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Posted by: SFJCody May 22 2008, 08:15 PM

Something I have not posted online before...
Back in 2003, as four spacecraft approached Mars, I wrote down on a piece of paper my guess (based on nothing more than public information & gut feeling) at what each craft's chance of success (either at landing or orbital insertion) might be.
My guesses were:

Nozomi: 15%
Beagle 2: 20%
MER A: 60%
MER B: 60%
Mars Express: 85%

In 2005 I guessed that MRO had a 90% chance of success

Now, in 2008, I'm going to put a figure on Phoenix. That figure is:

55%


What do you think? Too low? Too high?

Posted by: john_s May 22 2008, 08:23 PM

Too low according to my gut, which reports in at about 82%...

Posted by: SFJCody May 22 2008, 08:26 PM

Good to know that planetary pros are more optimistic!

Posted by: djellison May 22 2008, 08:54 PM

I've been trying to figure this out for myself. I decided that Phoenix has a better chance than Lewis Hamilton has of not winning the Monaco Grand Prix.

67% is the figure I've come up with. 2/3rds - which, by chance, is the ratio of powered decent landings on Mars.

Doug

Posted by: ElkGroveDan May 22 2008, 09:03 PM

I'll say 83% which is the ratio of successful U.S. Mars landing attempts (5 of 6).

Posted by: tedstryk May 22 2008, 09:04 PM

With all the MPL discussion and the fact that we haven't found it, I am left wondering about something. MARDI on Phoenix was turned off because of fear that it would interfere with the EDL sequence and cause the mission to crash. I wonder if that is what did MPL in? If the generally accepted failure mode is wrong, this would be a favorite of mine (in terms of preference, not necessarily likelihood), because Phoenix has already worked around it.

Posted by: ugordan May 22 2008, 09:08 PM

My greatest paranoia, when it comes to Mars landers, is landing on rocks, tipping over craters or other rough terrain features. It's the one thing you can't (just yet) control and it in the end depends upon luck. I can't really quantify my gut feeling of Phoenix' chance of successful landing, but I'm sure glad they picked a really flat target area.

Ted, my wondering about MPL led me to think it could have in fact been the terrain that got to MPL in the end. As opposed to Phoenix site, some of that terrain is dreadful (although low illumination angle brings this effect up).

Posted by: ustrax May 22 2008, 09:22 PM

My gut feeling...having into account the previous uncharted abysses to be (not encouragin isn't it?)...:

^100%!

Let us have faith...in what faith can help us...

I am really trustful about Phoenix...trustful about a mission marking a new ground...

Posted by: centsworth_II May 22 2008, 09:23 PM

I'd say 90%... I think they're getting better.

Posted by: kwan3217 May 22 2008, 09:30 PM

Around 90%. I have seen many movies and animations of this thing working, and none of it not, so I'm conditioned to think it will work.

Posted by: SFJCody May 22 2008, 09:42 PM

Unless you count the two DS2 probes as landers, which would make it 5/8

Posted by: mcaplinger May 22 2008, 09:43 PM

The probability that the software bug with the leg deployment on MPL caused its failure is something greater than 50%. The probability that the MARDI/PACI issue caused it is a very small number (1:100000 would be my off-the-cuff guess). So I'm going with the software bug (which has also already been addressed for PHX.)

Posted by: SpaceListener May 22 2008, 10:53 PM

I have high trust about the Phoenix's EDL plan which is much better prepared than any previous Mars landing spacecraft.

However, there is one thing that cannot control the safe landing is the condition of the terrain which Phoenix will land on Green Valley in spite of the fact that the terrain is believed to be very smooth in "General Terms". After combining the three factors, I am puting that the success factor in landing safely on Mars is about 80%.

Posted by: nprev May 23 2008, 02:20 AM

Gotta go with 90% or greater. They've learned a LOAD of lessons, have the best weather recon in place ever, and hardware keeps getting more & more reliable. It's all evolutionary.

Posted by: centsworth_II May 23 2008, 02:23 AM

Right. I don't see why you would use the overall average for success, which includes the steepest part of the learning curve.

Posted by: climber May 23 2008, 04:04 AM

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

Posted by: nprev May 23 2008, 04:35 AM

Thanks for the nod, Climber, but it was actually Centsworth II that cited the learning curve phenomenon...I am in complete agreement with him.

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

Posted by: dvandorn May 23 2008, 04:41 AM

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

Posted by: mike May 23 2008, 04:45 AM

I say the odds of a successful landing are 100%.

Posted by: climber May 23 2008, 04:53 AM

According to this (Doug post) I would have said short for the MERs
Edited : better sized picture

Posted by: kwan3217 May 23 2008, 06:28 AM

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.

Posted by: Decepticon May 23 2008, 07:31 AM

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%

Posted by: Zvezdichko May 23 2008, 07:38 AM

With regards to your opinion, the powered descent phase is just 40 seconds, not 5 minutes.

Posted by: Tesheiner May 23 2008, 08:02 AM

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%.

Posted by: edstrick May 23 2008, 08:10 AM

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.

Posted by: akuo May 23 2008, 08:49 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.

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

Posted by: ugordan May 23 2008, 09:24 AM

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.

Posted by: edstrick May 23 2008, 09:34 AM

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"

Posted by: climber May 23 2008, 10:35 AM

So it's 5% only for you?

Posted by: MahFL May 23 2008, 12:49 PM

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 ?

Posted by: djellison May 23 2008, 01:26 PM

5mph they keep saying - 2.5ish m/sec

2.5 m/sec to a standstill in, say, .25 seconds - 1G.

Atmospheric entry and the chute-deployment snap will be much higher than that, 6, 7, 8, 9 G sort of figures.

Doug

Posted by: Stu May 23 2008, 01:32 PM

To be honest I can't even bring myself to think of a figure; a little part of me thinks that doing so would jinx the mission, so sorry, no percentage from me. I do, though, think that it's quite unlikely Phoenix will land on perfectly flat ground, having seen the latest HiRISE images. There are so many mounds, trenches and ridges that I'm pretty confident that our first images of the landscape will show the horizon at an angle.

I just finished work for the long Bank Holiday weekend, and I'm not in again until Tuesday afternoon. Strange to think that the next time I walk through the door at work we'll either have a new probe on Mars, sending back new pictures and data, or we'll all be spectators to another Beagle- or MPL-like interplanetary post-mortem...

My "gut feeling" isn't a percentage, it's a word: sick...

Posted by: djellison May 23 2008, 02:11 PM

I am genuinely beginning to get a physical reaction to the tension of the whole thing. Phoenix is making me physically nervous already. Quite what I'll be like on Sunday I don't know.

Doug

Posted by: nprev May 23 2008, 02:23 PM

Be chilly, you guys, keep an even keel...really, it's gonna be alright. Don't know why I know it, but I know it.

Posted by: jamescanvin May 23 2008, 02:29 PM

Me too, I've already got that nervous-butterfly's-in-stomach feeling., I'm going to be wreck come Sunday night!

Made the decision today to take Tuesday and Wednesday off work next week, in addition to the Bank Holiday Monday, to recover and work full time on Phoenix data*.

* That in the spirit of this thread I'm 90% sure we'll have by then.

James

Posted by: Zvezdichko May 23 2008, 02:41 PM

Same here. I woke up early with a stomach pain

We all know everything will be all right, but I don't know why I'm worried

Posted by: tim53 May 23 2008, 02:42 PM

I just realized that MPF also "went long", as the trajectory was from NE to SW.

This may be nothing more than a coincidence, though. Different years, different atmospheric models.

Beagle II may likely have gone downrange from the center of the landing ellipse, since it "landed" near in time to the MER landings. This should aid our search, somewhat.

-Tim.

Posted by: nprev May 23 2008, 02:56 PM

What's weird is that I sweated blood before both of the MERs, and I'm actually...serene?!...for Phoenix. Now I'm worried about the fact that I ain't worried!

EDIT: Ahh, got it. After watching V1 & V2 as a kid (to say nothing of the Apollos), I trust powered landings, and am confident that Phoenix has learned all relevant lessons from MPL.

Posted by: djellison May 23 2008, 03:22 PM

I thought that was the case (with the landing at night) but I wasn't sure enough to say anything

Doug

Posted by: tanjent May 23 2008, 03:31 PM

This is what markets are good for. We can all exchange our best guesses, and we all feel a great emotional stake in the outcome. But a pecuniary stake tends to weed out the casual guessers and weight those remaining according to their confidence in a) the quality of their information and their having the experience and judgment to apply it effectively.

An outfit called Intrade has a similar market for the probability of the Google Lunar X prize being won by 2012.

http://www.intrade.com

It's probably not the only one. I think Lloyd's used to quote odds on a whole range of possible binary events.

It's too late to do anything about Phoenix over the weekend, but maybe we should encourage the Intrade people to float a similar issue based on the successful landing of MSL. If it seems crass to think about monetary payoffs when the really important value is something like "raising the consciousness of humankind" then pledge your future proceeds to the Planetary Society!

I think I'll be on the sidelines though, because my expertise is pretty much on the level of keeping my fingers crossed. Accordingly, if pressed, my best guess would have to be 50-50 with no apologies to either side. Anyway, it's just our left brains that feel compelled to quote odds about the probabilities. There is complete unanimity with respect to our hopes. 100% probability on that.

tanjent

Posted by: Decepticon May 23 2008, 03:47 PM

Whoa! I put 5 Mins!

I should of put 5 seconds.




Im so worried.

Posted by: centsworth_II May 23 2008, 03:56 PM

Ok, but 5%? Even the most pessimistic outlook should have it at no lower than 50%. All this worry about the powered landing has me wondering how TWO Vikings ever made it to the ground in one piece, not to mention countless (by me anyway) Lunar landers -- including manned! I think powered landings are a pretty well explored territory. Heck, that last 30 seconds could well be the most sure part of the EDL sequence! I've got myself convinced anyway.

Posted by: Zvezdichko May 23 2008, 03:59 PM

You are right, of course, but this technology hasn't been used for decades! A lot of people working on the projects have already retired. That's a lot of experience to lose!

Also, the pulsed thrusters. I have some worries on how they keep the spacecraft stable.

Posted by: centsworth_II May 23 2008, 04:03 PM

I guess they proved themselves in all the testing... or they wouldn't be flying.

Posted by: ugordan May 23 2008, 04:19 PM

For some reason this reminds me of the story of Saturn V J-2 engines that were undoubtedly tested and tested again on the ground and proved themselves robust. Then came Apollo 6 and a mysterious failure of 2 of those engines. Turns out they weren't actually tested in an environment they were meant to operate in - effectively pure vacuum and there was a design failure that only showed up in actual vacuum operation. I'm not implying something similar will happen on Phoenix, not by a long shot. It's merely an anecdote how unknown variables can always be in the hiding somewhere.

There's no such thing as the ultimate test, for that you'd have to be there, fly the exact same profile as in the real thing many times and see whether any problems crop up. Everything else is just an approximation and modeling. The devil's always in the details. That said, I'm sure the Phoenix testing was quite adequate, the thing I worry the most is the actual touchdown.

Posted by: nprev May 23 2008, 04:25 PM

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.

Posted by: climber May 23 2008, 04:30 PM

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.

Posted by: MahFL May 23 2008, 05:03 PM

So if one of the legs hits a 0.5 meter high rock dead center, what are the chances of survival of Phoenix ?

Posted by: centsworth_II May 23 2008, 05:25 PM

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

Posted by: Zvezdichko May 23 2008, 05:44 PM

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.

Posted by: ustrax May 23 2008, 06:14 PM

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...

Posted by: imipak May 23 2008, 07:31 PM

There's also http://www.longbets.org/, 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 http://catless.ncl.ac.uk/Risks for anyone interested in real-world systems failures of all sorts - some tragic, some expensive, some amusing.

Posted by: mcaplinger May 23 2008, 08:36 PM

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/news/phoenix-20080508.html

Posted by: Alex Chapman May 23 2008, 09:17 PM

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

Posted by: centsworth_II May 23 2008, 10:01 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.

Posted by: SFJCody May 23 2008, 10:18 PM

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

Posted by: climber May 24 2008, 03:10 AM

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

Posted by: Nice Guy May 24 2008, 05:12 AM

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.

Posted by: climber May 24 2008, 05:25 AM

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 !

Posted by: centsworth_II May 24 2008, 05:40 AM

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

Posted by: edstrick May 24 2008, 09:59 AM

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.

Posted by: dmuller May 24 2008, 10:46 AM

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

Posted by: ugordan May 24 2008, 10:56 AM

I think edstrick might have had http://www.jpl.nasa.gov/news/phoenix/phx20080327.php 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.

Posted by: Sunspot May 24 2008, 11:01 AM

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

Posted by: Zvezdichko May 24 2008, 11:06 AM

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.

Posted by: Doc May 24 2008, 11:06 AM

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......

Posted by: dmuller May 24 2008, 11:09 AM

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

Posted by: Doc May 24 2008, 11:15 AM

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?

Posted by: Zvezdichko May 24 2008, 11:21 AM

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

Posted by: Doc May 24 2008, 11:28 AM

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?

Posted by: dmuller May 24 2008, 11:32 AM

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

Posted by: SFJCody May 24 2008, 11:32 AM

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!

Posted by: Zvezdichko May 24 2008, 11:47 AM

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)...

Posted by: Doc May 24 2008, 11:50 AM

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

Posted by: PhilCo126 May 24 2008, 12:10 PM

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

Posted by: climber May 24 2008, 12:51 PM

Both would be happy to get the Pole position

Posted by: climber May 24 2008, 12:58 PM

What about wearing a Polar Cap?

Posted by: nprev May 24 2008, 12:59 PM

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

Posted by: tedstryk May 24 2008, 01:07 PM

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.

Posted by: climber May 24 2008, 02:31 PM

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)

Posted by: Alex Chapman May 24 2008, 03:45 PM

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.

Posted by: Juramike May 24 2008, 04:32 PM

He gets both Gold and Silver medals.

Posted by: imipak May 24 2008, 05:42 PM

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)

Posted by: Nice Guy May 25 2008, 03:18 AM

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.

Posted by: edstrick May 25 2008, 10:45 AM

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).

Posted by: Stu May 25 2008, 10:48 AM

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...

Posted by: Shaka May 25 2008, 06:59 PM

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

Posted by: marsbug May 25 2008, 07:28 PM

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!

Posted by: ElkGroveDan May 25 2008, 10:17 PM

Let's take it over to the http://www.unmannedspaceflight.com/index.php?showtopic=5157

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