Neil Gehrels Swift Observatory

Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a NASA three-instrument space observatory for studying gamma-ray bursts (GRBs) and monitoring the afterglow in X-ray and UV/visible light at the location of a burst. It was launched on 20 November 2004, aboard a Delta IIlaunch vehicle. Headed by principal investigatorNeil Gehrels until his death in February 2017, the mission was developed in a joint partnership between Goddard Space Flight Center (GSFC) and an international consortium from the United States, United Kingdom, and Italy.

The burst detection rate is 100 per year, with a sensitivity ~3 times greater than the BATSE detector aboard the Compton Gamma Ray Observatory. The Swift mission was launched with a nominal on-orbit lifetime of two years. Swift is a NASA MIDEX (medium-class Explorer) mission, operated by Pennsylvania State University. It was launched as MIDEX-3, following FUSE (MIDEX-0), IMAGE (MIDEX-1) and WMAP (MIDEX-2). An Announcement of Opportunity (AO) for the first Medium-class Explorer (MIDEX) missions was issued in March 1995.

Swift was designed to study gamma-ray bursts, but later came into use as a general-purpose multi-wavelength observatory, particularly for the rapid follow-up and characterization of astrophysical transients of all types. In 2020 Swift received an average of 5.5 Target of Opportunity observing proposals per day, and observed about 70 targets per day, on average.

In 2026 Swift's orbit had been lowering, mostly in the previous two years, because an increase in solar activity had expanded the Earth's atmosphere enough to slow Swift due to atmospheric drag. A mission to raise Swift to a higher orbit to prevent it from falling to Earth was launched on 3 July 2026. However, NASA announced on 19 August that the mission was unsuccessful in boosting Swift to a higher orbit, and NASA expects it to re-enter the atmosphere around the end of 2026.