On October 4, 1957, in the midst of the Cold War, the Soviet Union successfully launched the first man-made satellite into an orbit 560 miles above Earth.

The basketball-sized Sputnik I, designed to collect information about the sun and cosmic radiation, ushered in an era of fear for some Americans who recognized that rockets strong enough to carry the 184-pound satellite could also carry ballistic missiles armed with nuclear weapons thousands of miles.

Now, more than 40 years later, the satellites themselves have the ability to direct such weapons to specific targets.

"Over a third of the bombs dropped in Afghanistan were satellite guided," said John Pike, director of Globalsecurity.org, a Web site designed to inform the public about space defense policy. Pike added the entire air campaign against Taliban forces was being run in Saudi Arabia.

Since the 1960s, satellites have become an almost indispensable tool for the U.S. military, which uses them for navigation, communication, intelligence gathering and weather forecasting.

"It is my opinion that the rapid military success we've had in Afghanistan on the technology side could only be possible because of satellite technology," said Mike Jacobs, who teaches a satellite communications course in the College of Engineering.

Jacobs gave several examples of how military forces around the world utilize satellites. They make it possible for navy ships in the Indian Ocean to target Tomahawk Cruise Missiles, allow troops to call home and, using lasers, can take pictures of the ground through cloud coverage.

"We can listen to Osama Bin Laden on his walkie-talkies," Jacobs added.

Earlier this year, Lockheed Martin Corporation launched the Milstar II satellite, which will be used in combination with three other Milstar satellites by the Department of Defense for a variety of military purposes. According to the Lockheed Martin Web site, the Milstar system allows for all branches of the U.S. armed forces to communicate with each other on a secure network.

In addition to ground-to-space communications, the satellites are the first of their kind to be able to communicate with each other, which increases the security of the network.

Satellites can orbit at two levels above the Earth, Jacobs said. Those in lower Earth orbits are used commercially for things like cell phone communication and can also take pictures of the ground from a rotation at least 100 miles above the Earth.

Geostationary satellites operate 22,300 miles above the equator. Because they rotate with the Earth, they don't move from their specific location, Jacobs said. These are mainly used as relay satellites; they can transfer signals from lower satellites, which have a limited range, around the world.

When the military first began using satellites for communication, only large units had access to the technology, Jacobs said. Now individual special operations can carry satellite equipment, such as hand-held GPS navigation tools. Jacobs said much of the hand-held communication the military uses now goes through the Iridium satellites, originally designed by Motorola for cell phones.

"Satellites have made people out in the middle of nowhere equal to people in urban settings," said Jan Janssen, who works in satellite communications for the Department of Defense.

Satellite technology, however, comes at a great cost.

"They are probably the biggest single expense in the U.S. government," Jacobs said.

There are several reasons for the $1.25 billion price tag attached to the four-satellite Milstar system. To begin with, they take between three and five years to design and build.

Jenssen said the most important aspect of design is that it doesn't weigh any more than it has to and doesn't use any more fuel then it has to. This is a particular challenge because satellites must also be prepared to deal with the harsh atmosphere of space, which includes continuous radiation.

In addition, because there is no way anyone can go into space to repair them, satellites must also be equipped with back-up systems that extend their life in case something fails, as well as software that enables them to be maneuvered away from things like space debris.

Generally systems can last between 10 and 20 years.

Pike said satellites are a bargain considering all they can do for the military and civilians. Presently, Pike estimates there are 100 satellites orbiting the Earth at varying degrees of use.

"The reason you cannot get a precise estimate," Pike said, "is because they are like Macarthur's old soldiers; they don't die, they just fade away."