High Altitude Airship
The capabilities of airships to provide a very effective radar platform have long been recognised, but only now, as enabling technologies have been developed, is this programme beginning to mature. One use that the airships are particularly suited for is in providing a long-endurance high-altitude platform for radar and other surveillance systems. This capability has come into particular focus in the USA following the events of 9/11 and have caused all departments tasked with securing the countries borders to consider how a more effective system can be deployed.
North American Aerospace Defence Command (NORAD) have plans to deploy 11 high altitude airships to provide overlapping radar coverage of all maritime and southern border approaches to the CONUS. The unmanned airship, known as the Stratospheric Platform System (SPS), would be capable of maintaining an almost geostationary position at around 70,000ft, well above the jet stream and other weather features. The prototype SPS will need to be capable of lifting a payload of 2 tons to 70,000ft be able to be controlled from a ground station and provide an unobstructed view for the onboard sensors – future developments may eventually see an SPS developed with 5 or 6 times greater payload capability.
Filled with helium to provide lift, the SPS would need to be capable of generating a considerable amount of energy and converting this into sufficient thrust to remain on station. It would clearly be impractical and inefficient to carry large amounts of fuel internally and so the SPS will be have to be capable of generating most of its thrust requirements on station. The power requirements will be met by a combination of thin-film photovoltaic (PV) cells, capable of generating voltage from sunlight, mounted on the external surface of the SPS, together with internal fuel cells to provide power during periods of darkness. In theory, the SPS should be capable of remaining on station for up to six months at a time, provided helium loss is kept to a minimum and sufficient electrical power can be generated.
On 29 September 2003 the Missile Defense Agency (MDA), which oversees the High Altitude Airship (HAA) programme, selected Lockheed Martin's Maritime Systems & Sensors sector based in Akron, Ohio, to build the unmanned lighter-than-air vehicle over competing bids by Aeros and Boeing. Lockheed Martin's highly autonomous, helium-filled design is 152.4m long, 48.7m in diameter, with a volume of 1.5 million m3, said Ronald Browning, the company's director of surveillance systems business development. It carries four electric motors with vectorable large twin-bladed propellers, two on each side of the vehicle. Barber characterised the airship as "a great marriage" of old lighter-than-air technologies and new innovations. The latter include high strength-to-weight ratio materials for the airship's skin and thin-film photovoltaic cells to generate power from sunlight for the vehicle's propulsion and the additional 10 kilowatts necessary to operate the airship's payload. The company is now under a $40 million contract to mature its airship design through a critical design review in mid-2004. Much will hinge on the success of this programme, provided the airship performs as planned it will probably usher in a platform that could be used for many other applications.
By early 2007 it became apparent that, despite many new technologies and advances in this area, Lockheed were still struggling to achieve the design goals of the development programme. The difficulties of attempting to balance payload weight and available power still appear beyond current technology and in early 2007 it was announced that the programme would be terminated. However, the requirement for this platform remains extant and I doubt we have heard the last of this of this concept. As and when the necessary technology is sufficiently mature, I imagine the High Altitude Airship will once again re-appear.