The race is on to develop unmanned aircraft that can safely share airspace reserved for civilian aviation.

There's both military and commercial interest in having unmanned aircraft that can fly unaided by human pilots, most of the time.

Initially, unmanned aircraft likely to be released for sharing airspace with civilian airliners will have the option to require a pilot. Eventually, however, they could go unmanned and fly into airspace used by manned airliners using devices on board and control centers on ground, industry data indicated.

The idea of civilian aircraft flying virtually at the mercy of unmanned craft cruising in their midst has delayed commissioning of such craft, both for practical and psychological reasons. But support for unmanned craft joining civil aviation is catching on, reports indicated.

Several companies are deep into research and development of optionally piloted aircraft. Among these, Aurora Flight Sciences of Manassas, Va., is experimenting general aviation Diamond DA42 planes to be able to market it as intelligence, search and reconnaissance planes.

Mav6 Blue Devil 2 airship has been designed to run pilotless or to have a pilot on board when required. The aerospace company, which has headquarters in Vicksburg, Miss., has designed the Blue Devil 2 airship to accommodate a pilot when necessary.

The 370-foot airship can hover at 20,000 feet for five days and function as a network hub for drones and ground sensors and as a surveillance craft.

Northrop Grumman used a pilot to show off their Firebird last year but the company says the plane can fly just as well without a pilot.

Industry analysts said the research and development drive toward pilotless planes was rooted both in defense priorities to deploy an optionally piloted aircraft in difficult conditions and in defense needs to find new uses for unmanned aircraft that are likely to be made idle with the pullout from Afghanistan.

Hundreds of Predator class unmanned aircraft and some high-flying Global Hawks planes are likely to become available with the drawdown in Afghanistan.

Support for letting unmanned craft fly in civilian airspace already exists. Exports point out that most unmanned aircraft fly on instruments and according to flight plans filed with the U.S. Federal Aviation Administration. Even as unmanned aircraft fly pilotless they are actually controlled from the ground or use instruments on board.

Aircraft flying below 18,000 feet depend more on visual flight rules and therefore are dependent on human control. For this reason, drones flying below 18,000 feet can only operate in designated flight corridors or predetermined air corridors with special permissions.

Current aviation research aims to change all that and make unmanned aircraft navigable in spaces usually populated by piloted craft. However, current technologies are too unwieldy to be deployed with effectiveness or safety.

Devices such as radar, cameras and transponders on board unmanned aircraft will need to be much lighter than they are now to make such craft safe to use in civilian air spaces. Experts have suggested different options to let unmanned aircraft fly but deployment in most cases may await successful introduction of sense-and-avoid technologies on board unmanned aircraft rather than with ground control.

Analysts said despite the support being given to unmanned aircraft sharing civilian air spaces, there were still unanswered questions about the market potential for the aircraft.

Many military establishments are likely to reject outright any mixing of civilian aviation with unmanned defense aviation until the craft can be designated 100 percent safe to use in environments over populated areas.