by Greg Mehall, TES Systems Engineer, ASU
Phil Christensen flipped the switch. It worked! On September 28th we passed a major milestone. All of the electronic components of the Thermal Emission Spectrometer (TES) were connected to the optical and mechanical systems, and for the first time, the Mars Global Surveyor TES was turned on. At that point, TES was ahead of schedule by about a month!
As the April 1, 1996, deadline for delivering TES to Lockheed Martin in Denver, Colo., approaches, engineers at the Santa Barbara Research Center (SBRC) are working diligently to integrate and test the instrument.
All of the subsystems that go into TES were completed before the end of September. These are: (1) electronics, (2) mechanical subsystem, and (3) optics. The electronics control the instrument and process the infrared data we will obtain from Mars, the mechanical systems move the mirrors used to obtain the data, and the optical systems include the mirrors and small telescopes that focus infrared light on the detectors. There are three detector arrays, each can see a 9 km by 6 km (5.7 mi. by 3.8 mi.) area on the martian surface.
Cut-away view of MGS TES showing optical components. Alignment of the optics was a major milestone for TES engineers.
While the electronics were being tested, final assembly and alignment of the optical components on the TES aft optics plate was happening in another part of the SBRC lab. After optical parts were attached to the aft optics plate, they needed to be aligned to each other so that the infrared energy collected by the TES is properly directed to the detector arrays. Alignment of these components is extremely important because it directly affects the performance of the TES.
A major part of the TES spectrometer is called the "beamsplitter." It is made of Cesium Iodide. For TES to work really well, we spent two weeks in October installing and characterizing three different beamsplitters. We then picked the best of the three, and were able to improve TES's performance by 20%.
When all of the optical components were finally attached, we used equipment in the lab to simulate the signal that the TES would see when looking at Mars. We analyzed this signal to characterize TES's Field of View. Using these data, we could determine if the instrument was properly aligned. After several tries, the final assembly and alignment of the TES optics was completed at the start of November.
We are now putting TES through a series of tests, because with any spacecraft instrument, there can be unforeseen interactions that occur when you integrate the entire system. When this testing is complete, the seven electronic modules will be stacked and tested for two weeks in a thermal/vacuum chamber, to simulate conditions in space.
Meanwhile, we will also be testing the optical/mechanical assembly. This will last through delivery of the instrument and will help us to understand how well the instrument performs under various conditions. We will calibrate the instrument so that the scientists who use the TES data can interpret it accurately. I will update you on these tests in the next edition of TES News. To Mars!
Mars Global Surveyor will travel 770 million kilometers (478 million miles) and perform four trajectory correction maneuvers (TCMs) on its trip to our neighboring planet. In this NASA drawing, the tick marks represent 30-day intervals; delta-V is "change in spacecraft velocity." Dates for each event are given in parentheses.