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December 18, 1996

12:00 p.m. Pacific Standard Time

Sojourner, a 10-kilogram (22-pound) rover tucked away on a petal of the Mars Pathfinder spacecraft, got a 'wake up' call on Dec. 17 from flight controllers at NASA's Jet Propulsion Laboratory. After waking up, Sojourner conducted an internal health check and sent data back to the flight team that all was well.

The Pathfinder flight team was ecstatic with the rover data, which showed that all systems within the rover were operating normally. In addition, data from the rover's main science instrument -- the alpha proton x-ray spectrometer -- showed that it was operting properly.

"The rover woke up, did its internal health check, sent the lander its status data and went back to sleep, all as planned," said Art Thompson, rover operations team member. "All subsystems were verified as being in good health."

Pathfinder continues to perform very well on its 500 million-kilometer (310 million-mile) journey to Mars, the team reported. Currently the spacecraft is 4 million kilometers (2.5 million miles) from Earth, traveling at a speed of 3.1 kilometers per second (7,000 miles per hour). Its destination, Mars, is currently about 190 million kilometers (118 million miles) away. All temperatures and power utilization of the lander and cruise stage remain at their predicted levels for this phase of the mission.

The spacecraft was spun down from 12.3 rpm to 2 rpm on Dec. 11. Flight controllers first instructed the spacecraft to turn to a Sun angle of 50 degrees and an Earth angle of 32 degrees. This allowed them to use all four operating Sun sensors. The spacecraft executed the commanded spin down to the normal cruise spin rate of 2 rpm in steps of 2 rpm at a time.

Once the normal spin rate was established, the team turned on the spacecraft's star scanner on Dec. 12. Star scanner data allows the spacecraft to establish full, three-axis knowledge of its orientation in space. This is the normal cruise attitude control mode and the one in which all trajectory correction maneuvers will be performed.

While Sun sensor #5 continues to work well after a software fix, the flight team continues to investigate the cause of the loss of Sun sensor head #4. The team expects to reach a likely conclusion on the cause of the problem within the next month or two.

Dave Gruel, Pathfinder flight director at JPL, conducted the Dec.16 health check of the lander science instruments, including the atmospheric sensor instrument and meteorology (ASI/MET) package and the imager. Temperature, pressure and accelerometer readings from the atmospheric/meteorology instrument verified it was in normal working order. Power and dark current measurements received from the imager while it was imaging the darkness around it, confirmed that the instrument was working properly, Gruel said.

Richard Cook, Pathfinder mission operations manager at JPL, reported today that Pathfinder has been fully checked out for this phase of the mission and that all subsystems are "go" for a successful seven-month cruise to Mars.

The next major in-flight event will be Pathfinder's first trajectory correction maneuver, which is scheduled for Jan. 4, 1997.

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