The Pentagon’s push in recent years for small rockets that can loft satellites on short notice has focused on the development of new launchers, but the military is beginning to turn its attention to an option with a proven track record.

The U.S. Air Force announced May 22 that it had ordered two launches from Orbital Sciences Corp. using the Dulles, Va.-based company’s Minotaur rocket, which is built from decommissioned ICBM stages. Air Force officials also said they are considering additional Minotaur orders.

The two launches are worth $23 million, according to an Orbital Sciences news release issued on May 25.

The Minotaur will carry the second and third TacSat payloads, which are part of the Pentagon’s effort to experiment with small spacecraft that can be controlled directly by military commanders, according to a May 22 news release from the Air Force Space and Missile Systems Center in Los Angeles.

TacSat-1 is scheduled to be launched by Space Exploration Technologies (SpaceX) of El Segundo, Calif.

Using the Minotaur, particularly if launches are purchased in large quantities, might be cheaper than paying to dispose of the ICBM stages that are used with the rocket, according to Pentagon and congressional sources.

The Strategic Arms Reduction Treaty of 1992 between the United States and former Soviet Union requires that the countries reduce their ICBM arsenals and dispose of the missile stages or convert them for space launch.

While the Pentagon is looking at a variety of types of launchers for the Operationally Responsive Space (ORS) effort, the Minotaur rockets “can probably contribute the most to ORS in the near-term based on their available quantities and their existing, proven solid rocket components,” according to a recent paper written by Pentagon officials.

The paper was written by Air Force Col. Tom Doyne, a strategist in the Pentagon’s Office of Force Transformation; Peter Wegner of the Air Force Research Laboratory’s space vehicles directorate; Air Force Lt. Col. Randy Riddle of the Air Force Space and Missile Systems Center’s Detachment 12; and Mike Hurley, Mark Johnson, and Ken Weldy of the Naval Research Laboratory.

That paper, titled “A TacSat and ORS Update,” was distributed at the 4th Responsive Space Conference in late April in Los Angeles .

Pentagon and congressional officials have expressed interest in the Orbital rockets as a way for the military to launch the TacSats faster while keeping options for the future open.

Orbital Sciences officials made that point as well during the Responsive Space Conference in April in a paper titled “Responsive Low Cost Launchers Available Today, Orbital Launching While Others Are Talking.”

Rockets under development for ORS “have lit tle to no actual launch history and are subject to schedule and cost growth risks that are not unusual with new launch vehicle developments,” according to the paper, which was written by Keith Emerson, Orbital’s manager of business development and Scott Schoneman, the company’s manager of mission development.

“While we have heard much discussion of savings in the launch industry in the last couple of years[,] we have seen one unsuccessful launch and many PowerPoint presentations on the transformation that is yet on the horizon,” Emerson and Schoneman wrote. “Orbital stands ready to provide responsive space launch capabilities that are far down the learning curve, continue to prove launch success, and have the benefit of launching while the alternative discussions continue.”

The U.S. Air Force currently is funding launches by SpaceX , as well as development work by AirLaunch LLC of Kirkland, Wash.

However, SpaceX’s Falcon 1 rocket failed to deliver its payload to orbit in its maiden launch earlier this year. While congressional and military sources interviewed for this article said the Pentagon should not give up on SpaceX, they also said that the military needs to have a rocket that it can rely on.

Elon Musk, SpaceX founder and president, said that the first launch should be viewed as a “learning experience” rather than a failure.

“Every launch vehicle organization in the world has had numerous missions not work out as planned, and SpaceX is no exception,” Musk said in a May 24 e-mail.

The company is adding a variety of corrective actions as a result of the experience with the first launch including an additional human check on all work on the rocket; 10 times as many software health-monitoring checks; and design improvements intended to reduce human error and resist corrosion, Musk said.

AirLaunch’s QuickReach system may offer capabilities not found in a traditional ground-launched rocket like the Falcon 1, the Pentagon and congressional sources said.

AirLaunch’s concept uses an unmodified C-17 cargo aircraft to carry an expendable rocket to an altitude of roughly 7 kilometers to 11 kilometers. The aircraft then drops the rocket, which ignites after it is a safe distance away from the plane, and takes its payload to orbit.

Using a C-17 to launch the rocket could free the military from being tied to launching rockets from its two current ranges, and could offer some measure of cloaking space launches in secrecy, the sources said.

However, space officials could run into difficulty finding available C-17s due to the high demand for those aircraft for current operations, sources said.

AirLaunch President Debra Facktor Lepore said the company has been working closely with the Air Force to ensure the availability of C-17s for launches beyond its planned demonstration launch in 2008. The heavy interest in ORS from major military commands will likely help to secure the aircraft as well, she said in a May 23 interview.

“The C-17 can play a very powerful role in space lift, not just airlift,” Facktor Lepore said.

Upcoming milestones for AirLaunch in 2006 include completion of the rocket’s payload fairing and a drop test of a mockup of the rocket, both of which are scheduled in early June, Facktor Lepore said.

AirLaunch’s previous drop test, which took place in September, used a dummy mockup of the rocket that weighed about 23,000 kilograms; the next one, also a mockup, will weigh more than 29,000 kilograms, which brings the company closer to the actual rocket’s projected weight of 33,000 kilograms, she said.