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Could this be applied to landing in thin atmospheres?

Posted by: Ekkehard Augustin - Mon Jul 18, 2005 1:11 pm
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Could this be applied to landing in thin atmospheres? 
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Post Could this be applied to landing in thin atmospheres?   Posted on: Mon Jul 18, 2005 1:11 pm
Would the following work? Assumed several or each space vehicle is to land at the same place on a planet with a thin atmosphere like that of Mars the atmosphere under the vehicle can be blown up to the vehicle and focussed on it. the stream of "air" would go to a parachute and/or to the down-side of the vehicle which should be optimally shaped for this purpose.

May be complete nonsense - I simply had this idea because I thought of the CO2 freezing out on the martian surface. If it could be gathered in and made sublimating it would go up from the ground to some altitude - perhaps a directed stream could be created. This stream could substitute the blow of bracing rockets partially perhaps.

It would make sense at spaceports only.

What about it? Silly and stupid nonsense?



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Post    Posted on: Mon Jul 18, 2005 2:45 pm
Hmmmmmmmmmm. I guess it all depends on how long you can make the exhaust stream of high velocity air. That, and how well your reentry craft can hit it's target of high-pressure air. I'm wondering, if it were possible to create a very large artificial high-pressure front, (say with a battery of GINORMOUS fans, 100's of meters in diameter.) Of course, this would mean creating low pressure areas somewhere else on the planet.
I'm no engineer, so I have no idea if any of this is possible either, but that's some superb outside-the-box thinking, Ekke, and I thank you for getting my ball rolling! :D 8)


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Post    Posted on: Mon Jul 18, 2005 2:56 pm
Basically, you're talking about putting the retrorockets on the ground instead of the vehicle. The biggest problem is one that Marshall saw: focusing the stream. Which won't happen. In a very low pressure environment, you can't keep a high-pressure area together for long enough to actually get to the vehicle. At least, not without a really really big straw.

Not a completely bad idea, though -- I'll play with it for a while and see if anything might work.

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Post    Posted on: Mon Jul 18, 2005 4:12 pm
In between my own thoughts have gone further too and I already detected such problems.

In principle I didn't have in mind special altitudes.

a) What about creating an air cushion simply when the vehicle is a few meters above the ground? This could reduce the required thrust of the bracing rockets.

b) The landing site may be underground normally isolated from the atmosphere by a gate. When a vehicle is close enough high the landing site will be set to very high pressure compared to the pressure of the thin atmosphere. In between the vehicle is closer and the gate opens. Then the loacally very thick atmosphere is released to the atmosphere and reaches the vehicle immediately - the vehicle is braced that way. It dives into the underground landing site. When it is completely inside the gates closes and the pressure increases again - continuing to brace the vehicle. "underground" doesn't necessaryly mean to dig into the ground - craters can be used or a portion of one of a deep canyon. In principle it could be tested on Earth.

c) The air cushion thought reminds me to the Hovercrafts crossing the Channel. They have a special equipment to keep the air cushion below them. I don't know what it's made of but something like that vehicles could be equipped by too. It could be much larger providing much more volume. While approaching the ground the vehicle could let down that equipment - when it is assured that it will touch the ground. Then the CO2 can be pressed into it - creating a high pressure air cushion quickly.

...



Are there more alternatives?



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Post    Posted on: Tue Jul 19, 2005 4:49 pm
Hmm, aerobraking on a planet w/ a thin atmosphere, huh? What would really be useful is some sort of system for slowing down a craft orbiting the moon, b/c I think that as long as you have an atmosphere, parachutes and heatsheilds can take care of you pretty well. Interesting concept though. It reminds me of the idea of using huge ion beam generators to give a solar-sailcraft a boost or brake.


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Post    Posted on: Tue Jul 19, 2005 6:41 pm
Perhaps I should provide more context of thoughts the idea is embedded in: I remember that Burt Rutan and others consider a vertical landing to be very dangerous and of more risk that horizontal landing.

But horizontal landing like on Earth isn't possible in thin atmospheres - so it seems a little bit as if vertical landing can't be avoided.

Now in a thin atmosphere a vertical landing will be much more dangerous than in the earthian atmosphere which means that the risk is significantly higher. This has become evident by several failed landings of unmanned probes on Mars.

The current solution is the adding of parachutes and airbags to the use of retro-rockets. But should that applied to manned vehicles too really? Nothing against the parachutes if they would have an impact on those much heavier manned vehicles at all - but what may the impacts of being bumped around by the airbags on the crew be when they touch down on or better impact the martian surface? And would they work at all given the ´larger weight of the manned vehicle?

Now the idea I had will not and can't be applied at the first manned Mars mission. But if Mars should be colonized one day or simply tourists should travel there or even in the case of a manned permanent Mars station safety should be increased as much as possible. In the case of the permanent station the safety has to include the safety of the station.

Because of all this I simply tried to find a theoretical way to providely temporary thick air - and in between I am playing around with the idea to do so at Earth too if safetyy could be increased.

Regarding high safety of landings on the Moon as well as on the jovian moon Europa I reminded the landing on Eros where the probe was made spiralling down and had a soft landing. At a moon I wopuldn't use the theoretical idea described above because it would be a waste of atmosphere and ressources.



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Post "Aerobraking" on the Moon   Posted on: Wed Jul 20, 2005 12:16 am
Let me respond to these ideas by mentioning a Lunar landing idea. Start with a long series of gas jets or small explosives, buried under lunar regolith. Provide timed activation of these just as a spacecraft passes over on a very low orbital pass. The spacecraft could plow through the rising dust and achieve the equivalent of “aerobraking”. The upward momentum of the impacted dust (or even “lift” from vertical recoil) could counteract the modest lunar weight of the craft, and the deceleration would then not be time critical. (A much longer deceleration path then normally required could be provided in case the aerobraking was unusually weak.) This would work equally well with low velocity “cold” gas vents – rather like what you suggested for Mars. The dust density could be adjusted along the path for fairly uniform deceleration. The dust would produce far more erosion of a heat shield than would gas, but even carefully screened dust would be really cheap! The increase in Lunar transport economics would be huge, over three times the delivered cargo for the same mass accelerated out of Low Earth Orbit.

Your Mars idea would be workable – but don’t try to use it to eliminate aerobraking or parachutes: both are too effective and reliable to eliminate. The problem on Mars is that even an extra large parachute reaches the surface with too much velocity for safe “landing”. If you don’t want to use my “Prairie Lander” scheme to minimize the complexity of rocket braking for touchdown, then your idea could be made to work. It isn’t a question of increasing the air pressure or density, for those can’t really be confined for more than a millisecond. It is more appropriate to simply provide an upward gas jet at about 30 meters per second for the few seconds required. The parachute descending into this jet (even on Mars) would decelerate and actually stop until the gas flow rate was reduced. There are situations where a Ballute (Balloon-Parachute) will actually be trapped in such a gas jet. Otherwise, it could be steered to facilitate the capture and landing.


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Post    Posted on: Wed Jul 20, 2005 10:22 am
Hello, rpspeck,

I have in mind what you are describing - no elimination of aerobraking or parachutes but adding the upward gas jet.

Regarding the Moon I had another idea in between which might avoid the use of gas at the Moon - I suppose thatv the gas would be lost. But the idea may be unrealistic or utopic:

Is there are fluid the Moon could hold and simply needs to be protected against the solar wind and the sun? If yes then deep craters could be filled by that fluid and covered by a gate. The gate would be opened when a vehicle is going to land - it would splash into the fluid like the Apollos splashed into the ocean or t/Space's CXV will splash into the ocean.

That fluid would have to provide similar buoyancy as water and should be used then at Mars too. At Europa water could be used because it is already there and obviously seems to be held because of freezing it. It would have to be melted temporarily while covered by a gate.

But are their any in-situ ressources at Moon or Mars which could be used to produce such a fluid or would it have to carried there?

At Mars this could be added to the initial idea - the CO2 would be above the fluid and go up, help brake the vehicle and then the braked vehicle would splash into the fluid to be braked more until it is stopped.

Are there such fluids?



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Post    Posted on: Sun Oct 30, 2005 3:44 pm
What about removing the braking rockest from the vehicle and installing them so that they can direct the exhaust to the vehicle to be decelerated?

This would be like deceleration by Magbeam but not using the ionized particles of the solar wind - these would be replaced by the exhaust.

It could be done from ground as well as from orbit.

What about it? Does it require to high precision which can be achieved in the Magbeam-case only?

It could be apllied for landing on Earth too if it would work.



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Post    Posted on: Sun Oct 30, 2005 8:16 pm
I'm not entirely sure what you're talking about with that last idea. Could you please clarify?

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Post    Posted on: Mon Oct 31, 2005 7:51 am
I was thinking theoretically merely. Actually vehicles have to carry their breaking rockets with them - including the propellant. This means additional weight. The theoretical idea now was to remove the breaking rockets and to install them in an orbit or at a surface so that their exhaust is directed to the arriving vehicle and decelerating it this way.

I seem to have done a spelling error - has that caused your question?

Just this moment I suppose that the exhaust wouldn't provide that large a force as the thrust provided by retrorockets (do I use correct this term?).

The idea now looks silly to me - it was just a theoretical idea for replacement of a deceleration Magbeam by it.



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Post    Posted on: Tue Nov 01, 2005 12:16 am
Ekkehard Augustin wrote:
Just this moment I suppose that the exhaust wouldn't provide that large a force as the thrust provided by retrorockets (do I use correct this term?).


That's the problem: you're basically trying to use the rockets to create a "wind" that the incoming vehicle would catch and slow down on. The problem being that the exhaust will expand so quickly (because it's in a vacuum) that it will be practically nothing by the time it gets to the spacecraft. Besides that, every action has an equal and opposite reaction. All you'll do is move the station as much as you move the incoming vehicle.

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Post    Posted on: Tue Nov 01, 2005 6:13 pm
Hmm, perhaps an aeroshell that would create a trap for the (relatively small) atmospheric pressure, and a surface-mounted laser which could then heat the shock front so that it had an increased amount of pressure... of course, then you end up with thermal problems. That's engineering for you: everything is a trade-off.

Personally, i think chutes, ballutes, and airbags are your best bet for Mars and similar scenarios.


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Post    Posted on: Wed Nov 02, 2005 7:25 am
Hello, spacvecowboy

to readjust the focus of my question a little bit - what about using such an idea from surface only?

If the braking rockets are installed at the surface sending their exhaust straight up into the atmosphere towards the landing vehicle then the thrust couldn't move the rockets since the planet has that much more mass.

There could be a battery of such rockets then which could decelerate the vehicle. Of course that's lokking very very dangerous and the force of the exhaust may be still much too weak.

The idea is to use such a method on Earth also



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Post    Posted on: Wed Nov 02, 2005 5:12 pm
Ekkehard Augustin wrote:
There could be a battery of such rockets then which could decelerate the vehicle. Of course that's lokking very very dangerous and the force of the exhaust may be still much too weak.


You got it.

Personally, ballutes are *very* cool.

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