"The fact that the crew members remained unharmed, in one piece, was very lucky. Everything could have ended much worse," the source was quoted as saying by the Interfax news agency. Their fate was "on a razor's edge," he said.

South Korea's first astronaut and her Russian and US colleagues on Monday said they were recovering well after an unconventional "ballistic" descent to Earth on Saturday that landed hundreds of kilometres (miles) off target.

Interfax's source said the Russian-designed Soyuz landing capsule was facing the wrong direction when it entered the atmosphere, depriving it of the protection of its heat-resistant shield.

"If the hatch had been burnt through and the nearby... parachute damaged, the crew might not have survived," the source was quoted as saying.

Korean scientist Yi So-Yeon was returning from a nine-day visit to the International Space Station with NASA's Peggy Whitson and Russian cosmonaut Yury Malenchenko, who each spent over six months on board.

All rights reserved. copyright 2018 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.