SpaceX aims to launch another load of space station supplies for NASA, including a critical docking port needed by new US crew capsules set to debut next year.
The unmanned Falcon rocket is scheduled to lift off early on Monday. Excellent weather is forecast for the launch.
Aboard the rocket is a replica of the docking port destroyed in a SpaceX launch accident last summer. This is port No.2.
NASA needs at least one and preferably two of these ports for crew capsules under development by both SpaceX and Boeing.
Americans have been stuck riding Russian rockets to the International Space Station since shuttles stopped flying five years ago this month. The SpaceX Dragon and Boeing Starliner capsules will ease this Russian dependency.
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SpaceX, meanwhile, will try to land its leftover booster back at Cape Canaveral Air Force Station, just kilometres from the Falcon launch pad.
The California-based company wants to reuse its rockets to save time and money. It's only landed a used first-stage booster on land once, back in December. Three other boosters touched down vertically on an ocean platform, after delivering spacecraft to orbit.
SpaceX's vice-president of flight reliability, Hans Koenigsmann, said on Saturday that the company plans to launch its first recycled booster this northern autumn.
The SpaceX Dragon cargo ship, meanwhile, holds food, science experiments and equipment - including the all-important docking port.
The SpaceX Dragon is the only supply ship capable of returning items to Earth from the space station.
