Wheel Trouble, ...down to 5 good wheels? Options

[Guest_Sunspot_*]

Was Spirit supposed to drive today?

http://qt.exploratorium.edu/mars/spirit/fo...67P1211R0M1.JPG

No movement.

[helvick]

How sure are we of the 280 Whr "death" number? It's hard to believe that Spirit couldn't hunker down with overnight deep sleeps and infrequent comm passes and at least survive with much less than that. Could it be that SS was really talking about a minimum power level for usability, rather than a survival limit?

Well you can read how SS phrased it in the April 17 2005 update on his blog. He isn't particularly explicit about what happens below that level just that "We think that the rovers can't survive at power levels much lower than 280 watt-hours". There have been other comments from the team to the rovers dying when power drops below 300whr but I can't find them at the moment.

There has already been some discussion on this in the Oppy Vs Spirit Power Consumption thread. Any additional insight would be welcome.

[djellison]

Was Spirit supposed to drive today?

Nope. Charging day

Doug

[akuo]

Was Spirit supposed to drive today?
http://qt.exploratorium.edu/mars/spirit/fo...67P1211R0M1.JPG
No movement.

That image is from yestersol, but there shouldn't be movement tosol anyway. The Spirit update says that tosol (783) is a battery recharging sol.

BTW, I like how they have started to add the plans for the next few sols in the rover updates.

[Bob Shaw]

How sure are we of the 280 Whr "death" number? It's hard to believe that Spirit couldn't hunker down with overnight deep sleeps and infrequent comm passes and at least survive with much less than that. Could it be that SS was really talking about a minimum power level for usability, rather than a survival limit?

Edit: Plenty of discussion on this subject in this topic. My impression is that we know a lot more about power availability than about power requirements.

I think there *are* certain genuine limits, such as with regard to the batteries and the way they get charged/discharged. Certainly, if they get frozen then they'll be damaged, and may take no more charge. That might leave us with a MER which the DSN can ping, but does little else, ie EOM.

Bob Shaw

[Guest_Oersted_*]

I think we're all happy that the team was pretty conservative in their time estimates to reach a good slope on the hill. It is exactly that kind of planning that will make this situation most probably survivable. - Apart from that, this is reminding me more and more of Apollo 13's homecoming, when they were also scrounging for every little amp they could find anywhere, to power up the command module with the minimum power...

[nprev]

On the weakly positive side, I hope that the wheel motor circuit is dead open (if it has to be open at all, I mean...rats! ) This will at least remove a little bit of load from Spirit's energy budget, though I know that the other wheels will more than overwhelm this due to extra torque requirements. A short to any part of the vehicle chassis from a hanging wire or a blown winding could prove fatal at this point...

[marsman]

In today's press release below, there are a few additional tidbits of information about SPIRIT's wheel problem and current driving expectations.


Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown/Erica Hupp (202) 358-1726/1237

NASA Headquarters, Washington


News Release: 2006-039 March 17, 2006

Mars Rovers Get New Manager During Challenging Period

NASA's long-lived Mars rovers demand lots of care as they age and the Martian winter approaches.

Dr. John Callas, newly named project manager for NASA's Mars Exploration Rover mission, is coordinating the work to meet these challenges. He is a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. He was named project manager after earlier roles as science manager and deputy project manager for the Spirit and Opportunity rovers.

"It continues to be an exciting adventure with each day like a whole new mission," Callas said. "Even though the rovers are well past their original design life, they still have plenty of capability to conduct outstanding science on Mars. The JPL operations team and the remote science team working on the project are the best in the solar system at what they do. It is a pleasure and a privilege to lead such an outstanding team and great mission."

One of Spirit's six wheels has stopped working. Dragging that wheel, the solar-powered rover must reach a slope where it can catch enough sunshine to continue operating during the Martian winter. The period of minimum sunshine is more than 100 days away, but Spirit gets only enough power for about one hour per day of driving on flat ground. And the supply is dropping fast.

Spirit's right-front wheel became a concern once before, when it began drawing unusually high current five months after the January 2004 landing on Mars. Driving Spirit backwards redistributed lubricant and returned the wheel to normal operation. This week, during the 779th Martian day of what was originally planned as a 90-Martian-day mission, the motor that rotates that wheel stopped working.

"It is not drawing any current at all," said JPL's Jacob Matijevic, rover engineering team chief. One possibility engineers are considering is that the motor's brushes, contacts that deliver power to the rotating part of the motor, have lost contact. The motors that rotate Spirit's wheels have revolved more than 13 million times, far more than called for in the rovers’ design.

Spirit's solar panels have been generating about 350 watt-hours of electricity daily for the past week. That is down about 15 percent since February and less than one-half of their output during the Martian summer.

The best spot for Spirit is the north-facing side of "McCool Hill," where it could spend the southern-hemisphere winter tilted toward the sun. Spirit finished studying a bright feature called "Home Plate" last week and is driving from there toward the hill. It has approximately 120 meters (about 390 feet) to go. Driving backwards with the right-front wheel dragging, the rover needs to stop and check frequently that the problem wheel has not snagged on anything and caused other wheels to slip excessively. Expected progress is around 12 meters (40 feet) per day under current conditions.

Opportunity is closer to the equator, so does not need to winter on a slope like Spirit. Opportunity spent most of the past four months at "Erebus Crater." It examined layered outcrops, while the rover team determined and tested a strategy for dealing with degraded performance by a motor in the shoulder of its robotic arm. Opportunity left Erebus this week and is on a 2 kilometer (1.2 mile) journey to a giant crater called "Victoria."

Callas has worked on the Mars rovers' mission since 2000 and five other Mars missions since joining JPL in 1987. He succeeds Jim Erickson, who switched to a leadership role with NASA's Mars Reconnaissance Orbiter. Callas grew up near Boston and graduated from Tufts University, Medford, Mass. He earned his doctorate in physics from Brown University, Providence, R.I.

JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rover and Mars Reconnaissance Orbiter projects for NASA's Science Mission Directorate.

[odave]

News Release: 2006-039
<snip>
The period of minimum sunshine is more than 100 days away
<snip>
It has approximately 120 meters (about 390 feet) to go. [...] Expected progress is around 12 meters (40 feet) per day under current conditions.

Those numbers make me feel better, though I know anything can happen at any time. I assume the 120 meter figure is to the nearest possible "good" slope. Here's hoping Spirit can make it to a windy spot too!

[SteveM]

NASA's long-lived Mars rovers demand lots of care as they age and the Martian winter approaches.

Dr. John Callas, newly named project manager for NASA's Mars Exploration Rover mission, is coordinating the work to meet these challenges. He is a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. He was named project manager after earlier roles as science manager and deputy project manager for the Spirit and Opportunity rovers.

Let me make a few off-topic comments.
This change must not have been unexpected. A biographical sketch of Callas appears in a recent report he co-authored: Distributed Operations for the Mars Exploration Rover Mission with the Science Activity Planner.

Dr. John L. Callas received his Bachelor's degree in Engineering from Tufts University in 1981 and his Masters and Ph.D. in Physics from Brown University in 1983 and 1987, respectively. After completing his doctorate in elementary particle physics in 1987, he joined the Jet Propulsion Laboratory in Pasadena, California to work on advanced spacecraft propulsion, which included such futuristic concepts as electric, nuclear and antimatter propulsion. In 1989 he began work supporting the exploration of Mars with the Mars Observer mission and has since worked on seven Mars missions. In 2000, Dr. Callas was asked to join the Mars Exploration Rover (MER) Project as the Science Manager. Dr. Callas continues as the Science Manager for the highly successful Spirit and Opportunity rovers. Recently, Dr. Callas has begun serving as a Mission Manager on MER, as an additional duty, as the rovers continue their great success on the surface of Mars. In addition to his Mars work, Dr. Callas is involved in the development of instrumentation for astrophysics and planetary science, and teaches mathematics at Pasadena City College as an adjunct faculty member. In his spare time, he mentors students interested in science and works with schools classrooms on science projects.

His 11 publications listed in the Astrophysical Data System (1983-2006) focus on remote sensing involving spacecraft using the radio and gamma regions of the spectrum.

[Jeff7]

Wow, looking at today's hazcam footage at the Exploratorium. (I might be a bit behind on this though, so forgive me if this is old news.)
Looks like it's doing pretty well, considering a totally frozen wheel.
It also looks like there might be more salt deposits there by the wheel.

[Guest_Sunspot_*]

http://qt.exploratorium.edu/mars/spirit/re...75P1311R0M1.JPG

Sort of moved... I wonder what they were trying to do.

[mars_armer]

Looks like too much slip (yawing to the left).

RF wheel, from forward hazcam:


LF wheel, from rear hazcam:

[mars_armer]

Left rear wheel:



Left front wheel:



Looks like a good thing that it stopped. This is a dicey situation given the RF wheel problem.

I wonder if there's any advantage to be gained by steering the RF?

[Shaka]

Left rear wheel:



Left front wheel:



Looks like a good thing that it stopped. This is a dicey situation given the RF wheel problem.

I wonder if there's any advantage to be gained by steering the RF?

I guess I'm not as adept at understanding the 'language' of the wheels as you are. Can you explain how to interpret the haz photos? I would say that the left-rear wheel (facing front) has run into the 'popcorn mesa' and been unable to climb it (or else we just stopped at this point by programming). As a result the other wheels churned a bit and the forward wheels (facing aft) slid a little to the left before we stopped. Can we carry on and run over the popcorn, or do we need to skirt it to the left? Or is that what we are about to find out?