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Shuttle Mission Begins Its Ambitious Map of the World The longest rigid structure in space was deployed as part of an effort to map almost all of the populated areas of the world in three dimensions. 
Shuttle's location when it began mapping the world The Defense Department had a requirement to map as much of the world as possible in three dimensions. Obvious tactical applications include terrain maps for cruise missiles and better pre-battle flight simulators for fighter pilots flying in to enemy territory. The data also has commercial applications ranging from where to place cellular telephone towers to planning the impact of how a new dam changes an area's drainage system. NASA's Jet Propulsion Laboratory recommended reflying the existing Space Radar Laboratory hardware with an important addition, a second receive-only antenna positioned a fixed distance from the shuttle for single pass interferometry. The dual antennas act like stereo vision generating different phases which are combined through software to generate the three dimensional image. The most practical way to fly a separate antenna in formation with the shuttle is with an extendible mast. Similar smaller booms have been used for previous shuttle experiments and are planned for the International Space Station's solar arrays. SRTM's 197 foot (60 meter) mast is twice as long as the previous record for an extended object in space. The mast's clever design enabled it to be compressed in to a canister just one twentieth its extended length. Technical specifications for the mast can be found at the following location: http://www.aec-able.com/corporate/srtm_spex.htm
That long a boom is both a technical and safety challenge. From a
technical point-of-view it has to be extremely stiff, and have an extremely
low coefficient of thermal expansion. In many ways it's similar to
maneuvering any long object, you've got to make extremely careful small
movements to avoid letting it get away from you. From a safety
point-of-view anything which extends over the side of the shuttle's cargo
bay has to have an emergency jettison capability in case the shuttle has to
return to Earth quickly.  Radar antenna mast extended from shuttle (Source: NASA TV) By 12:32 am, 11 hours and 47 minutes after the shuttle's launch it was ready to begin mapping the world. At this point the shuttle was on its ninth orbit, traveling over the Maldive Islands in the Indian Ocean. Over the next ten days the SRTM payload will map over 72% of the world's land areas, encompassing over 95% of the world's population. Note, the author is a full-time aerospace writer covering the space shuttle and other aspects of the space program with over 15 years of experience. Please contact the Editor for additional details.
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