NASA launches Space Shuttle Discovery on STS-48 to deploy the Upper Atmosphere Research Satellite.

Space Shuttle Discovery is a retired American Space Shuttle orbiter. The spaceplane was one of the orbiters from NASA's Space Shuttle program and the third of five fully operational orbiters to be built. Its first mission, STS-41-D, flew from August 30 to September 5, 1984. Over 27 years of service it launched and landed 39 times, aggregating more spaceflights than any other spacecraft as of December 2024. The Space Shuttle launch vehicle had three main components: the Space Shuttle orbiter, a single-use central fuel tank, and two reusable solid rocket boosters. Nearly 25,000 heat-resistant tiles cover the orbiter to protect it from high temperatures on re-entry.

STS-48 was a Space Shuttle mission that launched on September 12, 1991, from Kennedy Space Center, Florida. The orbiter was Space Shuttle Discovery on her 13th flight. The primary payload was the Upper Atmosphere Research Satellite (UARS). The mission landed on September 18 at 12:38 a.m. EDT at Edwards Air Force Base on runway 22. The mission was completed in 81 revolutions of the Earth and traveled 3,530,369 km (2,193,670 mi). The 5 astronauts carried out a number of experiments and deployed several satellites. The total launch mass was 108,890 kg (240,060 lb) and the landing mass was 87,440 kg (192,770 lb).

The Upper Atmosphere Research Satellite (UARS) was a NASA-operated orbital observatory whose mission was to study the Earth's atmosphere, particularly the protective ozone layer. The 5,900-kilogram (13,000 lb) satellite was deployed from Space Shuttle Discovery during the STS-48 mission on 15 September 1991. It entered Earth orbit at an operational altitude of 600 kilometers (370 mi), with an orbital inclination of 57 degrees.

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