Bengaluru (Karnatka ) [India], July 14: Former Scientist and Professor at Indian Institute of Astrophysics, RC Kapoor, on Monday, said that docking requires very accurate and carefully orchestrated manoeuvres. It is not a simple process of two spacecraft coming together, as even a slight firing of thrusters alters the orbit and creates a positional mismatch between the chaser and the target.
Speaking to ANI, Kapoor said, "Docking requires very accurate and carefully orchestrated manoeuvres. It is not so easy. As you remember, when the docking was about to take place, there was a lot of tension. It's not a simple matter of just bringing two objects together. Each time a thruster fires, the orbit changes slightly. So there's always a slight mismatch between the positions of the chaser and the target, and it takes extremely careful alignment to get them to engage properly."
He explained the mechanism further. "Docking involves magnetic guides that pull the capsule gently, allowing for a soft capture. Then, latches are used to ensure a hard capture. Only after confirming there's no leakage and that cabin pressure is stable, does the crew proceed with further operations."
On the process of undocking, Kapoor said, "Now the entire sequence is reversed. The capsule is currently in a hard-capture state with the ISS. Before undocking, pressure levels must be equalised, and the cargo, including instruments and waste, must be transferred. Then, all four astronauts, in full gear, board the capsule and take their positions."
"Coordination between ground control and the space station is critical. The latches are released, shifting the capsule into a soft-capture state. The actual undocking happens at an extremely slow speed--just a few centimetres per second. The capsule then slowly increases its distance from the ISS and exits its safety zone, which typically takes around 20 minutes," he added.
Describing the return trajectory, Kapoor noted, "After undocking, the capsule enters a gradually lowering orbit, while the ISS continues in its own path around 400 kilometres above the Earth. This descent phase can take several hours or even a full day, depending on the calculated trajectory."
He added, "Re-entry is defined at an altitude of about 100 kilometres above Earth. That's when the capsule begins encountering atmospheric resistance, causing temperatures to soar up to 1800-1900°C. A heat shield protects the astronauts from this intense heat."
"At a specific height, any external hardware like solar panels is jettisoned. The spacecraft then descends under controlled speed. Around 5-6 kilometres above sea level, drogue parachutes deploy to slow the fall, followed by the main parachutes," Kapoor explained.
"Finally, the capsule lands in the ocean at a manageable speed. High-speed recovery boats approach the landing site, retrieve the capsule, and transport it to a recovery ship. The astronauts are then taken for medical checks and standard post-mission procedures including quarantine," he asserted.
Meanwhile, Group Captain Shukla, a key member of the Axiom-4 mission, spent his time aboard the ISS engaged in scientific and technical operations alongside astronauts from other countries.
The crew was scheduled to undock from the ISS on July 14 at around 4.35 PM IST, with splashdown expected in the Pacific Ocean off the coast of California at approximately 3 PM IST on Tuesday, July 15, with the return journey taking around 22 hours.