The move, quietly implemented March 1, has begun to generate criticism. But defense officials described it as a prudent attempt to deny adversaries easy access to "sensitive" -- though not classified -- information.
"These satellites are absolutely critical," not just in the current military campaign in Yugoslavia but also for other missions around the world, said Air Force Maj. Perry Nouis of the U.S. Space Command in Colorado. "There are a lot of adversaries out there that know we're heavily reliant on these systems. . . . The information is not classified, but we're making it more difficult for them to have access to it."
Before the new policy was introduced, the tracking data on military satellites was routinely provided to NASA's Orbital Information Group Web site, which is responsible for global distribution of unclassified information on orbiting spacecraft and debris. From now on, Nouis said, the information will be released only to selected parties on a case-by-case basis; for example, if it is needed to avoid an orbital collision.
There are about 600 operational satellites in orbit around the globe, Nouis said, of which half are U.S. government and commercial craft. Roughly 100 are U.S. military (including classified national security) satellites that play roles ranging from communications to reconnaissance to the navigational guidance that delivers cruise missiles to their targets.
The Web site -- http://oig1.gsfc.nasa.gov -- had provided information about an object's location in orbit, and its highest and lowest distances from Earth.
Such information no longer will be provided, Nouis said, on any military communications, missile warning, imagery and surveillance craft, or on the Navy's popular constellation of 27 Global Postioning Satellites, which are used not only to guide attacking missiles but also for a variety of civil and commercial navigational purposes. (Until now, orbital data on classified satellites had been included but without identifying them. Now it will not be included at all, Nouis said.)
The change does not affect a panoply of civilian scientific and commercial satellites, including weather satellites operated by the National Oceanic and Atmospheric Administration, officials said.
Steven Aftergood, director of the project on government secrecy for the Federation of American Scientists, said the revised policy "is just one instance of a larger withdrawal of public information from the World Wide Web by [the Defense Department] in recent months, a swing of the pendulum away from the [post-Cold War] openness that existed until a year or two ago. . . . To me, it's a disturbing development."
That openness, he said, was driven in part by deliberate government policy but was also partly the result of rapidly developing information technologies.
Aftergood said interested parties could get most of the withheld information by other means, with a little extra work, and that some aspects of the policy, such as inclusion of the GPS system -- which by its very design broadcasts its positions -- "is a reflexive gesture of habitual secrecy that makes no objective sense."
Quinton Barker, operations manager of the Orbital Information Group at NASA's Goddard Space Flight Center, said yesterday that he was busy trying to draft a response to users of the Web site who have written to complain about the information cut-off.
The objections number several dozen, he said, out of some 2,000 users around the world, including amateur astronomers, scientific researchers and satellite operators. He said the Web site contains information about some 5,000 unclassified objects in orbit, including spacecraft (defunct as well as operational) and debris. His group is responsible for maintaining the definitive historical record on unclassified objects launched to orbit since the Space Age began, Barker said.