STS-31 — Hubble Deployment

Background

By the late 1980s, astronomers had waited decades for a large optical telescope positioned above Earth's distorting atmosphere. The concept, long championed by astronomer Lyman Spitzer, had finally taken physical form: the Hubble Space Telescope, a 2.4-metre reflecting telescope built jointly by NASA and the European Space Agency, capable — in theory — of resolving objects some seven times more sharply than the best ground-based instruments of the era. Delivering it safely to orbit required solving an unusual logistical problem. Hubble's operating altitude of roughly 615 kilometres was substantially higher than a typical Shuttle mission, demanding a near-maximum performance ascent and leaving the crew with a tighter safety margin than most of their colleagues had faced. The assignment fell to Space Shuttle *Discovery* and a five-person crew selected for both piloting precision and scientific depth.

Commander Loren Shriver and Pilot Charles Bolden were responsible for flying *Discovery* to an orbit no Shuttle had previously reached. Mission Specialists Bruce McCandless and Kathryn Sullivan — both veterans of earlier spacewalks — were trained to conduct contingency EVAs if Hubble's solar arrays or antennas failed to deploy automatically. Steven Hawley, a veteran astronaut and astronomer, was assigned to operate the Shuttle's robotic arm and carry out the telescope's release. Together they represented one of the more technically diverse crews the Shuttle program had assembled.

Ascent and Orbit

*Discovery* lifted off from Kennedy Space Center's Launch Pad 39B on 24 April 1990. The launch had already endured several delays — a hydrogen leak, a faulty sensor, and unfavorable weather had all pushed the date back across preceding days — making the eventual liftoff a moment of considerable relief for the team. Approximately eight minutes and thirty-four seconds after launch, the Shuttle reached orbit, having climbed to an altitude that set a record for a crewed American spacecraft at the time. The high orbit was essential: Hubble needed to sit above the charged-particle environment that would have degraded its sensitive instruments at lower altitudes, and its planned servicing missions would need to find it where it was left.

Once on orbit, the crew opened the payload bay doors to reveal the telescope secured in its cradle — a cylinder roughly the size of a school bus, wrapped in the silver and white thermal blankets that would become one of the most recognizable forms in the history of spaceflight.

Deployment

The central event of the mission came approximately nineteen and a half hours after launch. Hawley used the Remote Manipulator System arm to lift Hubble carefully out of the payload bay and raise it into free space. The telescope's solar arrays were commanded to unfurl to provide it with power; one of the two arrays initially balked, prompting a tense period of troubleshooting before it eventually deployed. Sullivan and McCandless stood ready in their suits, prepared to go outside and assist manually if necessary, but a revised command sequence solved the problem without requiring an EVA. With both arrays extended and drawing power from the Sun, Hawley released Hubble into its own independent orbit — a moment that marked the formal beginning of what NASA hoped would be a decades-long era of discovery.

The release was visually striking: the great telescope drifting away from *Discovery*'s payload bay against the blackness of space and the curve of the Earth below. Hawley, an astronomer by training, later described the sight in terms that reflected both professional appreciation and simple awe, though the crew maintained the measured composure characteristic of Shuttle-era mission culture throughout.

Complications and the Return

In the days following deployment, ground controllers began the painstaking process of activating Hubble's systems and pointing the telescope at calibration targets. It was during this checkout phase — after *Discovery* had already departed — that engineers discovered the telescope's primary mirror had been ground to the wrong shape, a defect known as spherical aberration. The flaw was extraordinarily small in physical terms, a deviation of roughly 2.2 micrometres at the mirror's edge, but its optical consequences were severe: Hubble could not focus starlight to the sharp point its designers had promised. The error originated in the mirror-polishing process and had gone undetected during ground testing.

*Discovery* itself landed at Edwards Air Force Base approximately five days after launch, completing a mission that had proceeded nearly flawlessly from the Shuttle's perspective. The crew had delivered the telescope precisely where it needed to be. What awaited Hubble in orbit, however, would require years of effort to remedy.

Legacy

The spherical aberration that greeted Hubble's first light images threatened to transform one of NASA's greatest achievements into an embarrassment. Instead, it became the premise for one of the agency's most celebrated recoveries. In December 1993, the crew of STS-61 installed corrective optics — a device called COSTAR and a replacement camera — restoring Hubble to its designed capability. The images that followed redefined what astronomy could show the world: the Hubble Deep Field, the expansion rate of the universe measured through distant supernovae, the atmospheres of exoplanets, the surfaces of Pluto and distant moons, and pillars of star-forming gas that entered popular culture as icons of cosmic scale.

STS-31 is the indispensable first chapter of that story. Without the precision of *Discovery*'s ascent, the careful choreography of Hawley's robotic arm work, and the readiness of the EVA crew to intervene at a critical moment, none of the subsequent servicing missions or scientific returns would have been possible. The mission placed into orbit an instrument that would go on to produce more than a million observations, contribute to thousands of scientific papers, and fundamentally alter humanity's understanding of the universe — beginning with a single, careful release, nineteen and a half hours into the flight.