Shukla’s return journey: From 0.1 m/s to 7,800 m/s before a splashdown in the Pacific

On the evening of July 14, Indian astronaut Group Captain Shubhanshu Shukla will begin his 23-hour journey back to Earth from the International Space Station (ISS). He will pilot the Dragon C-213 spacecraft as part of the four-member Axiom-4 mission.

The crew, onboard the ISS since June 26 following their launch from the Kennedy Space Center in Florida on June 25, has spent the past two days preparing to undock. Their preparations have included completing handover formalities, concluding research tasks, and packing and stowing cargo.

The Dragon spacecraft is scheduled to undock at 4:35 pm IST on Monday. The crew will board the spacecraft at least two hours prior, after validating all systems and completing mandatory checks.

Once the crew enters the Dragon, strap themselves in and power up the spacecraft’s propulsion, navigation and communication systems, the physical undocking will begin. The entire process is autonomous with the crew monitoring it for any manual override in case of any contingency.

Following the command to undock from the ISS after the final “go” has been received from mission control, the Dragon’s docking mechanism will disengage and small thrusters will fire to slowly move the spacecraft away from the ISS.

The spacecraft will initially move at the rate of 10 cm per second to ensure a safe distance from the space center. This ensures a safe separation without disturbing the station’s orbit or operations. The crew monitors the trajectory and orbital parameters during this phase. At noon in India, the ISS was over the southern Allantic Ocean at an altitude of 425 km.

The Dragon will then execute a series of delta-velocity burns, that is firing its multiple thrusters, to increase its distance from the ISS and adjust its orbit for re-entry. These burns are carefully calibrated to position the spacecraft for a safe return trajectory.

Shukla, an IAF fighter pilot and test pilot who underwent intensive training with NASA and Axiom Space, will monitor the trajectory and orbital parameters to ensure that the spacecraft follows the planned departure path. The crew will remain in constant communication with mission control to address any contingencies.

Once safely away from the ISS, the Dragon will execute a de-orbit burn to lower its orbit and begin the descent toward Earth. This burn is critical for aligning the spacecraft with the designated splashdown zone in the Pacific Ocean.

From 0.1 meters per second at the time of separation, the spacecraft’s speed will increase to about 7,800 meters per second or 28,000 kmph.

When the spacecraft re-enters Earth’s atmosphere, the crew will experience significant g-forces as well as thermal and physical stress. The crew trained at NASA’s Johnson Space Center to handle the transition from microgravity to Earth’s gravity.

Re-entry will be at an altitude of about 180 km and the exterior will heat up to 2000 degrees Celsius due to atmospheric friction. The spacecraft’s heat shield, made of PICA-X material, a carbon derivative, will protect the spacecraft and crew during re-entry.

At approximately a height of 5.5 km or 18,000 feet two drogue parachutes will deploy to stabilize and slow the spacecraft. Four main parachutes will deploy at around 6,000 feet to reduce the speed of descent to about 24 kmh or 6-7 meters per second for a safe splashdown in the Pacific Ocean near the coast of California. The splashdown is expected on July 15 around 3:00 PM India time.

SpaceX’s, the firm that built and launched the Dragon, will position a recovery ship in the vicinity of the splashdown point. Initially small boats with trained and specially equipped technicians will approach the floating spacecraft and carry out safety checks for damage, radiation or any other contamination.

The dragon will them be hoisted onto the recovery ship and the crew will finally disembark, while teams will secure the cargo and research material. The crew will undergo preliminary medical evaluations and health check before being ferried ashore and then being transported to a secure NASA facility for a full post-mission recovery process.

This will include physical fitness assessments to evaluate balance, reflexes, cardiovascular function and immune response, psychological evaluations to assessing the astronauts’ mental state and ability to readjust to Earth’s gravity and targeted exercises to help them regain their strength and coordination.

India