A little more than two days after its rousing Tuesday night liftoff from the storied Space Launch Complex (SLC)-41 at Cape Canaveral Air Force Station, Fla., Orbital ATK has successfully delivered another Cygnus cargo ship to the International Space Station (ISS). The perfect rendezvous and capture of the OA-6 spacecraft at 6:51 a.m. EDT Saturday, followed by a physical berthing at the Earth-facing (or “nadir”) port of the station’s Unity node at 10:52 a.m. EDT, also came a couple of days after Expedition 47 Commander Tim Kopra shared a remarkable image of a vast crater in Western Africa with his 70,600 Twitter followers. The crater obviously impressed his newly-arrived crewmate Jeff Williams. “@Astro_Jeff calls this the Earth’s bull’s eye,” Kopra tweeted Thursday.
And certainly, the Expedition 47 crew—which, in addition to Kopra and Williams, also includes Russian cosmonauts Yuri Malenchenko, Oleg Skripochka and Alexei Ovchinin, together with Britain’s Tim Peake—scored a bull’s eye of their own by snaring OA-6 with the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm. This weekend is expected to be a busy one, as the crew opens the hatch into Cygnus early Sunday and accesses some 7,228.9 pounds (3,279 kg) of supplies.
As outlined in AmericaSpace’s OA-6 preview article, this mission kept with tradition, in that its name honored a former U.S. astronaut who had contributed significantly either to commercial space endeavors or to space exploration as a whole. However, OA-6 differs significantly from the rest. Whereas Orbital ATK’s four previous successful Cygnus missions paid homage to past spaceflight luminaries—specifically former astronaut and Orbital executive G. David Low, veteran shuttle commander C. Gordon Fullerton, five-time shuttle flier Janice Voss and “Original Seven” Mercury selectee Donald “Deke” Slayton—OA-6 carried name which was much more personal to the ISS Program. It was named “Spaceship (SS) Rick Husband”, for the man who not only commanded the final voyage of shuttle Columbia in early 2003, but was also part of shuttle mission STS-96 in mid-1999, which performed the first docking with the infant space station. In paying tribute to Husband’s “spirit for exploration”, Orbital ATK previously noted that OA-6 marks the first occasion that one of its Cygnus ships has been named for an astronaut who actually participated in the mammoth ISS construction task.
Following Wednesday’s launch, the Cygnus proceeded smartly through a series of crisp rendezvous and phasing maneuvers to reach the space station. Its two lightweight UltraFlex solar arrays were successfully unfurled, in a fan-like fashion, a couple of hours of achieving orbit, each spanning 12.1 feet (3.7 meters) when fully deployed. Shortly after 5 a.m. EDT Saturday—with Kopra and Peake at a Robotic Workstation (RWS) in the multi-windowed cupola—the Expedition 47 crew called a “tally-ho” on the cargo ship, as it came within 3,300 feet (1,000 meters). Overseeing the rendezvous from the “White” Flight Control Room (FCR) at the Johnson Space Center (JSC) in Houston, Texas, were Flight Director Gary Horlacher and, at the Capcom’s console, Canadian Space Agency (CSA) astronaut Jeremy Hansen. (Interestingly, fellow Canadian astronaut David Saint-Jacques was at the same console during December’s capture of the OA-4 Cygnus.) “Pretty cool @OrbitalATK #Cygnus cargo vehicle in Mission Cntrl,” quipped Hansen in a 5:15 a.m. tweet, displaying a model of the cargo ship. “Slightly better than the spacecraft I built as a kid.”
Passing high above New Guinea, the “rock-solid” OA-6 Cygnus reached its first “Hold Point” at a distance of 820 feet (250 meters) from the space station shortly after 5:35 a.m. Fifteen minutes later, Houston and Orbital ATK’s Cygnus Flight Control Room in Dulles, Va., granted unanimous approval for the spacecraft to proceed within the so-called “Keep-Out Sphere” (KOS). This virtual exclusion zone, which Cygnus entered at 5:55 a.m., extends 660 feet (200 meters) around the ISS to prevent the risk of a collision. A series of calls from Peake during this period signified that Cygnus was executing a perfect rendezvous, with an estimate from Mr. Horlacher that the grapple time had been slightly refined to 6:47 a.m., a few minutes later than originally planned.
After crossing the continental United States, the station and its incoming visitor approached orbital sunrise over the Dominican Republic, as they neared the second Hold Point at 100 feet (30 meters). This point was reached a little after 6:20 a.m. and was expected to be relatively short period of holding, with clearance granted by both control centers at 6:27 a.m. to proceed inward. “Houston and Dulles Mission Controls “go” for final approach,” it was noted. “Astronauts reviewing robotics procedures before #Cygnus moves in for capture.” The spacecraft reached its 30-foot (10-meter) Capture Point at 6:37 a.m. With Kopra at the controls of the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm and Peake backing him up, the pair were given a “Go for Capture” at 6:39 a.m.
By this stage—flying high above the Southern Indian Ocean, off the southernmost tip of South Africa—the OA-6 spacecraft had entered “Free Drift”, with all thrusters disabled to ensure that no disturbances were imparted between the two vehicles. Meanwhile, the space station itself entered a strict phase of “Attitude Hold”, reliant upon its suite of Control Moment Gyroscopes (CMGs). “Vehicle capture is where ISS motion control really shines,” AmericaSpace was told in previous comments by ISS Flight Controller Ben Honey. “It’s not so much a vehicle as a stable stationary platform, from which to joystick the arm in.”
“@Astro_Tim is going in for the cosmic catch with #Canadarm2,” tweeted CSA at 6:45 a.m., as Kopra extended the robotic arm to grapple the cargo ship. With the glittering Cygnus displaying its impressive size, Kopra positioned the Latching End Effector (LEE) over the spacecraft’s grapple pin, thereby setting the final pieces in place for a picture-perfect capture at 6:51 a.m. EDT. “GOTCHA!” tweeted Orbital ATK, as its fifth Cygnus safely arrived at the space station, whilst CSA noted: “Cosmic catch complete! Nice flying, @Astro_Tim! That is one sweet Easter egg.” Added Jeremy Hansen: “Great capture. #Cygnus now in hands of #Canadarm2! Mission success! Great team all around.” Not to be left out, Tim Peake shared what he described as a “View from the Office”: two images of himself and Kopra at work in the cupola and another of Canadarm2 and Cygnus, just before capture.
The warmth of the congratulatory messages paled, though, when compared to the poignant words of Kopra himself. “Cygnus capture is complete and we’re Go for Cygnus post-capture reconfig,” he initially reported to Hansen, before paying tribute to the man whose sacrifice ultimately brought down the final curtain on the shuttle program and laid the foundations for the future. “We’re really honored to bring aboard SS Rick Husband to the International Space Station,” Kopra said. “It recognizes a personal hero to so many of us and this’ll be the first Cygnus honoree who was directly involved with the construction of this great station.”
“Excellent words, Tim,” Hansen replied. “Couldn’t be better said.”
Today’s grapple marked the 17th overall capture of a cargo ship by Canadarm2, which was installed aboard the space station by the STS-100 shuttle crew, way back in April 2001. For almost seven years, the “Big Arm” has supported the capture and berthing of five H-II Transfer Vehicles (HTVs) on behalf of the Japan Aerospace Exploration Agency (JAXA), seven SpaceX Dragons and (including OA-6) five Cygnuses.
Over the course of the next two hours, the Robotics Officer (ROBO) in Houston and the U.S. Orbital Segment (USOS) crew of Expedition 47 worked to maneuver Cygnus toward its installation position on the Earth-facing (or “nadir”) Common Berthing Mechanism (CBM) of the Unity node. The physical berthing of the cargo ship occurred in two parts, with the astronauts overseeing “First Stage Capture”, in which hooks from Unity’s nadir CBM extended and grabbed Cygnus to pull their respective CBMs into contact. This was followed by “Second Stage Capture”, wherein a series of 16 bolts—four gangs of four bolts apiece—were driven to rigidize the two spacecraft in a tight, mechanized embrace.
That effort was met with some delay, due to the “stretching-out” of Canadarm2. According to NASA’s Rob Navias, the geometry of reaching Unity proved more complex than reaching the Harmony node, where all previous Orbital ATK Cygnuses—with the exception of last December’s OA-4—have berthed. Coupled with a slight misalignment of Ready-to-Latch (RTL) indications and a lack of Ku-band downlink coverage through the Tracking and Data Relay Satellite System (TDRSS), Flight Director Scott Stover elected to postpone the bolting procedure about an hour behind the original timeline. Doing so would also allow controllers to benefit from a wider “window” of Ku time.
At length, First Stage Capture was completed a little after 10:40 a.m. EDT, followed by Second Stage Capture a few minutes later at 10:52 a.m. Current plans are for the hatches into Cygnus to be opened early Sunday, kicking off almost two months of operations with Orbital ATK’s latest visiting vehicle. The spacecraft is due to remain berthed to the station until 20 May, which, if this schedule holds, will represent the second-longest stay-time of any U.S. commercial vehicle at the ISS.
A busy period of station operations lies ahead, with SpaceX’s Dragon expected to launch no sooner than 8 April on the Commercial Resupply Services (CRS)-8 mission. With Dragon expected to berth at the nadir port of the Harmony node, this will mark the first time that both of NASA’s Commercial Cargo providers—Orbital ATK and SpaceX—will have been represented on-station at the same time. And with Russia’s Progress M-29M cargo ship due to depart on Tuesday, 29 March, and be replaced in short order by Progress MS-2, the coming month will see multiple visiting vehicles attached to the ISS. The piloted Soyuz TMA-19M and Soyuz TMA-20M are presently docked at the Russian Orbital Segment (ROS) and with two Progresses and both Dragon and Cygnus also in place throughout April, this will see the rare simultaneous occupation of as many as six ISS ports.
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