# Mars Global Surveyor

NASA Mars Orbiter
Courtesy of NASA's National Space Science Data Center

The Mars Global Surveyor mission is designed as a rapid, low-cost recovery of the Mars Observer mission objectives. The science objectives involve high resolution imaging of the surface, studies of the topography and gravity, the role of water and dust on the surface and in the atmosphere of Mars, the weather and climate of Mars, the composition of the surface and atmosphere, and the existence and evolution of the Martian magnetic field.

The spacecraft will arrive at Mars around September 1997, after a 10-month cruise phase. After four months, aerobraking and thrusters will convert the original elliptical capture orbit into a nearly circular, two-hour polar orbit. Mapping operations will begin in January 1998. The spacecraft will be in a "sun-synchronous" orbit so that each image will be taken with the sun at the same mid-afternoon azimuth. Data will be acquired for one Martian year (approximately two Earth years). The spacecraft will also be used as a data relay for later U.S. and international missions over the following three years.

The Mars Global Surveyor will consist of six primary investigations. The Mars orbital camera will take high resolution surface images on the order of a meter or so. It will also take lower resolution images of the entire planet over time to enable research into the temporal changes in the atmosphere and on the surface.

The thermal emission spectrometer is a Michelson interferometer that will measure the infrared spectrum of energy emitted by a target. This information will be used to study the composition of rock, soil, ice, atmospheric dust, and clouds.

The Mars orbital laser altimeter (MOLA) will measure the time it takes for a transmitted laser beam to reach the surface, reflect, and return. This time will give the distance, and hence the height of the surface. Combining these measurements will result in a topographic map of Mars.

Radio science investigations will measure the Doppler shift of radio signals sent back to Earth. This will allow precise determination of changes in the orbit, which will allow for a model of the Mars gravity field. As the spacecraft passes over the poles on each orbit, radio signals pass through the Martian atmosphere on their way to Earth. The way in which the atmosphere affects these signals allows determination of its physical properties.

A magnetometer will be used to determine whether Mars has a magnetic field, and the strength and orientation of the field if one exists. An electron reflectometer will measure remnant crustal magnetization.

The Mars relay experiment consists of an antenna which will route received signals through the Mars observer camera for transmission to Earth. The relay will be used to support surface landers and rovers from other Russian, European, and U.S. missions.

Space History

##### Views of the Solar System Copyright © 1997 by Calvin J. Hamilton. All rights reserved.