With no near-term funding for a new satellite program to discriminate ballistic missile warheads from debris and decoys, the U.S. Missile Defense Agency is examining unmanned aerial systems (UAS) as an alternative.

The agency terminated plans this year to design and build a follow-on to the two orbiting Northrop Grumman Space Tracking Surveillance System (STSS) satellites, which have been used to launch a ship-based SM-3 successfully against a target. “We want to go to space,” says Rich Matlock, director of advanced technology for the MDA. But fielding a constellation of satellites capable of acquiring a target and tracking it through the midcourse of flight is far too expensive a goal for now. So the MDA is focusing on experimenting with using unmanned aircraft to look up at targets to augment discrimination and targeting information from a network of ground-based radars.

The MDA has purchased and been testing at least four Raytheon MTS-B payloads—the standard payload for the Air Force Reaper made by General Atomics. The goal, however, is to test the upgraded MTS-C, which will include multiple electro-optical sensors: long-wave infrared, mid-wave infrared, short-wave infrared, visible/near-infrared monochrome and a color/low-light television system. “MDA is testing the 'as delivered' capabilities of the sensor suite and making modifications to improve its capability for ballistic missile defense missions,” says the agency's Rick Lehner. The addition of the long-wave sensor in MTS-C is helpful in tracking cold bodies, such as missiles and warheads after booster burnout, or plumes and exhaust.

MTS-C ground testing will be conducted in the next two months, Matlock said during a presentation at the 16th Annual Space and Missile Defense Symposium here this month. Flight-testing of the sensor on a Reaper is slated to start by the end of 2014. But the use of a ground-based MTS-C during a ballistic missile flight test will begin next month and continue through 2017, Lehner says.

So far, Reapers equipped with the MTS-B (the standard payload used in Afghanistan and Yemen) have been used to observe missile defense tests. Ultimately, the MDA would like to see if stereo data collected from multiple high-flying unmanned aircraft could provide an offboard cue to launch an SM-3 from an Aegis ship. This capability was proven using the STSS satellites during a February flight test, but barring a replacement satellite system, the MDA sees UAS as a gapfiller.

Though the MQ-9 is being used in the agency's tests, Matlock's presentation included a picture of the Northrop Grumman RQ-4B Global Hawk as a possibility and Lehner says Boeing's Phantom Eye demonstrator could also be an option. The agency is “exploring experimental opportunities” to use these platforms, he says. General Atomics is under a $661,000 contract to establish sensor performance against ballistic missile targets; a follow-on contract worth about $30 million is expected shortly to demonstrate stereo tracking with two Reapers in a flight test.

“We still have a little ways to go to get to 65,000 ft.,” Matlock says of the UAV options. The Global Hawk, designed to fly higher than the Reaper, typically orbits under 60,000 ft. when fully loaded. It has not yet been used to carry such a payload or operate in this application in tests, he acknowledge.

While UAS are viewed as a near-term option, these long-dwell systems are the objective platforms for carrying a yet-to-be-developed laser designed for boost-phase kill, Matlock says.

The MDA canceled the YAL-1 747-400F-based Airborne Laser (ABL) testbed after its final flight last year. The massive chemical laser was used to demonstrate beam control, optics and the ability to use directed energy to shoot down a ballistic missile target. But it proved too complex to build, maintain and field.

“It was a little bit of a bittersweet experience,” Matlock said of the program, which was led by Boeing. Lessons, however, are feeding into the agency's plans for UAV-borne lasers.

ABL featured a bulbous nose that carried the optics necessary to focus and direct the chemical laser; this presented aerodynamic challenges for the aircraft. The goal with an unmanned aircraft solution is to fly at 60,000 ft. or higher to operate above the distortion from clouds in the atmosphere (eliminating some of the complex beam-control parts). This should allow for a more simple design in the optics and reduced operating speed, Matlock says.

The MDA is still chasing solid-state lasers, fiber lasers and hybrid lasers, he says, in an effort to avoid using caustic chemicals for the kill mechanism.

The agency is working with the Massachusetts Institute of Technology's Lincoln Laboratory; Lawrence Livermore National Laboratory, Calif.; and the Defense Research Projects Agency to develop payloads. “Getting them from laboratory units to something we can fly will take some time,” he adds.