The picture shown here shows Bruce McCandless II using a Manned Maneuvering Unit (MMU), a jetpack attached to his space suit, in 1984. This was the first untethered spacewalk in history.
What is an EVA? EVA stands for Extravehicular Activity, although many people just think of and refer to them as spacewalks. The definition of an EVA is when any part of an astronaut leaves their vehicle and goes out into space. EVAs are some of the most exciting and important missions that astronauts will ever have to do.
There are three different kinds of EVAs: scheduled, unscheduled, and contingency.
Scheduled EVA: A scheduled EVA is, in the best case, the only kind an astronaut will have to do. Scheduled EVAs are filed at NASA, and are added to the mission plan. Then, at the scheduled time, they are performed. This is usually a small task, like doing some work on the exterior of the ship.
Unscheduled EVA: An unscheduled EVA happens when an unforeseen problem pops up on a mission, and the mission cannot be completed unless an EVA takes place. In that case, the astronauts notify NASA (National Aeronautics and Space Administration), prepare the equipment, and carry on with the new plan. For example, in 2007 Russia performed an unscheduled EVA from the ISS, cutting off a troublesome antenna that was preventing a shuttle from docking.
Contingency EVA: A contingency EVA is an unscheduled EVA that urgently needs to happen for the safety of the ship and the crew. Contingency EVAs are worst-case scenarios, and would be acted on in case of something like engine failure or a similar serious event.
What technology do astronauts use on EVAs? As you may of guessed, astronauts need technology for EVAs. Otherwise they would deteriorate in the vacuum of space. These are some of the pieces of equipment used on EVAs:
Space suit: The suit that astronauts wear in space lets them breathe purified, pressurized oxygen and keeps them from freezing or falling apart. The suit has a shocking 12 layers of insulation, and is thick and bulky. Normal air has too low of a pressure for the suit, so astronauts need 100% oxygen. Since space shuttles mimic Earth's air, (78% nitrogen, 21% oxygen), astronauts need to sit in a breathing chamber aboard the shuttle for a few hours to prepare for the air they will breathe while on an EVA. Then, the air either is funneled to the astronauts through a cord, or comes straight out of a life-support pack that can be attached to the back of the suit.
In-suit drink bags: In case astronauts get thirsty while in an EVA, there is a bag of water stored in the back of the suit, and a valve comes out into the helmet for astronauts to sip from. There was an application of this technology that let astronauts eat in their suits, notably chewing a fruit bar, but NASA decided to get rid of that feature after astronauts complained that it was too crumbly and floated around in their helmets.
Safety tether: One of the other most important pieces of equipment that a space walker will use, the safety tether is a 55-foot-long cord that is anchored to the astronaut's waist. The other end is anchored to the spaceship. This stops the astronaut from floating away, as well as allowing astronauts to "reel" themselves in when they need to come back in. The suit also incorporates smaller cords that tether tools to the astronaut's arms.
MMU: An MMU (Manned Maneuvering Unit) is another tool that can be used instead of a safety tether; MMUs can be likened to jetpacks. They are attached to the astronaut's spacesuit and use jet propulsion to navigate. As seen at the top of this page, Bruce McCandless II was the first person to leave a spacecraft with a MMU.
A hand-held maneuvering unit is a smaller propulsion unit that can fit in the palm of an astronaut's hand, even with their thick gloves. It lets them "traverse" the outside of the ship and helps them get from place to place far easier in the vacuum of space.
Notable EVAs For a long time, walking through space had been dreamed about everywhere. Several space agencies had started to think about how it could be done, and as part of the great space race between the USA and the Soviet Union, the Soviets decided to test the concept. They sent cosmonaut Alexei Leonov, for the world's first EVA, on the Voskhod 2 mission, and it was a success, although Leonov's suit expanded and he nearly couldn't fit through the entry hatch trying to get back inside. In response, largely thanks to the large rivalry between the two countries, USA astronaut Ed White (left) went up on the Gemini shuttle in an equally successful EVA; this set the stage for hundreds more to come. Moon Landing: In 1969, Neil Armstrong and Buzz Aldrin performed an EVA on the moon's surface as part of the Apollo 11 mission, while Michael Collins stayed on the shuttle. This was the first of several lunar EVAs. HST Servicing Missions: The HST (Hubble Space Telescope) Servicing Missions (1993) were to repair the newly launched space telescope of the same name. The missions took place over a decade and a half. There were 5 missions in total; 1, 2, 3A, 3B, and 4. Mission 1, in 1993, was the first time astronauts performed an EVA on any space telescope. The mission successfully corrected a flaw in the telescope's primary mirror. Mission 2, in 1997, was a major upgrade to the wavelength range, allowing astronomers back on Earth to see farther than ever before. Mission 3A (1999) was supposed to be "preventive maintenance," but it quickly turned into a more urgent mission when the fourth of six gyroscopes failed, meaning that the telescope could no longer function. An unscheduled EVA was approved while the telescope was "put to sleep," entering a dormant stage while the astronauts quickly switched out the gyroscopes. Mission 3B, (2002), the second part of mission 3, replaced some solar panels and added some new instruments. With the removal of the Faint Object Camera, none of the original instruments still remained on the telescope. Mission 4, (2009), added new instruments, the Cosmic Origins Spectograph and the Wide-Field Camera.