WASHINGTON — In response to the U.S. Defense Department’s growing need for aerial surveillance and reconnaissance in Afghanistan, Lockheed Martin Mission Systems & Sensors is ramping up production of its 35-meter tethered airships, known as aerostats, a company official said June 2.

Bethesda, Md.-based Lockheed Martin’s lighter-than-air Persistent Threat Detection System (PTDS) craft are designed to provide around-the-clock surveillance to protect convoys, detect improvised explosive devices, observe the battlefield and provide communications links. The aerostats were first deployed operationally by the U.S. Army in 2004, and the service had fielded nine of them by the beginning of 2010.

Lockheed Martin was under contract to deliver 20 PTDS units to the Army, and on April 14 received a $142.1 million preliminary contract to begin work on another 17 units, according to a Defense Department press release. The final contract for full construction of the units is still being negotiated, Ron Browning, Lockheed Martin’s director of business development for lighter-than-air programs, said in an interview. By this fall, Lockheed Martin is expected to have delivered all 37 PTDS units, he said.

The additional PTDS units are part of a larger effort to put more eyes in the sky to watch over coalition forces in Afghanistan. Ashton Carter, the Pentagon’s top acquisition official, in April said the department is increasing by a factor of 20 the number of airships in Afghanistan.

The PTDS aircraft are filled with about 2,100 cubic meters of helium and float between 800 and 1,500 meters above the ground, connected to a trailer-mounted mobile mooring station with a tether. The tether not only serves to hold onto the aircraft but also provides power to the system’s payload and contains fiber optic cable for transmitting data to and from the payload, Browning said. Ten Lockheed Martin personnel operate each PTDS unit in the theater.

The PTDS primary payload collects visible and infrared streaming video that can be delivered to troops on the ground almost as soon as it is collected. The aerostats also can be used to host communications payloads, connecting troops who are not within line-of-sight of one another, Browning said. Under optimal conditions, the PTDS provides a coverage area with a radius of about 160 kilometers, he said.

“This system gives you a lot of opportunities to tailor mission equipment that you might want to attach for different missions, so you’re not constrained to a certain box,” Browning said.

Many of the PTDS components are purchased from other companies. The flexible envelope that gets filled with helium  is manufactured by ILC Dover of Frederica, Del., and the various payloads come from other companies, Browning said.

Army spokesman Brandon Pollachek was unable to make Army officials available for an interview by press time.

In addition to their use in U.S. military operations abroad, Lockheed Martin also provides lighter-than-air craft for homeland security missions. A larger variant of the company’s aerostat called the Tethered Aerostat Radar System has been used since the 1980s for border monitoring, Browning said. Six of these 64-meter-long blimps dot the United States’ southern border performing counter-drug and air sovereignty missions, and are also capable of some surface monitoring, Browning said. Two more of the craft float high above Florida and Puerto Rico.