On 123 occasions between March 1965 and September 1994, astronauts and cosmonauts had clambered outside their spacecraft and maneuvered themselves around in the harsh and unforgiving vacuum of space. They had used handhelds, tethers and specialized backpacks to prevent them from losing physical contact with their vehicles and inadvertently floating away into the void. But when STS-64 astronauts Mark Lee and Carl Meade ventured outside shuttle Discovery’s airlock on the morning of 16 September 1994—a quarter-century ago, this month—they wore something quite different and wholly new on their space suits. Known as the Simplified Aid for EVA Rescue (SAFER), it provided a self-rescue tool for its wearer and its descendants are today routinely used by spacewalkers aboard the International Space Station (ISS).
Unlike Martin Marietta Corp.’s bulky Manned Maneuvering Unit (MMU)—first trialed by Bruce McCandless in February 1984 and later employed operationally to service NASA’s Solar Max observatory and retrieve the stranded Palapa-B2 and Westar-VI commercial communications satellites—SAFER was never intended for the repair or upgrade of spacecraft.
Rather, it was a design solution for the shuttle program’s requirement for spacewalkers to rescue themselves in the event of becoming detached from their tether during an Extravehicular Activity (EVA). It had long been recognized that it was be hugely difficult to undock the shuttle from the ISS, rendezvous and retrieve a lost crew member, then redock in a safe manner. As such, and true to its name, SAFER would provide a “safer” means of going about spacewalking. And on STS-64, it would be the United States’ first untethered EVA in a full decade.
Developed by the Automation and Robotics Division at NASA’s Johnson Space Center (JSC) in Houston, Texas, SAFER weighed 83.1 pounds (37.7 kg), less than a third as much as the MMU, and was equipped with 24 fixed-position compressed nitrogen thrusters. It was powered by a 28-volt battery pack and included an automatic attitude-hold mechanism and six degrees of freedom.
Unlike the MMU, it had no bulky “arms” for hand controllers, but was instead fitted with thruster “towers”, extending up the sides of the backpack, and on STS-64 Lee and Meade would operate it from controls hard-secured to their suit’s torso units. More recently, in its ISS configuration, SAFER’s controller is embedded within one of the thruster towers and is swung out by the tug of a lanyard.
When the STS-64 crew was announced in November 1993, it comprised five spaceflight veterans: Commander Dick Richards, Pilot Blaine Hammond and Mission Specialists Susan Helms, Carl Meade and Mark Lee. Unusually, in February 1994, a sixth crew member—“rookie” astronaut Jerry Linenger—was assigned as a fourth Mission Specialist. “This assignment,” noted NASA’s news release, “was made to more efficiently distribute the crew workload for this complex flight.” Years later, Linenger’s primary recollection from STS-64 was watching Lee and Meade, “totally free of the shuttle, and the Earth below them”, which he described as “one of those pictures that’s pretty much imprinted in my brain, even though I wasn’t doing the spacewalk”.
Before flight, Lee and Meade spent considerable time working with the SAFER engineers and performing evaluations on the ground. They were tasked with moving no further than 27 feet (8 meters) from Discovery herself, operating within a “box” of area in the forward payload bay, and were assigned to familiarize themselves with SAFER and execute a programmed series of test inputs on the compressed nitrogen thrusters and a series of translation, tumbling and precision maneuvering exercises.
Emerging from the shuttle’s airlock, the spacewalkers activated their helmet lights for greater illumination in orbital darkness and set about a standard translation to gain their bearings. Neither man had been outside before, although Lee had worked extensively on EVA techniques and actually helped develop the procedures for a “contingency” spacewalk during shuttle mission STS-51D in April 1985. Now, on his first EVA, he was so anxious to begin testing SAFER that he completed barely half of his translation, before steeling himself to fly the new unit.
“The first thing we did was a little familiarization maneuver, then we did a gaseous nitrogen calibration, to make sure that the fuel we were using in orbit was very comparable to what we did in training,” he said at the post-flight press conference. “When we got back after the calibration, we found out that the consumption was exactly as we planned, so I got to do a few optional maneuvers. I went in front of the windows to do some rolls and yaws to try to see how much “cross-coupling” there was when you weren’t using the attitude-hold feature of the SAFER.”
As each spacewalker performed his SAFER tests, the other was involved in tool setups and evaluations for subsequent tasks. Aided by Helms, who was operating the shuttle’s Remote Manipulator System (RMS) arm, Lee and Meade took turns standing in a mobile foot restraint and “tumbling” his buddy. The tumbled astronaut then activated SAFER’s automatic attitude-hold system to stabilize himself and maneuver towards the robotic arm, which Helms pulled away to simulate a separation rate of about 0.2 feet (6 cm) per second.
The astronauts quickly determined that the device used less nitrogen than predicted, and on one occasion Meade “rolled” Lee at about two revolutions per minute, somewhat quicker than planned, but his SAFER successfully stabilized him without incident. They evaluated their capability to replenish gaseous nitrogen from a recharging unit in the payload bay and flew the unit precisely along the length of the RMS.
Overall, SAFER’s first trial was a huge success, with the only problem of note arising from glitches with the battery-powered Electronic Cuff Checklist, which was capable of storing 500 pages of information, including graphics and photographs on its small screen. On a number of occasions, it did not respond to commands when the upper-middle sextant was depressed and efforts to update its contents resulted in an error message being displayed. However, it remained usable and Lee and Meade spoke glowingly of its performance later. Unlike previous printed notebooks—attached to the space suit cuff, which held 25-50 pages of notes, usually detailing critical functions, such as emergency operations—the Electronic Cuff Checklist and its touch screen enabled its wearer to scroll through much more information in support of more complex EVAs.
It could also be updated electronically from one of the orbiter’s laptop computers. For this assessment, Lee and Meade wore an Electronic Cuff Checklist on the left arm of their suits and a standard, printed checklist on the right arm. The EVA lasted six hours and 51 minutes and formed the capstone of a dramatic and multi-faceted 11-day mission. Next weekend’s AmericaSpace history feature will reflect on the other side of STS-64, which showcased virtually all of the shuttle’s capabilities: from scientific research to technology demonstrations and from satellite deployment to rendezvous, proximity operations and retrieval.
The second part of this article will appear next weekend.