The first flight of Space Exploration Technologies Corp.’s (SpaceX) Falcon 1 launch vehicle will be delayed until at least May as the company carries out additional testing on the new rocket.

The Falcon 1 was initially expected to launch in January 2004, but that date has slipped repeatedly due to a variety of issues. The rocket then was slated to launch this month, but that date has been moved out at least eight weeks as SpaceX performs additional testing on the rocket’s main engine and flight termination system as well as fixing minor systems engineering challenges encountered as the company assembles the vehicle, said SpaceX president and founder Elon Musk.

The company has delayed the initial launch date several times as it has uncovered issues during testing, and spent time retesting the fixes, Musk said in a telephone interview Feb. 28

The Falcon 1 will carry a small U.S. Air Force satellite called TacSat 1 in its maiden voyage. TacSat 1 is part of an Air Force effort to demonstrate the use of inexpensive satellites tailored to specific contingencies that can be launched on short notice.

In a December interview, Robert Dickman, who was the deputy for military space in the office of the undersecretary of the Air Force at the time, said that rockets like the Falcon may be key enablers for the use of small satellites in the future.

Musk is advertising rides on the Falcon 1 rocket, which is expected to cost him under $100 million to develop, at $5.9 million per launch plus range fees.

The Air Force is eagerly anticipating the Falcon launch, but is not overly concerned about the repeated delays on the effort, said Dickman, who left the Air Force in February to serve as executive director for the American Institute of Aeronautics and Astronautics.

The service would prefer to see SpaceX take a cautious approach and address any areas of concern rather than cut corners on the quality of the rockets to stay on schedule, Dickman said.

The main holdup at this point has been additional flight testing on the thrust termination system used by the Falcon rocket, Musk said. Unlike other U.S. space launch vehicles that rely on explosive systems to abort a flight in midair, the Falcon 1 uses a system that shuts down the rocket’s boosters, allowing it to land in the ocean, he said.

Russian rockets as well as Sea Launch have used thrust termination systems.

Using the thrust termination method, rather than having explosives on board, makes it easier to handle the Falcon rocket, Musk said. This reduces the pre-launch procedures needed for the handling of hazardous materials, possibly cutting expenses by about 5 percent, and could cut handling procedures by about a week, he said.

The lack of on-board explosives also simplifies the recovery of the Falcon rocket after launch, Musk said. Roughly 80 percent of the rocket’s components are designed to be reusable if the first stage can be recovered, he said. The rocket employs a parachute to ease the landing of that stage .

Bringing the launch vehicle down over the water rather than exploding it in the air also reduces the risk that rocket debris could stray from the cleared flight path to a populated area, Musk said. Aborting a rocket’s flight in mid air is never desirable, but a crash into the ocean would produce only a small explosion with debris that is far easier to contain, he said.

While the thrust termination system will help keep the cost of Falcon 1 launches down, it has added to the development cost of the rocket, Musk said. SpaceX is continuing to test the system to ensure that it will shut the rocket down properly to meet the Air Force’s range safety standards, he said.

Manufacturing issues with the Falcon 1’s main engine also have contributed to the launch delay, Musk said. Some of these issues could have been ignored if the first Falcon 1 rocket was simply a prototype, but SpaceX wants to ensure efficiency and reliability throughout its manufacturing line, he said.

SpaceX hopes to be ready to test the rocket on the launch pad at Vandenberg Air Force Base in California in about four weeks. This test will involve fueling and firing the rocket’s main engine for about five seconds, Musk said.

If all goes well in the test, the Falcon 1 should be ready to launch in May, Musk said. But if the test reveals problems, SpaceX would need to review them before deciding on a path forward, he said.