STS-26 was the 26th NASA Space Shuttle mission and the seventh flight of the orbiter Discovery. The mission launched from Kennedy Space Center, Florida, on 29 September 1988, and landed four days later on 3 October 1988. STS-26 was declared the "Return to Flight" mission, being the first mission after the Space Shuttle Challenger disaster of 28 January 1986. It was the first mission since STS-9 to use the original Space Transportation System (STS) numbering system, the first to have all its crew members wear pressure suits for launch and landing since STS-4, and the first mission with bailout capacity since STS-4. STS-26 was also the first U.S. space mission with an all-veteran crew since Apollo 11, with all of its crew members having flown at least one prior mission.

The mission is technically designated STS-26R, as the original STS-26 designation previously belonged to STS-51-F (also known as Spacelab-2). Likewise all flights with the STS-26 through STS-33 designations would require the R in their documentation to avoid conflicts in tracking data between the old and new flight designations.

The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft where it was the only item funded for development. The first (STS-1) of four orbital test flights occurred in 1981, leading to operational flights (STS-5) beginning in 1982. Five complete Space Shuttle orbiter vehicles were built and flown on a total of 135 missions from 1981 to 2011, launched from the Kennedy Space Center (KSC) in Florida. Operational missions launched numerous satellites, interplanetary probes, and the Hubble Space Telescope (HST), conducted science experiments in orbit, participated in the Shuttle-Mir program with Russia, and participated in construction and servicing of the International Space Station (ISS). The Space Shuttle fleet's total mission time was 1,323 days.Space Shuttle components include the Orbiter Vehicle (OV) with three clustered Rocketdyne RS-25 main engines, a pair of recoverable solid rocket boosters (SRBs), and the expendable external tank (ET) containing liquid hydrogen and liquid oxygen. The Space Shuttle was launched vertically, like a conventional rocket, with the two SRBs operating in parallel with the orbiter's three main engines, which were fueled from the ET. The SRBs were jettisoned before the vehicle reached orbit, while the main engines continued to operate, and the ET was jettisoned after main engine cutoff and just before orbit insertion, which used the orbiter's two Orbital Maneuvering System (OMS) engines. At the conclusion of the mission, the orbiter fired its OMS to deorbit and reenter the atmosphere. The orbiter was protected during reentry by its thermal protection system tiles, and it glided as a spaceplane to a runway landing, usually to the Shuttle Landing Facility at KSC, Florida, or to Rogers Dry Lake in Edwards Air Force Base, California. If the landing occurred at Edwards, the orbiter was flown back to the KSC atop the Shuttle Carrier Aircraft (SCA), a specially modified Boeing 747.

The first orbiter, Enterprise, was built in 1976 and used in Approach and Landing Tests (ALT), but had no orbital capability. Four fully operational orbiters were initially built: Columbia, Challenger, Discovery, and Atlantis. Of these, two were lost in mission accidents: Challenger in 1986 and Columbia in 2003, with a total of 14 astronauts killed. A fifth operational (and sixth in total) orbiter, Endeavour, was built in 1991 to replace Challenger. The three surviving operational vehicles were retired from service following Atlantis's final flight on July 21, 2011. The U.S. relied on the Russian Soyuz spacecraft to transport astronauts to the ISS from the last Shuttle flight until the launch of the Crew Dragon Demo-2 mission in May 2020.