By the time this article appears, a new airship design supported by US military funding may have become the second to complete its first flight event this year.
A third airship programme is trailing a few months behind, with at least two more to enter flight testing within two years.
The resurgence of the buoyant aircraft type has been sudden, and the range of new designs diverse.
They span the range of altitude from 20,000ft (6,090m) to the stratosphere, of missions from surveillance to cargo, of lifting power from conventional to hybrid, of crewing from optionally-piloted to fully unmanned - and of endurance, from a few weeks to a decade.
Military spending leaves no doubt about the sincerity of the military's interest.
© Lockheed Martin
The Lockheed P791 hybrid airship (above) was defeated by Northop's SkyTug for the LEMV contract
In barely more than five years, a total of more than $1.13 billion has been invested in the US military's four biggest airship programmes, with a $149 million contract awarded to the Lockheed Martin high altitude airship (HAA) in 2005.
The US also handed $400 million to Lockheed for the Integrated Sensor Is the Structure (ISIS) in 2009, $500 million to Northrop Grumman in 2010, for the long-endurance multi-intelligence vehicle (LEMV) and $80 million to start-up MAV6, for the Blue Devil Block II airship.
Beyond those programmes are several groups working on smaller contracts, or still looking for support.
These include two new hybrid airships still looking for a commercial or military customer: Aeros Aeroscraft and the Lockheed/Aviation Capital Enterprises (ACE) SkyTug.
The latter is based on the Lockheed P791 hybrid airship, which was defeated by Northrop for the LEMV contract.
So far, military officials have not committed to continue any single programme beyond the prototype and demonstration phase.
Untethered, manned airships were once valued patrol vessels in the military inventory, but largely disappeared about 55 years ago as fixed-wing patrol aircraft reached maturity.
In the last decade, unmanned aircraft systems have redefined the expectations for long-endurance flights.
Frank Pace, president of General Atomics Aeronautical Systems (GA-ASI), recalled a time in the early 1990s when the company had to persuade the US Air Force that the Predator unmanned aerial vehicle (UAV) should be designed with 24h endurance, not 10h as the Air Force requested.
Now military officials in every branch want even more endurance than the 36h flying range of Northrop's RQ-4 Global Hawk.
The new objective for several development projects is to keep an aircraft on patrol for at least several days, if not weeks.
Options for meeting this ultra-long range requirement include hydrogen-powered fixed-wing UAVs, including the AeroVironment Global Observer and Phantom Ray. But the military also has funded Lockheed's HAA to meet the same requirement, leading to the high-altitude long-endurance demonstrator (HALE-D) taking the skies on 20 March.
Designed to carry a 226kg (500lb) payload with a 3kW onboard power supply, HALE-D was expected to demonstrate the feasibility of an airship performing a communications relay mission.
The airship's first flight, however, ended less than 3h after it began, due to an anomaly that is still being investigated.
The airship reached only a little higher than half the objective altitude of 60,000ft, before being commanded to descend.
Its payload was still transmitting data to the ground station even after the vehicle landed atop a patch of trees in southwest Pennsylvania.
Lockheed considers the flight a partial success, as the vehicle demonstrated both lift-off and a functioning payload.
The HALE-D is unusual, in that it is as an airship designed to fly above 60,000ft, but it is otherwise a conventional blimp that uses lighter-than-air gas as a lifting mechanism.
Such airships are limited by physics to lifting payloads that weigh less than the amount of air displaced by the gas envelope.
Lighter-than-air craft are also more difficult to handle on the ground, as winds can complicate the process of landing and unloading passengers or payload.
The alternative to these airships is a hybrid that relies on some combination of aerostatic, buoyant and aerodynamic forces to generate lift. Such hybrid airships have existed for nearly a century, but have seen a recent surge in innovation.
A new design of hybrid air vehicles mixes elements of a buoyant airship and a fixed-wing aircraft for lift, and a hovercraft for taxiing on the ground.
The design stems from the work of Roger Munk, an airship pioneer who died last year.
After HALE-D's first flight, the second airship scheduled to follow is the Northrop/Hybrid Air Vehicles' (HAV's) LEMV.
Munk founded UK-based Hybrid and spent a decade promoting the hybrid airship design, but died just a few months before it was selected by the US Army to perform a $500 million demonstration.
In late June, Northrop announced it had started inflating the first of 19 sections within the aluminium hull of the LEMV. Separately, the company had already received pylons, nacelles and production engines from German firm Centurion Engines (formerly Thielert).
As of late June, LEMV was still on track for first flight by late July or August. The location of the first flight is still undisclosed.
Northrop officials have discussed assembling the airship in either Tillamook, Oregon, or Lakehurst, New Jersey - both former airship bases.
Northrop vice president Alan Metzger, briefing reporters on LEMV at the Paris air show in June, declined to confirm the location.
The Northrop LEMV is still based on the hybrid design pioneered by Munk - and still bears his mark. Munk's contoured and flattened hull is still present, with a pair of longitudinal side lobes.
Unlike many previous hybrid airships, the LEMV does not have a circular cross-section. Its more elliptical shaping is designed to provide lift similar to an aircraft wing.
Indeed, the LEMV relies on aerodynamic shaping to generate nearly half of the vehicle's lift, with the helium-filled gas envelope providing the rest.
Underneath each side lobe is a pair of air cushions, which are intended to greatly simplify ground operations.
The air cushions help to moor the aircraft on land by sucking down on to the surface, eliminating the need to tie down the aircraft with ropes.
"Hybrid airships have been around a long time," Metzger said in June. "But there really hasn't been one built in modern times of this magnitude."
Following a roughly three-month period of flight tests, Northrop plans to deliver the LEMV to the US Army's Space and Missile Defense Command (SMDC) later this year.
The army intends to deploy the LEMV to Afghanistan, where it will instantly become one of the most capable intelligence-gathering assets in the country.
Northrop estimates that a single LEMV airship can perform the work of 15 equivalent fixed-wing medium-altitude aircraft.
Its intelligence payload includes nine independent systems, including a communications interceptor, four electro-optic/infrared cameras, three communications relay antennas and a synthetic aperture radar for ground moving target indication with 360º coverage.
LEMV, however, may not be the only new airship deployed to Afghanistan early next year.
The air force has quietly funded a more conventional airship - the M1400 - under the Blue Devil Block II programme.
It is being developed by US-based firm MAV6, a defence company now headed by David Deptula, a former lieutenant general who served as deputy chief of staff for intelligence, surveillance and reconnaissance until retiring in December.
Neither Northrop nor MAV6 officials consider themselves in competition with the other, although both vehicles are designed to provide a similar multi-intelligence capability at medium altitude. That is where the similarities end.
The M1400 "is based on a conventional lighter-than-air airship", Deptula said. For MAV6, the objective is drive a new revolution in intelligence, surveillance and reconnaissance (ISR) capability, not in airship design.
The air force intends to deploy to the M1400 early next year to Afghanistan with a variety of sensors - including possibly wide-area airborne surveillance systems, such as the Sierra Nevada Gorgon Stare.
Deptula envisions that the Blue Devil Block II programme can evolve into much more than just another medium-altitude ISR platform with longer endurance.
With computing power equivalent to 2,000 single-core servers stored onboard, the MAV6 vision for the M1400 is to become the central node in the air force's constellation of surveillance and intelligence aircraft.
FILTER MEANINGLESS INFORMATION
In this vision, surveillance platforms including the RQ-4, E-8C, LEMV, MQ-9 and others would transmit sensor data directly - via line-of-sight link - to Blue Devil, which would use its onboard servers to process the data and filter out meaningless information.
The remainder would be sent to ground stations, reducing the need for increasingly valuable bandwidth capacity.
"People are just beginning to realise the tsunami of data coming off these platforms," Deptula said.
Source: Flight International