Instrumentation Modeling for NASA’s Next Mars Rover Mission

By Dr. Talso Chui, Nasa Jet Propulsion Laboratory, Pasadena, CA, USA

Scheduled to launch in the fall of 2009 with the goal of reaching Mars in October 2010, NASA’s Mars Science Laboratory (MSL) is a robotic rover that will look for signs of habitable environments on the Red Planet. One of the instruments selected to ?y aboard the MSL is the Chemistry and Mineralogy (CheMin) instrument. Capable of performing both x-ray diffraction and x-ray ?uorescence analyses of powdered rock samples, CheMin will catalog the chemical and mineral composition of rocks it examines.

Concept illustration of NASA’s Mars Science Laboratory (MSL)

To test the viability of CheMin, Dr. Talso Chui — a principal scientist in the Ap¬plied Low Temperature Physics Group at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, CA — and his team used COMSOL Multiphysics to perform thermal modeling of the instrument. There were two important questions the group wanted answered: Do the electronic components overheat, and is the pressure too high after turning the x-ray source on? “We are interested in whether certain components are too hot,” explained Dr. Chui. “The junction temperature should be kept below 120°C.”

For the simulation, the model was structured into four components — one for each circuit board and one for the high voltage power supply (HVPS) can and mechanical structures. Using the command “File>Merge Component,” all of the objects in a component were combined into a single composite object. The model featured 898,969 mesh elements, 282 domains, and 2,680 boundaries. The run time for the simulation was approximately 45 minutes.

“The COMSOL package took care of all of the different types of physics involved [in performing the simulation],” said Dr. Chui. “The software was very helpful because it can solve very complicated geometry.” He found that using COMSOL Multiphysics was an economical way to explore various design options, since the simulation uncovered multiple problems. For example, the transformer potting material turned out to be above 80° C, which may cause hardening over time; the pressure was close to 100 psia, which is too high; and the pressure gauge was too hot at 120°C.

Dr. Chui has used COMSOL software for a variety of other projects. He worked on the “world’s most accurate clock,” which uses a mercury ion lamp in its design. He chose COMSOL to simulate how hot the lamp can become. He also has used COMSOL for many different magnetic-shield modeling applications. “One thing I find particularly attractive with this package is that you learn the basics and then can apply it to different physics like magnetic modeling, superconducting shielding and so on,” he said. “These are totally different from thermal analysis, but once you learn the basic package, there is very little you need to learn in order to apply it to other areas.