* 9-12:A SAFER Way To Space Walk* TOVIEW IMAGES GO TO:

http://www.nasaexplores.com/show2_912a.php?id=03-050&gl=912

space walk using safer and the robotic armIt’s a science fiction movie nightmare situation. An astronaut is working outside his spacecraft in the vacuum of space when something happens—his tether breaks, a satellite hits him, or an evil computer pushes him away from the ship. However it happens, the end result is the same. The astronaut ends up floating away from his spacecraft into the endless void of space, with no way to rescue himself. It’s a horrible fate, but a new device for space walking will ensure that it only happens in the movies.

Space walks, or *extravehicular activities* (EVAs), are an important part of the assembly of the International Space Station (ISS). By the time the Station is complete, its construction will have required more than twice as many space walks as were previously performed in the entire history of spaceflight. Unlike the Space Shuttle, the Space Station cannot maneuver to rescue a free-floating EVA crew member. NASA is determined to make sure that none of the over 150 ISS assembly space walks ends up like the movie nightmare. One of the ways the agency is doing this is with a device called Simplified Aid For EVA Rescue (SAFER). Essentially a “life jacket” for space walks, SAFER is a self-contained maneuvering unit worn by astronauts like a backpack. The system relies on small nitrogen-jet thrusters to let an astronaut move around in space.

safer is worn on the back of a space suit like a backpackIts relatively small size and weight allow for convenient storage on the Station, and let EVA crew members put it on in the Station’s airlock. However, the small size was achieved by limiting the amount of propellant it carries, meaning that it can only be used for a limited time. That is why SAFER is intended primarily for emergency rescue, and not as an alternative to tethers, safety grips, and the Canadarm2 robot arm as a means of getting around the Station. Astronauts control the SAFER device using a hand controller attached to the front of their space suits, and computers assist in its operation. The system has an automatic attitude hold function, in which the onboard computer helps the wearer maintain course. SAFER's propulsion is provided by 24 fixed-position thrusters that expel nitrogen gas and have a thrust of 3.56 Newtons (0.8 pounds) each. SAFER was first tested in 1994 aboard the Space Shuttle Discovery, when astronaut Mark Lee became the first person in 10 years to float freely in space.

space walk using a tetherSpace walking has come a long way since the early days. In June 1965, astronaut Ed White became the first American to conduct a space walk. His space suit was smaller than later EVA suits, since it did not carry its own oxygen supply. Instead, a hose to an oxygen supply on the Gemini capsule connected White. Bundled with the oxygen hose were electrical and communication wires and a safety tether. While outside the spacecraft, White was able to maneuver himself outside the spacecraft using a handheld air-pressure gun. However, it quickly expended its supply of gas. On Gemini 10 and 11, a hose to a nitrogen tank aboard the spacecraft connected a modified version of the handheld device. This allowed the astronauts to use it for a longer period of time. Another maneuvering unit was developed for the Gemini program, but was never used during an EVA. This larger device would have been worn like a backpack.

Astronauts conducted extensive EVAs during the Apollo program. Most of that time was spent on the surface of the Moon, rather than in the free fall of space. Walking on the Moon meant that astronauts had to be able to leave their craft, untethered, in self-contained space suits. It also meant that the astronauts did not require microgravity-maneuvering units. Such devices were tested inside the Skylab space station. Among them were “jet shoes,” a foot-controlled maneuvering unit designed to leave the astronaut’s hands free. Backpack and handheld units were also tested.

spacewalk using saferThe next extravehicular space walks were not until the Space Shuttle era began in the early 1980s. The Shuttle features cargo bay doors that allow astronauts easy access to the vacuum of space. The Gemini and Skylab research led to the development of a Manned Maneuvering Unit (MMU) for Space Shuttle astronauts. The nitrogen-jet-powered MMU was essentially a self-contained spacecraft that an astronaut wore like a backpack. The MMU was first used on the 10^th flight of the Space Shuttle. Astronaut Bruce McCandless became the first person to fly freely, untethered in space in February 1984. The MMU was used a total of nine times on three Space Shuttle missions in 1984, but has not been used since. Tethers, grips, and other restraints proved more than adequate for space walks in a Shuttle cargo bay. The Canadarm robot arm proved itself ideal for recovery of satellites and other tasks outside the Shuttle. SAFER, which has been described as a simplified version of the MMU, has two advantages over the earlier system. It is a more convenient size and weight and ideal for an astronaut rescue device outside the Space Station.

SAFER is a rare type of technology—the kind that is built hoping that it won’t be used. So far, tethers, safety grips, and the robot arm have proved adequate to safely keep astronauts where they are supposed to be during space walks. But if they ever fail, SAFER will be ready.

Courtesy of NASA's Space Operations Missio