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28-Jan-08 | Reentering spy satellite may have been Delta payload

Numerous news sources (AP via the Washington Post, The New York Times, Observer, Globe and Mail) have reported a U.S. spy satellite that is out of control and is expected to fall back to Earth some time in late-February or early-March. Although the government is not providing specifics on the spacecraft, speculation is pointing toward the National Reconnaissance Office’s L-21, also known as USA 193, which launched aboard Delta 322 in December 2006. L-21 “carried sophisticated cameras to take high-resolution pictures and test equipment intended for use on the broader Future Imagery Architecture (FIA) program”[Reuters] and was delivered into the correct (low altitude, high inclination) orbit by its two-stage 7920 vehicle, but was soon declared a loss due to its failure to communicate with ground control.

Early estimates of its size—“about 20,000 pounds and the size of a bus”—presumed that the satellite is one of the massive Keyhole-class spy birds that were once launched aboard giant Titan-IV rockets. If it is L-21 instead, these figures would be grossly overstated. L-21’s weight was classified “for official use only,” but given the payload capacity of the Delta II it would have been on the order of 4,000 pounds and about the size of a four-door sedan.

Since it cannot be controlled, there is no way of knowing exactly when and where the satellite will reenter the atmosphere. Most news outlets are focusing on the potential of the debris to damage something, or injure someone, both of which carry relatively insignificant odds. Given the highly-classified nature of the satellite—independent observers have been unable to determine even the most basic parameters of it, such as whether it was designed to use solar panels—it may be more pertinent to consider the potential for sensitive technology to fall into the wrong hands.

Another issue that has been raised is the possibility that L-21 might carry a radioisotope thermoelectric generator, or RTG, as its power source. Whether this is the case is unclear: the NRO refuses to confirm or deny; a professional analyst deems it “unlikely,” yet is the same person who overestimated the size of the craft; meanwhile amateur skywatchers have published grainy photographs of L-21 that purport to show a lack of solar panels, implying an alternative power source. Regardless, current RTG design makes the chance of a containment rupture fairly remote, even in the case of a hard landing, and the fuel pellet is in a ceramic form that resists heating and vaporization; the odds of environmental impact are extremely low. (In the case of close contact, the highly corrosive hydrazine thruster fuel poses a greater health risk, and the U.S. military is developing contingency plans to quickly retrieve any debris should L-21 end up on land.)


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