In a recent press conference (think it was this one: http://www.ustream.tv/recorded/18431005) one of the MSL engineering managers was asked this question. He said it's because of both the weight of MSL and the landing accuracy requirements. They considered a boatload of configurations before deciding on this one.
The landing sequence isn't actually that much more complicated than that of the MERs. It just needs to be much more precise because you must make a soft touchdown instead of dropping the rover from a height. See http://www.youtube.com/watch?v=tma2pt0k6UQ
While I share your enthusiasm, I'd like to point out some problems with "Sending rovers to all the planets": 4 of them are gaseous giants, literally no solid ground to land on. Venus is a no go too with its crushing atmospheric pressure, sulfuric acid clouds and 400+ c° temperatures.
Where there's a problem, there's at least one solution. I have no idea how to building a bot that can run science experiments in 400+ °C sulfuric acid clouds, but I bet its possible.
Because Mars is a pain in the ass to land heavy gear on.
There's too much gravity, too little atmosphere, and we haven't perfected AI. You can't rely entirely on parachutes, the air bags they used on the last few landings won't hold up to something so heavy, and landing with direct use of retrorockets would pretty much require a human pilot to be sure of -- and even if we had a human pilot, the enormous amount of dust it would kick up is problematic.
No, they couldn't. They are two completely different beasts, and present totally different engineering challenges. Or, to be more precise, Mars presents difficult engineering challenges, Moon doesn't.
Even if they had the budget for a 1-ton lunar probe, landing on the Moon bears almost no resemblance to landing on Mars. The Moon's gravity is 0.16g to 0.38g on Mars, and the Moon has no atmosphere at all. This makes direct rocket landings far easier and completely changes the landing profile.
Obviously the Moon is a very different environment, but it's also much closer to home (which makes it a lot easier to find out what went wrong). It's a little cheaper in terms of fuel, and the trip is much shorter. We can't say we have any recent experience with easy rocket moon landings either.
There are so many new ideas being employed for the first time I don't feel sure it will work. I assume they did several crane drop tests indoors, but I don't know if they did outdoor tests with a chopper attached to the crane module to see how stable the crane platform needs to be and with the crane module using its own rockets (tethered to a tower, maybe) to control its position while a reduced mass rover simulator touches down. Like I said, tons of new ideas, hardware and software that have never been used (and that won't be used together until they get to Mars) that will all have to work perfectly the first time.
Again, I'm all in to sending this rover to Mars, but shouldn't we be sending rovers to the Moon for some time now? These people are much smarter than either you or me, but it doesn't change the fact engineering progresses incrementally and it seems we are jumping up the stairs and skipping steps. I only hope we don't break a leg here.
I am an engineer. We don't like complicated things.
Of course. I wouldn't suggest landing on the Moon something that never landed on Earth. I wouldn't land on the Moon (or Mars) anything that didn't land reliably over Earth a hundred times, until we understand thoroughly what can go wrong.
I would be perfectly confident with a device you could trow it out of a plane, that would parachute until a reasonable altitude, engage rockets to hover and lower a rover to the surface a dozen times without incident.
It'll be at least 30 years until we can inspect the crash site to learn what went wrong.
For the Moon, we would use rockets, or a crane attached to a vehicle with rockets. For Mars (and Earth, or Titan) we add parachutes to the mix because there is an atmosphere. From hovering-stage until rover deployment, everything is the same except for wind, which would be absent on the Moon.
The idea is that you have to lower a car-sized rover from a hovering rocket-powered platform that has to remain relatively still regarding the ground. On Mars, the platform would use parachutes to slow it down. On the Moon it may not be needed at all, but you would use rockets, if you still needed the hovering platform approach (say, landing a very heavy habitation module).
Throwing the probe out of a plane, letting it descend on parachutes for some time and then making it hover using rockets until it gently deposits a rover on the surface seems a good way to make sure we know how to do all the required steps for a successful deployment on Mars. Lots of important variables are very different - Mars' atmosphere is very thin, so the crane would have to use far more power to slow itself down (or a much larger parachute), but the gravity is lower, so the rover would descend more slowly and it would require less power to hover. There could be some wind, but the forces applied to the vehicle would be different than what would be on Earth (Martian atmosphere is thin, but the winds are faster). The whole operation appears to me somewhat similar.
It would at least prevent us forgetting how it's done ;-)
I think it'd be worth, and relatively easy, to operate a rover on the Moon. Remember we don't always know what we should have learned until after we try. This Mars rover is a huge step. Huge steps is someting engineers should learn to avoid.
Maybe they are expecting 'trouble'. Certainly they seem to be downplaying the fact that they are deploying an autonomous robot with a laser that can vapourise stone.
#12: MMRTG Nuclear Power Source. Deviating from its predecessors, Cursorily will be powered by 10 pounds of plutonium dioxide. Earlier, solar power rovers, had to hibernate during long periods of darkness, and at times these hibernations proved mission ending (http://en.wikipedia.org/wiki/Spirit_rover#Stationary_researc...).
Is it me or on all the pages of space.com you cannot find a single link to the NASA website? As soon as you try to get more about the project, you are sent to previous stuff on space.com but no links to the original source, that is, the NASA website. Very annoying...
I hope this rover actually does land successfully - with its RTG power source it could last for decades!