Can we control where debris will land?
In some cases, we can control the location of the debris footprint by performing a deorbit maneuver. If the satellite or rocket stage has propulsive capability, it can be commanded to execute one burn or a series of burns designed to lower the orbit perigee so that the object will reenter at a specific location. This same type of maneuver is used to deorbit manned spacecraft at the end of a mission. Very few satellites and rocket stages have sufficient propulsion capability to perform a controlled deorbit, however.
For larger objects, which pose a hazard to people and property on the ground, a controlled deorbit is most desirable since this technique assures that the debris impacts in the ocean. A good example is NASA’s deorbit of the 14,000-kg Compton Gamma Ray Observatory (CGRO) into the south Pacific Ocean. More than 35 percent of CGRO’s mass was expected to survive reentry, and the falling debris would be a hazard to humans if it fell in the wrong place. After the failure of one of its three gyroscopes in December 1999, the decision was made to deorbit CGRO in a controlled manner before its remaining gyroscopes could fail. CGRO was safely deorbited in the Pacific Ocean on June 4, 2000, via four thruster burns.
Current U.S. government standards state that the risk from any reentry will not exceed 1 in 10,000. If we do not or cannot control where it will land, we must minimize the risk by ensuring that the spacecraft breaks into small pieces during reentry. Techniques for designing spacecraft for eventual disposal are part of a strategy called “design for demise” (see AIAA’s Aerospace America, “Design for Demise,” February 2012).
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