In aviation and in space, a drone refers to an unpiloted aircraft or spacecraft. Another term for it is an “unmanned aerial vehicle” or UAV. On Earth, drones are often used for military purposes because they don't put a pilot's life at risk in combat zones. Also, drones don't require rest, enabling them to fly as long as there is fuel in the craft and there are no mechanical difficulties.
Technically speaking, space-borne drones could include cargo spacecraft, satellites and machines that leave Earth, although they aren't usually referred to as such. Perhaps the best example of a drone in space is the U.S. military's mysterious X-37B spacecraft, which has made multiple flights into orbit for hundreds of days. Its mission is highly classified, leading to speculation about what it is doing.
Drones have been around for almost as long as airplanes have been used in warfare (1911), and that's not even including bomb-filled balloons that were first used by Austria in the mid-1800s.
The Navy developed some limited "air torpedoes" during World War I, but left the concept aside until World War II. At that time, according to The Nation, the Navy began a program called Operation Anvil. Remote-controlled B-24 bombers were used to deliver explosives to German bunkers, but the program was a "disaster," according to the article. Many planes crashed or exploded prematurely.
For decades afterwards, the United States focused on using rockets while doing some development into drones. The first big demonstration of them came during the 1991 Gulf War, when the United States deployed UAVs – showing how advances in computer technology made it possible.
It's a difficult job today to keep track of the number of drones being used. In the Air Force alone, it has been reported that nearly one in three of its aircraft are drones; that's 7,494 UAVs in 2012. Outside of the United States, at least 50 other countries are reported to use unmanned aerial vehicles.
Drones for other applications
In the United States, the Federal Aviation Administration has been cautious about allowing unpiloted vehicles to zip around. There are numerous safety concerns – they could crash into buildings, interfere with airspace or cause other problems.
In February 2015, however, the FAA moved to allow limited use of drones. The draft rules would keep the aircraft within the operator's line of sight, limit flights to daytime, and also regulate matters such as how the operator is certified.
Should the drones be approved for agricultural use, it has the potential to revolutionize the industry. In an article for The Conversation, drones were mentioned as part of a network of technologies to help out farmers, including GPS, autonomous machines and creating more robust varieties of plants.
Certain companies are also considering sending out drones to do deliveries, which could reduce the cost of using drivers for door-to-door service. Amazon is advertising a future service called "Prime Air," which is intended to send deliveries to customers in 30 minutes or less. They have written a letter of application to the FAA for this service.
Drones are sometimes used by government agencies for safety reasons, such as monitoring storms and hurricanes without putting pilots at risk. One example is the Hurricane and Severe Storm Sentinel (HS3), a five-year test program using unmanned surveillance aircraft called Global Hawks. It's a collaboration among NASA, the National Oceanic and Atmospheric Administration (NOAA) and Northrop Grumman. Other reported uses of drones have been in applications such as search and rescue and in-air 3-D mapping.
Drones in space
Perhaps the closest thing to a UAV in space is the X-37B, which looks like a miniature version of NASA's now-retired space shuttle. The unpiloted spacecraft has had three missions and was deployed on a fourth in May 2015.
Most of its work is highly classified, making it difficult to say what it does up there for so long. However, the Air Force has some information available about the fourth mission. In an e-mail with Space.com in May 2015, Air Force spokesperson Capt. Chris Hoyler said the X-37B would have an experimental propulsion system and an investigation into how well materials perform in space.
"We are excited about our fourth X-37B mission," Randy Walden, director of the Air Force Rapid Capabilities Office, said in a statement in May 2015. "With the demonstrated success of the first three missions, we’re able to shift our focus from initial checkouts of the vehicle to testing of experimental payloads.”
While not technically called a drone, it could be argued that several of the spacecraft that visit the International Space Station are unmanned aerial vehicles as they carry only cargo on board, with no pilot. There are several of these vehicles, including Russia's Progress spacecraft, the (now-retired) European Space Agency Automated Transfer Vehicles, SpaceX's Dragon and Orbital Science's Cygnus.
From time to time, a space agency will test vehicles in space before putting people on it, which happened in the Mercury, Gemini and Apollo programs. (The space shuttle was never tested without pilots on board.) In 2014, NASA sent its Orion spacecraft high into orbit in an unpiloted test.