[X] My Assistant

[Phil Stooke]

Time for a new thread... we should be starting up right about now after conjunction, and if no other targets have popped up our plucky rover should be heading south within days. This should be quite a scenic trip, so sit back and enjoy the fun.

Phil

[Phil Stooke]

This looks like a good place to add a note of caution about Lunokhod driving distances. They will have to be recalculated based on the LROC images. When the actual Lunokhod 2 tracks are compared with the original Soviet-era map, it looks to me like they landed slightly north of the expected location, drove a bit further south than they thought, then east, and finally ended up further north than they thought. Some extra distance will probably come out of a recalibration of the drives (maybe they allowed for more wheel slip than actually occurred). A new mapping effort is under way at MIIGAiK - they already did Lunokhod 1 and are working on Lunokhod 2. Maybe by LPSC next year we will have a result. Just a caution - we might break the record and then have to break it again!

Phil

[climber]

Did you also notice that we (I on the Spirit & Oppy Statistics) used to get 35890 for Apollo 17 rover and this is also used on the New Mexico Museum's but Nasa says 35744...and tthey can't be wrong
Phil, do you think all Moon driving distances will have to be reevaluated?
Thanks

[serpens]

Did you also notice that we (I on the Spirit & Oppy Statistics) used to get 35890 for Apollo 17 rover and this is also used on the New Mexico Museum's but Nasa says 35744...and tthey can't be wrong.
Phil, do you think all Moon driving distances will have to be reevaluated?

Did they zero the odometer before deployment or did it still have acceptance test distance logged, compensated for in the distance / direction from start point software? ie. The distance on moon will be less than the total recorded? Comparing the Apollo rovers to the MER is really a chalk and cheese approach and the outcomes depend on how you squint when assessing. For example: if you look at distance and time deployed the Apollo 15 rover is the champ. 0.152 kilometers per minute. Apollo 17 comes in second at 0.135. Opportunity can go down in history as the slowest ever rover in terms of distance /time.

[djellison]

Opportunity can go down in history as the slowest ever rover in terms of distance /time.

You could make up a million different statistics all pretty much as meaningless as the next. Distance travelled vs average distance from earth. Distance travelled per KG of vehicle mass. Number of individual drives. Number of locations visited. Total longevity etc etc etc

[serpens]

You could make up a million different statistics all pretty much as meaningless as the next. ...

Exactly my point. Comparing the distance achieved by a lunar 'car' and a martian robotic rover is meaningless. The really big deal is comparing the longevity and distance achieved by Opportunity compared to design requirements and mission success parameters. I have used Opportunity as an example of outstanding reliability engineering and remote diagnosis and rectification. I stand in awe of those who designed and built her.

[MahFL]

..compared to design requirements....

JPL engineers admitted the MER's were overengineered and that the 90 day mission time was very likely to be exceeded, barring some unforseen problem. So comparing to the 90 day required time is not really a valid reference point. The main reason Sprit died was it got trapped in sand and could not tilt it's solar panels to the Sun. That of course could have happend on the first drive if fate had meant that to happen.

[djellison]

JPL engineers admitted the MSL's were overengineered and that the 90 day mission time was very likely to be exceeded, barring some unforseen problem

I assume you mean MER.

I can assure you - all mechanisms etc are tested to 3x the required lifetime. That's not 'over engineered' - that's called engineering margin to guarantee a good shot at reaching your requirements. It's JPL policy. It puts the bellcurve of expected failure centered beyond 90 days.

Squyres has been on record - years after landing - saying he thought maybe 120, if everything went perfectly maybe 180 sols. I'd be interested in exactly where you see JPL engineers describing MER as 'overengineered'. That's not a phrase I've ever heard them use. Required engineering margin....yes. Not 'overengineered'

Plus - the dust was STILL expected to kill the rovers very shortly after 90 sols. This paper by the late great Jake Matijevic details the expected liftspan of the rovers...

http://trs-new.jpl.nasa.gov/dspace/bitstre...9/1/02-0732.pdf

Slide 3 explicitly states that the expected useful lifespan of the rovers was 100 sols for MER-B at the 'Hematite' site ( aka Meridiani ) and 92 sols for MER-A at Gusev.

So - maybe you might find an engineer on Sol 500 saying "We obviously tested for more than 90 sols". But BEFORE launch - I challenge you to find any engineer on record stating they expected the rovers to last significantly longer than 90 days. I don't think you'll find it.

[MahFL]

I think I may have equated 'margin' with 'over engineering'.
I still think though the team was staying with the 90/180 day thing, as the costs for a 10 year mission would not have been at the time favorably looked at by the beancounters...... . There was even conjecture at one time one rover would be turned off to save said beans .

[djellison]

I still think though the team was staying with the 90/180 day thing, as the costs for a 10 year mission would not have been at the time favorably looked at by the beancounters......

And the paper I linked to proves otherwise.