After a month-long stay at the International Space Station, NASA and SpaceX are ready to support the return of the CRS-24 Cargo Dragon back to Earth. Currently, ground controllers are targeting 10:40 AM EST (15:40 UTC) on Sunday, January 23, for the undocking of the Dragon spacecraft from the Harmony module’s zenith – or space-facing – port.

Once the spacecraft undocks from the Station, it will perform a series of maneuvers to lower its orbit and re-enter Earth’s atmosphere. This will set it up to splash down off the coast of Florida at approximately 12:44 AM EST on Monday, January 24.

The landing of the Dragon spacecraft will conclude the CRS-24 mission, which is SpaceX’s fourth resupply mission to the International Space Station (ISS) under the Commercial Resupply Services 2 (CRS2) contract. The CRS 2 contract employs the Dragon 2 spacecraft, as the Dragon 1 spacecraft was retired at the end of the initial CRS contract. Since its inaugural flight, Dragon 2 has flown nine times — four crewed and five uncrewed.

This mission began when Cargo Dragon C209-2 lifted off from Launch Complex 39A (LC-39A) at Kennedy Space Center on December 21, 2021. Launched aboard the Falcon 9 booster 1069, this was the capsule’s second flight.

Falcon 9 and Cargo Dragon C209-2 vertical on LC-39A ahead of launch. (Credit: NASA)

Unlike the Crew Dragon spacecraft, Cargo Dragons are not given names and thus are only denoted by a serial number. The hyphenated number at the end represents the number of flights the capsule has performed – including the current mission. C209 first flew during the CRS-22 resupply mission in June of 2021. Following its return, it was refurbished and prepared for the CRS-24 mission.

Just one day after launch, Dragon docked to the ISS – delivering over 3,000 kilograms of science experiments, instruments, supplies, hardware, and Christmas presents. Following hatch opening, the ISS crew began using the experiments brought up to the orbiting laboratory.

Some of the research highlights include the German Aerospace Agency’s study Bioprint FirstAid, which demonstrated that a portable handheld bioprinter can create a patch of tissue using the patient’s own skin cells, reducing healing time. In addition, the crew undertook a study that aims to improve the delivery of cancer drugs by crystallizing monoclonal antibodies. This can then be used to treat several different cancers.

CRS-23 Cargo Dragon C208-2 approaches the ISS in August 2021. (Credit: NASA)

When Dragon departs the Station, some experiments will remain, while others return home. Some of the experiments returning home Saturday are:

The Light Microscopy Module: Sponsored by NASA’s Division of Biological and Physical Sciences, this state-of-the-art light imaging microscope will be returning to Earth after operating for 12 years aboard the International Space Station. This module allowed observation at the microscopic level and supported various colloid research, plant studies, and thermophysical experiments.
InSPACE-4: Standing for Investigating the Structure of Paramagnetic Aggregates from Colloidal Ellipsoids, the experiments aimed at studying the assembly of small structures from colloids using magnetic fields. The samples returning from this study will provide insights into the fabrication and manufacturing of new materials using nanoparticles.
Cytoskeleton: Funded by the European Space Agency (ESA), this experiment attempts to acquire more information about different events happening inside a mammalian cell and to learn how microgravity affects it. The samples returning from this mission will help teams study and develop countermeasures to help astronauts maintain optimum health during long-duration space missions in the future.

Apart from the research experiments, six components are returning to earth for further tests, evaluations, and possible refurbishment for future reflight. These components are:

Hydrogen Dome: One of the critical components responsible for generating oxygen on the ISS, the Hydrogen dome was removed and replaced following a period of the observed end of life characteristics.
Urine Processing Assembly Distillation Assembly: This equipment supports urine processing and distillation in orbit.
Avionics Air Assembly Fan: Previously installed in the Water Process Assembly on the Tranquility module.
Rodent Research Transporters: Used to support the rodent investigations during this mission.
Total Organic Carbon Analyzer: Returning after 7 years of continuous operations, this hardware is designed to assess the carbon levels in the recovered water onboard the ISS.
CO2/Relative Humidity Sample Containers: This shuttle-era technology is modified to collect payload samples and support other critical exploration development objectives.

Undocking and splashdown timeline

Prior to undocking, the small pressurized area between Dragon and the Station’s hatch — known as the vestibule — will start depressurizing. This is to avoid an outburst of gas once the vehicle undocks.

While that’s in progress, NASA and SpaceX teams will conduct a go/no-go poll to make sure everything is set for undocking. Once given a GO, the teams at SpaceX’s mission control in Hawthorne, California will command the Dragon spacecraft to begin the undocking procedures. These include the retraction of umbilicals and the opening of two sets of hooks.

A Crew Dragon (above) and Cargo Dragon (bottom) docked to the ISS in September 2021. (Credit: ESA/NASA/Thomas Pesquet)

Once the mechanical systems let go of the Dragon spacecraft from the ISS, it will make use of its onboard Draco thrusters to perform a set of two undocking burns to separate itself from the port. These will be followed up by four Depart Burns – occurring shortly after the undocking burns – further distancing the spacecraft from the ISS.

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The Dragon spacecraft will exit the approach ellipsoid, which is an imaginary four by two kilometer-wide ellipsoid that governs all vehicles departing or arriving at the ISS. Dragon will then carry out the third depart burn, followed by the fourth and final burn.

After all four departure burns are completed, Dragon will initiate a nine-minute and 18-second departure phase burn. This will significantly lower its orbit. Following the burn, Dragon will stay in this orbit for quite a while as it prepares for the separation of the claw, followed by the trunk.

The trunk will remain in orbit for several months, but will eventually succumb to atmospheric drag and destructively enter the Earth’s atmosphere.

After trunk separation, Dragon will conduct its final burn – the deorbit burn. As its name suggests, this burn will deorbit the spacecraft and set its course to land off the coast of Florida.

Splash down of a Dragon 2 spacecraft. (Credit: SpaceX)

Following the deorbit burn, Dragon will close its nosecone and maneuver heatshield-first to prepare for re-entry. As it enters Earth’s atmosphere, Dragon will experience temperatures upwards of 1,500 degrees Celsius due to the compression of air ahead of it, generating a large amount of heat and plasma. This plasma will interfere with the spacecraft’s communications, resulting in a planned loss of signal (LOS) with mission control.

About ten minutes later, the teams will have acquisition of signal (AOS) with Dragon. The capsule will deploy its drogue parachutes, which will stabilize the capsule and begin to slow it down. This will be followed by the four main parachutes which will further slow the capsule before the splashdown. Once it is safely in the ocean, SpaceX’s recovery teams will secure the capsule and load it onto the recovery vessel, bringing it back to Port Canaveral. From there, it will be moved to one of SpaceX’s facilities for inspections and refurbishment before its next flight to space.

(Lead image: Cargo Dragon C209 docked to the ISS during the CRS-24 mission. Credit: NASA)

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