Orbital Sciences Corp. today announced that its first Cygnus cargo ship must wait until Saturday, 28 September for rendezvous and berthing at the International Space Station (ISS). Launched atop the Antares rocket last Wednesday from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., Cygnus is completing the requirements of the Commercial Orbital Transportation Services (COTS) Demonstration Mission to showcase its capabilities, ahead of a series of eight Commercial Resupply Services (CRS) flights for NASA, beginning in December.
Laden with 1,300 pounds of non-critical supplies, payloads, and equipment for the space station’s Expedition 37 crew of Commander Fyodor Yurchikhin and Flight Engineers Karen Nyberg and Luca Parmitano, Orbital’s long-awaited mission is designated ORB-D and its first two days of flight were relatively problem-free. The two-part spacecraft—which comprises a Service Module (SM) and a Pressurized Cargo Module (PCM) and is powered by a pair of gallium arsenide solar arrays and receives propulsion from a set of hydrazine and nitrogen tetroxide thrusters—demonstrated three of its key demonstration objectives during this timeframe. These included testing its “Position and Control” capability to orient itself properly in space, deactivating its thrusters and operating in “free drift” and performing a simulated abort maneuver.
By midday EDT Saturday, Cygnus was about 250 miles “behind” the ISS, with rendezvous and berthing targeted for early the next morning. However, at 1:30 a.m. EDT Sunday, Orbital announced that the capture and berthing operation had met with delay. “Cygnus … established direct data contact with the International Space Station and found that some of the data received had values that it did not expect, causing Cygnus to reject the data,” Orbital reported. “This mandated an interruption of the approach sequence. Orbital has subsequently found the causes of this discrepancy and is developing a software fix. The minimum turnaround time to resume the approach to the ISS following an interruption such as this is approximately 48 hours due to orbital mechanics of the approach trajectory.” Uploading and testing of the new software patch was scheduled to take place early Monday, and Cygnus was expected to commence its second rendezvous a few hours later.
However, in view of impending Wednesday afternoon launch of Soyuz TMA-10M and a new crew of Russian cosmonauts Oleg Kotov and Sergei Ryazansky, together with NASA astronaut Mike Hopkins, it was considered prudent by NASA and Orbital to postpone the rendezvous until the next available opportunity on Saturday. “This new schedule will allow the Orbital operations team to carefully plan and be well-rested before starting the critical final approach to the space station,” said Frank Culbertson, Orbital’s Executive Vice President and General Manager of the Advanced Programs Group. “Meanwhile, Cygnus has all the resources needed to remain in orbit for an extended period of time.”
As will be described in an AmericaSpace preview article for Soyuz TMA-10M—scheduled to appear on site tomorrow (Tuesday)—the launch of Kotov, Ryazansky, and Hopkins is planned from the Baikonur Cosmodrome in Kazakhstan at 4:58 p.m. EDT Wednesday (2:58 a.m. local Kazakh time Thursday). The three men would then execute a complex four-orbit, six-hour “fast rendezvous” profile, with docking at the ISS anticipated at 10:47 p.m. EDT. Taking into account the heavy workload of the astronauts and cosmonauts—and with Tuesday previously earmarked as a light-duty day for Yurchikhin, Nyberg, and Parmitano—the combination of activities “resulted in a tight schedule” about which neither NASA or Orbital felt wholly comfortable.
NASA has reported that more details about the ORB-D rendezvous operation will be released closer to the weekend, but the arrival of Cygnus promises to be a complex affair. Approaching the ISS from “behind” and “below,” the spacecraft will perform several stops to check its progress and the performance of its systems, before proceeding to the next hold point. Finally, it will enter the “Keep Out Sphere” (KOS)—a virtual zone extending about 660 feet around the space station to prevent collisions—and its final halt point will occur at a distance of about 35 feet. Cygnus will then deactivate its thrusters, operating in a free drift attitude, and will be grappled by the 57-foot-long Canadarm2 robotic arm and berthed at the “nadir” (or Earth-facing) port of the Harmony node.
Plans call for Italian astronaut Luca Parmitano, based in the Cupola, to be the primary arm operator, with Karen Nyberg backing him up from a secondary work station in the U.S. Destiny laboratory. With the new crew members in attendance by the weekend, additional eyes, ears, and brains will enhance the likelihood of a successful rendezvous and berthing. After its arrival, leak checks and power connections will be established and the crew will enter the cargo ship, initially wearing masks and eye protection to counter against the presence of interior dust or debris. Cygnus is slated to remain berthed at the ISS until 22 October, after which it will unberthed—again via Canadarm2—and intentionally destroyed in the upper atmosphere.
If all goes well, Orbital intends to launch its first “dedicated” Cygnus mission (designated “ORB-1”) under the $1.9 billion Commercial Resupply Services (CRS) contract with NASA on about 8 December. Working on this schedule, it has been reported that the ORB-1 Cygnus will depart the ISS on 10 January 2014, after which SpaceX’s CRS-3 Dragon will fly in mid-January. This craft will occupy Cygnus’ former spot at the Harmony nadir port and is expected to remain attached to the station for a month. Unlike Cygnus, however, Dragon has the capacity to survive atmospheric re-entry and return to an ocean splashdown. Two Progress cargo vessels from Russia are also expected to deliver supplies and equipment to the space station in November and February.