W. David Thompson took me to task in his June 6 commentary [“MDA Was Right To Kill STSS,” page 19] for writing a “badly misinformed” assessment of the Space Tracking and Surveillance System (STSS). I had argued that STSS technology is an essential component in any near-term missile defense architecture, and that flight tests of two demonstration satellites launched in 2009 prove the technology is viable.

It was a big relief to U.S. defense officials in May when the first geosynchronous satellite in the Space Based Infrared System (SBIRS) successfully reached orbit. The new spacecraft is equipped with sensors that will provide the first indication of hostile missile launches, nuclear explosions and other heat-generating events around the globe relevant to national security.