Nonetheless, outside experts believe that the number of satellites involved is in the dozens -- compared to roughly half a dozen imaging satellites now in orbit. Analysts estimate the contract's total value at over $4 billion.

Despite a gradual opening in recent years, NRO remains one of the most secretive government agencies. The agency's logo (pictured) was classified until 1994. But outside experts make informed estimates of NRO activity through various means -- for example, by watching the size and frequency of rocket launches carrying classified payloads.

NRO is believed to currently operate three "electro-optical" satellites that capture visible-light or infrared images, and two radar satellites that can see through clouds or in darkness. (NRO also operates satellites that eavesdrop on radio communications and track electronic patterns produced by warships or other systems.)

According to John E. Pike, space policy director at the private Federation of American Scientists, the Future Imagery Architecture is likely to consist of three electro-optical satellites, and as many as two dozen small radar satellites. The emphasis of the program, he believes, is to provide "real-time battlefield surveillance" in future wars.

Marco Caceres, senior space analyst at the Teal Group, a consulting firm, also believes that the Future Imagery Architecture program will include "dozens" of satellites. NRO's goal, he says, is to "spread the risk" by launching smaller, cheaper satellites. In August 1998, a Titan IV launch accident destroyed an NRO satellite whose value has been estimated at more than $700 million.