STS-95 was a Space Shuttle mission launched from Kennedy Space Center, Florida on 29 October 1998, using the orbiter Discovery. It was the 25th flight of Discovery and the 92nd mission flown since the start of the Space Shuttle program in April 1981. It was a highly publicized mission due to former Project Mercury astronaut and United States Senator John H. Glenn Jr.'s return to space for his second space flight. At age 77, Glenn became the oldest person to go into space, a record that remained unbroken for 23 years until 82-year-old Wally Funk flew on a suborbital flight on Blue Origin NS-16, launching on July 20, 2021, which in turn was broken by William Shatner at age 90 on October 13, 2021. Glenn, however, remains the oldest person to reach Earth orbit. This mission is also noted for inaugurating ATSC HDTV broadcasting in the U.S., with live coast-to-coast coverage of the launch. In another first, Pedro Duque became the first Spaniard in space.

The mission's objectives involved investigating life-sciences experiments, using the SpaceHab module to perform these experiments on Senator Glenn. Scientific objectives on this mission were not limited to furthering an understanding of the human body, but also to increase astronomical understanding with regards to the Sun, and how it affects life on Earth. The Spartan 201 spacecraft was released by the crew, flying free from the Shuttle, studying the acceleration of the solar wind that originates in the Sun's solar corona. The mission lasted just under ten days, with Discovery completing its voyage by landing at the Kennedy Space Center's Shuttle Landing Facility.

The launch was rare in that the official launch weather forecast provided by the 45th Weather Squadron was 100 percent for favorable weather for launch as well as the Shuttle Landing Facility.

Bill Clinton became the second incumbent U.S. president to witness a rocket launch, joined by his wife Hillary on the roof of the Vehicle Assembly Building; and the only one to attend a Shuttle launch (President Richard Nixon witnessed the launch of Apollo 12).

The primary objectives included conducting a variety of science experiments in the pressurized Spacehab module, the deployment and retrieval of the Spartan free-flyer payload, and operations with the HST Orbital Systems Test (HOST) and the International Extreme Ultraviolet Hitchhiker (IEH) payloads carried in the payload bay.

Spacehab
The Spacehab module flown on STS-95 was provided by Spacehab, Inc., a private company. The Spacehab system provided additional pressurized workspace for experiments, cargo and crew activities. Spacehab modules supported various Shuttle science missions along with several of the joint Shuttle-Mir missions.

For STS-95, a single-module Spacehab flew in the forward portion of Discovery's payload bay, with the crew gaining access to the module through the airlock tunnel system. A variety of experiments sponsored by NASA, the Japanese Space Agency (NASDA) and the European Space Agency (ESA) focused on life sciences, microgravity sciences and advanced technology during the flight.

Spartan
The Spartan 201-5 free-flyer was deployed and retrieved using the Shuttle's mechanical arm. It was designed to investigate physical conditions and processes of the hot outer layers of the Sun's atmosphere, or solar corona. While deployed from the Shuttle, Spartan gathered measurements of the solar corona and solar wind. NASA expected that information collected during this mission would lead to a much better understanding of the solar winds that directly influence orbiting satellites and weather conditions on Earth which in turn impact television and phone communications. This was the fifth flight for the Spartan payload; it originally flew on the STS-56 mission in April 1993. On its previous mission, STS-87 in November 1997, Spartan developed problems shortly after being deployed from the Shuttle and had to be brought back into the Shuttle's payload bay by spacewalk. These problems were due with the attitude control system for fine pointing toward solar targets, and Spartan was cleared for use again on STS-95. Its mission was to successfully perform the same experiments from the previous year.