Jeff7
Lifer
- Jan 4, 2001
- 41,596
- 20
- 81
Heck, a lot of engineering and research went into getting rovers intact to the surface of Mars. The airbag idea almost didn't make it, as it was difficult to find a lightweight yet very strong fabric. Yes, it must be lightweight too - sending stuff into space is just a bit more expensive than shipping something by UPS.
Those rovers hit the ground hard too - think they esimated something like 50mph, giving about 40G's of impact force. No gentle ride there. So you can't use airbags for the delicate parts in the Genesis capsule.
Perhaps some kind of rockets on the side instead of parachutes? They've got a big problem though - major expense for the rockets themselves, as they can't be simple single-burn things, they need fine controls, for the fuel, for a computer that can keep the things steady during and after reentry. All of that adds a great deal of weight, and complexity, which means a LOT more things that can go wrong. Instead of a simple pyrotechnic device and a parachute, now you've got a complicated computer control system and sophisticated rockets - any one of them fails, and you're screwed, but this time it's just more expensive. And with all the extra weight (and fuel), the impact will be a lot more violent - greater velocity, and a possible explosion. NO chance of recovering anything useful when the capsule is scattered across a few thousand square meters.
A parachute and a hook - simple. Airbags - simple. And Cassini - it didn't use a massive, ludicrously expensive rocket to send it directly to Saturn. It used gravity assists from a few planets to get it there.
Simplicity is important - but complexity can be needed (like the Mars rovers themselves) to get a lot of good data back efficiently. Delicate balance between the two.
Talk about failures - don't forget some successes. The Voyager probes are still returning data, and they were launched in the 70's! Their power output is diminishing from their plutonium power sources, but they're still able to run a few instruments, as well as the high gain antenna of course. I think the bitrate is only a few bytes per second, but it's still enough to return useful data.
Or the Ulysses probe. Launched in October of 1990 for a 5 year mission. It's still working. Granted, its power output is also diminishing, thus exposing it to temperatures that are nearly allowing its propellant to freeze, but it should survive.
From what I've read, the missile defense system that they're testing now has trouble hitting stationary targets like weather balloons. Good luck hitting a supersonic missile.
Not entirely to waste - the main probe did return useful data while it was in the halo orbit. It has been sent on a long-term orbit of the sun for a continued mission.
Yes, things are cheaper now. NASA sent two very complex rovers to Mars for around $850 million, and they've survived more than twice their original life expectancy; Spirit will be at 270 sols probably sometime late next month. And Spirit has driven over 6x farther than it was expected to last.
There was the expensive Mars Observer back around 1990 that simply vanished. Probes started to get cheaper after that.
They used fragile collectors made of various high-purity elements. Apparently an impact would damage them.
As has been said - reentry is not easy. Making it gentle is very difficult. Gathering pristine samples of solar wind is also not an easy task. Combining the two? Good luck with that. NASA tried, and almost succeeded. One thing went wrong and screwed it all up.
Something can go wrong right at the start of the mission. Galileo's mission almost ended before it started - the main antenna never deployed. Luckily, it did have a low-gain antenna, which was able to get most of the job done. Without that, the mission would have been scrapped by a few sticks that didn't swing into place.
There's the other thing too - by the time you really realize there's a problem, and react to it, the thing is already going to be way below the helicopters, or else still moving too fast.
Speaking of redundancy, just read Sean O'Keefe's statement. In which he mentions, "The spacecraft was designed in a way to give us the best chance at salvaging the valuable science payload should we suffer a landing like the one we witnessed today." Maybe they did try to prepare for the worst, while still staying within their weight, size, and monetary budgets.
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