Cold motor causes Spirit to remain parked for a day
BY JUSTIN RAY
SPACEFLIGHT NOW

Posted: 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.


Spirit has remained parked since its Monday night workday. It will examine the dune features to its left before continuing to the Bonneville Crater. Credit: NASA/JPL
 
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 happen?"

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.

Status quicklook
NASA has approved an extended mission for the Mars Exploration Rovers, handing them up to five months of overtime assignments as they finish their three-month prime mission.


Check the status center for complete coverage.


Spirit Poster
This new poster features some of the best images from the Mars Exploration Rover Spirit.
 U.S. STORE
 U.K. & WORLDWIDE STORE

Apollo 12 tribute DVD set

New! Featuring the jovial crew of Pete Conrad, Dick Gordon and Alan Bean, the Apollo 12 mission was struck by lightning shortly after liftoff but proceeded on the second successful exploration voyage to the lunar surface. This three-disc DVD brings the mission to life with extraordinary detail.
 Choose your store:
U.S. - U.K. - E.U. - Worldwide

Fallen Heroes special patch
This special 12-inch embroidered patch commemorates the U.S. astronauts who made the ultimate sacrifice, honoring the crews of Apollo 1, Challenger and Columbia.
 Choose your store:
U.S. - U.K. - E.U. - Worldwide

Women in Space
Women of Space: Cool Careers on the Final Frontier is for girls, young women, and anyone else interested in learning about exciting careers in space exploration. Includes CD-ROM.
 Choose your store:
U.S. - U.K. - E.U. - Worldwide

Mars rover poster
This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
 Choose your store:
U.S.

An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.
 Choose your store:
U.S.

Expedition 18 patch & pin
The official embroidered patch and lapel pin for the International Space Station Expedition 18 crew is now available to from our stores.
 U.S. STORE: PATCH | PIN
 WORLD STORE: PATCH | PIN

Ares patch
The Ares Project will develop two new rockets to launch astronauts back to the Moon under NASA's Vision for Exploration. The Ares 1 will employ a single space shuttle solid rocket booster to loft the Orion crew capsule. The gigantic Ares 5 will haul the equipment and cargo needed for such lunar voyages. This is the Ares emblem.
 U.S. STORE




Apollo patches
The Apollo Patch Collection: Includes all 12 Apollo mission patches plus the Apollo Program Patch. Save over 20% off the Individual price.
 U.S. STORE

Columbus mission patch
The official astronaut embroidered patch of Atlantis' STS-122 mission that launched the Columbus science lab in February is available to U.S. customers from our store.
 U.S. STORE

Apollo 11 special patch
Special collectors' patch marking the 35th anniversary of the historic Apollo 11 moon landing is now available.
 Choose your store:
U.S. - U.K. - E.U. - Worldwide

Inside Apollo mission control
An insider's view of how Apollo flight controllers operated and just what they faced when events were crucial.
 Choose your store:
U.S.

The ultimate Apollo 11 DVD
This exceptional chronicle of the historic Apollo 11 lunar landing mission features new digital transfers of film and television coverage unmatched by any other.
 Choose your store:
U.S. - U.K. - E.U. - Worldwide

Next ISS crew
Own a little piece of history with this official patch for the International Space Station's Expedition 11 crew. We'll ship yours today!
 Choose your store:
U.S.

Get e-mail updates
Sign up for our NewsAlert service and have the latest news in astronomy and space e-mailed direct to your desktop (privacy note: your e-mail address will not be used for any other purpose).
Enter your e-mail address:
MISSION STATUS CENTER

INDEX | PLUS | NEWS ARCHIVE | LAUNCH SCHEDULE
ASTRONOMY NOW | STORE

ADVERTISE

© 2008 Pole Star Publications Ltd