The primary payload aboard STS-73 was the United States Microgravity Laboratory (USML-2). USML-2 continued a cooperative effort between the United States government, universities and industry to study science and technology in microgravity. Some of the experiments carried on the USML-2 payload were suggested by the results of the first USML mission that flew aboard Columbia during the STS-50 mission in 1992. USML-1 provided insights into theoretical models of fluid physics, the role of gravity in combustion and flame spreading, and how gravity affects the formation of semiconductor crystals. USML-2 built on that foundation. Technical knowledge gained from USML-1 was incorporated into the mission plan to enhance procedures and operations. Where possible, investigators refined their hardware to increase scientific understanding of basic physical processes on Earth and in space, as well as prepared for more advanced operations aboard the International Space Station and other future space programs. The experiments carried as part of the USML-2 payload covered a variety of scientific disciplines including fluid physics, materials science, biotechnology and combustion science.
Life Sciences experiments performed during this mission included several Detailed Supplementary Objectives (DSOs). A DSO is a NASA-sponsored investigation performed by Space Shuttle crewmembers, who also serve as the test subjects. These studies require minimal crew time, power and stowage. Biomedical DSOs focus on operational concerns, including space motion sickness, cardiovascular deconditioning, muscle loss, changes in coordination and balance strategies, radiation exposure, pharmacokinetics and changes in the body's biochemistry.
Other payloads carried on board STS-73 were the Orbital Acceleration Research Experiment, Space Acceleration Measurement System, Three Dimensional Microgravity Accelerometer, Suppression of Transient Accelerations By Levitation Evaluation, and the High-Packed Digital Television Technical Demonstration System.
The Shuttle Columbia touched down after a successful 16-day mission at Kennedy Space Center in Florida on November 5, 1995.