with Simon Mansfield
Surveyor Increases Aerobraking Pace
JPL - January 13, 1997 - Over the winter holidays, a relatively stable Mars atmosphere has allowed the Surveyor flight team to achieve slightly faster than normal aerobraking progress in terms of reducing the size of the spacecraft's orbit. Currently, the spacecraft takes 23.5 hours to complete one revolution around Mars. This orbit period is nearly 45 minutes less than that predicted for this time one month ago.
During the last three weeks, some of the passes through the atmosphere have resulted in an air resistance force experienced by the spacecraft as high as 0.35 newtons per square meter. In contrast, the pressure target as specified by the baseline aerobraking plan measures only 0.25 newtons per square meter. Much of the increase in aerobraking progress has come as a result of this differential. However, because the dust storm season on Mars lasts for several more months, the atmospheric advisory group has informed the flight team that the stable atmospheric conditions may not continue.
In terms of long-range process, Surveyor has completed nearly 87 revolutions around the red planet since arriving last September. The current plan involves aerobraking until late March or early April to shrink the orbit to just under 12 hours. At that time, aerobraking will be temporarily suspended by raising the low point of the orbit out of the atmosphere. This plan will allow for a concentrated period of science data collection during the summer of this year. The summer pause is also necessary so that Mars will be at the right place in its orbit around the Sun when the spacecraft begins mapping operations in March 1999.
After a mission elapsed time of 428 days from launch, Surveyor is 201.62 million miles (324.47 million kilometers) from the Earth and in an orbit around Mars with a high point of 20,346 miles (32,744 km), a low point of 75.8 miles (122.0 km), and a period of 23.5 hours. The spacecraft is currently executing the P88 command sequence, and all systems continue to perform as expected. The next status report will be released on Friday, January 30th.
EARTH INVADES MARS
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