[meteorite-list] Spirit Rover Update: Right-Front Wheel Rotations

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 18 Dec 2009 13:17:15 -0800 (PST)
Message-ID: <200912182117.nBILHGdu027615_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2009-201

Right-Front Wheel Rotations
Jet Propulsion Laboratory
December 17, 2009

Spirit's right-front wheel, which had stopped operating in March 2006,
revolved with apparently normal motion during the first three of four
driving segments on Sol 2117 (Wednesday, Dec. 16) but stopped early in
the fourth segment of the drive.

The rover's right-rear wheel, which stalled nearly three weeks ago,
remained immobile during the entire Sol 2117 drive. The other four
wheels all drove forward in this part of the continuing attempt to
extricate Spirit from the sand trap where it is embedded. The sol's
total commanded motion was 10 meters (33 feet) worth of wheel rotations.
The resulting movement of the rover was about 2 millimeters (0.08 inch)
forward and 4 millimeters (0.16 inch) downward. That ratio of forward to
downward is well below what would be necessary over longer distance for
extrication. Part of the downward motion on Sol 2117 resulted from the
right-front wheel digging in as it rotated about 10 times.

Engineers are analyzing results from the Sol 2117 drive and from
electrical tests conducted prior to the drive. Movement of the
right-front wheel for about 3.5 minutes was a surprise, despite an
indication from an electrical-resistance test on Sol 2113 (Saturday,
Dec. 12) that some motion might be possible by the long-disused wheel.
It is not clear whether the wheel will work again, since it stopped
during the final drive segment. It is also not clear whether extrication
from the sand trap would be possible even with an operable right-front
wheel.

The drive conducted on Sol 2117 had been planned for one sol earlier,
but was delayed after analysis of the Sol 2113 test led to discovery of
a new electrical issue on Spirit. Engineers learned that a persistent
voltage now exists between the rover electric ground and the rover
chassis where no voltage should exist. This condition might be related
to problems with the right-rear wheel.

Spirit ran diagnostic tests related to this grounding issue on Sol 2117
prior to driving and during the drive. The single-point ground showed a
sustained minus 5 volts that increased to minus 25 volts whenever any of
the six wheel-driving motors or four wheel-steering motors were powered.
This suggests the unusual electrical behavior is associated with the
rover motor controller board since the behavior is seen with all 10
motors associated with that electronics board. The rover has other
motors not related to the wheels, but the persistent voltage has not
been associated with any of those.

The plan ahead is to perform another set of low-voltage tests on the
three right-side wheels and then command another four-step forward
drive. This drive would not use the right-front wheel in conjunction
with the others, but that wheel would be driven briefly by itself after
each step to gain more information about its possible usefulness.

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

2009-201
Received on Fri 18 Dec 2009 04:17:15 PM PST