by Greg Mehall, TES Systems / Payload Engineer, Arizona State University
On Schedule for April '96:
Work on Mars Global Surveyor's Thermal Emission Spectrometer (TES) continues at feverish pace at the Hughes Santa Barbara Research Center (SBRC) in Goleta, California. SBRC is on track for an April 1, 1996, delivery of TES to the spacecraft contractor, Martin Marietta of Denver, Colorado. This delivery date is now less than one year away. The schedule is much tighter than SBRC has seen for previous spacecraft instruments, such as the mid-1970's Viking Mars infrared thermal mappers and the 1960's-70's Mariner missions.
Mars Global Surveyor (MGS), with the TES experiment led by ASU geology professor Philip Christensen, will leave for Mars in early November 1996. It will reach the Red Planet in September 1997, and is planned to systematically map the martian surface through at least January 2000.
Increased ASU Involvement:
In order to meet the extremely aggressive April 1, 1996, delivery date, Arizona State University (ASU) has been playing a more integral role in fabricating and testing the MGS TES than was the case for the TES flown on the lost Mars Observer spacecraft. I work at ASU and live in Arizona, but as TES Systems Engineer, I will be spending most of my time in California at SBRC over the next year helping with the electronics, optics and mechanics of TES. ASU has also hired retired SBRC employees George Cannon and Harvey Persh to work as lead Manufacturing Engineer and High-Reliabilty Parts Manager, respectively. All three of us worked in the same capacities on the Mars Observer TES instrument, giving us valuable insight into the fabrication of the new TES for MGS. Dr. Phil Christensen is also active in the effort, as he was for Mars Observer. Hopefully, this greater partnership between ASU and SBRC will allow us to meet our tight schedule.
Work Progresses on TES Electronics:
One of the biggest hurdles we had in 1990-91 on the Mars Observer TES was the completion of the electronics module. This part of the instrument controls all of the uplink (commands sent by radio to MGS TES in space), downlink (data radioed to Earth from MGS TES), and control of the TES. The electronics module consists of seven multi-layered electronic boards that have a lot of high-reliability, space-qualified electronic components. Most of these components take many weeks to procure from vendors (i.e., the companies that make the various parts). Luckily, all of these parts have arrived at SBRC and we are able to proceed with the fabrication and testing of the electronic subassemblies. For example, the TES Control Processor Memory Board is completely through testing. As long as we avoid any major problems, the electronics should be ready for integration into the instrument in August, a month ahead of schedule.
The Optical Parts of TES:
A majority of the optical components that we will be using in the MGS TES are flight spares from the Mars Observer TES. The most complicated portion of the TES optics is located on the aft optics plate (see diagram below). This is the optical bench of the TES and it contains the interferometer motor and optics, the thermal and solar radiometer optics, and the three detector arrays. This portion of the TES generates the thermal infrared spectra that scientists will use to study the composition of the martian surface and atmosphere.
We currently have two spare spectrometer detector arrays from Mars Observer in stock. These detectors have significantly better performance than the one we flew on Mars Observer and should improve the scientific capability of the MGS TES instrument. One of these arrays will be selected and installed in the instrument in June. When all of these optical assemblies are installed and aligned they will be integrated with the electronics module. If everything proceeds on schedule this should happen in August.
TES Mechanics-- and ASU Connection:
The mechanical assembly of the instrument main housing has also started in the last couple of weeks. The main structure of the TES consists of the the electronics module housing, the telescope and pointing mirror housing, and and aft optics plate and housing. The housings that enclose the electronic module subassemblies are being fabricated by the ASU Physical Sciences Machine Shop. This is a unique oppportunity for ASU to directly participate in the making of space-quality parts for a NASA mission, and allow ASU to play a more active role in design and fabrication of future NASA missions. The ASU shop has completed work on four of the five housings that make up the electronics module housing. These parts were delivered to SBRC and exceed the quality of the same parts flown on Mars Observer. The aft optics plate is complete; the housing for the aft optics plate is the only major change to the MGS TES design. This new design will give the TES aft optics better protection against contamination and misalignment.
Coordination with Martin Marietta of Denver:
The MGS spacecraft Critical Design Review (CDR) will be held at Martin Marietta, Denver the week of May 1-5, 1995. Dr. Christensen and I will be attending this review which will present the final design of the spacecraft and its subsystems. This review is important because the spacecraft design will be finalized and should not change after the review and will allow us to finalize the TES interface to the MGS spacecraft. We will also be attending an Integration and Test meeting at Martin Marietta in the beginning of June. The purpose of this meeting is to discuss the integration, testing and calibration plans for the TES after we are delivered to Martin Marietta. We are also starting to design the Mission Operations plan for the TES instrument with engineers at the Jet Propulsion Laboratory (JPL) in Pasadena, California. Much of the preliminary mission design is available through JPL's Mars Global Surveyor Home Page on the Internet at http://mgs-www.jpl.nasa.gov/mgs-home.html. Overall, the MGS TES effort is moving along quite well. We will keep you posted as more details are resolved.
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Major components of MGS TES. Some of the parts labeled here are described in the article above.
Edited by K.S. Edgett, April 1995