The primary payload of STS-26 was the NASA Tracking and Data Relay Satellite-3 (TDRS-3) attached to an Inertial Upper Stage (IUS) that placed it into geosynchronous orbit; it became the second TDRS deployed. Secondary payloads on the mission included the Physical Vapor Transport of Organic Solids (PVTOS), Protein Crystal Growth (PCG), Infrared Communications Flight Experiment (IRCFE), Aggregation of Red Blood Cells (ARC) Isoelectric Focusing Experiment (IFE), Mesoscale Lightning Experiment (MLE), Phase Partitioning Experiment (PPE), Earth-Limb Radiance Experiment (ELRAD), Automated Directional Solidification Furnace (ADSF) and two Shuttle Student Involvement Program (SSIP) experiments. The Orbiter Experiments Autonomous Supporting Instrumentation System-I (OASIS-I) recorded variety of environmental measurements during various inflight phases of orbiter.
Detailed Supplementary Objectives (DSOs) were also performed on this mission. A DSO is a NASA-sponsored investigation that is performed by SpaceShuttle crewmembers, who serve as the test subjects. These studies are designed to 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.