STS-40

In June 1991, the Space Shuttle Columbia lifted off for its eleventh flight, a nine-day mission designated STS-40. Onboard was the Spacelab module configured for Spacelab Life Sciences 1 (SLS-1), which marked the fifth Spacelab mission overall and the first ever focused entirely on biology. This flight also made history as the first space mission to include three women among its crew.

The launch was originally scheduled for May 22, 1991, but was scrubbed less than two days prior when a vendor analysis flagged a leaking liquid hydrogen transducer in the orbiter’s main propulsion system. Engineers worried that any of the nine liquid hydrogen or liquid oxygen transducers jutting into fuel and oxidizer lines might snap off and get sucked into the engine turbopumps, potentially causing a failure. Additional problems emerged: one of Columbia’s five general-purpose computers failed completely, as did a multiplexer-demultiplexer controlling hydraulics, ordnance, and Orbital Maneuvering System/Reaction Control System functions in the aft compartment. Both the computer and the multiplexer-demultiplexer were replaced and tested. One liquid hydrogen and two liquid oxygen transducers were swapped out upstream, near the 17-inch disconnect area protected by an internal screen. Three liquid oxygen transducers in the engine manifold were also replaced, while three liquid hydrogen transducers in that area were removed and their openings plugged. The launch was reset for June 1, 1991, at 8:00 a.m. EDT, but was postponed again after several failed attempts to calibrate inertial measurement unit 2. That unit was swapped and retested, pushing the launch to June 5. Columbia finally launched successfully at 9:24:51 a.m. EDT on June 5, 1991, with a launch weight of 114,290 kg. IMAX cameras captured the liftoff, and footage later appeared in the 2015 documentary *Journey to Space*.

As the fifth dedicated Spacelab mission and the first solely for life sciences, SLS-1 used the habitable module to conduct the most detailed and interconnected physiological measurements in space since the Skylab missions of 1973–1974. The subjects included humans, 30 rodents, and thousands of tiny moon jellies (*Aurelia aurita*). Of the 18 primary investigations, ten involved humans, seven involved rodents, and one used jellyfish.