US$10 million skin for DARPA's remarkable ISIS stratospheric airship

“Once we solve the antenna weight, size, and integration challenges, ISIS must contend with the fifth challenge, annual wind storms. These can last for several days and exceed 80 knots in some locations. This will challenge the airship’s ability to stay on station. The propulsion power scales as the cube of the wind velocity, so we must find a way to store large amounts of energy in reserve for use during peak winds. We will need technologies with ten times the specific energy density of today’s lightest batteries.

“The airship itself presents another challenge. The airship’s ability to lift mass scales in proportion to its volume, but the wind drag and propulsion power only scale in proportion to its cross-sectional area. Therefore, as the size of the airship increases, the lifting ability grows more than its drag. If the airship can be made large enough, the severe mass limits on the antenna and the energy storage systems can be relaxed.

“Conventional airship concepts are limited to about ten million cubic feet, due to ground handling issues. We are open to new ideas for airship and ground handling concepts that overcome these limits and allow the airship to grow much larger. The final challenge is to take full advantage of the unique features of ISIS which have never been available in any previous radar system. For example, ISIS will have an extremely narrow beamwidth and operate from a fixed location continuously for a year or more. This means that ISIS can deal with clutter in a totally new way.

“We have entered the final phase of the Knowledge-Aided Sensor Signal Processing and Expert Reasoning program (or KASSPER). KASSPER makes use of a significant amount of information about site specific details and prior sensor collects. KASSPER uses this information to get a much better estimate of the clutter competing with the target returns.

“Focusing on airborne GMTI systems, KASSPER incorporates a “look-ahead” process where the critical information is sent to the radar high-speed adaptive processors for real-time use in clutter estimation. We have a demonstration set-up at the SPO booth where you can see the dramatic improvement KASSPER provides in radar performance. As an example, SAR imagery can be used to locate the large, stationary scattering points. This can reduce the false target detections by 12dB over conventional space-time adaptive processing algorithms. If we can get this kind of performance improvement for a relatively small radar, constantly moving over different terrain, just think what we might be able to do with ISIS!

“We would like to hear your ideas for how we can take advantage of ISIS’s unique persistence capability to extend the KASSPER concept to provide even better performance in high clutter urban areas. A one year feasibility study is just beginning. It is important for us to get the best ideas from many different disciplines in order to make the ISIS program a success. Therefore, toward the end of the year, we will be hosting an ISIS workshop to bring interested system integrators and component developers together to discuss the ISIS concept and technology challenges Early next year we will put out a BAA for the ISIS technology development and objective system design. As I have already discussed, careful attention to the integration of every subsystem is critical; therefore we will require that teams be formed to address the total design and development of ISIS.

“ISIS will have sensor capabilities never before achieved. It will have unprecedented sensitivity, an extremely narrow beam and continuous year long persistence from a single location ant 70,000 feet. My challenge to you is this – think about ways to address the following: weight, calibration, beamformer, integration, power, and signal processing issues. I further challenge you to go beyond that and think of ways to use ISIS capabilities to enable new classes of IFF, target identification, communications, intelligence or something else completely new.

“If the idea is innovative enough, we may even consider starting a whole new program to address it.

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