Sunita Williams’ return to Earth: Why SpaceX’s Dragon takes 17 hours while Russia’s Soyuz returns in just 3.5 hours |
After spending nine months at the International Space Station (ISS), NASA astronauts Butch Wilmore and Sunita Williams have begun their journey back to Earth aboard SpaceX’s Crew Dragon spacecraft. The return mission, which commenced in the early hours of Tuesday, is expected to conclude with a splashdown off the Florida coast by early evening, provided weather conditions remain favorable.
NASA’s decision to bring the astronauts back using SpaceX’s Dragon capsule marks the end of a prolonged stay in orbit that was initially planned to last only a few days. The duo had arrived at the ISS aboard Boeing’s Starliner capsule in June 2024, but a series of technical malfunctions left the spacecraft unfit for their return. As a result, they were integrated into NASA’s long-duration space mission before being scheduled for a return aboard the SpaceX Dragon.
Why SpaceX’s Dragon takes 17 hours to return while Russia’s Soyuz does it in 3.5 hours
Unlike Russia’s Soyuz spacecraft, which can bring astronauts back to Earth in just 3.5 hours, the SpaceX Dragon capsule takes approximately 17 hours to complete its return journey. The extended duration is due to several carefully planned factors that prioritize crew safety and landing accuracy.
Factors affecting the return time:
Orbital alignment and Earth’s rotation:
- The ISS orbits Earth at a speed of approximately 28,000 km/h (17,500 mph) at an altitude of around 420 km.
- A return journey requires precise alignment with designated landing zones, meaning the Crew Dragon cannot initiate descent immediately after undocking.
Deorbit burn and atmospheric re-entry:
- To safely return, the spacecraft must perform a controlled deorbit burn, adjusting its trajectory toward the targeted splashdown site.
- Unlike the Soyuz, which follows a more direct ballistic descent, Crew Dragon’s descent is carefully managed to ensure a smoother ride.
Heat and parachute deployment:
- During reentry, the capsule experiences extreme heating due to atmospheric friction, necessitating a gradual descent to avoid excessive stress on the spacecraft and crew.
- At high altitudes, parachutes deploy to slow the spacecraft’s descent, ensuring a safe landing.
Weather and landing conditions:
- SpaceX selects landing sites based on optimal weather conditions, ocean currents, and the positioning of recovery ships.
- If conditions at the primary landing site are unfavorable, the capsule may stay in orbit longer before initiating reentry.
Sunita Williams and Butch Wilmore return to Earth: Plan and timeline
NASA’s carefully planned return operation began late Monday night (ET), when Wilmore and Williams boarded the Crew Dragon capsule, sealed the hatches, and began pre-departure preparations.
Key events in the return mission:
- 11:05 PM (ET), Monday: The astronauts boarded the Crew Dragon capsule and secured the hatch. They then donned their flight suits and performed a series of system checks.
- 1:05 AM (ET), Tuesday: The spacecraft autonomously undocked from the ISS.
- 5:57 PM (ET), Tuesday: The Dragon capsule is expected to splash down off the coast of Florida.
NASA has been live-streaming key moments of the mission, including the undocking sequence, deorbit burn, and splashdown procedures. Once the capsule safely lands, recovery teams will retrieve the astronauts and transport them to Houston’s Johnson Space Center for post-mission evaluations.
Mission significance and future implications
The return of Wilmore and Williams marks the conclusion of an extended mission that was initially designed as a short-duration test flight for Boeing’s Starliner capsule. However, following Starliner’s propulsion system issues, NASA deemed it too risky for a crewed return, prompting an alternative arrangement with SpaceX.
The successful completion of this mission will be a testament to the versatility of the Crew Dragon spacecraft, which has become a crucial part of NASA’s commercial crew program. Additionally, it highlights the ongoing challenges faced by Boeing’s Starliner program, which has encountered repeated delays and technical failures.
