Efforts to inflate the flexible habitat, known as the Bigelow Expandable Activity Module (BEAM), got under way at about 9 am (1300 GMT).
Space scientists monitoring the expansion at mission control in Houston, Texas early Saturday expressed optimism that they were having early success this time around, as images on NASA television showed the module slowly expanding after receiving three initial bursts of air.
“BEAM (is) continuing to slowly expand,” said NASA spokesman Daniel Huot.
“Everything going smoothly so far this morning, seeing good expansion both along the length and the diameter of BEAM. The pressure is well within what was expected.”
NASA is testing expandable habitats astronauts might use on the Moon or Mars in the coming decades. Operations to expand the module were led by NASA astronaut Jeff Williams. A first attempt on Thursday was not successful.
NASA said that after a series of leak checks and other preparations, space station astronauts will enter the habitat through the station’s Tranquility module.
The US space agency said astronauts will re-enter the module several times a year, throughout the two-year technology demonstration, to retrieve sensor data and assess conditions inside the unit.
Bigelow, which developed the first-of-its-kind habitat as part of an $18 million contract with NASA, said it supported the decision to pause the expansion.
Fully expanded, the module should reach a size of 13 feet long (four meters) by 10.5 feet (3.23 meters) wide.
The initial plan was for astronauts to venture inside multiple times over the next two years to take readings from sensors inside the pod and to test how well it might protect against space radiation.
NASA said that if the expansion runs into problems in these first tests in space, the astronauts may deflate the habitat and try again in the coming days.
Astronauts were scheduled to enter the oblong structure for the first time on June 2, according to the initial timeline.
The plan called for the crew on board the space station to venture into the module several times a year to collect data from interior sensors — particularly to see how well it protects people against radiation in space.
The inflation process may be better described as “unfolding” since it takes very little air to bring the pod to full size, experts said.
The space station crew was to expand BEAM by introducing a small amount of air from the orbiting lab via a manual valve on the BEAM bulkhead.
Only about 0.4 pounds per square inch (psi) was supposed to be needed to expand BEAM to its full shape.
Eight air tanks inside BEAM, once activated, were set to bring the pod to full pressure, requiring about 42 pounds of air to fully pressurize BEAM’s internal volume of 565 cubic feet (16 cubic meters).
Expandable habitats’ benefit lies in the little space they take up in spacecrafts’ cargo holds while providing greater living and working space once inflated.
But key questions that remain to be answered include how well pods would protect people against solar radiation, space debris and the temperature extremes of space.