Aviation Week & Space Technology January 30, 2008
Columbia Data Aids Sat Re-entry Planning
By Craig Covault
Re-entry debris data and analysis derived from the space shuttle Columbia accident is being applied to Pentagon studies of how much of the failed National Reconnaissance Office NROL-21 spacecraft will survive re-entry heating and strike Earth in late February or early March.
Several hundred pounds of spacecraft debris could land anywhere between 58.5 deg. north and south latitude. The orbit overflies all of the world's most populated areas. But statistically, the debris is far more likely to land harmlessly in an ocean, since water underlies more than 90 percent of the ground track.
Details emerging from the program indicate that the satellite is a small NRO/Boeing Future Imaging Architecture (FIA) radar reconnaissance technology demonstration satellite, according to several analysts including GlobalSecurity.org, a national security think tank.
GlobalSecurity.org analysts also believe that the body of the satellite was likely built by Orbital Sciences Corp., based near Washington's Dulles International Airport.
Contrary to news media reports that say the spacecraft is as large as a school bus weighing up to 20,000 pounds, the failed satellite is actually one of the smallest launched in the last several years by the NRO, and is nowhere near that size.
The main body of the spacecraft is no more than about 15 feet long by about 8 feet wide, and likely is smaller than that - based on the limits of the Delta II payload shroud.
The spacecraft was launched from Vandenberg Air Force Base, Calif., on Dec. 14, 2006, but failed shortly after the successful launch because the vehicle's software became locked in a safe-hold status.
The satellite was launched into an initial 351 x 367 kilometer (218 x 228 mile) orbit, inclined 58.5 deg. Orbital drag has now reduced that to 271 x 282 km (168 x 175 miles), with the satellite descending 2,310 feet per day, according to Canadian analyst Ted Molczan.
Pentagon preparations have included using data from the Columbia accident to better understand how much of NROL-21 will survive re-entry. This week marks the five-year anniversary of the Feb. 1, 2003, re-entry accident that resulted in the loss of Columbia and her seven-member crew.
The Columbia debris has been made available over the past several years to researchers studying how much of which type spacecraft materials can survive re-entry and strike the surface. Those data are now being used operationally for the first time by Pentagon, NASA and NRO analysts to calculate better how much debris will survive as the NRO spacecraft plunges into the atmosphere at 17,500 mph initially.
Experts believe most of the satellite will burn up, but some very lightweight pieces or extremely dense materials will survive the re-entry and fall within an ellipse on the surface that can't be determined this far ahead of impact.
A National Security Council official said that some of the debris could involve hazardous materials, such as hydrazine propellant residue that does not fully burn up. The spacecraft's hydrazine tanks are full of the toxic maneuvering propellant, and past experience with both Columbia and smaller spacecraft re-entries indicates that hollow lightweight propellant tanks can survive re-entry and impact the ground.
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