Space Shuttle Discovery launched on April 8, 1993, on a nine-day flight designated as STS-56. The mission's primary goal was the second flight of the Atmospheric Laboratory for Science and Applications (ATLAS 2) and the fifth flight of the Shuttle Solar Backscatter Ultraviolet experiment (SSBUV-5). 

ATLAS 2 consisted of instruments from NASA, France, Germany and Belgium that were flown on ATLAS 1 in 1992. The core instruments consisted of:

• Active Cavity Radiometer Irradiance Monitor (ACRIM)
• Measurement of the Solar Constant (SOLCON)
• Solar Spectrum Measurement (SOLSPEC)
• Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)
• Atmospheric Trace Molecule Spectroscopy (ATMOS)
• Millimeter-Wave Atmospheric Sounder (MAS). 

STS-56 also carried the Spartan-201 free-flying payload, the Solar Ultraviolet Experiment (SUVE), and the Shuttle Amateur Radio Experiment (SAREX II).

In-cabin experiments included:

• the Hand-Held, Earth-Oriented, Real-Time, Cooperative, User-Friendly, Location-Targeting and Environmental System (HERCULES), developed by the Naval Research Lab (NRL) which allowed astronauts to point a camera at Earth's surface and record the latitude and longitude of the feature; 

• the Radiation Monitoring Equipment-III (RME-III), an experiment that measured the exposure of ionizing radiation on the Space Shuttle; 

• the Cosmic Radiation Effects and Activation Monitor (CREAM), designed to collect data on cosmic ray energy loss;

• the Air Force Maui Optical Site (AMOS), which recorded the shuttle glow phenomena. 

Also onboard STS-56 was the Commercial Material Dispersion Apparatus (MDA) ITA Experiments (CMIX-2), a set of 30 experiments for research on microgravity effects on biology; the Space Tissue Loss-3 (STL-3); and the Physiological and Anatomical Rodent Experiment (PARE-03).