SAFER Makes It Safe to Walk in Space

Astronaut Rick Mastracchio is shown here working in space during STS-131 wearing a SAFER EVA system. NASA

It's like a scene from a science fiction movie nightmare: an astronaut is working outside a spacecraft in the vacuum of space when something happens. A tether breaks or maybe a computer glitch strands the astronaut too far from the ship. However it happens, the end result is the same. The astronaut ends up floating away from the spacecraft into the endless void of space, with no hope of rescue.

Thankfully, NASA developed a device for space walking that keeps an astronaut safe while working "outdoors" to prevent such a scenario from happening in real life. 

Safety for EVAs

Space walks, or extravehicular activities (EVAs), are an important part of living and working in space. Dozens were needed just for the the assembly of the International Space Station (ISS).  Early missions by both the U.S. and Soviet Union also relied on space walks, with astronauts tethered to their spacecraft by lifelines.

The space station cannot maneuver to rescue a free-floating EVA crew member, so NASA got to work to design a safety harness for astronauts who would be working around it without direct connections. It's called "Simplified Aid For EVA Rescue" (SAFER): 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.

Its 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. It's intended primarily for emergency rescue, and not as an alternative to tethers, and safety grips. Astronauts control the unit with 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.

EVAs and Safety

Space 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. 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. The Moon missions had EVAs starting with Apollo 11, but these were on the surface, and required the astronauts wear full space suits. Skylab astronauts made repairs to their systems, but were tethered to the station.

In later years, especially during the shuttle era, the Manned Maneuvering Unit (MMU) was used as a way for an astronaut to jet around the shuttle. Bruce McCandless was the first to try one out, and the image of him floating free in space was an instant hit. 

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 NASA built hoping that it won't be necessary to use it. 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.