After 186 days in space on the International Space Station, it is time for European Space Agency astronaut Tim Peake, American Tim Copra and Russian Yuri Malenchenko to return to Earth. But their return is fraught with danger.
"It (return to Earth aboard the Soyuz capsule) is physically extremely violent," Chris Hadfield, retired Canadian astronaut told The Guardian. "We often describe it as 15 explosions followed by a car crash."
At 11:22 am IST on Saturday, the Soyuz capsule will undock from the ISS.
Inside, Peake and his companions will be wearing a pressurised suit, tight 'space pants' that stop blood rushing from their legs to heads, and they will have drunk a solution to stop them from becoming dangerously dehydrated, the Daily Mail reported, adding that once on board, in their individually moulded plastic seat, the module will slowly unlock and springs will push it away -- at four inches per second.
According to media reports, it will take just six minutes to cover 107 km -- the outer wall of the capsule will heat to around 3,000 degree fahrenheit.
The engines will then fire, and the module will spend around two hours orbiting the earth.
At an altitude of 408 km and orbiting at a top speed of 27,358 Kmph, they will fire the main engine for precisely four minutes and 37 seconds to slow the spacecraft and take it out of orbit.
At an altitude of 99 km, the capsule will begin to brake further as it reaches the top of the atmosphere -- and the cosmonauts will feel gravity for the first time since their launch from Baikonur last December.
But before re-entry, the Soyuz must shed two modules that are no longer needed. Explosive bolts fire and release the unwanted service and orbital modules, leaving only the bell-shaped descent module containing the crew. The firing of the bolts feels like someone is attacking the capsule with a sledgehammer, The Guardian reported.
Eventually, when the parachutes and thrusters deploy, the capsule will be slowed to just 27 Kmph. Retro-rockets fire moments before impact to bring the touchdown forces to a minimum -- but it is still likened to the force of a small car crash.
"It is probably the most dangerous time of the mission," Britain's only other astronaut, Helen Sharman told Sky News.
"It's when it is most likely to leak air and if the capsule isn't properly orientated it can burn up. It is lumpy and bumpy, more physically demanding than the launch," she said, adding, "It peaks at about 5.5G, which compared to weightlessness is incredibly heavy. It's hard to breathe because your rib cage is forced down onto the lungs."
Hadfield said: "You see the fire that envelops the vehicle, like you're flying a meteorite home. Being crushed and burned and torched many thousand degrees. It's like you're flying through a blast furnace."
"They will be hurled about, shaken, spun, crushed, and snapped around like crazy when the parachutes open, and then they will crash into the Earth. And then, if it is a windy day in Kazakhstan, the vehicle will roll end over end until it finally creaks to a stop."
During his time in space, Peake worked up to 14 hours a day, participating in more than 250 experiments devised by scientists from around the world. They included numerous studies of his own body’s responses to the space environment involving his brain, lungs, stomach, muscles, bones, skin, immune system and body clock. The tests will continue as he begins a lengthy process of rehabilitation back on Earth.
While weakened muscles recover quickly after a long spell in space, it can take up to three years for bones to return to normal. Despite their strict exercise regime, astronauts on average lose up to 1.5% of their bone mass for each month spent in space.
Peake was originally scheduled to return at the beginning of June, but his homecoming was delayed when the launch of the replacement crew was pushed back.