NASA launches Space Shuttle Discovery on STS-51.

STS-51 was a NASA Space Shuttle Discovery mission that launched the Advanced Communications Technology Satellite (ACTS) in September 1993. Discovery's 17th flight also featured the deployment and retrieval of the SPAS-ORFEUS satellite and its IMAX camera, which captured spectacular footage of Discovery in space. A spacewalk was also performed during the mission to evaluate tools and techniques for the STS-61 Hubble Space Telescope (HST) servicing mission later that year. STS-51 was the first shuttle mission to fly a Global Positioning System (GPS) receiver, a Trimble TANS Quadrex. It was mounted in an overhead window where limited field of view (FoV) and signal attenuation from the glass severely impacted receiver performance. Full triple-redundant 3-string GPS would not happen until 14 years later with STS-118 in 2007.

September 12 is the 255th day of the year in the Gregorian calendar; 110 days remain until the end of the year.