IPB

Welcome Guest ( Log In | Register )

2 Pages V   1 2 >  
Reply to this topicStart new topic
no MARDI images from Phoenix
mcaplinger
post Nov 14 2007, 03:26 AM
Post #1


Senior Member
****

Group: Members
Posts: 1230
Joined: 13-September 05
Member No.: 497



http://www.msss.com/msl/mardi/news/12Nov07/index.html


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
nprev
post Nov 15 2007, 01:20 AM
Post #2


Senior Member
****

Group: Moderator
Posts: 6830
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Sad news, but a good decision. I hope that integration testing in ALL areas is still aggressive & ongoing while there are still six months or so to do something about any other unexpected problems.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
mcaplinger
post Nov 15 2007, 02:23 AM
Post #3


Senior Member
****

Group: Members
Posts: 1230
Joined: 13-September 05
Member No.: 497



QUOTE (nprev @ Nov 14 2007, 05:20 PM) *
Sad news, but a good decision.

Out of curiosity, is there any increase of failure probability that you would have judged acceptable? E.g., what about a 1 in a million chance, or 1 in a billion?

People who say that the risk of doing something is 0 are probably just not thinking hard enough.


--------------------
Disclaimer: This post is based on public information only. Any opinions are my own.
Go to the top of the page
 
+Quote Post
nprev
post Nov 15 2007, 02:35 AM
Post #4


Senior Member
****

Group: Moderator
Posts: 6830
Joined: 8-December 05
From: Los Angeles
Member No.: 602



Wasn't so much the probability of occurrence as the nature of the conflict. Potential interference with IMU inputs during EDL (where, obviously, they're needed the most) is scary indeed, and I'm sure that the Phoenix team is not at all anxious to repeat the MPL disaster (which, admittedly, arose from completely different root causes; the point is the same).

Losing the imagery is far better than accepting even a very small risk of losing the vehicle, so gotta vote WAY on the side of caution here; think they did the right thing. We're all well aware of how problematic landing on Mars has been historically; don't think that we need to take unnecessary chances. To quantify a little bit anyhow, here's where I'd put this on a probability vs. consequences plot, and it ain't makin' it.

EDIT: Just to clarify, I am in no way trying to denigrate MARDI or its science return. Context data is invaluable, and it's really a damn shame that we won't get it from an instrument of this quality. However, given the fact that the spacecraft is in flight and no work-around appears evident, mission assurance needs have to take precedence.
Attached thumbnail(s)
Attached Image
 


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
ugordan
post Nov 15 2007, 08:37 AM
Post #5


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (nprev @ Nov 15 2007, 03:35 AM) *
Losing the imagery is far better than accepting even a very small risk of losing the vehicle

Except that in this business there's always at least a "very small risk of losing the vehicle". Most of the time it's much greater than 1 in a 1000, realistically speaking. Personally, I think this decision was influenced by too great of a paranoia. There's trying to lower the realistic risk beyond that what's feasible and then there's trying to lower the mathematically calculated risk. This decision seems to me to be more of the second one in nature, not that much is gained while quite a bit of nice science is lost.


--------------------
Go to the top of the page
 
+Quote Post
mchan
post Nov 15 2007, 11:57 AM
Post #6


Member
***

Group: Members
Posts: 593
Joined: 26-August 05
Member No.: 476



From the release:

"changing the timing within the EDL sequence would have necessitated additional testing, and arguments were raised that the human and time resources for this testing were in short supply."

Could human and time resources have been allocated to do adequate testing? What would it have taken (money, borrowing people from other projects)? Sounds like a management call.
Go to the top of the page
 
+Quote Post
tedstryk
post Nov 15 2007, 12:04 PM
Post #7


Interplanetary Dumpster Diver
****

Group: Moderator
Posts: 4159
Joined: 17-February 04
From: Powell, TN
Member No.: 33



QUOTE (mchan @ Nov 15 2007, 11:57 AM) *
From the release:

"changing the timing within the EDL sequence would have necessitated additional testing, and arguments were raised that the human and time resources for this testing were in short supply."

Could human and time resources have been allocated to do adequate testing? What would it have taken (money, borrowing people from other projects)? Sounds like a management call.


I believe the problem was discovered with only a few days until launch.


--------------------
Go to the top of the page
 
+Quote Post
mchan
post Nov 15 2007, 12:41 PM
Post #8


Member
***

Group: Members
Posts: 593
Joined: 26-August 05
Member No.: 476



The original problem of potential interference between reading MARDI and IMU data was found before launch. Then there was the fallback to taking one image which would have fit in the MARDI internal buffer. But the there was the 2nd problem of how to take one image with minimal risk. The evaluation of the 2nd problem led to dropping even the one image from the landing plan.
Go to the top of the page
 
+Quote Post
djellison
post Nov 15 2007, 01:24 PM
Post #9


Administrator
****

Group: Chairman
Posts: 13603
Joined: 8-February 04
Member No.: 1



The cut from many images to one image was nasty - and I admit I really feel sorry for the MSSS guys who've lost two MARDI's now. The cut from one image to none in some respects makes a bit of sense, if the funds can be freed up to fly MARDI as a result. One PHX-MARDI image, or an HD MSL-MARDI movie....that's not a hard call to make imho. Of course, ideally, the answer would be 'both'.

Doug
Go to the top of the page
 
+Quote Post
tedstryk
post Nov 15 2007, 02:31 PM
Post #10


Interplanetary Dumpster Diver
****

Group: Moderator
Posts: 4159
Joined: 17-February 04
From: Powell, TN
Member No.: 33



This reminds me (on a much smaller scale, since with HIRISE, the science to be gained from MARDI isn't in the same ballpark as this example) of the decision to not use the remote sensing instruments during Galileo's approach to Jupiter after the tape recorder anomaly. Wes Huntress angered a lot of people with his decision. Granted, given the performance of the tape recorder for the rest of the mission, the data probably could have been taken. However, had the tape recorder had another glitch and the probe data been lost (or worse, had it snapped outright and essentially ruined the LGA-based mission plan), there would have been hell to pay, and on the heels of Mars Observer, which had failed only two years earlier, may have been catastrophic for the entire planetary program. Chances are, taking the MARDI images would be fine. But given the coverage the mission would get if they ignored a known glitch and crashed (even if it was later proven not to be the cause). I think the only way a successful Phoenix (or the MER, for that matter, since they are still kicking...um, I mean rolling) would get that kind of coverage is if they photographed a martian dog walking up and urinating on the lander's leg (or rover's wheel - just walking by probably wouldn't get as much coverage as a failure).


--------------------
Go to the top of the page
 
+Quote Post
stevesliva
post Nov 15 2007, 03:44 PM
Post #11


Senior Member
****

Group: Members
Posts: 1156
Joined: 14-October 05
From: Seattle
Member No.: 530



QUOTE (mchan @ Nov 15 2007, 06:57 AM) *
Could human and time resources have been allocated to do adequate testing? What would it have taken (money, borrowing people from other projects)? Sounds like a management call.


And sometimes managers think that 9 women can have a baby in a month...
Go to the top of the page
 
+Quote Post
Greg Hullender
post Nov 15 2007, 06:46 PM
Post #12


Senior Member
****

Group: Members
Posts: 1009
Joined: 29-November 05
From: Seattle, WA, USA
Member No.: 590



Also, try to remember that even estimating risk is difficult. Especially for one-of-a-kind events.

--Greg
Go to the top of the page
 
+Quote Post
SpaceListener
post Nov 16 2007, 01:26 AM
Post #13


Member
***

Group: Members
Posts: 242
Joined: 19-August 07
Member No.: 3299



How will Phoenix land with a reasonable safety on Mars without the asist of MARDI? Perhaps, it will use the altimeter rader to measure the height from the surface?
Go to the top of the page
 
+Quote Post
mchan
post Nov 16 2007, 02:53 AM
Post #14


Member
***

Group: Members
Posts: 593
Joined: 26-August 05
Member No.: 476



MARDI was never required to support descent and landing operation. You may be thinking of DIMES in the MER EDL which was intended to remove excess horizontal velocity. Phoenix uses a Doppler radar for vertical and horizontal velocity measurements which feed into the descent control loop.
Go to the top of the page
 
+Quote Post
nprev
post Nov 19 2007, 06:04 PM
Post #15


Senior Member
****

Group: Moderator
Posts: 6830
Joined: 8-December 05
From: Los Angeles
Member No.: 602



QUOTE (ugordan @ Nov 15 2007, 12:37 AM) *
Except that in this business there's always at least a "very small risk of losing the vehicle".


Oh, yeah, man, no doubt; should've clarified that comment a bit. What I meant was that it seems unwise to accept a known risk in addition to the unknowns and the uncontrollables. If MARDI was essential for EDL, then by all means this would be an acceptable risk; since it's not, then mitigating it is appropriate.

Not that I'm not severely bummed... sad.gif ...was really looking forward to those images, and I feel bad for the MARDI investigators. Sometimes systems engineering is anything but kind...


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post

2 Pages V   1 2 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 23rd April 2014 - 02:43 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.