Another attempt will be made today to launch the American space agency's new astronaut capsule.
The Orion ship is designed to carry crews beyond Earth to destinations such as asteroids, the Moon and Mars.
Nasa wants to test it first on an unmanned mission before allowing astronauts to climb aboard.
Efforts to fly this brief demonstration sortie were frustrated on Thursday by high winds and a technical problem with the launch rocket.
Engineers expect to overcome the latter; the weather on the other hand is a little more uncertain.
The forecast is deteriorating, but only a few minutes of favourable conditions are required to get Orion away.
The launch window here at Cape Canaveral runs from 07:05 to 09:44 local time (12:05 to 14:44 GMT).
As ever, mission managers will endeavour to take the earliest opportunity available to them.
Orion's Delta IV-Heavy rocket will head east out over the Atlantic and on to a two-lap circuit of the Earth.
On the second orbit, the Delta will push Orion to an altitude of 5,800km (3,600 miles), before releasing it to make a fast fall back to the planet.
The capsule is expected to attain speeds close to 30,000km/h (20,000mph) as it comes into the atmosphere.
The pressing air is likely to generate temperatures on the ship's underside of up to 2,000C.
This is one of the main goals of the mission - to test the ship's thermal protection systems.
If Orion survives the trial by fire, it will then use a series of parachutes to make a splashdown in the Pacific, about 1,000km (600 miles) west of the California Baja Peninsula.
From start to finish, the mission should last no longer than four-and-a-half hours.
US Naval support vessels will be on station in the Pacific to recover the capsule and bring it back to land for future testing activities.
Orion is reminiscent of the Apollo command ships that took men to the Moon in the 1960s and 1970s, but bigger and with cutting-edge systems.
It is being developed alongside a powerful new rocket called the Space Launch System (SLS). This will have its own debut in 2017 or 2018 - again unmanned.
The first crewed outing for both the SLS and Orion is likely to be in 2021, when two astronauts will travel around the Moon.
The future beyond that is less well defined.
Nasa has ideas for visiting an asteroid, with others hopeful that a return to the lunar surface might be possible at some stage.
The ultimate dream, of course, is to get people to the surface of the Red Planet.
SLS and Orion represent the core capabilities for achieving this, but the daunting undertaking would require a range of additional technologies that are a long way from being procured.
The US space agency talks of no earlier than the 2030s for a Mars mission.
Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos