[meteorite-list] Cold Motor Causes Spirit To Remain Parked For A Day

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:21 2004
Message-ID: <200402112032.MAA27263_at_zagami.jpl.nasa.gov>


Cold motor causes Spirit to remain parked for a day
February 11, 2004

A missed communications window caused by a cold antenna motor on the Mars
Exploration Rover Spirit prevented the robot from racking up any additional
distance on its odometer Tuesday night.

"Yesterday was an operational issue day with Spirit. We did not get the
morning high-gain antenna pass. As a result of that, we did not get sequences
loaded up (into the rover)," project manager Pete Theisinger told reporters in a
teleconference today.

As the Sun rose for the start of Spirit's 38th workday on Mars, the Pancam
Mast Assembly was creating a shadow on the high-gain antenna gimbal
motors. The motors have heaters to ensure they are warm enough to move. But
the cold temperatures in the shadow were too great for the heaters to
overcome, causing the motors to stall when trying to point the lollipop-shaped
antenna to face Earth.

"The colder you get, the more current you have put into the motors to get it to
move. So we set those limits. Because we were in the shade, we did not set
high enough current limits for the motors," Theisinger explained.

"When we first started to do the high-gain antenna session yesterday, we
started out by going to a (calibration), which goes to a hard-stop. The way the
motor knows it has gone to the hard-stop is it stalls against the hard-stop.
Because we had set the current limits so low, it stalled immediately, thought it
was at the hard-stop. Then when it continued on with its high-gain antenna
session, it was pointed off in a different direction than we expected. So we got
no data down.

"We did a high-gain antenna session later in the day when things had warmed
up. That went just fine. We looked at all of the telemetry, and everything is just
perfect. It was just this failure to understand that we are going to run cold in the
morning and we need to either wait till later in the day when the shadow left the
actuators or apply more heat with the heater we have.

"We've taken steps to fix that operationally now so we don't have those issues
in the future."

Without having the high-gain antenna session in the morning, controllers
weren't able to load the day's driving commands into the rover.

"That situation plus diagnosing what situation we had and making sure we
were really okay took all of the day. So they chose not to drive yesterday,"
Theisinger said.

Once the communications trouble began, controllers began troubleshooting to
narrow the possible cause.

"You really don't try and prejudge until you get to the end of the story,"
Theisinger said.

"They got a beep from the low-gain (antenna) and that told them the sequence
didn't get in, and it also told them that at least at the time of the beep the
telecommunications channel was working just fine. And so they thought maybe
they had a high-gain antenna pointing problem.

"They commanded a low-gain session and they got that, and so they knew
once again the telecommunications was fine. And that comes down with a
whole bunch of fault information, which said we were not in fault protection and
there were not fault responses running. So that was a whole bunch of good
news. The question then became why did the high-gain antenna session not

Engineers determined the problem had to be a mis-pointing of the high-gain
antenna. Since the rover was not in X-band fault, Spirit didn't know the
antenna was facing the wrong direction. In addition, controllers determined that
Spirit had marked all of the telemetry as sent, meaning the craft thought it had
completed a communications session with Earth using the antenna.

"That got them pretty much focusing on thermal pretty quickly. So I don't think
they were too alarmed as they walked through the possible scenarios. They got
on the trail pretty quickly."

On the upcoming Sol 39 workday at begins Wednesday evening (U.S. time),
Spirit will snap microscopic imaging of tiny dunes to its left and then drive
upwards of 25 meters on its continuing trek to Bonneville Crater.

Meanwhile, the Opportunity rover remains healthy as it drives along the
bedrock outcropping, taking imagery and science data.
Received on Wed 11 Feb 2004 03:32:12 PM PST

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