STS-66 further advanced comprehensive effort to collect data about sun's energy output, chemical makeup of the Earth's middle atmosphere, and how these factors affect global ozone levels.

Also considered a primary payload was the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere-Shuttle Pallet Satellite (CRISTA-SPAS), continuing joint NASA-German Space Agency (DARA, now the DLR) series of scientific missions.

Millimeter Wave Atmospheric Sounder (MAS), collected nine hours of observations, measuring distribution of water vapor, chlorine monoxide and ozone at altitudes between 12 and 60 miles (20 to 100 kilometres (62 mi)), before computer malfunction halted instrument operations.

Flying at distance of about 25 to 44 miles (40 to 70 kilometres (43 mi)) behind the Shuttle, payload collected data for more than eight days before being retrieved and returned to the cargo bay.

For retrieval of CRISTA-SPAS, a different approach method to the spacecraft was successfully tested as a prelude to the upcoming U.S. Shuttle/Russian Space Station Mir docking flights.

Called R-Bar approach, it is expected to save propellant while reducing risk of contamination to Mir systems from orbiter thruster jet firings.