Working Aloft

Astronaut Dan Barry at work on the ISS

"The bravest are surely those who have the clearest vision of what is before them, glory and danger alike, and yet notwithstanding, go out to meet it."

-Pericles

To build the International Space Station, Earth orbit will serve as a construction site. Astronauts will perform more spacewalks during construction than have been conducted since spaceflight began (more than two and a half times as many). Over 150 spacewalks will be needed to complete the job. The astronauts will be assisted by the inch-worming robotic arm, the two-fingered Canada hand, and a free-flying robotic eye camera that can circle and inspect the station. 

The Autonomous Extravehicular Activity Robotic Camera Sprint (AERCam Sprint) is an experiment planned to demonstrate the use of a prototype free-flying television camera for remote inspections of the exterior of the ISS.

Let’s start by listening to the astronauts who have gone on spacewalks to build the ISS talk about their job. You can just read the text of their interviews or click on the pictures to watch the video interviews.

Space Suits

To explore and work in space, human beings must take their environment with them because there is no atmospheric pressure and no oxygen to sustain life in the vacuum of space. Inside the spacecraft, atmosphere can be controlled so that special clothing isn't needed; but when outside, humans need the protection of a spacesuit.  Check out A Day in the Life of A Space Walker!

Earth's atmosphere is 20% oxygen and 80% nitrogen from sea level to about 75 miles up, where space begins. At 18,000 feet, the atmosphere is half as dense as it is on the ground; and at altitudes above 40,000 feet, air is so thin and the amount of oxygen so small that pressure oxygen masks no longer do the job.  Above the 63,000-foot threshold, humans must wear space suits that supply oxygen for breathing and that maintain a pressure around the body to keep body fluids in the liquid state. At this altitude, the total air pressure is no longer sufficient to keep body fluids from boiling.

Astronaut James Voss prebreathing in the airlock

Space suits for the Space Shuttle are pressurized at 4.3 pounds per square inch (sea level), but because the gas in the suit is 100% oxygen instead of 20%, the person in a space suit actually has more oxygen to breathe than is available at an altitude of 10,000 feet or even at sea level without the space suit. Before leaving the Space Shuttle to perform tasks in space, an astronaut has to spend several hours breathing pure oxygen. This procedure is necessary to remove nitrogen dissolved in body fluids, and thereby, to prevent its release as gas bubbles when pressure is reduced, a condition commonly called "the bends."

The space suit also shields the astronaut from deadly hazards. Besides providing protection from bombardment by micrometeoroids, the space suit insulates the wearer from the temperature extremes of space.

Working Aloft

Because of the unprecedented complexity of assembling so many pieces in orbit, there are always challenges to face during orbital construction work. But to prepare for the challenges, engineers and astronauts methodically practice procedures, prepare tools, and test equipment. NASA has been building experience during more than a decade of spacewalking flight tests.

Cosmonaut Yuri Malenchenko on EVA during STS-106

Few aspects of ISS assembly tasks are easy. For example, on the STS-92 flight, the robot arm operator Koichi Wakata had to pick up and attach large pieces of equipment without a direct line of sight out the Shuttle's window.

IInstead, astronauts such as Wakata rely on an artificial space vision system developed by the Canadian Space Agency, and the directions of spacewalkers positioned outside the Shuttle. The margin for error is slim. If a crew fails to attach a new component correctly for some reason, the station assembly sequence can come to a halt.

Astronaut James Voss working on STS-101 to construct the ISS

Space Station Extravehicular Activities

Astronaut Carl Walz, a member of the fourth crew that will live aboard the International Space Station, tries on a Soyuz space suit

The Joint Airlock Module, which has the capability to be used by both Russian and U.S. space suit designs, consists of two sections, a "crew lock" that is used to exit the station and begin a spacewalk, and an "equipment lock" used for storing gear.

The equipment lock is used for overnight "campouts" by the crew, during which time the pressure in the Joint Airlock Module is lowered to 10.2 pounds per square inch (psi) while the rest of the station remains at the normal sea level atmospheric pressure of 14.7 psi. The night spent at 10.2 psi in the Airlock purges nitrogen from the spacewalkers' bodies and prevents decompression sickness, commonly called "the bends," when they go to the 4.3 psi pure oxygen atmosphere of a space suit. Station crewmembers could perform a spacewalk directly from the 14.7 psi cabin atmosphere, but they would have to go through a several hours-long prebreathe of pure oxygen first.

Joint Airlock Module in Testing

Astronaut Jeff Williams working on the ISS

The Airlock "campout" shortens the pure oxygen prebreathe time to only minutes for the crew. The protocol is similar to a procedure commonly used in advance of Space Shuttle spacewalks, in which the Shuttle's cabin pressure is lowered to 10.2 psi at least a day ahead of the EVA. Since the Joint Airlock Module became operational, the philosophy of spacewalk training has shifted due to the increasing complexity of the station and the ability of the station crew to perform spacewalks.

Rather than attempting to train station crewmembers for every EVA task they may be called upon to perform during a mission, training increasingly aims toward providing crew members with a general suite of EVA skills. The station's growing size and complexity make it virtually impossible for astronauts to train for every possible contingency and maintenance EVA, as is the case in training for Shuttle missions. 

Tools in Space

Astronaut Steven Smith and John Grunsfeld repairing the Hubble Space Telescope

NASA, in recognizing the challenge of building the International Space Station, has for more than a decade been working on developing and flight-testing the equipment needed for spacewalks and refined spacewalk training procedures.

In order to build spacewalk experience among astronauts, engineers and flight controllers, over a dozen "practice" spacewalks were conducted during Space Shuttle flights since 1991. The three servicing missions for the Hubble Space Telescope on STS-103 helped to prepare crews, trainers, ground control teams, and engineers for the tools and techniques needed to build the ISS. Many of the astronauts who gained experience during these "practice" spacewalks brought that knowledge to bear during  spacewalks for the station's assembly.

The flight-testing of EVA equipment designed for use aboard the International Space Station began on the first spacewalk NASA conducted after the Space Shuttle's return to flight following the Challenger accident.

On Shuttle mission STS-37 in April 1991, Astronauts Jerry Ross and Jay Apt performed a space walk to test the Crew and Equipment Translation Aid cart designed for use in assisting astronauts to move about the football-field-long truss of the completed station.

Astronaut Jerry Ross working during the "night" on STS-88 the first ISS assembly mission

Since 1991, other spacewalks have evaluated new tethers, tools, foot restraints, techniques for handling large masses, a jet pack "life jacket," space suit enhancements, and even the planned station lettering and toolboxes.

Space Robotics

Astronaut Nancy Currie working the robotic arm

It allows the Shuttle arm to be operated with great precision even when visibility is obstructed. The system was used operationally during the first assembly mission, STS-88, as astronaut Nancy Currie, with her view partially obstructed, attached the first station component, the Zarya control module, to the second component, the Unity connecting module. Read more about the Space Vision System.

Canada also is building the new Space Station Remote Manipulator System, a 55-foot-long arm that will be launched early in the station's assembly sequence.

The station arm will have the new capability to move around the station's exterior like an inchworm, locking its free end on one of many special fixtures (called Power and Data Grapple Fixtures) placed strategically around the station, and then detaching its other end and moving forward. In addition, the station arm will later ride on a Mobile Servicing System platform that will move on tracks along the length of the station's 360-foot truss, putting much of the station within grasp of the arm.

Canada also is providing the new robotic "Canada Hand" for the station, called the Special Purpose Dexterious Manipulator (SPDM). The "hand" consists of two small robotic arms that can be attached to the end of the main station arm to conduct more intricate maintenance tasks. 

Two other robotic arms will be on the International Space Station. A European Robotic Arm (ERA), built by the European Space Agency will be used for maintenance on the Russian segment of the station. 

ERA will assist in the installation, deployment and replacement of Solar Array Drive and arrays of the Russian Science and Power Platform (SPP), inspection of the Russian segment of the Space Station, support/transfer of EVA cosmonauts, transfer of Orbital Replacement Units and other assembly tasks. The arm consists of 2 End-Effectors, 2 Wrists, 2 Limbs and 1 Elbow joint together with electronics and cameras. Both ends act as either a “hand” for the robot or the base from which it can operate.

Canada Hand (Click to enlarge)

European Arm (Click to enlarge)

Japanese robotic arm

In addition to mechanical arms, other robotics that may be used aboard the station include a free-flying robotic camera called AERcam. A prototype of AERcam was tested during a 1997 Space Shuttle mission.  AERcam could be used to inspect the exterior of the station, including the acre of solar panels. Read more about the AERcam.

The Station Suit

In addition to new spacewalking tools and techniques, astronauts will have an enhanced space suit. The Shuttle space suit, or Extravehicular Mobility Unit (EMU) as it is technically called, was originally designed to be maintained between flights by specialists on Earth.

This is a difficult requirement for astronauts living and working on the space station. The EMU is now being improved for use on the ISS. Click here for details about the EMU.

Astronaut Jeff Williams in a suit test

The space suit will be stored in orbit and will be certified for up to 25 spacewalks before it must be returned to Earth for refurbishment. It can be adjusted in flight to fit different astronauts, and it can be easily cleaned and refurbished onboard the station between spacewalks. In addition, assembly work on the station will be done in much colder temperatures than are experienced during most Space Shuttle spacewalks. Unlike the Shuttle, the station cannot be turned to provide the optimum sunlight to moderate temperatures during a spacewalk.

Enhancements to the suit to better prepare it for assembly and use aboard the station include: easily replaceable internal parts; reusable carbon dioxide removal cartridges; metal sizing rings that allow in-flight suit adjustments to fit different crewmembers; new gloves with enhanced dexterity; a new radio with more channels to allow up to five people to talk at one time; warmth enhancements such as fingertip heaters and a cooling system shutoff; new helmet-mounted floodlights and spot lights; and a jet-pack "life jacket" called SAFER to allow an accidentally untethered astronaut to fly back to the station in an emergency.  For a detailed history of space suits, "Walking to Olympus", click here.

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