Undock to splashdown: Here is how SpaceX brings back astronauts from ISS

After completing 60 days in orbit at the International Space Station, astronauts Bob Behnken and Douglas Hurley are set to return home on August 1. The two astronauts will detach from the ISS on board Crew Dragon as part of Demo-2 test flight, which will splashdown on August 2. 

With the Demo-2 flight, Nasa will complete a mission designed to test SpaceX’s human spaceflight system, including launch, docking, splashdown, and recovery operations. The two astronauts had docked with the ISS after the historic launch on board the SpaceX Falcon 9 on May 31 from the United States.  

The two astronauts have been part of several science experiments on board the ISS, including two extravehicular spacewalks conducted by Bob Behnken to repair the station for continuous usage. 

While the final location of the splashdown is yet to be announced, NASA has selected seven potential splashdown sites for Crew Dragon off the coasts of Pensacola, Tampa, Tallahassee, Panama City, Cape Canaveral, Daytona, and Jacksonville. According to the administration, "the locations are selected using defined priorities, starting with selecting a station departure date and time with the maximum number of return opportunities in geographically diverse locations to protect for weather changes. Teams also prioritise locations which require the shortest amount of time between undocking and splashdown based on orbital mechanics, and splashdown opportunities that occur in daylight hours."

The average time between undocking from the ISS and landing on the planet takes roughly six hours to 30 hours depending on the position of the station with respect to the splashdown site in this case. 

The final location of the splashdown is yet to be announced.

How will the return look like? 

After a farewell on board the ISS, the two astronauts will lock themselves in the Endeavour spacecraft and the undocking will begin after 5:15 pm. As the hooks holding the Crew Dragon retract, there will be two very small engine burns immediately to separate the spacecraft from the station. Once flying freely, Dragon Endeavour will autonomously execute four departure burns to move the spaceship away from the space station and begin the flight home.

According to Nasa, "several hours later, one departure phasing burn, lasting about six minutes, will put the Crew Dragon on the proper orbital path to line it up with the splashdown zone. Shortly before the final deorbit burn, Crew Dragon will separate from its trunk, which will burn up in the Earth’s atmosphere. The spacecraft then executes the deorbit burn, which commits it to return and places it on an orbit with the proper trajectory for splashdown."

As the hooks holding the Crew Dragon retract, there will be two very small engine burns immediately to separate the spacecraft from the station.

Six minutes of blackout at 17,500 miles per hour

Engineers at the JPL said that the spacecraft would be travelling at 17,500 miles per hour and the maximum temperature it will experience on re-entry is approximately 3,500 degrees Fahrenheit. The re-entry process will create a communication blackout between the spacecraft and Nasa Mission control, which is likely to last for about six minutes. 

Once the spacecraft enters the Earth's atmosphere, two sets of parachutes will deploy at an altitude of 18,000 ft slowing it down to 350 miles per hour. Further along, four main parachutes will deploy at about 6,000 feet bringing it down to approximately 119 miles per hour as it splashes into the final site. 

Boeing received a $4.2-billion deal to develop a capsule called the CST-100 Starliner. (Source: SpaceX)

SpaceX teams will be on location to recover the capsule from water as the companies press two recovery ships — the Go Searcher and the Go Navigator — into the Gulf of Mexico and the Atlantic Ocean off the coast of Florida. Nasa added that immediately after exiting the Crew Dragon capsule, Behnken and Hurley would be assisted into a medical area on the recovery ship for an initial assessment before being flown to the Ellington Field in Houston.

Meet the astronauts

Dough Hurley: The first Crew Dragon spacecraft commander, Dough Hurley is a retired US Marine Corps Colonel who has previously flown on two spaceflights. He served in the Navy as a fighter pilot, trained to fly on F/A-18 Hornet and became a test-pilot in 1997. He was selected to be an astronaut in the year 2000. Hurley made his first spaceflight in July 2009 as the pilot for STS-127, which was followed by STS-135 aboard space shuttle Atlantis, the last mission in July 2011.

The two astronauts are space veterans and spent 90 days on the current mission.

Bob Behnken: Robert "Bob" Behnken is a US Air Force Colonel who is on his third trip to space, having logged over 708 hours into the orbit with over 37 hours of spacewalks. He flew into space with the STS-123 in 2008 and STS-130 in 2010. Behnken has logged more than 1,500 flight hours and flown 25 different types of aircraft, according to his Nasa biography. He had been selected for the astronaut programme by Nasa in 2000.