With the U.S. space shuttle program officially retired, private companies are being asked to fill the void. If all goes as planned, the first privately owned spaceship could dock at the International Space Station this week.

As we saw on Saturday, though, there is a lot that can go wrong.

SpaceX’s Falcon 9 was set to launch, but was aborted a half-second before liftoff, due to a faulty valve that caused high pressure in the spaceship’s fifth engine.

“This is not a failure,” Gwynne Shotwell, president of Hawthorne, California-based SpaceX, said during a  press conference.

“We aborted with purpose. It would be a failure if we were to have lifted off with an engine trending in this direction.”

Now, replacing the valve that caused the problem, SpaceX is going to attempt another launch this week, they announced.

The company statement simply reads, “Engineers replacing failed valve on engine #5 following today’s abort. Data review Sunday, if all looks good next attempt is Tues. May 22 at 3:44 AM ET.”

If the launch is successful, the docking would take place on Friday.

SpaceX's Falcon 9 rocket will send the unmanned Dragon capsule toward the station in order to deliver supplies, including food, clothes and science equipment to the space station.

The mission is being sponsored by NASA's COTS (Commercial Orbital Transportation Services) program, which seeks to find commercial U.S. vehicles that can take over the space program after the program was retired this year.

SpaceX was awarded a COTS contract in 2006 and in 2010 became the first privately owned company to launch, orbit and recover a spaceship.

The launch this week is the final test for the company before it can start making these kinds of deliveries regularly. They are under contract to fly twelve missions, while will net them $1.6 billion.

The mission is the final test flight scheduled for SpaceX before it can begin running regular delivery missions to the outpost. The company is contracted to fly at least 12 of these for NASA at a total price tag of $1.6 billion.

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