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?

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

Good to know that planetary pros are more optimistic!

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

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

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.

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).

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...

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

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.

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

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.)

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%.

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.

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

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

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!!!

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

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

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

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.

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%

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

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%.

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.

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 :-)

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.

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"

So it's 5% only for you?

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 ?

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

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...

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

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.

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

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

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.

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.

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

Doug

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

Whoa! I put 5 Mins!

I should of put 5 seconds.




Im so worried.

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.

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.

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

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.

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.

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.

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

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.