Following a launch in late August and a month-long stay in orbit, SpaceX and NASA welcomed the return of the CRS-23 (Commercial Resupply Services 23) mission from the International Space Station (ISS). Cargo Dragon undocked from the station on Thursday, September 30, at 13:12 UTC, with a splashdown in the Atlantic Ocean occurring on schedule Friday, October 1, at 03:00 UTC.
CRS-23 used Cargo Dragon C208-2, a Cargo Dragon 2 spacecraft from SpaceX. The spacecraft concluded its second flight to space when it splashed down on Friday, previously launching on the CRS-21 mission in December 2020.
Unlike Crew Dragon missions, Cargo Dragon spacecraft are not named and instead are referred to by their serial number. Crew Dragon spacecraft are given their names by the first crew that flies in them.
The mission began on August 29, when a Falcon 9 launched from historic LC-39A at NASA’s Kennedy Space Center in Florida. The following day, Cargo Dragon C208-2 successfully docked to International Docking Adapter-2 (IDA-2), the forward-facing docking port on the Harmony module of ISS.
Crew Dragon Endeavour (top) and Cargo Dragon C208-2 (bottom) docked to the International Space Station – via ESA astronaut Thomas Pesquet on EVA-77
Typically, Dragon CRS2 (Commercial Resupply Services 2) missions will dock to the IDA-3 zenith (upward-facing) docking port to allow the station’s robotic arm to access Dragon’s trunk, where unpressurized cargo is carried. However, for CRS-23, no payloads were carried in Dragon’s trunk, and Crew-2 Dragon Endeavour is currently docked to the IDA-3 zenith port. So, instead of docking to IDA-3, C208-2 docked to IDA-2, as it was the available port.
CRS-23 is the third mission under SpaceX’s CRS2 contract with NASA, wherein Cargo Dragon 2 vehicles are used. The Cargo Dragon 1 spacecraft was retired after CRS-20, the final flight under the initial CRS contract, and the Cargo Dragon 2 vehicles were made operational soon after. To date, there has been a total of eight Dragon 2 flights — four crewed flights and four uncrewed flights.
Following docking and hatch opening, ISS crew members began using the experiments brought up to the station during launch. C208-2 brought the station a robotic arm test demo, student spaceflight experiments, a retinal imager, and more. Upon return, some experiments will stay onboard the ISS while others return home. Some of the experiments returning home Friday are:
- Ring Sheared Drop (RSD) experiment
- Cells used in JAXA’s Anti-Atrophy investigation
- Genes in Space-8
The RSD experiment investigates how protein aggregates called amyloid fibrils develop without the interference of a solid container. Amyloid fibrils may be related to diseases such as Alzheimer’s, Parkinson’s, and type 2 diabetes.
Images showing the use of the RSD device- via Joe A. Adam and Patrick M. McMackin
On Earth, scientists have to take into account how the proteins interact with the container they’re in due to gravity, which can affect the results of the experiment. In the microgravity environment on the ISS, the RSD experiment uses surface tension on a drop of liquid to analyze the proteins.
In the RSD device, a single drop of liquid containing proteins is pinned between two rings. One ring rotates while the other stays stationary, creating shear flow.
During its stay on the ISS, the RSD experiment confirmed that the surface tension concept tested by the RSD device works for containing protein solutions in space. Fluid tested in space will be returned by CRS-23 and analyzed for protein fibril formation and fibril structure development in labs. The results from the RSD study could greatly improve our understanding of how amyloid fibrils develop and are transported.
Another experiment returning to Earth is the Japan Aerospace Exploration Agency’s (JAXA’s) Anti-Atrophy investigation. The investigation tests how biomaterials inhibit muscle atrophy in microgravity, including a muscle loss inhibitor and a muscle-growth acceleration material.
Lastly, the Genes in Space-8 experiment monitors the expression of genes that control liver enzymes. The quantity of these liver enzymes can fluctuate, greatly affecting how the body metabolizes some drugs.
Before traveling to the ISS, samples for the experiment were prepared on Earth. The samples launched to the ISS while frozen and will return in a cold freezer onboard CRS-23. While on the ISS, each experiment was imaged and filmed in detail.
Some of the experiments returning on CRS-23 will be analyzed quickly after splashdown before gravity has had the chance to greatly affect them. A few experiments may be taken to labs at the Kennedy Space Center for testing following landing.
This capability is fairly new and allows scientists to look at samples immediately following their return to Earth before the planet’s conditions begin affecting the experiments. These experiments will then be returned to their home labs for a more in-depth analysis later.
Dragon C208-2 was undocked from the ISS at 13:12 UTC (9:12 AM EDT) on Thursday. Following undocking, Dragon performed numerous maneuvers with its Draco thrusters to move away from the ISS. The thruster firings also put Dragon in an orbit that passed over the planned landing location.
Undocking was monitored by ground controllers at SpaceX mission control (MCC-X) in Hawthorne, California, as well as NASA ground controllers in mission control at the Johnson Space Center (MCC-H) in Houston, Texas.
Before performing the deorbit burn, Cargo Dragon separated the unpressurized trunk, which covers the capsule’s heat shield. Although the trunk will be left in orbit, the orbit of the trunk will gradually decrease over time until it burns up upon reentry.
After trunk separation, Dragon used a set of Draco thrusters around the docking port to perform the deorbit burn. Following the completion of the deorbit burn, the nosecone that encloses the docking port closed.
The deorbit burn reduced Cargo Dragon’s speed, and the capsule began to decrease in altitude until it begins reentering the Earth’s atmosphere. During reentry, the capsule was facing heat-shield-first, allowing the shield to deflect the extremely energetic and hot conditions of reentry — protecting the capsule and its precious experiments.
Following reentry, Dragon deployed a set of drogue parachutes after decelerating to a sufficient speed. The drogue chutes further slowed the vehicle before the four main parachutes deployed. The main parachutes reduced the descent rate to a velocity safe for splashdown.
After splashdown, teams on one of SpaceX’s numerous recovery vessels will begin to safe the vehicle and pull it onboard the vessel. A helicopter will be present on the ship to rush time-sensitive payloads from the recovery vessel to Kennedy Space Center for post-flight analysis.
The remaining cargo will be offloaded once the recovery vessel and Dragon return to port.
(Lead image: CRS-23 Cargo Dragon C208-2 reenters over Florida – via Julia Bergeron for NSF)
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