Nearly six months of aerobraking operations concluded today as the flight team raised the low point of Surveyor's orbit out of the Martian atmosphere. This maneuver was accomplished shortly after 1:00 a.m. PST as the spacecraft's onboard flight computer commanded the main rocket engine to fire for 6.6 seconds. The burn occurred at the high point of the 201st orbit and raised the low point of the orbit from 77.7 miles (125.0 km) up to 106.0 miles (170.6 km).
"From my point of view, it was an excellent execution of the maneuver," commented Surveyor's navigation chief, Dr. Pat Esposito. According to the navigation team, the burn altered the spacecraft's velocity by 9.8 miles per hour (4.4 meters per second) and was precisely executed. Compared to the original 45-hour orbit after arrival at the red planet last September, this post-aerobraking orbit takes 11 hours, 38 minutes, and 38 seconds to complete.
Later in the afternoon on the 202nd orbit, the flight team transmitted commands to activate the science payload. At this time, active instruments include the Magnetometer, Mars Orbiter Camera, and the Mars Orbiter Laser Altimeter. The Thermal Emission Spectrometer will be activated the week of March 29th. In addition, the radio science team continues to collect data about Mars' gravity and atmosphere by analyzing the radio signals that Surveyor transmits back to Earth.
For the next five months, the temporary aerobraking hiatus will allow the science teams to collect data near the low point of every orbit. Aerobraking will resume on September 11th with the goal of reducing the orbit period to less than two hours by February 1999. The current hiatus is necessary so that Mars will be in the proper position in its orbit around the Sun when mapping commences next spring.
Some of the payload activity highlights this month include measurements of the thickness of the north polar ice caps by the laser altimeter, and attempted targeting of the Viking 1, Viking 2, and Mars Pathfinder landing sites by the camera. Imaging of the Cydonia region, location of the so-called "face on Mars," will also be attempted. Because targeting exact locations on the ground from orbit requires extreme precision, normal uncertainties in the spacecraft's position and pointing capability will limit the probability of success to between 30% to 50%.
After a mission elapsed time of 505 days from launch, Surveyor is 222.10 million miles (357.43 million kilometers) from the Earth and in an orbit around Mars with a high point of 11,100 miles (17,865 km), a low point of 106.0 miles (170.6 km), and a period of 11.6 hours. The spacecraft is currently executing the P203 command sequence, and all systems continue to perform as expected. The next status report will be released on April 17th.
Status report prepared by:
Office of the Flight Operations Manager
Mars Surveyor Operations Project
NASA Jet Propulsion Laboratory
California Institute of Technology
Pasadena, CA 91109