SpaceX’s CRS-6 Dragon unberthed from the International Space Station (ISS) and was released from the grip of the Station’s “Big Arm” on Thursday. The resupply ship then completed homeward leg of her trouble-free orbital adventures, with a splashdown in the Pacific Ocean expected less than six hours after parting ways with the orbital outpost.
The SpX-6/CRS-6 Dragon was launched uphill by the Falcon 9 v1.1 in April, arriving at the ISS three days later for berthing.
A smooth rendezvous by the spacecraft culminated in her capture by Italian astronaut Samantha Cristoforetti.
(Animation created by Artyom Zharov, via L2’s huge collection of Dragon arrival hi res images)
This included 500 kilograms (1,102 lb) of items and provisions for the station’s crew, 518 kilograms (1,142 lb) of station hardware and equipment, 16 kilograms (35 lb) of computer and electronic equipment and 23 kilograms (51 lb) of hardware for EVAs.
The remaining 844 kilograms (1,860 lb) of the Dragon’s payload was taken up by scientific hardware and experiments, including critical materials to directly support about 40 of the more than 250 science and research investigations.
Also making the trip was a new espresso machine for space station crews and a new team of mousetronauts in the Rodent Research-2 payload.
Unlike all other operational Visiting Vehicles, Dragon will return a large amount of ISS cargo, with more than 3,000 pounds of mass – including crew supplies, hardware and computer resources, science experiments, space station hardware and trash – heading back to Earth.
Preparations for Dragon’s return began with the translation of robotic assets.
Canadian robots had been busy with work outside of the Station, involving the latest Robotic Refuelling Mission (RRM) objective, before being called upon to prepare for releasing the Dragon.
This saw the Special Purpose Dexterous Manipulator (SPDM) stowed on the Mobile Base System (MBS) Power/Data Grapple Fixture (PDGF) 2 by the Space Station Remote Manipulator System (SSRMS), which then took a ride on the Mobile Transporter – known as a walk off – to Node 2 to grab hold of the Dragon.
Inside the Station, the crew completed the loading of Dragon’s downmass, before conducting a checkout of the COTS UHF Communication Unit (CUCU) Crew Command Panel (CCP) that the crew will use to communicate with the Dragon capsule while she is flying free in the vicinity of the station.
To kick off that homecoming, the long sequence of events – that will ultimately lead to Dragon safely bobbing up and down in the Pacific Ocean – saw the ISS crew initiate the unberthing of Dragon from the Node 2 Nadir CBM, via the release of 16 bolts around the CBM berthing collar on the ISS side, performed in four sets of four bolts to ensure even unloading on the CBM interface.
Dragon’s removal was commanded by Canadian Space Agency (CSA) ground controllers, working with the ISS Flight Control Room at the Johnson Space Center.
With the SSRMS holding on to the Dragon – and the bolts released through the opposite process that saw first and second stage capture – the “big arm” pulled Dragon away from the port.
Dragon was maneuvered to a release position approximately 30 feet below the ISS.
Once in the release position, the time came for Dragon and the ISS to part ways.
This procedure was initiated by the release of the snares holding the SSRMS Latching End Effector (LEE) to the Dragon Flight Releasable Grapple Fixture (FRGF) – effectively “letting go” of the Dragon.
MCC-H controllers first checked the lighting conditions were acceptable ahead of the 7:04 am Eastern release.
With the SSRMS retracted safely clear of the spacecraft, Dragon conducted three departure burns to depart to vicinity of the ISS, edging away from the orbital outpost, with small thruster firings to push down the R-Bar.
This departure towards the edge of the ISS’ neighborhood was monitored by the CUCU and controllers on the ground.
The third burn was the larger of the firings, which sent Dragon outside of the approach ellipsoid, at which point SpaceX controllers inside MCC-X at SpaceX’s Californian facility took full control of the mission.
Dragon then enjoyed a free-flying phase on-orbit, during which time she completed a critical action – closure of the GNC bay door, to which the FRGF is mounted – before conducting the de-orbit burn at 11:49 am Eastern.
The 10 minute deorbit burn was conducted by the spacecraft’s Draco thrusters.
The umbilical between Dragon and her Trunk then disengaged, prior to the Trunk separating from the Dragon capsule.
As the spacecraft moved into Entry Interface (EI), she was protected by the PICA-X heat shield – a Thermal Protection System (TPS) based on a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material, designed to protect the capsule during Earth atmospheric re-entry, and is even robust to protect Dragon from the high return velocities from Lunar and Martian destinations.
Once at the required velocity and altitude, Dragon’s drogue parachutes deployed, followed by Dragon’s main parachutes, easing the vehicle to a splashdown in the Pacific Ocean off the coast of California at around 12:42 pm Eastern.
Three main recovery boats soon arrived on station, with fast boats racing to meet the Dragon shortly after she hit the water, allowing for the recovery procedures to begin.
The vehicle was powered down and then hooked up to the recover assets.
Dragon was transported to the port of Los Angeles, prior to a trip to Texas for cargo removal.
The next Dragon to head to the Station will be the CRS-7 mission, which is currently scheduled to launch on June 26.
This date is a small slip from the previous NET (No Earlier Than) date, based on the evaluations taking place into the manifest changes caused by the failure of the Russian resupply craft Progress M-27M.
(Images: via L2’s SpaceX Special Section, which includes over 1,000 unreleased hi res images from Dragon’s flights to the ISS. Other images via NASA and SpaceX)
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