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There was a dead zone during SRB burn Those alone made it a serious death trap, if you're designing man-rated systems, you like the big boosters to be liquid f

by hga 10y ago

There was a dead zone during SRB burn Those alone made it a serious death trap, if you're designing man-rated systems, you like the big boosters to be liquid fueled because you can turn them off if needed, and in many if not most of the relevant failure modes they'll effectively do that anyway. And getting back to my point, as echoed by others, none of these equal a launch escape system, a "Get me the hell out of here!" system for when things have gone horribly and irretrievably wrong with the main system. Particularly unforgivable when it was billed as a boring space truck, when in reality it needlessly ran on the hairy edge in many of its systems. Add the post-Apollo NASA's public works attitude, and we ended up with NASA killing two shuttles and their crews.

digi_owl 10y ago
Best i recall, NASA wanted liquid boosters etc, but congress nixed it for pork barrel reasons.
- hga 10y ago
  In an analysis published in Science that I read, the biggest driver was development cost. SRBs, in fact, the kludge of the big tank, were all done to minimize that, while drastically driving up operational costs, which, of course, were several elections down the road and sort of hidden/not entirely undesired for what had become almost entirely a public works program. By the same token, I heard first hand from the guy who developed the reentry vehicle that the crazy scheme of Apollo which left us with no operational hardware off the earth was done because it spent "a billion" (8 billion in 2016 dollars) more in Texas, where LBJ just happened to hail from, and back then the race to the moon project was explicitly hailed as a way to spend money in the South and increase its tech know-how.
  - msl 10y ago
    Could you elaborate a bit? What was "the crazy scheme of Apollo?"
    - hga 10y ago
      Read pretty much any SF story about getting to the Moon with chemical rockets prior to NASA, and it involves two transfer stations, one generally manned in LEO, and one in lunar orbit, manning seriously optional. You use rockets optimized to get from earth to the LEO station, to transfer between the two stations, then one to get to and from the Moon. Cheaper, and you keep long lived and potentially permanent assets up there, anything you loft to LEO is done at tremendous expense, course. Two flies in the ointment for assets beyond LEO and not under a lot of lunar soil/rock: Apollo was primarily a political stunt to convince the rest of the world our technology as good or better than the USSR's, who'd we'd let get out into space first to get them to establish the open skies principle that orbiting over someone else's territory wasn't spying (something they were insisting up to a week or month before Sputnik). Such assets were superfluous for the stunt, plus there was a very strong RFK/LBJ prejudice against any hint of military utility in NASA's space program. That plus internal politics which allocated the initial catch-up job to a group which was only good at making truly impressive launch pad explosions put us on the back foot in terms of getting out into space, and the Soviets made a fairly serious effort to beat us to the moon, e.g. look up the N1 rocket. Second, and seldom remembered is that the whole program was predicated a quiet Sun cycle, that's the determining reason I've read why the last two missions were canceled, the program had sufficient delays that it was getting into the danger zone, and Nixon wasn't about to kill an Apollo crew. For some SF coverage of this, read Heinlein's Podkayne of Mars where during an interplanetary voyage all the passengers and crew had to huddle for a while into the small shielded space the craft had for such an event.
      - msl 10y ago
        I am not sure I would call not building two space stations for the purposes of the program crazy. Remember, that the Apollo program was initiated before anyone had performed an orbital rendezvous of any kind. For quite some time the preferred (by most) approach to the moon landing was direct ascent [0], as rendezvousing seemed just too scary. The approach of sending a large, but modular spacecraft all the way to the moon also proved to have the ability survive some rather interesting failure modes [1] so maybe it was not so crazy after all? [0] https://en.wikipedia.org/wiki/Direct_ascent https://en.wikipedia.org/wiki/Direct_ascent [1] https://en.wikipedia.org/wiki/Apollo_13#Accident https://en.wikipedia.org/wiki/Apollo_13#Accident
exDM69 10y ago
> ... if you're designing man-rated systems, you like the big boosters to be liquid fueled because you can turn them off if needed ... The SRBs had a way to turn them off by opening two exhaust ports near the top that would let the gasses out and neutralize the thrust. But it's still a bit iffy, which is why cryogenic liquid fuels are the most common choice for human-rated launchers.
- logingone 10y ago
  Knowing little about this stuff, would it not be possible, and preferable, to eject them? Also, how realistic would it be to turn off liquid boosters, as they seem to usually fail with an immediate explosion?
  - hga 10y ago
    Given the massive thrust they produce, and how close they are to delicate things like the tank, it's hard to imagine a system that could possibly work. It would be exquisitely difficult to get the vectors just right, so they wouldn't bush against the tanks or worse, and even if you pull that off, their exhaust will have bad effects as they pass by. Short of not using them at all, exhaust ports at the top as mentioned by exDM69 sound like least worst option.
- hga 10y ago
  Errr, I should have said "(gently) throttle down", since that's potentially in the menu of options for liquid fueled rockets. What you're talking about sure sounds like an inherently violent deceleration. And the tops of those SRBs are uncomfortably close to the tank and the LOX tank in it at the top.... As you say, "a bit iffy", at the very minimum.
sandworm101 10y ago
Dead zones aren't limited to the use of SRBs. For instance, we don't know whether SpaceX will have dead zones or not. I can see one big one in that SpaceX's launch profile is much taller than traditional rockets (more up, less horizontal to aid in recovery of the first stage). A failure of the second stage to ignite may leave the capsule in a place where it won't survive the steep re-entry, falling more vertically than a the normal horizontal albeit faster re-entry. The data needed for such a determination is still hidden behind SpaceX's "proprietary" launch profiles.
- manicdee 10y ago
  Why would a capsule designed for Mars-return reentry with propulsive landing not survive sub-orbital reentry?
  - sandworm101 10y ago
    If you are moving very fast horizontally you slow in the upper atmosphere and your trajectory, in part, follows the curve of the earth. The net result is that you slow down through hundreds of kilometers of progressively thicker air. On the other hand, if you have no horizontal velocity you are falling like a rock into a much shorter slice of air. It gets much thicker very quickly. Either the capsule cannot survive the force of the thicker air, or it doesn't have enough time to slow down before hitting the ground. Horizontal re-entry also allows the capsule to 'fly' by trading horizontal velocity for lift, keeping it in the upper atmosphere for longer. That isn't an option when falling strait down.

by hga 10y ago

digi_owl 10y ago

Best i recall, NASA wanted liquid boosters etc, but congress nixed it for pork barrel reasons.

hga 10y ago
In an analysis published in Science that I read, the biggest driver was development cost. SRBs, in fact, the kludge of the big tank, were all done to minimize that, while drastically driving up operational costs, which, of course, were several elections down the road and sort of hidden/not entirely undesired for what had become almost entirely a public works program. By the same token, I heard first hand from the guy who developed the reentry vehicle that the crazy scheme of Apollo which left us with no operational hardware off the earth was done because it spent "a billion" (8 billion in 2016 dollars) more in Texas, where LBJ just happened to hail from, and back then the race to the moon project was explicitly hailed as a way to spend money in the South and increase its tech know-how.
- msl 10y ago
  Could you elaborate a bit? What was "the crazy scheme of Apollo?"
  - hga 10y ago
    Read pretty much any SF story about getting to the Moon with chemical rockets prior to NASA, and it involves two transfer stations, one generally manned in LEO, and one in lunar orbit, manning seriously optional. You use rockets optimized to get from earth to the LEO station, to transfer between the two stations, then one to get to and from the Moon. Cheaper, and you keep long lived and potentially permanent assets up there, anything you loft to LEO is done at tremendous expense, course. Two flies in the ointment for assets beyond LEO and not under a lot of lunar soil/rock: Apollo was primarily a political stunt to convince the rest of the world our technology as good or better than the USSR's, who'd we'd let get out into space first to get them to establish the open skies principle that orbiting over someone else's territory wasn't spying (something they were insisting up to a week or month before Sputnik). Such assets were superfluous for the stunt, plus there was a very strong RFK/LBJ prejudice against any hint of military utility in NASA's space program. That plus internal politics which allocated the initial catch-up job to a group which was only good at making truly impressive launch pad explosions put us on the back foot in terms of getting out into space, and the Soviets made a fairly serious effort to beat us to the moon, e.g. look up the N1 rocket. Second, and seldom remembered is that the whole program was predicated a quiet Sun cycle, that's the determining reason I've read why the last two missions were canceled, the program had sufficient delays that it was getting into the danger zone, and Nixon wasn't about to kill an Apollo crew. For some SF coverage of this, read Heinlein's Podkayne of Mars where during an interplanetary voyage all the passengers and crew had to huddle for a while into the small shielded space the craft had for such an event.
    - msl 10y ago
      I am not sure I would call not building two space stations for the purposes of the program crazy. Remember, that the Apollo program was initiated before anyone had performed an orbital rendezvous of any kind. For quite some time the preferred (by most) approach to the moon landing was direct ascent [0], as rendezvousing seemed just too scary. The approach of sending a large, but modular spacecraft all the way to the moon also proved to have the ability survive some rather interesting failure modes [1] so maybe it was not so crazy after all? [0] https://en.wikipedia.org/wiki/Direct_ascent https://en.wikipedia.org/wiki/Direct_ascent [1] https://en.wikipedia.org/wiki/Apollo_13#Accident https://en.wikipedia.org/wiki/Apollo_13#Accident

exDM69 10y ago

> ... if you're designing man-rated systems, you like the big boosters to be liquid fueled because you can turn them off if needed ... The SRBs had a way to turn them off by opening two exhaust ports near the top that would let the gasses out and neutralize the thrust. But it's still a bit iffy, which is why cryogenic liquid fuels are the most common choice for human-rated launchers.

logingone 10y ago
Knowing little about this stuff, would it not be possible, and preferable, to eject them? Also, how realistic would it be to turn off liquid boosters, as they seem to usually fail with an immediate explosion?
- hga 10y ago
  Given the massive thrust they produce, and how close they are to delicate things like the tank, it's hard to imagine a system that could possibly work. It would be exquisitely difficult to get the vectors just right, so they wouldn't bush against the tanks or worse, and even if you pull that off, their exhaust will have bad effects as they pass by. Short of not using them at all, exhaust ports at the top as mentioned by exDM69 sound like least worst option.
hga 10y ago
Errr, I should have said "(gently) throttle down", since that's potentially in the menu of options for liquid fueled rockets. What you're talking about sure sounds like an inherently violent deceleration. And the tops of those SRBs are uncomfortably close to the tank and the LOX tank in it at the top.... As you say, "a bit iffy", at the very minimum.

sandworm101 10y ago

Dead zones aren't limited to the use of SRBs. For instance, we don't know whether SpaceX will have dead zones or not. I can see one big one in that SpaceX's launch profile is much taller than traditional rockets (more up, less horizontal to aid in recovery of the first stage). A failure of the second stage to ignite may leave the capsule in a place where it won't survive the steep re-entry, falling more vertically than a the normal horizontal albeit faster re-entry. The data needed for such a determination is still hidden behind SpaceX's "proprietary" launch profiles.

manicdee 10y ago
Why would a capsule designed for Mars-return reentry with propulsive landing not survive sub-orbital reentry?
- sandworm101 10y ago
  If you are moving very fast horizontally you slow in the upper atmosphere and your trajectory, in part, follows the curve of the earth. The net result is that you slow down through hundreds of kilometers of progressively thicker air. On the other hand, if you have no horizontal velocity you are falling like a rock into a much shorter slice of air. It gets much thicker very quickly. Either the capsule cannot survive the force of the thicker air, or it doesn't have enough time to slow down before hitting the ground. Horizontal re-entry also allows the capsule to 'fly' by trading horizontal velocity for lift, keeping it in the upper atmosphere for longer. That isn't an option when falling strait down.