 "Nasa astronauts Sunita Williams, left, and Butch Wilmore are on their way back to Earth. File Photo/AP")
Nasa astronauts Sunita Williams and Barry “Butch” Wilmore are finally on their way back to Earth after spending nine months in space. The duo departed the International Space Station (ISS) aboard a SpaceX capsule along with two other astronauts on Tuesday (March 18).
The Crew Dragon spacecraft undocked from the space station at 10:35 am IST, marking the beginning of the 17-hour trip back to Earth. The capsule is expected to splash down off the Florida coast at 3:27 am IST on Wednesday. After their return, the two US astronauts will have to adjust to life with gravity which comes with its own challenges .
But what is splashdown and why is it the preferred method to bring astronauts back from space? We will answer for you.
What is splashdown?
Splashdown refers to the landing of spacecraft on a body of water through parachutes. It is a popular tactic to get astronauts home safely from space .
A spacecraft heading back to Earth has to be slowed as it has a lot of kinetic energy.
Drag is generated as the spacecraft hits air particles in the Earth’s atmosphere, creating friction that slows it down. The friction transforms the spacecraft’s kinetic energy into thermal energy or heat.
“All this heat radiates out into the surrounding air, which gets really, really hot. Since re-entry velocities can be several times the speed of sound, the force of the air pushing back against the vehicle turns the vehicle’s surroundings into a scorching flow that’s about 2,700 degrees Fahrenheit (1,500 degrees Celsius),” Marcos Fernandez Tous, Assistant Professor of Space Studies, the University of North Dakota, explained in a piece for The Conversation last year.
There is not enough time during splashdown for a vehicle to reach such a velocity so as not to crash. So, space agencies opt for other methods to safely land a spacecraft.
Nasa uses parachutes to decrease the speed of a spacecraft and ensure the safe landing of the crew aboard. Its Orion’s parachute system, which has 11 parachutes, is deployed at 9,000 feet in altitude and a vehicle speed of 130 mph. The main parachutes slow down the crew module to a landing speed of 17 mph, as per the US space agency.
But even with parachutes the spacecraft cannot crash against a hard surface and needs something to absorb the impact. Water is a good shock absorber and this is how splashdown came to be.
Why landing on dry land isn’t preferred
As Tous wrote for The Conversation, water has low viscosity and quite lower density than hard rock which makes it suitable for landing spacecraft. Moreover, he said that there is a higher chance of the vehicle hitting a water body while falling from space as the liquid covers 70 per cent of the planet’s surface.
Landing on dry land is not ideal as if it is an uneven surface, the spacecraft could overturn or even roll down a slope. It is also a pretty bumpy ride for the crew.
“It’s kind of like a series of explosions followed by a car crash,” Michael Lopez-Alegria, a former Nasa astronaut who returned from the International Space Station on the Russian spacecraft Soyuz in 2007, told Smithsonian Magazine. “After seven months in space, it doesn’t feel great.”
In 1976, the Soyuz witnessed a near-fatal accident when, upon re-entry, the capsule blew off course and came down on a partly frozen lake. The crew was lucky to survive.
However, there are also cons of a watery crash landing. Ken Bowersox, another Soyuz landing veteran, told Smithsonian Magazine that he believes land is safer than water. “On land, you can have a little bit of a rough landing and still crawl out of the vehicle,” he noted. “If things don’t go well on water, it can get exciting pretty fast.”
The Soyuz re-entry in 2003 saw the capsule land more than 200 miles (322 km) away from its intended target of the steppes of Kazakhstan.
But “we just waited a few hours,” Bowersox recalled. “Out on the water, it would have been a lot less comfortable.” He compared the impact to the aircraft carrier landings he practised as a US Navy pilot. “It gets your attention, but it’s not worse than a carnival ride,” he added.
As for what astronauts see when they look out the spacecraft’s window during re-entry, just a wall of fire, says Nasa.
With inputs from agencies