Editor's Note: This is an advanced copy of a story appearing in the December 1 edition of Aviation Week & Space Technology.

A National Reconnaissance Office secret space mission, important for tracking potential terrorist movements involving ships, is poised for liftoff this week from Vandenberg AFB, Calif.

The 13,700-lb. payload of 2-3 ocean surveillance spacecraft is to be launched as early as about 2 a.m. PST Dec. 2 on board a U.S. Air Force/Lockheed Martin Atlas-Centaur. The overall booster and payload combined are valued at roughly $500-600 million.

The Atlas rocket blasts off from the SLC-3E pad at Vandenberg in September 2001 with an NRO payload. Photo: Karl Ronstrom for International Launch Services

This will be only the second military mission to use the 196-ft. Atlas IIAS/Centaur from Vandenberg. The first was a related secret mission in 2001 that may have had a partial payload failure.

The flight is part of a U.S. military space launch surge set to loft four more military spacecraft through February in addition to the NRO satellites.

Those flights include use of a Russian-powered Atlas IIIB to orbit a Navy UHF military satcom here Dec. 16, followed Dec. 20 by the launch of a new USAF Global Positioning Satellite (GPS) on a Boeing Delta II.

They are to be followed in about January by another GPS and, in February, the launch of a Defense Support Program missile-warning satellite on a Titan IVB/IUS. The GPS replacements are especially important because the critical in-orbit GPS constellation has begun to degrade with age.

The five military space missions through February have a combined hardware value of about $1.5 billion. And the Vandenberg mission this week is bringing to light more detail on space-based ocean surveillance, one of the more secret U.S. space intelligence operations.

Both the difficulty and importance of NRO's space ocean surveillance role, in connection with the Navy and Coast Guard, has been elevated since the Sept. 11, 2001, terrorist attacks. The need to track thousands of civilian ships worldwide has intensified given the potential for seemingly harmless shipping to be involved in nuclear, chemical or biological terrorist operations. It was easier to track Soviet warships than a far larger number of civilian ships with unknown cargos and crew.

There are about 14 operational NRO ocean surveillance spacecraft, according to respected military space analyst Ted Molczan. Since the late1980s they have been launched in groups of three that fly in triangular formations. Each satellite in a group is separated by about 30 mi.

Each formation returns data on the location and direction of ships within view of its elint and interfrometry sensors. A global real-time computer database on all ship movements is updated as data from each group of satellites are continually merged with data from other similar formations as well as Navy and Coast Guard air and sea surveillance.

Since the late 1980s, each three-satellite constellation has been launched together. Through the 1990s, heavy Titan IV boosters were used to launch each group. The NRO then made a major shift to the Atlas-Centaur, building a large new pad facility at Vandenberg for the project.

The Atlas-Centaur is a highly specialized launcher because of its liquid hydrogen-fueled Centaur upper stage powered by Pratt & Whitney RL10 engines. Until the new Vandenberg installation, such launchers had only been flown from the Cape and rarely used for low- and medium-altitude orbits most often employed by NRO.

Although inaugurated in 1999 with NASA's launch of the Terra environmental satellite, the new Vandenberg facility was built more specifically for the reconnaissance office.

The first, and so far only, Vandenberg NRO Atlas-Centaur mission was launched in September 2001 carrying just two ocean surveillance payloads.

That was unusual since ocean surveillance formations normally involve three spacecraft. After launch, word began to circulate in intelligence circles about a significant problem with the mission, possibly involving failure of a third satellite to separate from the launcher.

Operational details are classified so it remains to be seen whether the flight scheduled for this week will deploy two or three spacecraft. Whatever the number, they will be placed into about a 685 X-750-mi. orbit inclined 63.4 deg. The Centaur is to do this using a two-burn profile following separation from the Atlas, augmented with four solid motors.

In a mission that will be visible to the Los Angeles region, conditions permitting, the Atlas will fly a southern trajectory just off the California coast. The Centaur will fire initially for 10 min. 44 sec. to, first, inject the NRO payload into an 155 X-620-mi. elliptical parking orbit.

See a map of the launch trajectory here.

The Centaur/NRO payload stack will fly south until the southern extreme of the orbit -- over southern South America. The ground track will then curve northeast up the Indian Ocean off Madagascar before the Centaur is ignited for its second burn lasting only 11 sec.

Depending upon when in its secret launch window the vehicle is fired, the overall ground tracks can vary between what are designated "early, optimal or late" trajectories. This will govern whether the spacecraft are released over the northern Indian Ocean or over the border between India and Pakistan. The mission, designated Medium-Launch Vehicle MLV-14, is being managed overall by International Launch Services.

The spacecraft will continue to circle Earth between 63.4 deg. N. and S. Lat., an orbit that provides extensive surveillance of all the oceans while also enabling best overall management of the multiple ocean surveillance constellations. Although deployed close together the satellites, whether two or three, will use their on-board propulsion to move away from each other to form the desired surveillance spread. This will take about a month of operations and checkout.