November 3, 2011
During the past decade’s operations in Afghanistan and Iraq, the U.S. military has come to rely heavily on the continuous presence overhead of both manned and unmanned aircraft. Unmanned aircraft are particularly attractive for such missions because they can be designed to remain in the air beyond the physical endurance of human air crews and because they do not put people at risk during operations in potentially hostile airspace.
Airships—also known as lighter-than-air vehicles—have been proposed as alternatives to some of the aircraft (such as the Predator) that the Department of Defense (DoD) currently uses for those missions. At the request of the Chairman of the Senate Armed Services Committee, CBO examined DoD’s plans and proposals for airships in a collection of exhibits with descriptive text shown below.Recent Development Efforts for Military Airships
CBO’s Findings in Brief
Unmanned airships—such as those depicted in Exhibit 1—have the potential to remain in the air many times longer than would be practical for conventional aircraft. Consequently, the military services are exploring a variety of designs for unmanned airships capable of carrying ISR (intelligence, surveillance, and reconnaissance) sensors (see Exhibit 3). The technology needed to field airships for ISR could also be applied to airships meant for airlift (that is, the transportation of people, equipment, or other cargo). Whether airships designed to carry cargo would be manned or unmanned would depend on the specific missions they would perform.
CBO examined the potential capabilities of airships for ISR and airlift missions, and found that:
- If the speed, payload, and endurance proposed for unmanned airships can be achieved, the resulting craft could serve effectively in the ISR and airlift roles;
- Airships’ performance characteristics would provide some advantages and suffer from some disadvantages relative to those of the conventional aircraft currently used for ISR and airlift missions; and
- Airships would present new operational challenges such as greater sensitivity to weather conditions and the need to provide unique types of maintenance and support.
Because the development of the technology needed for modern military airships is at an early stage, in most cases cost estimates would be highly speculative; therefore, CBO did not examine the costs of airships. Although CBO compared the capabilities of airships with those of other aircraft, assessing their cost effectiveness would require analyzing costs as the relevant technologies are developed.
Use of Airships for Intelligence, Surveillance, and Reconnaissance
As shown in Exhibits 4 through 9, CBO examined two types of airships—high-altitude and low-altitude models—when providing comparisons with conventional unmanned aircraft systems for ISR. The Air Force and the Army have already entered into contracts to purchase low-altitude ISR airships for eventual use in Afghanistan. High-altitude models are in earlier stages of development. CBO found that:
- Unmanned airships have the potential to perform ISR tasks with greater efficiency than conventional unmanned aircraft systems, as they could remain aloft for much longer periods. Airships may also offer greater basing flexibility because they could operate without the need for a long runway, but they would probably offer less flexibility to operate in poor weather conditions.
- Like other unmanned aircraft besides stealth ones, ISR airships would probably be used primarily in secure airspace. If, however, airships encountered air defenses, their survival would depend on the specific circumstances of the engagement. Relative to fixed-wing aircraft, airships operating at high altitude (around 60,000 feet or higher) could be more difficult to detect and would be out of range for most surface-to-air missiles or guns. In contrast, airships operating at low altitudes would probably be easier to detect than conventional aircraft because of their lower speed and much larger size.
- Because airships sacrifice speed in exchange for endurance relative to fixed-wing aircraft, they might offer less flexibility to quickly shift the location of ISR orbits in response to changing circumstances on the ground.
- Advances in airship technology have not been tested in actual operations, and considerable risks remain. Many of the technologies needed for critical systems—propulsion and power, flight control systems, and sensors able to operate for weeks or months without maintenance—are in the early stages of development. Furthermore, the military has little contemporary experience operating, maintaining, and supporting airships, including, for example, storing the helium gas needed to fill airships.
Use of Airships for Airlift
As discussed in Exhibits 10 through 13, although most current interest in airships is in ISR platforms, airships could also be developed to move equipment, supplies, or people within or between combat theaters. Airships would have several advantages over other means of transportation. In particular:
- Airships are likely to rely on fixed ground facilities to a lesser extent than conventional aircraft, which need airbases, and ships, which need seaports. Airships, therefore, could deliver large payloads to locations that lack such facilities.
- Cargo airships capable of carrying a few hundred tons would offer larger payloads but lower speed than conventional aircraft, and smaller payloads but higher speed than ships.
- If airships prove to be as fuel-efficient as their proponents assert, airships might be able to operate at substantially lower cost than existing aircraft, although savings from lower fuel consumption could be offset by costs that have not yet been identified or quantified.
Airships used for airlift would still have the disadvantages discussed above for ISR missions, such as greater sensitivity to weather conditions and vulnerability to hostile fire if required to fly over unsecured territory. Whether or not airships would be worthwhile additions to the military’s mobility forces will depend on the progress of their technological development, their acquisition and operation costs relative to those of conventional aircraft, and the utility of their unique combination of payload, speed, and basing flexibility.
Alec Johnson, formerly of CBO’s National Security Division, prepared the analysis, with assistance from David Arthur.