A spying eye was put into the sky Friday by America's mightiest unmanned rocket, probably destined to replace an aging imaging satellite in the country's reconnaissance spacecraft fleet.

The Titan 4B rocket blasts off from a cloudy Vandenberg. Photo: Air Force Staff Sgt. Pam Taubman

The Lockheed Martin-built Titan 4B rocket blasted off from Space Launch Complex-4 East of Vandenberg Air Force Base in California at 2121 GMT (5:21 p.m. EDT; 2:21 p.m. PDT) after a brief two-minute wait to avoid colliding with an object already in space.

The $350 million booster streaked southward on its journey to place a top-secret National Reconnaissance Office payload into a sun-synchronous orbit above Earth with an inclination of around 97.9 degrees to the equator.

As the most powerful U.S. expendable rocket in service today, the Titan 4B is capable of launching payloads weighing 38,800 pounds into low-Earth orbit around the planet's poles from Vandenberg.

The twin solid rocket boosters provided the thrust for Titan's first minutes of flight before burning and out separating to fall into the Pacific Ocean below. The two liquid-fueled stages of the Titan's central core were left to fire before deploying the hush-hush cargo into orbit 9 minutes and 32 seconds after liftoff.

"Score another Mission Success for the U.S. Air Force/Lockheed Martin Titan 4 team," G. Thomas Marsh, president of Lockheed Martin Space Systems Company-Astronautics Operations said in a post-launch statement. "Thanks to all of the companies and organizations that contribute to the Titan 4 team, we can be proud of orbiting another important national security payload for the NRO."

This marked the 31st successful launch of a Titan 4 vehicle in 33 flights, not counting the upper stage failures that doomed two missions after separating from the Titan 4 core vehicle in 1999.

Titan punches through the low clouds hovering above the launch pad Friday. Photo: Air Force Senior Airman Jeanette Copeland

Although the NRO won't reveal the identity of the Titan's cargo, three available clues have allowed observers to determine this is most likely a Keyhole-type photo-electronic satellite:

• The rocket's 189.9-degree flight azimuth to a sun-synchronous orbit is exactly what Keyhole imaging spy satellites require.
  
  
• The rocket featured a 66-foot long nose cone, or payload fairing. This fairing size has been used during the previous Keyhole launches on Titan 4s.
  
  
• Thirdly, Ted Molczan, an experienced hobbyist satellite observer from Toronto, Canada, determined that the orbit of an aging Keyhole satellite passed over Vandenberg at launch time. That means, in all likelihood, the Titan rocket launched into the orbital plane of the Keyhole known as USA 116 to replace the six-year-old craft.

Thought to have been built by Lockheed Martin and TRW, the satellites resemble the Hubble Space Telescope with a barrel and solar wings. However, they have a propulsion module with engines and fuel for orbital maneuvering as the craft peer down at Earth's surface instead of the far reaches of the Universe like Hubble.

Although this new satellite has been on the books for years, its launch comes at the time when America needs all the reconnaissance information it can get for the war on terrorism. Optical spy satellites like Keyholes can aid in such tasks as planning military strikes and monitoring movements of groups in Afghanistan.

Friday's launch was the one and only Titan 4 flight from Vandenberg in 2001. Two Titan 4s were also flown from Cape Canaveral in Florida earlier this year.

The next mission is scheduled for January 14 when a Milstar communications relay satellite will be lofted to orbit from the Cape. The next Vandenberg shot isn't planned until July 3 with another NRO payload onboard.

Despite the gap between Titan 4s from Vandenberg, Space Launch Complex-4 will remain active with a pair of Titan 2 refurbished ICBMs scheduled to fly from the site's West pad. A military DMSP weather satellite is due for launch on November 14, followed by a civilian NOAA weather satellite next March 21.