Spacecraft Assembly

Thermal Vacuum Testing

We are varying the temperature of the walls around the spacecraft to simulate the hot moon, the cold moon, deep space, or sunlight, and we measure the Orbiter temperature in different locations to observe the heat flow through the system. We compare these observations to our predictions and adjust the thermal model accordingly. When we are done, we will be better able to predict Orbiter temperatures at the moon. At the same time, we are confirming that all components properly operate over a range of temperatures and in vacuum. This is what we call "Thermal Vacuum Testing". (Right) The orbiter in the thermal vacuum chamber. The -X end of the spacecraft has red covers over the thrusters. The high-gain antenna (HGA) boom is in its deployed configuration. The Orbiter's z-axis is pointed down, just like it will be in orbit around the moon.

October 30, 2008 The pressure around LRO right now is 1.3 x 10-6 torr - high vacuum, equivalent to the pressure at Space Shuttle altitudes. At this pressure, all heat transfer is either through conduction or radiation - no cool breeze to take the heat away from our electronics.
November 20, 2008 LRO thermal vacuum testing is continuing. We completed balance testing, where we confirm the performance of our temperature control system, two weeks ago. We spent last week reconfiguring the chamber for cycling, hooking up extra equipment to the Orbiter in order to perform a full set of electrical testing. Now LRO is back under vacuum. Our balance testing uncovered a mistake in the analysis of the power dissipated in the solar array gimbals. Our gimbals were getting much hotter than we expected, so we will add an extra radiator and test it out after Thanksgiving. We have also worked through a couple other problems uncovered by the rigors of the thermal vacuum test. Overall, the Orbiter is doing well. This week, we completed hot cycle #1, and some operations testing. We are currently executing cold cycle #2. We will perform four cycles. About Thermal Vacuum Testing The last major phase of a mission's environmental testing at GSFC. [Watch Video]	(Above) Day shift monitoring telemetry from the Orbiter
December 18, 2008 As of 6:30am today, we have completed our thermal vacuum testing and the Orbiter power is off. We are re-pressurizing the chamber this morning. We expect to have the Orbiter back in the clean room by the middle of next week. We now have well over 2000 hours of powered testing on the spacecraft, with over 600 of that in vacuum. We did encounter a few problems during our testing, but that is why we test-we want to find the problems here on Earth, where they are fixable. Our new gimbal radiator worked well. The outer cable wrap and actuator stayed cool enough throughout the testing this month. The inner cable wrap, which is inside the avionics module, was still running a bit too warm during out hottest testing. Over the next several weeks, we will decide exactly how to handle this situation. Our vacuum testing has provided us with the data we need to predict the performance. We will use these predictions to decide whether we will need to perform any operational work-arounds, like off-pointing the array, during the hottest cases. In addition to the gimbal radiator, we made two other changes to the Orbiter based on the early part of our thermal vacuum testing. Our adjustments to the LEND and LOLA radiators worked exactly as we intended. We will now be able to operate LEND 10 degrees Celsius cooler during the hot orbits, reducing the stress on the instrument. LOLA's smaller radiator will provide more margin for the heaters in the cold case, without the instrument overheating when it is hot. Overall, this thermal vacuum test went very smoothly. Most of the temperature predictions were only a few degrees from expected. The heaters and radiators performed beautifully, keeping everything within limits. The instruments and the spacecraft components all met performance requirements throughout the temperature range. We now know that the spacecraft can survive the brutal thermal extremes around the moon. All that remains before we ship to Florida is a final run of our Comprehensive Performance Test and some operations testing (in addition to cleaning up a lot of paperwork!).

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