Monday, August 22, 2005

Escape rockets for unmanned satellites

Re: Is an EELV safe enough to launch people without "man-rating" it first?

In a May 2003 hearing (before he was head of NASA), Griffin commented “What, precisely, are the precautions that we would take to safeguard a human crew that we would deliberately omit when launching, say, a billion-dollar Mars Exploration Rover (MER) mission? The answer is, of course, ‘none’. While we appropriately value human life very highly, the investment we make in most unmanned missions is quite sufficient to capture our full attention.”

Since then, he's had a change of heart. NASA's line right now is that man-rating an EELV booster is more expensive than designing a new shuttle-derived vehicle.

I agree with the change of heart, at least. Unmanned satellites generally don't have reentry and landing systems packaged with them, as manned vehicles must. If a satellite did have a reentry and landing system, for the expensive portion of the satellite, seperately engineered to be fail-safe for other reasons, I suspect the insurance companies would be quite interested in adding escape rockets to the launcher, to recover the billion-dollar-satellite in the case that the $100-million-dollar launcher blows up or simply fails to get it into a reasonable orbit.

So escape rockets are a good example of something we would deliberately omit from the Mars Exploration Rover. Ironically, the MER does have a reentry and landing system, but one designed to work in the thin atmosphere of Mars. It would have been much different, e.g. heavier and more expensive, if it were also required to get the rover down, safely, into the mid-Atlantic after a failed booster shot.


  1. Ambivalent,
    Actually, escape rockets for unmanned payloads aren't a dumb idea at all. But I'd prefer flying on a reusable vehicle that had intact abort designed in from the start instead of relying on a band-aid like launch escape systems.

  2. Jon,

    How much LEO payload do you figure a typical launcher would lose were it to have an escape system? I don't know much about this stuff, but just winging it, I see:

    * 5% for parachute recovery
    * 10% for payload shroud / watertight enclosure, that stays on until orbit is secure.
    * 5% for the hypersonic aerobrake necessary to recover after an upper stage failure.
    * 5% for the escape rocket itself
    * 5% for additional payload structure to take the shock of splashdown.

    ...and these add-ons are cumulative, in the sense that the escape rocket has to pull the aerobrake and parachute free, etc. So I get -34% payload. In the ideal case, that's a 34% increase in cost-per-kg to LEO. If insurance is about the same price as the launcher, the escape tower might make sense if the insurace went down by about a third, which seems at least possible.

    I'll also note that once you can assure some sort of orbit, you could blow off the escape rocket and return mass. So the economics for GTO launchers could be better than they are for LEO launchers... assuming a backup mission can be assembled in time, find the failed launcher, rendezvous, and kick it up to the right orbit, which all seems terribly implausible.