PDA

View Full Version : Air cushions and the moon.



Sever
2005-Feb-21, 05:37 AM
I had thought of this for some writing on NationStates and I've been discussing it with Colt, he seems to like it. I tried thinking outside the box for this one. :)


My basic and rather poor doodle which lays out the idea (http://img43.exs.cx/img43/7756/daverisonaeroshell9ul.png)

My idea is that the exhaust gases of a lander would be trapped under a inflatable shell or skirt which would also act as landing gear (it is rib stiffened and has a kelvar outerskin). I've also thought about conducting a low power burn and using the exhaust to move the lander around on the surface(in case the lander lands on unstable terrain, lands offcourse or just needs to be moved). The system would weigh less then a solid set of legs. The crew would leave the craft and walk over the shell(on a path with a non-skid covering) and go down some steps to the surface.

But would it work?

pghnative
2005-Feb-22, 03:19 PM
I had thought of this for some writing on NationStates and I've been discussing it with Colt, he seems to like it. I tried thinking outside the box for this one. :)
But the problem is that the gases need to be outside the box also!

Unless I misunderstand, you are trying to use the rocket to slow the spacecraft as well as supply inflation gas for some sort of airbag. But unless the gases escape the spacecraft, there will be no net thrust and the spacecraft won't slow down.

Romanus
2005-Feb-22, 03:51 PM
This sounds a bit like the "airbag" concept used on the MERs and Pathfinder. If so, you'll have to slow the probe a lot to get this to work. Both of those spacecraft--especially the MERs--were slowed down by the atmosphere and parachutes before they landed. On the Moon however, the lander would have to approach the surface at a substantial fraction of orbital speed (from 1.68 km/s and below), unless it were braked considerably by retrorockets.

SAMU
2005-Feb-22, 07:53 PM
Sounds like you are describing a rocket inflated hovercraft. Interesting idea.

But the original LMs had rigid legs and they only had to withstand a drop of about 6 feet max in lunar gravity, a 1 foot Earth equivalent drop.

Conventional springs and shocks would have done the same thing with less weight and you could put wheels on the lander as well.

The question is; would the "hovercraft" aperatus and rocket fuel or wheels, shocks and motor to move the entire lander weigh less than a smaller rover vehicle and carrying compartment?

Sever
2005-Feb-25, 02:09 AM
(I didn't realize this thread had any replies till this morning, so sorry about the gravedigging).
Now to make some more points.(My understanding of physics is rather limited due to the fact I don't get to take it untill Gr.11).




I had thought of this for some writing on NationStates and I've been discussing it with Colt, he seems to like it. I tried thinking outside the box for this one. :)
But the problem is that the gases need to be outside the box also!

Unless I misunderstand, you are trying to use the rocket to slow the spacecraft as well as supply inflation gas for some sort of airbag. But unless the gases escape the spacecraft, there will be no net thrust and the spacecraft won't slow down.

Actully I mean to inflate the shell before landing with external cansiters(thats what those oviod thingies are on the exterior of the orbital phase, it would be jettisoned on take off). Wouldn't the exhaust gases be deflected(if thats the right word) from the lunar surface into the shell?



But the original LMs had rigid legs and they only had to withstand a drop of about 6 feet max in lunar gravity, a 1 foot Earth equivalent drop.

Conventional springs and shocks would have done the same thing with less weight and you could put wheels on the lander as well.

The question is; would the "hovercraft" aperatus and rocket fuel or wheels, shocks and motor to move the entire lander weigh less than a smaller rover vehicle and carrying compartment?


Well, I really only want to use the "hovercraft'" ability to move around the landing site(in case it landed and a rock blocked the landers ladder or something). For exploration I'm sending a LFV (

This sounds a bit like the "airbag" concept used on the MERs and Pathfinder. If so, you'll have to slow the probe a lot to get this to work. Both of those spacecraft--especially the MERs--were slowed down by the atmosphere and parachutes before they landed. On the Moon however, the lander would have to approach the surface at a substantial fraction of orbital speed (from 1.68 km/s and below), unless it were braked considerably by retrorockets.
Well I suppose I could replace the shell with a toriod airbag... *idea buld starts blinking*

W.F. Tomba
2005-Feb-25, 03:24 AM
Are there supposed to be holes in the bottom of the airbag to allow the exhaust gases to escape? Or does the bag not cover the nozzles? I'm confused about what you mean by "trapped under" the inflatable airbag, and your drawing doesn't help much. Where are the exhaust gases being emitted?

Sever
2005-Feb-25, 03:32 AM
Are there supposed to be holes in the bottom of the airbag to allow the exhaust gases to escape? Or does the bag not cover the nozzles? I'm confused about what you mean by "trapped under" the inflatable airbag, and your drawing doesn't help much. Where are the exhaust gases being emitted?

Its just a inflatable shell. The nozzles are not covered. Sorry about not making that clearer. :oops:

Colt
2005-Feb-25, 03:41 AM
Ok. This is how it works from what I understand:

1. The landing vehicle is 100 meters above the surface and the gas charge is fired which inflates the shell/cushion/landing balloon.

2. Once the lander is in the right spot a few feet above the suface the engine is either cut out allowing it to drop onto the shell or the engines are fired at very low power to trap some of the gases under the shell allowing for a gentler landing.

3. Lander is down and the cosmonauts step out onto the shell and down a stairway on its side.

-------

1. The lander fires its main rocket and lifts a few meters off of the ground.

2. Explosive bolts are fired to release the shield and it's left to drop back to the surface. It is released in flight because if it was released on the ground and the rockets would fire, it would try to rise up unsecured. Not good.

- Colt