Orbital Sciences Corp. bade a fond farewell to its first Cygnus cargo ship yesterday, as the hugely successful Demonstration Mission—designated “ORB-D”—concluded with a fiery plunge into the upper atmosphere, burning up over the Pacific Ocean, to the east of New Zealand. Launched on 18 September, Cygnus arrived at the International Space Station (ISS) 11 days later and spent a little more than three weeks berthed at orbital outpost, bringing 1,300 pounds (590 kg) of equipment and supplies to the resident Expedition 37 crew. As described in a recent AmericaSpace article, Cygnus was unberthed from the space station’s Harmony node and released into free flight at 7:31 a.m. EDT Tuesday. It then performed a series of thruster firings to position itself into a “disposal corridor” for Wednesday afternoon’s destructive re-entry.
Far from being “the end,” this is actually only the beginning for Orbital’s relationship with the ISS. The ORB-D mission completed the critical Commercial Orbital Transportation Services (COTS) requirement, and Orbital can now press ahead with its $1.9 billion Commercial Resupply Services (CRS) contract with NASA, which calls for eight more Cygnus missions by 2016 to transport a total of around 44,000 pounds (20,000 kg) of payloads to the multi-national outpost. Fittingly, yesterday’s departure of ORB-D coincided with Orbital’s shipment of the Service Module for its next Cygnus mission—known as “ORB-1″—to the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., from where it is scheduled to launch around 15 December. “Something poetic about first #Cygnus re-entering Earth’s atmosphere same day second Cygnus ships to launch site,” Orbital tweeted to its 17,000 followers.
Shortly before 2 p.m. EDT Wednesday, Orbital tweeted that Cygnus had successfully completed the final “burn” of its maneuvering thrusters to begin the re-entry. Following Tuesday’s unberthing and separation from the ISS—and loaded with an estimated 3,000 pounds (1,360 kg) of trash and other disposable items—the cargo ship transitioned to its own internal power supplies and passed beyond the critical 660 foot (200 meter) “Keep Out Sphere” (KOS), which extends around the space station as a virtual exclusion zone. Shortly thereafter, Cygnus executed a burn of its thrusters to commence its departure from the vicinity of the ISS and prepare for its End of Mission.
Early Wednesday, the cylindrical spacecraft completed a “braking burn” to reduce the low point (or “perigee”) of its orbit to about 112 miles (180 km), producing an orbit of 112 x 260 miles (180 x 420 km). This orbit was due to be lowered by another burn a little after 1:41 p.m. EDT, which reduced the perigee still further to only 80 miles (50 km). In Cygnus’ final hours of life, Orbital Sciences tweeted a request for “anyone in New Zealand who happens to see #Cygnus reentry, please take a picture or video and post.” It was noted that since the dying cargo ship would be traveling from the south to the north, New Zealand’s South Island would be a good vantage point for observations.
Already, NASASpaceflight.com had highlighted a Notice to Airmen (NOTAM) of the dangers posed by surviving Cygnus debris in New Zealand’s Auckland Oceanic Flight Information Region (FIR), extending from 1-5 p.m. EDT Wednesday. According to Airways, a subsidiary of the New Zealand Government whose responsibility for all air control movements encompasses New Zealand’s entire controlled airspace, the Auckland Oceanic FIR covers about 16 million square miles (26 million square km) of the Pacific and Tasman Oceans, from the South Pole to just 5 degrees south of the equator. It was this region which provided the setting for Cygnus’ final death-throes and which now serves as its grave.
Shortly after the completion of Cygnus’ final, 7-minute-long thruster firing to begin its descent, Orbital tweeted revised computations of 2:16:28 p.m. EDT for the exact time of Entry Interface (EI) with the “sensible” atmosphere. Loss of Signal with the spacecraft, it said, was anticipated 3 minutes later. Finally, at about 2:22 p.m. the company announced that “We have lost the signal from #Cygnus. Re-entry accomplished. Represents the official completion of our COTS program with @NASA partners.” Orbital also paid tribute to ORB-D’s namesake, the late G. David Low, a former shuttle astronaut and Orbital senior executive under whose leadership the COTS and CRS relationship with NASA was conceived, matured, and reached fruition. “We’re sure its namesake would be proud of the Orbital and NASA team,” it was noted.
“With the COTS development phase now successfully completed, we are now turning our full attention to the eight operational resupply missions covered by our Commercial Resupply Services contract with NASA,” said Frank Culbertson, Orbital’s Executive Vice President and General Manager of its Advanced Programs Group. “Each Cygnus is capable of delivering a large quantity of pressurized cargo, totaling up to 20,000 kg over the eight missions, including crew supplies, spare parts and equipment, and scientific experiments for the ISS. We are looking forward to starting these missions in December.”
Unlike SpaceX’s Dragon cargo ship—which can survive atmospheric re-entry and perform a parachute-assisted ocean splashdown—Cygnus is intended to burn up at the end of each mission. According to NASASpaceflight.com, the second Cygnus will rendezvous and berth at the ISS on 18 December and will spend about three weeks in residence, with departure planned for 10 January 2014. Further missions (ORB-2 and ORB-3) are tentatively manifested for launch in May and October 2014.
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