USA-205, also known as Space Tracking and Surveillance System-Advanced Technology Risk Reduction (STSS-ATRR), and previously as Block 2010 Spacecraft Risk Reduction is a satellite formerly operated by the United States Missile Defense Agency. It was launched to demonstrate new technology for missile detection early warning systems (MDEWS). The technology demonstrated on STSS-ATRR was used in the development of the Space Tracking and Surveillance System (STSS) part of the Space-Based Infrared System (SBIRS). It was launched on a Delta II 7920-10C launch vehicle from Space Launch Complex 2W (SLC-2W) at the Vandenberg Air Force Base (VAFB) in California, at 20:24:25 UTC on 5 May 2009 into a

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

(SSO). The launch was conducted by United Launch Alliance. Operational and administrative control of the Space Tracking and Surveillance System-Advanced Technology Risk Reduction (STSS-ATRR) satellite was transferred to Air Force Space Command (AFSPC), effective 31 January 2011. In addition to successfully demonstrating required on orbit system performance parameters for a prototype sensor technology, STSS-ATRR conducted Space Situational Awareness and related operations on an as-capable basis.

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Spacecraft launched in 2009 Spacecraft launched by Delta II rockets USA satellites Early warning satellites {{US-spacecraft-stub