The two-stage rocket is aiming for a 730-nautical-mile circular orbit inclined 58 degrees to the either side of the equator where it will deploy a pair of demonstration satellites for the Space Tracking and Surveillance System, a $1.5 billion project known as STSS Demo.
The satellites will be used by the U.S. Missile Defense Agency to test the "birth to death" tracking of missiles from launch to re-entry. NASA is lending its expertise to the oversee the Delta rocket flight and getting the satellites into space on behalf of the MDA.
Liftoff from pad 17B is targeted for 8 a.m. EDT (1200 GMT) at the opening of an hour-long window. Officials gave approval to proceed with the countdown at their Launch Readiness Review held Monday following several days of delays.
Ground crews loaded the Delta 2 rocket's second stage with a storable hydrazine propellant mixture and nitrogen tetroxide oxidizer on Sunday. The fuels will power the stage's main engine during the two firings needed to place the satellites into the planned orbit around the planet.
The pad gantry should be retracted to reveal the 12-story rocket just before midnight Tuesday. The overnight hours will be spent finishing preps ahead of starting the Terminal Countdown at 5:20 a.m. EDT launch morning.
The main question mark going into the launch attempt is the weather. Air Force meteorologists say there's a 50-50 chance clouds and coastal rain showers will interfere with the schedule.
"A tropical wave bearing the remnants of Hurricane Fred is currently over the Bahamas. The timing of this feature over the peninsula is the key forecast issue. Unfortunately, the wave has slowed its westward motion and is now forecast over our area Tuesday through Wednesday afternoon, increasing rain probability during the launch window," forecasters say.
"The main weather concern on launch day will be cumulus clouds and precipitation associated with this system.
"In the event of a launch delay, we will see gradually improving conditions as the tropical wave continues to move westward, away from the launch area."
The odds of acceptable weather on Thursday and Friday increase to 60 and 70 percent, respectively.
The STSS Demo mission has been in the works for years. Northrop Grumman built the spacecraft and was responsible for overall satellite integration, plus the ground control system. The satellites' sensors were made by Raytheon.
"The STSS Demo program represents an investment of approximately $1.5 billion in cutting edge technologies, spacecraft assembly and test, and spacecraft operations center capability," the MDA told Spaceflight Now.
The two craft, weighing nearly 5,000 pounds at launch and each having pairs of power-generating solar wings, are equipped with infrared and visible sensors to spot missile launches, track the vehicles through space and observe the entry back into the atmosphere. By working together from separate vantage points in low-Earth orbit, their imagery will combine to provide 3-D tracking of objects.
"The STSS satellites will demonstrate the unique value of a space-based sensor for the Ballistic Missile Defense System. Space-based systems have inherently long range, are not limited by geographic constraints, and collect infrared tracking and discrimination data that complements conventional ground and sea-based radars."
The U.S. government has long considered fielding constellations of missile-tracking satellites like STSS. Whether such a system is constructed could hinge on how these two demonstration craft perform.
For decades, the Defense Support Program spacecraft have flown in geosynchronous orbits to warn of enemy missile launches. Those satellites use infrared telescopes to spot the superhot plumes of boosters during initial ascent. But STSS is designed to identify and follow missiles throughout all phases of flight.
"STSS will demonstrate the key functions of a space-based sensor, passing missile tracking data to missile defense interceptors with the accuracy and timeliness necessary to enable them to successfully intercept missile targets," says Northrop Grumman.
"STSS is the U.S. Missile Defense Agency's only space-based midcourse tracking system. Using onboard sensors capable of detecting infrared and visible light, STSS will become part of land-, sea-, air- and space-based Ballistic Missile Defense System sensors."
The MDA has no funding or firm plans for developing any satellites beyond the two demonstration craft launching Wednesday. The real-life results from space using MDA's own missile test-launches, including two specifically configured for STSS viewing, could give the political boost needed for Congress to fund a future operational program.
"The greatest hedge against missile defense threats of all ranges remains a highly available early missile tracking capability from space. Decisions on any follow-on programs will be made based on the performance of the STSS satellites," MDA told Spaceflight Now.
The STSS Demo mission is expected to last two to four years.
These two craft follow a quasi-classified research and development testbed satellite launched in May aboard a Delta 2 rocket from Vandenberg Air Force Base in California. Valued at $400 million, that mission is known as the Advanced Technology Risk Reduction, or
STSS-ATRR.An earlier research craft called the Near Field Infrared Experiment, or NFIRE, was launched for the MDA in 2007 aboard a Minotaur rocket from Wallops Island, Virginia. It tested sensor technology to provide high resolution imagery of missiles and their plumes.
The Missile Defense Space Experimentation Center at Schriever Air Force Base in Colorado Springs is the control site for the four satellites under the MDA umbrella.
"Collections by all four satellites provide a unique opportunity to validate technology and sensor performance from different platforms," the MDA says.
Watch this page for complete live coverage of Wednesday morning's countdown and launch, including play-by-play updates and streaming video.
SPACE.com -- Experimental Missile Defense Satellites to Launch Wednesday
