Why didn't the Space Shuttle bounce back into space as many times as possible so as to lose a lot of kinetic energy up there? Announcing the arrival of Valued Associate #679: Cesar Manara Unicorn Meta Zoo #1: Why another podcast?If there was a non-rotating skyhook in Earth orbit, what would re-entry be like after dropping from its foot?Why didn't the Space Shuttle have a launch escape system?How many Solid Rocket Boosters were there in the Space Shuttle program?Why didn't NASA use the shuttle to make a profit?While decending from orbit can a blimp glider skip an atmosphere to shed speed?Is getting IN or OUT of orbit easier for the Space Shuttle?Why didn't the space shuttle SRBs have wings and tires?Why didn't the SRBs of the Space Shuttle use carbon instead of aluminium?How many times were there thirteen people inside the ISS? Is it hard on the station?Why didn't the space shuttle use non-foam-shedding external tanks?Why can't you just parachute down right from orbit?
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Why didn't the Space Shuttle bounce back into space as many times as possible so as to lose a lot of kinetic energy up there?
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Why didn't the Space Shuttle bounce back into space as many times as possible so as to lose a lot of kinetic energy up there?
Announcing the arrival of Valued Associate #679: Cesar Manara
Unicorn Meta Zoo #1: Why another podcast?If there was a non-rotating skyhook in Earth orbit, what would re-entry be like after dropping from its foot?Why didn't the Space Shuttle have a launch escape system?How many Solid Rocket Boosters were there in the Space Shuttle program?Why didn't NASA use the shuttle to make a profit?While decending from orbit can a blimp glider skip an atmosphere to shed speed?Is getting IN or OUT of orbit easier for the Space Shuttle?Why didn't the space shuttle SRBs have wings and tires?Why didn't the SRBs of the Space Shuttle use carbon instead of aluminium?How many times were there thirteen people inside the ISS? Is it hard on the station?Why didn't the space shuttle use non-foam-shedding external tanks?Why can't you just parachute down right from orbit?
$begingroup$
From this video, I got know that Space Shuttle did reentry around 5000 miles away from landing site. It's angle of attack is maintained around 40 degrees during re-entry. If it is more than that, it bounces back to space.
Why don't we let the Shuttle bounce back into space many times as possible and skim a lot of atmosphere so that it loose lot of kinetic energy over there? I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
space-shuttle reentry
edited 55 mins ago
MackTuesday
1033
asked 21 hours ago
SRDSRD
32318
$endgroup$
add a comment |
$begingroup$
From this video, I got know that Space Shuttle did reentry around 5000 miles away from landing site. It's angle of attack is maintained around 40 degrees during re-entry. If it is more than that, it bounces back to space.
Why don't we let the Shuttle bounce back into space many times as possible and skim a lot of atmosphere so that it loose lot of kinetic energy over there? I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
space-shuttle reentry
edited 55 mins ago
MackTuesday
1033
asked 21 hours ago
SRDSRD
32318
$endgroup$
$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
7
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago
add a comment |
$begingroup$
From this video, I got know that Space Shuttle did reentry around 5000 miles away from landing site. It's angle of attack is maintained around 40 degrees during re-entry. If it is more than that, it bounces back to space.
Why don't we let the Shuttle bounce back into space many times as possible and skim a lot of atmosphere so that it loose lot of kinetic energy over there? I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
space-shuttle reentry
edited 55 mins ago
MackTuesday
1033
asked 21 hours ago
SRDSRD
32318
$endgroup$
From this video, I got know that Space Shuttle did reentry around 5000 miles away from landing site. It's angle of attack is maintained around 40 degrees during re-entry. If it is more than that, it bounces back to space.
Why don't we let the Shuttle bounce back into space many times as possible and skim a lot of atmosphere so that it loose lot of kinetic energy over there? I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
space-shuttle reentry
space-shuttle reentry
edited 55 mins ago
MackTuesday
1033
asked 21 hours ago
SRDSRD
32318
edited 55 mins ago
MackTuesday
1033
asked 21 hours ago
SRDSRD
32318
edited 55 mins ago
MackTuesday
1033
edited 55 mins ago
MackTuesday
1033
edited 55 mins ago
MackTuesday
1033
1033
asked 21 hours ago
SRDSRD
32318
asked 21 hours ago
SRDSRD
32318
asked 21 hours ago
SRDSRD
32318
32318
$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
7
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago
add a comment |
$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
7
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago
$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
7
7
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
Your thinking is reasonable as far as it goes...
But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere.
Within five minutes you'll either be toast from heating or jelly from pulling 15-20 gees.
In this answer I did a calculation for a different spacecraft (a Dragon capsule) with lift to drag between 0 and 0.3 and the scenario was always the same. Being significantly slower results in falling too deeply to quickly, and the higher density results in huge heat production and unsurvivably large accelerations.
answered 21 hours ago
uhohuhoh
41.7k19158522
$endgroup$
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
add a comment |
$begingroup$
Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle:
- As uhoh points out, a skipping reentry results in losing lateral speed at a very high altitude. In turn, you lose the ability to control your descent rate. By the end of entry you'd practically be in a free-fall which the vehicle would be unlikely to survive due to the heat and/or stress of attempting to pull out of the dive.
- The shuttle's thermal protection system was not designed to withstand long drawn-out reentries. Here's a quote from the "Entry, TAEM, and Approach/Landing Guidance Workbook":
On the flip side of high surface temperatures, there are high backface temperatures. If
you fly at high temperatures for a long time, heat will flow through the tiles to the
aluminum underneath. This can happen if you fly a low drag profile. In fact, backface
temperature is the current low limit to the drag profile. - Several other systems weren't designed for long drawn-out reentries either. The APUs only have the fuel capacity to run for about 110 minutes, which wouldn't be enough to support both launch and an extended reentry. The radiators, which were cold-soaked before entry, may have needed additional capacity to absorb heat build up during entry. The RCS may have needed more reserves.
- Flying a low-drag profile gives you less margin for error. Flying a middle-of-the-road drag profile means you have room to increase or decrease your drag as necessary in order to make the landing site. If your designed flight path is already on the low-end and you end up in a low energy condition, there's not much you can do about it.
- It's not impossible to develop guidance for a skipping reentry, but it is definitely a more difficult problem.
I suspect there are other reasons I haven't thought of.
On the flip side, I can't think of any advantages. The shuttle's reentry was already comparatively gentle (well under 2g's the whole time) and the heat was perfectly managable as-is.
answered 15 hours ago
Bret CopelandBret Copeland
53437
$endgroup$
$begingroup$
This is a very thorough answer,+1!
$endgroup$
– uhoh
15 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
2
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
|
show 2 more comments
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
Your thinking is reasonable as far as it goes...
But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere.
Within five minutes you'll either be toast from heating or jelly from pulling 15-20 gees.
In this answer I did a calculation for a different spacecraft (a Dragon capsule) with lift to drag between 0 and 0.3 and the scenario was always the same. Being significantly slower results in falling too deeply to quickly, and the higher density results in huge heat production and unsurvivably large accelerations.
answered 21 hours ago
uhohuhoh
41.7k19158522
$endgroup$
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
add a comment |
$begingroup$
I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
Your thinking is reasonable as far as it goes...
But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere.
Within five minutes you'll either be toast from heating or jelly from pulling 15-20 gees.
In this answer I did a calculation for a different spacecraft (a Dragon capsule) with lift to drag between 0 and 0.3 and the scenario was always the same. Being significantly slower results in falling too deeply to quickly, and the higher density results in huge heat production and unsurvivably large accelerations.
answered 21 hours ago
uhohuhoh
41.7k19158522
$endgroup$
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
add a comment |
$begingroup$
I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
Your thinking is reasonable as far as it goes...
But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere.
Within five minutes you'll either be toast from heating or jelly from pulling 15-20 gees.
In this answer I did a calculation for a different spacecraft (a Dragon capsule) with lift to drag between 0 and 0.3 and the scenario was always the same. Being significantly slower results in falling too deeply to quickly, and the higher density results in huge heat production and unsurvivably large accelerations.
answered 21 hours ago
uhohuhoh
41.7k19158522
$endgroup$
I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out.
Your thinking is reasonable as far as it goes...
But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere.
Within five minutes you'll either be toast from heating or jelly from pulling 15-20 gees.
In this answer I did a calculation for a different spacecraft (a Dragon capsule) with lift to drag between 0 and 0.3 and the scenario was always the same. Being significantly slower results in falling too deeply to quickly, and the higher density results in huge heat production and unsurvivably large accelerations.
answered 21 hours ago
uhohuhoh
41.7k19158522
edited 1 hour ago
answered 21 hours ago
uhohuhoh
41.7k19158522
answered 21 hours ago
uhohuhoh
41.7k19158522
answered 21 hours ago
uhohuhoh
41.7k19158522
41.7k19158522
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
add a comment |
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
3
3
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
$begingroup$
uhoh, you just owe to the community the tools (Excel formulas, I believe) you used to make these charts.
$endgroup$
– Arris
4 hours ago
3
3
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
$begingroup$
@Arris uhoh is all about the python, not XL.
$endgroup$
– Organic Marble
4 hours ago
2
2
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
It's "lose", not loose. Too short for me to do an edit.
$endgroup$
– Monty Harder
2 hours ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
$begingroup$
@MontyHarder thank you for that. For some reason those two wires are permanently crossed.
$endgroup$
– uhoh
1 hour ago
add a comment |
$begingroup$
Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle:
- As uhoh points out, a skipping reentry results in losing lateral speed at a very high altitude. In turn, you lose the ability to control your descent rate. By the end of entry you'd practically be in a free-fall which the vehicle would be unlikely to survive due to the heat and/or stress of attempting to pull out of the dive.
- The shuttle's thermal protection system was not designed to withstand long drawn-out reentries. Here's a quote from the "Entry, TAEM, and Approach/Landing Guidance Workbook":
On the flip side of high surface temperatures, there are high backface temperatures. If
you fly at high temperatures for a long time, heat will flow through the tiles to the
aluminum underneath. This can happen if you fly a low drag profile. In fact, backface
temperature is the current low limit to the drag profile. - Several other systems weren't designed for long drawn-out reentries either. The APUs only have the fuel capacity to run for about 110 minutes, which wouldn't be enough to support both launch and an extended reentry. The radiators, which were cold-soaked before entry, may have needed additional capacity to absorb heat build up during entry. The RCS may have needed more reserves.
- Flying a low-drag profile gives you less margin for error. Flying a middle-of-the-road drag profile means you have room to increase or decrease your drag as necessary in order to make the landing site. If your designed flight path is already on the low-end and you end up in a low energy condition, there's not much you can do about it.
- It's not impossible to develop guidance for a skipping reentry, but it is definitely a more difficult problem.
I suspect there are other reasons I haven't thought of.
On the flip side, I can't think of any advantages. The shuttle's reentry was already comparatively gentle (well under 2g's the whole time) and the heat was perfectly managable as-is.
answered 15 hours ago
Bret CopelandBret Copeland
53437
$endgroup$
$begingroup$
This is a very thorough answer,+1!
$endgroup$
– uhoh
15 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
2
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
|
show 2 more comments
$begingroup$
Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle:
- As uhoh points out, a skipping reentry results in losing lateral speed at a very high altitude. In turn, you lose the ability to control your descent rate. By the end of entry you'd practically be in a free-fall which the vehicle would be unlikely to survive due to the heat and/or stress of attempting to pull out of the dive.
- The shuttle's thermal protection system was not designed to withstand long drawn-out reentries. Here's a quote from the "Entry, TAEM, and Approach/Landing Guidance Workbook":
On the flip side of high surface temperatures, there are high backface temperatures. If
you fly at high temperatures for a long time, heat will flow through the tiles to the
aluminum underneath. This can happen if you fly a low drag profile. In fact, backface
temperature is the current low limit to the drag profile. - Several other systems weren't designed for long drawn-out reentries either. The APUs only have the fuel capacity to run for about 110 minutes, which wouldn't be enough to support both launch and an extended reentry. The radiators, which were cold-soaked before entry, may have needed additional capacity to absorb heat build up during entry. The RCS may have needed more reserves.
- Flying a low-drag profile gives you less margin for error. Flying a middle-of-the-road drag profile means you have room to increase or decrease your drag as necessary in order to make the landing site. If your designed flight path is already on the low-end and you end up in a low energy condition, there's not much you can do about it.
- It's not impossible to develop guidance for a skipping reentry, but it is definitely a more difficult problem.
I suspect there are other reasons I haven't thought of.
On the flip side, I can't think of any advantages. The shuttle's reentry was already comparatively gentle (well under 2g's the whole time) and the heat was perfectly managable as-is.
answered 15 hours ago
Bret CopelandBret Copeland
53437
$endgroup$
$begingroup$
This is a very thorough answer,+1!
$endgroup$
– uhoh
15 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
2
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
|
show 2 more comments
$begingroup$
Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle:
- As uhoh points out, a skipping reentry results in losing lateral speed at a very high altitude. In turn, you lose the ability to control your descent rate. By the end of entry you'd practically be in a free-fall which the vehicle would be unlikely to survive due to the heat and/or stress of attempting to pull out of the dive.
- The shuttle's thermal protection system was not designed to withstand long drawn-out reentries. Here's a quote from the "Entry, TAEM, and Approach/Landing Guidance Workbook":
On the flip side of high surface temperatures, there are high backface temperatures. If
you fly at high temperatures for a long time, heat will flow through the tiles to the
aluminum underneath. This can happen if you fly a low drag profile. In fact, backface
temperature is the current low limit to the drag profile. - Several other systems weren't designed for long drawn-out reentries either. The APUs only have the fuel capacity to run for about 110 minutes, which wouldn't be enough to support both launch and an extended reentry. The radiators, which were cold-soaked before entry, may have needed additional capacity to absorb heat build up during entry. The RCS may have needed more reserves.
- Flying a low-drag profile gives you less margin for error. Flying a middle-of-the-road drag profile means you have room to increase or decrease your drag as necessary in order to make the landing site. If your designed flight path is already on the low-end and you end up in a low energy condition, there's not much you can do about it.
- It's not impossible to develop guidance for a skipping reentry, but it is definitely a more difficult problem.
I suspect there are other reasons I haven't thought of.
On the flip side, I can't think of any advantages. The shuttle's reentry was already comparatively gentle (well under 2g's the whole time) and the heat was perfectly managable as-is.
answered 15 hours ago
Bret CopelandBret Copeland
53437
$endgroup$
Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle:
- As uhoh points out, a skipping reentry results in losing lateral speed at a very high altitude. In turn, you lose the ability to control your descent rate. By the end of entry you'd practically be in a free-fall which the vehicle would be unlikely to survive due to the heat and/or stress of attempting to pull out of the dive.
- The shuttle's thermal protection system was not designed to withstand long drawn-out reentries. Here's a quote from the "Entry, TAEM, and Approach/Landing Guidance Workbook":
On the flip side of high surface temperatures, there are high backface temperatures. If
you fly at high temperatures for a long time, heat will flow through the tiles to the
aluminum underneath. This can happen if you fly a low drag profile. In fact, backface
temperature is the current low limit to the drag profile. - Several other systems weren't designed for long drawn-out reentries either. The APUs only have the fuel capacity to run for about 110 minutes, which wouldn't be enough to support both launch and an extended reentry. The radiators, which were cold-soaked before entry, may have needed additional capacity to absorb heat build up during entry. The RCS may have needed more reserves.
- Flying a low-drag profile gives you less margin for error. Flying a middle-of-the-road drag profile means you have room to increase or decrease your drag as necessary in order to make the landing site. If your designed flight path is already on the low-end and you end up in a low energy condition, there's not much you can do about it.
- It's not impossible to develop guidance for a skipping reentry, but it is definitely a more difficult problem.
I suspect there are other reasons I haven't thought of.
On the flip side, I can't think of any advantages. The shuttle's reentry was already comparatively gentle (well under 2g's the whole time) and the heat was perfectly managable as-is.
answered 15 hours ago
Bret CopelandBret Copeland
53437
edited 5 hours ago
answered 15 hours ago
Bret CopelandBret Copeland
53437
answered 15 hours ago
Bret CopelandBret Copeland
53437
answered 15 hours ago
Bret CopelandBret Copeland
53437
53437
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This is a very thorough answer,+1!
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– uhoh
15 hours ago
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+1 for the limitations due to other systems.
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– Organic Marble
10 hours ago
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The APU's a non-issue (it had power for days) but everything else seems right.
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– Joshua
8 hours ago
2
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@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
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– Bret Copeland
5 hours ago
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@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
|
show 2 more comments
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This is a very thorough answer,+1!
$endgroup$
– uhoh
15 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
2
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
$begingroup$
This is a very thorough answer,
+1!$endgroup$
– uhoh
15 hours ago
$begingroup$
This is a very thorough answer,
+1!$endgroup$
– uhoh
15 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
+1 for the limitations due to other systems.
$endgroup$
– Organic Marble
10 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
$begingroup$
The APU's a non-issue (it had power for days) but everything else seems right.
$endgroup$
– Joshua
8 hours ago
2
2
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@Joshua no, the APUs had very little fuel reserves. See the Shuttle Crew Operations Manual page 2.1-2: "The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds.... The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute."
$endgroup$
– Bret Copeland
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
$begingroup$
@BretCopeland: Seems I mixed it up with the on-orbit fuel cells. nasa.gov/topics/technology/hydrogen/fc_shuttle.html
$endgroup$
– Joshua
5 hours ago
|
show 2 more comments
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$begingroup$
To be clear, it's not AoA which prevents the shuttle from skipping; it's banking - pointing the lift vector sideways instead of up. An increase in AoA from 40° would most likely reduce the chance of skipping.
$endgroup$
– Bret Copeland
16 hours ago
7
$begingroup$
5000 nautical miles away. The answer is in the video but easy to miss; he notes very quickly, and only once, that slowing too much: you'll drop out the sky like a rock (which is the penultimate concern at all times only to 'rapid unplanned disassembly'). It's bad enough that it's already a flying brick.
$endgroup$
– Mazura
13 hours ago