In launching Hurley and Behnken from NASA’s Kennedy Space Center on May 30, SpaceX became the first private company to send people into orbit.
The pair is expected to splash down off the coast of Florida just after 14:40 local time (19:40 BST) on Sunday.
A successful landing would mean America once again has a fully serviceable, fully certified means of getting its own people into orbit and back.
This capability was lost when the country retired its shuttles in 2011.
The US space agency Nasa and its commercial partner, SpaceX, have chosen a splashdown location well away from Hurricane Isaias, which looks as though it will track up the eastern coast of Florida.
Waiting recovery vessels are therefore being directed to the Gulf of Mexico, to waters off Pensacola and Panama City, in western Florida.
Mission controllers are following strict guidelines on permissible wind and wave conditions and will study the latest forecasts before giving a final "go" for re-entry.
But neither SpaceX nor NASA can declare success until the two men are home safe. During reentry, the Crew Dragon must hurtle back through Earth's atmosphere at up to 25 times the speed of sound, which requires the spacecraft to weather temperatures up to 3,500 degrees Fahrenheit.
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It's a high-speed descent, initially at several kilometers per second, and will see Endeavour experience heating of up 2,000C on its shielded underside as it pushes down through the atmosphere.
Two sets of parachutes are programmed to deploy - a drogue system at about 5,500m (18,000ft) in altitude when the capsule is still moving at approximately 560km/h; and then four main chutes, at 1,800m in height, which should gently deposit the vehicle on the ocean surface.
As is always the case with a re-entry, there will be a few minutes of radio silence as hot gases (plasma) temporarily envelop the craft.
It's 45 years since the last US crewed capsule made an ocean splashdown. That was an Apollo vehicle that returned to the Pacific after meeting up with a Soviet Soyuz craft above the Earth.
Doug Hurley said he'd read the reports from the time and discovered that astronauts could experience some nausea when bobbing about on the water waiting for recovery.
"There are bags if you need them, and we'll have those handy," he told reporters on Friday. "We'll probably have some towels handy as well. If that needs to happen, it certainly wouldn't be the first time. Folks that fly in space know that sometimes going uphill can have an effect on your system and sometimes coming downhill is the same way."
Cubepost, Aug 2, 2020
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