The degradation of the U.S. missile early warning constellation that has prompted the Defense Department to scramble to acquire a gap-filler satellite is likely the result of an on-orbit failure involving the most recently launched Defense Support Program (DSP) satellite, according to a Russian satellite-monitoring group.rnObservations by the Russian Academy of Science's International Space Observation Network (ISON) and amateur radio operators indicate the DSP-23 satellite stopped transmitting in mid-September and began drifting in October.rnThe DSP-23 satellite was launched in November 2007, the last of a generation of missile warning satellites that began launching in the 1970s. The next-generation Space Based Infrared System satellites being built by Lockheed Martin have been delayed for years by technical problems and now will begin launching no earlier than 2010.
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