HOUSTON — The Japan Aerospace Exploration Agency’s HTV-4 resupply craft departed the International Space Station on Sept. 4, clearing a U.S. segment berthing port for Orbital Science Corp.’s Cygnus resupply capsule, which awaits liftoff from the Mid-Atlantic Regional Spaceport on Virginia’s eastern shore under the demonstration phase of NASA’s Commercial Orbital Transportation Systems (COTS) program.

Shortly after the HTV-4 departure, a NASA Flight Readiness Review (FRR) cleared the two-stage Antares rocket and its Cygnus supply capsule loaded with 1,540 lb. of ISS cargo for a Sept. 17 liftoff at 11:16 a.m. EDT. The Dulles, Va.-based company will have through Sept. 29 to launch the mission, under its current FAA licensing agreement, though it may have to adjust to any changes in Orbital Sciences’ scheduled Sept. 6 launch of NASA’s Lunar Atmosphere and Dust Environment Explorer mission as well as a planned late September Russian ISS crew launch.

“We had a very thorough discussion,” NASA’s Mike Suffredini, the ISS program manager, told a post-FRR news briefing. “We are not working any issues.” Bill Gerstenmaier, NASA’s associate administrator for human exploration and operations, chaired the FRR.

A successful launch of the Antares and subsequent berthing of the Cygnus would mark the long-sought introduction of a second NASA-nurtured U.S. space station commercial resupply capability in the aftermath of the space shuttle’s 2011 retirement.

By meeting all of its COTS milestones on the demonstration flight, Orbital Sciences will be eligible to launch the first of eight resupply missions agreed to under a $1.9 billion NASA Commercial Resupply Services (CRS) contract awarded in December 2008.

SpaceX, NASA’s first COTS partner, achieved the COTS demonstration milestone in 2012 and has carried out two CRS missions under a 12-mission, $1.6 billion NASA contract.

With a successful liftoff, Cygnus will aim for a rendezvous with the ISS on Sept. 22 and remain berthed for 30 days, said Frank Culbertson, Orbital Sciences executive vice president. The company will be ready to launch its first CRS mission within 47 days of the demonstration mission’s conclusion, Culbertson said.

Astronauts Karen Nyberg of NASA and Luca Parmitano of the European Space Agency used the station’s Canadian-built 58-ft.-long robot arm on Sept. 4 to release the departing HTV-4 at 12:20 p.m. EDT. JAXA’s unpiloted HTV-4 rendezvoused with the ISS on Aug. 9, delivering 3.6 tons of pressurized and unpressurized supplies, including research gear and spare parts. The fourth of JAXA’s resupply craft launched since 2009 departed the ISS filled with trash and is scheduled to burn up in the Earth’s atmosphere on Sept. 7 at 2:34 a.m. EDT.

A series of instruments on the HTV-4 as well as video recording instrumentation on the ISS will observe the re-entry for a structural breakup analysis.

If successful, the Cygnus mission will satisfy the company’s development responsibilities under a $288 million NASA COTS agreement reached in February 2008.