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A Sneak Peek at the First Digital Three-D Map of the World While engineers troubleshoot a problem with a malfunctioning thruster radar scientists are enthusiastically examining their first three dimensional radar images from the SRTM flight. The German X-Band team released an image showing New Mexico, and NASA's Jet Propulsion Laboratory (JPL) released images of Rio Sao Francisco, Brazil and the St. Pierre & Miquelon Islands on Monday. The thruster is an extremely simple cold gas system mounted within the shuttle's cargo bay. Orbital mechanics causes the long boom to try to push itself vertical, similar to how a sail tries to rotate to the orientation for the least wind resistance. The shuttle can use its thrusters to hold the proper orientation, but it's expensive in terms of propellant. So engineers came up with a small thruster, not much more sophisticated than a compressed air pump at a gas station. Two tanks hold 265 lbs. of compressed nitrogen in the shuttle's cargo bay. A simple electrically controlled valve controls the flow of the gas. A regulator reduces the pressure of the gas and flexible air hoses carry the gas to the top of the mast. An orifice aims the flow in the proper direction. It only creates about a third of an ounce of thrust but it's enough to keep the proper orientation. The astronauts sent the command to open up the latch valve and the thruster began operation, but used up the nitrogen gas faster than anticipated. Ground controllers asked the astronauts to shut off the valve while they examined what could have gone wrong. A second attempt lowered the gas consumption to the proper level but didn't generate any thrust. Possible causes include a piece of ice in the line, an obstruction, or a small leak. NASA emphasizes that they're continuing the troubleshooting and as of now there's no impact to the mission's duration. While the troubleshooting of the thruster goes on the mapping of the world continues. By the third day of the mission the amount of the world mapped in three dimensions had tripled. The radar had 'painted' 54.4 million square kilometers of the Earth at least once, the equivalent are to Europe and Asia put together. Every 90 seconds over land the SRTM maps the equivalent area to the state of Florida. Only a small percentage of the data collected by the radar system can be transmitted to the ground. The remaining data is stored on data cartridges. While the world map won't be available for another two years there are a few 'sneak peek' images. Scientists on the ground are processing the data they receive on the ground to verify that the hardware is working properly and their preflight predictions are correct. As a byproduct some sample scenes have been released as images. The actual DEM modules will not be available until after the mission's completed and the data's been properly calibrated. The first C-Band images show the St. Pierre & Miquelon islands close to Newfoundland but owned by France and a portion of Brazil. Existing maps of that portion of Brazil include the warning Scientist Mike Kobrick noted "there's a phrase that really characterizes the lack of information on this map - 'relief data unreliable' - not anymore." This is typical of the kind of thing we see in the Amazon Basin, there isn't very much relief, very much natural radar albedo. When we suddenly jump to that third dimension it became obvious that there was significant relief in this scene, there's subtle low relief that was really a drainage system. You can measure the slope within the drainage system - completely invisible in the [2-D] radar image. That's the kind of additional information you get by adding the third dimension." 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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Exclusive - Shuttle Mission Begins Its Ambitious Map of the World (Feb. 12, 2000)
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