Orbital’s Cygnus spacecraft berthed following ISS arrival
Orbital’s Cygnus spacecraft has marked her second arrival at the International Space Station (ISS), this time under its Commercial Resupply Services (CRS) call sign of CRS-1. After proving its ability to conduct what was a complicated rendezvous with the orbital outpost last year, the ORB-1 spacecraft was grabbed by the Station’s robotic arm at 11:08 UTC on Sunday.
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Following launch atop of the Antares rocket on Thursday, Cygnus continued to perform without issue during its 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 over the past few days has been 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.
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 on Sunday morning.
These 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 was called the Joint Operations Phase (JOPS), as overviewed in documentation acquired by L2.
This critical approach period – also known as Proximity Ops – involved 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 was a number of different settings employed for Cygnus’ arrival.
As with SpaceX’s Dragon, Cygnus stalked 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, it entered the KOS (Keep Out Sphere).
Once inside the KOS, Cygnus demonstrated that it could hold and retreat, prior to receiving the go – via polling – to proceed, mirroring the tasks it underwent during the ORB-D mission.
Following a review of the data – including the passing of the final milestone relating to the lock on of the LIDAR sensors – a final go was given for Cygnus to approach to the capture point.
Cygnus was using Jena LIDARs (Light Detection And Ranging) sensors for this mission, as it did for the ORB-D flight.
Cygnus will eventually – from ORB-2 onwards – begin to incorporate the use of the TriDAR vision system – designed by Canadian company Neptec, with the support of NASA and the Canadian Space Agency.
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.
With 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 arrival, as Cygnus closed in for grapple at 11:08am UTC, prior to robotic operations to berth the new arrival, a process that was completed – via first and second stage capture – at 1:05pm UTC.
Now berthed, the ISS crew 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 Monday morning. However, the crew had the option to press ahead with the procedures during Sunday, which they completed with ease.
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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 was hooked up, and the spacecraft cleared of any dust prior to becoming safe to ingress without eye protection and masks.
With the hatch open, crewmembers began cargo removal operations, a phase of the mission known as the Berthed Operations Phase (BOPS).
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.
Instead, 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 its 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.
It is possible that additional missions will be ordered, 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).
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