STS-40 (Columbia / SLS-1)

Background

By the late 1980s, NASA's Space Shuttle programme had established Spacelab — the pressurised research module built by the European Space Agency and carried in the orbiter's payload bay — as its primary platform for orbital science. A succession of Spacelab missions had investigated materials processing, astronomy, and atmospheric physics, yet one domain had remained without a dedicated flight: the life sciences. Researchers studying the physiological consequences of spaceflight had long argued that a full mission devoted entirely to biomedical investigation was necessary to move beyond the piecemeal data collected as secondary experiments on earlier flights. STS-40, flying under the payload designation Spacelab Life Sciences-1 (SLS-1), was the answer to that argument.

Planning for a life-sciences Spacelab had begun in the early 1980s, but the 1986 Challenger accident forced a wholesale restructuring of the Shuttle manifest and delayed SLS-1 by several years. When the mission was finally manifested aboard Columbia — the heaviest and most capable orbiter, well suited to the mass demands of a fully outfitted Spacelab module — it carried with it the accumulated aspirations of an entire research community. The scientific objectives centred on understanding how the cardiovascular system, the musculoskeletal system, the neurovestibular system, and kidney function each respond to the removal of gravitational loading. Answering those questions was considered essential both for planning longer-duration human missions and for advancing fundamental physiology.

Crew and Preparation

The seven-person crew was selected to blend operational expertise with direct scientific competence. Commander Bryan O'Connor and Pilot Sidney Gutierrez handled vehicle operations, while Mission Specialists James Bagian, Tamara Jernigan, and Rhea Seddon, along with Payload Specialists Drew Gaffney and Millie Hughes-Fulford, carried primary responsibility for the science programme. Bagian was a physician, Seddon a surgeon, Gaffney a cardiologist, and Hughes-Fulford a cell biologist — an unusually deep concentration of biomedical expertise on a single flight. Crucially, the crew were not merely operators of the experiments: they were also the subjects. Each astronaut underwent baseline measurements in the months before launch, establishing individual physiological benchmarks against which in-flight and post-flight data could be compared.

Preparation was correspondingly rigorous. The crew trained extensively on the experimental protocols, practising blood draws, urine collections, lower-body negative-pressure tests, and the careful handling of the rodent and jellyfish specimens that formed the animal component of the payload. More than a dozen American research institutions contributed experiments to the manifest, and coordinating that scientific programme while maintaining crew proficiency in Shuttle systems represented a significant organisational challenge.

The Flight

Columbia lifted off from Kennedy Space Center on 5 June 1991. Within the first nine minutes of flight the vehicle reached orbit, and the transition to weightlessness that the entire mission had been designed to study began immediately. The Spacelab module was activated, and the crew settled into a demanding around-the-clock schedule divided across two shifts, ensuring that experiments continued without interruption throughout the day.

The investigations addressed several interlocking research themes. Cardiovascular studies examined how fluid shifts toward the upper body in weightlessness affect heart size, stroke volume, and blood pressure regulation. Neurovestibular experiments probed the confusion the inner ear experiences when the familiar gravitational reference disappears — work directly relevant to the space motion sickness that affects a significant proportion of astronauts in their first days on orbit. Renal and hormonal studies tracked changes in fluid and electrolyte balance. The musculoskeletal programme monitored early indicators of bone and muscle loss. Complementing the human investigations, rodents carried aboard provided tissue samples that could not ethically be obtained from crew members, and jellyfish larvae were used to study the development of gravity-sensing organs in a weightless environment.

The pace was relentless. Crew members rotated through the role of subject and experimenter, collecting samples and operating equipment while simultaneously submitting to the very measurements they were administering to one another. Despite the workload, the mission proceeded smoothly. After a flight lasting approximately nine days, Columbia performed its deorbit burn and landed at Edwards Air Force Base on 14 June 1991, completing a mission elapsed time of just over 218 hours.

Legacy

STS-40 occupied a landmark position in the history of human spaceflight research. As the first Spacelab mission dedicated entirely to life sciences, it demonstrated that a Shuttle crew could sustain a comprehensive, hypothesis-driven biomedical research programme across a multi-day flight — a proof of concept that shaped how NASA designed subsequent life-sciences missions. The data gathered informed preparations for long-duration stays aboard Mir and, later, the International Space Station, where the physiological challenges documented during SLS-1 would be confronted on a far greater timescale.

The mission also had a broader cultural significance. The crew's composition — including two female mission specialists and the first female payload specialist from the biological sciences — reflected the expanding diversity of the astronaut corps and the growing recognition that life-sciences research required scientists who were themselves practitioners in the field. Hughes-Fulford's cell-biology experiments, in particular, opened lines of inquiry into how microgravity affects cellular behaviour that continued long after Columbia returned to Earth.

A follow-on mission, STS-58 (SLS-2), flew in 1993 and built directly on the protocols and lessons of STS-40, extending the duration and expanding the research questions. Together the two flights established the methodological foundation for human physiological research in orbit that persists to the present day. STS-40 remains the definitive early demonstration that the Space Shuttle could serve not only as a transportation system but as a genuine orbiting laboratory for the scientific study of human life itself.