Nasa is expected to announce as early as Saturday whether the US astronauts stuck on the International Space Station (ISS) can come home with the glitchy Boeing Starliner spacecraft that took them there or will need to wait for a SpaceX vehicle – which would be another embarrassment for the embattled rival plane-maker. Then SpaceX plans next week to launch one of its riskiest missions yet, to attempt the first ever private-sector spacewalk, with innovative slim spacesuits and a cabin with no airlock. “Nasa’s decision on whether to return Starliner to Earth with astronauts aboard is expected no earlier than Saturday, August 24, at the conclusion of an agency-level review,” the space agency said in a statement. Starliner launched its first two astronauts into space in June as a crucial test before it can receive Nasa approval for routine flights. But what was supposed to be an eight-day mission docked to the ISS has been drawn out by months after the capsule sprang leaks and some of its thrusters failed. The agency administrator, Bill Nelson, will attend the agency-level review, the statement said. Boeing for months has sought to quell fears about the Starliner issues with new test data the company has claimed validates the spacecraft’s safety for astronauts. Nasa is weighing that data against its low appetite for risk in the mission, one of four Starliner flights since 2019 to suffer mishaps. The agency has prepared a backup plan to make two seats available on an upcoming SpaceX Crew Dragon mission that the Starliner crew – the veteran Nasa astronauts Suni Williams and Butch Wilmore – could use. If that option is chosen, Wilmore and Williams would not come home until that mission’s conclusion in February 2025, and Starliner would be brought back to Earth empty in the meantime. Boeing has struggled to develop Starliner and compete with SpaceX’s similar but more experienced Crew Dragon. Boeing has taken $1.6bn in losses on the Starliner program, securities filings show. The US jet company has been reeling in recent years after crashes involving its 737 Max model and, on a newer version of that plane, a terrifying incident in January where a door panel blew out mid-flight, which is still being investigated. Boeing is under pressure from upstart SpaceX, the company created by the tech entrepreneur Elon Musk, who also founded Tesla, the terrestrial electric vehicle maker, and now owns the social media platform, X, formerly Twitter. Jared Isaacman, a billionaire entrepreneur, will join a retired military fighter pilot and two SpaceX employees in the launch for the mission that will include a spacewalk on Tuesday aboard a modified Crew Dragon craft. The plan is for them to embark on a 20-minute spacewalk 434 miles (698km) into space two days later. Until now, walking into the empty expanse of space has only been attempted by government astronauts on the ISS, which is in orbit 250 miles above Earth. SpaceX’s five-day mission, dubbed Polaris Dawn, will swing in an oval-shaped orbit, passing as close to Earth as 118 miles and as far as 870 miles – the farthest any humans will have ventured since the end of the US Apollo moon program in 1972. The crew will wear slimline spacesuits in a craft modified so it can open its hatch door in the vacuum of space – an unusual process that removes the need for an airlock. “They’re pushing the envelope in multiple ways,” the retired Nasa astronaut Garrett Reisman said in an interview with Reuters. “They’re also going to a much higher altitude, with a more severe radiation environment than we’ve been to since Apollo.” Isaacman bankrolled the mission with an estimated $100m. Joining Isaacman will be the mission pilot Scott Poteet, a retired US Air Force lieutenant colonel, and SpaceX senior engineers Sarah Gillis and Anna Menon. “There’s not a lot of room for error,” said Reisman.