At first glance, the new website is a clear improvement over the old OIG system, which featured different levels of access.

Registered OIG users, who provided at least some personal information, were allowed to download and share up to 500 two-line elements, or TLEs - the numbers that define a spacecraft's orbit - every day.

So-called "superusers," who had to provide more details about their identities and justify their need for TLEs, were allowed to download the entire list. They also had to agree not to redistribute the complete data set.

Only about 1,100 people were ever registered to use OIG and of that total, only two dozen or so were superusers. But many of the registered users redistributed data on special interest satellites - the 100 brightest, for example, or amateur radio satellites - to tens of thousands of other hobbyists and commercial users.

Space Track makes everyone a superuser, giving anyone whose registration request is accepted access to the entire unclassified TLE database.

But in a major change that has raised alarms across the satellite tracking community, Space Track requires all users to agree up front not to "transfer any data, including, but not limited to, the analysis of tracking data, or other information received through this website or any services described herein to any third party without the prior express approval of the Secretary of Defense or his delegatee."

Anyone who violates the restriction will be barred from the website and "other enforcement action may also be pursued."

The vast majority of commercial, academic and amateur satellite watchers obtain their data from OIG users who redistribute or post TLEs on various websites. Under the Space Track user agreement, operators of such websites would need Defense Department approval to continue operations.

Lt. Col. David Maloney is overseeing implementation of the Space Track website for Air Force Space Command at Peterson Air Force Base, Colo. He said his organization had not yet received Pentagon guidance on how the user agreement should be interpreted.

He said he did not know how the new program would affect hobbyists and organizations like Heavens-Above, how requests to share TLEs would be handled or how long it might take to get an answer one way or the other. That's an issue because satellite orbits change on a daily basis.

Critics in the civilian satellite tracking community point out Space Track operates primarily on the honor system and that any registered user could simply email data to a third party. As such, they say, the user agreement primarily hampers legitimate users.

Depending on how that agreement is interpreted, commercial satellite operators, space debris researchers, academics and hobbyists could be unable to pass TLEs along to other observers without direct permission from the Air Force.

Equally alarming to hobbyists, one could argue that generating a satellite visibility prediction based on a Space Track TLE could be interpreted as "analysis" and thus banned without specific Pentagon approval.

"I'm a bit worried, but what more can I do?" Chris Peat, operator of Heavens-Above, said in a telephone interview from Germany. "If they tell me to stop doing it, I'll have no choice but to comply. If they cut off my access, I can't get the elements. It's not just my source, that's the source for everybody."

T.S. Kelso, a respected satellite tracking expert with the private Center for Space Standards and Innovation, operates a long-standing website called CelesTrak (http://www.celestrak.com) that provides TLEs to more than 20,000 users around the world. In an interview, he said the Air Force has not yet defined what is even meant by the term "analysis."

"Does that mean you can't distribute analysis of tracking data that shows limitations and vulnerabilities of the current Space Surveillance Network?" he asked. "Or does it mean something like Heavens-Above, that takes TLEs and generates pass predictions?"

In conversations with Air Force officials, he said, "rather than 'yeah, it means that' or 'no, it doesn't mean that,' I got 'well, that's an interesting question. We'll have to think about that.'"

But because the law includes a provision for Defense Department approval of redistribution requests, it "recognizes there are going to be instances where redistribution of data and some analysis is a perfectly acceptable and encouraged thing," Maloney said.

Students almost certainly will be able to include TLEs in research papers, he said, and tracking data almost certainly will be available for presentation at conferences and in similar academic settings. But as of early February, he had no guidance on how the new policy might apply to commercial satellite operators, their subcontractors or hobbyists.

"I think there are a lot of researchers right now that are looking at it and going 'well gee, it might mean that I can do that but if I read it the wrong way and they take legal action against me, I'm in trouble,'" Kelso said. "They're reluctant to do that and it's putting a chill on the research community."

That ambiguity is especially frustrating given the widely held view that legitimate users are being bound by a potentially restrictive user agreement that an adversary could simply ignore. Consider the following scenario:

"The NASA site shuts down and all the sudden this site pops up in China and it's got all the TLEs on it," Kelso said. "And the guy who runs this site isn't even a registered user on your system. What are you going to do? They can't take legal action against somebody in China. What are you going to do? Cut off everybody who says they're registered coming from China?

"For all you know, it's somebody in England who's downloading it and giving it to them," Kelso said. "I mean there's no way to enforce this. Why even go there? And they have no answers. It's pretty frustrating right now. They just haven't really thought through the implications."

As for Heavens-Above, Peat said he plans to continue posting satellite pass predictions until the Air Force clarifies its policy.

"The problem is, it's not clear," he said. "They've got this usage policy statement on the new Space Track web site, which is a bit ambiguous. It says you can use the TLEs - otherwise there's no point to being able to download them - but you can't pass them on to other individuals and you can also not use analysis of the TLEs.

"My policy will be to carry on. At the moment, I show the actual TLE used to make predictions on the bottom of the table on the orbit page. I'll remove that. But I will continue to make predictions. I mean I have no choice, really, that's what my site is all about."

If the hobbyists' fears of a more restrictive interpretation of the Space Track user agreement pan out, they vow to continue - and expand - their efforts to track satellites on their own.

"Well, you can look at it as the end of the world, or you can look at it as one hell of an incentive and opportunity to upgrade our technology," said one veteran satellite analyst who asked not to be named.

At present, the community generates and maintains TLEs for about 130 satellites not listed in the OIG/Space Track database. Some of those are listed by Heavens-Above. TLEs for NASA satellites - the space station, the Hubble Space Telescope and others - already are freely available directly from NASA and space agency officials said no changes to that policy are planned.

The amateurs generate TLEs for classified satellites by monitoring military launches, which cannot be hidden, and then spending the time necessary to spot their payloads. Based on precise timings of multiple satellite passes, hobbyists around the world, using computers and their own custom software, can calculate a TLE.

"This measure, like so many security measures taken post-9/11, is completely ineffective in improving security," McDowell said. "It merely gives the impression that you're trying to do something. The initial reaction of any security people anywhere following a crisis is all right, all information is now secret."

But a determined adversary could "subvert this very easily and not only that, even if you made it secure, what the hobbyists have shown is ... in a couple of years you (could) have a set of bad guys who are much better equipped than they previously were for relatively little expense on their part."

Kelso agreed, saying "the guys who are responsible for implementing this really don't use the data and they're not familiar with what's going on in the community. So they have this vision that if they don't help people, they're just not going to be able to do this. Well, I've seen people develop their own elements.

"The Air Force guys don't have a clue what's already being done," he said. "They have this vision that the only way someone's going to be able to do this is if they spend millions of dollars. They're just not really up to speed."

The Air Force pilot program is intended to determine the "feasibility and desirability" of providing satellite tracking data to non-government users. The feasibility of the project is not in question. Whether the government will find it "desirable" to continue sharing tracking data after that remains to be seen.