Sunita Williams' homecoming: How do astronauts survive a fiery re-entry?

With Sunita Williams and Butch Wilmore set to return to Earth after nearly nine months in space, let's look at how the astronauts' return takes place

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In the morning of March 16, a SpaceX capsule successfully transported four astronauts to the International Space Station (ISS) as part of a crew rotation mission. This arrival paved the way for the return of Sunita Williams and Butch Wilmore, who had been stranded aboard the ISS for nearly nine months.

 

The Crew-10 astronauts began their journey on the evening of March 14 (local time) with a launch from Nasa’s Kennedy Space Center in Florida. After approximately 29 hours, their SpaceX Crew Dragon capsule successfully docked with the ISS at 4:04 am GMT (9:34 am IST) on March 16, Sunday.

 

This is no routine crew rotation; the world watches with bated breath as Williams and Wilmore, stranded aboard the station due to a malfunction in Boeing’s Starliner spacecraft, await their long-overdue return. The capsule is scheduled for an ocean splashdown off the Florida coast at approximately 5:57 pm ET Tuesday (3:27 am IST Wednesday).

 

The journey home from the International Space Station is nothing short of breathtaking—astronauts go from a blistering 28,800 km/h to a complete stop in just three hours. But how does their space capsule survive the fiery plunge through Earth’s atmosphere and make a safe landing? Let's find out

How do astronauts return to earth?

The return of space capsules carrying astronauts to Earth is a meticulously planned process involving multiple critical stages. Here’s a step-by-step breakdown of how it happens: 

Deorbit burn (Re-entry Initiation)

The spacecraft has to first stop orbiting the earth and slow down enough to be pulled back by Earth's gravity. It does so by firing the spacecraft’s thrusters in the opposite direction of travel. The capsule reduces its speed just enough to begin descending toward Earth. It also has to ensure precise timing and trajectory to target the designated landing zone.

Capsule separation

If the spacecraft has multiple modules (e.g., a service module and crew module), unnecessary sections are jettisoned. The service module, which contains fuel tanks and power systems, is discarded as it is no longer needed. Only the crew module (capsule), carrying the astronauts, continues its journey toward Earth.

Atmospheric re-entry

As a spacecraft hurtles toward Earth, it carries immense kinetic energy. When it enters the atmosphere, friction with air molecules creates drag, slowing it down. This friction converts kinetic energy into intense heat, which the spacecraft must withstand during re-entry. The spacecraft collides with atmospheric particles, generating intense heat—up to 1,600°C (2,900°F). A heat shield absorbs and dissipates the heat, often through a process called ablation (burning away in layers). Astronauts experience high G-forces, sometimes up to 4-5 times Earth’s gravity.

Parachute deployment

Once the capsule slows down significantly in the lower atmosphere, a series of parachutes deployed to further reduce its speed. The practice is to first deploy the Drogue Chutes (small chutes) to stabilise the capsule, which ejects when the vehicle’s velocity falls below about 2,300 feet per second (700 meters per second). The main parachutes then deploy next, significantly slowing the descent for a safe landing.

Landing (splashdown or ground landing)

The speed of descent is still not slow enough to ensure a soft landing. The capsule can't simply crash onto a hard surface—it needs a softer landing. Researchers figured out that water serves as a natural shock absorber, leading to the concept of splashdown, where capsules safely land in the ocean.

 

Depending on the mission, the capsule lands either in the ocean or on solid ground:

• Ocean splashdown: Used by Nasa’s Apollo missions, SpaceX’s Crew Dragon, and Boeing’s Starliner. The capsule lands in a pre-designated ocean area and is recovered by ships.
• Ground landing: Used by Russia’s Soyuz capsules, which deploy retrorockets just before touchdown to soften impact on land.

Crew recovery

Once landed, rescue teams quickly retrieve the astronauts:

• Navy or Coast Guard vessels recover ocean-landed capsules. Divers secure the capsule and assist astronauts out.
• Helicopters and ground crews assist with land landings, ensuring astronaut safety.

Post-landing medical checkups

After spending time in microgravity, astronauts undergo medical evaluations:

 

Reacclimating to Earth’s gravity: Their muscles and bones have weakened due to weightlessness, requiring monitoring and physiotherapy.

Health assessments: Medical teams check for any adverse effects from re-entry forces and space travel.

 

This entire process ensures a safe and controlled return for astronauts from space.

 

The concept of splashdown has a long and complex history, dating back to 1961 when the US first used Mercury re-entry capsules for crewed ocean landings. These capsules, shaped like a cone, reentered the atmosphere base-first, with astronauts seated upright inside.

 

Elon Musk’s SpaceX has successfully executed seven flawless splashdowns of its Dragon capsules between 2021 and June 2024 during their return from the ISS. The company has relied on splashdowns to safely recover its Dragon capsules after missions, ensuring minimal damage to critical components. This allows it to refurbish and reuse them for future flights, significantly cutting costs and making space travel more affordable.

 

As more space agencies and private companies venture into space, splashdowns remain the preferred re-entry method. With growing ambitions beyond Earth, we can expect many more splashdowns in the years ahead.