Robert Detwiler

Power System Cognizant Engineer

Retired

Norristown, Pennsylvania

In late 1972, I was hired into NASA’s Jet Propulsion Laboratory to develop the Voyager power subsystem design. My background included engineering on the Phoenix missile and F-15 radar transmitter at Hughes Aircraft. The opportunity to work at a world-class laboratory like JPL was the pinnacle of my career aspirations. Job satisfaction on a design task for the Voyager spacecraft was fulfilling in the sense that I was contributing to a challenging mission of scientific discovery for the benefit of mankind.

The job I had was to lead a design team in developing a power system that interfaced with a radioisotope thermoelectric generator (RTG) supplying electrical power to Voyager’s power distribution bus. This was a new power source for JPL spacecraft and the power bus regulator scheme turned out to be the prototype for the future Galileo and Cassini missions. Additionally, the mechanical systems division planned to use new, untried dual shear plate (DSP) packaging for Voyager’s subsystems. Since the power hardware consisted of bulky components like transformers and power semiconductors that dissipated large amounts of heat, we became one of the test cases for this packaging concept. The design task was to ensure that all power semiconductors operated within a temperature range that ensured at least a five-year mission lifetime. Our preliminary design for the power electronics used two bays in the spacecraft bus.

We selected Electro Optical Systems (EOS) in Pasadena to perform the detailed Voyager power hardware design and flight hardware fabrication. In the time frame of the preliminary power design, the spacecraft system design team expressed the need to seek opportunities for denser electronic packaging to provide additional space within the 10-sided spacecraft bus. The EOS mechanical design team came up with an extremely dense packaging design for all the discrete power components incorporating a cordwood-welded module design. Denser packaging techniques and electrical design to reduce power bay dissipations allowed the power electronics to be housed in one spacecraft bay, freeing up space for the spacecraft systems engineer to incorporate additional hardware within the spacecraft bus. This was a significant achievement requiring a lot of detailed electrical and thermal design, and resulted in the power bay having a density equivalent to that of seawater. The power design team was able to reduce its volume from 20 percent of the bus assembly to 10 percent. I remember this event as a significant achievement for the Voyager power design team.

Design responsibility for the Voyager power subsystem was one of the most rewarding and unforgettable experiences of my engineering career. My daily interactions across the JPL engineering matrix on Voyager-specific issues and problems provided me with a host of friendships and a knowledge base on implementation of a long-lived spacecraft. Who could have predicted that this hardware would still be functional some 40 years after launch?