SpaceX is trying to land a rocket booster on what it calls an autonomous spaceport droneship, essentially a floating platform at sea.

UPADTE, Feb. 28: With seconds to go before liftoff, SpaceX scrubbed the launch Sunday evening just after the engines fired. The flight computer detected a problem and aborted the launch. Earlier in the evening, a boat had entered the range, creating a safety issue. It is not clear when the launch would be rescheduled.

UPDATE, Feb. 25: Less than two minutes before Thursday's launch SpaceX postponed the flight. It did not immediately explain why it held the launch, or when it would be made up.

UPDATE, 6:20 p.m.: SpaceX tweeted about 25 minutes before Wednesday's launch that it would postpone the mission until Thursday. Weather conditions on Wednesday had been 60 percent favorable.

SpaceX is scheduled to launch a commercial satellite to space Wednesday evening, and will once again try to land the rocket’s first stage on a platform floating in the Atlantic Ocean.

But this time the company founded by tech billionaire Elon Musk says that “a successful landing is not expected.”

In December, the company successfully landed the first stage at a ground-based pad at Cape Canaveral Air Force Station, a key step toward what many say will lower the cost of space travel. Typically, the first stages of rockets are discarded after launch, landing in the ocean. But since they are the most expensive part of the rocket and house the main engines, Musk and others have been on a quest to find a way to land and reuse them.

The company has also tried to land the rocket on floating platforms, coming close but ultimately failing to remain upright. And it warned it is not optimistic this time. SpaceX is trying to launch a communications satellite for SES, a communications company that is sending a satellite to provide high-definition video and Internet service to parts of Asia. But the heavy satellite is headed for what’s known as Geostationary Transfer Orbit, more than 22,000 miles away. The great distance requires more velocity, and that makes it more difficult than previous attempts for the booster to turn around and land.

The launch is scheduled for 6:46 p.m. from Cape Canaveral Air Force Station with a 90-minute launch window.

Wondering how Falcon 9's first stage will attempt to fly back to Earth on our next launch? Image courtesy of SpaceX.