Parachute for non-atmospheric bodies

[HoloYolo]

Alright, before you call me an idiot, let me explain. So it's in the future. Someone is trying to land on the Moon. They have retro-thrusters, and as they get close to the surface, they deploy these...parachutes. The dust kicked up from the surface get caught in the parachutes and help in the landing. The guy lands, and tucks them back in the lander. So, what do you think? I think it would be a great idea if possible.

[Nibb31]

But it isn't possible so it's a stupid idea.

[Slam_Jones]

There's a small problem with this idea...

The laws of physics.

[HoloYolo]

But it isn't possible so it's a stupid idea.

Sir, please be more polite. You were extremely rude.

- - - Updated - - -

There's a small problem with this idea...

The laws of physics.

Is it gravity? I didn't think about that.

[sal_vager]

Yeah guys, don't be harsh about this, how about you explain nicely why this wouldn't work?

[Darnok]

I can be done... instead of parachute use solar sail-like materials http://en.wikipedia.org/wiki/Solar_sail

Of course before your parachute (solar sail) lading you would have to send drone + power plant + energy canon, so this canon would shoot massive charge and slow down your lander.

It would be very expensive, but possible

[Slam_Jones]

-snip-

Is it gravity? I didn't think about that.

Well, let's think about this. On earth (or other atmospheric bodies), the 'chute is dragging against the air. Since Earth (in this example) has a thick enough atmosphere, that means the chute is encountering a lot of resistance on the way down. Because of the nature of air, it's constantly affecting the chute. No matter how much air is affected by the chute, there will always be more to replace it. In this case, the chute is being dragged through the air.

Now, on a non-atmospheric body (the Moon) there's essentially nothing for the chute to drag against. Even if there were dust being kicked up from the boosters, it would never have enough energy or consistency to properly push on the chute. In this case, the chute is not being dragged, but instead pushed against (likely in inconsistent bursts).

Another way to think of it: drag your hand through water, noting the resistance. It's consistent and (relatively) strong. If you put a finite amount of energy into your hand, it will be stopped rather quickly. Now if you drag your hand through the air, you'll notice there's a huge difference. The air is less consistent and easier to push through, and less energy is required to continue the work.

Parachuting on Earth is like dragging your hand through the water. Parachuting on the Moon would be like holding your hand steady and blowing on it. Inconsistent, and too weak to really make a difference.

The amount of dust you'd have to put in the air would be so much that you might as well just stick to boosters. Plus, it'd be insanely hard to make sure that ALL (or the VAST majority) the dust kicked up goes to the chute, and not just off to the side.

At least, that's what I'm thinking. I'm no scientist, though, so I could be wrong.

Edited March 18, 2015 by Slam_Jones

[Dkmdlb]

I can be done... instead of parachute use solar sail-like materials http://en.wikipedia.org/wiki/Solar_sail

Of course before your parachute (solar sail) lading you would have to send drone + power plant + energy canon, so this canon would shoot massive charge and slow down your lander.

It would be very expensive, but possible

If you have to land the power plant + cannon to the surface using traditional methods, why not just send the lander instead?

[magnemoe]

Well, let's think about this. On earth (or other atmospheric bodies), the 'chute is dragging against the air. Since Earth (in this example) has a thick enough atmosphere, that means the chute is encountering a lot of resistance on the way down. Because of the nature of air, it's constantly affecting the chute. No matter how much air is affected by the chute, there will always be more to replace it. In this case, the chute is being dragged through the air.

Now, on a non-atmospheric body (the Moon) there's essentially nothing for the chute to drag against. Even if there were dust being kicked up from the boosters, it would never have enough energy or consistency to properly push on the chute. In this case, the chute is not being dragged, but instead pushed against (likely in inconsistent bursts).

Another way to think of it: drag your hand through water, noting the resistance. It's consistent and (relatively strong). Now if you drag your hand through the air, you'll notice there's a huge difference. The air is less consistent and easier to push through.

Parachuting on Earth is like dragging your hand through the water. Parachuting on the Moon would be like holding your hand steady and blowing on it. Inconsistent, and too weak to really make a difference.

At least, that's what I'm thinking. I'm no scientist, though, so I could be wrong.

Yes the closest I can come is an lander with skirt, this will capture the trust close to ground, downside is the up wash of the hot exhaust who would get into places it should not go, in short you have to secure area under the skirt for corrosive gases and heat making it far less practical than better landing legs.

[Darnok]

If you have to land the power plant + cannon to the surface using traditional methods, why not just send the lander instead?

Maybe power from that power plant could be cheaper than rocket fuel on lander + cost of sending that rocket fuel to Moon?

With multiple landings, costs of power plant would be acceptable, for single landing it is of course stupid approach

[Deutherius]

What Slam_jones said. Also, even though you would push the moon dust around with your downward thrust, with conventional nozzle placement most of that dust would get pushed sideways, not up (think about blowing hard on fine sand). I don't see a way that could be useful to the landing craft itself. Anyway, the parachutes would be extra mass, which is not desirable (especially when it's useless mass).

Edited March 18, 2015 by Deutherius
typo

[Meecrob]

Well technically you could fire rockets into parachutes I think?

[smjjames]

Well technically you could fire rockets into parachutes I think?

You'd just rip apart the chutes that way, regular ones anyhow. Besides, they wouldn't even unfurl in the first place because no atmosphere.

Edited March 19, 2015 by smjjames

[Meecrob]

I was thinking it out in my head to a cartoon-y thought. In reality, I'm sure we could easily spend too much money on a rocket-assisted parachute system. I'm seriously just suggesting this to fit in with the OP's question. No such thing as a stupid question. The stupidity starts when you don't think of alternatives.

[Bill Phil]

The Moon has an atmosphere. It's microscopic, but hey...

Using parachutes and rockets to land is a bit, questionable. No offense or anything. But you should use one or the other (for atmo worlds) unless you have a small enough chute.

It would be cool, though...

[Meecrob]

No offense taken, Bill. I was only trying to present a (silly) way to use parachutes without atmosphere.

[J.Random]

Well technically you could fire rockets into parachutes I think?

That would (not) work kinda like this:

[Deutherius]

Well technically you could fire rockets into parachutes I think?

Wouldn't do much, but it would probably be hilarious.

[Meecrob]

Haha, now I know to say I am being sarcastic.

PS the hilariousness would be worth it in itself. 100k subs on youtube for sure.

...Ok maybe 1k subs.

Edited March 19, 2015 by Meecrob

[Scotius]

That would have to be enormous cloud of dust. Even on Earth a lander\capsule needs kilometers of atmosphere to slow down sufficiently under parachutes. You will not produce a cloud of dust approaching our atmosphere's density on the Moon - at least until you decide to blow up a sizeable chunk of its mass.

[magnemoe]

http://media2.giphy.com/media/IgcPOrsk9AhGw/200_s.gif

Wouldn't do much, but it would probably be hilarious.

That idea work in a way, the air from the fan will be reflected backwards, mythbusters tested it, however is far less effective than dropping the sail and turning the fan around.

[lajoswinkler]

That idea work in a way, the air from the fan will be reflected backwards, mythbusters tested it, however is far less effective than dropping the sail and turning the fan around.

Indeed, the thing works because some of the momentum-carrying fluid is escaping the system (unlike the scenario where a sailor pushes the sail using his hands), but applied to landing on celestial bodies is absolutely a total failure. It can't work.

[EdFred]

When you can pick yourself up by the ankles, you'll be able to use parachutes on the moon.