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Phobos-Grunt
Guest_BruceMoomaw_*
post Dec 19 2005, 02:30 AM
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Exactly the same problem applies for a human-sized lander (30-100 metric tons) ANYWHERE on Mars -- because a lander 64 times more massive than another of generally similar design will have only 16 times as much forward aeroshell area to brake it during entry.

This was the subject of Rob Manning's COMPLEX talk, which didn't make it into my final "Astronomy" article. No practical parachute design can be big enough to solve the problem; nor can high lift/drag aeroshells (like the "Ellipsled" proposed to aerocapture Neptune Orbiter, or even a winged vehicle) solve it.

The only possible solutions are (1) rocket engines capable of firing out the lander's bottom at supersonic speeds BEFORE it deploys its chute (as Ed suggests), or (2) a huge, 20-30 meter diameter decelerator capable of working at hypersonic speeds -- either rigid (in which case it must survive the heat of entry), or inflatable and deployed after the heating is over. Any of these three possible solutions, as you can imagine, will require a hell of a lot of new engineering work. Indeed, Manning says grimly: "These technologies are at very low TRL and have very uncertain outcomes on their success...We do not have high-likelihood Mars EDL systems to choose from." An advance test flight of any such general design will be necessary, with a lander weighing 10% as much as the actual manned lander. Yet another serious problem for those more eager than I am to see Footprints On Mars. Even the sample-return lander (about 1200 kg) will require a radically new parachute design.
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ljk4-1
post Dec 19 2005, 02:38 AM
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QUOTE (BruceMoomaw @ Dec 18 2005, 09:30 PM)
Exactly the same problem applies for a human-sized lander (30-100 metric tons) ANYWHERE on Mars -- because a lander 64 times more massive than another of generally similar design will have only 16 times as much forward aeroshell area to brake it during entry. 

This was the subject of Rob Manning's COMPLEX talk, which didn't make it into my final "Astronomy" article.  No practical parachute design can be big enough to solve the problem; nor can high lift/drag aeroshells (like the "Ellipsled" proposed to aerocapture Neptune Orbiter, or even a winged vehicle) solve it.

The only possible solutions are (1) rocket engines capable of firing out the lander's bottom at supersonic speeds BEFORE it deploys its chute (as Ed suggests), or (2) a huge, 20-30 meter diameter decelerator capable of working at hypersonic speeds -- either rigid (in which case it must survive the heat of entry), or inflatable and deployed after the heating is over.  Any of these three possible solutions, as you can imagine, will require a hell of a lot of new engineering work.  Indeed, Manning says grimly: "These technologies are at very low TRL and have very uncertain outcomes on their success...We do not have high-likelihood Mars EDL systems to choose from."  An advance test flight of any such general design will be necessary, with a lander weighing 10% as much as the actual manned lander.  Yet another serious problem for those more eager than I am to see Footprints On Mars.  Even the sample-return lander (about 1200 kg) will require a radically new parachute design.
*


Another problem to consider when landing on Mars with retrorockets: The fine powdery surface grains would spread far and wide and sandblast anything nearby. Better have landing pads far from the base, unless they come in on an airplane.

http://www.news.cornell.edu/Chronicle/05/1...e_research.html

How much surface dirt did the Vikings kick out when they landed? Considering how much they wanted to find microbes at the landing site, and they could not move around, I am surprised in some ways that they did not think of another landing method to disturb the ground as little as possible.


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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JonClarke
post Dec 19 2005, 03:03 AM
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QUOTE (ljk4-1 @ Dec 19 2005, 02:38 AM)
How much surface dirt did the Vikings kick out when they landed?  Considering how much they wanted to find microbes at the landing site, and they could not move around, I am surprised in some ways that they did not think of another landing method to disturb the ground as little as possible.
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Not Much wink.gif Viking had three landing engines with 18 nozzles fueled by specially purified hydrazine monopropellant. The hydrazine would not contaminate the ground and the 18 nozzles were specifically designed to minimise erosion on the ground. Some effects were noted though not particularly severe.

Jon
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JonClarke
post Dec 19 2005, 03:07 AM
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QUOTE (BruceMoomaw @ Dec 19 2005, 02:30 AM)
This was the subject of Rob Manning's COMPLEX talk, which didn't make it into my final "Astronomy" article.  No practical parachute design can be big enough to solve the problem; nor can high lift/drag aeroshells (like the "Ellipsled" proposed to aerocapture Neptune Orbiter, or even a winged vehicle) solve it.
*


Do you haver a link to his COMPLEX work - abstracts, reports, etc?

Jon
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Guest_BruceMoomaw_*
post Dec 19 2005, 03:33 AM
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Unfortunately, no -- at least for this document. I can keep looking for other documents with different names on ths subject, though -- or, failing that, at least type in the print in his PowerPoint presentation as an attachment here later on.

As for the Vikings: they shut off their engines at 3 meters altitude (versus 4 for the lunar Surveyors) -- and, as you say, they deliberately used a design of clustered small nozzles to minimize ground disturbance.
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edstrick
post Dec 19 2005, 07:12 AM
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Note regarding the Viking clustered engines: During testing of candidate engines -- maybe they already knew - that above a very few millibar pressures, a conventional bell-shaped engine nozzle's plume collapsed from a nearly hemisphereical plume to a focussed jet, as the plume detached from the nozzle. Simulated Viking landings in vaccuum chambers dug serious pits in the dirt and scattered it all over everywhere and everything. The Surveyor and Apollo LM engines would have done the same if Moon had a Mars like atmosphere.

Of course, the idiots we know who claim we never went to the moon don't know this. It's one of their stupid fallacies, that the rocket engines should have dug deep craters under the LM.
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JonClarke
post Dec 19 2005, 09:09 AM
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I was under the impression that Viking shut down just above the surface. "On Mars" however says that it occurred when the pads touched the ground.

Jon
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Guest_BruceMoomaw_*
post Dec 19 2005, 10:16 AM
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I may have to scrounge for confirmation, but I'm absolutely sure from what I read at the time that the engines shut off at 10 feet up. They were, after all, extremely concerned on that mission about the possibility of contaminating their surface samples with terrestrial organics.
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RNeuhaus
post Dec 19 2005, 03:52 PM
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I don't think that the next manned mission to Mars would be a spaceship bigger than the Moon Landing because of the already discussed reasons (low Martian density, not-uninform density atmosphere, high delta velocity (5-6 k/s).

The most practical design would be multiples spaceship, one for manned, the other for cargo (oxigen, food and water) and the other for return. This is only valid for the present time technology and let us see how the technology will improve within 20 years. smile.gif

About landing Phobos, it has other kind of challenges. Since it is orbiting from west to east 3 times a day (every 8:08 hour approx.) at 9,350 km from Mars and its is synchronous orbit radius to Mars. The spaceship would have to make many aerobraking orbits around Mars and have a much bigger fuel tanks in order to reduce its velocity before landing on the regolith covered by half meter of dust surface. Perhaps, it might have some ice as a water supplies to spaceship. Luckly it has no axis-rotation so the logistics for landing would not so complicated as to land to Eros or Itokawa.

Rodolfo
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Guest_AlexBlackwell_*
post Feb 22 2006, 04:21 PM
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Note that Zakharov et al. have an abstract to be presented at the upcoming EGU General Assembly 2006.
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Bricktop
post Mar 10 2006, 09:03 PM
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Video of Phobos-Grunt

mms://restart.roscosmos.ru/Media/FOBOS2.wmv
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GravityWaves
post Mar 25 2006, 05:32 PM
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Soyuz is soon launching from Europe's Kourou
mellow.gif
Their arianespace PDF files are online,
but it seems to a big download hundreds and hundreds of pages
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Guest_AlexBlackwell_*
post Mar 26 2006, 05:43 PM
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Does anyone have any objections to merging this thread with the "Phobos-Grunt a reality?" thread?
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Guest_AlexBlackwell_*
post Mar 26 2006, 08:16 PM
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I hope no one objects. I went ahead and merged the two topics.
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Decepticon
post Mar 30 2006, 01:26 PM
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I can't believe how many burns this probe needs to make!

I don't know about this one folks.

I have to admit Russian probes look cool. cool.gif
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