By Edward Herlik

Colorado Springs, CO (March 18, 2008) – Military and commercial pioneers have turned to satellites for decades when requirements demanded persistence, access to hostile territory or 24/7 communication. Low orbiters can overfly a point of interest perhaps five times a day. Satellites operate above sovereign airspace making them politically and physically less vulnerable than aerial vehicles. Geosynchronous orbits allow essentially instant communications all day and every day, albeit at the cost of relatively large and expensive ground equipment. That capability is possible with much smaller satellite telephones by shifting the technology burden to a constellation of communication satellites in low orbits.

Those capabilities are being slowly and predictably duplicated on very long endurance Unmanned Aerial Systems (UASs). Traditionally termed UAVs for Unmanned Aerial Vehicles, capability developments include extending the endurance of conventional fixed wing systems to perhaps a week. Global Hawk variants will carry more fuel and Boeing has proposed a hydrogen powered system, for example.

To be truly persistent, a UAS cannot carry rapidly depleted expendables. Solar powered systems with fuel cell or battery storage seem to meet that criteria. NASA Dryden sponsored Helios, essentially a flying wing covered in solar panels with a high pressure hydrogen fuel cell that reached very high altitude in 2001.

That development continued in partnership with AeroVironment to produce follow-on UASs such as Zephyr (pictured above) and Centurion (pictured below). Those improved aircraft are designed to operate well above 20km as communication relays.

Given that conventional aircraft expend approximately 80% of their energy generating the forward motion required for lift, there has also been varying interest in lighter than air vehicles. Airships generate lift by trapping lighter than air gas and so expend energy only for flight operations such as propulsion and mission operations such as communication.

Under Chief of Staff General John Jumper, the Air Force worked toward airships for various missions including communications relay and optical surveillance. Those efforts were cancelled when he retired in 2005. Army Space Command is attempting to continue that work and has cooperated with Southwest Research Institute on several of the few flying prototypes seen anywhere. The Missile Defense Agency funded airship work for a time. Lockheed-Martin developed the High Altitude Airship (pictured below) proposal for coastal missile defense before it was cancelled without a flying prototype.

Sanswire proposed several variants on such airships though with rigid frames rather than the overpressure, nonrigid design favored by Lockheed-Martin. That civilian development included communications capability, such as cell phone service, and data relay in place of terrestrial cable. Work ended when Sanswire’s parent company experienced financial difficulties. Both Sanswire’s and Lockheed-Martin’s programs may return in some form.

UASs promise several significant advantages over satellites. Parking over a point for a week or longer, perhaps for as long as a year, significantly reduces the need for satellite service in that area. Ordinary line of sight radios are often sufficient for communications. Cell phones and tactical radios carried by combat infantrymen fall into that category. Photography is also much easier from 20 rather than 400 kilometers altitude. Payloads may be returned for maintenance or upgrade and do not require a space rating.

Space and the upper atmosphere pose very different hazards, though neither environment is benign. UASs avoid the hard vacuum and radiation of space while satellites are not subject to wind and little-understood weather hazards such as sprites. Overall, airships offer the least challenging combination of atmospheric conditions without the vibration and potential G-loading probable in fixed wing aircraft.

Finally, extreme endurance UAS operations will mirror satellite operations in that the customer will not be concerned with vehicle issues. The persistent platform will be flown to and held in a designated orbit while its payloads operate autonomously. Atmospheric vehicles will have become satellite-like in their performance and perhaps interchangeable in their customer’s perceptions.

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