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landings right on targets

Posted by: Ekkehard Augustin - Thu Aug 23, 2007 12:53 pm
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landings right on targets 
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Post landings right on targets   Posted on: Thu Aug 23, 2007 12:53 pm
It seems that it wasn#t known where martian probes would land exactly and precisely in the past. It seems to me that this was so also at the lunar landings of the arly seventies for example.

While this may have to do with not having selected of a landing site as precise as a few meters it will be required once there is a base on the Moon or in the future on Mars.

The Space Shuttles have shown that precisely landing on Earth can be managed but they also used the air by their wings and the airplane-like equipments.

How difficult are such precise landings on the Moon or on Mars? And waht ways can they be done?



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Post    Posted on: Thu Aug 23, 2007 1:04 pm
Since Mars shot are parachute or airbag, they are inherently unpredicatable (wind shear). Apollo landings were hand landed I think, because they didnt have detailed images of the landing site, so needed to look to find flat enough areas (wasnt it the first manned landing that nearly ran out of fuel trying to find a landing stop?)

Powered landing are the only way to be very specific. The shuttle has a runway to land on that guaranteed usable, so thats easy, if it didnt it would need power to fly around until it found one!

As to determining accuracy, laser guidence in the same way at missles? Shine laser at landing point and home in on that? Radar to help with alititude?

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Post    Posted on: Thu Aug 23, 2007 2:23 pm
The Vikings entered Mars orbit before landing but all the recent landing missions have entered the atmosphere directly, without first entering Martian orbit. It would certainly seem to me to be a much more difficult navigation problem to land exactly at a previously chosen spot that way. And of course the airbag landing can result in the space craft bouncing and rolling for a kilometer or more from the point where it first touches the ground.

I know Apollo 11 landed rather far from its intended target and they went to great pains to improve the navigation for Apollo 12 because they wanted to land at the same location as the earlier unmanned Surveyor III space craft. They succeeded and landed only 163 meters from Surveyor III. Of course all the Apollo space craft entered lunar orbit and passed over the landing site several times before landing.

I would think that a base would have a radio beacon that the space craft could home in on to make a very exact landing, much closer than 163 meters.


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Post    Posted on: Sat Nov 10, 2007 4:44 am
How do you get the Beacon there accurately? With a Google Rover?

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Post    Posted on: Sat Mar 01, 2008 9:49 am
An article under www.welt.de is reporting something similar to an article under www.space.com today. The space.com-article seems to be about a concrete project that is work on while the german article is reporting about ideas or concepts for the near future.

The german article says that NASA has in mind to launch 4 to 6 penetrators to the lunar surface from the Altair-lander. These scouts would do several tasks but interesting here is that according to that article they are to serve as position lights for the landing - to assist it and enable precise control of the landing flight.

The article also says that NASA plans to install a Lunar Positioning System allowing navigation of a precision of one meter. Work on this will begin next year - may be this is what the space.com-article is referring to.



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Post    Posted on: Mon Apr 14, 2008 9:28 am
I believe that gravitational anomalies are a bit of a problem on unexplored planets, I tkink thats how they lost a few orbiters around the Luna and Mars in the past. Planets are not ideal spheres with evenly distributed mass that engeneers assume them to be, consequently more often than not they crash into said planets not to mention miss their landing sites, enter unstable orbits and generally misbehave themselves.

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Post    Posted on: Fri May 30, 2008 3:18 am
Horus wrote:
I believe that gravitational anomalies are a bit of a problem on unexplored planets, I tkink thats how they lost a few orbiters around the Luna and Mars in the past. Planets are not ideal spheres with evenly distributed mass that engeneers assume them to be, consequently more often than not they crash into said planets not to mention miss their landing sites, enter unstable orbits and generally misbehave themselves.


Mars and Luna both have 'blotchy' gravitational fields. In fact, a stable orbit for Luna was finally found only last summer (IIRC). There's no molten core and since things cooled they are now 'lumpy'. Not very scientific, I know, but hopefully descriptive ;)
They both have pretty extreme terrain too - very high hills and deep valleys...
I don't know that's how they 'lost' orbiters before, although it does tend to shorten life of the project since it takes a lot more propellent to stay in a low-Luna orbit (and you need to stay lower to get better science).


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Post    Posted on: Fri May 30, 2008 8:43 am
Mars Phoenix has just demonstrated, that even a direct atmospheric entering (without going into orbit first) with powered landing only in the very last moments of descent can pretty much land on target.
Of course this was a rather large target and that precision is not sufficient to "hit" a lunar/mars base, but with powered descent from orbit this shouldn't be any big problem today.

One has to always remember, that todays cars and cellphones have more processing power than the Apollo spaceships.


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Post    Posted on: Sun Dec 28, 2008 4:10 pm
Just this moment I thought of the task to identify a location to land at as a something required to land accurately on a selected site.

The identification is the easier the less the site is going to be changed because images of the site can be applied the better.

And after each take-off from the site more actual images can be provided that involve changes caused by the take-off and the past landing. angle of view as well as angle to the sun might be adjusted by software.



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