By Joey Roulette and Steve Gorman
HOUSTON, April 10 (Reuters) - The four Artemis II astronauts, returning from the world's first crewed moon voyage in over half a century, hurtled back toward Earth on Friday aboard their gumdrop-shaped Orion spacecraft, headed for a splashdown in the Pacific Ocean off Southern California.
The finale to NASA's celebrated 10-day mission was expected to begin with separation of Orion's crew capsule from its service module, followed by a fiery re-entry through Earth's
atmosphere and a six-minute radio blackout before the capsule parachutes into the sea.
If all goes well, U.S. astronauts Reid Wiseman, Victor Glover and Christina Koch, along with Canadian astronaut Jeremy Hansen, will end up bobbing safely in the ocean aboard their Orion capsule, dubbed Integrity, shortly after 8 p.m. ET (0000 GMT) off the coast of San Diego.
The quartet blasted off from Cape Canaveral, Florida, on April 1, lofted into an initial Earth orbit by NASA's giant Space Launch System rocket before sailing on around the far side of the moon, venturing deeper into space than any humans before them.
STEPPING STONE TO MARS
In so doing, they became the first astronauts to fly in the vicinity of the moon since the Apollo program of the 1960s and '70s. Glover, Koch and Hansen also made history as the first Black astronaut, the first woman and first non-U.S. citizen, respectively, to take part in a lunar mission.
The voyage, following the uncrewed Artemis I test flight around the moon by the Orion spacecraft in 2022, marked a critical dress rehearsal for a planned attempt later this decade to land astronauts on the lunar surface for the first time since Apollo 17 in late 1972.
The ultimate goal of the Artemis program is to establish a long-term presence on the moon as a stepping stone to eventual human exploration of Mars.
In a historical parallel to the Cold War era of Apollo, the Artemis II mission has played out against a backdrop of political and social turmoil, including a U.S. military conflict that has proven unpopular at home.
For many in a global audience captivated by the latest moon shot, it reaffirmed the achievements of science and technology at a time when big tech has become widely distrusted, even feared. Opinion polling showed broad public support for the aims of the mission.
CRITICAL TEST OF HEAT SHIELD
The return to Earth will put the Orion spacecraft through a critical test of its heat shield, which sustained an unexpected level of scorching and stress on re-entry during the 2022 test flight. As a result, NASA engineers altered the descent trajectory for Artemis II in order to reduce heat buildup and lower the risk of the capsule burning up.
Still, with Orion plunging into the atmosphere at some 25,000 miles per hour (40,235 kph), temperatures outside the capsule are expected to soar to around 5,000 degrees Fahrenheit (2,760 degrees Celsius).
The recalibrated final descent path also has narrowed the size of the potential splashdown zone, limiting target landing options in case of foul weather at sea. NASA officials said on Thursday that forecasts for the preferred splashdown zone looked favorable.
Just as critical as the performance of the heat shield are several other factors, including achieving the spacecraft's precise descent path and re-entry angle through a series of course-correction blasts of its jet guidance thrusters.
The last of three such jet propellant "burns" was scheduled for Friday afternoon, roughly five hours before splashdown.
Once the capsule hits the top of the atmosphere, it takes less than 15 minutes, including a six-minute radio blackout, before two sets of parachutes are deployed and the capsule floats into the sea.
NASA says it will take about another hour for recovery teams to secure Orion, hoist it onto a ship and assist the astronauts in exiting the capsule one by one.
At the flight's peak, the crew reached a point 252,756 miles from Earth, exceeding the previous record of roughly 248,000 miles set in 1970 by the crew of Apollo 13.
(Reporting by Steve Gorman in Los Angeles and Joey Roulette in Houston; Editing by Bill Berkrot)
