posted 07-31-2010 10:52 AM               

Meanwhile, the shuttle, it is argued, must "ride the rocket" at minimum until SRB burn out, and in all the profiles I know of, must continue flight until all the ET fuel is consumed.

My question is... why?

Why can't the orbiter after reaching some minimum altitude (say 20,000ft - the height of the Approach and Landing tests in 1977) simply eject from the stack and land/ditch anywhere - even on the beach or in the water if it can't make it back to a runway landing.

This procedure, if developed, would reduce the orbiters exposure to unrecoverable danger to the first 30 seconds or one minute of flight as opposed to riding the RTLS profile for up to 10 minutes as currently devised.

Wouldn't such a procedure be preferable to the cumbersome (and possibly unrealistic) system of jumping out on an escape pole in case of a malfunction? Or riding around for 7-10 minutes using all the fuel in the rocket stack before finally returning to the Cape or doing a transatlantic abort?

Certainly this must have been thought of and rejected for some reasons I can't understand, and likely won't believe even if it were explained.

posted 07-31-2010 03:06 PM               

My point, is that a controlled separation would not destroy the vehicle, and that is the key to my whole question. Why does RTLS particularly require a full consumption of all the fuel in the tank, it's gotta separate from that tank in the atmosphere anyway after the fuel is consumed, so it seems to me totally within the realm of possibility to design an escape separation procedure that takes the high speeds into account.

Furthermore, I'm not necessarily just discussing this for the sake of the "Mark 1" (current tech) orbiters, but more or less as a possible engineering exercise for the 2nd generation shuttle that will inevitably be built by industry or otherwise. However I do think that the current design is robust enough to perform such a task.

Speaking of Challenger, the orbiter crew compartment came through the event relatively unharmed. If they had such an escape mechanism (and a few seconds warning either from sensors or the RSO using a telescope) I think the whole vehicle could have easily driven straight ahead on its own inertia, and turned around in due time using powered flight controls. Maybe it doesn't make it back to the runway but a controlled descent through the atmosphere to a ditching or beach landing would certainly have saved the crew if not the vehicle.

posted 08-01-2010 12:13 PM               

quote:

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Originally posted by Aeropix:
Why does RTLS particularly require a full consumption of all the fuel in the tank, it's gotta separate from that tank in the atmosphere anyway after the fuel is consumed, so it seems to me totally within the realm of possibility to design an escape separation procedure that takes the high speeds into account.

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I would have thought that separating from an ET that still had thousands of pounds of fuel in it sloshing about would be a highly risky maneuver. The ET would be unlikely to continue on a predictable path at separation, with a high risk of collision with the orbiter.

posted 08-01-2010 04:29 PM               

More then likely, the orbiter would hang on the aft struts, pitch "up" (i.e. down relative to the Earth) and then rip apart due to the dynamic and aerodynamic loads. If it just ripped the struts off the ET, then you would end up with another fireball like Challenger when the LH2 hits the SRB plumes (probably no concussive force as Challenger had none, but it could be nasty). Plus, the main engines act as a side thrust load in addition to the SRBs, so doing a MECO in preparation for ET sep while still under SRB thrust would likely cause the ET and SRBs to pitch down relative to the Earth as well. Do that too far, you get another aerodynamic side load which would likely shread the ET if it happens too fast.

As for beginning an RTLS recovery manuever down low at about 35,000 feet (as I recall that was the altitude for the Enterprise ALT tests, not 20,000), the orbiter would be too far down range and heading in the wrong direction to make it back. Speed at 35,000 on ascent is maybe a little over mach 2. When Enterprise was cut loose from the 747, it was very near to the landing strip and pointing in about that direction. Trying to do too tight a turn would scrub off enough speed that the thing would drop like a rock and shuttle ditching characteristics are NOT good at all (forget the beach).

As for the capsule recovery method, indeed the crew cabin did survive more or less intact on Challenger and Columbia, but it broke apart rather quickly in Columbia's case. You can't just strap a parachute to it though as it would still need some sort of stabilization system and a structure that can withstand a land impact and stay afloat in water (at least long enough for the crew to get out, which might be awhile if there are injuries). That in turn adds weight to the design, which would reduce payload capacity.

posted 08-03-2010 05:08 AM               

The SRBs for example are indeed steerable, and take a pretty big weight penalty in the design phase for having steerable exhaust cones. With 30 years of additional computer technology since the original design, surely a small backup steering computer/laser ring gyro can be added to the SRB/tank to guide this away from the orbiter in case of an SRB lit abort.

As to the tank being partially loaded with propellant and therefore having unpredictable characteristics in case of an early separation, again with today's computers surely an "abort computer" could constantly monitor this and adjust the orbiter's controls in such a way that it could separate cleanly.

All this being said, I guess the fact that the last SRB redesign and conservative launch rules have made such escape maneuvers less useful due to the reliability of the SRB.

posted 08-03-2010 07:43 AM               

Somewhere in another thread that I've failed to trace I believe it was the general opinion that once the SRBs fired one had to ride them until depletion. This would seem to exclude either early separation or shut down.

posted 08-03-2010 07:55 AM            

quote:

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Originally posted by moorouge:
I believe it was the general opinion that once the SRBs fired one had to ride them until depletion.

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posted 08-03-2010 07:37 PM               

quote:

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Originally posted by Aeropix:
However I bring up this topic because I believe that these are challenges that could be very easily engineered into a next generation orbiter,

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1. The SRBs can't be steered away
   1. the SRBs wouldn't know which way is "away"
      
   2. The handoff from shuttle to SRB guidance is not a trivial task and would require the SRB guidance to be up and running at a moments notice
      
   3. SRB guidance would be just as complex as any other launch vehicle guidance system
      
   4. As an SRB maneuvers, it rotates around its CG. This means as the nose rotates 5 feet away, the aft rotates 5 feet closer

2. Slosh is not an easy thing to model and it is not a trivial task

posted 08-15-2010 02:18 AM               

If the subject is too design a Shuttle Mark II. Why do we have to save the whole orbiter?

Surly the aerodynamics forces would break apart the vehicle. But why save the whole vehicle, when all we have to save is the crew compartment.

Small SRBs attached to the main orbiter would get it to about 5,000 ft. high enough for the crew to bailout.

On the other end of the flight, the crew cabin would have an ablation shield to protect the crew.

posted 08-15-2010 11:43 AM               

quote:

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Originally posted by Lou Chinal:
Why do we have to save the whole orbiter?

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Hindsight is 20-20, of course, and one needs to look at why the concept was to save the whole orbiter in the first place: The system was going to be reliable enough for comparisons to airline operations, and the image is apt.

posted 08-15-2010 12:22 PM               

quote:

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Originally posted by Hart Sastrowardoyo:
Sure there are (usually) individual lifejackets and cushions as well as life rafts, but when an airplane is in trouble, you don't have the passengers bail out in flight nor do you separate the passenger compartment. You bring the whole airplane back.

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It goes without saying that the shuttle flies in much more dangerous regimes than the average passenger aircraft, with a much higher risk of failure. One must engineer the vehicle with the amount of risk in mind. Also, remember that more dangerous aircraft types (such as jet fighters) do indeed have a provision for the crew to escape from the aircraft in the event of a disaster.

For most regular commercial aircraft, the passenger compartment takes up a large portion of the fuselage...so it's more practical to return the whole aircraft to the ground in an emergency. On the shuttle, the crew compartment is a small space at the front of the vehicle that could feasibly be separated in the event of an emergency, reducing the need to keep the entire orbiter intact for a safe recovery.

posted 08-15-2010 09:04 PM               

Even with the Apollo spacecraft, land landings were a bit of a questionmark. Walt Cunningham's book talked about one memo from John Young where he pretty much shot down the idea of trying to certify a land landing for the Apollo craft. At best it would have made the couches survive, but not necessarily the crew. And in that case it was only three people coming back. Early Orion testing included a land landing system, but weight and complexity issues for that led to it getting deleted. Personally I think they should have continued development of a land landing system, given that fishing the capsules out of the ocean requires help from the US Navy for each recovery.

Only emergency system to date that seemed to have the ability to recover more then three crewmembers to a land landing was the cancelled X-38. But of course it never got to an all up test in an intended production configuration, so we will never quite know how it would have done in that regard.

Could an ejectable crew cabin system be developed for a possible shuttle mark 2, yes it could. The biggest hurdle will come down to time and money though as it did with Shuttle mk 1. From an engineering standpoint, the reason for not developing a system is that you are spending so much time trying to certify the rest of the vehicle to operate normally with so many safeguards to such an extent that such a system won't be needed. So it comes down to the point of why carry it since it will likely never get used and carrying it will mean less cargo capacity due to the weight penalty. It is a harsh reality and I don't see it getting any better unless someone was willing to put fourth the funding or sacrifice the weight to do this.

The work would not be easy. For starters, a crew cabin designed to hold seven people in a spacecraft is about as large and heavy as a main cabin in an airliner. Not only are the people there, but so is the instrumentation and the insulation needed to keep them alive on orbit. The computer systems of shuttle are designed to work in a normal atmospheric environment for heat removal, not a vacuum. The weight involved was probably equivalent to maybe another 4 or 5 astronauts. Granted integrated electronics these days can size those systems down, but those new systems again would have to be certified for flight operations. The structure would have to be designed in such a way to handle structural loads as part of both a larger vehicle and by itself. Then that structure would also have to be designed to survive either water or land landing impact. It would also need some way to stabilize its flight characteristics on launch or reentry, or else the regime where it could be utilized would have to be cut down. If it is intended for a full reentry by itself, then it needs some of the sharp corners rounded off, or else it will have the air drag of a brick and it will burn up even with a heat shield due to hot spots in the structure. Doing that also means you will increase the complexity of any electrical, life support or fuel lines going into the cabin as well as they can only enter through certain points that will have to be cut off and covered for reentry.

posted 08-30-2010 12:41 PM               

A shuttle with airline like technology will have to wait for the next generation.

If the shuttle has taught anything is that an escape system must be designed in from the beginning.

The proposal of this topic was just to see if there were any creative juices flowing out there.