with Simon Mansfield
Surveyor Slow Slide Down The Gravity Well
JPL - November 19, 1997 - Operations on the Mars Global Surveyor mission continue to proceed smoothly one week after the resumption of aerobraking. This week, the flight team performed several small thruster firings to gradually drop the low point of the orbit back into the upper fringes of the Martian atmosphere.
Currently, the low point of the orbit lies at an altitude of 77.3 miles (124.4 km). Friday night, at the high point of orbit #41, Surveyor will perform another thruster firing to slow down and lower the low point of the orbit by another four kilometers. The new low point altitude will cause the spacecraft to experience an air resistance force of 0.21 Newtons per square meter on every subsequent aerobraking pass.
This amount of force is approximately one-third as strong as that proposed by the original plan, and is nearly equal to the average force as prescribed by the new mission plan. To put these force values in perspective, chief navigator Dr. Pat Esposito estimates that the orbit period will shrink at a rate of about 24 minutes per revolution as a result of flying through the atmosphere.
After a mission elapsed time of 372 days from launch, Surveyor is 183.58 million miles (295.44 million kilometers) from the Earth and in an orbit around Mars with a high point of 27,578 miles (44,383 km), a low point of 77.3 miles (124.4 km), and a period of 34.8 hours. The spacecraft is currently executing the P41 command sequence, and all systems continue to perform as expected. The next status report will be released on Wednesday, November 26th.
During a recent press briefing at JPL, scientists showed stunning new images of layered rock and sediment in the canyon walls of Valles Marineris on Mars. Other images of an ancient valley hint at the presence of active sand dunes and dried-up ponds. The new images are available here.
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