SpaceX will make a second attempt in the coming hours to get NASA astronauts Doug Hurley and Bob Behnken into orbit.

On May 27, the Dragon capsule’s flight to the International Space Station (ISS) was postponed because of poor weather at Florida’s Kennedy Space Center.

Forecasters say conditions on May 30 will probably be touch and go again.

It follows the spectacular explosion on May 29 of a rocket prototype at SpaceX’s R&D facility in Texas.

SpaceX has been trialing a new design for a future vehicle it calls Starship. The latest model was destroyed in the blast.

The development work at Boca Chica, close to the Mexican border, is entirely separate from SpaceX’s commercial crew activities with NASA.

Doug Hurley’s and Bob Behnken’s lift-off at Kennedy is scheduled for 15:22 EDT.

There’s huge focus on their mission because it will mark the first time that the US has been able to launch its astronauts to the ISS since the retirement of NASA’s space shuttles in 2011.

It will also be the first occasion that NASA has used a private company to transport one of its crews to orbit.

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However, people were wrong if they thought this attention added to the pressure to get the astronauts off the ground, said NASA Administrator Jim Bridenstine.

“We will launch when we are ready,” he told reporters.

“I’ll tell you, the President and the Vice President were proud of the NASA team and the SpaceX team for making the right call for the right reasons.”

The first launch attempt in the week was scrubbed just 16 minutes before the designated launch time. There had been much electrical activity in the air throughout the day, and controllers concluded it wouldn’t be prudent to proceed with the flight.

At the moment of postponement, Doug Hurley and Bob Behnken were sitting in their Dragon capsule atop its Falcon rocket with the booster fuels being loaded below them.

The frustration was that the countdown was going so smoothly; engineers had seen no technical issues of concern. The vehicles were in perfect shape to begin their ascent.

On May 30, they will follow exactly the same routines. The astronauts will head out to the pad about three hours prior to 15:22 EDT. A SpaceX “close out” team will help them strap into their capsule seats, and then it will be a case of running through the pre-flight checks with controllers.

If the launch goes ahead, Doug Hurley and Bob Behnken have about a 19-hour flight to the ISS. They’ll use that time to try out systems onboard the Dragon capsule, including having a go at manual flying. They’ll also need to get some sleep after what will have been a long day.

The astronauts are expected to stay at the ISS for between one and four months before returning to Earth.

SpaceX, which is run by the tech billionaire Elon Musk, has a $2.6 billion contract with NASA to provide six crew flights to the space station. The first of these is scheduled for the end of August, assuming nothing untoward happens on Doug Hurley’s and Bob Behnken’s demonstration.

Boeing has a similar contract, but it is a year at least behind SpaceX in its development timeline.