BOSTON – The Defense Advanced Research Projects Agency (DARPA) has awarded contracts to three companies to design a system combining many of the most attractive features of satellites and unmanned aerial vehicles.

Dubbed “Vulture,” the system is envisioned as an unmanned aircraft that can loiter over areas of interest for five years at a time, according to an April 21 DARPA news release.

Jan Walker, a DARPA spokeswoman, said the agency does not envision a point where aircraft can entirely replace satellites. Satellites offer features including far less vulnerability to enemy attack than aerial systems, Walker said in an April 24 written response to questions. Vulture is envisioned as sharing satellites’ ability for remote software upgrades from the ground, she said.

An aircraft like Vulture could offer far greater persistence and sensor resolution than a low Earth orbiting satellite, she said. The Vulture concept also could allow for on-station repair and hardware upgrades, a capability the military will not have with its satellite fleet until it develops an operational variant of a system like Orbital Express, an autonomous rendezvous spacecraft that DARPA demonstrated between March and July 2007, Walker said.

A system like Vulture also could have better ability maneuver to avoid a potential attack than a satellite, she said.

“Vulture will leverage space satellite operations and design paradigms, in which long life and extreme reliability are routine, and bring this concept to the realm of aircraft operations, in order to provide a level of mission reliability previously unknown in aircraft operations,” according to the DARPA news release. “Vulture will provide pseudo-satellite benefits such as increased platform availability and consistent and persistent coverage, and allow smaller fleet sizes.”

DARPA awarded a one-year contract worth $3.6 million to Aurora Flight Sciences of Manassas, Va., on March 19; and on April 17 awarded one-year contracts worth $3.8 million to Boeing Integrated Defense Systems of St. Louis; and $4.3 million to Lockheed Martin Skunk Works of Palmdale, Calif., Walker said.

The companies will develop possible options for vehicle designs that focus on reliability and mission assurance, as well as risk reduction plans for key technology, according to the DARPA news release. The companies are not developing payloads, though a payload is expected to be included in flight tests planned for later in the program.

Crucial aspects of the system likely will include the ability to collect energy or be refueled in flight, in-flight docking and transfer mechanisms, and highly efficient propulsion systems, according to the DARPA news release.

DARPA will make a decision on whether to down-select between the current contractors following completion of the one-year contracts, Walker said. The agency has not yet decided how many contracts will be awarded for a flight test involving a subscale version of the Vulture concept that would stay aloft for three months, or a full-scale demonstrator that will stay up for one year, or when those demonstrations will take place, she said.

DARPA’s 2008 budget for the Vulture program is $6.5 million. The agency is requesting $11 million for the effort in 2009.

Boeing noted in an April 21 news release that one of its key teammates for the competition, QinetiQ LTD of the United Kingdom, currently is developing a solar-powered unmanned aircraft intended to fly at high altitudes for long periods of time. That aircraft is being developed for both the U.K. Ministry of Defence and U.S. Defense Department under the Zephyr Joint Capabilities Technology Demonstration. QinetiQ will leverage technology developed under the Zephyr effort for the Vulture program, according to the Boeing news release.

The vehicle developed under the Vulture concept is intended to be capable of carrying a 454-kilogram payload that operates with 5 kilowatts of power, according to the Boeing news release.

Aurora also is working on a solar-powered concept for the Vulture competition, according to an Aurora news release issued April 21. That vehicle would operate in the stratosphere for the duration of its mission, according to the news release.

This type of vehicle could have a wide-range of applications ranging from providing telecommunications to an entire region to weather prediction and climate research, according to the Aurora news release.

Melissa Dalton, a Lockheed Martin spokeswoman, said that Skunk Works is collaborating with Lockheed Martin Space Systems to best blend the capabilities of airborne and satellite-based sensor and communications platforms on the Vulture effort.