HUNTSVILLE, Ala. — The U.S. Missile Defense Agency (MDA) plans to continue testing the use of Reaper unmanned aerial vehicles for ballistic missile target discrimination in the near term because taking that mission to space is still too costly.

The agency terminated plans this year to design and build a follow-on to the two orbiting Space Tracking Surveillance System satellites, which have been used to launch a ship-based SM-3 successfully against a target. “We want to go to space,” said Rich Matlock, director of advanced technology for 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 the near term.

Instead, MDA is experimenting with using unmanned aircraft to look up at targets, providing additional discrimination and targeting information. MDA has purchased at least four Raytheon MTS-B payloads for this purpose. But the goal is to test the upgraded MTS-C, which will incorporate a long-wave infrared detector into the system. Long-wave infrared is optimized for tracking cold bodies, such as missiles and warheads after booster burnout, or plumes and exhaust.

Ground testing will be conducted on the improved system in the next two months, Matlock said during a presentation at the 16th Annual Space and Missile Defense Symposium here Aug. 15. Flight testing is slated to start by the end of 2014.

Thus far, General Atomics Reapers equipped with the MTS-B (the standard payload used in Afghanistan and Yemen) have been used to observe missile defense tests. The MTS-B would expand the system’s capabilities. Ultimately, the MDA would like to see if stereo data collected from multiple high-flying unmanned aircraft could provide an off-board cue to launch an SM-3 from an Aegis ship. This capability was proven using the STSS satellites during a February flight test.

Though the MQ-9 Reaper has been used and will continue to be used in the agency’s tests, Matlock’s slide presentation included a picture of the Northrop Grumman RQ-4B Global Hawk as a possibility for this application.

“We still have a little ways to go to get to 65,000 feet,” Matlock said 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 acknowledged.

While UAVs are viewed as a near-term option as MDA continues to eye a space-based system for discrimination and targeting, these long-dwell systems are the objective platforms for carrying a yet-to-be-developed laser designed for boost-phase kill.

MDA canceled the YAL-1 747-400F-based Airborne Laser testbed after making 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 a system to build, maintain and field.

“It was a little bit of a bittersweet experience,” Matlock said of the program, which was led by Boeing. But lessons from the experience 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 option is to fly high — 60,000 ft. or higher — to get above the distortion presented by clouds in the atmosphere (eliminating some of the complex beam-control parts).

This should allow for simpler optics and reduced operating speed, Matlock said.

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 experts at the Massachusetts Institute of Technology Lincoln Laboratory, Mass.; Lawrence Livermore National Laboratory, Calif.; and the Defense Research Projects Agency to develop payloads. But the power and weight requirements of such a system are highly demanding, especially when coupled with an unmanned aircraft designed for long dwell times.

“Getting them from laboratory units to something that we can fly will take some time,” Matlock says.