Crew-4 prepares to undock from the ISS ahead of return to Earth


After living and working aboard the International Space Station (ISS) for close to six months, Crew-4 and its crew of international astronauts are preparing to undock from the orbiting laboratory and begin their return to Earth.

The four-person crew, consisting of NASA astronauts Kjell N. Lindgren, Robert Hines, Jessica Watkins, and European Space Agency (ESA) astronaut Samantha Cristoforetti, are expected to depart the ISS aboard Crew Dragon Freedom on Friday, Oct. 14, 2022, at 15:35 UTC.

Crew-4 launched on April 27, 2022, aboard a SpaceX Falcon 9 rocket. The booster used on the mission was B1067-4, the same booster that launched a previous NASA/SpaceX crew mission, Crew-3.

The Dragon used on this mission is C212. C1212 was officially named Freedom by the crew of Crew-4, as the first crews of a new Crew Dragon spacecraft choose the name of the vehicle.

Upon undocking from the International Docking Adapter-3 (IDA-3) zenith (or space-facing) port of the ISS’s Harmony node, Crew Dragon Freedom will perform a series of four departure burns to safely maneuver Crew Dragon and its crew away from the station.

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The first departure burn, known as departure burn zero, begins just a few seconds after undocking and will last approximately 16 seconds. Departure burn zero will take the spacecraft up and around the station in preparation for the next series of burns. Once the burn concludes, Crew Dragon Freedom will enter a short coast phase ahead of its next burn.

A few minutes after undocking, departure burn one will begin. Lasting approximately 20 seconds, this burn will take the spacecraft on a trajectory to the front of and below the ISS. Shortly after this burn concludes, Dragon will exit the “keep-out sphere,” an imaginary safety boundary extending 200 meters away from the orbiting laboratory.

Once out of the keep-out sphere, Freedom will enter the “approach ellipsoid,” another imaginary boundary around the Station. However, instead of extending 200 meters away from the ISS, the approach ellipsoid extends 4 x 2 x 2 kilometers around the ISS.

After departure burn one concludes, the crew will be given the go-ahead to doff, or take off, their suits. The crew wears their suits during the undocking procedures as a safety precaution.

The ISS keep-out sphere, approach ellipsoid, and other regions. (Credit: NASA)

Departure burn two is the next burn, coming 50 minutes after the completion of departure burn one and lasting approximately 44 seconds.

After one more coast phase, Dragon will perform the fourth and final departure burn, lasting just over one minute. Once the final burn is complete, Dragon will be in a stable low-Earth orbit approximately 10 km below the ISS.

Once all departure burns are complete, the next major milestone will be the separation of Dragon’s trunk, which is followed shortly after by the de-orbit burn. During the de-orbit burn, Freedom will fire its four forward-facing Draco engines, which are located around the docking port at the nose of the capsule, and perform the longest burn of the mission. Following the completion of the burn, the docking port nosecone will close in preparation for re-entry.

During re-entry, the mission will enter a communications blackout period. At this time, the intense heat and plasma that forms around the vehicle due to Dragon’s immense speed prevent ground stations from exchanging communications with the crew and the spacecraft. This phenomenon is not unique to Dragon, however, as every crewed spacecraft in history that has returned to Earth has experienced some sort of blackout period during re-entry.

Falcon 9 (B1067-4) launches Crew-4. (Credit: SpaceX)

After the plasma phase of re-entry, Freedom will continue to slow down as it descends through the atmosphere, which becomes thicker and thicker the lower the spacecraft gets. Once Freedom has detected that it is at a certain altitude and velocity, it will deploy its two drogue parachutes and slow down to ~350 miles per hour.

The parachutes will partially deploy at first before fully inflating in a process known as reefing. Reefing allows parachutes to open in a slower and more-controlled manner to avoid higher loads on the vehicle and crew during descent.

Shortly after full drogue inflation, the drogue parachutes are cut and the main parachutes are deployed. The four main parachutes will also reef to ease the loads on the vehicle and crew.

The main parachutes will slow the vehicle down from ~350 miles per hour to around ~15 miles per hour for splashdown. After descending under the main parachutes for several minutes, Crew-4 will splash down either in the Gulf of Mexico or in the Atlantic Ocean east of Florida, pending weather conditions at the time of splashdown.

Splashdown of Crew Dragon Resilience during the private Inspiration4 mission in September 2021. (Credit: SpaceX)

Following splashdown, SpaceX’s Dragon recovery ship Shannon in the Gulf or Megan in the Atlantic will support Dragon and crew recovery operations. Shannon, previously named GO Navigator, was renamed in February 2022 in honor of NASA Astronaut Shannon Walker, the first female astronaut to fly aboard a SpaceX spacecraft.

If weather forces the splashdown location to the Atlantic Ocean, SpaceX recovery ship Megan will support Crew-4 recovery operations. Like ShannonMegan is named in honor of the second female astronaut to fly aboard Crew Dragon, Megan McArthur.

Before the recovery vessel approaches Freedom, the capsule will be visited by two of SpaceX’s recovery fast boats. The purpose of these small vessels is to quickly approach the spacecraft and ensure that Freedom is safe enough to be lifted out of the water and onto the deck of the ship.

Additionally, these fast boats will recover the capsule’s parachutes, which are cut from the spacecraft at the moment of splashdown. Once an all-clear call is given, crews from the fast boats begin preparing the capsule for the lift.

Once safely on the deck of the vessel, SpaceX’s recovery crews will perform one final check of the capsule to ensure there are no propellant leaks or other hazards ahead of crew egress. Crew egress will then follow in quick succession with each crew member being assisted out of the capsule, officially concluding SpaceX’s Crew-4 mission to the International Space Station.

(Lead image: Crew Dragon Freedom docked to the ISS. Credit: NASA)

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