Michael Ashley’s Quick Study, “The care and feeding of an Antarctic telescope” (Physics Today, May 2013, page 60), was an enjoyable read. His comment on equipment overheating at ambient temperatures below −60 °C and the trickiness of thermal design brought back memories of a similar problem I experienced as the South Pole satellite communications engineer. The South Pole Marisat-GOES Terminal satellite communications ground station (see the photo at right) supported intercontinental communications to the Amundsen–Scott South Pole Station through two old but still viable highly inclined geosynchronous satellites, Marisat-F2 and GOES-3. Not surprisingly, ground station operations and support for this large, complex system in the extreme temperature environment occupied much time on and off ice during my seven years with the program.
For several years after the terminal commenced operation in 2001, unexplained oscillations in the uplink solid-state power amplifier (SSPA) output were observed. They affected link performance and produced corresponding oscillations in the strength of signals received by satellites, particularly for GOES-3, which required an uplink power level more than five times that needed for Marisat-F2.
The SSPA electronics and power-supply equipment had forced-air cooling. While performing annual equipment maintenance in the terminal’s shelter and monitoring the SSPA output one summer day, we serendipitously noticed the output changing at the same frequency as shelter temperature fluctuations in response to intervals of cooling-fan operation. Clearly, ambient air temperature and its ability to cool were factors in the SSPA output. The South Pole experiences a wide range of atmospheric pressure values, equivalent to altitudes between approximately 3050 m and 3600 m but typically staying around 3200 m in the summer. Midsummer temperatures usually range between −40 °C and −25 °C. A 1998 memo1 by Jingquan Cheng at the National Radio Astronomy Observatory stated that cooling efficiency can decrease by about 15% at 3000 m. Apparently, that efficiency reduction affected the ability to cool electronics by the forced-air cooling system. Anecdotally, flat-panel plasma displays installed in the new station suffered premature failure, no doubt due to a similar problem with insufficient cooling at altitude.
The solution was relatively simple. We moved the SSPAs to the lowest rack location, disconnected the outside air inlet fan at the bottom of the shelter, and permanently opened the inlet fan vent slightly. The move placed the SSPAs in a cooler location—thermal stratification is quite noticeable—and reliance on only the exhaust fan at the top of the shelter evened out temperature and corresponding SSPA output variations. Hopefully, our experience can be used by others contemplating electronic equipment operation at high altitude.