Washington (AFP)

The first astronauts to have reached the International Space Station aboard an American aircraft in almost 10 years "hoped" on Saturday to be able to return to Earth this weekend as planned despite Hurricane Isaias which threatens Florida.

"We will go into the descent and ditching phase once we have undocked, hopefully later today," US astronaut Doug Hurley said in a farewell "ceremony" to his colleagues from the ISS, broadcast live by NASA.

"The teams are working very hard, especially given the weather conditions in Florida for the coming days, we appreciate their efforts because we know these decisions are not easy," he added.

Bob Behnken and Doug Hurley departed Cape Canaveral on May 30 in a SpaceX-based Crew Dragon capsule, created by eccentric entrepreneur Elon Musk, and are scheduled to return Sunday afternoon off the coast of Florida.

For now, undocking is still scheduled for 19:34 (23:34 GMT) on Saturday, about two hours after the capsule hatch has closed, which will mark the start of their journey. The arrival in the Atlantic Ocean remains scheduled for 14:42 (18:42 GMT) Sunday.

But NASA says it is closely monitoring the progress of Hurricane Isaias which, after hitting the Bahamas, is approaching Florida. The US space agency will make a decision about six hours before undocking based on many criteria, including wind speed, wave heights or rain in the area.

If the weather was too bad, this would complicate the arrival of the capsule, but also its safe recovery by pre-positioned ships.

"The hardest part was getting us into orbit, but the most important thing is getting us home," said Bob Behnken a few hours before the deadline.

The operation is indeed delicate, even if last year, the Dragon capsule accomplished this mission empty and without incident. Atmospheric reentry will test the resistance of the heat shield. Then, you will have to rely on large parachutes to slow the descent to the ocean.

- Dinosaur in zero gravity -

Speaking to his son and that of his colleague, Bob Behnken brandished a small colorful dinosaur, chosen by the children to accompany them in "this historic mission" and which he let fly in weightlessness for a few moments.

“The apatosaurus is coming home with your dads!” He told them, surrounded by his two Russian colleagues, Anatoly Ivanishin and Ivan Vagner, and the head of the mission, Captain Chris Cassidy.

"We say goodbye to our two friends and colleagues," said the latter, saying to himself both "sad" to see them go and "delighted" that the ISS has new ways "to bring and do leave "astronauts.

Bob Behnken and Doug Hurley became the first astronauts to be transported to the International Space Station, 400 km from Earth, by a private company, under contract with NASA.

The flight, whose departure had already been postponed due to changing weather conditions, also marked the first manned flight launched from the United States since 2011, when the space shuttles were shut down. Americans have since been traveling on Russian rockets.

NASA has tasked SpaceX, which had been delivering cargo to the ISS since 2012, to develop a new space taxi, and if the current mission is certified safe, the Americans will no longer depend on the Russians for access to space.

For three billion dollars, granted since 2011 as part of a fixed price contract, SpaceX has promised NASA six round trips to the ISS, with four astronauts on board.

French astronaut Thomas Pesquet said this week that he will in turn travel aboard Space X's Crew Dragon for his second mission to the ISS in spring 2021.

© 2020 AFP