Conceptual Design of a High-Resolution, Low Cost Topographic Mapping Mission

There is a need for space-based topographic mapping missions which are an order-of-magnitude less costly than the $100M-class missions currently planned by NASA and the commercial community. The Stereo Imaging Long-Look Satellite (STILLSAT), having a mass of approximately 100 kg, is designed for 5m instantaneous field of view (IFOV) to meet most of the topographic requirements of both the science and cartography community. The resulting Digital Elevation Models (DEM) are predicted to have 10m (absolute) contour intervals, geo-corrected by ground datum. Frame and panoramic cameras from Apollo 15, 16, and 17, as well as ESA's Metric Cameras and the U.S. Large Format Camera have been cited by photogrammetrists as advantageous for topographic map production. The use of a CCD framing camera for stereo imaging was discussed by JPL in 1979 but dismissed because CCD technology was not yet mature enough. By capitalizing on recent advances in CCD technology and instituting a concept of shared stability and pointing responsibility between the bus and payload, it is now possible to consider such an advanced mission. This paper will focus on the system engineering trades resulting from mission requirements that dictate earth/satellite motion compensation to achieve very high spatial resolution, as well as off-axis cross track imaging to maximize target acquisition. The mission is approached from an integrated design paradigm wherein science, instrument, bus, and ground operations objectives are simultaneously weighed to achieve extremely low cost, low power, and reliable mission elements. The initial STILLSAT mission operations plan is to obtain multiple stereo images at base height ratios of 1.0 within targets-of-opportunity of 100km in diameter to support specific science objectives. STILLSAT is designed for line-of-sight pointing to within 0.1 degree and can image off-axis up to 20 degrees in the cross track direction. The total spacecraft and mission operations cost is expected to be well under $5M (not including launch) and is being initially proposed as a Student Explorer Development Initiative (STEDI) project to the Universities Space Research Association's Advanced Design Program. A launch could occur within 24 months of go-ahead. Progressively advanced concepts of this approach will be discussed, those which can map much larger regions of the Earth through use of larger detector arrays and mosaicked images. It is even conceivable that a STILLSAT-derived single global mapping satellite or constellation of simpler satellites could provide worldwide coverage. This approach holds promise for both scientific and commercial applications.