Orbital’s Cygnus spacecraft has completed its ORB-1/CRS-1 mission, following its departure from the International Space Station (ISS) at 11:41 am UTC on Tuesday. The commercial vehicle was removed from its Earth-facing port of the Harmony module port and then released, ahead of what was destructive re-entry to end its mission.
The first Commercial Resupply Mission for the Cygnus has been extremely successful.
A flawless launch atop of the Antares launch vehicle on January 9 was followed by a trouble-free rendezvous and berthing just a few days later.
ORB-1 delivered 1,466 kilograms (3,232 lb), out of a maximum of 2,000 kg (4,400 lb).
The ISS crew soon got to work, unloading the cargo contained within the vehicle’s PCM. This involved the crew removing the “top layers” on PORT and STBD pallets to make room in PCM.
They then removed components of the Secondary Structure as required, ahead of emptying the FWD and AFT pallets to gain access to the Standoff pallets, which they emptied and repacked.
With the payloads removed, the crew began to fill Cygnus back up with trash items, via a reverse sequence. A total of 2,800 lbs of trash was packed into the spacecraft.
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.
This 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.
Ahead of unberthing, the ISS crew had to make one final check on power cables associated with the removal of Cygnus from the Common Berthing Mechanism (CBM).
“Cygnus Unberth and Release Preparations: The crew closed the Cygnus hatch, demated the Cygnus umbilicals, and installed the CBM Controller Panel Assemblies (CPAs) in preparation for unberth and release,” noted L2 ISS notes.
“After the N2N hatch was closed and vestibule depress had begun, ground teams reviewing crew closeout photos identified damage on one of the CPA power cables. The vestibule was repressurized, and the crew ingressed the vestibule to inspect the cable.
“The damage was limited to the external Teflon braiding; there was no damage to the shielding or cables underneath. The crew was given a Go to re-close the N2N hatch and the vestibule was depressurized. Following vestibule depress, ground controllers successfully completed the CBM preparations for demate.”
With the ISS management clearing the vehicle for unberthing, the first task was to complete vestibule depressurization, prior to releasing the 16 bolts that had secured Cygnus to the ISS. The 16 bolts were driven in two stages, with the SSRMS holding a firm grip on the spacecraft.
Once released, Cygnus was then carefully translated 10 meters away from the Station, eased through pre-planned manuevers to position the vehicle into its release stance.
The Latching End Effector on the end of the Station’s arm then drove the snares to literally let go of Cygnus, allowing it to be free once again, followed by the ISS crew slowly moving the arm back away from the ship from their viewing position in the Cupola’s Robotic Work Station (RWS).
With Cygnus able to abort, had it wandered back towards the arm – as was the case with the HTV-3 unberthing – controllers both at MCC-Dules and MCC-Houston conducted system checks, prior to the opening departure burn.
This initial departure was a commanded abort, a nominal procedure to allow the HTV console to inform Cygnus it can begin to move away.
Cygnus then began a half-lap flyaround of the ISS, looping behind the Station, before swinging under and infront of the outpost, with its final venture to the V-Bar being 1,200 kms in front of the ISS – as Orbital’s team in Dulles carefully guided the spacecraft away from the ISS.
An exclusive video from one of the Cygnus mission sims is available in L2.
It then made the decent – via two standard burns and the final deorbit burn – towards a destructive re-entry, with break up occurring high above the Pacific Ocean at 75 km altitude on Wednesday.
“Cygnus has reentered Earth’s atmosphere marking the end of the ORB-1 CRS-1 mission for NASA,” Orbital tweeted in what was the only mention of the End Of Mission for the spacecraft.
The spacecraft was named the SS C. Gordon Fullerton after the STS-3 and 51-F astronaut who passed away in 2013 at the age of 78.
(Images: via L2’s Cygnus Section 0 Containing presentations, videos, a vast set of unreleased hi-res images from Cygnus’ two missions, interactive high level updates and more, with additional images via Orbital and NASA).
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