Columbia launched from Kennedy Space Center on October 20, 1995 at 9:53 AM EDT and landed at Kennedy on November 5 at 6:45 AM EST. The shuttle orbited 256 times at an altitude of 150 nautical miles at an inclination of 39 degrees and travelled 6.6 million miles. The mission lasted 15 days, 21 hours, 52 minutes, and 28 seconds.
At almost 16 days this was the longest mission to date. The crew took time out to tape the ceremonial first pitch for Game Five of baseball World Series, marking first time the thrower was not actually in the ballpark for the pitch.
STS-73 marked the second flight of U.S. Microgravity Laboratory (USML) and built on the foundation of its predecessor, which flew on Columbia during Mission STS-50 in 1992. Research during USML-2 concentrated within the same overall areas of USML-1, with many experiments flying for a second time. The crew divided into two teams to work around the clock in a 23-foot (seven-meter) long Spacelab module located in Columbia’s payload bay.
Research was conducted in five areas: Fluid physics; materials science; biotechnology; combustion science; and commercial space processing.
The experiments went smoothly. In some cases, results re-confirmed existing theories, while in other cases results were new and unique. Highlights included unprecedented results from the Surface Tension Driven Convection Experiment, which flew for second time and studied in great detail basic fluid mechanics and heat transfer of thermocapillary flows, motions created within fluids by non-uniform heating of their free surfaces. Oscillations observed on USML-2 samples had never been observed on Earth, and researchers controlling the experiment from the ground were able to pinpoint when fluid flows transitioned from stable to unstable. The research had direct applications on Earth, in that unwanted fluid flows during melting and resolidifying can create defects in high-tech crystals, metals, alloys and ceramics.
Flying for first time was the Fiber Supported Droplet Combustion experiment. More than 25 droplets of a variety of fuels were ignited, confirming theories about how fuels burn in microgravity. Results revealed larger droplet extension diameter — size of drop as it burns out — than are capable of being studied on Earth, with burning times 10 times longer. Data confirmed scientific predictions about burn rate and the amount of fuel left over after the fire goes out. This allowed investigators to refine old theories and possibly develop new ones about byproducts such as soot and smog.
Five small potatoes were grown from tubers in the Astroculture plant growth facility. USML-2 marked the final test flight of the Astroculture hardware, with the unit set to become available commercially for sale or lease. Technologies incorporated in the Astroculture hardware design were already are finding application on Earth. For example, the technology behind light-emitting diodes (LEDs) that provide high levels of light on-orbit within limited electrical power found its way into energy-efficient lighting systems for large-scale commercial plant nurseries. Successful on-orbit growth demonstrated Astroculture’s usefulness as a plant growth facility and showed edible foods could be grown in space.
A record number of Protein Crystal Growth (PCG) samples — around 1,500 — were flown on USML-2 and initial results indicated many had produced crystals which will be further studied after landing. Other crystal growth experiments were equally successful. In the Crystal Growth Furnace, which flew for first time on USML-1, a crystal was grown for the first time as a liquid bridge to minimize contact with the container wall, thus decreasing the number of defects in crystal. Eight semiconductor crystals were grown, and also a very thin crystal and two crystals which could lead to products such as computer chips that were faster and used less power than traditional computer chips.
Columbia was crewed by Commander Kenneth D. Bowersox, Pilot Kent V. Rominger, Payload Commander Kathryn C. Thornton, and Mission Specialists Catherine G. Coleman, Michael E. Lopez-Alegria, Payload Specialists Fred W. Leslie and Albert Sacco, Jr.