Near Space Fills Communications Gap

Signal, Nov 2005 by Lawlor, Maryann

Extended connectivity emerges out of thin air.

The combination of a low-tech platform and a high-tech radio is extending beyond-line-of-sight communications from 10 miles to more than 400 miles. The approach employs small hydrogen balloons that are sent into the near-space realm-defined as from 65,000 feet to 325,000 feet above Earth toting two AN/PRC-148 radios that relay ground-to-ground, air-to-ground and ground-to-air voice and data communications. Although the capability was developed to address a combat-mission need statement and is scheduled to be deployed to theaters of operation in December, the benefits of this technique also could extend to homeland security as well as emergency relief efforts such as assistance in the aftermath of Hurricane Katrina.

The U.S. Air Force Space Battlelab, Schriever Air Force Base, Colorado, began exploring the prospect of using the near-space realm to extend military communication capabilities two years ago when it invited experts from academia, industry and the military to share information about their work in this field. Col. Patrick P. Rhodes, USAF, commander of the battlelab, relates that the inquiry revealed that commercial applications already were underway as was research and development of different types of vehicles and sensors. Encouraged by the data from these efforts, his organization began pursuing the work as a way to fill a gap in military over-the-horizon communications.

"The mission we were attacking was the needs of the tactical air control parties [TACPs]-the guys who are on the ground. The TACPs have to have line of sight with airplanes and/or their fellow ground members to communicate with a handheld PRC-148 radio. We said, 'Let's see if we can shorten the time chain for passing information.' So we took a couple of PRC-148 radios, pretty much duct-taped them together and made them a trans-receiver if you will," Col. Rhodes explains.

Space Data Corporation, Chandler, Arizona, provided the maneuverable platform to transport the radios into near space: hydrogen-filled latex balloons that are approximately 10 feet in diameter and a 6-pound payload that includes the vetting and ballasting equipment, a parachute and a tracking device. Free-floating balloons travel at the whim of the wind, and the company spent substantial time on vetting and ballasting systems research and development so ascent and descent could be controlled. As a result, the platform can be positioned at an altitude where wind speed is minimal, which is in the 80,000-foot range, and remain there.

Persistent connectivity can be accomplished by a technique called constellation replenishment, Col. Rhodes explains. "Depending on the winds aloft, your area of regard may be traversed by the balloon in from 3 to 12 hours. So if the current balloon is beyond the area that you're interested in, you launch another balloon. These balloons last, and in the commercial effort in Arizona, they launch an average of around three balloons a day, twice a day," he says.

When connectivity cannot be maintained or is no longer needed, a parachute-release system brings the radios to Earth where they may be recovered. Free of the weight, the balloon ascends until it bursts just like a weather balloon. However, work is currently underway on a new recovery system that involves a glider that could be programmed to deliver the radio or sensor payload to a specific location.

To examine the feasibility of the radio-bearing balloons in military applications, the battlelab conducted a proof of concept demonstration in March called Combat SkySat. Lt. Col. Richard A. Lane, USAF, director of initiative demonstrations, Air Force Space Battlelab, explains that the battlelab team chose the AN/PRC-148 radio because it weighs less than 2 pounds and the bandwidth range is from 30 to 512 megahertz. Thals Communications Incorporated, Clarksburg, Maryland, manufactures the radios. Space Data can package two radios into a payload that weighs less than 6 pounds, which facilitates coordination with the Federal Aviation Administration.

"Space Data has their own repeater in the 900-megahertz range, and the [circuit] card weighs ounces versus 5 pounds for two PRC-148s. So that's how we see the future: an even more disposable circuit card versus full-blown flying two radios hooked together," Col. Lane offers.

Prior to Combat SkySat, the battlelab team conducted eight test flights because the AN/PRC-148 had never been used at high altitudes and the team was concerned it might not operate in the thin-air environment. Although performance was good, some overheating took place in the 95,000-foot range, the colonel says, so the engineers decided to keep the balloons in the 65,000- to 75,000-foot range for the demonstrations.

Three communications scenarios were explored during the three-day event: ground to ground, air to ground and ground to air. Several communications bands were examined, including AM, FM, ultrahigh frequency and very high frequency. Both secure and nonsecure modes also were studied.