Six weeks after the first Falcon 9 rocketed into orbit, pieces of the second launcher have begun arriving at Cape Canaveral for a shakedown flight of SpaceX's Dragon capsule in September, according to the company's top executive.

The Falcon 9 rocket's first stage inside the hangar at pad 40 on Thursday. Credit: SpaceX

The Falcon 9 first stage pulled into Cape Canaveral Thursday after a truck ride from SpaceX's test site in central Texas.

The stage was placed inside the company's rocket assembly hangar at launch pad 40. Officials said they untarped the rocket and completed initial inspections Thursday night.

Engineers plan more testing over the next several weeks to make sure the stage and its nine Merlin engines are ready for flight.

The Falcon 9 upper stage should arrive in Florida by August, according to Elon Musk, SpaceX's founder and CEO.

The objective of the privately-built rocket's second mission is to send the first operational Dragon spacecraft to orbit, where it will briefly test its propulsion, pressure, communications, guidance, navigation and control systems.

"It's really just testing the core functionality of the system," Musk said. "Can it go up there, can it maneuver around, does it maintain integrity, maintain communications, can it re-enter?"

SpaceX is developing the Dragon to ferry cargo to and from the International Space Station beginning next year. The company says the capsule could also be modified to carry humans to orbit within about three years, making the Dragon a leading candidate to win a slice of NASA's plans to procure commercial operators for human transportation to space.

The Falcon 9's first launch June 4 placed an inert Dragon capsule in orbit, but the craft stayed attached to the rocket's second stage. Engineers are methodically reviewing all of the Dragon's systems for the more ambitious upcoming test flight.

Artist's concept of a Dragon spacecraft orbiting Earth. Credit: SpaceX

"It's really driven by Dragon's schedule," Musk said in an interview. "At this point, Falcon 9's design is done, so there are really no changes being done between Flight 1 and Flight 2. This is the first time we're launching an operational Dragon, so that's where the development schedule risk lies."

The Dragon should be shipped to Cape Canaveral sometime in August, but Musk cautioned it is difficult to predict exactly when it will be ready.

"Then there's about a month of preparation, and we'll try to launch in September, I think," Musk said. "It's impossible to predict the exact end of the development schedule."

The Falcon 9 was scheduled to launch around Sept. 9, but the company decided this week to install manual drain valves to back up solenoid valves on the Dragon. That decision will add a few weeks to the schedule, according to Musk.

"There are a bunch of little things like that adding time to the schedule," Musk said.

SpaceX is reconsidering the duration of the Dragon demonstration flight, which was slated to last three orbits, or approximately five hours.

"There's a slight debate internally," Musk said. "It will be somewhere between one and three orbits. We haven't made a firm decision on that point."

The Dragon's heat shield will also be put to the test during re-entry. The capsule's blunt end is coated with phenolic impregnated carbon ablator, a resistant insulator used by NASA's Stardust mission that returned comet samples to Earth.

The ablator, called PICA-X for short, was tested inside an arc jet laboratory at NASA's Ames Research Center at Moffett Field, Calif.

"It's actually the most powerful stuff known to man. Dragon is capable of re-entering from a lunar velocity, or even a Mars velocity with the heat shield that it has," Musk said.

Two redundant drogue parachutes and three main chutes will slow the craft to a gentle landing in the Pacific Ocean a few hundred miles off the coast of California.

Artist's concept of Dragon descending under three main parachutes. Credit: NASA

Musk said SpaceX is tweaking two parts of the Falcon 9 rocket to resolve issues observed in the first flight.

Roll torque from the first stage's nine engines triggered an unexpected twisting motion as the rocket ascended from the launch pad.

"It was more than we expected, but we did expect to see that roll torque," Musk said. "The bottom line is it's a very simple fix. We're going to recalibrate the engines to take out that roll torque."

The engines were programmed not to control the vehicle's rolling motion at the moment of liftoff because engineers were worried the twisting motion could damage the launch pad's hold-down system.

A few minutes later, the second stage began a dramatic spin as the rocket reached space. The roll was captured in views from an on-board camera.

"The roll on the second stage was also a non-fatal situation. We think the actuator may have overheated due to radiative heating from the nozzle," Musk said. "This is speculative, but we can trace the problem down to the roll actuator itself."

More insulation will be added around the actuator to prevent the same problem on the next launch.

"I almost feel concerned that they're aren't more issues," Musk said. "We're continuing to look for near-misses, but we haven't seen any yet. The staging was just spot-on. It went out super straight, no issues there. Ignition was great."

SpaceX was hoping to recover the Falcon 9's first stage in the Atlantic Ocean, but the rocket broke apart as it fell back to Earth.

A restart of the second stage engine also did not go as planned.

"We initiated a short restart on the other side of the Earth," Musk said. "That was not part of the default mission. We're sort of saying no comment on that one, except to say that it did initiate the restart, and it did light the engine. We're not happy with how it did that."

The upper stage may not have been in the correct orientation for the engine's second ignition due to the rolling motion in the stage's first burn, Musk said.

"I really don't want to cast any aspersions on the flight, when it was never one of the goals," Musk said.