DARPA's Solar Powered Radar Blimp to Hover 12 Miles over Future Battlefields

A high-altitude reconnaissance and surveillance platform, the Integrated Sensor Is the Structure (ISIS) is a tall order—literally. The unmanned airship, which measures 450 feet in length, will soar 70,000 feet above Earth for up to 10 years. It's not exactly the Goodyear blimp, and—in case you haven't guessed already—it's designed to cover more than the Super Bowl.

ISIS, like all blimps, is filled with helium, but comparisons end there. Hovering in the stratosphere, safely out of range of most surface-to-air or air-to-air missiles, ISIS is designed to provide unsurpassed situational awareness with a surveillance range of 187 miles for individuals on the ground and 373 miles for advanced cruise missiles.

From its parking space in the heavens, ISIS will have an excellent vantage point for surveillance and tracking. For example, objects on the ground can't disappear from the view of ISIS behind trees or mountains. "It's not just point coverage, like a view of a city," says Perry Hamlyn, head of MITRE's Advanced Wireless Electronics department. "You can see significant areas of an entire region."

As its name implies, ISIS features a highly creative design that takes the performance-to-mass ratio to a new level. In comparison with a conventional airship, in which the payload is two or three percent of the system mass, the ISIS payload will approach 30 percent.

An Unmanned Sensor Requiring Less Support

The system study for ISIS began in 2004 at the Defense Advanced Research Projects Agency (DARPA). In essence, ISIS offers more intelligence for less cost. "The whole idea behind ISIS is that the cost of the logistics is reduced considerably," says Weiqun Shi, a group leader in MITRE's Advanced Wireless Electronics division. "You don't have people in the air; you don't have multiple planes to keep an orbit going. Once you've launched an airship, it could be used 24 hours a day, seven days a week, with no humans on board. Think of it as an enormous, autonomous, unmanned sensor with years of persistence in surveillance and tracking of air and ground targets."

ISIS offers a compelling cost savings over existing reconnaissance aircraft that depend on forward-based logistics. At an airspeed of 60 knots sustained and 100 knots in a sprint, ISIS can deploy globally in 10 days from a permanent ground station in the continental United States. Current costs associated with reconnaissance—a local air base, multiple aircraft for a single mission, air crews, ground crews, fuel supplies, and maintenance facilities—will no longer be required.



New Designs for Enabling Technologies

To develop a stratospheric, airship-based, autonomous, unmanned sensor requires new technologies. The challenge for ISIS is to integrate an extremely lightweight, phased array radar into an airship platform. This involves three enabling technologies: the hull material, active-array antenna, and power system.

The hull material, which has significantly reduced fabric mass over the current state of the art, is a key design feature. It has to be stronger, lighter, and last 10 times longer than conventional hull material. This is a huge task.

Another distinguishing characteristic of ISIS is that the performance of its active-array antenna is based on size, not power. The exceedingly lofty height of ISIS allows the integrated airship-radar to use its aperture—not high power—to meet radar performance requirements. This approach, which exploits the platform's size and at the same time conforms to its limitations on weight and power, allows for the elimination of heavy high-power electronics. In addition, low-power transmit and receive modules based on low-cost "cell phone" technology contribute to the design requirements.

Energy generation and storage present another significant design challenge. ISIS includes novel power systems for the airship that are based on solar-regenerative power. Solar cells collect energy from the sun and create hydrogen and oxygen from water during the day. At night, the hydrogen and oxygen are recombined in the fuel cell, which releases energy that allows the airship to operate after dark. Fuel cells were chosen for energy storage since they offer the best mass-to-energy storage ratio when compared to batteries and other storage systems.

"We developed solar availability and system energy models, performed trade studies, and provided technical support to ISIS from the early concept phase all the way up to the current demonstration phase," says Hamlyn. "Throughout the program, we have been helping the contractors and the government ensure the technical feasibility of the project."

Testing Viability of the Total System

In its capacity as a manager of federally funded research and development centers, MITRE is able to play a critical role in working with the various contractors associated with the ISIS program. "We have been involved in all major technical challenge areas and have influenced the contractors toward viewing the viability of the total system, not just individual parts," says Shi. "For example we have tried to help all those working on ISIS understand how much power the whole system needs and the trade-offs associated with various options."

"Even though each subsystem—airship, radar, and energy generation and storage—is defined individually, we're helping the individual subsystem teams understand the complex interactions," adds Hamlyn. "All the systems have to react appropriately to each other in order to make the ISIS system possible."

The Air Force and DARPA have signed an agreement to develop a small demonstration prototype by 2014. Currently, ISIS is in phase three, which includes demo system design, large-scale integration, high-fidelity flight test simulation, demonstration system build, and flight demonstration. Much more remains to be done between now and the 2014 airship demonstration. "We are looking forward to seeing a revolutionary new ISR [intelligence, surveillance, and reconnaissance] capability for the future battlefield," says Hamlyn.

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