Because of rough seas in the Atlantic, SpaceX called off a test on Saturday that would have destroyed a rocket in flight to demonstrate that its spacecraft are safe for astronauts.

The company will now try to conduct the test on Sunday between 8 a.m. and 2 p.m. Eastern time.

Since 2012, the company founded by Elon Musk has been flying to the International Space Station for NASA, but it has never before carried a human crew, only cargo. In a final major milestone before it is ready to start taking NASA astronauts to the station, SpaceX will test a system that is to rescue astronauts in case of an emergency during launch.

The main objective of this test is to show that we can carry the astronauts safely away, said Benji Reed, director of crew mission management for SpaceX, during a news conference on Friday.

This flight of a Falcon 9 rocket with a Crew Dragon capsule on top is known as an in-flight abort test. It will not have any astronauts aboard, and it will not be like most launches where were really hoping for it not to be exciting, said Kathy Lueders, manager of the commercial crew program for NASA.

About 84 seconds after launch, the Falcon 9 rocket will shut off its nine engines, simulating a failure, and powerful thrusters on the Crew Dragon will ignite to propel the capsule away. The force of that sudden departure will destroy the rocket, possibly even causing it to explode.

Probably a fireball of some kind, Mr. Reed said.

After reaching an altitude of about 25 miles, the Dragon will then drop off the trunk, or bottom half of the spacecraft, and small thrusters will push the capsule into the correct vertical orientation before parachutes deploy. It is to splash down in the Atlantic Ocean just 10 minutes after launch.

While weather on Saturday looked favorable at the launchpad, waves and winds were high at the splashdown site.

If the test is successful, Ms. Lueders said, the next Crew Dragon mission, which is scheduled to take two NASA astronauts, Douglas G. Hurley and Robert L. Behnken, to the space station, could launch as soon as early March.

A success in SpaceXs in-flight abort test would bring NASA closer to the culmination of its strategy of turning to private companies SpaceX and Boeing for providing transportation for its astronauts. In the past, NASA built and operated its own vehicles, like the space shuttles.

Delays have pushed back the first commercial crew flights by a couple of years, but NASA hopes that the first crewed missions will take off this year. In California, SpaceX is completing construction of its next Crew Dragon capsule and plans to ship it to Florida within a few weeks.

Last month, Boeing launched its capsule, called Starliner, in a test flight without astronauts, but a problem with the spacecrafts clock led to calling off a planned docking at the space station. Boeing and NASA are investigating what went wrong and NASA will decide whether it will allow astronauts on the next Starliner flight, or if it will require Boeing to first repeat the uncrewed orbital test flight.

Since the retirement of the space shuttles in 2011, NASA has had to rely on Soyuz rockets built by Russia for taking astronauts into orbit. It is looking to buy one or two more seats from Russia, at a cost of more than $80 million apiece. If SpaceX and Boeing experience further delays, NASA will have to cut the number of astronauts at the space station, which would limit the amount of scientific research.

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SpaceX Test Delayed to Sunday - The New York Times