WASHINGTON -- Earth-orbiting listening posts are on active duty in the United States-led war on terrorism. Signal-seeking spacecraft not only play a critical role in eavesdropping on nations from on high, but also within the borders of the U.S itself.

Hints and speculations about the true nature and capabilities of these "all ears" spacecraft have reached folkloric proportions.

Some reports suggest that cell phone traffic, ground line chats and faxes, telexes and satellite telecommunications links, as well as Internet emails are intercepted around the planet. Once electronically gobbled up, the information is sifted by supercomputers loaded with souped-up software to flag keywords of special interest to a network of must-know-it-all intelligence communities.

In the United States, not surprisingly, officials are mum on whether Echelon even exists. Real or not, for some individuals, the very hint of such a system conjures up images of Big Brother, out-of-control snooping, willy-nilly wiretapping and civil liberties violations.

Still, many hope such high-tech electronic surveillance is on full alert and doggedly trying to uncover the whereabouts of terrorist Osama bin Laden and his gang.

Others even encourage the use of listen-in-and-learn spacecraft to spy within U.S. borders, and see it as one more potential tool for the efforts of the new Office of Homeland Security.

Some, however, feel that Echelon's time has already come and gone.

Eavesdropping from space is certainly not new.

During the heady and sweaty days of trying to keep a reliable eye on the former Soviet Union, President Dwight Eisenhower approved the construction and launch of a secret reconnaissance satellite project, eventually known as the Galactic Radiation and Background experiment, or GRAB.

Sent into space in June 1960 -- but billed as a science project to measure the Sun's radiation -- GRAB's true purpose was to snag electronic air-defense emissions. The tiny satellite, developed by the Naval Research Laboratory, represented America's first "ears" in space. GRAB-1's orbit around Earth sent it through the energy beams from Soviet radar whose pulses traveled straight and far beyond the horizon into space.

GRAB-1 collected and recorded those pulses, transmitting the data to "collection huts" at various ground sites within the satellite's field of view. Information gleaned by the spacecraft was then taken by courier aircraft to the United States for assessment by the National Security Agency (NSA) and others. A GRAB-2 was orbited in June 1961.

GRAB data yielded technical intelligence about Soviet radar, enabling U.S. military planners to script effective war plans. The electronic intelligence satellites nosed-in on the Soviet Union from orbit, relaying details unobtainable by Air Force and Navy ferret aircraft that flew along accessible borders in Europe and the western Pacific.

One of the pillars of U.S. intelligence is the collection and analysis of "signals intelligence," or "SIGINT" for short.

Over the decades, a variety of costly satellites have made their way into orbit, each outfitted with mega-antennas crafted to snare weak signals drifting through the ether.

Magnum, Ryolite, Jumpseat, Orion, Chalet, Aquacade, Vortex -- these are among the names tagged to these patrolling sentinels of the deep by space watchers. To what degree any of these satellites may have, or are now, playing a role in Echelon data gathering and distribution is hazy.

On October 10, a secret data relay satellite for the National Reconnaissance Office (NRO) rocketed from Cape Canaveral, Florida. According to Aviation Week & Space Technology, the new relay satellite could be used to route data involved in U.S. counter-terrorism operations or intelligence data specifically related to military operations in Afghanistan.

Echelon is very real, explains Jeffrey Richelson, a senior fellow with the National Security Archive in Washington, D.C. He has pointed out that some of the oratory concerning Echelon and its abilities may be "over-the-top." But the fact that a U.S.-promoted effort to operate an electronic eavesdropping network with global reach "should come as no surprise," he explains.

Similarly sanguine is Richard Best, Jr., a specialist in national defense at the Congressional Research Service (CRS), in the Foreign Affairs, Defense, and Trade Division. The CRS is a research arm of the U.S. Congress.

"There has been a capability for many years to listen for specific words, to filter them out. But in terms of listening to every conversation or every email throughout the world, that's just wild speculation," Best told SPACE.com.

"My sense is that [the word] Echelon is loosely used, probably more outside the intelligence community than inside the community. It's involved, I believe, in electronic surveillance, but maybe I'm wrong, of non-military targets and they do it in cooperation with other countries," he said.

But sometimes those cooperative allies may also be targets. In mid-September, a special investigative committee reported to the European Parliament that Echelon was fact, not fiction. The conclusion came after a study was undertaken to review allegations that Echelon was intercepting private and commercial communications, mainly via satellite, for American industrial espionage purposes.

The committee could not substantiate that the United States was utilizing Echelon to the disadvantage of European businesses. Nonetheless, steps were taken by the European Union to block the intrusive nature of Echelon.

Has it also become fair play for U.S. intelligence-gathering agencies to turn satellites and other devices on Americans?

History serves as a reminder that the Nixon White House ordered the NSA to target the anti-war movement in the 1970s. On the other hand, to help thwart terrorism inside America today, growing sentiment among the citizenry seems to be a "do what it takes" attitude.

In the United States, and particularly in view of the events of September 11, Best said, there is growing understanding of the need to "collect what you can."

But if such an intelligence-hungry system like Echelon is real, why was there no warning from its operators that a massive attack on home soil was imminent?

Given 20/20 hindsight, Best said, one could go back and perhaps see a pattern. "People for whatever reason didn't see the pattern at the time. Whether in retrospect they should have, or whether there was no reasonable expectation that they could have…that's the question and I'm not going to sit here and speculate on that," he said.