# Are lunar landings without chemical rockets possible?

1. Feb 8, 2013

### guss

If a satellite tries to land on the moon without rockets to counter the force of gravity, it comes in too fast and crashes into the surface destroying itself. A satellite would be orbiting at approximately 1.8 km/s or so at a 50km altitude, and come in for landing from that height which would speed it up an additional .4 km/s. All in all we are probably talking 1.2km/s in the horizontal direction and 400 m/s in the vertical direction upon touchdown. It would I was thinking there may be some type of airbag that could deploy, and allow it to roll on the surface which would slow it down in the vertical direction. Maybe have it land on a downward slope for a bit of a softer landing?

Just something interesting I was thinking of. Any ideas?

2. Feb 8, 2013

### Mech_Engineer

It might help if you thought of the problem from a practical standpoint. You're talking about trying to bring something from 4300 km/hr in the horizontal, and 1400 km/hr in the vertical, to a stop. There's just no way to do that with an airbag and keep the accelerations reasonable.

Taking into account just the vertical speed, if we assume your airbag is 10m thick (that sounds like a pretty big airbag), you're talking an acceleration of -8,000 m/s^2 (-816g), not even including the 182 rpm spin rate that would be induced from impacting the surface at 4300 km/s. Your airbag would also have to be made out of material that is tough enough to handle hitting the very abrasive lunar surface (basically ground silica glass) at that speed, probably not possible with any existing technology.

3. Feb 18, 2013

### crazyswede

The answer to this question relies heavily on how you define a landing. In general terms a lunar landing without a chemical rocket is very easy to do as long as you are aimed at the surface and you hit said surface. If you require the landing device/object to be usable afterwards then this conversation changes completely ;)

4. Feb 18, 2013

### MatsNorway

Yes landing... in one piece.. and functional.

5. Feb 22, 2013

### 2milehi

No atmosphere to dissipate any energy like on Mars.

6. Mar 27, 2013

### MatsNorway

There was a swedish rocket that used ion engines. Terribly weak engines they said. but in the future perhaps those would be able to counter the gravity enough to make a landing.