Orbital’s Cygnus spacecraft made its second attempt to dock with the International Space Station (ISS) on Sunday morning, resulting in a successful capture and berthing by the Space Station Remote Manipulator System (SSRMS). A week has passed since a discrepancy in the GPS data between the ISS and Cygnus resulted in the need to delay rendezvous and berthing, allowing Orbital controllers to uplink a line of code into the spacecraft’s software.
ORB-D Rendezvous and Berthing –
Per L2 information, the post-flight review – known as the “24 hour quick look review” – noted no issues with the launch phase of ORB-D. Further reviews have also concluded the launch was completely issue-free.
Bidding farewell to Antares – and completing what is known as the Integrated Launch Operations Phase (ILOPS), for the ascent and insertion element of the mission – Cygnus immediately began completing numerous first-time operations, stretching out its solar arrays before setting its sights on the orbital outpost.
The Cygnus vehicle – under the control of Orbital at MCC-Dulles – then prepared for a series of well-practiced demonstrations over its four day period of catching up to the ISS.
Known as the Phasing Operations Phase (POPS) – for the pursuit of the ISS – Cygnus has a task sheet of 10 specific demonstrations to complete during its four-day in-orbit journey to rendezvous with the ISS.
These demo elements have been intertwined with orbital operations such as Delta V burns to raise its orbit, the first of which was successfully completed early into the mission.
Cygnus’ flight profile – as seen in an expansive overview presentation acquired by L2 – involves chasing the ISS from behind and below.
Following another burn, the team carried out free drift and abort demonstrations – known as Demos 2a and 2b – marking the completion of the first demonstration milestones under the ORB-D requirements.
With Cygnus closing in on the ISS’ neighborhood, along with its altitude showing a large up curve per the flight profile, the spacecraft completed a total of four Delta V burns to get within a four kilometers of the ISS’ altitude.
The trouble-free flight of the new spacecraft was marked by a NASA Mission Management Team (IMMT) providing approval for Cygnus to continue its pursuit of the Station, along with a provisional green light for berthing to take place.
However, last Sunday’s rendezvous was always going to be one of the more tricky elements of the mission, as Cygnus starts to track and communicate with the ISS.
With Cygnus around 15km from the ISS, a problem was noted with the GPS readings between Cygnus and the ISS – one of the key demo requirements – resulting in an abort being called.
Expanding on the specifics, information acquired by L2 cited the problem related to the specifying of GPS time as key to the problem on Sunday.
The complex issue only required a relatively simple solution, as explained in a recent article published on this site.
Closing in on the ISS once again, the two spacecraft had to show they have 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).
This critical approach period – 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 will be 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 demos to test its systems.
As the Orbital spacecraft sneaked up the R-bar, under the ISS, it entered the KOS (Keep Out Sphere).
Once inside the KOS, Cygnus demonstrated that it can hold and retreat, prior to receiving the go – via polling – to proceed.
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 will be given for Cygnus to approach to the capture point.
The focus then switched to capturing the spacecraft via the ISS’ Space Station Remote Manipulator System (SSRMS) – which reached out and grappled Cygnus at 11am GMT. The spacecraft was then berthed on the Station, with second stage capture confirmed at 12:44pm GMT.
Once 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 occurred early on Monday morning.
“Cygnus receives power via PVGF; overnight park position not required for capture delay. Current timeline gets through berthing, start of vestibule ops & Cygnus activation via ISS power jumpers on rendezvous day. Hatch open and ingress is the following day,” noted an associated overview presentation (L2).
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 now open, crewmembers began cargo removal operations, during its month-long stay, 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.
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, hopefully with a smile on its face, following a successful demonstration that paved the way for its siblings to each take a turn in providing full CRS operations.
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.
Preparations are already in full swing for the ORB-1 mission, with hardware already being processed at its Wallops base.
(Images: via L2’s Antares/Cygnus Section – Containing presentations, videos, images, interactive high level updates and more, with additional images via Orbital and Neptec).
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