3 ms·

The earth is an even closer place to land on.

by jerrya 15y ago

rbanffy 15y ago
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.
- pavel_lishin 15y ago
  And how do you translate what you learned from a parachute landing on Earth to the moon? It's like assuming that you can easily swim five miles because you can easily jog five miles.
  - rbanffy 15y ago
    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.
    - ars 15y ago
      No one is arguing about the need for testing. They are saying that testing on the moon adds nothing.
      - rbanffy 15y ago
        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.

The earth is an even closer place to land on.

by jerrya 15y ago

The earth is an even closer place to land on.

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.

pavel_lishin 15y ago
And how do you translate what you learned from a parachute landing on Earth to the moon? It's like assuming that you can easily swim five miles because you can easily jog five miles.
- rbanffy 15y ago
  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.
  - ars 15y ago
    No one is arguing about the need for testing. They are saying that testing on the moon adds nothing.
    - rbanffy 15y ago
      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.