ORB-2 Cygnus completes ISS rendezvous and berthing

by Chris Bergin

Orbital’s ORB-2 Cygnus spacecraft has successfully rendezvoused and berthed with the International Space Station (ISS) on Wednesday morning. The American spacecraft, partly built in Italy, guided in by Canadian sensors and grabbed by an American astronaut using another Canadian asset – Space Station Remote Manipulator System (SSRMS) – completed her arrival at 6:36 Eastern.

ORB-2 Cygnus Arrival at ISS:

Following her successful launch atop of the Antares rocket on Sunday, Cygnus continued to perform without issue during her transition from the Integrated Launch Operations Phase (ILOPS) – used for ascent and insertion – to the Phasing Operations Phase (POPS) segment of the mission – used for the pursuit of ISS.

Cygnus’ goal during her orbital exploits was one of patiently driving down the orbital highway ahead of entering the ISS’ neighborhood, otherwise known as the “”Keep Out Sphere (KOS)”.

Up until this key point, Orbital controllers at the Mission Control Center (MCC-D) in Dulles had full control over the vehicle, with NASA controllers at the Mission Control Center in Houston (MCC-H) joining the team for the tricky rendezvous and berthing of the Cygnus.

The S.S. Janice Voss – as this spacecraft is named – already has the Delta velocity maneuvers one (DV1) through seven (DV7) completed ahead of Wednesday’s final leg, along with a plane maneuver required to position the spacecraft for capture.

On the Station, there were a number of key items that had to be confirmed as showing they were in good working order to allow Cygnus to be eased towards its berthing.

ISS panel to be used for arrival, via L2These items included a strong communication link, required not least for the ability to manually abort the approach – or at least retreat – in the event of problems.

This phase of the mission is called the Joint Operations Phase (JOPS),as overviewed in documentation acquired by L2.

This critical approach period – also known as Proximity Ops – involves Cygnus using the JEM PROX system for direct communications with ISS, effectively resulting in the use of 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.

Z23As with SpaceX’s Dragon, Cygnus was tasked with stalking the ISS, slowly creeping up to its target via a large series of approach milestones to test its systems.

As the Orbital spacecraft eased up the R-bar, under the ISS, she entered the KOS (Keep Out Sphere).

Once inside the KOS, Cygnus demonstrated that she could hold and retreat, prior to receiving the go – via polling – to proceed, mirroring the tasks it underwent during the ORB-D and ORB-1 missions.

Following a review of the data – including the passing of the final milestone relating to the lock on of the spacecraft’s sensors – a final go was given for Cygnus to approach to the capture point.

Image from testing, via L2During the previous two missions, Cygnus has employed Jena LIDARs (Light Detection And Ranging) sensors for this mission.

However, as was originally planned, Cygnus is now incorporating the use of the TriDAR vision system – designed by Canadian company Neptec, with the support of NASA and the Canadian Space Agency (CSA).

This system provides real-time visual guidance for navigation, rendezvous and docking procedures – and was successfully tested as a parting gift from the Shuttle fleet, flying on three missions, namely with Discovery on STS-128 and STS-131, prior to its final shuttle trip with Atlantis on STS-135.

Z22With everything going to plan, the focus then switched to capturing the spacecraft via the ISS’ Space Station Remote Manipulator System (SSRMS).

The Station’s arm was already reaching out ahead of her new arrival, as part of the preparations for the berthing tasks that were primarily conducted by NASA’s Steve Swanson.

As Cygnus closed in for grapple – at 6:36 Eastern, the robotic operations berthing tasks were then conducted, with first and second stage capture required. Slightly ahead of schedule, this operation was completed at 8:53 am Eastern – confirming Cygnus’ safe berthing with the ISS.

Now Cygnus is successfully berthed, the ISS crew will begin vestibule ops and Cygnus activation via ISS power jumpers on rendezvous day, documented as a nine hour procedure.

Hatch opening and ingress was scheduled to occur early on Thursday morning. However, as per usual, the crew used the option to press ahead with the procedures during Wednesday.

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Cygnus’ hatch is very similar to a standard US segment hatch, albeit slightly smaller, making it a familiar sight to the ISS crewmembers. A ventilation duct will be hooked up, and the spacecraft cleared of any dust prior to becoming safe to ingress without eye protection and masks.

Inside CygnusWith the hatch open, crewmembers will begin cargo removal operations, a phase of the mission known as the Berthed Operations Phase (BOPS).

A total of 1,664 kg (3,669 pounds) of supplies for the station are onboard this Cygnus, including research investigations, crew provisions, hardware, and science experiments from across the country.

Cargo ops involves the crew removing the “top layers” on PORT and STBD pallets to make room in PCM. They will then remove components of the Secondary Structure as required, ahead of emptying the FWD and AFT pallets to gain access to the Standoff pallets, which they will empty and repack.

The reverse sequence will be employed until the vehicle has been repacked, although all the return cargo won’t be classed as downmass, because – unlike Dragon – Cygnus won’t be returning to the ground or water.

Re-entryInstead, it’ll be sent on a path to a destructive re-entry.

The final phase of the mission – a reverse of the berthing procedures – is called the Descent & Reentry Operations Phase (DROPS), as Cygnus ends her life in a disposal corridor during entry, marking the conclusion to what will be the first of a series of CRS mission for the Cygnus fleet.

The deal to carry out ISS resupply flights – under the $1.9 billion CRS contract – encompasses eight missions between 2012 and 2015 carrying approximately 20,000 kg of cargo to the ISS.

Additional missions will be ordered via the CRS2 contract awards in the near future, based on the recent US decision to back an extension of the ISS’ lifetime to 2024.

(Images: via L2’s Cygnus Section – Containing presentations, videos, a vast set of unreleased hi-res images, interactive high level updates and more, with additional images via Orbital and NASA).

(Click here: http://www.nasaspaceflight.com/l2/ – to view how you can support NSF and access the best space flight content on the entire internet).

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