Going To Mogollon..., ...and points South Options

[Bill Harris]

It was already said that those structures seen on previous hazcam pics (well, in all sort of cameras and filters...) were delicate.

[attachment=3535:attachment] (138k)
But what about these ones? It looks like the smallest touch could broke them.

[attachment=3536:attachment] (138k)
PS: It's time to open a new thread, don't you think so?

Good idea. That topic was "tired" and had the cord showing.

Delicate, to be sure. One thing I've noticed is that the "ledge-forming" rocks are a layer and extend to the right and left of where we camped out. I wonder if that feature is related to the bluff at Mogollon Rim?

We need to check out the "mobile dust" at that site and see if there has been more movement during the stopover.
--Bill

[Guest_Sunspot_*]

The tech probs are really stacking up...Im begining to think that Opportunity will spend her last days around Erebus.

[djellison]

The tech probs are really stacking up...Im begining to think that Opportunity will spend her last days around Erebus.

Mobility wise, Opportunity is in fairly good health. Once they get that arm stowed, we'll be under way I'm sure.

Doug

[Marcel]

Mobility wise, Opportunity is in fairly good health. Once they get that arm stowed, we'll be under way I'm sure.

Doug

I don't understand why they completely stow the arm as soon as a long drive needs to be done. Why is this so important ? Do they really think something will break while the arm is in "half stowed" position (over the solar panel) ? They drive 5 mm's a second. It's not " bumping", it is like a snail creeping across the terrain ! I've been asking this to myself for a long time. Maybe i oversee something, but the risk of another winding breaking in the faulty joint (thereby completely disabling the possibility to UNstow the IDD for the rest of the mission) looks much higher to me, than the chance of breaking something because of driving in the alternative (half stowed) position. There are two primairy windings in these motors aren't there ? There's only one left. And forcing a higher current trough it at this stage (while materials are getting old) doesn't make sense to me. I'm puzzled. It has been unstowed AFTER a pretty bad situation of stalls and erronous behaviour. LEAVE IT THERE ! Or maybe i'm not informed well enough....

[djellison]

I don't understand why they completely stow the arm as soon as a long drive needs to be done. Why is this so important ? Do they really think something will break while the arm is in "half stowed" position (over the solar panel) ? They drive 5 mm's a second. It's not " bumping", it is like a snail creeping across the terrain !

If you hunt back in the movie archive at the JPL site, you'll see some rover driving videos - ditto the NOVA programs - and given that there's essentially a tiny tiny bit of suspension within the wheels but nothing else - it's quite a rough ride even over the fairly flat rocks and terrain we have here.

Given that suprisingly bumpy ride, the mass of the instruments on the IDD, and the leverage they'd have on the joints and motors when in the 'hover' position, there is a real risk of damage to IDD joints, motors, even the front of that array and the nearest instrument.

Hence the high-park for short drives, and the proper drive for longer driving campaigns.

Doug

[mars_armer]

The simulations that have been run with an unstowed arm involve a single wheel sideslipping off a rock and free-falling some distance. This scenario isn't too unlikely, even when driving slowly. And Doug is right, the "suspension" is very hard so the rover and arm get a good jolt when that happens. The worst thing is that the unstowed arm gets thrown sideways as well.

The arm design was highly optimized to stay within a very tight mass budget (~4 kg for the arm, and the instrument package is ~2 kg). Because of those constraints, the arm was never designed to take these kinds of loads. A single-wheel drop off a 3-centimeter rock edge gets pretty close to the documented capability of the arm when in the hover-stow position.

Something else to remember is that the joint 1 winding failure was almost certainly caused by thermal cycling (remember the stuck heater on Oppy's shoulder). So the expectation is that the joint will fail completely from a thermal cycle, not from operation. So for longer drives, where they can't see the terrain in advance, it is considered fairly safe to stow the arm before driving and then unstow after the drive. (Of course, there's still the occasional stall because it's tricky operating the motor with a broken winding.)

Hope this helps explain the logic behind what they are doing.

[jamescanvin]

The simulations that have been run with an unstowed arm involve a single wheel sideslipping off a rock and free-falling some distance. This scenario isn't too unlikely, even when driving slowly. And Doug is right, the "suspension" is very hard so the rover and arm get a good jolt when that happens. The worst thing is that the unstowed arm gets thrown sideways as well.

The arm design was highly optimized to stay within a very tight mass budget (~4 kg for the arm, and the instrument package is ~2 kg). Because of those constraints, the arm was never designed to take these kinds of loads. A single-wheel drop off a 3-centimeter rock edge gets pretty close to the documented capability of the arm when in the hover-stow position.

Something else to remember is that the joint 1 winding failure was almost certainly caused by thermal cycling (remember the stuck heater on Oppy's shoulder). So the expectation is that the joint will fail completely from a thermal cycle, not from operation. So for longer drives, where they can't see the terrain in advance, it is considered fairly safe to stow the arm before driving and then unstow after the drive. (Of course, there's still the occasional stall because it's tricky operating the motor with a broken winding.)

Hope this helps explain the logic behind what they are doing.

Perfect!

I am surprised how tricky it seems to be operating the broken motor, I would have expected it to be very predictable. But then what do i know, I'm a scientist not an engineer!

James