QUOTE (Tesheiner @ May 13 2009, 03:49 PM)
My 2c: because there's more pressure on the left wheels due to the 10º roll?
Yes I agree it.
.
What I am afraid is that the soil which Spirit is sitting has a similar sort of composition in all sides. The soil firmness of left side (face toward the north) is already broken due to as you have said. I suspect that around soil might have some fews (4-8 cm) of deposit sand caused by eons of years. The deposit sand has already covered the other layer of soil, basalt silica of the ancient water-rich environment. This soil has a peculiar property that it does not get as bond as the other kind of soil. So it is like to sugar. That is driving crazy to the wheels.
A similar type of sand on Earth, the car is not able to get out unless the tire is deflated, put something (table, stone, etc.) below the tire or get help of pulling from other car.
Meanwhile the position of Spirit is not at the center of the gravity but inclined between 10-12 degree on the left wing (facing to north). That means, when it tries to roll, the wheels on the left wing will sink more than the right wing ones if all wheels rotates at the same time. I am not sure about the height of Spirit's belly to the surface. Maybe between 30-40 cms. Thus, I hope that below of basalt silica must have some kind of much firmer soil not so deep to permit Spirit to grip and advance.
At this point, I still don't know if the Spirit has a nice type of slippage blocking on every 6 wheels like of some sophisticated 4x4 trucks. If it is true, the traction would be fantastic by by trying not to slip any wheel and at the same time any wheel trying to grip the surface whenever as much as possible. Does Spirit have that capability? I am afraid it is not. The slippage capability of Spirit will be done manually, as an example, 10 revolutions on the right side and 2 revolutions on the left side. A complicated sequence of timing programming. Needs a good doses of gut feeling to calculate it!
All at all, the most important is to evaluate the surface (properties, inclination, stones, etc.) not around Spirit but up to 10 meters of radius as an example).
Finally, I wish you have a plentiful time and calm during the lab testing studying all possible options. Let God save our dear lady.