[QUOTE=H3Knuckles]
This is something I’ve often wondered about. Given the example of Apollo 13, and the dramatically increased distances and operational time-frames we’d be talking about, might it not be reasonably to hold off on such a venture until we could build two separate vessels (each designed to support one crew, but able to accomodate twice that in an emergency), then train two crews, and hold one in reserve in case of emergency?
I know, I know, it’d cost a fortune and take time, but wouldn’t that be the ultimate precautionary measure for the first time we make each milestone step in space travel? Just an idle thought.
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The problem here is one of orbital ballistics; unless you are proposing sending two vessels and crews simultaneously (and I’m taking by your statement of “hold[ing] one in reserve” to mean that you’re not) then this will do you no good. Once you’ve launched the first one on its way, there is simply no way a second craft, propelled on a low energy Hohmann-type orbit is going to catch up to the first. It will in fact be in an entirely different orbit, and even if you can manage to have both craft cross orbits simultaneously, they’ll be going a different directions at a different speeds, and at best can just wave at each other before speeding off into the blackness. And if the first craft is any distance away from Earth any intercept would take months, by which time any dire emergency will have resolved itself for better or worse. And the rescue craft will almost certainly not be able to make an effective return.
Now, if your plan is to send two or more craft on the same orbit, with the crew split between them, and capable of abandoning one craft, that is more feasible from a risk management point of view, and also brings in some other advantages, such as being able to justify building more test articles to evaluate reliability. The cost will almost certainly be more than building just one larger craft, but lower cost per unit. There may also be other benefits to mission flexibility and crew capability. But you’re also doubling your losses if some hazard (a large solar flare, for instancde) wipes out the entire mission, or some unforseen common flaw dooms both vessels, and I doubt anyone will be willing to bear more than the minimum cost for what is essentially a photo op mission.
Barring a dramatic improvement in propulsion technology, a manned Mars mission is little more than spacewonk fantasizing, and it certainly isn’t going to be done with the Constellation program hardware, even if that thing ever gets off the ground. Fortunately, our capabilities with unmanned missions are improving dramatically, and we’re able to obtain excellent scientific information at a fraction of the cost, and with minimal risk or hazard, compared to a hypothetical manned program. Crash a Mars Climate Orbiter into the planet because of a mixup in units and you become a joke; lose a manned mission for essentially any reason and you’ll be a pariah. There’s a reason that NASA is simultaneously risk adverse and risk ignorant, and the reason is as much from without as within.
Stranger