LOS ANGELES — In half a century of spaceflight, only a few countries have been able to send a capsule into space and have it return to Earth intact, a technological and financial feat reserved for the wealthiest of nations.

That may all change as early as Wednesday, when a Hawthorne, Calif.-based rocket venture plans to send an Apollo-like capsule into space and have it splash down in the Pacific, becoming the first commercial spacecraft to orbit the globe and survive the fiery re-entry back to Earth.

If the mission is successful, it would mark a major turning point for private spaceflight and a key milestone for SpaceX, a venture started by Silicon Valley entrepreneur Elon Musk.

“”When Dragon returns, whether on this mission or a future one, it will herald the dawn of an incredibly exciting new era in space travel,”” said Musk, the founder and chief executive of SpaceX, formally known as Space Exploration Technologies Corp.

The company, mostly on its own dime, has developed and built the Dragon capsule, which is considered a contender for the job of ferrying astronauts to and from the International Space Station after the space shuttle is retired in 2011. The Dragon is capable of carrying up to four astronauts into space.

In the unmanned test launch, the capsule would be lifted into space by a Falcon 9 rocket, also developed by SpaceX. The capsule is scheduled to orbit the Earth twice before re-entering the atmosphere and splashing down in the Pacific about 500 miles west of Southern California. The craft would deploy parachutes to slow its descent.

The entire undertaking is expected to take about four hours.

SpaceX said the mission would also include maneuvering the capsule during orbit through the use of its propulsion thrusters, transmitting telemetry data and recovering the 9,260-pound spacecraft as it bobs in the ocean.

If all goes as planned, the Dragon will be the nation’s first new human-capable spacecraft to orbit the Earth and return since the space shuttle first started flying nearly 30 years ago. It also would mark the first time that a space capsule would splash down in the ocean since the last Apollo mission in 1975.

Aside from the U.S., only four countries and one intergovernmental agency have been able to launch a spacecraft and have it successfully reenter the Earth’s atmosphere: Russia, China, Japan, India and the European Space Agency.

The Dragon capsule has been undergoing final preparations on a launch pad at Cape Canaveral along with the company’s massive Falcon 9 rocket, which made its first flight in June.

The launch had been slated for earlier in the week, but Monday the company revealed that cracks in an engine nozzle would delay the mission.

“”This is the first look at a program that could be the future of human space travel in America,”” said Tim Farrar, president of consulting and research firm Telecom, Media & Finance Associates in Menlo Park, Calif. “”The outcome could determine what direction NASA will go.””

He noted that the rocket industry is notoriously difficult to enter and littered with failed attempts. For example, a Russian government rocket carrying three satellites veered off course this week and crashed near Hawaii after blasting off from Kazakhstan.

SpaceX’s first rocket, the Falcon 1, failed three times before it carried a satellite into space.

“”It’s not an easy business to navigate,”” Farrar said. “”But thus far, they’ve done a lot in a short period of time.””

Musk, 39, who made a fortune when he sold online payment business PayPal Inc. in 2002, said he started SpaceX with the goal of developing and launching rockets at a fraction of the cost of the current generation of spacecraft. He said he’s poured about $100 million of his own money into the venture.

Musk pegs the cost of the average space shuttle flight at about $1 billion. Flights from SpaceX will run about $100 million, he said.

The selling point has attracted the government’s attention. NASA has invested more than $200 million in seed money to help the company develop and build the nine-engine Falcon 9 rocket, and it has awarded SpaceX $1.6 billion to have the Dragon capsule transport cargo to the International Space Station — which could start next year.

The mission has garnered particular attention in Washington, where a battle has been brewing over the future of NASA and whether the space agency should turn over more spaceflight to private ventures such as SpaceX.

In January, President Barack Obama scrapped plans for sending astronauts back to the moon and set a new direction for the space agency, urging it to award more contracts to smaller, privately funded start-ups.

But many in Congress whose states are set to lose thousands of jobs because of Obama’s directive are opposed to turning over more of the space missions to companies that they say are largely untested.

“”There are people watching this, who are hoping for failure,”” said Carissa Bryce Christensen, managing partner at Tauri Group, an Alexandria, Va., consulting firm that advises the space industry. “”One failure won’t ruin SpaceX. But if they get this right, it has the potential to change the nation’s spaceflight program forever.””