Cygnus OA-4 arrives at International Space Station
Almost three days after a United Launch Alliance (ULA) Atlas V rocket placed it in orbit, Orbital ATK’s Deke Slayton II Cygnus cargo ship arrived at the International Space Station, successfully resuming cargo resupplies from the United States.
Once the Cygnus was about 40 feet (12 meters) below the outpost, Expedition 45 Flight Engineer Kjell Lindgren used the outpost’s robotic arm to pluck the spacecraft from space. At 5:19 a.m. CST (11:19 GMT), the cargo ship was firmly grasped as the station was flying high above the Arabian Sea.
“Congratulations for a phenomenal team effort in delivering the Cygnus vehicle and its precious cargo,” radioed Lindgren to ground teams after capturing the vehicle. “Welcome aboard Deke Slayton.”
Ground teams, giving the station crew a break, then commanded the robotic arm to maneuver the spacecraft to about 3 feet (about 1 meter) below the Unity module in a pre-install position by 7 a.m. CST (13:00 GMT). After fine tuning proper alignment, the command was given to drive bolts connecting Cygnus to Unity, officially berthing the cargo ship to the orbiting outpost at 8:26 a.m. CST (14:26 GMT).
Cygnus’ approach operations began early morning on Wednesday. When the spacecraft was within about 2.5 miles (4 Kilometers) from the outpost, the first Go/No Go was given for the first approach burn, called ADV-1, by the BT-4 engine.
Once the craft was just under 1 mile (1.6 kilometers) away, it was verified that Cygnus could be commanded by the space station crew. The crew had the ability to give a few commands to Cygnus if problems had arisen: HOLD, which would stop the vehicles approach; RETREAT, which would send the spacecraft to its previous hold point; and ABORT, which would have commanded the cargo ship to perform a burn to escape the vicinity of ISS.
The next three approach burns pushed the spacecraft to only 820 feet (250 meters) from the station at around 4 a.m. (10:00 GMT) in an approach known as the R-Bar. This is an approach along the target’s radial vector – in this case, approaching from below the outpost.
During this time, Cygnus switched to Proximity Navigation Mode using data from the Triangulation and LIDAR Automated Rendezvous and Docking (TriDAR) system, a laser-based 3-D sensor used to collect 3-D data of ISS. This would allow the system to know its range and relative velocity.
Once at 820 feet (250 meters), teams at Mission Control in Houston and in Dulles, Virginia, polled to give permission to enter the station’s Keep-Out Sphere, an imaginary sphere with a radius of 656 feet (200 meters). At about 4:20 a.m., Cygnus crossed that imaginary point.
At 98 feet (30 meters), Cygnus entered another planned hold for teams to review spacecraft data and verify the cargo ship was ready for grappling by the robotic arm. At 5:01 a.m. CST (11:01 GMT), Deke Slayton II began its final approach to the capture point.
Less than 10 minutes later, the spacecraft arrived at its capture point at about 40 feet (12 meters) below the station and zeroed out any motion relative to ISS, before switching to Free Drift.
At 5:17 a.m. (11:17 GMT), Lindgren started to move the robotic arm to grab the spacecraft and eventually and berth it to the outpost.
This is the fourth Cygnus to berth with the orbiting outpost, and the first United States cargo ship to arrive at the station since June when SpaceX’s CRS-7 mission failed to reach orbit. Eight months prior to that, the Orbital ATK Orb-3 mission failed only seconds after launch.
Deke Slayton II is the first visiting vehicle to be berthed to the Unity. Earlier in the year, the station underwent a reconfiguration, involving the relocation of the Permanent Multipurpose Module from the nadir port of Unity to the forward port of the Tranquility module, in preparation for dual berthing operations. In January, if the schedule holds, SpaceX will launch its next Dragon cargo ship, which will berth to the nadir port of the Harmony module, and would mark the first time that two commercial vehicles would be berthed to the outpost at the same time.
This Cygnus is the first of the enhanced variants. It sports an extended pressurized cargo module and two circular UltraFlex solar arrays. It has inside some 7,745 pounds (3,513 kilograms) of cargo. That includes 2,604 pounds (1,181 kilograms) of crew supplies, 1,867 pounds (847 kilograms) of science hardware, 2,220 pounds (1,007 kilograms) of vehicle hardware, 500 pounds (227 kilograms) of spacewalking equipment, and 192 pounds (87 kilograms) of computer resources.
Hatches are scheduled to be opened between the Cygnus and the station on Thursday morning at 4 a.m. (10:00 GMT). It is expected to remain at the ISS for about two months.
Video courtesy of NASA
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity.