Pretty cool how they were able to land the Near spacecraft on the asteroid Eros.
But it got me thinking, instead of a one-shot mission to one asteroid, do we have the technology to build a probe that could explore the asteroid belt (and planets) indefinitely? E.g., using solar power for energy and the solar wind and gravity assists for propulsion?
And, I forgot to add, couldn’t we save a lot of money by building a standardized fleet of such probes? We could have a bunch of 'em operating at once. Our current approach to interplanetary exploration seems to involve a whole new platform for each mission.
The experiments we want to do on various things are so specific and complicated, building a standard fleet wouldn’t work. The requirements for an asteriod and Mars are completely different.
Regarding propulsion, I don’t know if anyone has been successful in building a “solar sail,” AFAIK it’s still theoretical. Alas, there is no way to propell something in space with electricity alone. 
Yeah, that’s true. I guess I mean more of a standard *platform[/] to which you attach whatever instruments are required for the mission at hand. It seems like (I don’t know if this is really true, just going by looks) every such mission is built around a whole new platform.
I can’t think of a solar sail being tested yet either. I think there was a spacecraft recently that tested an “ion propulsion engine” or something like that. IIRC this type of engine can have a much longer lifespan than a typical engine.
The answer to “Why doesn’t the space program do X?” (where X is technologically feasible, as your idea certainly is) is money.
Yah, it would be awesome to build a fleet of robotic craft to explore the asteroid belt. Sure, it would be more cost effective to build ten the same rather than ten all different. But you need bucks to build them, and more importantly, you need to pay people to manage the missions and reduce the data as they come down. You need Deep Space Network time for download. There are a lot of costs associated with space exploration beyond just building the spacecraft! Operating indefinitely means paying people indefinitely.
There’s a perfectly good spacecraft in orbit around Jupiter right now. (Okay, well, except for that pesky high-gain antenna SNAFU.) Know what they’re going to do? Crash it into the planet. Why? Ostensibly because radiation might cause a failure. Practically? Because they don’t want to dump any more money into the mission.
And before you get too sanguine about solar power, remember that NEAR was the Near-Earth Asteroid Redesvous. Main belt asteroids are 2 to 4 times as far away from the Sun. That means 1/4 to 1/16 as much sunlight! Incidentally, the distance means that propulsion demands will be a bigger issue than with NEAR. Gravity assissts are keen, but they also mean that the craft lifetime has to be longer to do the same amount of science, and if you want to use Venus, you have to engineer the craft to survive in a winder range of conditions.
The ion drive you’re thinking of was on Deep Space 1. A great success, but still considered experimental.
Thanks Pokadyne. I guess what this all reduces down to for me is the cost of constructing and launching a spacecraft versus the cost of operation and data collection while it is in space. Generally speaking, which is the more expensive half of a mission?
I was thinking if we could build a few reasonably flexible craft designed to last much longer than current ones, we could save money on launch and construction costs, while exploring much more of the inner solar system. Of course this would increase data collection needs, as you state. But couldn’t this cost, with increases in computer processing power and better software, be reduced as well? This would also reduce the number of people required.
Err, Podkayne … not Pokadyne.
From the NEAR FAQ:
(NEAR was the first of the Faster Better Cheaper missions, by the way.) So building the spacecraft and launching are, as you suspected, the lion’s share of the budget.
And yes, you’re right, if you have standardized procedures and software, you would have a little more efficiency in data-processing, but I really don’t know how much. An important thing that won’t scale is downlink time.
Looking at your proposal, I keep hearing a cash register ringing. 
“I was thinking if we could build a few [$$$cah-CHING$$$] reasonably flexible [$$$cah-CHING!$$$] craft designed to last much longer than current ones [$$$cah-CHING!$$$], we could save money on launch and construction costs, while exploring much more of the inner solar system.”
Designing longevity into a spacecraft is no easy task. Due to high lanch costs, there’s already a great incentive to optimize vs. cost/longevity. Space is a nasty and cruel place with lots of hard vacuum. thermal cycling, and electronics-busting radiation, and no opportunities to repair things that go wrong. Plus, there’s the whole issue of consumables. Like I said, if you want to explore the main belt, you’re going to have to outfit the craft with radiothermal generators, which have a finite lifetime. (Plus, you have to talk the Floridians into letting you strap a bunch of plutonium to some high explosives and light the candle.) A spacecraft meant to orbit several asteroids would need lots of propellant–and then you run into the rocket problem, of course. (More propellant makes the craft heavier so you need more propellant, etc.) Flybys would be much easier on the fuel–but you’d also get much less science. The ion drive or another advanced system would help with this, of course, but then you’re talking about spending a lot of money on a fleet of vehicles relying on a hardly-tested technology.
Gad, I feel like such a wet blanket. It’s really a nice idea in theory!
FWIW, one of the long-term visions of NASA administrator Daniel Goldin is to deploy a fleet of small AI robots that would explore things like asteroids. These small probes would land on an asteroid, study it, send info back, MINE it and create more fuel (or maybe even more probes IIRC) in order to fly off and study more objects.
Sounds a bit like a virus to me, but it’s an interesting idea.
Well, the “data crunching” side of this proposal could be done like the successful Seti@Home program, where you give the public something neat to look at, while using their processors to do the work for you, saving you money and precious network resources. Just an idea…