In comp.robotics.misc, mlm wrote:

(Ron) wrote in
. com:

http://marsrovers.jpl.nasa.gov/spotl..._20040309.html

Slip Sliding Away
Jet Propulsion Laboratory
March 09, 2004

On February 9, the wake up song for Opportunity was 'Slip
Sliding Away' by Simon and Garfunkel in honor of the
experience the prior day when Opportunity first tried to scoot
up the crater slope at Meridiani Planum. The ambitious rover
aimed for its target and willingly went forth up the slope;
nevertheless, Opportunity slipped and slid in the sand,
making it only half way to its target.

But ignorance is bliss, and while Opportunity's wheels had a
hard time gaining traction on the sandy surface, the rover's
brain (or computer) had a hard time grasping that it hadn't
successfully made it to its target. The little rover didn't have
to encourage itself to make it up the crater slope later by
chanting, "I think I can, I think I can," because the little rover
thought it actually did make it up the slope the first time.


All very nice Ron. Thanks again for sending on this detailed
explanation.

What is the message to draw from this? The rovers are incredibly stupid.
Perhaps, in fairness to the poor things, one should say that they have
incredibly stupid decision making software running them. Even the
vaunted independent navigation system is incredibly crude when you think
about it.

One wonders how much it would take to enable the rover to figure out that
it was not really moving as far as it thought. What about using
accelerometer data? Images? Doesn't the independent nav system look at
obstacles in the rover's path? If so, why can't it just figure out that
the obstacles haven't changed much despite the odometer clicking off 20
metres (65 feet for the metrically clueless).

Fact is these things are really only elaborate extensions of their
engineers egos. Far from the independent robots they are made out to be.

I would have expected a (or several) more reliable system for
measuring distance, such as some sort of radio distance ranging from
the base/platform (is it running or does it have any active
electronics in it after the rover goes down the ramp?) or Mars
sattelite, and/or a downward-facing camera and logic system such as in
a modern-day optical mouse, or looking at obstacles as you described.
OTOH, there's the engineering idea that the more complex something
is, the more likely it is to break down. They probably have opto
quadrature detectors in each wheel to detect its direction and speed,
which surely also detects stalled wheels and such, so using that for
distance measurement is 'good enough.'

Highly capable machines that don't really have a clue. A lot like pro
wrestlers.

Now you've insulted both pro wrestlers AND the rovers!

Mark

-----
http://mindspring.com/~benbradley