After nearly one month at the International Space Station, Orbital ATK’s Cygnus OA-5 spacecraft marked the end to its mission with a destructive re-entry on Sunday. Following a resupply mission to the orbital outpost, Cygnus conducted experiments and deployed cubesats, prior a nominal end of mission.
Cygnus OA-5 – The “Alan Poindexter”
The OA-5 flight of the Cygnus resupply craft to the International Space Station has been a resounding success in many regards.
Riding atop the newly redesigned Antares launch vehicle and upgraded Castor 30XL upper stage, the S.S. Alan Poindexter was the first Cygnus to climb to orbit aboard the Antares 230 series variant rocket and the first Cygnus to successfully use the Castor 30XL solid propellant upper stage for second stage operations.
The Castor 30XL upper stage technically debuted on the Orb-3 mission in October 2014; however, with that flight’s mission-ending mishap just seconds after liftoff, the Castor 30XL was never used on that flight and therefore made its in-flight debut with OA-5.
After being successfully inserted into orbit, the Alan Poindexter Cygnus began a prolonged, 6-day rendezvous with the Space Station – having to loiter in orbit behind ISS as the Soyuz MS-02 performed its launch, approach and docking operations with Station with three new crewmembers for the outpost.
This traffic congestion had not originally been planned for, with MS-02 originally scheduled to launch in September 2016 with Cygnus following in early October.
However, technical delays with Soyuz and hurricane related delays associated with Hurricanes Matthew and Nicole – the former affecting the Mid-Atlantic Regional Spaceport (MARS) in early October and the later affecting the Bermuda tracking station in mid-October – pushed the two missions to the same week.
When Soyuz and Cygnus finally headed toward their respective actual launches, the timelines were too close to permit both vehicles’ rendezvous – from a three-person crew timeline perspective on Station – in the order of their launch.
Thus, Soyuz with crew was given docking priority despite launching two days after Cygnus.
After arriving at Station and being berthed to the nadir port of the Unity module, the ISS crew has spent the last 30 days unloading 2,342 kg (5,163 lb) of supplies from Cygnus and repacking the craft with 1,300 kg (2,866 lb) of trash for disposal via burn up in Earth’s atmosphere.
With OA-5’s berthed mission at an end, astronauts aboard the ISS and ground robotic controllers at MCC-H unberthed Cygnus from Node-1 nadir and set the craft free for the next phase of its mission.
After being cleared for unberthing by MCC-H, the vestibule between Cygnus and ISS was depressurized before the 16 bolts that secure Cygnus to the Space Station were commanded to “drive” to their release positions.
The 16 bolts were driven in two stages and physically disconnected Cygnus from the main structure of the ISS while the SSRMS (Space Station Remote Manipulator System) held the spacecraft firmly in the grasp of its snares inside the Latching End Effector (LEE).
Once the bolts were released, ground robotic controllers at MCC-H carefully translated Cygnus 10 meters away from the Station and eased it through a series of maneuvers on the end of the SSRMS to bring the Alan Poindexter into its proper release attitude.
Once Cygnus is in position, MCC-H gave a “go” to release the snares inside the LEE.
At this point, astronauts Shane Kimbrough and Thomas Pasquet released the SSRMS LEE snares, “letting go” of Cygnus and allowing it to fly under its own systems.
The release occurred at 08:22 EST (13:22 GMT).
The SSRMS was then translated away from Cygnus while the craft held its position relative to the Station.
During this time, controllers in MCC-H, Cygnus Mission Control Center in Dulles (MCC-D), and astronauts in the Cupola module of the ISS carefully monitored Cygnus for any signs of misbehavior.
Had Cygnus not behaved as intended, any one of the three control facilities could initiate an emergency abort procedure to quickly and safely back Cygnus away from the ISS – though the odds of this being needed are always slim.
With all going to plan, the SSRMS moved to a safe distance and ISS controllers in MCC-H and Orbital ATK controllers at MCC-D conducted a series of system checks prior to Cygnus’ opening departure burns.
Cygnus then fleww itself out of the Keep Out Sphere (KOS) of the Station before eventually departing the Approach Ellipsoid, marking the point where joint operations between NASA and Orbital ATK will end.
Orbital ATK’s controllers in Dulles then took control of Cygnus for the remainder of its Low Earth Orbit journey.
Post-departure – Continued testing of fire safety systems for future spacecraft:
Like the OA-6 mission earlier this year, Cygnus OA-5 conducted a second critical mission for NASA following unberth.
This second phase of Cygnus’ mission began about five hours after its departure from the Space Station.
At this time, the Spacecraft Fire Experiment, or Saffire-II experiment, saw Cygnus controllers deliberately ignite a fire inside Cygnus’ pressurized cargo volume.
The inside of this special experiment module contains material samples commonly found on the ISS as well as those under selection for NASA’s Orion spacecraft.
Saffire-II, like Saffire-I, will continue to provide a safe way to study a realistic fire aboard a spacecraft.
But the uncrewed and end-of-mission destructive nature of Cygnus flights provides NASA a real, safe, in-flight test bed for understanding how a fire works, spreads, and dies in microgravity while exposed to the various materials a spacecraft is built from.
To this end, the results of the Saffire experiments on OA-6, OA-5, and OA-7 could help determine microgravity flammability limits for several spacecraft materials, help validate NASA’s material selection criteria, and help scientists understand how microgravity and limited oxygen affect flame size.
Saffire-II was scheduled to be a single-day experiment, after which Cygnus deployed four LEMUR CubeSats for NASA from an external deployer on Friday, 25 November.
The LEMUR CubeSats will add to a growing constellation of a remote sensing satellite constellation that provides global ship tracking and weather monitoring.
To achieve this milestone, Cygnus rose to her highest ever orbit of over 500 km.
Following LEMUR CubeSat deployment, Cygnus remained in orbit for two more days before controllers at MCC-D commanded OA-5 through a series of two deorbit burns on 27 November.
These burns tookl Cygnus into a destructive re-entry over the Pacific Ocean at around 23:30 UTC.
With the OA-5 mission completed, Orbital ATK and NASA will turn their attention in the new year toward final preparations for the launch of the OA-7 Cygnus mission – which will return to a United Launch Alliance Atlas V rocket from the Kennedy Space Center-owned, Cape Canaveral Air Force Station-operated SLC-41.
(Images: NASA; Orbital ATK)