Astronauts aboard the international space station 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 space station oxygen upgrades this year.

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

Built by Russian engineers, the Elektron device aboard the space station uses electrolysis to separate water into hydrogen and oxygen. (The hydrogen is then dumped overboard.)

The 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 space station crew, Expedition 12 commander Bill McArthur and flight engineer Valery Tokarev, also have installed an oxygen conservation system inside the station’s U.S.-built Quest airlock for use before spacewalks with a visiting shuttle, they added.

NASA’s oxygen factory

Once installed and operational — a process that could take months — the OGS will provide enough oxygen to support a full space station crew complement of six astronauts, NASA officials said.

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

Bagdigian said the OGS originally was 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 space station crew sizes, NASA officials said.

“We know that oxygen-generating systems in general have a lot of problems over the years during start-up,” William Gerstenmaier, NASA’s associate administrator for space operation, said in a press conference Feb. 6. “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 space station 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 station .

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

Orbiting oxygen

While the OGS is waiting to launch to the space station from NASA’s Kennedy Space Center in Florida, the oxygen-conserving ROOBA system is waiting in orbit for the 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,” said Dan Leonard, ROOBA’s primary designer for Boeing in Houston . “It’s basically a hose.”

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

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

“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 .”

ROOBA arrived at the space station 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.