After 31 days of docked operations at the International Space Station (ISS), SpaceX’s CRS-8 Dragon spacecraft completed the final aspect of its mission as astronauts aboard the Station unberthed the spacecraft to send it on its way toward a fiery reentry into Earth’s atmosphere for a splashdown and recovery in the Pacific Ocean, which was successfully completed on Wednesday.
Dragon’s heralded return to the International Space Station (ISS) after a one year absence began on 8 April 2016 when Falcon 9 launched the CRS-8 mission on its way to the orbital laboratory.
After sending Dragon on its way, the first stage of the Falcon 9 went on to perform the first successful rocket-powered landing on a barge in the middle of the Atlantic, a feat which has since been replicated once last week.
For Dragon, the flawless launch was followed by a clean deployment of its solar panels and a two-day orbital rendezvous dance with the ISS, which culminated in a grappling and berthing to the Harmony nadir port on the Station on 10 April at 11:23 UTC and 13:57 UTC, respectively.
The CRS-8 Dragon berthed with a total cargo mass of 3,136 kilograms (6,914 lbs), including the first-ever inflatable (expandable) module (Bigelow Expandable Activity Module – BEAM) to be attached to the ISS for testing in the human spaceflight arena.
In total, CRS-8 delivered 1,723 kg (3,799 lb) of internal supplies to the ISS and 1,413 kg (3,115 lb) of external equipment to the orbital laboratory.
Unlike all other operational Visiting Vehicles (VVs), CRS-8 Dragon is returning a large amount of ISS cargo and time-sensitive scientific experiments to Earth.
To this end, US crews aboard the Station spent Monday and Tuesday packing these critical items into Dragon.
Russian crewmembers did not assist with packing operations on Monday as the Russian Federation celebrated a national holiday, Victory Day, commemorating the 9 May 1945 surrender of Nazi Germany to the Soviet Union – which ended World War II in Europe.
In all, the CRS-8 Dragon is returning more than 1,678 kg (3,700 lb) of supplies – including crew supplies, hardware and computer resources, science experiments, space station hardware and trash – to Earth.
After packing Dragon and closing hatches, US and British astronauts translated the Canadarm2 (Space Station Remote Manipulator System – SSRMS) to the correct position for grappling and unberthing operations.
The crew then performed COTS UHF Communication Unit (CUCU) Crew Command Panel (CCP) checkout to verify that all communication assets with Dragon were fully operational prior to unberthing.
This CUCU CCP system is critical to Dragon’s free-flight proximity operations with the Station and ensures that emergency abort options remain actionable to protect the ISS from a misbehaving Dragon.
With those systems verified ready for unberthing, British astronaut Tim Peake initiated the unberthing of Dragon from the Node 2 (Harmony) Nadir CBM (Common Berthing Mechanism), via the release of 16 bolts around the CBM berthing collar on the ISS side.
The unbolting sequence was performed in four sets of four bolts to ensure even unloading on the CBM interface.
For CRS-8, the unberthing and departure process was a true international effort, with astronauts and controllers from three different countries (the United Kingdom, Canada, and the United States) actively participating, while one country (the Russian Federation) monitored the departure of Dragon from the ISS.
Once the sixteen bolts were released, Dragon’s removal from Harmony was commanded by Canadian Space Agency (CSA) ground controllers, working with the ISS Flight Control Room at the Johnson Space Center, known as MCC-H.
With the SSRMS holding on to Dragon, the SSRMS pulled Dragon away from the Harmony nadir port and maneuvered Dragon to its release position approximately 30 feet below the ISS.
Once in the release position, Dragon CRS-8 and the ISS parted ways.
This release procedure was initiated by loosening the snares that hold the SSRMS Latching End Effector (LEE) to the Dragon Flight Releasable Grapple Fixture (FRGF) – effectively “letting go” of Dragon.
The release of Dragon occurred at 09:19 EDT (13:19 UTC). The exact timing of release is based on lighting conditions and release readiness of Dragon, the ISS, and the control teams.
Once released, Tim Peake retracted the SSRMS clear of Dragon, after which the spacecraft conducted three departure burns to leave the vicinity of the ISS along the R-Bar.
This departure toward the edge of the Station’s neighborhood was closely monitored by the CUCU and controllers on the ground.
The third burn, and the largest of the firings, sent Dragon outside of the approach ellipsoid, at which point SpaceX controllers inside MCC-X at SpaceX’s Hawthorne, California, facility took full control of Dragon.
Dragon then entered a free-flying phase on-orbit, during which time the GNC (Guidance, Navigation, and Control) bay door was closed for reentry.
With all systems ready, Dragon performed a 10 minute deorbit burn with its Draco thrusters – a burn that began around 14:00 EDT (18:00 UTC).
Dragon then dropped into Earth’s atmosphere for a roughly 40min descent to the Pacific Ocean.
To properly prepare for atmospheric entry, the umbilical between the Dragon capsule and its Trunk disengaged prior to the Trunk’s separation from the capsule.
The capsule itself then oriented into the proper reentry position, with its PICA-X heat shield – a Thermal Protection System based on a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material – facing the direction of travel.
Once through entry heating, Dragon’s drogue parachutes deployed, followed by Dragon’s main parachutes – which eased the vehicle to a splashdown in the Pacific Ocean off the coast of California at around 14:55 EDT (18:55 UTC).
Dragon will then be joined by her recovery forces, after which she will be powered down and then hooked up to the recovery assets and taken aboard the primary recovery ship for transport back to California.
Once aboard the recovery ship, teams will enter the side hatch of Dragon and remove all time sensitive payloads and experiments.
These time-sensitive payloads will then be placed on a fast-return ship and immediately taken to the Port of Los Angeles, where they will then be shipped to NASA.
Dragon will take a more leisurely pace on the main recovery ship and arrive at the Port of Los Angeles later. After arriving at port, Dragon will be placed on a transport vehicle and trucked to McGregor, Texas, where the rest of the returned cargo will be removed.
(Images: SpaceX and NASA.)