[meteorite-list] Ageing Mars Rover Experiences Joint Problems

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Dec 9 12:51:44 2005
Message-ID: <200512091728.jB9HSWD19603_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn8434-ageing-mars-rover-experiences-joint-problems.html
 
Ageing Mars rover experiences joint problems
Kelly Young
New Scientist
08 December 2005

NASA's Mars rover Opportunity is showing signs of age - recently
experiencing problems with its shoulder joint. Engineers believe the
problem may stem from a heater that developed a fault shortly after landing.

It is not yet clear whether its instrument arm will ever be fully
functional again. The rover uses its arm to give four of its science
instruments close-up views of the alien rocks and soil.

"It could die tomorrow," says Mars rover project manager Jim Erickson.
"But it could live on, and we have to work around everything that fails
and still try to get the best science we can."

After the rover landed in January 2004, ground controllers noticed that
its shoulder joint heater switch was stuck in the on position. This
meant the joint would be warmed twice a day - once by the Sun during
daylight hours and a second time by the heater at night when prompted by
the joint's thermostat. This is almost twice the number of heating
cycles the joint was designed to withstand. In 2004, engineers opted to
let the rover "deep sleep" some nights as a way to turn off the heater
and conserve power.

With the heater problem, engineers predicted that the joint should
operate properly for 500 to 850 Martian days. As it turned out, the
rover clocked up 653 Martian days without problems. (A Martian day is 43
minutes longer than an Earth day.)

Shoulder joint

But on 25 November, the motor responsible for the shoulder joint's
side-to-side motion stalled when controllers tried to tell the rover to
unstow the arm so it could begin taking measurements of an outcrop of
layered rock. While driving, the robotic arm is stowed underneath the rover.

Currently, the prime suspect is a wire within the shoulder joint that
may have broken as a result of the frequent heating and cooling. Some of
the wiring is still intact, so the arm can still move, but the current
passing through it experiences twice as much electrical resistance.

If NASA concludes that this is indeed the problem, the question then is
how much longer the other wires in the joint will last.

As a precaution, mission managers are considering permanently placing
the robotic arm into a "joust position" rather than stowing it when
moving and then unstowing it when it is needed. In a human arm, this
would mean the fist would be held near the shoulder with the elbow
jutting out. That way, the shoulder joint motor would not be necessary.
Rather than the shoulder joint moving the arm from side to side, the
rover itself could move to position the arm.

Precious asset

"We've still got a precious asset on Mars," Erickson told New Scientist.
"I still want to get as much out of it as I can."

Within one to two weeks, Erickson and his team aim to have a plan for
Opportunity. Even without the arm, Erickson says the rover could
continue roaming about the planet, taking new pictures with cameras atop
the rover and measurements with its miniature thermal emission spectrometer.

Opportunity and its twin, Spirit, were only designed to last 92 Earth
days on the Martian surface. But Opportunity could now celebrate its
second Earth birthday on 24 January 2006.
Received on Fri 09 Dec 2005 12:28:32 PM PST