As the U.S. Air Force pushes forward with its plans to deploy small satellites intended to support tactical forces directly, the service is well aware that those systems will not be able to answer all the needs of its


Small satellites that can be launched on short notice can play a “limited” role to help fill in some of the gaps of existing constellations, or help to reconstitute capabilities that may have been disrupted by natural causes or intentional attacks, according to Col. Robert R. Walker, chief of the



space (ORS) division at Air Force Space Command in Colorado Springs, Colo.

“When there is no capability, the small sat capability brought to bear on an operational or tactical engagement may prove decisive to the joint force commander,” Walker said in a written response to questions on Aug. 1. “Hence, the adage that a limited capability is superior to no capability holds.”

It is too early to say at this point how much overall capability

small satellites might

provide to tactical forces, and how much useful time they might

spend over areas of interest, Walker said. The Air Force is still in the early phases of experimenting with TacSat-2, the first

small spacecraft intended to demonstrate an imagery and signals intelligence capability that can be controlled directly by commanders in the field.

The Air Force will have clearer answers about the amount of capability that it can promise from the small satellites as it goes through the selection process for operational work, Walker said.

However, a former Air Force Space Command official is

raising concern publicly that the small satellites may at best offer extremely limited capability to tactical forces, and at worst could siphon funds from other systems that truly can

meet their needs.

Ed Tomme, an

Air Force lieutenant colonel who retired from the service in February 2006, after having served as deputy director of the Tactical Exploitation of National Capabilities (TENCap)

program, said

investing in unmanned aerial vehicles or high-altitude balloons such as those that the Air Force

recently has begun to purchase could offer far more return on investment than small satellites in many tactical circumstances.

Tomme examined the potential capabilities of small satellites during his time with the TENCap program, which is dedicated to finding ways to exploit space-based capabilities for tactical users, and found that while they offered some limited capability over denied areas not inherent with aircraft, their time over targets was not useful in tactical scenarios.

Tactical forces often need information about a situation within 20 minutes of request, which would be difficult to provide without a large constellation of perhaps 50 satellites in low Earth orbit, Tomme said.

However, small satellites could prove more valuable to those with

more of a strategic focus who do not have the

tight time constraints facing tactical users, he said. In more strategic scenarios, small satellites

launched on short notice could be effective by

providing a limited capability in case standard satellites are unavailable due to natural circumstances like space weather or a deliberate enemy attack, Tomme said.

In the case of an imagery satellite that has been taken out by enemy attack, small satellites could provide a useful capability to users who do not need a near real-time response to their taskings, Tomme said.

Tomme, who currently is a senior technical advisor for sensing and imaging systems for General Dynamics Advanced Information Systems in Colorado Springs, said

his current position does not cause him to be biased against small satellites, and noted that General Dynamics had purchased Spectrum Astro of Gilbert, Ariz., in 2004 in part to be a player in the ORS market.

Tomme said that his views, which he has expressed in papers written for the Air War College and in a speech to the Responsive Space Conference in El Segundo, Calif., in April, have raised some tension within the company. He said

he believes that having a better understanding of the capabilities of small satellites will

enable the company to make better offerings to the government.

Tomme, who had pursued astronaut training while in the Air Force, says he is an advocate for space systems, but that those capabilities “can’t be funded on the backs of warriors who may die if they have the wrong equipment.”

Different missions dictate how much time a satellite will be useful over a particular area, Tomme said. Signals intelligence satellites, for example, offer more useful time overhead on each pass because their sensors do not have the same requirements for gathering data at particular angles as satellites for other missions, and can gather useful data without operating continuously, Tomme said.

A signals intelligence satellite operating in a 500-kilometer circular orbit over Iraq could pass overhead about 10 times a day and spend about 8 minutes overhead each time, at a cost per hour of $43,000, said Tomme. His cost estimate is

based on a satellite costing $20 million, and does not include operations costs.

Imagery satellites, whose sensors become less effective at providing useful data to analysts when not looking directly down at areas of interest,

could pass overhead five times a day

, spending about one minute and 40 seconds of useful time over the target, at a cost of $429,000 per hour, Tomme said. Having a “snapshot every hour” would have little utility to tactical forces, he said.

While some Pentagon officials have talked about possibly allowing commanders in multiple theaters to task the same small satellite as it passes over their respective region, battery power constraints with small satellites would make this difficult, Tomme said. To keep the weight of small satellites low, the military

likely will need batteries that require recharging when a sensor is not over its primary area of interest, he said. Thus, the cost of using a small satellite is unlikely to be able to be spread over several theaters, he said.

Air Force officials have talked about using highly elliptical, or “magic,” orbits to increase the time that a small satellite spends overhead in a particular theater. However, the radiation in these orbits

likely would require small satellites to have shielding that is too costly for the ORS business model, Tomme said.

While less expensive shielding could be used, it may be so heavy that it would lead to weight growth that would make the satellites too large to launch on small boosters, he said.

Walker acknowledged the radiation issue, but said that design features could compensate for its effects and enable a small satellite to last on orbit for about a year. Shielding is not the only option, he said, pointing to design features like “careful attention to grounding, selected component redundancy, and memory error detection and correction software.”