The Cause Of The Ares 1 Problem

"But that's the way that politics drives a government space program, and why it is so horrifically expensive."

I suspect that the same would apply to any private vehicle. Let us suppose that a priavet space craft suffered a catastrophic accident. Then let us suppose that during the design phase of the space craft a fix was considered that would have prevented the accident but was rejected because the fix would be expensive and complicated and the specific accident was considered unlikely. In that case I would suspect that the civil liability alone would be astonishing to behold.

Mark, it's quite possible that the LES actually increases the danger to the crew. This is a trade that a private entity would perform more rationally, with an eye to liability consequences, but documenting the trade so that it would have a good case in court to show why they didn't waste money on it. But for NASA, it is a political given that there will be a crew escape system, even if they risk killing a crew with it on a nominal mission. It's a band aid, like the escape pole in the Shuttle, except it's a much bigger performance hit.

"People have considered putting the escape motor underneath the capsule for this reason (I think that Mike Griffin even drew a napkin sketch"
.
that "people" have a NAME (and the first of them was NOT Mike Griffin...)

This is probably a naive question but why is it that the system can't be sized in such a way as to provide an escape mechanism for the crew capsule if fired early and extra impulse to the crew capsule if fired later? I.e., make it a stage. I'm sure the thrust level would be much higher for the abort case, given the urgency, but there are multiple motors fired simultaneously then, and perhaps consecutively if the system is used later for additional impulse.

Not my field, clearly, but it isn't apparent to me what the showstopper is with doing this. Perhaps more experienced heads will weigh in.

Good question, Jane. Believe me, it's been considered, both in OSP and in Orion (and probably Apollo as well, though I don't know enough of the history to know for sure).

The problem with it is that it adds complexity to the system, and provides many more failure modes on a nominal mission. You can't fire the engines sequentially, because of the thrust asymmetries you'd get. You could fire in pairs, but then you only reduce the acceleration by half, which is still pretty high. Also, if you're using it for nominal ascent, it has to pull not just the Command Module, but also the Service Module.

It is a trade that's been done, but it never comes out a winner. In fact, when a request came from NASA to look at it again a couple years ago during Phase II, we all commented that it must mean that the performance on the Ares 1 must be pretty sick for them to get that desperate.

If the Orion made a touchdown on land and if it used braking motors like the Soyuz. Then, couldn't those motors be beefed up a bit to serve tractor motor duty during ascent?

Perhaps one could make the escape system just one big motor placed on the nose of the capsule. The motor would point straight down instead of offset at an angle. Use a small kick motor to jettison the escape motor out to a save distance from the capsule until it pulls tight on some ultra strong/ultra light cabling and then ignite the escape motor.

The motor would point straight down instead of offset at an angle. Use a small kick motor to jettison the escape motor out to a save distance from the capsule until it pulls tight on some ultra strong/ultra light cabling and then ignite the escape motor.

Ummmm...yeah. What could go wrong?

Outrun the debris from an exploding booster? That seems damn unlikely. What kind of acceleration do you need to outrun debris that weighs mere ounces being accelerated by the explosion of tons of propellant?

I thought the Apollo escape rocket was entirely for the second scenario you suggested, where the Saturn booster failed after it was off the ground but before it had given the CM enough velocity to reach a safe height for a parachute landing. Since the Saturn took off verrrry slowly, compared to the Shuttle, this might be a while, no?

How about just strapping some solid-fuel boosters to the side of the SM? If you're too low, you ignite and fly the CM/SM as high as you can, then jettison the SM and do a parachute landing. Thrust is vertical. It's not very aerodynamic, so in a nominal mission you jettison the strap-ons before you get going very fast. It may not be especially safe when actually used, for the same reason the Shuttle has had endless trouble putting delicate machinery right next to burning solid-fuel missile boosters, but gee if your other option is certain death a 15% chance of death starts to look mighty good.

Also...surely the politics part of this is partly a matter of TV perception. I think people were more profoundly shocked by Challenger than Columbia. Exploding when you're 70 seconds off the ground in clear view of the TV cameras seems more shocking than being in space (acknowledged to be a dangerous place) and dying in some complicated way, or burning up on re-entry, and all people see is bright trails in the sky.

Arguably what NASA really wants is to prevent another Challenger; that is, the risk analysis is distorted by the fact that the risk to the agency's public image is highest at lift-off.

I wonder if the best way to make this monstrosity fly at this stage would be to go back to the methane-powered SM. Was not that more powerful *and* efficient than the current, conventional motor? If so, it would require less fuel to be carried up, and less fuel and therefore smaller tanks in the Upper Stage. All of which means less weight and more margin for stuff like Abort Motors and TO mitigation.

If course, the methane-powered SM is, indeed, that much better.

Carl,
IIRC (this is coming from an old conversation with Henry Spencer) there are three design cases that bound most LAS concepts:

Case 1: Pad Abort--vehicle has a failure on pad with crew inside. For capsules that land with parachutes, this sets the total impulse needed for the system (ie enough impulse to boost the capsule far enough away that the parachutes don't get damaged.

Case 2: Transonic Abort--during the transonic phase, if you try to separate from the booster (depending on the type of failure, it might be better to ride it out until its safely subsonic, but assuming you really do want to get out of Dodge ASAP...), the drag loads are at their worst, which sets the required thrust. One problem is that as the two bodies separate, you get a lower pressure bubble between them that make you use even more thrust.

Case 3: Max Q Abort--aborts at the point of maximum dynamic pressure tend to drive the structural and thermal requirements on the LAS and the boost protective cover.

Those are typically the driving forces on launch escape system designs.

Are there other ways of dealing with those cases? Sure. I'm personally a fan of using a liquid LAS/OMS with central, base-mounted engines, and a pure rocket landing. That allows the impulse to be much lower, gets rid of the BPC, and lowers the required thrust because you're now filling that bubble between the capsule and the stage with hot gas. Mark Hempsell suggested such in his "Excallibur" capsule design several years back (and probably before gm's parents allowed him to play on the intertubes...)

~Jon

Outrun the debris from an exploding booster? That seems damn unlikely. What kind of acceleration do you need to outrun debris that weighs mere ounces being accelerated by the explosion of tons of propellant?

It is assumed that you have a certain amount of warning time. At sea level, the shrapnel is assumed to be affected by air drag and slowed down fairly quickly (they're not rifle bullets). At altitude they'll travel farther and faster, but you'll still be accelerating, while they're decelerating. If you have time to get far enough away before the boom, the debris field will disperse spherically, and it's assumed that you can minimize the risk of a critical hit. I'm not sure what the current acceleration spec on the system is, but I've seen numbers from eight to twelve gees.

And let's not forget, the Russians *did* have a successful on-pad abort from a booster that was on fire and clearly about to violently disassemble at any second...

There was also the launch failure of Soyuz 18a (sometimes called 18-1). Sounds like a wild ride:

The launch proceeded according to plan until T+288.6 seconds at an altitude of 90 miles (145 kilometers), when the second and third stages of the booster began separation. Only three of the six locks holding the stages together released, and the third stage's engine ignited with the second stage still attached below it. The third stage's thrust broke the remaining locks, throwing the second stage free but putting the booster under an unanticipated strain that caused it to deviate from the standard trajectory. At T+295 seconds, the deviation became severe enough that the launch escape system automatically separated the Soyuz spacecraft from the third stage booster and then separated the orbital capsule of the spacecraft.

At the time when the safety system initiated separation the spacecraft was already pointed downward toward Earth, which accelerated its descent significantly. Instead of the pre-calculated acceleration in such an emergency situation of 15 g (147 m/s²), the cosmonauts experienced up to 21.3 g (209 m/s²). Despite very high overloading, however, the landing parachutes opened properly and slowed the craft to a successful landing after a flight of only 21 minutes.

The capsule landed south west of Gorno-Altaisk at a point 515 miles north of the Chinese border[1]. The capsule landed on a snow-covered slope and began rolling downhill towards a 500 foot sheer drop before it was stopped by the parachute becoming snagged on vegetation.

I wonder what sort of escape system this "Orion-ski" will use:

http://news.bbc.co.uk/2/hi/science/nature/7519723.stm

Hmm, interesting.

Now I'm back to wondering about Rand's original point: are trained astronauts really all that valuable, and is the probability of a disaster from which you can recover them really that likely?

I mean, nuclear attack subs do not carry escape pods for all their crew. If you get a serious hull puncture at depth (cf. Thresher) you just all die. I don't think there is much option for the pilot of an SR-71 if things go wiggy at Mach 3.

"Carl Pham wrote:

Hmm, interesting.

Now I'm back to wondering about Rand's original point: are trained astronauts really all that valuable, and is the probability of a disaster from which you can recover them really that likely?"

Yes, I agree. For example, we have been losing more soldiers per month in Iraq and Afghanistan than would be lost in several Ares launch disasters. Every month. Do we really hold soldiers lives to be so much cheaper than those of astronauts? Astronauts are volunteers, just as soldiers are. Astronauts however, can also voluntarily withdraw from a launch without being court martialed.

There is another point to make here, and I'll be crass enough to make it. Despite what NASA seems to think, the death of astronauts does not undermine the public's support for space exploration. What makes human space exploration interesting is that it is grandiose, awe-inspiring,..............and dangerous. And if nobody ever died doing it, well,.....then it wouldn't be dangerous.

How popular would NASCAR have become if there never any crashes?

Jane's staging idea got me thinking about a DC-X as a second stage. I also thought of a competition where there was some task to do at altitude. Everyone used rockets except for one team which used a balloon. The rockets were exciting but the balloon did the job better and won the competition.

Perhaps somebody should talk to Bezos or Rutan about balloons?

What happened with that Canadian group that was going to compete for the x-prize using a balloon lauch?

Regarding the use of the LAS during a nominal ascent, I discussed that with someone last year and was told that the structural attachment between the CM and the SM would likely be torn up in this situation.

Again, on firing the abort motor "sequentially": you can't do it - not because of thrust asymmetries, but because there is one solid propellant load - one combustion chamber - and four nozzles.

Also, given that the LAS weighs 16,000+ lbs, there's a penalty there for carrying it longer than needed.

Rand, I have a couple of comments.

With it, the estimate is a one in five hundred chance of losing a crew.

If you're using the ESAS numbers, the claimed odds (for the 5-segment with J-2X upper stage) are 1 in 433 for a loss of mission and 1 in 1918 chance of loss of crew.

Also, as Jon Goff has pointed out in the past, they're putting a lot of effort into safety during ascent, when this is actually one of the lesser hazards of a total lunar mission.

If I recall correctly, Jon actually went a bit further and noted that NASA is actually reducing risk during the launch by increasing the risk in the rest of the lunar mission.

Rand Simberg wrote:
"Ummmm...yeah. What could go wrong?"

Well you have to at least give me a few points for creativity. It would look cool in a movie, fo sho.

There are other design possibilities for an abort system that save weight.

I recall the Gemini 'B' added two extra motors to the normal cluster of four retro-rockets so that all six working together could provide escape thrust for the capsule. I believe the Soviet TKS spacecraft also combined the functions of launch escape and orbital retro-fire into the same propulsion system mounted on the nose of it's capsule.

With respect to the Soyuz 18a, note that at the time of the second (i.e. core) and third (i.e. upper) stage separation, the launch escape tower has already been jettisoned together with the fairing shortly after booster separation. The Soyuz spacecraft departed the upper stage using the service module engines.