In June, SpaceX, as the company is known, launched its 18-story Falcon 9 rocket and successfully flew it for more than nine minutes. It was the first privately funded U.S. rocket launch in decades. However, this week's scheduled mission to launch and return an unmanned, reusable Dragon capsule from low-earth orbit, anticipated to last for hours, poses many more challenges. Placing the vehicle into a such an orbit at speeds exceeding 17,000 miles per hour, then maneuvering through a fiery reentry and splashdown in the Pacific Ocean will require a flawless trajectory, a reliable heat shield and finally, perfect operation of the redundant parachutes, according to space experts.