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Gut feeling...
climber
post May 23 2008, 04:04 AM
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QUOTE (ElkGroveDan @ May 22 2008, 11:03 PM) *
I'll say 83% which is the ratio of successful U.S. Mars landing attempts (5 of 6).

So, It'll be 86% when Phoenix will be on the ground?
Not enough, not enough. As said by Nprev this doesn't include the learning curve.
Rui, I'm not going to say it during Euro 2008, but I'm with you on this smile.gif


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nprev
post May 23 2008, 04:35 AM
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Thanks for the nod, Climber, but it was actually Centsworth II that cited the learning curve phenomenon...I am in complete agreement with him. smile.gif

It's gonna work, even if I have to eat every damn peanut in central Los Angeles!!!


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dvandorn
post May 23 2008, 04:41 AM
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QUOTE (ElkGroveDan @ May 22 2008, 04:03 PM) *
I'll say 83% which is the ratio of successful U.S. Mars landing attempts (5 of 6).

True -- but of the five successful, 60% (three) were airbag landings, and only 40% (two) were of the rocket descent variety. And the one failure out of six was not only a rocket descent, it was the progenitor spacecraft to Phoenix.

Obviously, Phoenix has been tested and its EDL given more scrutiny than any other Mars lander to date, precisely because of that one failure. And Phoenix has been changed in many fundamental ways since its original construction as MPL's sister ship. So you can't read too much into the fact that Phoenix started out as MPL's near-twin. There are still many similarities, but this design has evolved a lot, at least partially due to the 12 MPL failure scenarios the review panel came up with (one of which had 12 different sub-scenarios). A fair amount of work went into redesigning the spacecraft and its operations to avoid each of the MPL failure scenarios, so you gotta think that increases Phoenix's odds.

But looking at the larger picture, if you look at all American unmanned rocket descent landings on all bodies, you get a success ratio of eight out of 11 (five of seven Surveyors, two of three Mars landers, and -- possibly stretching the point a bit -- NEAR), or roughly 73%. Add in manned rocket descent landings (six of six Apollo Lunar Modules), and you get 14 out of 17, or just over 82%.

So... all that said, my gut feeling is hovering somewhere between 65 and 75 percent. The one thing that concerns me is that the best terrain for Phoenix's mission seems to lie in the uprange and midrange portions of the ellipse -- the downrange portions seem rockier, with more vertical relief... i.e., generally less safe. I would guess this is because the downrange end gets into the pretty rubbly-looking ejecta blanket from that nearby big crater.

And if you look at the results of the three direct-approach American landers that succeeded (MPF and the MERs), each one of them landed at least somewhat long.

This time, anyway, if anything goes wrong, we'll have a lot better chance of knowing what happened than we did back in '99. For some reason, that unclenches my gut a little bit.

-the other Doug


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mike
post May 23 2008, 04:45 AM
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I say the odds of a successful landing are 100%.
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climber
post May 23 2008, 04:53 AM
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QUOTE (dvandorn @ May 23 2008, 06:41 AM) *
And if you look at the results of the three direct-approach American landers that succeeded (MPF and the MERs), each one of them landed at least somewhat long.
-the other Doug

According to this (Doug post) I would have said short for the MERs
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kwan3217
post May 23 2008, 06:28 AM
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Quotes removed. Better use the "add reply" button at the bottom of the page when replying to the previous post. Tesheiner

Both MERs are travelling from west to east, so both of them are long, A is only a little bit long, B is a lot long.

But surely by the mere fact of flying the MERs, we understand the aerodynamics of the shell better, and since Phoenix's shell is almost identical, if there is some systematic factor which made the MERs go long, it must be understood and modelled out of Phoenix's ellipse.
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Decepticon
post May 23 2008, 07:31 AM
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Nozomi: 10%
Beagle 2: 50%
MER A: 90%
MER B: 90%
Mars Express: 5%
MRO 95%

Phoenix 95% Up until the rockets fire. Just watching the animation makes the hair on my arms stand. The last 5 mins 5%


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Guest_Zvezdichko_*
post May 23 2008, 07:38 AM
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With regards to your opinion, the powered descent phase is just 40 seconds, not 5 minutes.
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Tesheiner
post May 23 2008, 08:02 AM
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Well, after a very detailed and accurate analysis --I left outside, checked the weather and direction of the wind. Had a drink at the coffee machine and it was quite ok. My email this early morning had no input from by boss-- I found the probability is 75%. tongue.gif
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edstrick
post May 23 2008, 08:10 AM
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I'll go with a guess at something like 85%.

5% un-caught hardware or software design failure,
somewhat less than 5% Mars doing something nasty, or shere bad luck (parachute lands on top of them, etc),
somewhat more than 5% part failure or manufacturing error.

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akuo
post May 23 2008, 08:49 AM
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QUOTE (Decepticon @ May 23 2008, 08:31 AM) *
Phoenix 95% Up until the rockets fire. Just watching the animation makes the hair on my arms stand. The last 5 mins 5%


What's the worrying part about retrorockets? MER used them too, and they *had* to stop the craft 10 metres in the air, and take into account the wind also.

Dropping from 10 metres with a bunch of airbags into unknown territory is still riskier in my opinion :-)



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ugordan
post May 23 2008, 09:24 AM
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QUOTE (akuo @ May 23 2008, 10:49 AM) *
What's the worrying part about retrorockets? MER used them too, and they *had* to stop the craft 10 metres in the air, and take into account the wind also.

Yes, but MER retros were in a different configuration. They were firing away from the spacecraft center of mass, essentially were pulling the craft upward, a more stable configuration than thrusting through the center of mass and pushing it up. In the latter case any asymmetry in rocket thrust creates torque on the spacecraft, trying to rotate it so and requires good active guidance. Those two systems are very different beasts so there's no use directly comparing them and their safety.


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edstrick
post May 23 2008, 09:34 AM
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Mars 6 (1973) used a similar system to Pathfinder and the MER rovers. Radar never told the retros to fire or the retros didn't fire or ...
Signals were lost at the estimated time of touchdown. Recent reports refer to some inferred excessive impact speed. (rather like Polar Lander)

"crunch"

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climber
post May 23 2008, 10:35 AM
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QUOTE (Decepticon @ May 23 2008, 09:31 AM) *
Phoenix 95% Up until the rockets fire. Just watching the animation makes the hair on my arms stand. The last 5 mins 5%

So it's 5% only for you?


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MahFL
post May 23 2008, 12:49 PM
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Frankly I am amazed ANY of them ever work, because it all seems very very complicated to me. I watched the EDL landing and when Pheonix hits the ground, er I mean land, it sure comes to an abrupt stop. Can someone tell me the G forces at landing, and what the lander is designed to withstand ?
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