The Mars Pathfinder spacecraft continues to perform nearly flawlessly on its 203 million kilometer (126 million mile) flight path to Mars. Currently the spacecraft is 1.8 million kilometers (1.1 million miles) from Earth, traveling at a speed of 3.2 kilometers per second (7,155 miles per hour). Temperatures and power utilization of the lander and cruise stage remain at predicted levels for this early phase of the mission.
The spacecraft's sun sensors are the only issue being watched closely on an otherwise beautifully performing spacecraft, the flight team reported. There are five sun sensor heads on board the spacecraft, two pointed along the craft's spin axis and three that are equally spaced around the circular cruise stage that look out at about 105 degrees from the spin axis. Of the five sensor heads, unit #4 on the spin axis is obscured or contaminated to the point of not being useful. Sensor #5, which is also on the spin axis, is providing good sun orientation data, but at a lower voltage than was expected. The other three sensor heads are working fine.
The flight team at JPL uploaded a software modification to the spacecraft on Saturday, December 7, which allowed the on-board attitude control system to use the sun sensor data from sensor #5 in its normal calculations of the spacecraft's orientation. The software patch was successful and the team was exuberant to see the spacecraft's attitude control estimators operating properly.
The team then began to prepare for turning the spacecraft more toward Earth to improve the telecommunications link. At the time, Pathfinder was about 58 degrees from the Earth, which is near the edge of the antenna's performance. Since this was to be the first time flight controllers used the propulsion module, they planned a small turn of two degrees to verify that everything was working properly. Thirty minutes later, they planned to turn the spacecraft an additional 20 degrees.
"The turn maneuvers were conducted successfully on Monday morning [December 12]," said Brian Muirhead, Pathfinder flight system manager. "The propulsion and attitude control systems worked properly and the spacecraft's spin axis is currently pointed about 44 degrees from the Sun and 37 degrees from Earth. The downlink performance improved as expected and we continue to communicate with Pathfinder at 1,185 bits per second."
The flight team is planning its next maneuver to spin the spacecraft down from 12.3 rpm to 2 rpm. The maneuver will be performed in the next few days, Muirhead said. Pathfinder's first trajectory correction maneuver remains on schedule, to take place on January 4, 1997.
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