A modified commercial surveying instrument for use as a Spaceborne rangefinder

We present a summary of the process used to create a reliable, mission-critical sensor from commercial off-the-shelf (COTS) technology for the Shuttle Radar Topography Mission (SRTM). Measuring the length of the SRTM interferometric baseline to an accuracy of 2 mm (1.6 /spl sigma/) is a key requirement. An electro-optical rangefinder instrument was recognized as the best option but funds and time were severely constrained. Therefore, the basic approach was to evaluate (though a series of quick tests) a robust commercial surveying instrument, make the necessary modifications for operation in space, followed by a rigorous test program. The result was the delivery of six flight-qualified units with accuracies of 1 mm and at a cost significantly lower than that available with traditional methods.