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August 8, 2012

Challenges of Designing Voltage Converters for a Mission to Mars

Dave Perchlik
RHA Coordinator, Senior Electrical Engineer, Crane Aerospace & Electronics

Power Channels: Packaging and Cooling, Power Components, Power Quality Protection, Switch-Mode Power

A flight to Mars offers significant challenges for the designer of voltage converters. Space can be a harsh environment with extreme temperatures, a wide range of shock and vibration and the bombardment of radiation. In addition to the environmental challenges, space bound equipment often must have reliable operation for 15 years or longer, including up to 5 years of ground test.

The effort of qualifying a space converter is significant and there is a tremendous advantage to using converters with proven performance in space. This long project life constrains the converter designer to using components that will continue to be available for decades. The use of highly integrated circuits is a risky proposition as they often reach end of life and undergo design changes along with fabrication changes. Discrete design using components with proven performance is often the best approach for space qualified converters. To ensure continued operation without failure, it is critical to perform the most conservative worst case analysis. Extreme Value Analysis with design margin to the requirements is the preferred approach to ensure reliable operation without fail.

Using individual components over a purchased IC provides the designer with more flexibility in the configuration and control of the circuit. Space can be a cold place with requirement for operation in cryogenic temperatures down to -130°C and up to 125°C. Device selection requires an understanding of performance at temperatures usually outside the vendor’s data sheet. Extensive temperature characterization is needed prior to device selection.

Getting into space is an intensive ride that requires close attention to mechanical design of the converter. The attachment method is critical, especially for the larger structures such as transformers and large capacitors. Even marking inks on the converter must be considered as spacecraft often have to meet requirements for Collected Volatile Condensable Material (CVCM) and Total Mass Loss (TML).

Once the converter makes it into space, it must withstand the exposure to radiation. Radiation exposure includes high and low dose ionizing radiation, Single Event Effects caused by heavy nuclei and Displacement Damage from high energy protons and neutrons. The universe is continually creating radiation and the converter must be designed to operate in this hostile environment. On Curiosity’s 8 month journey to Mars it was exposed to three significant solar particle events (SME, Solar Mass Ejections) along with continuous exposure to cosmic rays.

Graph Courtesy NASA/JPL-Caltech

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