The massive New Glenn rocket is seen as critical to Blue Origin's efforts to compete with Elon Musk's SpaceX, which dominates the commercial space industry.

But its inaugural mission has been delayed by several years.

Attempts to get off the ground this week were scuppered first by technical issues, then by bad weather at the Cape Canaveral Space Force Base in Florida.

"The vehicle looks good for tonight's window, but we're watching weather closely as clouds build over the Space Coast," a Blue Origin spokesperson said Wednesday. "If we're unable to launch, we'll make an attempt on Friday, January 17."

In both cases, the window runs from 1:00 am to 4:00 am (0600 - 0900 GMT).

A Space Force weather forecast put the chances of launch early Thursday at only 40 percent.

Raising the high-stakes rivalry, SpaceX also plans its next orbital test of Starship -- its gargantuan new-generation rocket -- for Thursday.