Dubai Airshow

Lighter-than-air craft gaining favor in Mideast

 - November 12, 2007, 4:44 AM
Using gas for lift is hardly new, but interest in the idea is making something of a resurgence here in the Middle East.

The public’s perception of the usefulness of lighter-than-air (LTA) flight largely ended in flames with the 1937 crash of the Hindenburg, but the advantages of LTA are many and have increasing application to today’s surveillance requirements. Inert helium now gets used rather than hydrogen, and while it’s heavier, helium still offers excellent lifting properties–roughly equivalent to 1 kilogram for every cubic meter of gas.

LTA platforms fall into two categories: airships–manned or unmanned–and tethered aerostats. Both offer outstanding long-endurance surveillance capabilities with heavy and large payloads, at low cost. Aerostats operate at up to 15,000 feet, with an effective coverage of 245,000 square kilometers at a radius of 280 kilometers. Most feature an “intelligent” tether that incorporates power supply for the mission system, two-way fiber-optic datalink for sensor data and control, and lightning protection.

Aerostats have fins to keep them directionally stable in the wind. The vehicle keeps its shape thanks to a ballonade, an internal bag that gets filled with air on the ground. As the aerostat (or airship) rises, the helium expands, countered by air expelled from the ballonade. As it descends during recovery, air gets pumped into the ballonade to offset the shrinking helium volume. It takes around 40 minutes to winch down an aerostat from 15,000 feet.

Contrary to popular opinion, LTA vehicles are highly survivable, mainly thanks to the low pressure differential that allows them to sustain numerous tears in the bag. The bag itself is transparent to radar, so that the radar cross-section is very low–the principal source of RCS being either the mission equipment or the tether in the case of an aerostat. The radar transparency of the bag allows large radar antennas to be carried inside rather than as external loads.

LTA in the region
Worldwide use of LTAs for military surveillance continues to grow, especially here in the Gulf region. The United Arab Emirates has 71-meter and 17-meter aerostats, plus a rapidly deployable aerostat for security operations. Kuwait also has a 71-meter aerostat. Both Saudi Arabia and Iraq are also looking at aerostats for border security surveillance, and it is known that further aerostats will be deployed in the region next year, although the nation(s) has not been identified.

Based on the successful use of the Lockheed Martin Tethered Aerostat Radar System (TARS) along its own southern border, the U.S. has deployed several LTA systems for use in Iraq and Afghanistan.

Employing a 17-meter aerostat and carrying air surveillance and fire control radars, the Raytheon Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System–better known as JLENS–provides an air surveillance function, especially against low-flying cruise missiles. A JLENS was deployed to Afghanistan during Operation Enduring Freedom, but was subsequently relocated to Iraq. The JLENS system is thought to be migrating to an unmanned airship platform for Iraq operations.

Lockheed Martin’s Persistent Threat Detection System (PTDS) became operational in Iraq in October 2004 and uses a 32-meter platform carrying an L3 Wescam EO/IR turret and other sensors, integrated into a ground defense system. It provides a quick-response “eyes on target” capability. Further PTDS systems were deployed to the theater in 2006.

A bright future for LTA
According to Gregory Gottlieb, a lighter-than-air consultant speaking at AUVSI’s Unmanned Systems Middle East conference on Saturday, the future of the LTA platform is bright. In the U.S. the stratospheric airship presents a promising avenue for persistent surveillance and as an alternative to satellites for some tasks. The attractions compared with satellites are many, the most obvious being low cost, and the ability to recover the mission payload for replacement or repair. Another emerging technology is the hybrid airship that combines gas lift with aerodynamic lift to allow for much larger payloads. Different roles for LTA platforms are being actively pursued, including the civilian applications and the weaponizing of airships for military missions.