For Questions That Don't Merit Their Own Thread

[JoeSchmuckatelli]

1 hour ago, cubinator said:

Say you had invented a material strong enough for a space elevator, and could make a cable of it that's long enough. How would you get the cable up into space? Pulling it straight up from the ground doesn't seem terribly efficient, and going into orbit would just wrap it around the planet. Even the lightest cable would probably be very heavy. Would you have to build the cable in orbit and then push one end down to the ground to anchor it?

I explored this on these threads a couple of months ago (*don't know how well the search function works - but you could find many of the excellent responses).  I came away with the sense that Space Elevators are a fantasy by people who really don't know how orbital mechanics work.  (Even though some really smart guys have tried to figure this out - and may justify it...)

AKA just not feasible.

 

EDIT: New Q

When using cryogenic fuels, the sides of rockets ice up: I'm presuming via condensation from the air.

How thick can this ice get?

Edited August 20, 2021 by JoeSchmuckatelli

[DDE]

6 minutes ago, JoeSchmuckatelli said:

I explored this on these threads a couple of months ago (*don't know how well the search function works - but you could find many of the excellent responses).  I came away with the sense that Space Elevators are a fantasy by people who really don't know how orbital mechanics work.  (Even though some really smart guys have tried to figure this out - and may justify it...)

I think it began with people who did remember that a release point would be in GEO, and that a counterweight is necessary.

Then the "gravity stops at the Karman line" crowd came in.

[JoeSchmuckatelli]

1 minute ago, DDE said:

release point would be in GEO, and that a counterweight is necessary.

Right - and that it might have to extend out from GEO just as the cable was being dropped toward the planet for both weight and leverage; which seems both absurd and impossible.

[tomf]

You would start with your cable in geostationary orbit and then simultaneously lower one end and raise the other. The centre of mass stays at geostationary so doesn't move relative to the earth. I think tidal forces should keep the down bit pointing down and up up but you might need to deliberately remove angular momentum to stop the whole thing spinning.

Eventually nice and gently the end of your cable touches down 

21 minutes ago, JoeSchmuckatelli said:

Right - and that it might have to extend out from GEO just as the cable was being dropped toward the planet for both weight and leverage; which seems both absurd and impossible.

If you change the shape the centre of mass cannot change, otherwise you could boost your orbit by rotating and pumping fuel the way you can in ksp. So if you extend two cables with weights in different directions the com has to remain at geo. 

What will happen is the elevator will start to spin to maintain angular momentum. Not sure if tidal forces are strong enough to keep that under control or if you are going to need thrusters to control it. Probably depends on the cable winching speed 

But in principle orbital mechanics aren't the issue

[JoeSchmuckatelli]

19 minutes ago, tomf said:

You would start with your cable in geostationary orbit and then simultaneously lower one end and raise the other. The centre of mass stays at geostationary so doesn't move relative to the earth. I think tidal forces should keep the down bit pointing down and up up but you might need to deliberately remove angular momentum to stop the whole thing spinning.

Eventually nice and gently the end of your cable touches down 

If you change the shape the centre of mass cannot change, otherwise you could boost your orbit by rotating and pumping fuel the way you can in ksp. So if you extend two cables with weights in different directions the com has to remain at geo. 

What will happen is the elevator will start to spin to maintain angular momentum. Not sure if tidal forces are strong enough to keep that under control or if you are going to need thrusters to control it. Probably depends on the cable winching speed 

But in principle orbital mechanics aren't the issue

Reading your post...  Here's what I envision you are saying:

To do this, you need a cable in GeoStationary Orbit that's approximately 69,580 km long, with a large weight in the center - with the length of the cable stretched out 'perpendicular' to the surface at 35,790 km altitude (GSO).  Then you simultaneously lift one end and drop the other so that the COM remains at 35,790 km... allowing one end to touch the planet and the 'counterweight' part of the cable to extend into space to a final altitude of 69,580km from mean sea level.

Is that correct?

[Terwin]

5 minutes ago, JoeSchmuckatelli said:

Reading your post...  Here's what I envision you are saying:

To do this, you need a cable in GeoStationary Orbit that's approximately 69,580 km long, with a large weight in the center - with the length of the cable stretched out 'perpendicular' to the surface at 35,790 km altitude (GSO).  Then you simultaneously lift one end and drop the other so that the COM remains at 35,790 km... allowing one end to touch the planet and the 'counterweight' part of the cable to extend into space to a final altitude of 69,580km from mean sea level.

Is that correct?

That is one option, but you can also just have a large mass that gets extended a shorter distance upwards, this makes the 'up' part of the elevator much less expensive, as you only need to keep the center of mass the same, not mirror everything 100%  

[JoeSchmuckatelli]

5 minutes ago, Terwin said:

That is one option, but you can also just have a large mass that gets extended a shorter distance upwards, this makes the 'up' part of the elevator much less expensive, as you only need to keep the center of mass the same, not mirror everything 100%  

I get that - but you still don't get away from the need to have a 36,000 km long cable ready to go.  What I remember from the past discussion was that building out from GEO towards the earth wasn't really a viable option.  However this 'leverage from center' thing could do it... I guess.  From what I remember, however, is that @kerbiloid pointed out that to succeed the 'cable' needed to be relatively rigid... and yet at that length any structure effectively becomes a cable anyway.... which then defeats the effort.  Any harmonics at all will cause the end to whip.

[StrandedonEarth]

2 hours ago, JoeSchmuckatelli said:

Reading your post...  Here's what I envision you are saying:

To do this, you need a cable in GeoStationary Orbit that's approximately 69,580 km long, with a large weight in the center - with the length of the cable stretched out 'perpendicular' to the surface at 35,790 km altitude (GSO).  Then you simultaneously lift one end and drop the other so that the COM remains at 35,790 km... allowing one end to touch the planet and the 'counterweight' part of the cable to extend into space to a final altitude of 69,580km from mean sea level.

Is that correct?

This is how it’s done in Kim Stanley Robinson’s “Red Mars “ trilogy, with a counterweight instead of more cable. It also describes what happens if that counterweight gets detached…

[K^2]

4 hours ago, tomf said:

You would start with your cable in geostationary orbit and then simultaneously lower one end and raise the other. The centre of mass stays at geostationary so doesn't move relative to the earth. I think tidal forces should keep the down bit pointing down and up up but you might need to deliberately remove angular momentum to stop the whole thing spinning.

It's a bit more complex than that. Cable has to vary in thickness for anything practical and the counterweight is quite a bit more massive than the cable. You'll also want to absorb as much angular momentum as possible into the counterweight, so cable release will be done at an angle. The net effect is that initial orbit will differ from GEO quite significantly, and I couldn't tell you off the top of my head if it's higher or lower. I'd need to do a math for a specific example.

[JoeSchmuckatelli]

1 hour ago, StrandedonEarth said:

This is how it’s done in Kim Stanley Robinson’s “Red Mars “ trilogy, with a counterweight instead of more cable. It also describes what happens if that counterweight gets detached…

Well... At only 100 tons per kilometer for a 6 inch diameter steel wire cable we should get started. 

36,000 Superheavy launches should get the first strand going - plus a few more for connectors... 

That's only 3,600,000 tons of steel for the first 6 inch strand... And steel is only running a bit over $700 per ton - $2,520,000,000 if we can get wholesale pricing, just for the cables, so maybe another $100,000,000 for the connectors (and other stuff) - so let's round up to $3bn... And then double that for the counterweight... So $6bn... Not quite within NASA's budget - so we need international partners. 

Whoops - I forgot launch costs - anyone know what Superheavy's cost per flight is projected? 

Oh... 

How thick do you think it needs to be before we can start lowering the cable? 

Edited August 20, 2021 by JoeSchmuckatelli

[kerbiloid]

An azure volumetric network like a sky-high forest of spiralling columns woven of fractal threads.

Edited August 20, 2021 by kerbiloid

[tomf]

10 minutes ago, JoeSchmuckatelli said:

Well... At only 100 tons per kilometer for a 6 inch diameter steel wire cable we should get started. 

If you try to build it out of steel I think the top of the cable has to have a thickness of something like the moon. Steel ain't gonna cut it.

Wikipedia mentions a proposal for a 20 tonne, hair thickness cable which successively larger climbers would climb adding more strands as they go.

[JoeSchmuckatelli]

4 minutes ago, tomf said:

a 20 tonne, hair thickness cable

Now I'm getting images of a galactic cheese slicer. 

If the hair-thickness, 36,000 km cable has the tensile strength to support its own 20 ton weight, what won't it cut through? 

Edited August 20, 2021 by JoeSchmuckatelli

[kerbiloid]

Through another hair-thickness, 36,000 km cable with the tensile strength to support its own 20 ton weight.

[JoeSchmuckatelli]

30 minutes ago, kerbiloid said:

An azure volumetric network like a sky-high forest of spiralling columns woven of fractal threads

So we can build that? 

[ARS]

So... while browsing for an idea about sci-fi vehicles, I saw a quote which basically sums up like this:

"Though the bomber is unlikely to be shot down, owing to it's heavy armor and redundant backup flight systems, the highly classified nature of it's existence means that the enemy must not be allowed to recover any remains of it should one of these get shot down. As such, this aircraft is fitted with sophisticated systems that it is designed to detonate and combust on impact, should it crash, melting the structural airframe and destroying any hardware designated as classified asset. Guaranteeing that none of it's remains are left in a condition that allowed the enemy to obtain any information about it."

Now, logically speaking, does it make sense to put such a system on actual top secret military hardware? The one that completely destroy the asset to prevent the opposing side to gather intelligence of it? (not counting espionage and defection of course) Because AFAIK, even the modern day stealth bomber like B2 doesn't have a system like that (mainly from that 2008 B2 crash near the runway, the wreckage is still there after it went lithobraking)

[kerbiloid]

7 hours ago, JoeSchmuckatelli said:

So we can build that? 

Build. Grow. Like crystals.

No we can't. Because we don't have the hair-thickness, 36,000 km cable has the tensile strength to support its own 20 ton weight.

7 minutes ago, ARS said:

bomber is unlikely to be shot down, owing to it's heavy armor

Bomber? Armor?

Only attackers have the armor sometimes (if call it so). Bombers have a pan under man.

12 minutes ago, ARS said:

does it make sense to put such a system on actual top secret military hardware? The one that completely destroy the asset to prevent the opposing side to gather intelligence of it?

Every serious plane has "Identification, friend or foe (IFF)" system, and a self-destruction charge in it. (Idk about Cessnas).

The supersecret U-2 hit in 1960 had a photocamera self-destruction
Not used, as it was activated on stage button ejection, but the pilot bailed out instead of ejecting because the cabin was deformed.

The secret bombers usuually don't fall on alien territory.
Otherwise if a secret bomber falls, another secret bomber may come and drop bombs on it.

Any demolition charge weights and may accidentally explode unintentionally, so only the most secret parts can be equipped.

Also if that U-2 camera didn't have too powerful charge, the pilot could explode it manually from cabin before bailing out, to destroy it at least partially.
But as he suspected a big boom, he didn't, so the camera stayed relatively intact at all.

[DDE]

4 hours ago, ARS said:

So... while browsing for an idea about sci-fi vehicles, I saw a quote which basically sums up like this:

"Though the bomber is unlikely to be shot down, owing to it's heavy armor and redundant backup flight systems, the highly classified nature of it's existence means that the enemy must not be allowed to recover any remains of it should one of these get shot down. As such, this aircraft is fitted with sophisticated systems that it is designed to detonate and combust on impact, should it crash, melting the structural airframe and destroying any hardware designated as classified asset. Guaranteeing that none of it's remains are left in a condition that allowed the enemy to obtain any information about it."

Now, logically speaking, does it make sense to put such a system on actual top secret military hardware? The one that completely destroy the asset to prevent the opposing side to gather intelligence of it? (not counting espionage and defection of course) Because AFAIK, even the modern day stealth bomber like B2 doesn't have a system like that (mainly from that 2008 B2 crash near the runway, the wreckage is still there after it went lithobraking)

It's rather difficult to build and maintain such a system. The ejection seats are a maintenance menace already, now imagine filling the rest of the plane up with pyrotechnic ordnance sufficient to completely destroy it.

I also think sci-fi understates how difficult it is to completely destroy something structural like a RAM skin (ordinary explosives would just scatter it) while overstating the importance of reverse-engineering. Generally even acquiring examples of enemy materials science isn't going to let you reverse-enginesr it within the sapce of days to months. Most of intel from wreckage would come from comms and computers, and destroying those (as described re: IFF) is a lot easier.

Only it doesn't seem to be done either. There are rumours that leading military powers send submarine recovery crews to pick up aircraft wreckages, and not necessarily their own.

[SunlitZelkova]

4 hours ago, ARS said:

So... while browsing for an idea about sci-fi vehicles, I saw a quote which basically sums up like this:

"Though the bomber is unlikely to be shot down, owing to it's heavy armor and redundant backup flight systems, the highly classified nature of it's existence means that the enemy must not be allowed to recover any remains of it should one of these get shot down. As such, this aircraft is fitted with sophisticated systems that it is designed to detonate and combust on impact, should it crash, melting the structural airframe and destroying any hardware designated as classified asset. Guaranteeing that none of it's remains are left in a condition that allowed the enemy to obtain any information about it."

Now, logically speaking, does it make sense to put such a system on actual top secret military hardware? The one that completely destroy the asset to prevent the opposing side to gather intelligence of it? (not counting espionage and defection of course) Because AFAIK, even the modern day stealth bomber like B2 doesn't have a system like that (mainly from that 2008 B2 crash near the runway, the wreckage is still there after it went lithobraking)

Not exactly related, but there was a discussion about what measures could be taken to prevent a country with US equipment from using it against the US if the country "turned". Some thought nothing short of putting an explosive charge in the cockpit would stop them, whereas some argued that due to the lack of software updates, for modern equipment at least, it would sooner or later become unserviceable.

Does not apply to older generation equipment (just take a look at Iranian F-14s).

10 minutes ago, DDE said:

Only it doesn't seem to be done either. There are rumours that leading military powers send submarine recovery crews to pick up aircraft wreckages, and not necessarily their own.

How would a sub recover aircraft wreckage?

There were some news reports (from normal news sources... not an official announcement) when the JASDF lost an F-35A that China and Russia were "looking for it". Just exactly how a decently sized surface action group which would be needed for such a recovery op would transit past either Okinawa or through the La Perouse Straight (it was lost in the Pacific) without having been noticed earlier and raising alarm, I don't know, which makes me skeptical of the accuracy of such reports.

[kerbiloid]

59 minutes ago, DDE said:

There are rumours that leading military powers send submarine recovery crews to pick up aircraft wreckages, and not necessarily their own.

https://en.wikipedia.org/wiki/Project_Azorian

[DDE]

57 minutes ago, SunlitZelkova said:

Does not apply to older generation equipment (just take a look at Iranian F-14s).

Last I heard, they aren't flyable exactly due to lack of spare parts.

57 minutes ago, SunlitZelkova said:

There were some news reports (from normal news sources... not an official announcement) when the JASDF lost an F-35A that China and Russia were "looking for it". Just exactly how a decently sized surface action group which would be needed for such a recovery op would transit past either Okinawa or through the La Perouse Straight (it was lost in the Pacific) without having been noticed earlier and raising alarm, I don't know, which makes me skeptical of the accuracy of such reports.

Usually such reports center around the GUGI ship Yantar, and her fleet of ROVs and two Consul submersibles (related to the Finnish-made civilian Mirs). So, not a surface action group.

That said, she usually has her transponder on, sometimes even when performing a side-looking sonar search pattern.

The Kashalot AGS I posted above, and her sisterships, have an even more discrete deployment method:

Edited August 21, 2021 by DDE

[mikegarrison]

On 8/20/2021 at 12:26 AM, TheSaint said:

No, silly, only vampires sparkle.

(My uncle worked for Raytheon during WWII, and retired in the 1970s. I heard all the stories, including how they worked on the microwave oven. )

This reminds me. I worked with a woman whose husband worked at Raytheon. This was back in the 1980s.

His paying job was to engineer radar detectors, so he also built his own police radar detector for his car. This was a time when the legality of radar detectors was still somewhat questionable (and before police started using lasers).

[kerbiloid]

12 minutes ago, mikegarrison said:

This was a time when the legality of radar detectors was still somewhat questionable (and before police started using lasers).

So, as now they build the anti-police laser detectors for personal cars, and as a by-product  - the anti-laser satellite protection.

Edited August 21, 2021 by kerbiloid

[DDE]

23 minutes ago, mikegarrison said:

His paying job was to engineer radar detectors, so he also built his own police radar detector for his car. This was a time when the legality of radar detectors was still somewhat questionable (and before police started using lasers).

 AFAIK back in the 1990s a Russian soeedgun manufacturer also sold an ECM station that would ostensibly only work long enough for you to hit the brakes.

[DDE]

Unclear which thread yet, if any.