Cots in space: Developing an Environmental Control System for Balloon-Borne Air-Cooled Electronics

The design and analysis of an environmental control system developed for a balloon-borne electronics payload is presented. Commercial off-the-shelf (COTS) air-cooled electronics were flown as part of the science mission payload for a NASA operated climate sensor called FIRST (far-infrared spectroscopy of the troposphere). The FIRST sensor was successfully flown in June 2005 as a stratospheric balloon-based demonstration of a new space sensor designed to measure the Earth´s thermal far-infrared signature (10-100 microns) at high spatial and spectral resolution. COTS electronics were selected for instrument operation, data processing and storage, and telemetry downlink functions based upon their low cost and immediate availability, two factors deemed critical to mission success given the short development cycle of the demonstration flight. Specific air-cooled computers were chosen based upon engineering experience in developing mission systems with same/similar electronics. This engineering ´heritage´ was deemed to have greatly reduced overall mission risk. Insuring operational functionality of the COTS electronics during ascent through the Earth´s atmosphere and operating at mission altitude of 36.6 km (120,000 feet) proved to be a challenging thermal engineering problem. Temperatures predicted using first-order hand calculations and more detailed finite element analysis (FEA) techniques are compared with data taken during the float mission sequence. Analysis procedures and assumptions are discussed. Common thermal analysis techniques (hand calculations, FEA) are shown to adequately predict system thermal response, provided that the variation in and complexity of the near-space thermal environment are adequately modeled. Post mission insights concerning the analytical approach and engineering assumptions are also presented