Early Friday morning, the National Aeronautics and Space Administration terminated an experimental rocket soon after it launched from the Wallops Flight Facility in Virginia. The rocket had veered off course and was in danger of landing in a populated area. How does NASA torpedo a rocket?
By turning it off. Contrary to some press reports, NASA didn’t “blow up” the rocket since a big explosion was precisely the scenario the agency was hoping to avoid. All guided vehicles are required to carry a network of electrically rigged explosives that can be detonated by radio commands from the ground, known as a “flight termination system.” This system allows the rocket to be disabled with a series of small explosions midflight, so it can fall safely to earth should NASA officials discover any dangerous malfunctions after launch.
In this case, the order to abort the flight triggered the FTS to shut down the rocket by deactivating both of its stages. (A rocket stage is a motor that contains its own igniter and propellant; each stage fires in turn, then falls off once it runs out of fuel.) Explosives on both stages detonated simultaneously, splitting open their casings and allowing the hot gases that power them to dissipate into the air. Without fuel for the stages, a neutralized rocket continues moving for as long as its momentum can carry it—and then (in theory) comes down within pre-established safe boundaries.
The decision to terminate a rocket flight is made by NASA’s range safety officers. Whenever a rocket is launched, engineers take into consideration that it might veer off course a bit, due to onboard system problems or external weather conditions. So prior to launch, these safety specialists determine how far, and in what direction, the rocket can travel without endangering people or property should it malfunction and fall. (Factors in these calculations include the size and type of the rocket, the planned flight path, whether the rocket has been tested before, and how densely the area around the launch facility is populated.) The range for Friday’s rocket allowed for approximately 16 degrees of deviation from the planned flight path. The safety officers monitored the rocket using both radar and onboard telemetry systems; soon after launch, it began veering south, putting it on course to pass out of the acceptable safety range. At that point the observers turned on the flight termination system.
The Wallops facility, which is the only launch base where NASA directly oversees range safety (all other launch sites are overseen by the Air Force), has handled an average of 20 to 25 rocket launches annually during the past two decades. The last time a rocket was terminated early at Wallops was in 1995, when the Conestoga 1620 disintegrated in midair 46 seconds after launch. In the case of the Conestoga—which, like Friday’s rocket, was on its maiden voyage—the vehicle began breaking up on its own, and the FTS was initiated as a backup precaution. (Manned space shuttles, which are launched from Kennedy Space Center, have similar termination systems; astronauts are given parachutes, survival suits, rafts, and other survival gear.)
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Explainer thanks Bryce Hallowell, Trina Patterson, and Kent Rominger of Alliance Techsystems and Keith Koehler and David Steitz of NASA.
