For the past half-century, space flight has been the domain of the world’s superpowers.

All that is set to change as soon as Saturday when SpaceX, the private rocket company in Hawthorne, Calif., will attempt to launch a spaceship with cargo into orbit, and three days later dock it with the International Space Station.

If successful, the mission could mean a major shift in the way the U.S. government handles space exploration. Instead of keeping space travel a closely guarded government function, NASA has already begun hiring privately funded start-up companies for spacecraft development and is moving toward eventually outsourcing NASA space missions.

The upcoming launch is “the first step in the handoff” to private industry, NASA Administrator Charles Bolden said. “Everybody realizes the importance of this mission,” he said. “Nobody will be rooting against SpaceX.”

But if the mission fails, it could trigger serious doubts about NASA’s decision to hand these responsibilities to a fledgling private space industry. Doubters have already begun to raise questions. Some former astronauts, members of Congress and space experts say the current plan to subcontract space missions is foolhardy. They say the plan is risky and that outer space is no place to roll the dice on unproven companies.

On launch day, it falls to SpaceX and its 40-year-old billionaire founder, Elon Musk, to prove they’re prepared.

With SpaceX engineers at the controls in Hawthorne, a towering rocket will blast off from a launch pad about 2,600 miles away in Cape Canaveral, Fla., and lift a gumdrop-shaped space capsule with a half-ton of food, water and other supplies up to the crew aboard the orbiting space station.

But delivering cargo isn’t the key mission — the space station is well-provisioned. The main purpose is to demonstrate that the space capsule can rendezvous with the $100 billion orbiting outpost and link up with the space station’s onboard computers. If all goes well, the crew aboard the space station will snag the spacecraft with a robotic arm and lead it in for docking. Weeks later it will be released and sent back to Earth.

“We’re ready to take that next step,” Musk said. “It’s been a long road to this point.”

Musk is a straight-talking modern-day industrialist cut in the mold of a young Howard Hughes. He’s led numerous start-up companies in a wide-range of industries, dating Hollywood starlets along the way.

The sandy-haired South African emigrant first made millions when he co-founded and sold online payment business PayPal Inc. to eBay Inc. in 2002 for $1.5 billion. Armed with his personal fortune and a Rolodex full of Silicon Valley venture capitalist contacts, Musk started SpaceX, or Space Exploration Technologies Corp., and co-founded electric car company Tesla Motors Inc. in Palo Alto.

In starting SpaceX in 2002, his goal was to make money by developing and launching rockets that could carry satellites into space at a fraction of the cost of the current generation of spacecraft.

The sales pitch as a low-cost alternative has resonated with NASA. With federal money in short supply and the space shuttle fleet retired, the space agency has experienced thousands of job cuts across the country at places such as Kennedy Space Center in Cape Canaveral, Johnson Space Center in Houston and Jet Propulsion Laboratory in La Canada Flintridge, Calif.

The U.S. government now has no way to space other than doling out $63 million for a seat on a Russian Soyuz rocket.

After years of study and approval from Congress, the space agency is moving to turn the job of carrying cargo and crews over to private industry at a lower cost. Meanwhile, NASA will focus on deep space missions to land on asteroids and Mars.

Still, some in Congress aren’t sold on the privatization plan.

“I believe NASA would better serve the American taxpayer by continuing to push the frontiers of human space travel in its own right,” said Sen. Richard Shelby, R-Ala. “There are no ‘private’ space companies; only taxpayer-funded ones that NASA has arbitrarily decided to call ‘commercial’ and hold to reduced standards of performance and accountability.”

Eugene Cernan, who was the last astronaut to walk on the moon in 1972, and Neil Armstrong, the first man to walk on the moon in 1969, testified before Congress in September about NASA’s decision to outsource space missions to private business. Cernan described NASA’s future plans as a “slide to mediocrity,” “third-rate stature” and “devastating.”

Earlier this month, the pair, along with Jim Lovell, commander of the Apollo 13 mission, wrote a letter to Congress saying they want safe spacecraft.

“We all agree that our country has painted itself into a corner and does not now, nor will for many years, have a U.S. government craft suitable for carrying cargo or crew to the International Space Station,” the astronauts wrote. “The reputation of our country … dictates that we do everything possible to ensure that any commercial crew service meets standards equal to those that we would enforce would the craft be government-owned and operated.”

NASA says it is working with SpaceX to ensure safe flights. It also has signed development contracts with lesser-known names in aerospace such as Sierra Nevada Corp. of Sparks, Nev., and Blue Origin of Kent, Wash.

Inside SpaceX’s Hawthorne complex, the company has a vast mission control center where engineers can keep real-time tabs on rocket launches at Cape Canaveral and on the mission itself. They monitor incoming data for anomalies, and if there are any, they can order the launch to be scrubbed or address the mission issues.

Musk recently sat at a workstation and discussed the coming launch date. A boyish smile spread across his face as he talked about the beehive of activity that will fill the room, which resembles NASA’s mission control center in Houston.

Then he grew cautious.

“There’s a real chance this mission doesn’t succeed — a lot can go wrong,” Musk said. “I mean, there’s a reason they call it rocket science.”

The company’s first rocket, the single-engine Falcon 1, failed three times before it successfully carried a satellite into space in 2008. That same year, NASA awarded SpaceX a $1.6 billion contract to transport cargo in 12 flights to the space station.

In addition to the NASA contract, SpaceX has commercial contracts worth more than $4 billion to launch satellites aboard its new, larger Falcon 9 rocket for various countries and telecommunications companies.

SpaceX has been planning this mission for more than 17 months. In December 2010, it became the first private company to blast an unmanned spacecraft — a capsule called Dragon — into outer space, have it circle Earth and return intact.

The company initially hoped to visit the space station with the Dragon less than a year later, but has faced repeated delays.

Now, if everything goes according to plan, success will come sometime in June, when the Dragon carries out the mission and eventually splashes down in the Pacific Ocean hundreds of miles west of Southern California. The craft will deploy parachutes to slow its descent after entering Earth’s atmosphere.

“I’m starting to get nervous just thinking about it,” Musk said. “Last launch, I couldn’t even sit down. It’s pretty nerve-racking.”