“Single String” Satellites Raise Missile-Warning Worries

When the Air Force launched its 23rd (and last) Defense Support Program satellite on November 12, 2007, it thought it was deploying an asset that would provide global warning of missile launches well into the next decade. Instead, the satellite failed in orbit ten months later, leaving the nation with an aging constellation of early-warning spacecraft and a successor program that was years behind schedule. Although government officials never discuss the status of the current constellation for security reasons, the possibility of a gap in missile-warning coverage early in the next decade cannot be dismissed.

Defense Support Program satellites have been the most important part of the strategic-warning network since they were first orbited in the 1970s. Three spacecraft in geostationary orbit above the equator can monitor most of the world for ballistic-missile launches and other major infrared events. When supplemented with additional sensors piggybacked on eavesdropping satellites that fly over the poles, they provide the earliest indication of potential hostile actions by countries like Russia and China that might affect America. But the latest, fifth-generation, satellites have a design life of five years, so most of the spacecraft currently in use are living on borrowed time.

Fortunately, there is considerable redundancy built into both the constellation and the individual satellites. But nothing lasts forever: eventually the satellites exhaust the fuel they need to maneuver, or on-board components begin failing. When all the backup systems for a function have ceased operating and users are down to their last option, the satellite becomes what is known as a “single string” spacecraft. In other words, the spacecraft could lose functionality at any time, with little warning. Some of the half dozen DSP satellites still operational have undoubtedly arrived at this point due to their age.

The loss of DSP-23 thus was a catastrophe for the missile-warning program that set off a scramble to identify “gapfillers” — sensors that could plug any holes in coverage if the next-generation Space Based Infrared System (SBIRS) encountered further delays. While SBIRS seems to be progressing slowly but surely toward deployment, there is no guarantee that launch vehicles will work as advertised, and there is no guarantee that legacy warning satellites will continue to function well beyond their design lives. Unfortunately, the search for alternative warning systems served mainly to highlight the obvious. The Space Based Infrared System must stay on schedule and get into orbit, because there are no timely alternatives. You could say the whole strategic-warning system is in danger of becoming “single string.”