like the B-52s and
>>>>> the old 737s with the cigar tube Pratt & Whitneys. Today's ultra high
>>>>> bypass jet engines are probably running 200 F exhaust (SWAG) assuming
>>>>> good mixing between the combustion air and the fanned air.
>>>>>
>>>>> I do not have a clue what the bypass ratio on the F-35, F-22, and B-2
>>>>> is. Probably at least 5:1 though since they have an afterburner also
>>>>> that probably complicates bypassing.
>>>>>
>>>>> Lynn
>>>> Can't find the bypass ratio, but the F-35B in STOVL mode is hot enough to damage the ground (or deck) under it (which curiously was not such a problem with the Harrier/AV8-B) https://theaviationist.com/2010/11/24/the-f-35b-heating-problems/
>>>>
>>>> The newly released document, hosted on a government building-design resource
>>>> site, outlines what base-construction engineers need to do to ensure that
>>>> the F-35B’s exhaust does not turn the surface it lands on into an
>>>> area-denial weapon. And it’s not trivial. Vertical-landing “pads will be
>>>> exposed to 1700 deg. F and high velocity (Mach 1) exhaust,” the report says.
>>>> The exhaust will melt asphalt and “is likely to spall the surface of
>>>> standard airfield concrete pavements on the first VL.” (The report leaves to
>>>> the imagination what jagged chunks of spalled concrete will do in a
>>>> supersonic blast field.)
>>> I found it. I was hopelessly optimistic at 5:1. The bypass ratio for
>>> the F-35 engine is 0.57:1. That means the exhaust is probably 500 F to
>>> 600 F.
>>> https://en.wikipedia.org/wiki/Pratt_%26_Whitney_F135
>>>
>>> Lynn
>> Well spotted. I have the impression that military requirements for supersonic speed and stealth (not letting radars see the fan blades) make high bypass ratios tricky, although https://en.wikipedia.org/wiki/Adaptive_Versatile_Engine_Technology might perhaps reach higher bypass ratios at times.
>
>Modern high bypass jet engines have huge first stage blades. That does
>seem to be a limit for stealthiness. Plus the afterburners might
>require a high inlet temperature.

There are two approaches to bypass - one is a larger fan the other
is a smaller core. The latter is the approach being used for the
next generation of military jet engines (e.g. HyTEC) along with
a feature called 'adaptive' that can dynamically change the
bypass ratio. There is an adaptive engine in development as a possible replacement
for the F135 engine used in the F35 under the ATTAM program.

See also 'ADVENT' (ADapative VErsitile ENgine Technology).