In the 1950’s it seemed like almost all of our rockets exploded during the launch. There were a lot of spectacular failures in those days and successes seemed rare. As we considered putting a man in a capsule on top of one of those rockets it was obvious that something was needed to get the pilot out of a bad situation in a hurry.
During the Gemini program, that method of “crew escape” consisted of ejection seats which were only slightly modified from those found in that era’s military jet fighter aircraft. This left a lot to be desired as we shall see.
But Max Faget, the innovative genius behind much of the engineering progress in NASA’s early days, had a brilliant idea. He invented something called the launch escape rocket system. A cluster of solid rockets attached to the top of the crew capsule could be activated in an emergency to pull the capsule and crew away from a disaster and let them use their normal recovery parachutes to land safely.
This was such a good idea that even other countries adopted this plan. On September 26, 1983, with their rocket exploding below them on the launch pad, the crew of Soyuz T-10-1 was whisked away from almost certain death to fly again another day. Gennady Strekalov and Vladimir Titov owe their lives to Max Faget . . .and a whole bunch of Russian rocket designers who built that launch escape system for the Soyuz spacecraft.
So Mercury and Apollo and the in-design Orion spacecraft use Launch Escape towers. In fact there is a test of the new launch escape rocket system for the Orion scheduled for next week out in Utah.
The shuttle, of course, adopted a different philosophy; a philosophy that, like a commercial airliner, “passenger” safety was provided by bringing the entire ship home safely. More about that in a later post.
Today I want to talk about ejection seats. Gemini had ejection seats and so did the shuttle for the initial flights. I don’t know much about the Gemini seats but the shuttle ejection system used on the first four flights was the best there was at the time. And it wouldn’t have done much good.
The shuttle ejection seats were taken from those used on supersonic military aircraft. Ejection at supersonic speeds has always been dangerous, probably life threatening. It is best if the ship holds together to get to subsonic speeds where survival is much more likely. At supersonic speeds, hitting the airstream is like hitting a brick wall. Not good. It may be the best option if you are facing certain death by riding a disintegrating ship, but even then it is not a great choice. The shuttle ejection seats were really there for the late stages of landing. If that big glider of an orbiter couldn’t make it to the runway, better to eject and bail out than try to crash land on rough territory. In that scenario having ejection seats actually made sense. In a later post I’ll talk about the entire entry regime, but just note that from the altitude of about 100,000 ft or lower and speeds from Mach 3 on down, the seats would probably have worked as advertised. An ejection at, say, 10,000 feet and subsonic speed would have been a very good bet in a that situation.
How about using the shuttle ejection seats on ascent?
Not good.
For example; an ejection on the launch pad would not get high enough for the parachute to open in time. Yep, you’d hit the ground from a few hundred feet altitude with the chute still unfurling. Not recommended. If your rocket was in the process of blowing up (remember Titov and Strekalov?) the blast overpressure would still be fatal at the distance the ejection seat would push you. As a final insult, the “landing” would be in the flame trench. So, an ejection off the launch pad was not a good idea for a shuttle crew.
During ascent, the capcom made the call “negative seats”. This occurred as the shuttle climbed above 80,000 feet. At that altitude the ejection seats would still work, and the pressure suit had sufficient oxygen get back down so you may ask, why was that a limit? Because an analysis of the speed and trajectory above that point resulted in enough air friction heating to melt the plastic faceplate of the helmet. And probably other things we didn’t analyse. But the basis for the call was the melting of the faceplate. So about 90 seconds into flight the ejection seats were useless and until at least 10 seconds into the flight there was not enough altitudefor the chutes to open. So if you ejected in those “safe” 80 seconds? Toasted by the solid rocket booster plumes going past you. If the stack held together and didn’t have “an overpressure event” or send shrapnel headed your way.
Nope, ejection seats during shuttle launch was not a good way to get out of a tight spot.
The Gemini situation was probably better in some ways, but still not great. Some retired Gemini engineer will probably post a comment with that information.
So all you future rocket designers please note: launch escape rockets are the way to get out of a bad launch situation.
Of course, the best thing is that your rocket should never to explode. But what are the odds of that?
Stay tuned for more discussion of this fascinating subject.