Selected by NASA in January 1990, Helms became an astronaut in July 1991. She flew on
STS-54 (1993),
STS-64 (1994),
STS-78 (1996),
STS-101 (2000) and served aboard the
International Space Station as a member of the
ISS Expedition 2 crew (2001). A veteran of five space flights, Helms logged 5,064 hours in space, including an
EVA of 8 hours and 56 minutes (world record at the time).
STS-54 Endeavour, January 13–19, 1993. The primary objective of this mission was the deployment of a $200-million NASA Tracking and Data Relay Satellite (TDRS-F). A diffuse X-ray spectrometer (DXS) carried in the payload bay, collected over 80,000 seconds of quality X-ray data that will enable investigators to answer questions about the origin of the Milky Way galaxy. The crew demonstrated the physics principles of everyday toys to an interactive audience of elementary school students across the United States. A highly successful
extra-vehicular activity (EVA) resulted in many lessons learned that will benefit International Space Station assembly. Mission duration was 5 days, 23 hours, 38 minutes, 17 seconds.
STS-64 Discovery, September 9–20, 1994. On this flight, Helms served as the flight engineer for orbiter operations and the primary RMS operator aboard
Space Shuttle. The major objective of this flight was to validate the design and operating characteristics of Lidar in Space Technology Experiment (LITE) by gathering data about the Earth's troposphere and stratosphere. Additional objectives included the deploy and retrieval of
SPARTAN-201, a free-flying satellite that investigated the physics of the
solar corona, and the testing of a new EVA maneuvering device. The Shuttle Plume Impingement Flight Experiment (SPIFEX) was used to collect extensive data on the effects of jet thruster impingement, in preparation for proximity tasks such as space station docking. Mission duration was 10 days, 22 hours, 51 minutes.
STS-78 Columbia, June 20 to July 7, 1996, Helms was the payload commander and flight engineer aboard
Columbia, on the longest Space Shuttle mission to date (later that year the STS-80 mission broke its record by nineteen hours). The mission included studies sponsored by ten nations and five space agencies, and was the first mission to combine both a full microgravity studies agenda and a comprehensive life science investigation. The Life and Microgravity Spacelab mission served as a model for future studies on board the International Space Station. Mission duration was 16 days, 21 hours, 48 minutes.
STS-101 Atlantis, May 19–29, 2000, was a mission dedicated to the delivery and repair of critical hardware for the International Space Station. Helms’s prime responsibilities during this mission were to perform critical repairs to extend the life of the Functional Cargo Block (FGB). In addition, she had prime responsibility of the onboard computer network and served as the mission specialist for rendezvous with the ISS. Mission duration was 9 days, 20 hours and 9 minutes.
Expedition 2 March 8 to August 22, 2001, was a mission to the International Space Station and Helms was a member of the second crew to inhabit the International Space Station Alpha. The
Expedition 2 crew (two American astronauts and one Russian cosmonaut) launched on March 8, 2001, on board
STS-102 Discovery and successfully docked with the station on March 9, 2001. The
Expedition 2 crew installed and conducted tests on the Canadian-made Space Station Robotic arm (SSRMS), conducted internal and external maintenance tasks (Russian and American), in addition to medical and science experiments. During her stay on board, Helms installed the airlock (brought up on the
STS-104 mission) using the SSRM. She and her crewmates also performed a 'fly around' of the Russian
Soyuz spacecraft and welcomed the visiting Soyuz crew that included the first
space tourist,
Dennis Tito. On March 11 she performed a world-record 8 hour and 56 minute spacewalk to install hardware to the external body of the laboratory module, that stood until 17 December 2024, when
Cai Xuzhe broke the record with
Song Lingdong for the longest spacewalk in human history, of 9 hours and 6 minutes. Helms spent a total of 163 days aboard the space station. She returned to Earth with the
STS-105 crew aboard
Discovery on August 22, 2001. ==Awards and decorations==