An inflatable habitat is set to go into space this evening, atop a private SpaceX rocket contracted by Nasa.
The inflatable room will attach to the International Space Station (ISS) for a two-year test and become the first such habitat to hold humans in orbit.
It was built by Nevada company Bigelow Aerospace and is intended to pave the way towards inflatable habitats for long space trips, including to Mars.
Its launch is the first Nasa cargo run for SpaceX since its June 2015 mishap.
The US space agency has scheduled lift-off for 16:43 local time (21:43 BST) from Cape Canaveral Air Force Station in Florida.
A capsule, containing the Bigelow Expandable Activity Module (Beam) alongside other supplies for the ISS and its crew of six, is scheduled to dock at the Space Station on Sunday morning, starting at around 10:30 BST.
After putting the Dragon capsule into orbit, SpaceX will make another attempt to land the main-stage booster of its Falcon 9 rocket on a floating platform in the ocean.
This feat, never accomplished in four bids to date, is part of the firm’s effort to kick off a new era of reusable rockets and affordable private space travel.
Despite the difficulties with its ocean platform configuration, SpaceX – run by tech entrepreneur Elon Musk – did successfully land a Falcon 9 on the ground, vertically, last December.
Meanwhile, the launch is a huge moment for Bigelow Aerospace, the project of real estate billionaire Robert Bigelow.
The company has launched prototype expandable habitats before, but none have been occupied by humans.
This 1,400kg contraption, once attached and inflated in about a month’s time, will be visited periodically by ISS personnel.
Made of many layers of fabric and covered with a flexible Kevlar-like material, the Beam will be tested to see how well it stands up to fluctuating temperatures and high levels of radiation.