Thirty years ago this week, in February 1984, NASA launched its 10th shuttle mission, with a five-man crew and a relatively “vanilla” pair of commercial communications satellites to be deployed from Challenger. However, that was where the “ordinary” nature of Mission 41B—the first flight to be officially redesignated with a somewhat clumsy nomenclature of letters and numbers—ended, for in pride of place on the crew’s patch was a jet-propelled space suit backpack, known as the Manned Maneuvering Unit (MMU). Described in yesterday’s history article, it would be flown by astronauts Bruce McCandless and Bob Stewart, during which time they would become the first “untethered” spacewalkers in history. And McCandless’ foray would yield one of the most famous space photographs ever taken; a photograph which ended up on the covers of National Geographic and Aviation Week and which, even 30 years later, still retains pride of place on many desktop wallpapers, screensavers, and pieces of wall art. It even sparked a bizarre copyright case involving the singer Dido.
For Bruce McCandless, who backed himself into the MMU in Challenger’s payload bay, early on 7 February 1984, it represented “a heck of a big leap” in terms of spacewalking technology and the culmination of his own personal odyssey. It was familiar ground for McCandless, who admitted that he was “probably not a representative EVA trainee” and had been “grossly over-trained.” Throughout the 1970s and 1980s he took every opportunity to get into a space suit, an altitude chamber, or a water tank and had participated extensively in EVA simulations on Skylab, Solar Max, and the Hubble Space Telescope.
In spite of their complexity, McCandless and Bob Stewart’s EVAs proved successful and the space suits and MMUs performed admirably. The only “nuisances” were static on the communication channels and difficulties attaching checklists to the suits’ arms. “In spite of the sound-does-not-travel-through-a-vacuum’ tenet of physics,” McCandless explained to this author in a March 2006 email correspondence, “it was noisy up there, thanks to two independent radio channels and plenty of people wanting to talk to me!” Then, just before leaving Challenger’s airlock, Stewart reported a caution and warning alarm, which indicated a pressure increase in his suit’s sublimator. However, after being switched off and back on again, it performed normally.
These subtle problems did not distract from the triumph of McCandless’ Buck Rogers-style flight that day. Despite the sci-fi analogy, said Mission 41B’s commander, Vance Brand, the MMU “didn’t have the person zooming real fast. It was a huge device that was very well-designed and redundant, so that it was very safe, but it moved along at about one to two miles per hour.” At his furthest distance from the shuttle, McCandless was 300 feet (90 meters) away, politely offering to clean Challenger’s cockpit windows as he floated over the flight deck. Watching intently from inside, an admiring Brand declined the offer.
Also watching intently, camera in hand, was Robert “Hoot” Gibson, Challenger’s pilot, and the person who snapped the photograph which would make history as one of the top five most-requested images from NASA. In an interview for the Smithsonian in 2001, he recalled the astonishing sight of McCandless flying the MMU. “Bruce first did a couple of brief test flights in the cargo bay, staying very close in case anything should go wrong,” Gibson explained. “As we were approaching sunrise on one of our daylight passes, he was cleared to make the translation out to 300 feet from the Shuttle.” Grabbing his Hasselblad, Gibson began shooting frame after frame. Since Challenger’s orientation was some 30 degrees from the vertical, McCandless appeared at a similar angle with respect to Earth’s horizon.
Gibson knew that any one of his images could easily make the cover of Aviation Week (they actually made two) and remembered taking multiple light settings and tweaking the focus five or six times for each photograph, before squeezing the button. The famous shot would come to be known as “Backpacking,” and, even today, McCandless possesses a goofy version in his home, in which his grown daughter pokes her head through the cut-out visor in a life-size reproduction at a Seattle museum. In 2005, McCandless explained that what he liked most about the image was its lack of identity; with his sun visor closed, it is impossible to see his face, “and that means it could be anybody out there … sort of a representation, not of Bruce McCandless, but mankind.”
This assertion gained a measure of irony in September 2010, when he sued the singer Dido for her unauthorized use of the image on the cover of her album, Safe Trip Home. Although NASA images are not bound by copyright, McCandless argued that the image infringed his “persona,” but the case was settled amicably early the following year.
Four days into Mission 41B, flying the MMU carried the experience of spaceflight to an even higher level; in fact, many spacewalkers have agreed that the sensation of floating above Earth with nothing between themselves and the fathomless expanse of the Universe is a decidedly ethereal one. During their tethered work in the payload bay, McCandless and Bob Stewart removed a failed television camera for replacement with an in-cabin unit and later installed it during their second EVA on 9 February. The MMU performed admirably, but ironically it was Brand who undermined its raison d’etre. The backpack had long been touted as being capable of more precise and intricate movements than the shuttle, but on Missions 41B and 41C the value of Challenger’s maneuverability and her Canadian-built Remote Manipulator System (RMS) mechanical arm were demonstrated … by retrieving a lost foot restraint.
“I don’t recall now whether it was before or after he went out with the backpack,” Vance Brand explained, years later, “but he was trying to reposition his foot restraint, so that he could get into it to do work. Our EVA equipment was generally tethered, but it somehow got away from him. I looked back and saw it floating away. I thought about it for a second or two and decided that the ground wouldn’t have time to come up with a decision whether we ought to chase it and go after it. It was going to get away from us very quickly, so I couldn’t see anything wrong with going after it. We chased it, Bruce caught it and we didn’t have to worry about encountering that as ‘space junk’ the next time we came around the world.”
Both MMU evaluations, read Martin Marietta’s post-mission report, “performed as expected and no anomalies were reported.” Overall, McCandless flew the MMU for 3.5 hours and Stewart for just under two hours. Yet, as has been noted, it was Challenger’s own maneuverability, demonstrated by Brand, which rendered its future much less certain. “We used the autopilot a lot,” Brand said later. “We had the capability to maneuver the ship in rotation with a hand controller, but more often than not, we just punched something into the computer and set up the digital autopilot such that we got an automatic maneuver. That saved fuel, as we could move at very slow rates. We tested the [Reaction Control System] jets on orbit for translation up or down, sideways or forward and back. On the night side of the Earth, when we translated the ship down, the upward-firing RCS jets were used to do that. At night, it looked like a Fourth of July display because you could look out over the nose and you could see these tubes of fire going up. They were fantastic visual effects.”
By so doing, Brand showed that the shuttle was capable of the same intricate motions as the MMU, and, on the next flight, Mission 41C in April, when a task involving the MMU was frustrated, the RMS would prove highly capable. Despite the MMU’s success during two satellite recoveries in November 1984, the superb maneuverability of the shuttle contributed to its ultimate demise. In fact, the year immortalized by George Orwell would be the only time the MMU was ever used in space. By the end of 1984, it had seen service on three shuttle missions, flown by six astronauts for a total of just 10.5 hours, spread across six spacewalks. Other assignments were expected, but, in the wake of the Challenger disaster, safety upgrades imposed by the Rogers Commission proved costly and the two flight units were mothballed.
More tellingly, MMU veteran George “Pinky” Nelson doubted, even in the heady days before January 1986, that the backpack would have flown again, except “maybe for a vehicle-to-vehicle rescue in a Columbia-like scenario, but not for any operations that were envisaged in the pre-Challenger program.” Like McCandless, he stressed that it was “well conceived and engineered but, unfortunately, the planned uses of the MMU were superseded by other capabilities that we developed, but couldn’t anticipate.”
Finally, when the Rogers presidential inquiry into Challenger’s loss presented its findings, renewed emphasis was imposed on increasing the safety of other shuttle components. “The cost of recertification,” recalled McCandless, “eventually killed it off. In the fall of 1989, there was an effort to fly the MMU again. A proposal was solicited from Martin Marietta for recertification and refurbishment for one Shuttle mission. It came in at $6.1 million, which was deemed too expensive, and despite some small sums for clean room environmental storage, just in case, they were eventually retired.” Today, the MMU flight unit first used by McCandless hangs in the Smithsonian. The other backpack was loaned to NASA’s Marshall Space Flight Center for possible future use as a “flying testbed” for autonomous rendezvous and docking systems, “subject,” said McCandless, “to the constraint that it be maintained in a condition that could be restored to flight configuration.” Both units, therefore, were mothballed until such time as their unique capabilities were needed again.
They never were.
A device known as the Simplified Aid for EVA Rescue (SAFER) was developed for the International Space Station (ISS), and the only other remotely viable role for the MMU was to assist with repairing the Hubble Space Telescope. However, this was dismissed, due to fears that plume impingement from its nitrogen-gas thrusters could damage the telescope’s optics.
This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the 43rd anniversary of Apollo 14, which completed the third manned landing on the Moon in February 1971 … and restored America’s lunar program in the wake of the ill-fated Apollo 13.