STSS is a system of two low-flying satellites and funding has come from the Missile Defense Agency. The program had been cancelled at one point and there is a five year break in press releases at its web site. According to DoD Buzz, STSS will provide a massive breakthrough in tracking equivalencies: equal to about 50 AN/TPY-2s or 20 sea-based x-band radars.
Though this effort was MDA funded, it has very significant space situational awareness (SSA) implications. Having SSA, broadly and informally defined as the ability to understand what’s going on in space, is a major Air Force concern and possible growth-area within the space domain.