Space Shuttle Theory

[JB0]

And, "its just Cheeze Its and KoolAid packets"... except, for efficiency, we would be shooting tons of Cheeze Its and KoolAid per shot, and last I check, a ton of KoolAid is still a ton. Penetration power may differ, but one ton moving at Mach 25 is going to leave a nice dent on anything it hits... provided the target survives the impact.

A ton of ANYTHING moving at mach 25 is going to pretty much obliterate the target. Penetration power is pretty much irrelevant.

There is a narrow band of re-entry angles where it is feasible.  Too fast/steep, you'll burn up even worse, too slow/shallow, you won't slow down enough and will bounce back up into the atmosphere. 

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So, if you screw up on re-entry, you either burn up in a fireball, or you freeze when your shuttle skips off into the Big Black. Either way, it's a risky business, and having only 2 shuttle failures is actually indicative of the professionism at NASA.

And we only lost one on re-entry.

Sadly, that was due to the ostrich belief. If you ignore a problem, it doesn't go away. Just because foam never ripped a hole in the RCC panels before didn't mean it wasn't possible. It just took a while for it to hit right.

The issue still stands though; the shuttle design is starting to throw up more problems than solutions. It's really time for an overhaul of the whole system.

It's not throwing a lot more issues up than before.

It's just that the inherent flaws are becoming more visible after the CAIB review's scathing indictment of the entire NASA culture.

They can't go back to just ignoring potential problems without getting roasted for it, particularly as administrator O'Keefe is VERY passionate about implementing ALL of the CAIB's recommendations, ESPECIALLY the ones that do more than fix the immediate problem.

Apollo 1 burned because NASA was cutting too many corners in the development of their moon mission.

Challenger burned because NASA was flying rockets in an environment they weren't spec'ed to fly in due to the risk of seal failure.

Columbia burned because NASA was ignoring objects falling at high velocities towards heatshield panels that weren't spec'ed for impact resistance.

Why risk a fourth crew to carelessness?

The above is an oversimplification of events, but at its core is quite accurate.

It was the logic of the CAIB in going beyond the technical reasons for the accident, and it was logic O'Keefe found very sound.

[Zentrandude]

think you guys are over thinking this abit. geostationary orbit been done alot of times but the main thing you guys are not mentioning that it requires alot of fuel to keep it up so it won't drop like a rock also it would need to hold the fuel and need thrusters on the bottom and blah blah blah.

[David Hingtgen]

Geostationary things tend not to ever come back. They don't worry about re-entry. And it doesn't take a lot of fuel to stay up---they are up very high and so gravity only has a slight effect--it takes years for their orbits to decay. Only a few nudges every once in a while, if that. Shuttles are often used to help "nudge" satellites back up, giving them a few more years of use. After a couple decades, they all fall down and burn up.

All the GPS satellites are a good example. They're not burning tons of fuel 24/7 to stay up. They'll come down, eventually. Will take many years, and their small fuel supply can nudge them back up a few times---but they'll need replacing eventually, once they burn up on reentry.

Edited August 3, 2005 by David Hingtgen

[JB0]

think you guys are over thinking this abit.  geostationary orbit been done alot of times but the main thing you guys are not mentioning that it requires alot of fuel to keep it up so it won't drop like a rock also it would need to hold the fuel and need thrusters on the bottom and blah blah blah.

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Hence why a railgun isn't a feasable launch system, even for supply capsules. You need guidance systems.

[Lynx7725]

last I check, a ton of KoolAid is still a ton. Penetration power may differ, but one ton moving at Mach 25 is going to leave a nice dent on anything it hits... provided the target survives the impact.

A ton of ANYTHING moving at mach 25 is going to pretty much obliterate the target. Penetration power is pretty much irrelevant.

Uhm, I was being facetious.

The issue still stands though; the shuttle design is starting to throw up more problems than solutions. It's really time for an overhaul of the whole system.

It's not throwing a lot more issues up than before.

It's just that the inherent flaws are becoming more visible after the CAIB review's scathing indictment of the entire NASA culture.

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Honestly? I think age is starting to cause the flaws to be more visible too. Of course, I'm not really certified to say anything much on it, but I would dearly like to see some additional progress in this area.

Having a "dead-stick" glider as our most replacable/ servicable aerospace asset strikes me as somewhat wrong.

[Zentrandude]

Geostationary things tend not to ever come back.  They don't worry about re-entry.  And it doesn't take a lot of fuel to stay up---they are up very high and so gravity only has a slight effect--it takes years for their orbits to decay.  Only a few nudges every once in a while, if that. Shuttles are often used to help "nudge" satellites back up, giving them a few more years of use.  After a couple decades, they all fall down and burn up.

All the GPS satellites are a good example.  They're not burning tons of fuel 24/7 to stay up.  They'll come down, eventually.  Will take many years, and their small fuel supply can nudge them back up a few times---but they'll need replacing eventually, once they burn up on reentry.

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then your not getting what hes trying to say he wants to have a geostationary object slowly going down to land.

[Lynx7725]

then your not getting what hes trying to say he wants to have a geostationary object slowly going down to land.

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Still won't happen.

Geostationary Orbit is a orbit at 35,786 km above ground, where your object appear to stay fixed over a location.. say, Washington D.C. The orbital velocity for a Geostationary Orbit is approximately 3.07kps.

If you go out of Geostationary Orbit, but wish to appear geostationary relative to Washington D.C., you have to increase your orbital velocity to compensate for your loss of gravitational potential energy. Meaning, you go lower, you fly faster.

Meaning, when you get to 0km above ground, your orbital velocity is so fast, you smack into the ground leaving an impact crater. That's provided you don't burn up on reentry or skip off the atmosphere due to your insertion angle.

EDIT: I think it's easier to explain if you consider the energy state of a shuttle.

At the start, the shuttle is in space, in orbit around the Rarth. It has an energy of X, comprising of Gravitational Potential Energy (GPE) of A (from its high position relative to Earth) and Kinetic Energy (KE) of B (from its orbital velocity). It also has a Heat energy of C (from its latent heat energy), but this is fairly small at this stage.

You drop the shuttle out of orbit, by principle of conservation of energy, X must be constant. Since C does not change (until it hits the atmosphere), a reduction in GPE (A ) must be compensated with an increase in KE (B ). So the shuttle must speed up.

But the Shuttle's eventual goal is to reduce both its GPE and KE to zero (relative to Earth). GPE, no problem, just drop down in altitude. KE is a problem, since each reduction in GPE will increase KE. But the shuttle must shed enough KE to bring it to zero.. and since the shuttle is a dead-stick glider, it can't burn thrust to reduce the KE to zero.

So, it instead uses the atmosphere and converts KE to increases Heat energy (C ) and use thermodynamics to dissipate the energy into the atmosphere. This allows the shuttle to reduce its KE to zero (by eventually getting slow enough to land and stop on the runway).

I think what happens is the shuttle will typically aim ahead of its intended landing point, reentry and slow down, and let Earth catch up via its rotation, and then land. It becomes a mathematical ballet.

Edited August 3, 2005 by Lynx7725

[Sundown]

You can't "slowly" come down.  Basically---To stay in orbit, you have to go fast.  If you slow down a LOT, then you'll come down FAST.  Which of course, "friction from dropping straight down" is just as bad as "friction from a 40 degree angle of attack". 

There is a narrow band of re-entry angles where it is feasible.  Too fast/steep, you'll burn up even worse, too slow/shallow, you won't slow down enough and will bounce back up into the atmosphere.

Burt Rutan's SpaceShipOne that won the X-Prize had an interesting way of dealing with reentry. The whole tail assembly was hinged and as the craft reentered, would fold upwards, doing what they referred to as "feathering". This significantly increased the drag the craft experienced at high altitudes, and by the time the craft encountered thicker atmosphere it was already slow enough to not worry about burning up. Thus it didn't need to follow precise reentry trajectories or carry heavy heat shielding. The craft's weight distribution when "feathering" also naturally caused it to stay upright, so there wasn't much worry about it coming in at the wrong angle or orientation. It would just eventually right itself.

Of course this was with a low-orbit craft that barely left the atmosphere. Not sure how practical it would be in other applications.

-Al

[Zentrandude]

then your not getting what hes trying to say he wants to have a geostationary object slowly going down to land.

316779[/snapback]

Still won't happen.

Geostationary Orbit is a orbit at 35,786 km above ground, where your object appear to stay fixed over a location.. say, Washington D.C. The orbital velocity for a Geostationary Orbit is approximately 3.07kps.

If you go out of Geostationary Orbit, but wish to appear geostationary relative to Washington D.C., you have to increase your orbital velocity to compensate for your loss of gravitational potential energy. Meaning, you go lower, you fly faster.

Meaning, when you get to 0km above ground, your orbital velocity is so fast, you smack into the ground leaving an impact crater. That's provided you don't burn up on reentry or skip off the atmosphere due to your insertion angle.

EDIT: I think it's easier to explain if you consider the energy state of a shuttle.

At the start, the shuttle is in space, in orbit around the Rarth. It has an energy of X, comprising of Gravitational Potential Energy (GPE) of A (from its high position relative to Earth) and Kinetic Energy (KE) of B (from its orbital velocity). It also has a Heat energy of C (from its latent heat energy), but this is fairly small at this stage.

You drop the shuttle out of orbit, by principle of conservation of energy, X must be constant. Since C does not change (until it hits the atmosphere), a reduction in GPE (A ) must be compensated with an increase in KE (B ). So the shuttle must speed up.

But the Shuttle's eventual goal is to reduce both its GPE and KE to zero (relative to Earth). GPE, no problem, just drop down in altitude. KE is a problem, since each reduction in GPE will increase KE. But the shuttle must shed enough KE to bring it to zero.. and since the shuttle is a dead-stick glider, it can't burn thrust to reduce the KE to zero.

So, it instead uses the atmosphere and converts KE to increases Heat energy (C ) and use thermodynamics to dissipate the energy into the atmosphere. This allows the shuttle to reduce its KE to zero (by eventually getting slow enough to land and stop on the runway).

I think what happens is the shuttle will typically aim ahead of its intended landing point, reentry and slow down, and let Earth catch up via its rotation, and then land. It becomes a mathematical ballet.

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now your realy over thinking it also i belive you need to slow down the shuttle not speed it up and already mention you need thrusters on the bottom and fuel and blah blah blah. oh yah also post link where you cut and paste that . Maybe we shouldnt use the shuttle as an test vechical for what the guy wants and use a old fasion orbital lander so ppl wont get confused.

sundown thats a good example about that.

[Lynx7725]

now your realy over thinking it also i belive you need to slow down the shuttle not speed it up and already mention you need thrusters on the bottom and fuel and blah blah blah. oh yah also post link where you cut and paste that  .  Maybe we shouldnt use the shuttle as an test vechical for what the guy wants and use a old fasion orbital lander so ppl wont get confused.

sundown thats a good example about that.

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Err.

It's not like I want to SPEED UP the shuttle, it's that it "naturally" speeds up when you drop in altitude. The unpowered shuttle can't avoid it; the shuttle can only use other "passive" means to shed the Kinetic Energy, and the way chosen was to shed it as heat.

Change it to a orbital lander, you get the same results. Drop it from orbit, it will gain KE while losing GPE. Unless it has some means of shedding or converting the KE to some other energy type, the orbital lander will smack into the ground at a high velocity. Not good.

Which is why old-fashioned orbital landers (like the Eagle) has retrothrusters. In energy terms, retros turns stored chemical energy (fuel) into counterthrust, reducing the KE of the orbital lander to somewhat survivable levels. Parachutes also work in a similar sense.

Sundowner is a powered vehicle.

Cut and paste what?

EDIT: Actually, I'm simplifying things. There are a lot of other factors such as changing mass, reentry angles, etc. etc. Lots of mathsy stuff. I'm just talking in basic physics terms, which leaves a LOT of the story unspoken.

Edited August 3, 2005 by Lynx7725

[Zentrandude]

K stop making a more complex statment of my examples this is MW not nasa.

A friend of mine is realy laughing on what your saying but he made a realy good point. For imaginary sake lets say a lander had thermonuclear engines and lots of time and what not so its just simple thrust. He said It would seem possible to land that way but realy hard to be perfect landing with the jet stream going to push it way off coarse.

also sundown is a person on the forums

[Lynx7725]

K stop making a more complex statment of my examples this is MW not nasa.

A friend of mine is realy laughing on what your saying but he made a realy good point.  For imaginary sake lets say a lander had thermonuclear engines and lots of time and what not so its just simple thrust.  He said It would seem possible to land that way but realy hard to be perfect landing with the jet stream going to push it way off coarse.

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Sure, if you can convert a thermouclear reaction into sustained thrust (such as the Orion engine posted earlier), then effectively you have a large amount of energy to play with, yeah, you can de-orbit a lander straight down -- because you got so much thrust, you basically ignore the gravitational pull, earth's rotation, etc. etc.

If you can have a system to do that, then, hey, we don't need to work so hard -- we got sustained energy out our backsides, so we simply don't care about "natural" laws.

Only issue here is that we don't have such a system at the moment, and, AFAIK, nothing even remotely like it in the near future.

[Zentrandude]

K stop making a more complex statment of my examples this is MW not nasa.

A friend of mine is realy laughing on what your saying but he made a realy good point.  For imaginary sake lets say a lander had thermonuclear engines and lots of time and what not so its just simple thrust.  He said It would seem possible to land that way but realy hard to be perfect landing with the jet stream going to push it way off coarse.

316797[/snapback]

Sure, if you can convert a thermouclear reaction into sustained thrust (such as the Orion engine posted earlier), then effectively you have a large amount of energy to play with, yeah, you can de-orbit a lander straight down -- because you got so much thrust, you basically ignore the gravitational pull, earth's rotation, etc. etc.

If you can have a system to do that, then, hey, we don't need to work so hard -- we got sustained energy out our backsides, so we simply don't care about "natural" laws.

Only issue here is that we don't have such a system at the moment, and, AFAIK, nothing even remotely like it in the near future.

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Lol stop doing that use that part of your brain called imagination I know you have it in you if you seen macross. In crazy land they have thermonuclear engines like valks and what not so thrust isnt an issue (talk about that one more time and ill put a helmet on you) and design a vechical yourself so 1. has extreme safety to crew 2. not needed to use heat resistant materials since in crazy land only materials avail is common stuff like steel/alum ect and 3. not violate other countries airspace since in crazy land you live in a small country surrounded by not so friendly countries wanting any excuses to invade.

[Lynx7725]

Well, can't say I didn't try...

[David Hingtgen]

I considered bringing up SpaceShipOne, but basically:

That's about the only ship that method will work for. It's no faster than an SR-71. Think of it as a really, really slow space shuttle that cannot orbit. Far slower, far less energy to bleed off.

[Zentrandude]

its ok forget what I said then since not like we building it ourselves (would be cool to see a MW spacecraft). though we could if we want.

[Sundown]

sundown is a person on the forums 

316797[/snapback]

Who also moonlights as a powered vehicle. Vroom!

-Al

[Zentrandude]

sundown is a person on the forums 

316797[/snapback]

Who also moonlights as a powered vehicle. Vroom!

-Al

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lol lay off the beans man too much octane.

[Stamen0083]

Sure, if you can convert a thermouclear reaction into sustained thrust (such as the Orion engine posted earlier), then effectively you have a large amount of energy to play with, yeah, you can de-orbit a lander straight down -- because you got so much thrust, you basically ignore the gravitational pull, earth's rotation, etc. etc.

If you can have a system to do that, then, hey, we don't need to work so hard -- we got sustained energy out our backsides, so we simply don't care about "natural" laws.

Only issue here is that we don't have such a system at the moment, and, AFAIK, nothing even remotely like it in the near future.

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Hah. I said exactly that in an earlier post, only not in so many words.

As for the rotating tiles idea, it's not that the tiles can't take it. Quite the contrary, the ceramic tiles are used precisely because it can handle lots of heat. The problem is that the damn things won't stay stuck to the shuttle long enough, and what the tiles are stuck to aren't strong enough to survive an impact from something the size and mass of a loaf of bread travelling at 500+ mph.

EDIT: Tiles are ceramic, not carbon. >_<

Edited August 3, 2005 by Stamen0083

[wwwmwww]

The shuttle comes down at just the right angle that it can bleed off speed/energy at just the rate that it can withstand the heat.  Other angles are either too hot, or won't bleed off the speed. 

Now, things like the Apollo capsules etc. do slow down a lot in orbit, but then come down FAST, almost vertically compared to shuttle. 

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So, if you screw up on re-entry, you either burn up in a fireball, or you freeze when your shuttle skips off into the Big Black.

316753[/snapback]

Correct me if I'm wrong but wasn't there talk from Nasa back at the time of the Columbia disaster that if they had known about the damage to the tiles they could have tried to came in at a shallower angle of re-entry? As I remember it, it was stated that it would have taken it easier on the damaged areas but since the overall re-entry would have taken longer the stuttle would have been exposed to the high temperatures for much longer and that could have damaged Columbia in other areas to the point she'd never be able to fly again.

Also I don't believe the Shuttle can "skip off into the Big Black". The shuttle is in orbit (unlike the Apollo capsule on the way back from the Moon). Any contact with the atmosphere will cause the shuttle to slow down. If the angle is too shallow it might skip but it will have lost energy and it will come back down and make contact with the atmosphere again as it no longer has the energy to stay in orbit. Think of a rock skipping across a pond. That said I'm no so sure a few skips before re-entry are bad thing. I'd tend to think any why of lossing that enegry as slowly as possible would be a good thing however I'm certainly not an expert in this area. The other part of this is the tiles only slow the transfer of heat. If one side of them were held at the heat of re-entry for long enough the other side would eventually get to that temperature too unless something was actively cooling it. I think that plays a roll in determining just how shallow an angle of re-entry can be used for the shuttle.

Carl

Edited August 3, 2005 by wwwmwww

[Stamen0083]

Somehow, I don't think people are reading my posts. Not at all...

Also posted earlier, this link details reentry:

http://www.aerospaceweb.org/question/spacecraft/q0218.shtml

[wwwmwww]

Burt Rutan's SpaceShipOne that won the X-Prize had an interesting way of dealing with reentry.  The whole tail assembly was hinged and as the craft reentered, would fold upwards, doing what they referred to as "feathering". 

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I really enjoyed watching the SpaceShipOne flights so PLEASE don't take this as me knocking that effort. It was a great accomplishment but it's very hard for me to see this craft or anything like it taking people to a hotel in orbit for example. To get to orbit you need more then just altitude. You need the lateral speed to stay in orbit or as soon as you shut off your engines you fall back to the Earth. That's just what SpaceShipOne did. The speed required to get the altitude is actually a very small part of the puzzle. You could probably get up there and back down again while never going over Mach 2. However to stay in orbit you need a speed of something like Mach 25. Burt Rutan is still an order of magniture away from being able to offer much more then a short joy ride at the moment. It's certainly a good step in the right direction but he's got a long way to go yet. If you were to carry SpaceShipOne to orbit in the Shuttle for example and were to let it then try that reentry maneuver on it's own I dare say the pieces that would make it back to Earth would probably be look worse then what was left of Columbia.

Carl

[Zentrandude]

The shuttle comes down at just the right angle that it can bleed off speed/energy at just the rate that it can withstand the heat.  Other angles are either too hot, or won't bleed off the speed. 

Now, things like the Apollo capsules etc. do slow down a lot in orbit, but then come down FAST, almost vertically compared to shuttle. 

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So, if you screw up on re-entry, you either burn up in a fireball, or you freeze when your shuttle skips off into the Big Black.

316753[/snapback]

Correct me if I'm wrong but wasn't there talk from Nasa back at the time of the Columbia disaster that if they had known about the damage to the tiles they could have tried to came in at a shallower angle of re-entry? As I remember it, it was stated that it would have taken it easier on the damaged areas but since the overall re-entry would have taken longer the stuttle would have been exposed to the high temperatures for much longer and that could have damaged Columbia in other areas to the point she'd never be able to fly again.

Also I don't believe the Shuttle can "skip off into the Big Black". The shuttle is in orbit (unlike the Apollo capsule on the way back from the Moon). Any contact with the atmosphere will cause the shuttle to slow down. If the angle is too shallow it might skip but it will have lost energy and it will come back down and make contact with the atmosphere again as it no longer has the energy to stay in orbit. Think of a rock skipping across a pond. That said I'm no so sure a few skips before re-entry are bad thing. I'd tend to think any why of lossing that enegry as slowly as possible would be a good thing however I'm certainly not an expert in this area. The other part of this is the tiles only slow the transfer of heat. If one side of them were held at the heat of re-entry for long enough the other side would eventually get to that temperature too unless something was actively cooling it. I think that plays a roll in determining just how shallow an angle of re-entry can be used for the shuttle.

Carl

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Think the skip off into deep space was a star trek thing but stamen's link is pretty interesting on the too high on the aoa.

[JB0]

Honestly? I think age is starting to cause the flaws to be more visible too.

No, we're just looking at them a LOT closer than we used to.

Like the current shuttle mission.

There was "grout" sticking up between some of the ceramic tiles.

They know its happened before, and that we've seen up to a quarter inch of it after the shuttle lands and who knows how much has burned off.

But the don't have a clue if this one is safe, because that's aLL they know. They've no clue as to how much burns off on re-entry.

...

So heres an idea tossed out there, what is there was a way to rotate the exposed tiles facing the Earth on descent? I gotta figure the tiles taking the biggest brunt are the ones along the shuttles belly.

The part that takes the brunt of things is actually the leading edge. That's why the front faces are all RCC panels instead of ceramic tiles.

The black parts get the hottest.

The belly DOES take more than the top, though.

I was never great at physics, but from what I remember, your space craft can be any shape in space and still move around if its got some kind of propulsion. 

In space, yes.

I always was told that the shuttle was designed just aerodynamically sound enough to land safely and have some basic flight capability.

And not burn up.

Aerodynamics don't mean anything in space.

In an atmosphere, they mean less friction, which means less heat.

So what if the living / crew areas of a shuttle were put inside some kind of cylindrical housing. Where the outer areas are all tiled and are rotating constantly. Kind of like having one ball inside another, where the inside one stays static but the outer one is connected by rails to spin around.

Obviously that would require some kind of parachute system and have water landings, but would that type of design reduce the heat exposure to a small number of tiles? Would it make it harder to find the right angle for entry at that shape? Would the rotation cause the craft to descend too quickly or throw off its trajectory by too much?

Well, it'd be a lot more complex, for very little gain. The tiles aren't a problem.

And it would greatly reduce the control you have over re-entry.

[JB0]

Lol stop doing that use that part of your brain called imagination I know you have it in you if you seen macross. In crazy land they have thermonuclear engines like valks and what not so thrust isnt an issue (talk about that one more time and ill put a helmet on you) and design a vechical yourself so 1. has extreme safety to crew 2. not needed to use heat resistant materials since in crazy land only materials avail is common stuff like steel/alum ect and 3. not violate other countries airspace since in crazy land you live in a small country surrounded by not so friendly countries wanting any excuses to invade.

What you describe is pretyt much impossible.

Just because you have a fusion reactor doesn't mean you have infinite thrust.

For one, you have to carry enough fusable material to keep the reaction going during the entire mission.

For two, you need enough reaction mass to jetison.

Once you run out of reaction mass, you lose the ability to maneuver in space, even if you brought enough hydrogen to run for a million years.

And reaction mass is simple newtonian physics. Every action has an equal and opposite reaction.

Eject a pound of stuff out at 30 miles an hour, you impart a momenteum of 30 miles an hour/pounds of space ship in the opposite direction.

As for the rotating tiles idea, it's not that the tiles can't take it. Quite the contrary, the carbon tiles are used precisely because it can handle lots of heat.

I think the tiles are ceramic, actually.

The problem is that the damn things won't stay stuck to the shuttle long enough, and what the tiles are stuck to aren't strong enough to survive an impact from something the size and mass of a loaf of bread travelling at 500+ mph.

I forget how many get shed with every re-entry, but it's a lot.

And we haven't had tile impact problems yet, just hte one RCC panel.

Though NASA did observe a "sandpapering" effect after one foam reformulation. The foam USED to powder off during liftoff.

As I recall, they reformulated it to stop that because it was putting nasty gouges in the tiles and they were worried about heatshield integrity.

Of course, chunks weren't considered an issue because "it never hit the shuttle before."

Correct me if I'm wrong but wasn't there talk from Nasa back at the time of the Columbia disaster that if they had known about the damage to the tiles they could have tried to came in at a shallower angle of re-entry?  As I remember it, it was stated that it would have taken it easier on the damaged areas but since the overall re-entry would have taken longer the stuttle would have been exposed to the high temperatures for much longer and that could have damaged Columbia in other areas to the point she'd never be able to fly again.

That was an idea they pitched.

It likely wouldn't ahve done any good, as any trajectory low enough to prevent blowtorching wouldn't have been too low to actually re-enter.

Also I don't believe the Shuttle can "skip off into the Big Black".  The shuttle is in orbit (unlike the Apollo capsule on the way back from the Moon). 

The Apollos were in orbit too. Just a larger orbit.

Any contact with the atmosphere will cause the shuttle to slow down.  If the angle is too shallow it might skip but it will have lost energy and it will come back down and make contact with the atmosphere again as it no longer has the energy to stay in orbit. 

If it bounced up, it GAINED energy. You can't go up against gravity without actually accelerating. And you can't accelerate without gaining energy.

Skipping off the atmosphere is sort of like jumping on a trampoline. You hit it, it bends a little, and then throws you back up.

Think of a rock skipping across a pond.

Now imagine gravity has only the slightest hold on that rock, and the rock has to fire thrusters to move down towards the water. And that the lake is curving away from the rock as it travels.

[wwwmwww]

Somehow, I don't think people are reading my posts. Not at all...

Also posted earlier, this link details reentry:

http://www.aerospaceweb.org/question/spacecraft/q0218.shtml

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Ok... just read it. This figure:

is very misleading. It implues you are nearly going strait down when you hit the upper limits of the atmosphere. That's incorrect, the first figure is much better.

This sentence "This feature is true in the case of the Space Shuttle, the only vehicle that currently uses a glide entry trajectory." is also incorrect. There was also the Energia-Buran Reusable Space System unless it's not considered "current".

And for an article about craft re-entering from a circular orbit these sentences are completely wrong "If the entry angle is too shallow, the vehicle will generate too little drag and not slow down enough to be captured by the Earth's gravity. The craft will instead skip out of the atmosphere and back into space with insufficient fuel to return to Earth again."

1. The craft is ALREADY captured by Earth's gravity. Where does the energy to escape this come from?

2. This might be true of a craft entering the atmosphere that isn't already in orbit but even in that case the angle of attack is independent of the fuel on board. There is NO need to tie those two together.

To me the only useful sentence there is this one "A vehicle using a skip trajectory can travel much farther downrange than either the ballistic or glide options allow, but the primary disadvantage is much higher aerodynamic heating." but even there it doesn't go into why. One would think that if you slow down slower you would generate less heat.

Happy now?

Carl

Edited August 3, 2005 by wwwmwww

[Zentrandude]

*slaps a helmet on jbo* its crazy land theory jbo the unlimited thrust/fuel thing is to simplify the issue. also in 50 years nasa may be using propulsing tech that we couldnt even dream of. hard to say.

sandblasting not sandpapering btw either way both does what your talking about and makes bathtubs black with the stuff that sticks to you.

[Stamen0083]

Ok... just read it.  This figure:

is very misleading.  It implues you are nearly going strait down when you hit the upper limits of the atmosphere.  That's incorrect, the first figure is much better.

I agree, actually. The starting points of the trajectories should have been at the orbit, not the upper edge of the atmosphere.

This sentence "This feature is true in the case of the Space Shuttle, the only vehicle that currently uses a glide entry trajectory." is also incorrect.  There was also the Energia-Buran Reusable Space System unless it's not considered "current".

It's not flying anymore, so no, it's not current.

And for an article about craft re-entering from a circular orbit these sentences are completely wrong "If the entry angle is too shallow, the vehicle will generate too little drag and not slow down enough to be captured by the Earth's gravity. The craft will instead skip out of the atmosphere and back into space with insufficient fuel to return to Earth again."

1.  The craft is ALREADY captured by Earth's gravity.  Where does the energy to escape this come from?

I think he means back into another orbit. He is probably referring to the gravitational slingshot effect, but on a much smaller scale. The craft won't have any fuel left to maneuver itself into position for another reentry and thus is stuck out there in a possibly decaying orbit. Or not.

2.  This might be true of a craft entering the atmosphere that isn't already in orbit but even in that case the angle of attack is independend of the fuel on board.  There is NO need to tie those two together.

Explained above.

To me the only useful sentence there is this one "A vehicle using a skip trajectory can travel much farther downrange than either the ballistic or glide options allow, but the primary disadvantage is much higher aerodynamic heating." but even there it doesn't go into why.  One would think that if you slow down slower you would generate less heat. 

Everytime the shuttle hits the atmosphere, it would heat up a little bit. Per the figure, the shuttle would hit the atmosphere quite many times before actually attempting to land, and every such time, it seems like the shuttle picks up speed to rise away from the atmosphere.

Happy now?

Carl

316921[/snapback]

:shrug:

*slaps a helmet on jbo* its crazy land theory jbo the unlimited thrust/fuel thing is to simplify the issue. also in 50 years nasa may be using propulsing tech that we couldnt even dream of. hard to say.

Stop talking crazyland theory. Like I said earlier, if we have unlimited power, nothing would be a problem.

Edited August 3, 2005 by Stamen0083

[Lynx7725]

Also I don't believe the Shuttle can "skip off into the Big Black".  The shuttle is in orbit (unlike the Apollo capsule on the way back from the Moon). 

Sucks to be me.

I was talking a little loosely. Yes, if the Shuttle skip off the atmosphere, the odds are good that it would come back... eventually. How eventually, is IMO a matter of luck; deltaV on departure, whichever celestial body which happens to be in the vicinity, etc. Heck, on a bad day the Shuttle may end up visiting Planet X.

The end result, given that the Shuttle don't carry that much fuel, is a short period of time to enact a rescue before the power and heating dies out. Once that's gone, it's a cold cold fate for the crew.. not too much difference from going into the Big Black, as far as the crew is concerned.

Somehow, I don't think people are reading my posts. Not at all...

316904[/snapback]

Sorry man, missed it in the shuffle.

No, we're just looking at them a LOT closer than we used to.

316909[/snapback]

You're probably right. Truth to be told, I'm sympathetic towards NASA. A lot of the problems they face has no precessor to guide them to good solutions, so they end up trying things, and in effect putting the crew's lives at stake with educated guesses.

And regardless of how we feel about beancounters, it's an unavoidable facet of this. Throw too much money into solving the problems, and you don't have assets to launch the darn thing. Put too much into theortical research, and you don't have enough to launch the darn thing.

So they do the best they can, and they do darn well, considering how aimless the space program has been for the last few decades. Perhaps their level of "acceptable risk" is a bit too high for the general public, but I do understand where the sentiment comes from.

[wwwmwww]

The Apollos were in orbit too. Just a larger orbit.

316918[/snapback]

You are correct of course. My bad. However was that orbit an orbit about Earth or an orbit about the Earth/Moon system?

Skipping off the atmosphere is sort of like jumping on a trampoline. You hit it, it bends a little, and then throws you back up.

316918[/snapback]

That's the first I've read anything about the atmosphere actually adding energy to the shuttle. I thought the friction with the atmosphere would result in kinetic energy being turned into heat and dissipated. Though most of that heat might just end up getting stored in the tiles at that altitude. Can you point me to an article on this trampline effect?

If it bounced up, it GAINED energy. You can't go up against gravity without actually accelerating. And you can't accelerate without gaining energy.

316918[/snapback]

This just doesn't sound quite right to me. Its possible to gain altitute without gaining any net energy. Through a rock up into the air. After it leaves your hand it has nothing left to give it energy yet it still continues to go up. It's turning kinetic energy into potential energy while the net energy stays the same. Actually its losing enegry due to friction the whole time. I think the shuttle would be doing the same thing. It would just be turning its forward kinetic energy into potential energy while it was gaining altitue. I don't believe it's accelerating... I think its decelerating.

Carl

[wwwmwww]

I think he means back into another orbit. He is probably referring to the gravitational slingshot effect, but on a much smaller scale. The craft won't have any fuel left to maneuver itself into position for another reentry and thus is stuck out there in a possibly decaying orbit. Or not.

316927[/snapback]

The Shuttle orbits the Earth about every 90 minutes I think. If the Shuttle lost enough energy to attempt re-entry and "skipped" off the atmosphere I don't see any mechanism for them to put themsleves into any other orbit that wouldn't intersect the atmosphere in at most 90 minutes. That is unless they fired some more rockets on the Shuttle. I don't believe any maneuvering would be required. I think they'd be trying another re-entry within 90 minutes regardless of rather they wanted to or not

Everytime the shuttle hits the atmosphere, it would heat up a little bit. Per the figure, the shuttle would hit the atmosphere quite many times before actually attempting to land, and every such time, it seems like the shuttle picks up speed to rise away from the atmosphere.

316927[/snapback]

Again I think the shuttle should SLOW down each time it raised away from the atmosphere. See my last post. However I think the real problem is the heat. Yes the tiles would heat up a little bit each time and being that high up they wouldn't be able to dissipate much heat into the atmosphere. They'd only be able to lose heat radiatively. If they are gaining heat fasther then they are losing heat for a long enough period of time you have a problem.

Carl

[Lynx7725]

I think the shuttle would be doing the same thing.  It would just be turning its forward kinetic energy into potential energy while it was gaining altitue.  I don't believe it's accelerating... I think its decelerating.

316932[/snapback]

You have a point.. the Shuttle is likely to have lost energy overall. The problem is, it's decelerating.. in the wrong direction. To get the Shuttle back on track will need energy to redirect the vector back towards something that's approaching reasonable, and while I'm sure NASA plans for contingency, I'm not sure how much of a reserve the Shuttle typically carries on board.

[wwwmwww]

Yes, if the Shuttle skip off the atmosphere, the odds are good that it would come back... eventually.

316931[/snapback]

See my last post. Eventually I believe is less then 90 minutes. They aren't going to starve or freeze in that time.

Carl

[Zentrandude]

If it bounced up, it GAINED energy. You can't go up against gravity without actually accelerating. And you can't accelerate without gaining energy.

316918[/snapback]

This just doesn't sound quite right to me. Its possible to gain altitute without gaining any net energy. Through a rock up into the air. After it leaves your hand it has nothing left to give it energy yet it still continues to go up. It's turning kinetic energy into potential energy while the net energy stays the same. Actually its losing enegry due to friction the whole time. I think the shuttle would be doing the same thing. It would just be turning its forward kinetic energy into potential energy while it was gaining altitue. I don't believe it's accelerating... I think its decelerating.

Carl

316932[/snapback]

sounds like perpetual motion to me.

Edited August 3, 2005 by Zentrandude

[Kin]

thnx for the info guys.

Another plan which would take ages... to create a man made 30km high mountain.

Edited August 3, 2005 by Kin