CRS-12 Dragon completes her ISS mission with splashdown return

by Chris Bergin and Chris Gebhardt

SpaceX’s CRS-12 Dragon unberthed from the ISS ahead of a return to a Pacific Ocean splashdown on Sunday, concluding the spacecraft’s latest resupply mission. Dragon returned with 3,800 pounds of cargo, highlighting her unique downmass capability for NASA. Splashdown occurred at 10:14 AM Eastern Time (07:14 local time on the West Coast).

As always, Dragon began her journey atop the Falcon 9 rocket.

Launch from KSC’s 39A occurred last month, via an issue free ascent – carried to orbit by the Second Stage, while the booster made another successful return to LZ-1.

As the time it was the 6th Falcon 9 RTLS landing and the 14th overall successful landing of the Falcon 9 first stage.

The primary goal of the mission saw Dragon stalk the ISS prior to her arrival for berthing.

Grabbed by the Space Station Remote Manipulator System (SSRMS), Jack Fischer and Paolo Nespoli carefully translated Dragon to its pre-install position 3.5 m away from Node-2 Harmony’s nadir port.

This marked the official arrival of 2,910 kilograms (6,415 pounds) of cargo to the station. This included 1,652 kilograms (3,642 lb) of pressurized cargo and the 1,258-kilogram (2,773 lb) ISS Cosmic Ray Energetics and Mass (ISS-CREAM) instrument which was carried in Dragon’s Trunk.

ISS-CREAM was removed from the Trunk by the SSRMS and handed over to its robotic colleague the Japanese Robotic Arm (JEM-RMS) via the work of the ground controllers.

It was then installed on the Kibo module’s Exposed Facility (JEM-EF) for a three-year investigation, is intended to monitor extremely-high-energy cosmic rays, measuring their charge and energy.

The SSRMS then moved into operations to prepare for the departure of Dragon as the ISS crew filled the vehicle with its downmass.

“SpaceX12 Dragon Grapple: The SSRMS was maneuvered from the post-Latching End Effector (LEE) A survey park position to the SpX-12 Dragon capture position,” noted L2 ISS Status information. “SSRMS then grappled Dragon nominally. The SSRMS was powered down to Dual String Keep Alive (DSKA). Dragon release is scheduled for this Sunday.”

The ISS crew also checked out the vital communication system that will be employed during the departure of Dragon.

“Commercial “Off-The-Shelf (COTS) Ultra High Frequency (UHF) Communication Unit (CUCU) and Crew Command Panel (CCP) Checkout:  In preparation for the upcoming SpaceX-12 unberth and release, the crew coordinated with ground teams to activate the CUCU System and performed a successful checkout of CCP serial number 3,” added the status information.

“CCP and CUCU provide a command and telemetry communications link between ISS and Dragon during free flight operations in the vicinity of ISS.”

Saturday marked the unberthing of the vehicle from Node 2.

Whilst being firmly held in the snares of the Latching End Effector (LEE) on the end of the SSRMS, bolts securely fastening Dragon to the nadir (Earth-facing) Common Berthing Mechanism of Node-2 Harmony were driven to the retract position, freeing Dragon from its berthing port on the Station.

The Station crew then maneuvered Dragon on the end of the SSRMS away from the main structure of the ISS to its release point 10 meters from the orbital lab.

Expedition 53 Flight Engineer Paolo Nespoli of ESA (European Space Agency) with the assistance of station Commander Randy Bresnik of NASA – working in the Cupola lab of the ISS – commanded the release of the LEE snares holding the spacecraft.

The exact time of release is always subject to change from the announced plan due to lighting conditions, communications coverage, and day-of timeline activities. CRS-12’s release was marked as at 4:40 AM Eastern.

Once the LEE snares were released, the SSRMS backed away from Dragon as the craft held its position at the 10m mark.

Once the Station’s arm is cleared to a safe distance, Dragon conducted a series of three small thruster firing departure burns that move the capsule down the R-Bar (Radial Vector) and away from the International Space Station toward Earth (when viewed in relation to ISS orientation and Dragon movements with respect to Earth).

During the initial stage of departure, Dragon will be under the control of its own computer programming, with the Station crew and controllers at Mission Control Houston in Texas for NASA having primary control over the spacecraft.

As Dragon pushes down the R-Bar, the largest of the three thruster departure burns will impart enough Delta Velocity (Delta-V) change to Dragon to push it outside of the approach ellipsoid.

The approach ellipsoid is a 4 km by 2 km oval-shaped region around the International Space Station that extends 2 km in front of and 2 kilometers behind the ISS along the velocity vector (V-Bar) and 1 km above and 1 km below the Station along the R-Bar.

Once Dragon cleared the approach ellipsoid 1 km below the ISS, primary control of the vehicle shifted from NASA to SpaceX controllers in Hawthorne, California.

Dragon conducted several hours of free flight activities as controllers at Mission Control SpaceX prepared the vehicle for the end of its mission.

This included the closure of the Guidance Navigation and Control (GNC) bay door on Dragon, creating a perfect thermal protection seal around the entirety of Dragon for entry.

At the appropriate time, Dragon’s Draco thrusters began a 10-minute firing sequence known as the deorbit burn to slow the capsule and place it on to the proper heading for entry into Earth’s atmosphere.

Following the deorbit burn, the umbilicals between Dragon and her external payload trunk were severed ahead of the trunk’s separation from Dragon itself.

Dragon then reoriented, with its heat shield out in front in preparation for Entry Interface (EI) – the moment Dragon reached the first traces of Earth’s upper atmosphere.

Once EI occurred, Dragon’s Thermal Protection System (TPS) protected it from the searing hot temperatures of reentry formed as the air molecules around Dragon are instantly heated and turned to plasma under the friction created by Dragon’s high velocity.

Dragon’s primary heat shield, called PICA-X, is based on a proprietary variant of NASA’s Phenolic Impregnated Carbon Ablator (PICA) material and is designed to protect Dragon during atmospheric re-entry.

PICA-X is robust enough to protect Dragon not only during ISS return missions but also during high-velocity returns from Lunar and Martian destinations.

Unlike the Dragon capsule, the Dragon trunk destructively burns up in Earth’s atmosphere.

Once safely through the plasma stage of reentry, Dragon’s drogue parachutes deployed, followed by the main chutes designed to ease the vehicle to a splashdown in the Pacific Ocean for recovery.

Recovery was attained by three main recovery vessels which were positioned near Dragon’s return location.

Fast recovery vessels deployed to begin collecting Dragon’s parachutes as recovery of the capsule itself was conducted by the primary recovery assets.

Once safely aboard the recovery vessel, Dragon was transported to the Port of Los Angeles and will then shipped to Texas for cargo removal.

Currently, Dragon is the only resupply vessel capable of returning experiments and equipment from the International Space Station as the three other in-service resupply vehicles (Progress, Cygnus, and the H-II Transfer Vehicle) all perform destructive reentries into Earth’s atmosphere.

Under the second Commercial Resupply Services (CRS-2) contract award, Sierra Nevada’s Dream Chaser spaceplane will join Dragon as only the second uncrewed vehicle capable of returning equipment and experiments from the Station.

With the conclusion of CRS-12, NASA’s next commercial resupply mission to the International Space Station will be SpaceX’s CRS-13 flight, which is currently targeting liftoff from LC-39A at the Kennedy Space Center in December.

(Images: NASA, SpaceX, and L2 artist Nathan Koga – The full gallery of Nathan’s (Falcon Heavy to Dragon to Starliner, MCT, SLS, Commercial Crew and more) L2 images can be *found here*)

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