>> Sunday, May 16, 2010
The problem with the technical posts is that I have to go fetch all the specifics to put them together. So they take longer. Still, I want to get this out so I'm continuing with it.
Clearly, given that the needs required to allow humans to return to earth are so significant, throwing a bit of hardware or samples in with the rest is relatively benign compared to effort to do so on an unmanned mission. By definition (for all manned missions where we expect our crew to return), the vehicle needs life support systems, heat shields, attitude controls rockets and/or flight controls, deorbiting rockets (and fuel), some sort of slowing down mechanism (chutes, retrockets, flight surfaces, etc) and, frequently, some sort of transponder so that we can find them. Add a few kg of extra equipment/samples/experiments, etc is really no big deal.
But, if you have an unmanned satellite or space vehicle, you are talking about adding ALL of this equipment that otherwise wouldn't be necessary - except the life support system. For a remote spacecraft (outside earth's orbit) just the rocket for return alone is a huge added weight and complication.
But, before the advent of the Shuttle, the US and the Russians were still limited to, at most, a few hundred kg of additional baggage as it were. Most Russian spacecraft, those that aren't manned, are designed to burn up during reentry. There was one model that could return unmanned but it's payload was tiny relative to the trouble (~150 kg). Soyuz TMA, the manned Russian craft used for the ISS, can return 50 kg (and sometimes a smidge more).
The Shuttle, however, can bring down tens of thousands kg of payload, in the payload bay and/or the middeck. Trash, experiments, satellites, equipment, modules. Of all the precedents the Shuttle inaugurated, a world where equipment that failed could be returned and evaluated (as has been done extensively with repaired items on the Hubble Space Telescope - and even refurbished and reinstalled), this accomplishment is perhaps the greatest triumph of them all.
Oh, don't get me wrong, it's impressive that it's largely reusable, but there are some down-sides to that. And it has a pretty impressive payload capacity to begin with, no doubt. But, a big enough rocket, we can get that much payload, and more, as far or farther. Getting it back down? I wonder if we'll ever be able to do so much again. I doubt it will be in my lifetime.
I hope I'm wrong about that.
There are many triumphs particular to the manned portion of space exploration, not the least of which is that sending man into space means you have to lick two tough problems - how to get him out there and how to get him back. History makes it pretty clear which one's tougher.