TES NEWS Volume 3, Number 4, November - December 1994

MGS Approved, TES Fabrication Begins

by K. Edgett (Arizona State University)

Mars Global Surveyor (MGS) funding for Fiscal Year 1995 was approved by Congress in late September. The federal 1995 fiscal year began on October 1, 1994. The MGS orbiter will launch in November 1996. MGS will carry five of the original seven instruments lost on Mars Observer, including the Thermal Emission Spectrometer (TES) project directed by Dr. Philip R. Christensen of Arizona State University (ASU). MGS will reach Mars in mid-September 1997 and begin a series of aerobraking maneuvers (using the atmosphere to slow the spacecraft) to put it in a circular mapping orbit by January 1998.

Martin Marietta Co. of Denver, Colorado, has begun construction of the MGS spacecraft. A Preliminary Design Reveiw was held in late October 1994 to discuss the engineering and flight plan. One major issue that came up as a result of the design review was "mass margin." There is a limit as to how much mass (MGS should be about 1047 kilograms at launch) that a Delta II rocket can send toward Mars. The MGS design is well within the limit, but spacecraft engineers commonly assume that the final product will have a greater mass than the original plans indicate, because mass usually increases as the spacecraft is built and engineers discover the need for slight design changes. (more text following figure below)

Mars Global Surveyor as it will look in its mapping configuration from January 1998 through at least January 2000. (Figure courtesy Martin Marietta, NASA, and JPL)

Over the two-week period following the Preliminary Design Review, MGS engineers and scientists worked hard to figure out what could be removed from the spacecraft to decrease its mass. One idea considered was to fix the high gain antenna to the side of the spacecraft (the present design has the antenna at the end of a long boom, as in the drawing above). This change would save considerable mass, but was rejected because it would have a severe impact on the science capabilities of MGS. By mid-November, a set of mass reductions that include changes in wiring and structure appeared to be the most likely course of action.

Work on the science instruments for MGS is underway, including a new TES being assembled at the Hughes Santa Barbara Research Center (SBRC) in Goleta, California. Work has already begun on some of the electronic boards for TES. As of October, about half the parts needed for the new TES had been acquired, the rest were in the process of being purchased. Steve Silverman, a TES engineer at SBRC, said that the electronic boards will be complete by June 1995. The optical and mechanical systems for TES will be built simultaneously. The plan is to have TES ready for testing and calibration by the end of December 1995, with delivery to Martin Marietta around April 1, 1996.

The schedule is extremely tight, and the situation took a precarious turn in mid-1994. Like many aerospace companies today, the Hughes corporation is undergoing a period of downsizing and reorganization. Hughes has decided to close SBRC, which built some of the instruments flown on the 1960s and 1970s Mariner and Viking Mars missions, and move the operation to another facility at El Segundo, near Los Angeles, California. SBRC will complete the transition by December 1995, at about the same time the TES should be ready for testing. If the TES remains on schedule, the instrument will be completed before moving to El Segundo for the calibration tests. However, if the TES is moved earlier than December 1995, the change could have a major impact on the schedule. A delay of 1 or 2 months might result. The TES team and JPL are working closely with SBRC engineers to ensure that TES will be ready in 1996.

Figures and More Information:

Mars Surveyor Artwork from the 94-95 Arizona Mars Education Guide

Jet Propulsion Laboratory Mars Global Surveyor HOME PAGE

Back to Contents of TES News November - December 1994

Edited by: K. S. Edgett

Arizona Mars K-12 Education Program / edgett@elvis.mars.asu.edu