Airships, blimps, aerostats, balloons, dirigibles, zeppelins – once aloft, these very different lighter-than-air (LTA) platforms look very much alike. They also tend to get lumped together with the worst LTA disaster in history, the fiery destruction of the German zeppelin Hindenburg as it was preparing to land at Lakehurst, N.J., on May 6, 1937.

That accident – which the majority of the 97 passengers and crew aboard survived – effectively ended what had been a highly successful and comparatively safe two decades of passenger, mail, and cargo service. The airborne ships carried thousands of passengers across Europe and to the United States and South America. In its two years of operations, the Hindenburg alone made more than 40 transatlantic crossings. Overall, it was a far less disastrous record than the history of ocean-going ships.

Airships also are the oft-forgotten heroes of World War II, floating above the ocean, on the lookout for Nazi submarines and other threats to Allied convoys. According to the U.S. Navy, of some 89,000 ships escorted by military blimps during the war, not one was lost to enemy action.

The government commissioned more than 150 blimps during World War II, some of which remained in service for the first decade or so of the Cold War, helping keep track of Soviet operations as part of the U.S. anti-submarine warfare (ASW) mission.

However, their inherent vulnerabilities and improving technologies on surface ships, submarines and ASW aircraft eventually led to the end of military airships, with the last retired from service by the U.S. Navy on Aug. 31, 1962. The Navy briefly considered bringing them back in the 1980s, but Congress canceled funding for the project in 1989. Several subsequent attempts to revive them also fell to the budget axe, including the Missile Defense Agency’s (MDA) High-Altitude Airship (HAA) as recently as 2007.

New technologies and materials appear to be giving LTA yet another chance to return to service as a viable platform for military and homeland security applications. Unlike many earlier versions, however, the 21st century vehicle – at least in the near term – is seen as an unmanned platform, with primary missions of persistent intelligence, surveillance, and reconnaissance (ISR) and communications relay.

And while the Navy was the primary operator of airships in the past, the Army seems to have taken the lead now, looking at a variety of concepts, from low (10,000 feet) tethered to high altitude (60,000 feet) free-flying platforms. Which is not to say the Army is alone. The Air Force, Navy, DARPA (Defense Advanced Research Projects Agency), Coast Guard, Border Patrol, and a wide range of companies, large and small, also have indicated interest and, in some cases, are actively pursuing research and development (R&D) programs.

When the subject of LTA arises, the general public tends to think of either the Goodyear blimp, floating a few hundred feet above an outdoor sporting event, or the Hindenburg in flames. Unlike the latter, which was filled with highly volatile hydrogen, nearly all subsequent airships instead use the inert gas helium to provide lighter-than-air buoyancy.

Ongoing U.S. R&D programs include DARPA’s Integrated Sensor IS Structure (ISIS); the Army Space and Missile Defense Command/Army Forces Strategic Command’s (SMDC/AFSC) HiSentinel, High Altitude/Long Endurance Demonstrator (HALE-D), Long Endurance Multi-Intelligence Vehicle (LEMV), and Rapid Aerostat Initial Deployment (RAID); the Army Program Executive Office Missiles & Space Cruise Missile Defense Project Office’s Joint Land-attack cruise missile defense Elevated Netted Sensor System (JLENS). Some are follow-ons to previously canceled programs, such as HAA.

“From a DoD perspective, an airship can provide continuous communications on the battlefield and stare you don’t have today,” Rick Judy, a space systems analyst at SMDC/AFSC’s High Altitude Technology Division, said. “From a homeland security perspective, it could be used when communications are lost, as happened during Katrina, or on the border, for surveillance; so anywhere, CONUS or OCONUS, where there is a need for continuous stare or communications, designed for whatever the mission requirement and operating area may be.

“The first thing we have to do is show the technology is viable, which we have not yet done. We have systems ready to go, so we just need to launch those, show what they can do, and then see what happens. If we show the technology is something that can be used, I believe you will see airships capable of giving you quick reaction, carrying specific payloads, launch on the battlefield, and probably heavy lift in the near future, taking payload where you need it, quickly. And possibly even transporting troops around the battlefield – although not over the oceans.”

On June 15, 2010, Northrop Grumman Aerospace Systems sector won a competitive bid for a $517 million contract from SMDC/AFSC to develop three LEMV systems within 18 months. LEMV is intended to remain aloft at 20,000 feet for up to three weeks. In addition, company officials say their design provides a plug-and-play capability to readily integrate into the Army’s existing common ground station command centers for unmanned aerial vehicles (UAVs).

“It is critical that our warfighters are equipped with more enabling integrated ISR capability to tackle today’s and tomorrow’s conflicts,” Northrop Grumman Program Manager Alan Metzger said. “Our offering supports the Army’s Joint Military Utility Assessment that this disruptive innovation must meet the Army’s objective of a persistent unblinking stare while providing increased operational utility to battlefield commanders. Part of our innovative offering includes open architecture design in the payload bay to allow sensor changes by service personnel in the field.”

The Army’s HiSentinel program, meanwhile, is looking at a high-altitude, solar-powered stratospheric airship, operating unmanned at altitudes exceeding 60,000 feet for 30 days or more. It is intended as a spiral development effort, leading to a family of low-cost airships carrying small to medium payloads (20 to 200 pounds) that can be tactically launched from remote, austere sites. The primary objective is to provide warfighters with a rapid-response communications relay, netcentric communications, and persistent ISR capability.

JLENS, which comprises two tethered platforms working in tandem, shares some aspects with the High-Altitude Airship demonstrator Lockheed Martin was building for the MDA until the program was canceled due to “budgetary constraints” in 2007. The JLENS aerostats are being built by TCOM (Elizabeth City, N.C.), under contract to Raytheon, which is producing the system’s surveillance and fire-control radars.

The first of the 242-foot-long aerostats made its maiden flight 10,000 feet above the Air Force’s Utah Test and Training Range, north of the Army’s Dugway Proving Ground, in April.

“The JLENS aerostat is a derivative of other aerostats being flown,” according to Army Deputy Program Manager Jonathan Williams. “It originally began with a 71-meter platform, but we needed a little more lift because of our weight and so are the only ones currently using a 74-meter aerostat. And that 3-meter change gave us much more volume and lift advantage.”

The semi-rigid aerostat is filled with helium, balanced with outside air to handle ascent and descent. It is designed to operate in up to 60-knot winds and survive up to 100 knots and to take lightning strikes, passing those through the tether to the ground without damaging any on-board electronics. Another part of the system is a mini-weather station that monitors nearby lightning strikes, winds, and storms, allowing the operators time to lower the aerostats to the ground if a big storm is approaching.

A JLENS “orbit” comprises two aerostats, one carrying a surveillance radar providing 360-degree coverage over a large area beneath for initial target identification. That is then passed to the fire-control radar on the second aerostat, which develops a more refined target ID. If the target is confirmed as hostile, its location is then passed on to appropriate weapon systems to engage.

“This mission is designed to go after cruise missiles, although we can see a lot of other things that help provide the battlefield commander with situational awareness,” said Army JLENS Product Manager Dean Barten. “For the cruise missile mission, we use an orbital altitude of 10,000 feet. At that point, we run out of tether.

“The radars put out a lot of power, enabling us to see small things at large distances, but putting that power system on the aerostat would take a lot of weight and reduce the size of the radar, so the power goes up the tether. The data also comes down the tether, so we can pump out a lot of data compared to transmitting by radio waves.”

JLENS is designed to remain airborne for 30 days, be brought down for about 8 hours of maintenance, then raised back to operational altitude for another 30 days. While the operation sounds relatively simple, it actually involves a large number of personnel and equipment.

As currently configured, a JLENS orbit or battery comprises 128 soldiers, two aerostats, three different surveillance radar ground control stations, and two fire-control ground stations – both using supercomputers – communications stations, a 110,000-pound mobile mooring station, a 70-foot tower for each aerostat, tractor-trailers to haul the mooring stations, and a power station with two diesel turbines per system.

Even so, Barten said, JLENS is a bargain compared to alternative ways to provide persistent, over-the-horizon surveillance and fire control defense against cruise missiles, UAVs, tactical ballistic missiles, large-caliber rockets, surface-moving targets, and enemy aircraft.

“Compared to something like an AWACS [Airborne Warning and Control System], which requires a huge runway, five aircraft, full crews, and maintenance, we’re probably about one-tenth the cost. And at that altitude, we’re also more capable than an AWAC,” he said.

Proponents of airships for persistent surveillance applications – in combat theaters, over national borders, as part of anti-smuggling and anti-piracy efforts, etc. – claim those increased capabilities at lower cost also apply when compared to the use of UAVs, satellites, and other manned aircraft, such as J-STARS. Indeed, some go so far as to claim the Navy and Air Force have deliberately thwarted airship programs that appeared to be succeeding to protect funding for those “sexier” and more expensive programs.

“Whether or not the people who control the expenditure of funds in the DoD or investment capital in the commercial sector are smart enough to pick up on this is something we can only speculate about, but the need is so obvious and the application so straightforward, it is almost pathetic it has not already been done,” said former Pentagon Director of Air Warfare Chuck Myers, a retired combat/test pilot who now runs a Virginia-based mini-think tank called AeroCounsel Inc.

Former Air Force Lt. Col. Ed Herlik, who worked on high altitude airship survivability issues at the USAF Space Command until 2006, agrees, but also believes those programs that are still under way are not likely to succeed.

“Mid-level and extremely high altitude are very different animals,” he said. “The mid-altitude cannot survive the environment. LEMV is designed to fly between 15,000 and 25,000 feet above sea level; ground levels in the operating areas of Afghanistan are equivalent to the Rocky Mountains – 15,000 feet – and have the worst weather in the world, which would destroy it even before the enemy could get a shot. It might have worked in Iraq, but it’s too late for that. So I would say the mid-altitude stuff is dead.

“Extremely heavy lift hybrid ocean-going ships have some potential, but will have to be hardened against weather. However, the extreme endurance ones that fly above the jet stream – about 65,000 feet – and operate like satellites have some potential because most of the problems there have been solved. The weather at those altitudes is very benign, especially at mid latitudes. You are above the jet stream, so wind is very predictable, steady state and slow. And if you control the air, there is no military threat, either.

“Radiation is really only UV, which is a fabric issue. It does create a problem for the payload bays, however, because you are not low enough for the air to insulate, but also not high enough for space to be an insulator. You are in the middle, where your biggest problem is arcing within the payload. So you really don’t want to be miniaturized, because that makes it easier for arcing to destroy your electronics. Or you need to be pressurized, which screws up the weight. That’s really not a bad problem, though, because you just use larger, easier-to-make circuit boards without going to extreme mini or rad-hard.”

Dr. Bob Boyd, advanced development projects program manager at the Lockheed Martin Skunk Works, has been working on a hybrid airship design that blends an aerodynamic shape with the buoyancy of a helium-filled envelope.

“We learned, surprisingly, these technologies all work pretty well and are as cost-effective as expected, with a lot of interesting applications. We’re trying to find the right avenues to employ the technology, but a lot of people think airships are old technology that we went away from because they didn’t work or couldn’t do the job,” he said. “It turns out some of the challenges that were difficult for the buoyant technologies to overcome 30 to 50 years ago have now been dealt with by today’s technology.

“For example, one of the biggest challenges in the ’20s and ’30s was flying over the ocean into weather they didn’t know was there because there was no way to see weather out there. Almost all airship accidents were due to that. In the modern era, you really do know what weather is out there, around the globe, all the time, so you can keep your buoyant system out of trouble. That technology wasn’t developed for airships, but it benefits the airship application.”

Lockheed Martin’s P-791 hybrid prototype also was used, midway through the decade, to validate a new air-cushion landing and ground-handling system.

“The mooring system was another challenge, with people going out and grabbing ropes. Even today, large vehicles require a truck. But our system allows the airship to self-moor, so you don’t require a ground system or giant mooring tower, which makes them far more practical,” Boyd explained. “It is much like a hovercraft. What looks like suction cups under the vehicle allow that, but also perform a gripping function that allow the vehicle to grip the ground in a parking mode.

“With a hybrid, we don’t have the same amount of helium lift as the weight of the system – perhaps 10 to 20 percent is aerodynamic, so when you slow down, the vehicle descends. As a result, you don’t have to release helium, which is a logistics nightmare. Helium is not really a lifting gas here, but a structural element designed to keep air out. The lift is actually a lack of air rather than a presence of helium.”

While LTA vehicles have been around for more than a century, in one form or another, and the only change in lifting gas has been from volatile hydrogen to inert helium, Boyd said there are four areas in which enabling technologies have enhanced their potential to return to military – and expanded commercial – service.

“Materials is No. 1. Airships are made of fabrics and the strengths of those fabrics now are many orders of magnitude higher per pound than in the ’20s and ’30s. And much, much lighter and more durable, enabling a lighter and smaller airship to carry the same payload for a significant improvement in efficiency,” he said. “Situational awareness is another, from understanding what weather you have to deal with now and two days from now to knowing where you are down to tens of feet, where you are flying and being able to control and handle that – and, in the case of unmanned, control from a long distance.

“Modern flight control systems are another. Airships are relatively easy to fly when the weather is nice, but a lot trickier when it’s not. Bringing modern flight technology to an airship enables a lot more capability than in the past, from flying in a lot more challenging conditions to taking off and landing in more difficult terrain. Fourth are subsystems technologies, such as our air-cushion landing system, modern air pressurization systems, helium detection – a variety of small-scale but helpful technologies that make the overall system more reliable, safer, and easier to maintain in the long term. And that robustness is really important for the military user.”

Not all LTA efforts are still in the lab or undergoing field tests. Since 2003, Raytheon Integrated Defense Systems has delivered more than 500 Rapid Aerostat Initial Deployment (RAID) systems to the Army for deployment in Iraq and Afghanistan.

“RAID systems are comprised of a sensor suite elevated on aerostats or towers. These are flexible, modular systems tailored to the customer’s situational awareness needs, provide force protection and serve as a force multiplier, allowing forces to focus on mission objectives,” said Raytheon’s RAID program manager, Peter Choate.

“The RAID program has established a level of credibility within the customer community which has enabled them to recognize and appreciate the value that elevated persistent surveillance systems provide the combatant. Based on this success, the demand continues to grow and the technology continues to improve.”

Power is a major challenge for long endurance LTA platforms, for both payloads and propulsion. Florida-based Sanswire Corp., working with Tao Technologies GmbH (Germany) and the University of Stuttgart, is proposing some new approaches to both.

Sanswire’s SAS-51, for example, is the world’s first solar-powered airship, according to the company’s vice president for operations, Dan Erdberg. Sanswire also is working with L-3 Corp. to incorporate ISR sensors on board its STS-111 Mid-Altitude/Long Endurance blimp, which they hope to begin flight testing by year’s end.

“Power is provided by a vectoring thrust internal combustion engine in the head segment, running on a fuel gas mixture that is compressed and fed into the engine. It is similar to natural gas cars, except ours are not carried in a liquid state but as a gas under pressure,” Erdberg said. “The entire tail section is filled with the fuel gas [an ethane mixture], which is neutrally buoyant, so you don’t change the dynamics of the airship as you burn fuel. We pump air into the tail to keep its shape.

“The inner bag contains fuel gas, the outer bag contains air. As fuel gas depletes, more air is pumped into the outer envelope to retain shape. Small winglets on each segment act as stabilizers and provide additional lift. We’re currently testing handling of the gas, which is combustible under pressure, and how to safely transport it. It’s not like hydrogen – there has to be some sort of ignition source beyond what happened with the Hindenburg, for example. There also is an opportunity to have it filled with helium and use solar and hydrogen fuel cells instead of the compressed gas.”

As with UAVs, which appeared and disappeared from military planning and R&D budgets for decades before finally gaining a solid foothold during the first Gulf War, lighter-than-air vehicles have gone from a highly successful record during World War II to occasional, short-lived efforts during the past half-century. But improved technologies, increasing demand from combat theaters in Southwest Asia to counter-piracy efforts off the coast of Africa to U.S. border patrol requirements have opened another opportunity for their return, especially when potential commercial applications are included.

“I would guess, if all the efforts are successful, within the next 10 years or so you would see some pretty sizable airships flying, hopefully with the heavy-lift capability to carry large amounts of payload – whether cargo, disaster relief, or even people – into whatever area it is needed,” predicted I. Steve Smith, HiSentinel program manager at Southwest Research Institute. “Like a lot of things, if you build it, they will come. I really believe, if you get something flying, people will come out of the woodwork with all sorts of applications, including flying small systems within the atmospheres of Venus and Titan, on which some studies already have been done.

“It’s hard to imagine what may be available 10 or more years from now in terms of sensors, although I would expect to see much lower power, weight, volume. Look at what we had only five years ago compared to sensor technology now; they’ve probably come down in all those by an order of magnitude. So you will see a lot more stuff and more frequencies, better able to sense what is going on, whether for military use, disaster relief, or research on other planets. Which means you can put a lot more stuff on a large airship or make a smaller airship. It all comes down to mass.”

This article was first published in The Year in Defense: Aerospace Edition, Summer 2010.