Cape Canaveral: NASA moved its grounded Artemis moon rocket from the launch pad back to its hangar Wednesday for more repairs.

The slow-motion trek at Florida's Kennedy Space Centre was expected to take all day. The 322-foot (98-metre) Space Launch System rocket had spent a month at the pad ready for potential liftoff, but encountered a series of problems serious enough to require a return to the Vehicle Assembly Building, about 4 miles (6.4 kilometres) away.

Managers ordered the rollback over the weekend after the rocket's helium pressurisation system malfunctioned. Already delayed a month by hydrogen fuel leaks, the launch team had been targeting March for astronauts' first trip to the moon in decades. But now the Artemis II lunar fly-around by a US-Canadian crew is off until at least April.

All four astronauts were at the US Capitol on Tuesday night for President Donald Trump's State of the Union address as invited guests, since the flight delay means they no longer need to quarantine.

AP