Orbital ATK’s Cygnus resupply ship has completed its rendezvous at the International Space Station (ISS) on Tuesday morning. Cygnus launched to orbit on Orbital ATK’s Antares rocket from Wallops on Sunday, a day later than planned due to a Range violation during the Saturday attempt, which resulted in a 24 hour delay to the cargo ship’s arrival at the ISS.
Cygnus OA-8 Arrival:
Immediately following its launch, Cygnus – named S.S. Gene Cernan – successfully entered its target orbit and deployed its lightweight solar arrays. The launch came after a scrub with minutes to go during the first attempt due to a wayward plane in the Range. The second attempt launched at the end of the window due to wayward boats in the hazard area. Thankfully they departed the exclusion zone just in time.
With Cygnus in orbit, Orbital ATK mission controllers in Dulles, Virginia, spent the early days of Cygnus’ mission uploading and executing the first of a series of rendezvous phasing burns (called DV – Delta Velocity burns) to refine the vehicle’s trajectory toward the Station.
The first DV burn lasted approximately 10 minutes, and was designed to raise Cygnus from its initial near-circular 230km orbit to the 400km orbit of the ISS.
A similarly long DV burn followed, again to raise Cygnus to its proper orbital altitude.
This was then followed by a planned phasing burn to align Cygnus into the exact orbital corridor of the Station and then by a final set of DV burns to bring Cygnus to its “Go/No-Go for Joint-Ops” decision point, which it reached roughly five hours prior to capture.
Once Cygnus has received the “go” from MCC-H (Mission Control Center – Houston) for Joint Ops, Cygnus slowly approached the Station to the Joint Targeting Reference Point (JTRP), which it arrived at just over three hours prior to capture.
From this point until capture and berthing, every step of the rendezvous required a strong communications link through the JEM (Japanese Experiment Module) PROX system between Cygnus, the ISS, and ground controllers.
This communication structure ensured the ability to manually abort – or at least retreat – Cygnus’ approach to the Station in the event of a problem with the spacecraft or the ISS.
Once at the JTRP, Cygnus ceased relative motion with the ISS and awaited a second Go/No-Go decision from MCC-H.
At this point, Cygnus was in the Joint Operations Phase (JOPS) of approach, as overviewed in documentation acquired by L2.
With MCC-H providing a “go” to proceed, Cygnus then performed the first of four ADV thruster burns (ADV1) to begin moving closer to Station.
During these proximity ADV burns, Cygnus – until capture – made use of the TriDAR vision system designed by Canadian company Neptec with the support of NASA and the Canadian Space Agency.
TriDAR – tested during several Space Shuttle missions – provides Cygnus controllers with real-time visual guidance for navigation, rendezvous and docking procedures.
After Cygnus’ completed her first two ADV burns, the ISS maneuvered to capture attitude – a 5 minute process that took place just over two hours prior to targeted capture time.
Then MCC-H issued another Go/No-Go decision regarding two more ADV burns for Cygnus, which took the spacecraft to its 250m hold point below the ISS.
Cygnus then pulsed its thrusters and enter the KOS.
Up until this point, Orbital ATK controllers at their facility in Dulles had full control over Cygnus.
Once Cygnus entered the KOS, NASA controllers at MCC-H were joined by the Orbital ATK team for the tricky rendezvous and berthing of Cygnus.
Just under half an hour prior to capture, Cygnus arrived at the 30m Hold Point.
Five minutes later, Cygnus received the “go” to proceed to the capture point, at which time it departed the 30m Hold Point just over 15 minutes prior to capture.
Cygnus then arrived at its capture point 12m from the ISS, 8 minutes prior to the first capture attempt.
Astronauts Paolo Nespoli and Randy Bresnik used the Station’s 17.5m Space Station Remote Manipulator System (SSRMS) robotic arm to grab hold of Cygnus at approximately 10:04 UTC.
After Cygnus was firmly in the SSRMS’s grip, the crew maneuvered the craft to Node-1 Unity (delivered by Space Shuttle Endeavour during the first ISS construction mission in December 1998) where the craft will be berthed for a planned two month stay at the ISS.
The SS Gene Cernan is carrying 3,338 kilograms (7,359 lb) of cargo for the International Space Station.
This includes 1,240 kilograms (2,734 lb) of supplies and provisions for the space station crew, 851 kg (1,875 lb) of space station hardware, 34 kg (75 lb) of computer equipment and 132 kg (291 lb) of hardware for use in performing spacewalks.
Scientific equipment and experiments make up 740 kilograms (1,631 lb) of the cargo, while a 109-kilogram NanoRacks CubeSat deployer is mounted on the outside of the spacecraft and will be used to release fourteen CubeSats after Cygnus leaves the station.
Cygnus is expected to remain at the International Space Station until early December.
(Images: Orbital ATK, NASA, L2 content via L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)