STS-41-B (Challenger)

Background

By the early 1980s, NASA engineers and astronauts had long envisioned a device that would allow a spacewalking crew member to operate entirely without a tether — to become, in effect, a self-contained human spacecraft. The hardware that would make this possible was the Manned Maneuvering Unit (MMU), a nitrogen-propelled jetpack designed to attach to the back of a spacesuit and give a single astronaut full six-degrees-of-freedom control in the vacuum of space. Development of the MMU proceeded through the late 1970s and into the shuttle era, and STS-41-B was selected as its operational debut.

The mission launched aboard Space Shuttle *Challenger* on 3 February 1984, carrying a crew of five: Commander Vance Brand, Pilot Robert Gibson, and Mission Specialists Bruce McCandless, Ronald McNair, and Robert Stewart. Brand was a veteran of the Apollo-Soyuz Test Project; the others were making their first spaceflights. McCandless, however, was no newcomer to the MMU concept — he had been intimately involved in its development for more than a decade, making him the natural choice to fly it first. The mission's primary objectives included the deployment of two commercial communications satellites and a comprehensive evaluation of the MMU during extravehicular activity (EVA).

The Flight

*Challenger* reached orbit approximately eight and a half minutes after liftoff, and the crew quickly settled into an ambitious flight plan. Early in the mission, the crew deployed the Westar VI and Palapa B2 communications satellites. Both deployments were executed correctly, but the satellites' perigee kick motors misfired, leaving them stranded in a uselessly low orbit rather than the intended geostationary altitude. The loss of two expensive commercial payloads was a significant setback, though it would eventually prompt a dramatic salvage mission on a later flight.

Despite the satellite failures, the mission pressed forward with what many in the astronaut corps and the engineering community considered the most consequential objective of all: the untethered EVA evaluations.

The Untethered Spacewalk

At approximately 69 hours and 26 minutes into the mission, the payload bay doors of *Challenger* were open and the stage was set for a moment unlike anything in the history of human spaceflight. Bruce McCandless — suited in the Extravehicular Mobility Unit and with the MMU latched to his back — eased away from the shuttle's airlock, fired the MMU's nitrogen thrusters, and flew free. He was not attached to the vehicle by any line or cable. He was alone in space.

McCandless maneuvered to distances of roughly 300 feet and then approximately 320 feet from *Challenger*, making him the first human being to orbit Earth independently of a spacecraft — what the press quickly dubbed the first human satellite. The image captured by a camera aboard *Challenger* showing McCandless as a lone figure against the blue curve of Earth and the absolute black of space became one of the most reproduced photographs in the history of exploration. The entire exercise was conducted with methodical precision; McCandless moved outward incrementally, verifying the MMU's controls and handling qualities at each station before proceeding farther.

Mission Specialist Robert Stewart also flew the MMU during the same EVA sequence, providing additional handling-quality data and demonstrating that the device could be reliably operated by more than one crew member. A second set of EVAs later in the mission gave both McCandless and Stewart additional opportunities to evaluate the unit's performance, including tests with a device intended to simulate the capture of a free-floating satellite. The EVA evaluations were judged a thorough success.

Landing and Legacy

After a mission lasting just over eight days, *Challenger* performed its deorbit burn and descended toward Florida. At approximately 191 hours and 30 minutes after launch, the orbiter touched down at Kennedy Space Center — the first shuttle landing at KSC rather than at Edwards Air Force Base in California. That touchdown itself was a milestone, validating the Florida landing strip and reducing the logistical cost and delay of ferrying the orbiter back across the country after each flight.

The legacy of STS-41-B is anchored in the MMU and what it represented. The device subsequently enabled the capture and repair of satellites that would otherwise have been lost, most notably during STS-51-A later in 1984 when Westar VI and Palapa B2 — the same two satellites that had been stranded on this mission — were physically retrieved by astronauts flying the MMU. In that sense, the failure and the triumph of STS-41-B were inextricably linked.

More broadly, McCandless's solo flight crystallized something that had previously existed only in concept: that a human being, with the right hardware, could operate as an independent spacecraft. The photograph of him suspended in the void became a cultural shorthand for the audacity of human spaceflight, appearing on magazine covers, in textbooks, and in museum retrospectives for decades. The MMU itself was eventually retired from operational use and replaced by the Simplified Aid for EVA Rescue (SAFER), a smaller emergency-only device — a sign not that the concept had failed, but that the shuttle program had matured and the risk calculus had changed.

For Bruce McCandless, Ronald McNair, Robert Stewart, Robert Gibson, and Vance Brand, STS-41-B represented a mission that exceeded expectations in the ways that mattered most. The satellites were lost; the spacewalks were flawless. History remembered the latter.