Spacewalk!

"Adventure is worthwhile."

- Amelia Earhart  

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A space suit is used for spacewalks or extravehicular activities (EVAs) to keep a person alive in the vacuum of space.  Soviet cosmonaut Alexei Leonov performed the first EVA in March 1965 when he floated outside his spacecraft for 12 minutes. Fewer than 3 months later, astronaut Edward H. White II became the first American to step outside for 22 minutes. These brief excursions into the vacuum of space tested the human ability to venture outside an orbiting spacecraft protected only by a pressurized space suit. Subsequent EVAs showed that space travelers could perform useful work while floating outside their spacecraft or walking on the surface of the Moon.  

The space suit that was used by the early astronauts in the Mercury, Gemini, and Apollo Program was redesigned for use on the space shuttle. The first EVA of the space shuttle era was performed during the STS-6 mission in April 1983. During the 3-hour spacewalk, astronauts Story Musgrave and Donald Peterson tested various aspects of the newly designed shuttle space suit.

Since then, many EVAs have been performed to repair satellites such as the Hubble Space Telescope and to develop and verify the techniques that are being used to build the International Space Station.  

Click here to read the NASA Brief, Wardrobe for Space.

There are three types of EVAs:  

The majority of EVAs conducted in the shuttle program have been planned EVAs. Only a couple of times has an unscheduled EVA been performed. No contingency EVAs have been necessary, but two astronauts are trained for contingency EVAs for every mission.  

All training for EVAs planned during the space station assembly program is performed at this facility. Click here to watch some videos of EVA training done for STS-101, an International Space Station assembly flight.  

The upper and lower torsos connect around the waist by a joint ring. Attached to the back of the upper torso is the portable life-support system, which contains enough oxygen and electric power for 8 hours of operation. The astronauts wear a cooling and ventilation garment for temperature regulation inside the suit. Click here for more information on the liquid cooling garment.  

The time spend prebreathing pure oxygen is partly dependent on the pressures established in the shuttle cabin and in the space suits. NASA life sciences researchers have developed procedures to maximize astronaut safety and productivity and to minimize the time spent prebreathing oxygen.  

EVA preparations begin the day before, when the equipment is checked out by the astronauts to make sure that everything works properly. Also, the pressure inside the crew cabin is lowered from 14.7 psi to 10.2 psi. About 2.5 hours before the extravehicular activity begins, the astronauts start to breathe pure oxygen during the prebreathing activity. This pure oxygen washes out the nitrogen dissolved in the blood.  

When the pressure inside the airlock is at vacuum (matching the conditions of space), the outer door is opened and the astronauts exit into the payload bay of the shuttle.  

During EVAs, astronauts are tethered to the spacecraft.  One astronaut usually "stands" on the end of the robotic arm and is maneuvered by an astronaut inside the cabin.  The second astronaut (and they always work in pairs for safety reasons) is the free floater who moves using hand and footholds located throughout the payload bay. Astronauts wear "Snoopy" caps (named after the cartoon Flying Ace, Snoopy) that contain their communications headset so they can be in touch with each other, the flight crew, and the Mission Control Center at all times. A drink bag and a diaper are provided for all EVAs.  

Astronauts have retrieved and repaired satellites, practiced using maneuvering units, assembled pieces of the International Space Station, and sometimes gotten to enjoy the view. An EMU is really a complete spaceship of its own, it has its own life support system, and, with a mobility unit backpack as astronaut can even travel from place to place on his/her own. Astronauts have a red stripe or no stripe on their suit arms and legs to tell them apart.

Click here to watch the Go for EVA! NASA video. Learn how space suits work and the kinds of jobs astronauts perform while spacewalking!

 

EVA Research

NASA research and technology development supports the development of EVA and life support systems. This work decreases the size of life support systems while increasing their efficiency and reliability. Technologies developed for space life support systems include sensors, biotechnology, environmental monitors, waste processors, air regenerators, water purifiers, and heat regulators.  These technologies can also be used to improve the quality of life for people on Earth. In addition space, life scientists study the effects of the space environment on human performance to ensure the safety and productivity of future missions. This human factors research is used to develop the technology to improve the effectiveness, safety, and performance of astronauts living and working in space.  

Click here for space suit information and activities.  

EVA tools  

As Apollo space suits were being developed for walking on the surface of the Moon, a special set of tools was designed to assist astronauts in their sample-collecting task. The Apollo suits were stiff, and bending at the waist was difficult and awkward. The problem of picking up rocks and soil samples was solved by creating long-handled sampling tools such as scoops and rakes. Because bulky space suit gloves made grasping difficult, tool handles were made thicker than normal.

Tools also need some sort of attachment system so that, if an astronaut should "drop" them, the tools will not float away. Colliding with a socket wrench left in orbit by some earlier space mission could be disastrous.  

For example, the handles of tools are often enlarged so they will take less energy to hold. A space suit glove is similar to a thick leather welder's glove in bulk. Try wearing a pair of heavy ski gloves and doing some small assembly operations, such as screwing a small nut on a bolt or screwing in a tiny screw. How difficult is it?  

Because the suit glove is pressurized, the astronaut's fingers extend when at rest. Closing the fingers around a tool handle takes a continuous application of force. Quite simply, small-handled tools take more force to hold than do large-handled tools. This caused muscle strain on the astronaut's hands.  Grab a ball with one hand and squeeze it for 2 or 3 minutes without stopping.  How does your hand feel?  

To keep control of tools, each tool has some sort of tether or locking system. A socket wrench has a key that has to be inserted into a holder before a socket can be installed at the end of the wrench. Once the key is removed, the socket is locked on to the wrench and cannot be removed without use of the key. A short tether and clip enables the astronaut to hang on to the wrench in case it is dropped. There is even a tether on the key! Rechargeable power tools for driving bolts are also used by spacewalkers.

Just imagine if every time you put something down (without putting it away) in your garage, it was gone by the time you needed it! Having all these tethers is kind of like wearing a tool belt in space. When you need the tool, you know just where it is. Luckily, because things don't weigh anything, you can have a lot of heavy tools on your tool belt. They just are bulky and sometimes get in the way. Click here to watch some videos of EVAs done for the Hubble Space Telescope.  

 

Astronaut Maneuvering Units

During the first American EVA, Edward White experimented with a personal propulsion device, the hand-held maneuvering unit (HHMU). The HHMU tested by White was a three-jet maneuvering gun. Two jets located at the ends of rods and were aimed back so that firing them pulled White forward. A third jet was aimed forward to provide a braking force.

By holding the gun near his center of mass and aiming it in the direction in which he wanted to travel, White was able to propel himself forward. Stopping that movement required firing the center jet. The propulsive force of the HHMU was produced by releasing compressed oxygen from two small, built-in tanks.  

Although the HHMU worked as intended, it had two disadvantages. First, produce the desired motion, it had to be held as close to the astronaut's center of mass as possible. Determining the center position was difficult because of the bulky space suit White wore and was a matter of guesswork and experience. Second, precise motions to position an astronaut properly during an activity, such as servicing a satellite, were difficult to achieve and maintain and proved physically exhausting.  

On the Gemini IX mission, a backpack maneuvering unit was carried. However, problems with the unit prevented Astronaut Gene Cernan from testing it. Following the Gemini Program, the next space experiments that tested maneuvering units for EVAs took place during the second and third manned Skylab missions. This device was tested only inside the spacecraft, but the experiment confirmed that a maneuvering device of that design was both feasible and desirable for future EVA use. Five of the six astronauts who flew in those two missions accumulated a total of 14 hours testing the advanced device, called the AMU, or astronaut maneuvering unit.  

The AMU was shaped like a large version of a hiker's backpack. Built into the frame was a replaceable tank of compressed nitrogen gas. Controls for the unit were placed at the ends of "armrests." To move, the astronaut worked rotational and translational hand controls. Propulsive jets of nitrogen gas were released from various nozzles spaced around the unit. The 14 nozzles were arranged to aim top-bottom, front-back, and right-left to produce 6 degrees-of-freedom in movement. The AMU could move forward and back, up and down, and side to side, and it could roll, pitch, and yaw.

With the 11 additional nozzles, precise positioning with the AMU was far simpler than with the HHMU of the Gemini Program. The astronaut was surrounded by the unit, which took the guesswork out of determining center of mass and make control much more accurate. The astronaut could move closely along the surface of a curved or an irregularly-shaped object without making contact with it.  

The AMU led to the MMU, or manned maneuvering unit, for use during early space shuttle flights. It was designed to operate in the microgravity environment of space and under the temperature extremes found there. The MMU was operated by a single space-suited astronaut. The unit featured redundancy to protect against failure of individual systems. It was designed to fit over the life-support system backpack of the shuttle EMU.  

When carried into space, the MMU was stowed in a support station attached to the wall of the payload bay near the airlock hatch. Two MMUs were carried on a mission, with the second unit mounted across from the first on the opposite payload bay wall. The MMU controller arms were folded for storage; but when an astronaut backed into the unit and snapped the life-support system into place, the arms were unfolded. To adapt to astronauts with different arm lengths, controller arms could be adjusted over a range of approximately 13 centimeters. The MMU was small enough to be maneuvered with ease around and within complex structures. With a full propellant load, its mass was 148 kilograms.

The fuel powered 24 nozzle thrusters placed at different locations on the MMU.  To operate the propulsion system, the astronaut used his or her fingertips to manipulate hand controllers at the ends of the MMU's two arms. The right controller produced rotational acceleration for roll, pitch, and yaw. The left controller produced acceleration without rotation for moving forward-back, up-down, and left-right. Coordination of the two controllers produced intricate movements in the unit. Once a desired orientation was achieved, the astronaut could engage an automatic attitude-hold function that maintained the inertial attitude of the unit in flight. This freed both hands for work.  

The MMU was used on three Shuttle missions in the mid-1980s. On STS-41C, Astronauts James Van Hoften and George Nelson used the MMU to capture the Solar Maximum mission satellite and to bring it into the Orbiter’s payload bay for repairs and servicing. Their work increased the lifespan of the satellite. The final MMU mission was STS-51A, which flew in November of 1984.

The propulsion unit was used to retrieve two communication satellites that did not reach their proper orbit because of faulty propulsion modules. Astronauts Joseph Allen and Dale Gardner captured the two satellites and brought them into the Orbiter payload bay for stowage and return to Earth.  

In 1994 a new device, called the simplified aid for extravehicular activity rescue (SAFER), was flown by Astronauts Mark C. Lee and Carl J. Meade a few meters away from their Orbiter. SAFER is a smaller unit than the MMU and is designed as a self-rescue device for use on the International Space Station. Although it is unlikely, an astronaut could become separated from the station during an EVA and a shuttle might not be available to retrieve the crewmember. In that event, the crewmember would use the propulsive power of SAFER to return to the station structure.

SAFER

Questions to think about:

In the next chapter, you will look at a variety of benefits from the Space Shuttle Program that have helped us here on Earth.  

Next... Spinoffs from Space!