After more than a month at the International Space Station (ISS), Orbital Sciences Corp. will bring its ORB-1 Cygnus cargo ship back to Earth with a fiery Viking-like funeral this week. Unberthing from the Earth-facing (or “nadir”) port of the station’s Harmony node is scheduled to take place at 5:30 a.m. EST on Tuesday, 18 February, with Expedition 38 crewmen Mike Hopkins and Koichi Wakata controlling the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm from the Robotic Workstation (RWS) inside the multi-windowed cupola. The Cygnus vehicle, named in honor of former shuttle astronaut C. Gordon Fullerton—who died last August—is due to be released into free flight by Canadarm2 at 6:40 a.m. EST, after which it will be maneuvered into a “disposal corridor,” preparatory to its seven-minute de-orbit “burn” Wednesday morning.
Launched on 9 January, atop Orbital’s home-grown Antares booster from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., the ORB-1 mission has proven an enormous success. Cygnus ferried 2,780 pounds (1,260 kg) of payloads, supplies, experiments, and belated Christmas gifts to the station’s incumbent Expedition 38 crew of Russian cosmonauts Oleg Kotov, Sergei Ryazansky, and Mikhail Tyurin, NASA astronauts Mike Hopkins and Rick Mastracchio, and Japan’s Koichi Wakata. After a number of maneuvers, the cargo ship was grappled by Canadarm2 and berthed at the Harmony node on 12 January. “The arrival capped the first successful contracted cargo delivery by Orbital Sciences,” explained NASA in a post-berthing news release.
The Dulles, Va.-based aerospace company received a $1.9 billion Commercial Resupply Services (CRS) contract from NASA in December 2008, whose language requires eight Cygnus missions by 2016 to haul a total of 44,000 pounds (20,000 kg) of supplies, payloads and equipment to the ISS. As part of the requirements for these missions, both Orbital and SpaceX—NASA’s second CRS partner—were required to first execute a satisfactory Commercial Orbital Transportation Services (COTS) demonstration flight. SpaceX completed the COTS mission of its Dragon cargo ship in May 2012, followed by Orbital’s ORB-D test flight of Cygnus in September-October 2013. With the enormous success of both missions, Orbital and SpaceX were cleared to begin their dedicated CRS commitments. SpaceX has already flown two of its six contracted CRS flights, in October 2012 and March 2013, whilst ORB-1 represents the first CRS mission by Orbital. As a result, the United States now has two fully-fledged private contractors restocking the space station.
When Canadarm2 releases Cygnus at 6:40 a.m. EST tomorrow, it will bring to an end 37 days of joint operations. In the seconds after unberthing, Hopkins and Wakata will issue a planned “Abort” command, which will instruct the cargo ship to retreat away from the ISS. Laden with up to 2,800 pounds (1,270 kg) of trash and other disposable items, Cygnus will transition to its internal power supply, and after about three minutes it will pass beyond the critical, 660-foot (200-meter) “Keep Out Sphere” (KOS), a virtual exclusion zone around the space station. And three minutes after that, at about 6:46 a.m., it will complete a separation “burn” of its maneuvering thrusters to depart for good.
According to NASA, the unpiloted cargo ship will fire its engines for the final time at 8 a.m. EST Wednesday and will be burn up over an uninhabited stretch of the Pacific Ocean. Unlike SpaceX’s Dragon cargo vehicle—which can survive atmospheric re-entry and perform a parachute-assisted ocean splashdown—Cygnus is intended to be destroyed at the end of each mission.
With the completion of its ORB-1 mission, the playing field between Orbital and SpaceX has begun to level. The Hawthorne, Calif.-based launch services organization, headed by PayPal entrepreneur Elon Musk, will launch its third Dragon mission (SpX-3) in mid-March, followed by two others in July and November. Meanwhile, Orbital’s second dedicated mission (ORB-2) is expected to launch in early May, followed by ORB-3 in October. Each cargo flight will spend approximately a month berthed at the ISS.