[X] My Assistant

[SFJCody]

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?

[djellison]

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

[ElkGroveDan]

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

[dvandorn]

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

[climber]

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
Edited : better sized picture

Attached image(s)

 

[kwan3217]

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.

[tim53]

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.

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.

[djellison]

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

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

Doug