SpaceX’s CRS-16 Dragon spacecraft has concluded the EOM (End Of Mission) phase of her mission following unberthing from the International Space Station (ISS) on Sunday. Dragon’s release from the Space Station Remote Manipulator System (SSRMS) occurred at 23:33 UTC, with splashdown in the Pacific Ocean expected around 05:10 UTC on Monday.
The conclusion to Dragon’s mission was expected earlier in the week. However, ISS managers opted to delay the EOM events to Sunday, due to poor weather conditions in the splashdown zone.
The CRS-16 Dragon was launched on Falcon 9 B1050.1 back in December. The launch was successful, however the booster failed to land at Cape Canaveral’s LZ-1 due to a grid fin system failure that saw the stage lose control after the entry burn.
Falcon 9 performs successful abort from RTLS to ocean splashdown after sending upper stage & Dragon on their way to ISS.
— Kerbal Space Academy (@KSpaceAcademy) December 5, 2018
Despite the spin, the booster still managed to abort to a water landing and was towed back to Port Canaveral a few days later. It is not clear if the booster will fly again, but it’s unlikely it will be refurbished for a customer flight. Elon Musk did intimate it might be used on an internal test flight of some sorts in the future.
The capsule contains 1,598 kilograms (3,523 lb) of cargo to be unloaded by the astronauts aboard the space station, while the trunk carries additional payloads for attachment to the outside of the ISS and houses critical vehicle systems including Dragon’s two solar arrays. The capsule is the only part of Dragon that is recovered; the trunk is jettisoned and burns up when it reenters Earth’s atmosphere.
Once Dragon arrived at the ISS, the spacecraft provided a multitude of payloads, with pressurized cargo including 304 kilograms (670 lb) of provisions for the crew, 191 kilograms (421 lb) of hardware for the US and international segments of the station and 11 kilograms (24 lb) for the Russian segment, 40 kilograms (88 lb) of computer equipment, 15 kilograms (33 lb) of hardware to support spacewalks and 1,037 kilograms (2,286 lb) of scientific equipment and new experiments.
In the Dragon’s Trunk were two payloads to be mounted to the outside of the space station. The Global Ecosystem Dynamics Investigation (GEDI) will use laser ranging to study the three-dimensional structure of features on the Earth’s surface such as forests, snowpacks and glaciers. GEDI consists of a LIDAR instrument which will use the reflection of light pulses to build up a profile of surface elevations. The instrument was mounted on the Exposed Facility (JEM-EF) of the Japanese Experiment Module, Kibo.
Ahead of the return trip, Dragon was packed with downmass and the hatch closed. Robotic ground controllers then used the robotic arm to detach Dragon from the Earth-facing port of the Harmony module to maneuver Dragon into the release position.
Dragon was released from the SSRMS at 23:33 UTC.
Once the LEE snares were released, the SSRMS was backed away from Dragon as the craft held its position at the 10 meter mark.
Once the Station’s arm was cleared to a safe distance, Dragon conducted a series of three small thruster firing departure burns that moves 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 was 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 imparts 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 includes 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.
SpaceX flight controllers at Hawthorne, California commanded Dragon’s Draco thrusters to fire for 12 minutes and 53 seconds – retrograde – in the deorbit burn that enabled Dragon to slip out of orbit for its descent back to Earth.
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 placed 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) protects 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 is attained by three main recovery vessels which were positioned near Dragon’s return location. The main recovery vehicle had already set sail earlier this week.
Fast recovery vessels deploy to begin collecting Dragon’s parachutes as recovery of the capsule itself will be conducted by the primary recovery assets.
Dragon’s parachute-assisted splashdown usually occurs 410 miles southwest of Long Beach, California. However, the splashdown zone was moved further south for this return. It will take about two days for Dragon to be brought back to the Port of Los Angeles for its cache of cargo and scientific experiments to be unloaded.
The ISS crew spent the majority of the second half of Dragon’s stay loading Dragon’s pressurized capsule with key items to be returned to Earth, including numerous time-sensitive experiments, which will be the first items to be removed.
Dragon will eventually take a road trip to SpaceX’s test center at McGregor in Texas for the complete cargo removal.
CRS-17 is the next Dragon mission to the ISS, currently scheduled for March.