After three years of development, SpaceX's privately-made Falcon 1 rocket is set for its debut launch Saturday from a seven-acre isle in the Central Pacific. Liftoff remains targeted for 4 p.m. EST (2100 GMT).

Space Exploration Technologies Corp. founder Elon Musk cautions, however, that delays could be inevitable for this critical inaugural launch.

"This is a brand new rocket from a brand new launch site, so I would characterize that time as the first launch attempt. Miracles can happen and it may actually happen on that exact time, but it is not a certainty," he told reporters at a news conference last week.

The day's launch opportunity extends four hours to 8 p.m. EST (0100 GMT).

Be sure to check out some spectacular images of the rocket at the launch pad. You can see the photo collection here.

This will be the first ground-based orbital launch of its kind to originate from the U.S. Army's Kwajalein base in the Marshall Islands. An air-launched Pegasus rocket did ascend to orbit from the range carrying NASA's HETE gamma-ray observatory a few years ago.

A 25-member SpaceX team will oversee Saturday's countdown. While the Falcon rocket is fueled at the pad the company has built on the tiny island of Omelek, the launch team will be controlling operations from a separate island.

The bare-bones pad does not feature a large mobile service gantry or bulky umbilical tower. The rocket is mounted atop a ground pedestal, and is supported by the transport trailer that it has been riding since being assembled at SpaceX headquarters in El Segundo, California. The rocket and trailer duo was wrapped in a protective covering and shipped by barge from the U.S. to Kwajalein this summer. That trailer has continued to service Falcon even after it was erected upright on the pad.

A pole-like structure next at the pad routes umbilical lines to the rocket stages and to the nose cone the enclosing the payload -- the Air Force Academy's cadet-built FalconSat 2 craft. The rocket is fed with a highly refined kerosene propellant and super cold liquid oxygen to power the engines of its two stages.

The first stage main engine, called Merlin, will transfer to internal power as the countdown passes T-minus 2 minutes, 30 seconds, SpaceX says. The rocket's avionics switch to onboard battery power 30 seconds later.

The countdown's autosequencer takes over at T-minus 45 seconds. With a half-minute till launch, pressurization of the rocket's tanks occurs.

Merlin ignites when the main propellant line opens, two internal ignitors fire off and helium spins up the engine's turbopump. Merlin will roar to full throttle as the countdown passed the T-0 point, while undergoing a computer-controlled check of vital signs to ensure all systems are working properly before the 70-foot vehicle is unleashed to fly.

Generating about 77,000 pounds of thrust, the rocket should clear its pad umbilical mast in about 7.5 seconds as it climbs away on a trail of fire.

"Some rockets turn faster than others, depending upon the trajectory. In this case it is going to go almost straight up until it is out of sight," Musk said, predicting how the launch will appear.

Falcon reaches the region of maximum aerodynamic forces, or MaxQ, at T+plus 76 seconds.

Merlin consumes its supply of fuel and shuts down at T+plus 2 minutes, 49 seconds. A second later, the separation system jettisons the parachute-equipped first stage to fall into the Pacific for retrieval.

The Kestrel second stage engine, operated by tank pressure and not a turbopump, is lit by redundant torch igniters at T+plus 2 minutes, 54 seconds. This firing will accelerate the rocket and payload into the targeted orbit around Earth of 250 by 310 miles and inclined 39 degrees to the equator.

The two halves of the five-foot diameter nose cone separate at T+plus 3 minutes, 14 seconds, after the rocket has climbed high enough to escape the atmosphere. The FalconSat 2 spacecraft will be exposed once the shroud falls away.

The second stage burns for more than seven minutes, with Kestrel producing about 7,000 pounds of thrust in vacuum, until finally shutting down at T+plus 9 minutes, 12 seconds.

Deployment of FalconSat 2 occurs at T+plus 9 minutes, 30 seconds, completing the main objective of the launch.

SpaceX mission designers have planned for the second stage to perform a collision avoidance maneuver to back the rocket motor away from FalconSat starting about 10 seconds after separation. Later, the stage will re-ignite the Kestrel engine to demonstrate its re-start capability, something that would be required when launching heavier payloads or flying into other types of orbits than the one FalconSat 2 will use.

Back in the Pacific, a recovery ship stationed about 600 miles downrange from the launch site will retrieve the first stage, which SpaceX has built to be reusable. The stage carries Global Positioning System equipment, a radio direction finder and two sonar beacons -- one forward and one aft. Ballistic predictions and radar will be used to project the impact point and the rocket's devices will steer the recovery forces to the right spot.

"We have a lot of ways of finding the stage, and we really want to bring it back no matter what shape it's in," Musk said.

After being cast free from the second stage, the plummeting first stage releases a high-speed drogue chute to slow the fall, then the main chute pulls out. The splashdown speed is expected to be about 25 feet per second, Musk said.

The retrieval ship will tow the stage to an atoll where waters are calm. It will be loaded aboard the vessel and brought back to the harbor in Kwajalein.