Unmanned aerostats furnish vital geospatial intelligence

Sensor payloads perform at optimum levels in benign environment

Persistent stare aircraft aren’t new. But tethered aerostats — unlike free-roaming blimps — can carry quickly reconfigurable sensor payloads and stay aloft for weeks or months of intelligence, surveillance and reconnaissance. Several dozen currently hover above Afghanistan.

Sensor technology is the linchpin. Each aircraft’s payload array typically includes Global Positioning System, radars, full-motion video, electro/optical (E/O) systems and infrared sensors.

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Variants now in demand include the Army’s Persistent Threat Detection System and Persistent Ground Surveillance System. PTDS contractor partners are Lockheed Martin, L-3 Communications and Northrop Grumman. The U.S. Naval Aviation, in conjunction with SRI International's Sarnoff unit, oversees the PGSS program.

PTDS is a tactical solution that enables links among ISR assets, cuing ground forces to positions of insurgents, including those who plant improvised explosive devices. 

“PTDS flies an industry-leading [L-3 Communications WESCAM MX20Lite] EO/IR sensor with laser rangefinder," said Lt. Col. Robert Helms, the Army's product manager for robotic and unmanned sensors. "Full-motion video is output directly to the supported tactical operations center and disseminated via a Web portal on the theater network."

Some aerostats also have Northrop Grumman’s STARLite Ground Moving Target Indicator/Dismount Moving Target Indicator radar integrated and deployed with the WESCAM sensor.

PTDS allows flexible integration of different payloads. “Modular, independently switchable power supplies, a multiport Ethernet switch, and several payload mounting locations are available…. Integration and certification is a brief, straightforward process,” Helms said.

Nine PTDS sites fly two MX20 STARLites, and five have both a STARLite radar and an MX20 camera. The technology provides commanders a decisive advantage in spotting enemy forces. The latest PTDS iteration launched in April.

“PTDS [now hosts] a wide array of sensors," Helms said, adding, "Communications suites are also being upgraded in support of the C5ISR Task Force,” encompassing, for example, the Single Channel Ground and Airborne Radio System and AN-PRC-117G radios.

Soon, a second EO/IR sensor will appear on all deployed PTDS aerostats, and Helms hopes to install the Kestrel EO/IR wide-area sensor by this December. Once deployed in theater, they’ll “get configurations to enhance the communications architecture.”

Helms said PTDS “has proven very robust [and is] performing magnificently…with 95 percent operational availability and high [meantime between failure] for all components. The EO/IR sensors have MTBFs well beyond specifications.”

Future integrations are on the table without “jeopardizing our ability to support the rapid fielding of systems,” he said.

"The beauty is that it provides a benign operating environment for any payload," said Ron Browning, Lockheed Martin’s program manager for PTDS. "You don’t get any G-loads or shock loads and very limited vibration.” Also, compared to other systems requiring constant, performance-degrading on/off switching, PTDS’ 25- to 30-day duty cycle means “you turn on once, and turn off a month later.”

Browning noted the different lens-and-camera types packaged in the aerostat’s L-3 multihead WESCAM turret system. “Operators choose the one that will provide the best picture, given the mission and conditions, such as time of day.”

The military has a strong preference for sensors that can rotate 360 degrees because the aerostat can't be pointed, Browning said. “So we can look out to the sensors’ sweep limit, maybe doing that times two if there are two MX20s on board.”

Browning could not speak about recent aerostat/Shadow unmanned aerial vehicle tests using the Joint Tactical Radio System radio, but he said that “when you have an aerostat at 3,000 to 5,000 feet above ground level, you in essence have an antenna that high. So in terms of a relay capability for different radios and frequencies, you certainly [can] now provide that interaction…. The data can be streamed into a network” for multiuser access.

Lockheed Martin’s role is “overall system integration, combining different sensors’ capabilities into a system providing best possible output" for operators and soldiers, Browning said. "So it’s architecture, software, the physical installation and the transmission of data.” Being able to fly “where nothing else can and…having that capability overhead on a near-continuous basis is very attractive.” 

Lockheed Martin has sold and delivered 37 PTDS aerostats to date, and the Army has contracted for an additional 29.

John Jadik, Northrop Grumman's vice president of weapons and sensors systems, said the all-weather, all-temperature, day-and-night capable, GPS-equipped tool boasts four modes that are specific to the company’s STARlite:

  • Synthetic Aperture Radar: Generates an Earth map that’s transmitted to ground stations for analysis; creates overviews and specific object images, such as buildings, fences and stationary cars; facilitates mission planning for possible direct assault; and helps assess potential collateral damage.
  • Coherent Change Detection: Reveals tiny differences in maps of the same area over time, revealing disturbed earth and moved vehicles.
  • Moving Target Detection: Sees objects of interest up to 360 degrees around the PTDS. Data is laid over ground station maps, letting operators cue the optical sensors for positive ID, tracking and target designation.
  • Ground Moving Target Indicator: Pinpoints suspect vehicles from wide terrain and tracks them from start to endpoint.

The magic of STARlite-enabled PDTS “is that it [overlooks] a forward operating nase — a captive asset supporting your particular mission, so you’re not vying for priority" with other organizations, Jadik said.

DOD managers PGSS at the Naval Air Station in Patuxent River, Md. The program appears less mature than PTDS, though the lower-altitude aerostats are smaller than PTDS and can link to them.

PGSS' key sensor is TerraSight, a suite of video exploitation software and attendant ground station components from SRI International’s Sarnoff subsidiary. This C4ISR-enabling tool “fuses multiple real-time video and data feeds, overlaid onto a 3D terrain map for a complete operations-surveillance picture,” said Vince Peragano, Sarnoff's product development lead for TerraSight.

Operators view “one or more videos from the air, perfectly geo-registered and aligned to the underlying referenced terrain, giving…much larger situational awareness than just one camera’s field of view," Peragano said. "Every pixel has an accurate coordinate.”

The ground station “helps the PGSS deploy quickly and provide full situational understanding where it’s needed most. He said PGSS and PTDS have been tested together, and about 100 PGSS TerraSight systems are in Afghanistan. Of those, perhaps a third have been set up.

TerraSight can work with many mobile Army radars, Peragano said, including ARSS on Cerberus, M-STAR and SR-HAWK. In addition, “we have certification so we can be on classified nets, including SIPRNet, NIPRNet and Afghan Mission Network,” and the system can tie to the Force XXI Battle Command Brigade and Below blue force tracker.

In mid-May, DOD and Army hosted a successful demonstration of a TerraSight-equipped PGSS at Fort Belvoir, Va.

About the Author

David Walsh is a special contributor to Defense Systems.

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