The primary purpose of this mission was the deployment of the newly designed Hubble Space Telescope (HST). HST is the largest on-orbit observatory ever built and is capable of imaging objects up to 14 billion light years away. Unhampered by Earth's atmospheric distortion, resolution of HST images is 7 to 10 times greater than images from Earth-based telescopes. Orbiting at an altitude of 330 nautical miles, the telescope observes celestial sources such as quasars, galaxies, and gaseous nebulae. HST also monitors atmospheric and surface phenomena of the planets in Earth's solar system.
Life Sciences experiments on this mission included multiple Detailed Supplementary Objectives (DSOs). A DSO is a NASA-sponsored investigation performed by Space Shuttle crewmembers who serve as the test subjects. These studies required 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 included the IMAX Cargo Bay Camera, the Ascent Particle Monitor, the Protein Crystal Growth Experiment, the Radiation Monitoring Equipment-III, Investigations into Polymer Membrane Processing, the Shuttle Student Involvement Program Investigation of Arc and Ion Behavior in Microgravity experiment, and the Air Force Maui Optical Site experiment.
STS-31's landing was the first in which carbon brakes were used. The Space Shuttle Discovery touched down at Edwards Air Force Base, California on April 29, 1990.