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...

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

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

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

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

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

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.

I am also a fan of peanuts. Unsalted peanuts are fine- they're a good source of healthy fats.

Back to the original question, if one would try to summarize what has been said so far, our chances of success are ...Peanuts

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.

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 !

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

The EDL landing simulation video is 1.) time compressed, and 2.) overly dramatic. The on-engine wobbles and damn-near cavorting of the simulated lander, particularly just before touchdown, remind me of a T-Rex's hystrionical overacting in your typical cheap Dinosaur Dramatization.

Granted, a T-Rex could do a little scenery chewing.... but.

I agree ... be mindful of that EDL movie. It has lander separation at something like L - 25 secs, but according to the published nominal timeline, lander separation is at L - 45 secs or so, giving it twice as much time to stabilize and then topple over at the last instance anyway. The timeline shown is also shorter than the nominal timeline, but still within its +/-46 seconds of possible deviations.

Chance of success - well it's gonna be interesting. Given that so many things have to go right at the right time (cruise stage sep, attitude, parachute deploy, legs deploy, radar, lander sep, retro-rockets pulse firings, stabilization & attitude, retro-rockets cut-off, venting, solar panel deploy) ... well why shouldnt it work.

Daniel

I think edstrick might have had this movie in mind, not the EDL HUD simulation. In the former movie, the lander drops from the backshell a long way down, then ignites the engines (which don't pulse, btw) and wobbles crazily right up until one second before landing. Unecessary Hollywood-like dramatization if you ask me.

Nozomi - 5%
MER A - 65%
MER B - 65%
MRO - 85%
Beagle 2 - 0%
Phoenix - 70%

I just didn't get excited at all about Beagle 2, when I checked the news to see if they had received the expected signal - and they hadn't- I didnt feel anything - no disappointement at all - weird.

Good Luck to everyone on the Phoenix team

Beagle 2 - I gave about 30%
MER A or MER B - 85%, I was quite sure they will succeed
As for Phoenix I give 70%, because the powered descent adds some risk.
And finally for MSL - 40%, the skycrane might or might not work.

A quote from the recent post on the Planetary Society site;

"The northern autumnal equinox will arrive on Mars on December 26, 2008, bringing winter darkness to the north pole. Phoenix will not survive past this date. In fact, it may not survive beyond November"

Can we hope otherwise......

Ah yes that one is hardcore Hollywood! Just watch the stars zip by in the cruise phase at Worp 5 I guess they gotta sell it to the masses ... most people probably dont get too hooked up on a 20 second lander separation discrepancy like us

I share your anxiety Zvezdichko. I tend to find powered descent very unreliable. Atleast the engineers have learned from MPL by programming the spacecraft to deploy its legs while attached to the back shell. So i'ld give Phoenix a resonable 75-80% chance of succeding.

This brings up a curious (or rather silly) question from me; why did many landers in the past fail. Is it because of the MPL error or what?

Mars 2 failed because it entered the atmosphere in a very steep trajectory
Mars 3 failed on the surface
Mars 6 and 7 had microchip flaws.
Deep Space 2 - they were supposed to crash land

BTW-will the mission website provide realtime data of the signal strengh from Phoenix like they did with MRO when it arrived at Mars in 2005?

Whilst I share the 'fear' that the landing may go wrong, I dont see how recent history should contribute to the fear. Unless I miss something major, only one landing of US spacecraft post the Vikings went wrong: MPL. The record is quite good once you get to Entry Interface. Mars Observer and Mars Climate Orbiter didnt attempt to land, though the cause for the demise of Mars Observer (fuel pressurization) is yet to come for Phoenix. I dont know how comparable the technology / systems / economics were for Beagle 2.

Daniel

Seems strange that powered descent + landing legs has us so worried. Before Pathfinder airbags were seen as some weird Russian way of doing things that might not work!

I think it's because the powered descent hasn't been used successfully for decades (I'm not counting asteroid missions). Soviets used the powered descent on several lunar missions - the Lunokhods and Lunar Sample Returns. The airbag system has failed (Beagle 2, missions prior to Luna 9), and the Powered descent has failed in the past (MPL, Luna 15)...

From what I know, Beagle 2 had a lot of problems economically speaking as well as problems in management.
But how they managed to cram so many instruments int a 78kg cylinder is beyond me
That achievement merits a hats off. We can thank ESA for that

Well, it's not just EDL but EDFL ( Entry + Descent + Freefall + Landing )...
Agreed on the "lessons learned" bit mentioned in other posts but it has been since Mars Polar Lander that they tried to land this way

Both would be happy to get the Pole position

What about wearing a Polar Cap?

Okay, Climber gets the "Phoenix Pre-Landing Worst Pun Award"...

Actually, transistor flaws. Because of its effect on Mars 6, it hadn't been able to receive ground commands for six months when it entered the atmosphere, so it is amazing it came as close to succeeding as it did. It left Mars-7 unable to correct its trajectory, so it missed. Incidentally, Mars-7 did some interesting particle and fields stuff while in the asteroid belt, as well as studies of Jupiter's decametric radiation. Since Mars-6 couldn't be commanded, its bus was useless after the flyby.

I was so frustated not to win SpacEurope's
(actualy I didn't send any entry since I'm far from mastering Photoshop or whatever)

It may have packed a lot of instruments in its 78kg but it might as well have been carrying 78kg of bricks. If they had sacrificed a few of the instruments for more EDL margin and EDL communication we would have got something out of it and what a boost it would have been to UK space science.

He gets both Gold and Silver medals.

ker-BOOM! Splosh!!! Whoo-hoo, I got another one. More ammo, please, I'm going for the carp next. 8)

Happily, Phoenix is probably going to be the single most monitored arrival at Mars ever. I doubt the fate of Beagle had a huge impact on this planning, but it's had some value... it's all good, isn't it?

> Phoenix is: 29 hours, 52:44 from EDL interface (spacecraft event time)

I would like to point out that we try to learn from our failures.
When we lost a mission due to parts failures we improved our parts
screening procedures. Navigation failures have lead to more precise
nav techniques. Even the silly mistake that caused the MCO failure
("What d'ya mean there were no units in the file?!?") has lead to
increased rigor in interface definitions.

That being said, I have every confidence that if we do have a problem
on Sunday evening, it will be something new and completely unexpected.
The devils you know can be held at bay. It is the devil you don't know
is the one that will bite you.

The greatest threat to safe landing IMHO is uneven terrain. We are
designed to accommodate a 16-degree slope. But we are still coming in
without any obstacle avoidance. That risk is mitigated by careful site
selection. The boulder distribution analysis puts the probability of
an un-safe lander tilt on landing somewhere around 1%.

Here is an interesting factoid. MCO lead to basically one lesson
learned; Keep your units straight (sounds like we re-learned a
high-school physics lesson, but let's not go there...). But MPL, by
virtue of not revealing true root cause, has yielded more than a
dozen lessons. And chief among them is; Leave the radio on all the way
down (plasma black-out not withstanding). I find it strange that lack
of root cause would make MPL a far better teaching tool.

There is one point of concern regarding hearing the signal during EDL.

There's only one transmitter and frequency.

MER rovers transmitted S-band "tones" during descent, flagging milestones achieved during EDL.

The actual datastream was received by Odyssey (I presume not Mars Surveryor Orbiter) and recorded, the only near-real time info there was the total amount of megabytes recorded (way more than in a case of loss of signal at landing)

Phoenix only has the UHF signal. Everybody, including Green Bank on Earth, are listening to that. If (arbitrary example) some wire in the transmitter breaks at parachute deploy, they won't have any idea what happened till a perfectly OK lander turns on the alternate UHF (I do presume thay have one.. have not read the press kit yet).

Funnily enough I was just catching up with yesterday's media briefing, and this very subject came up. It is conceivable that we might not know if Phoenix has landed safely or not for up to 5 DAYS if there's a comms problem during EDL. Jeez, we'll all be climbing the walls by then... it'll be The Wait For Beagle all over again...

I've got a gut feeling I ate too many peanuts.
I'm switching to smokehouse almonds.

I'm still on my first bag, good luck and godspeed phoenix, congratulations to all who have worked so hard to bring her this far!

Let's take it over to the EDL discussion

http://www.unmannedspaceflight.com/index.php?showtopic=5157