U.S. officials are studying the possibility of shooting down the errant Lockheed Martin intelligence satellite that was launched into space for the National Reconnaissance Office (NRO).

The concern is that the spacecraft carries a full tank of hydrazine - a toxic propellant - that would have been used to reposition the satellite in orbit. Government analysts say the odds are that the tank will crack open during re-entry or than it will land in the ocean, which makes up 70 percent of the area where the breaking up satellite might land (DAILY, Jan. 30).

There also is concern in some quarters that debris could reveal U.S. national security secrets if recovered by other nations. It is expected to re-enter the atmosphere late this month or in early March.

Analysts at the U.S. Missile Defense Agency (MDA) and NRO have put hundreds of hours into analysis and have studied closely the accuracy of U.S. radars in Japan, Alaska and possibly elsewhere to give more targeting options to those assessing the danger of the satellite falling to Earth.

A senior official with insight into the planning says a rumor that the satellite carried a small, nuclear generator is "absolutely and totally incorrect." However, government agencies including MDA and NRO "are studying options that include" hitting the satellite with a weapon so that it breaks up in space - and ruptures the hydrazine tank - before beginning its descent.

If the hydrazine tank did hit a populated area intact, and depending on winds and the dynamics of "plumeology," the impact could affect humans - perhaps kill some - out to a distance of 20-30 yards, the official says.

Aerospace Corp., a California-based research organization that regularly advises the Defense Department, has assembled some basic data about falling satellites and what can be done about them. "For an orbiting object, shooting it down actually breaks the object into many pieces, some of which could be hazardous to other satellites," says the Aerospace Corp. "Many of the fragments will survive re-entry, but be spread over a much larger area. The pros and cons for a specific case would need to be examined."

Re-entering objects, including major items such as satellites, platforms and rocket bodies, have dropped 5,400 metric tons of material on the Earth in the past 40 years, the research group says.

However, "if a satellite or rocket body has propulsive capability, it can use rocket motor burns to target the re-entry into a desired area. The technique was recently used by NASA to ensure debris from the 14,000 kilogram [31,000-pound] Compton Gamma-Ray Observatory landed in the ocean," it says.

As to the threat, "One person was brushed on the shoulder by a piece of debris in 1997. She was not injured. Large, hazardous fragments can survive, but in most cases, debris from re-entered objects is never found or reported," Aerospace said.

MDA has several systems under development designed to perform intercepts in space, including the Ground-based Midcourse Defense (GMD) system, the ship-based Aegis ballistic missile defense system, and the Theater High-Altitude Area Defense (THAAD) system.