Would a rover on an asteroid float away because of the low gravity?

[sciencec]

TL;DR Summary

Would a rover on an asteroid float away because of the low gravity?

I’m wondering if a lander/rover landed on an asteroid with a very low gravity, and we wanted to make said rover move around the asteroid, would it “float” away because of the low gravity? Wouldn’t the normal force and the gravitational force equal 0? If we added a propulsion system, how would we know the amount of propulsion to “give” to the lander? I hope my questions are clear. Thank you!

 

[Tom.G]

Clever, those Japanese. They figured it out and are actually doing it!
https://www.google.com/search?&q=hopping+rover+on+asteroid+ryugu

 

[Orodruin]

Hopping aside, a rover would float away forever if it reached the escape velocity of the asteroid. The normal vs gravitational force does not have much to do with it as the asteroid is round and not flat. The question becomes one about the size of the asteroid vs how fast you want to be going.

 

[sciencec]

Hopping aside, a rover would float away forever if it reached the escape velocity of the asteroid. The normal vs gravitational force does not have much to do with it as the asteroid is round and not flat. The question becomes one about the size of the asteroid vs how fast you want to be going.

So there’d have to be a way to keep the rover from floating away forever. Would the propulsion system work?

 

[russ_watters]

Wouldn’t the normal force and the gravitational force equal 0? If we added a propulsion system, how would we know the amount of propulsion to “give” to the lander?

The gravitational field of an asteroid can be measured by sending something to orbit it. That will enable calculating the surface acceleration/gravitational force of thrust required. Yes, thrusters would work. They wouldn't be needed all the time, just when rolling over rough terrain that could cause the rover to jump off the surface.

However, the low gravity also means reduced traction, so a rover would be a very slow way to move.

 

[sophiecentaur]

However, the low gravity also means reduced traction, so a rover would be a very slow way to move.

A rover could move around much more quickly if it could fire pegs or grapples into the ground and attach tethers / walking legs. Wheels are clearly not the best solution and thrusters would probably be wasteful of fuel.
I heard mention of multi-legged walking rovers being potentially better than wheels even under planetary gravity in some situations. That makes sense as there are no roads available.

 

[russ_watters]

A rover could move around much more quickly if it could fire pegs or grapples into the ground and attach tethers / walking legs.

That seems cumbersome, but potentially doable.

Wheels are clearly not the best solution and thrusters would probably be wasteful of fuel.
I heard mention of multi-legged walking rovers being potentially better than wheels even under planetary gravity in some situations. That makes sense as there are no roads available.

I'm mostly not referring to getting around terrain, I'm talking about the difficulty of just moving at all. Anything that relies on friction or has the potential to bounce will be a major problem, and that includes legs. The g on that asteroid the Japanese landed on was .13 millimeters per second². A rover that relied on friction to move would take hours to accelerate to walking speed if it managed to stay on the ground.

 

[sophiecentaur]

The g on that asteroid the Japanese landed on was .13 millimeters per second2.

Wow - you really would have to 'pussyfoot around'. I can see the attraction of thrusters but there would be less fuel involved if the surface would allow some sort of attachment to the ground.
If the surface is very loose (most likely?) then the vehicle could collect a large bucket full of dust / rocks to provide ballast. But would that actually help? The escape velocity is still the same so the speed of movement wouldn't necessarily be improved; the ballast would need to be slung underneath and decoupled from the rover's varying vertical motion. Not a problem if very long spindly legs were used.