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Gut feeling...
nprev
post May 23 2008, 04:25 PM
Post #46


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One thing to remember is that flight control algorithms and, of course, processing ability have come a LONG way since Viking...and even since MPL. The F-117, F-22 and for that matter the C-17 really have no inherent aerodynamic stability; without advanced motion sensors, processing and feedback (to say nothing of at least triple if not quadruple or even quintuple channel redundancy) none of those things would even get off the ground.

The EDL video may be causing a little angst because Phoenix looks so wobbly after releasing the chute. No worries; she'll be busily solving partial differential equations of motion for attitude control at breakneck speed and applying the corrections via the thruster pulses accordingly.


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climber
post May 23 2008, 04:30 PM
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This topic is definitely the "hotest" topic of Phoenix's right now !
You know what? I'm going to bed in order to get used of Phoenix time (it's 6.30 pm here)
See you in another 7-8 hours. smile.gif


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MahFL
post May 23 2008, 05:03 PM
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So if one of the legs hits a 0.5 meter high rock dead center, what are the chances of survival of Phoenix ?
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centsworth_II
post May 23 2008, 05:25 PM
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QUOTE (MahFL @ May 23 2008, 01:03 PM) *
So if one of the legs hits a 0.5 meter high rock dead center, what are the chances of survival of Phoenix ?

Better to hit it with a leg than the belly.

"The Phoenix lander has legs that provide 0.33-0.45 m of clearance over a 1.75 square
meter area and solar arrays that sweep out a 6 square meter area with 0.5 m clearance."
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1094.pdf
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post May 23 2008, 05:44 PM
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QUOTE (nprev @ May 23 2008, 04:25 PM) *
The EDL video may be causing a little angst because Phoenix looks so wobbly after releasing the chute.


That's why I got concerned! The EDL shows the spacecraft almost tumbling. Now I think it's actually because the clip is trying to show us in 2 minutes what is being done in 7.
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ustrax
post May 23 2008, 06:14 PM
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QUOTE (MahFL @ May 23 2008, 06:03 PM) *
So if one of the legs hits a 0.5 meter high rock dead center, what are the chances of survival of Phoenix ?


That's one of Barry Goldstein worries also...when he was at spacEurope for the Live Q&A he said gave his answer to a similar question:

Marco - I have nightmares with a specific scenario…seing Phoenix landing in a mound’s slope, having some its legs with no support and…tumbling down…
What can you tell us to ease this nerve wrecking situation?...

BG - We have a very good understanding of our landing site, and there is only one area where there is a significant hill. Very unlikely that we will tip over, although not impossible! It is more likely that a rock could cause this. A combination of a 0.5 meter rock hitting a leg with a large horizontal velocity in the wrong direction!"

So, that is, indeed, a risk...


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imipak
post May 23 2008, 07:31 PM
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QUOTE (tanjent @ May 23 2008, 04:31 PM) *
An outfit called Intrade has a similar market for the probability of the Google Lunar X prize being won by 2012.


There's also LongBets, which I happen to have bookmarked for reasons we don't talk about here wink.gif

Regarding the supposedly improved odds over MPL due to the failure modes having been studied and removed - alas it isn't quite that simple. Suppose you change an element which has a 5% chance of a mission-killing failure, in order to fix that. Now, your changes themselves must be analysed for the the new failure modes they introduce - and of course these components don't have to work in isolation, they must work in the particular environment - which we can only approximate and simulate before launch - and whilst many other components are busy doing their thing. The worst case is that the fixes end up making failure more, not less, likely.

(Edit: ...and whilst current and next-gen fly-by-wire military hardware are incredible things,
(i) a lot more is spent on them than on Mars probes!
(ii) they can be tested in the real flight environment, and
(iii) http://www.youtube.com/watch?v=faB5bIdksi8 smile.gif

I'd recommend RISKS Digest for anyone interested in real-world systems failures of all sorts - some tragic, some expensive, some amusing.


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mcaplinger
post May 23 2008, 08:36 PM
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QUOTE (imipak @ May 23 2008, 11:31 AM) *
The worst case is that the fixes end up making failure more, not less, likely.

True, but in the case of MPL, the landing-leg deployment switch bug was high-probability and its fix is obviously correct.

AFAIK there were no changes to the control algorithms. There may have been some made to the radar processing. http://www.nasa.gov/mission_pages/phoenix/...x-20080508.html


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Alex Chapman
post May 23 2008, 09:17 PM
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My personal feeling is that the landing is going to go without a hitch. I think we will even get the postcard image in the first Odyssey overpass. The Phoenix folks have chosen an amazingly benign landing site and the ellipse has been plastered in HIRISE imagery so I don't think rocks are really an issue. They have also followed the mantra of "Test as you fly, fly as you test" more closely than anyone has before.

If there is a failure then there are just variables that the engineers couldn't foresee and at least this time we WILL know what happened. Gone are the silent landings of Beagle 2 and MPL and we are going to have telemetry recorded by three separate orbiters and that’s a world away from the MERS simple engineering tones.

It’s going to work, it’s going to find the ice the question is what about organics in the ice.

I am not superstitions and I don’t eat peanuts but I have to admit I am going to buy a pack and just have them on the desk. Oh and I might just have my fingers and toes crossed to smile.gif
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centsworth_II
post May 23 2008, 10:01 PM
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I love peanuts, I eat them every day. I'm eating peanuts right now.
I'll eat enough peanuts for everyone on landing day. Don't worry. smile.gif
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SFJCody
post May 23 2008, 10:18 PM
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QUOTE (centsworth_II @ May 23 2008, 11:01 PM) *
I love peanuts, I eat them every day. I'm eating peanuts right now.
I'll eat enough peanuts for everyone on landing day. Don't worry. smile.gif


I am also a fan of peanuts. Unsalted peanuts are fine- they're a good source of healthy fats.
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climber
post May 24 2008, 03:10 AM
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Back to the original question, if one would try to summarize what has been said so far, our chances of success are ...Peanuts biggrin.gif


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Nice Guy
post May 24 2008, 05:12 AM
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I worked on MPL, and MER (and Mars Observer as well for what it is
worth) and I can tell you when it works, it feels great. When it
doesn't work, it feels sort of like major organ removal with a rusty
spoon, and no anesthesia.

... about our chances on Sunday? I feel good. I am at peace. I know
the lengths this project has gone to in an effort to successfully land
and operate this vehicle. But at this point, whatever is gonna happen,
is gonna happen.

I do sort of get amused at the interest with which the folk in the
Mission Support Area watch the arriving telemetry. They will devour
every ounce of information as if catching some behavioral mis-step
early might lead to taking actions that could save the day. In
reality, by the time signal reaches Earth that the vehicle has entered
the atmosphere, the Lander is already on the surface... in one
condition or another. We might as well read about it in the newspaper.

Enjoy the ride on Sunday fella's. I will be in the Operations Center
in Tucson. You will recognize me in the corner of the televised images
as the guy not jumping up an down when we get signal from the
surface. Whatever is gonna happen, is gonna happen.
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climber
post May 24 2008, 05:25 AM
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Welcome to UMSF Nice Guy! You couldn't have choosen a better time!
Thanks to tell us the inside sorry but I envy you too much !




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centsworth_II
post May 24 2008, 05:40 AM
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QUOTE (Nice Guy @ May 24 2008, 01:12 AM) *
....You will recognize me in the corner of the televised images
as the guy not jumping up an down when we get signal from the
surface....

Of course we'll all be watching. But if you feel like jumping, go ahead. We won't hold you to this. biggrin.gif
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