Even Homes in Space

Need a Door

A new airlock soon to be installed on the International Space Station is critical for assembly and maintenance of the orbiting outpost.

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-- The International Space Station (ISS) may be the most technologically advanced house ever built, but at the moment it lacks something found in every home on Earth -- a front door!

Until now whenever astronauts onboard the ISS needed to venture outside for a spacewalk, they had to wait for a visit from the space shuttle. The ISS doesn't have an airlock that works with US spacesuits, but the shuttle does, and that's what spacewalkers have been using as an exit for their Extra-Vehicular Activities (EVAs).

Soon, however, the ISS will gain a new door of its own: the Joint Airlock Module (JAM). The six-ton airlock was manufactured by Boeing Company at the Marshall Space Flight Center in the same building where the Saturn V rocket was built that propelled humans to the Moon. Space shuttle Atlantis is slated to carry the new module to the space station on July 12th. If all goes as planned, assembly will begin on the fourth day of the STS-104 mission.

Above: The finished Joint Airlock Module at the Marshall Space Flight Center. The skinnier portion, which is 5 ft. (1.5 m) across and 9 ft. (2.7 m) long, is the only part normally exposed to the vacuum of space. [more pictures]

Astronauts installing the massive chamber will have two powerful helpers: the shuttle's robotic arm and the space station's advanced Canadarm2, which was added to the ISS in April. Canadarm2 will lift the airlock from the shuttle's cargo bay and maneuver it into position, while spacewalking astronauts ride on a foot platform attached to the end of the shuttle's arm.

Click on the image to view a 2 MB mpeg movie of Canadarm2 positioning the new Joint Airlock Module for attachment to the station's Unity module.

A key feature of the Joint Airlock Module is that it won't discriminate among spacesuits. Unlike the shuttle's airlock, where the communications system and connections for oxygen and coolant won't work with Russian suits, the Joint Airlock "will allow station-based EVAs with either the US spacesuits or, eventually, the Russian suits as well," says Hubert Brasseaux, the launch package manager for the upcoming shuttle mission.

The newly-installed airlock will get its first test when shuttle crewmates Mike Gernhardt and Jim Reilly use it for their third EVA of the STS-104 mission. The duo will exit the ISS and attach two high-pressure gas tanks -- one oxygen and one nitrogen -- to the outside of the Joint Airlock Module. These tanks (together with two others installed earlier in the mission) will replace air lost to the station when the airlock opens. They will also serve as backup air supplies for the ISS.

Installation of the airlock and the high pressure tanks will mark the end of the second phase of ISS assembly -- known around NASA as "ISS Phase Two." At that point, the crew will be living in a 15,000 cubic-foot (425 m3) home orbiting Earth -- more volume than a conventional three-bedroom house.

The Joint Airlock itself has two rooms, the "Equipment Lock" and the "Crewlock."

Above: Click on the image to view a 1.5 MB mpeg animation highlighting the major components of the new Joint Airlock Module.

"The Equipment Lock is similar to a locker room, in that it's the primary area where the crew members don and doff their spacesuits," explains Peggy Guirgis, EVA systems lead for the Joint Airlock. "It's also the primary area for servicing the spacesuits and stowing them."

The Crewlock, which is separated from the Equipment Lock by a hatch, is where spacewalkers open the outer hatch and actually begin their excursions into space. It's similar in size to the shuttle's airlock.



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Although the Joint Airlock Module is only 20 feet (6.1 meters) long, getting from one end to the other can be a slow process as astronauts prepare for their EVAs.

Even before they enter the airlock, astronauts must first spend time exercising on a stationary bicycle while breathing pure oxygen from a mask. The goal is to drive out nitrogen gas dissolved in their blood. The pure oxygen inside a US spacesuit provides only 4.3 psi (296 mbar) of pressure -- compared to 14.7 psi (1014 mbar) in the space station (equivalent to sea level on Earth). Astronauts subjected to such low pressures could contract "the bends" -- a condition familiar to SCUBA divers who surface too rapidly. The painful bends are caused by bubbles of nitrogen gas that leave solution in the blood and lodge in the body's tissues. Lowering the concentration of nitrogen in the blood by exercising and breathing pure oxygen avoids this problem.

: Like scuba divers who surface too rapidly, astronauts can suffer from the bends. Shuttle astronaut and veteran spacewalker Mike Gernhardt is a former commercial diver who helped develop the bends-beating exercise procedure for EVA's.

Next, spacewalkers float into the Equipment Lock where the ambient pressure is gradually lowered to 10.2 psi (703 mbar) -- which helps prepare their bodies for the even-lower pressures they will encounter inside their spacesuits. The astronauts don their spacesuits and double-check all of their equipment. Spacesuits are complex and bulky machines that weigh as much as 300 lbs. on Earth, so this can be a laborious process.

After another 60 minutes of breathing pure oxygen inside the suit, they move into the cramped quarters of the Crewlock. The Crewlock was built as small as possible to minimize the amount of precious air lost from the ISS to space. Air loss is further reduced by pumping most of the air in the lock back into the ISS before the astronauts begin their EVA.

The final act in this hours-long drama is opening the hatch. After a final check for leaks in their suits --spacewalkers are always checking for leaks-- the remaining air in the Crewlock (about 5 psi or 345 mbar) is vented overboard through a valve on the outer hatch. All hatches on the ISS operate manually, so EVA-bound astronauts must open the door themselves before they carefully make their way out into space.

Left: Astronauts say spacewalking is one of the most thrilling experiences of space exploration. But you can't venture outside without a door!

Leaving through the airlock seems a tortuous procedure, but it's surely worth the effort. Once in space, astronauts are rewarded by breathtaking views: the bright curving Earth below and pitch-black space sprinkled with stars above. Or is that space below and Earth above? Perhaps it doesn't matter. The station's new airlock will be a doorway to wonders no matter which end is up.

Even Homes in Space Need a Door

July 6, 2001

presented by ThursdaysClassroom.com Thursday's Classroom

Corner Would you like to use this story in your 6th to 12th grade classroom? These lessons might help:

Discussion Questions : Can your students answer these questions in less time than it takes an astronaut to get through the new Joint Airlock Module? [lesson plan] [activity sheet]

: Can your students answer these questions in less time than it takes an astronaut to get through the new Joint Airlock Module? [lesson plan] [activity sheet] Airlock Pantomime : In Hollywood movies astronauts zip in and out of their airlocks with little preparation. In real life it's an hours-long procedure. In this activity kids act out the steps for leaving the ISS. [lesson plan]

: In Hollywood movies astronauts zip in and out of their airlocks with little preparation. In real life it's an hours-long procedure. In this activity kids act out the steps for leaving the ISS. [lesson plan] Air Pressure Quickies: Many students think air is insubstantial. Not so, it's powerful stuff! Explore air pressure using these three simple activities. [lesson plan] [activity sheet]

Use this button to download the story and all the lessons and activities in printer-friendly Adobe PDF format:

SpaceFlight.nasa.gov -- NASA's human spaceflight home page

The Joint Airlock can accommodate up to 3 spacesuits at a time, and either U.S. or Russian suits can be used. Click on the image for a 2 MB animation of the interior of the airlock.

The Amazing Canadarm2 -- Science@NASA Story Crawling around the International Space Station like an agile worm, the newest Canadian robotic arm will be essential for building and maintaining the ISS.

Spacewalking -- from spaceflight.nasa.gov

Space Shuttle to Deliver New Doorway to Space -- Building and testing the new airlock was a team effort involving more than 12 contractors from two countries, as well as three NASA centers - the Marshall Space Flight Center, the Johnson Space Center, and the Kennedy Space Center. [more]

More pictures of the Joint Airlock Module -- courtesy of MSFC Public Affairs

Take a VR tour of the ISS -- can you find the Joint Airlock Module in this virtual reality space station?

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