Air Apparent: New Oxygen Systems for the ISS
The rack containing NASA's Oxygen Generation System build for the International Space Station arrives at Kennedy Space Center where it will be installed in a cargo module for launch aboard the space shuttle Discovery.
Credit: NASA/KSC.

Astronauts aboard the International Space Station (ISS) will be breathing easy after the next shuttle visit to the orbital research platform.

That flight, NASA's STS-121 mission currently slated to launch in May, will deliver the U.S.-built Oxygen Generation System (OGS) to the station in the second of two ISS oxygen upgrades this year.

"The basic technologies are the same as the Elektron," said Bob Bagdigian, NASA's project manager for regenerative environmental control and life support systems, in an interview.

Built by Russian engineers, the Elektron device aboard the space station uses electrolysis to separate water into hydrogen, which is dumped overboard, and oxygen. The 1,500-pound (680-kilogram) OGS rack works in much the same way, and will be able to provide 12 pounds of breathable oxygen daily under normal operations, NASA officials said.

The current ISS crew, Expedition 12 commander Bill McArthur and flight engineer Valery Tokarev, have also installed an oxygen conservation system inside the station's U.S.-built Quest airlock to be used before spacewalks during joint operations with a visiting shuttle, they added.

NASA's oxygen factory

Once installed and operational - a process that could take months - the OGS is expected to increase the space station's crew capacity up to its maximum six-person total, NASA officials said.

The largest ISS crews to date have been three-astronaut expeditions, though extended delays in station-bound shuttle flights since the 2003 Columbia accident have limited several missions to two astronauts each.

Bagdigian said the OGS was originally slated to fly aboard the station's Node 3, a hub for the bay window-like cupola and now grounded habitation module, but was later reworked to function inside the U.S.-built Destiny laboratory.

The shift will require some adjustments to Destiny - largely to vent waste hydrogen and provide power for the OGS - but will allow engineers a chance to shake down the oxygen system sooner and assist efforts to increase ISS crews sizes, NASA officials said.

"We know that oxygen generating systems in general have a lot of problems over the years during start-up," said William Gerstenmaier, NASA's associate administrator for space operation, in a press conference last week. "We think we'll have some problems with our oxygen generator system. We want to fly it early so we can work those out."

The Elektron device, for example, caused recurring headaches for flight controllers and ISS astronauts over several expeditions when it broke down repeatedly after in-space repairs. The unit was brought back online, ultimately in back-up mode, once spare parts were lofted to the ISS.

NASA officials said the OGS is one of two major parts of a comprehensive life support system for the ISS. A water reclamation system, which is slated to recycle wastewater and human urine, is also under development at Marshall Space Flight Center (MSFC) where the OGS was designed and tested.


While the OGS is waiting to launch toward the ISS from NASA's Kennedy Space Center in Florida, the oxygen-conserving ROOBA system is waiting in orbit for next shuttle's arrival.

The ROOBA, or Recharge Oxygen Orifice Bypass Assembly, sounds more complicated than it actually is, its builders said.

"It's very simple," explained Dan Leonard, ROOBA's primary designer for Boeing in Houston, Texas. "It's basically a hose."

The 25-foot (7.6-meter) ROOBA uses two hoses to link the space station's Quest airlock - home base for most ISS spacewalks in U.S. spacesuits - with a shuttle to draw oxygen directly from the orbiter's tanks. The measure not only conserves some ISS oxygen supplies, it also eases strain on airlock equipment that would otherwise have to replaced during the limited number of flights before NASA retires its shuttle fleet in 2010, Leonard added.

ROOBA will be used by astronauts to prepare themselves for spacewalks before they exit the ISS.

"Before you go outside into a spacewalk, you've got to breathe oxygen for a few hours to purge the nitrogen out of your blood because your spacesuit's at a very low pressure," said mission specialist Piers Sellers, one of two STS-121 spacewalkers, in a NASA interview. "If you didn't do that, you would get the bends very quickly. So it's important that you manage to get enough oxygen to purge the nitrogen out of your blood. You breathe it through a mask."

ROOBA arrived at the ISS aboard an unmanned Russian-built cargo ship after years of development work on the ground, though the real test will come during the STS-121 flight's three planned extravehicular activities, NASA officials said.

"It's always nice to get a part on orbit," Leonard said, adding that his team will keep a close watch on ROOBA during the upcoming spacewalks.