The U.S. Air Force will take a low-risk approach to developing an alternative satellite system for missile warning, but at the same time hopes to capitalize on recent advances in sensor technology to maximize the system's capabilities, according to service officials and documents.

Lt. Gen. Michael Hamel, commander of Air Force Space and Missile Systems Center in Los Angeles, said advances over the last 10 years could make the Alternative Infrared Satellite System (AIRSS) easier to build yet more capable than the Space Based Infrared System (SBIRS) it will replace. One key technology area cited by Hamel is imaging focal planes.

Speaking with reporters here at the 22nd annual National Space Symposium, Hamel said improvements in focal plane performance and reliability are comparable to those realized by the switch from analog to digital technology in electronic equipment.

The AIRSS came into being last year when the Air Force opted to truncate the chronically troubled SBIRS missile warning program. SBIRS was to include five dedicated satellites in geosynchronous orbit plus infrared sensors to be hosted by classified satellites operating in highly elliptical orbit. But after the cost ballooned from some $2 billion to about $10 billion, and the first launch slipped from 2002 to 2008, the service opted to reduce its purchase of dedicated satellites to no more than three.

Lockheed Martin Space Systems of Sunnyvale, Calif., won the SBIRS prime contract in 1996.

One of the biggest problems identified with the SBIRS program was inadequate systems engineering in the design phase of the program, which led to components that did not work properly when integrated together. For example, the Air Force and its contractors have struggled mightily with an electromagnetic-interference issue between the SBIRS infrared sensor and its host spacecraft.

The Air Force is trying to avoid similar problems on the AIRSS program.

In an April 4 solicitation on the U.S. government's Federal Business Opportunities Web site, the Air Force Research Laboratory requested proposals for system-level demonstrations of prototype AIRSS sensor hardware. These laboratory-based demonstrations would examine potential issues including vibration, shock and electromagnetic interference, the notice said.

"This approach is designed to offer the most iron-clad risk reduction for AIRSS, as opposed to striving for the greatest possible payload performance," the Air Force said in the notice.

The Air Force also is interested in component-level demonstrations of hardware such as focal planes, data processors and cooling systems, some of which could be the subject of flight experiments, according to the notice, issued by the research lab's Space Vehicles Directorate at Kirtland Air Force Base, N.M.

Hamel said risk reduction and performance are not necessarily at odds with one another. He said, for example, that the use of new focal plane array technology could lower the risk on AIRSS by reducing the number of moving parts on the spacecraft.

The dedicated SBIRS satellites actually have two sensors, one for scanning broad areas for possible missile launches and one that stares continuously at likely missile-launch sites. Focal plane arrays -- several focal planes operating together -- could provide the same broad-area coverage as the scanning sensors without the need for moving parts, he said.

During a brief interview here, Gary Payton, deputy undersecretary of the Air Force for space programs, raised the possibility of using focal plane arrays to combine the wide-area coverage and more-focused staring capabilities into a single sensor.

Loren Thompson, chief operating officer of the Lexington Institute, a think tank here, expressed concern that the Air Force might be biting off more than it can chew with the new focal plane technology.

Given the struggles to build the SBIRS satellites, the military's primary focus with the AIRSS effort should be on continuity of missile warning coverage, rather than trying to take advantage of technology that has not been proven effective in space, Thompson said.

Likely competitors to build the AIRSS system include Lockheed Martin; Northrop Grumman Corp. of Los Angeles; and Boeing Integrated Defense Systems of St. Louis.

Northrop Grumman built the existing Defense Support Program missile warning satellites and also is supplying the SBIRS infrared sensors. Bob Bishop, a spokesman for Northrop Grumman Space Technology of Redondo Beach, Calif., said the company is interested in AIRSS but is focused for now on the SBIRS program.

Steve Tatum, a spokesman for Lockheed Martin, also said his company is concentrating on SBIRS and declined comment the upcoming AIRSS competition.

Boeing has no significant role on the Defense Support Program or SBIRS, but has experience with surveillance satellites and sensors that is relevant to the AIRSS effort, said Joe Tedino, a spokesman for Boeing Space and Intelligence Systems of Seal Beach, Calif.

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