LOS ANGELES — When the Pentagon began planning its experiments with small satellites designed to provide more direct support to deployed commanders, military officials initially hoped to demonstrate the capability to operate the satellites within a day of launch, but some officials involved with the effort now believe that capability might be more challenging than initially envisioned.

Completing on-orbit checkout within 24 hours is far from impossible, according to Thom Davis, who is managing the TacSat-3 program at the Air Force Research Laboratory’s space vehicles directorate at Kirtland Air Force Base in New Mexico. The Air Force Research Laboratory demonstrated a capability to perform check out of a small satellite within about 12 hours in 2003 with the launch of the XSS-10 orbital rendezvous experiment, said Davis, who managed that project.

The Air Force Research Laboratory demonstrated a fast on-orbit check again in 2005 with XSS-11, a more complex follow-on mission, Davis said during a panel discussion on the TacSat programs at the American Institute of Aeronautics and Astronautics Responsive Space Conference here.

However, the sophistication of key instruments and components on a satellite could force officials to take more time to ensure that the satellite is ready to operate, Davis said. In the case of TacSat-3, which is expected to launch in late 2007, the hyperspectral imaging payload on the spacecraft could possibly have some limited capability within 48 hours, he said.

Troops likely would need to wait about a week to take full advantage of the spacecraft, driven in part by complex cooling subsystems, Davis said.

Mike Hurley, who is managing the TacSat-1 effort at the Naval Research Laboratory in Washington, also said the time needed to calibrate sensors for small satellites might be shortened to 24-48 hours, depending on the degree to which the military pushes the performance envelope with the payloads. Hurley noted that Orbcomm Inc. of Fort Lee, N.J., has deployed satellites that can be through the check out process shortly after reaching orbit.

TacSat-1 is expected to launch aboard a Space Exploration Technologies Falcon 1 rocket later this year. The launch of that spacecraft fell behind that of the second TacSat due to problems with the Falcon 1 rocket.

TacSat-2, which the Air Force launched in December aboard a Minotaur rocket built by Orbital Sciences Corp. of Dulles, Va., missed its goal of a one-day check out after a ground systems problem prevented operators from contacting the satellite for several days following launch.

Goals for experimentation with TacSat-4, which is expected to launch in late 2008, do not include an express checkout, according to Mark Johnson, program manager for the effort at the Naval Research Laboratory. While Johnson said that a one-day checkout for a spacecraft like TacSat-4 is likely possible, he said that program officials are instead planning to focus their time at the onset of the demonstration on the unique challenges associated with placing the spacecraft in a highly elliptical orbit that can maximize coverage time over areas of interest.

The Pentagon has not yet settled on a payload for the TacSat-5 demonstration.

The initial vision for Operationally Responsive Space called for launching and checking out a small satellite within a day or two of call up. Even under ideal circumstances, that time frame might not be fast enough to meet the needs of some troops on the ground looking for critical information such as what is over the next hill. In situations like that, troops generally need that information in less than 20 minutes and would need to rely on a capability that is already on orbit and readily accessible, according to Col. Pat Rayermann, who leads space and missile defense work in the office of the Army’s deputy chief of staff for operations.

Robert Davis, an Aerospace Corp. official supporting U.S. Strategic Command in Omaha, Neb., said officials developing small satellites need to avoid over-promising on the check-out time for their systems.

“It’s very easy to set those goals and not achieve them,” Davis said.

If Marine Corps Gen. James Cartwright, commander of the U.S. Strategic Command, is told that he will be able to use a satellite within two days of launch, he will expect to be able to use that spacecraft within “two days and one minute,” Davis said.

However, given the months that it generally takes to check out satellites following launch, many commanders would be pleased with a capability that can be activated within a few weeks, Davis said.

As the Pentagon launches TacSats, and continues development of common hardware and interfaces for small satellites, it may be able to reduce the time needed for orbital check, Thom Davis said.