Beginning its sixth flight Tuesday night, Orbital ATK’s Cygnus spacecraft lifted off atop an Atlas rocket to begin a two-month mission to the International Space Station. Liftoff of the OA-6 mission from SLC-41 at Cape Canaveral was on schedule at 23:05:51 local time (03:05 UTC on Wednesday), with berthing expected on Saturday.



Cygnus OA-6:

Tuesday’s launch was Cygnus’ second flight atop United Launch Alliance’s Atlas V rocket – standing in for Orbital ATK’s own Antares while Orbital modify the latter’s first stage.

Antares is expected to return to flight – sporting new RD-181 engines in place of the AJ-26 used previously – in late June with the next Cygnus mission, its first flight since a launch failure in October 2014.

Cygnus’ ability to launch on either Antares or Atlas was listed as a strength when NASA reviewed submissions for its Commercial Resupply Services 2 (CRS-2) contract, under which Orbital was awarded at least six additional launches in January.

These may be performed using either rocket. SpaceX was also awarded at least six missions for the Dragon spacecraft, as was Sierra Nevada Corporation for its Dream Chaser vehicle which is expected to fly in 2019.

Orbital developed the Cygnus spacecraft under NASA’s Commercial Orbital Transportation Services (COTS) program, having been awarded a contract for a demonstration mission in February 2008.

COTS contracts had originally been awarded to SpaceX – resulting in development of the Dragon – and Rocketplane Kistler (RPK), however Orbital were brought in after RPK failed to achieve contract milestones with its K-1 rocket. Later that year a series of operational missions were awarded to Orbital.

Cygnus began its demonstration mission in September 2013, remaining berthed at the ISS until late October. Following this operational missions were launched successfully in January and July 2014, however the third operational launch in October 2014 ended in failure after a turbopump exploded in one of the first stage engines of its Antares rocket.

With Antares grounded, Orbital purchased a launch from United Launch Alliance, with an option for a second. The first of these was performed successfully in December, with Tuesday’s launch engaging the option in that contract.

Like December’s launch, Tuesday’s OA-6 mission involves the enhanced version of the Cygnus spacecraft, with an enlarged pressurised cargo module and redesigned fuel tanks and solar arrays. Launching atop the Atlas, instead of the smaller and less powerful Antares, also allows the spacecraft to carry a greater mass of cargo.

OA-6 is carrying 3,395 kilograms (7,485 lb) of cargo to the station; including 777 kg (1,713 lb) of scientific hardware, 1,139 kg (2,511 lb) of provisions for the crew, 1,108 kg (2,443 lb) of station hardware, 98 kilograms (216 lb) of computer equipment and 157 kg (346 lb) of hardware for EVAs. Packaging accounts for the remaining 116 kg (256 lb) of the payload.

Experiments being carried to the space station aboard Cygnus include Meteor, a high-resolution imaging payload intended to capture video and still images of meteors as they enter the Earth’s atmosphere, to allow better study of their properties and composition.

Strata-1 is a materials science payload aimed at studying how asteroid regolith – or loose surface material – behaves in microgravity.

The research will benefit future missions aimed at landing on asteroids and small planetary satellites such as Phobos.

The Additive Manufacturing Facility (AMF) is a 3D printer which will be used to construct tools and equipment in orbit by building them in layers.

Cygnus is also carrying “Gecko Gripper” adhesive devices to be tested aboard the station for mounting small items to the walls of the outpost.

Following its departure from the space station, a group of CubeSats will be deployed from a Nanoracks dispenser mounted externally to the vehicle.

These include the twenty-strong Flock-2d contingent of Planet Labs’ large constellation of Earth imaging satellites and further spacecraft of Spire’s Lemur-2 constellation. Lemur-2, whose first four satellites were launched atop a PSLV last September, carry imaging payloads and AIS receivers to relay tracking information from ships at sea.

Once the CubeSats have separated, Cygnus will host the first of three Spacecraft Fire Safety Demonstration Project, or Saffire, experiments.

A fire will be started within the spacecraft’s pressurised compartment and allowed to burn freely for up to six minutes while observed by a suite of thermocouples, radiometers and cameras.

Since the Cygnus spacecraft is not designed to be recovered, the end of its mission provides the opportunity to perform these experiments, which are intended to provide a better understanding of how a fire might spread inside a manned spacecraft.

Cygnus spacecraft are named after former astronauts. OA-6 is named the SS Rick Husband, after the commander of Space Shuttle Columbia’s ill-fated STS-107 mission.

Husband, who also piloted Discovery during STS-96 – the second US mission to the International Space Station, joined NASA in 1995 having served as a fighter, instructor, test and demonstration pilot in the US Air Force rising to the rank of Colonel. He also served in the Royal Air Force under an exchange program.

Husband was killed in February 2003 when Columbia disintegrated as she reentered Earth’s atmosphere at the end of a two-week microgravity research mission. None of the seven astronauts aboard survived.

Cygnus launched atop an Atlas V rocket, flying in the 401 configuration. This version of the rocket uses a four-metre payload fairing and a single-engine Centaur upper stage, with no solid rocket motors attached to the first stage. The rocket had the tail number AV-064, and was the sixty-second Atlas V to fly.

The Atlas departed Space Launch Complex 41 (SLC-41) at the Cape Canaveral Air Force Station. Originally built for the Titan IIIC, the pad was also used by the Titan IIIE and Titan IV rockets before being torn down in 1999 to make way for the Atlas V.

For Atlas, SLC-41 was designed to follow a “clean-pad” approach, with no large fixed support structures at the pad. In recent months a new fixed tower has been constructed at the complex to support future manned missions with Boeing’s CST-100 capsule, allowing astronauts to board the vehicle. The rocket is fuelled and serviced through umbilicals attaching to a tower mounted upon its mobile launch platform.

Assembly of the Atlas takes place in the Vertical Integration Facility (VIF), to the south of the pad. Stacked atop a mobile platform the rocket is moved to the launch pad on rails, usually about a day ahead of liftoff.

The Atlas is a two-stage rocket, with a Common Core Booster (CCB) first stage powered by an RD-180 engine and a Centaur upper stage sporting an RL10C-1 engine. The first stage burns RP-1 propellant oxidised by liquid oxygen, while the Centaur is fully cryogenic – burning liquid hydrogen and liquid oxygen.

At about 2.7 seconds before the countdown reached zero, the RD-180 engine ignited and began building up thrust. At about T+1.1 seconds, the thrust produced exceeded the weight of the rocket and liftoff occurred. The rocket initiated a series of pitch and yaw manoeuvres 17.3 seconds later to put itself onto a 44.4-degree launch azimuth as it headed northwest over the Atlantic Ocean.

AV-064 reached Mach 1, the speed of sound, 82.6 seconds into her flight before passing through the area of maximum dynamic pressure, or Max-Q, 11.2 seconds later.

The first stage burned for four minutes and 15.5 seconds before its engine shut down. Six seconds later the spent stage separated, with the Centaur’s RL10 entering a prestart phase.

Ten seconds after stage separation the Centaur ignited to begin a single burn with a duration of thirteen minutes and 38 seconds. However, the burn appeared to last over a minute more than previously advertised.

Eight seconds after Centaur ignition, the Atlas’ payload fairing was jettisoned. For Tuesday’s mission the rocket flew with an Extra-Extended Payload Fairing (XEPF), which at 13.8 metres (45.3 feet) in length is the longest of the three four-metre (13-foot) diameter fairings available.

Following completion of the Centaur’s burn, Atlas coast for two minutes and 39 seconds before Cygnus separated, at twenty minutes and 58.5 seconds mission elapsed time over the Atlantic to the West of Ireland. The target orbit for spacecraft separation is 229.8 by 230.0 kilometres (142.8 x 142.9 miles, 124.1 by 124.2 nautical miles) at an inclination of 51.6 degrees.

About two hours and six minutes after launch, Cygnus deployed its solar panels before beginning a series of thruster firings over the next few days to manoeuvre itself towards rendezvous with the International Space Station.

Arrival at the station is expected on Saturday, when astronauts will use the station’s CanadArm2 robotic arm to capture the spacecraft and berth it to the nadir port of the Unity module. Cygnus is expected to remain at the station for close to two months, departing in late May ahead of the next Cygnus launch in June.

After performing the Saffire experiment, the SS Rick Husband will be deorbited to a destructive reentry.

Tuesday’s launch was the second of the year for the Atlas V and the third for United Launch Alliance – who also deployed the NROL-45 mission in February via the Delta IV rocket. ULA’s next launch – and the next for the Atlas V – is expected to come in early May with the MUOS-5 communications satellite for the US Navy.

Cygnus’ next flight is currently scheduled for June, subject to the Antares being ready to fly in its new Antares 230 configuration. A further Antares-powered Cygnus launch is slated for late December.

SpaceX will fly the next resupply mission to the station, with its Dragon spacecraft scheduled to lift off on the CRS-8 mission early next month resulting in both Dragon and Cygnus being at the ISS simultaneously.

(Images: via NASA, ULA, Orbital ATK and Jacques van Oene/Spacepatches.nl – also L2 Artist Nathan Koga – plus 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 ATK and NASA)

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