Berthing Complete: OA-4 Cygnus arrives at the ISS

by Chris Gebhardt

Orbital ATK’s “S.S. Deke Slayton II” Cygnus spacecraft has completed rendezvous and proximity operations with the International Space Station (ISS), allowing for capture and berthing following a two day orbital chase with the laboratory. Astronauts aboard the Station grappled Cygnus with the Station’s robotic arm at 06:19 EST Wednesday, prior to completing berthing a few hours later.

Rendezvous and capture:

Following her successful launch atop of a United Launch Alliance (ULA) rocket on Sunday, December 6, from the Cape Canaveral Air Force Station in Florida, Cygnus performed without issue during her multi-day orbital chase of the International Space Station (ISS), designed to slowly and carefully close the distance and orbital heights between herself and the orbiting laboratory.

2015-12-08-172641With a total spacecraft weight of 7,492 kg (16,517 lbs), the “S.S. Deke Slayton II” Cygnus spacecraft and its associated cargo and propulsion is the heaviest payload ever launched to this point by an Atlas V rocket.

Following its flawless launch, the Cygnus spacecraft successfully deployed its new lightweight solar arrays and spent the last two days performing a series of six rendezvous burns (DV burns) to refine its trajectory toward the Space Station.

The six rendezvous burns had already changed Cygnus’ velocity by 97.84 m/s during Tuesday.

The final two DV burns took place in the evening of Tuesday (Eastern Standard Time) to bring Cygnus to its Go/No-Go for Joint-Ops decision point – roughly five hours prior to capture.

Once Cygnus 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) – just over three hours prior to capture.

During this time and until capture and berthing, every step of the rendezvous process required a strong communication link between Cygnus, the ISS, and ground controllers to ensure that the ability to manually abort the approach – or at least retreat – in the event of problems with Cygnus or the ISS is maintained.

ISS panel to be used for arrival, via L2This phase of the mission is called the Joint Operations Phase (JOPS), as overviewed in documentation acquired by L2.

This critical approach period involves Cygnus using the JEM (Japanese Experiment Module) PROX system for direct communications with ISS.

This allows Cygnus to effectively use the same system Japan’s HTV uses for arriving at the ISS, as much as there are a number of different settings employed for Cygnus’ arrival than for HTV’s.

Once at the JTRP, Cygnus ceased relative motion with the ISS and awaited at second Go/No-Go decision from MCC-H.

Image from testing, via L2Approximately three hours before capture, the “go” from MCC-H was given, allowing Cygnus to perform 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 (CSA).

Cygnus’ TriDAR – which was tested during the Space Shuttle Program (SSP) by Atlantis – provides controllers with real-time visual guidance for navigation, rendezvous and docking procedures.

2015-12-08-182418The ADV2 burn followed ADV1 after approximately 34 minutes, after which the ISS maneuvered to capture attitude – a five minute process that took place just over two hours prior to targeted capture time.

Then, with just under two hours to go until capture, MCC-H issued another Go/No-Go decision regarding two more ADV burns for Cygnus.

With that “go” given, Cygnus performed the ADV3 burn – called the Approach Initiation Burn – approximately 1hr 40mins prior to capture.

The ADV4 burn followed at 1hr 27mins prior to capture and brought the Cygnus spacecraft to its 250m Hold Point 1hr 10mins prior to capture.

Z3AWith just under one hour until capture, MCC-H gave the “go” for Cygnus to depart the 250m hold point and enter the Keep Out Sphere (KOS) of the ISS.

With just 54 minutes to go until capture, Cygnus will pulsed its thrusters and entered the KOS.

Up until this point, Orbital ATK controllers at MCC Dulles (MCC-D) had full control over Cygnus.

At this point, however, NASA controllers at the MCC-H joined the Orbital ATK team for the final tricky rendezvous and berthing of Cygnus.

Then, 27 minutes prior to capture, Cygnus arrived at the 30m Hold Point.

2015-12-08-182522About 10 minutes later, Cygnus received the “go” to proceed to the capture point, at which point she departed the 30m Hold Point 17 minutes prior to capture.

Cygnus arrived at the capture point 12m from the ISS, allowing Kjell Lindgren – using the Station’s 17.5m Space Station Remote Manipulator System (SSRMS) robotic arm – to grapple the vehicle.

With Cygnus firmly in the SSRMS’s grip, Kjell maneuvered the craft to the Earth-facing Common Berthing Mechanism (CBM) port of the Node-1 Unity module, which was delivered to the ISS by the Shuttle Endeavour on the STS-88 mission.

Post-berth activities:

With Cygnus fully berthed to Harmony, the ISS crew will open the hatches between the two spacecraft and begin two months of docked operations. This was expected to begin on Thursday. However, the ISS crew – as per usual – got ahead of the timeline and opened the hatch later on Wednesday.

During this time, the ISS crew will unpack the 3,350 kgs (7,380 lbs) of cargo aboard the craft.

2015-12-08-182617This includes nearly 1,200 kg (2,600 lbs) of crew supplies, in the form of crew care packages, provisions, and food.

Moreover, Cygnus is also carrying nearly 1,010 kg (2,220 lbs) of vehicle hardware including crew health care system hardware, extravehicular robotics equipment, structural and mechanical equipment, flight crew equipment, electrical power system hardware, internal thermal control system hardware, and environment control and life-support equipment.

Also aboard Cygnus are 850 kg (1,870 lbs) of scientific investigations, including Space Automated Bio Lab, a new life science facility that will support studies on cell cultures, bacteria, and other micro-organisms; experiments created around the evaluation of flame-resistant textiles; and experiments that will study the behavior of gases and liquids and clarify the thermo-physical properties of molten steel.

2015-12-08-182702ISS crews will also unpack about 230 kg (500 lbs) of spacewalking equipment and 870 kg (1,920 lbs) of computer equipment for the Station.

After all of this is unpacked, the crew will then load Cygnus back up with disposal waste from the Station.

At the end of Cygnus’ OA4 mission to the Station, crews will close the hatches between the crafts, grapple Cygnus again with the SSRMS, and unberth it from the Station.

Once back in free flight, Cygnus will be commanded into a destructive reentry into Earth’s atmosphere.

At present, the next Orbital ATK flight of a Cygnus spacecraft to the ISS will be the OA-6 mission – which is currently slated to launch aboard a ULA Atlas V rocket from Cape Canaveral Air Force Station on 10 March 2016 at 05:00 UTC.

(Images: NASA, Orbital ATK, ULA and L2 – including Photos from Philip Sloss and renders from 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*)

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