Surveillance: Advances in UAV miniaturisation | ADM June 2009
Now, new operational concepts, such as cooperative behaviour protocols and swarming, are opening new missions for these small, low cost expendable UAVs.
Tom Muir | Canberra
Some 12 years ago, the US Defense Advanced Research Projects Agency (DARPA) began a multi-year development program to develop "micro aerial vehicles (MAVs)" with the goals of developing a microdrone whose largest dimension was no more than 15 centimetres (6 inches); would carry a day-night imager; have an endurance of about two hours; and be very low cost.
It would operate with a high degree of autonomy and was to be used in the squad-level (Australian fire-team) combat environment.
MAVs capable of hovering and vertical flight would be used to scout out buildings for urban combat and counter terrorist operations.
A MAV could be included in a pilot's survival kit.
A downed pilot could use it to keep a lookout for enemy search parties, or relay communications to search and rescue units.
The next phase focused on particular vendors interested in developing MAVs closer to operational specification with a typical mission requiring a modest 30 minutes duration and a range of one mile while operating in winds up to 20 mph.
As a result, a number of different MAVs were developed, some of the more interesting being:
• The Lockheed-Sanders MicroStar ,which has a 12 inch wingspan, electric propulsion, and is capable of autonomous flight with GPS navigation; and
• AeroVironment's Black Widow, a six inch wingspan aircraft that uses an electric motor for propulsion and weighs 80 grams.
The Black Widow and MicroStar MAVs demonstrated the possibility for significant miniaturisation in reconnaissance aircraft so long as mission duration and range remained small.
Both MAVs carry a color camera and use Lithium batteries for propulsion.
Several ornithopter designs were also built, most prominently the MicroBat from the California Institute of Technology, working with Aerovironment and the University of California LA.
The ornithopter design concept followed experiments conducted in the mid-1990s by Charles Ellington, a zoologist at the University of Cambridge, and his colleagues, in which mechanical analogues of insect wings were tested in a wind tunnel.
The group was only interested in studying the biomechanics of insects and was extremely surprised that somebody seemed interested in them.
Along with the flight prototypes, the DARPA effort considered subsystems design, such as lightweight electric motors, small fuel cell systems, plus navigation, control and sensor subsystems.
A large variety of corporations and universities designed MAV airframes, which met the original requirements, but they still lacked a sufficiently small propulsion system.
Electric motors were available, but battery technology was not yet advanced enough to power small electric motors sufficiently.
Because of this, chemical engines and motors were investigated.
One of the most interesting chemical engine designs was a micro jet, designed to run on natural gas.
The jet featured a small turbine, running within a two centremetre diameter silicon case.
Unfortunately, such an engine would run at an extremely high temperature, necessitating silicon carbide construction.
The DARPA MAV effort ended in 2000, with the results of the effort seen as somewhat negative, demonstrating that a 15 centimetre UAV was simply too small to be useful for military applications.
At least, that was the feeling at the time.
Now a decade later, MAVs are finding roles across civilian and military sectors.
But some more recent examples have received a warmer reception.
Exceptions to the rule
One of the most notable modern MAVs is the Draganflyer X6, a fully autonomous UAV, with sophisticated barometric, GPS, and imaging sensors.
It can also be operated by remote control - giving the pilot maximum flexibility and control over the flight plan.
It also has the unique ability of folding up to a very small form factor - making it easy to transport, launch and fly by one individual.
Weighing only 1 kg and able to be collapsed and inserted in a 5.5 inch tube 26 inches long, the Draganfly X6 is highly portable, and able to provide an aerial platform to get pictures or video of an area in its current state.
An operating noise level of only 60 decibels means that if there is any ambient noise the Draganflyer X6 is unlikely to be heard.
AeroVironment has developed a relatively small UAV the Pointer, designed for use by military forces for surveillance.
The Pointer was successful, but the military wanted a smaller unit, so AeroVironment designed a smaller version.
In 1999, the US army began using very small airplane style UAVs, including the RQ-11 Raven.
Developed by AeroVironment, the Raven has become the standard MAV used by the US army, marines, and several other nations.
The Raven is small enough to be assembled and launched by one person, and has an endurance of 90 minutes using rechargeable batteries.
The Raven has video cameras located in the nose cone and can relay live video back to the operator in real-time.
Another notable MAV was the Desert Hawk, developed by Lockheed Martin.
It is one of the smallest MAVs used by the US military, with a wingspan of only 52 inches and weighing 7 lbs.
It has an endurance of approximately one hour, and is usually launched using a bungee cord.
Honeywell has begun low-rate initial production of MAVs on a new line in Albuquerque, New Mexico, sized to manufacture up to 100 vehicles a month and the Miami-Dade Police Department plans a four-six month evaluation of Honeywell's ducted-fan MAV.
The gasoline-powered gMAV has just received an experimental airworthiness certificate from the US Federal Aviation Administration, clearing the way for the ground-breaking experiment.
Approval was granted following a demonstration flight for the FAA at a remote site in Laguna, New Mexico.
The wingless gMAV can take off and land vertically, transition to high-speed flight and hover and stare using electro-optical/infrared sensors.
Miami-Dade is buying one gMAV and leasing a second for the FAA-sanctioned technology demonstration.
The police department will operate the UAVs, and helicopter pilots from its aviation unit have been trained to fly the gMAV.
The 8.2-kilogram gMAV is Honeywell's second version of the man-portable UAV.
Compared with the original tMAV developed for DARPA, the gMAV has a larger outside diameter housing twice the fuel and providing an endurance exceeding 55 minutes at sea level.
Military gMAVs have been used in Iraq to detect improvised explosive devices.
The basic UAV has fixed sensors and Honeywell is developing a follow-on version with gimballed payload.
The company is also working on diesel-powered dMAV, which it expects to fly in 2008.
Another version is in development for the US Army's Future Combat Systems program.
Florida-based Prioria Robotics formally launched the Maveric unmanned aerial vehicle on 13 May this year.
Prioria's focus has been on demonstrating a basic, collision avoidance capability for a micro-UAV, enabling the aircraft to avoid trees, buildings and helicopters.
The challenge is to make a UAV smart enough to autonomously detect and steer clear of other objects in their flightpath.
For small UAVs equipped with a forward-looking camera, Prioria's approach is to integrate an on-board processor able to interpret the streaming visual data for collision avoidance cues.
That requires a combination of processor technology small enough and powerful enough, as well as algorithms sophisticated enough, to interpret the data and command the aircraft to take appropriate action.
Payloads get smaller too
As DARPA discovered 10 years ago, aside from their novelty, small and micro-sized UAVs have little to commend them if similarly miniature propulsion and electro-optical systems are unavailable.
But this is no longer the case and miniaturisation of payloads has sped the development highly capable MAVs with seemingly extraordinary capabilities.
As previously reported in ADM, ScanEagle has been trialled with a micro-synthetic aperture radar (NanoSAR).
If it was also equipped with a tactical common data link, it could handle forward observation tasks and other important ISR tasks for Australian troops equipped with L-3's ROVER III terminals.
Israeli Bental Industries is offering various mini-payloads for UAVs such as the MicroBAT Family.
As the smallest and most compact of small stabilized payload systems for mini and micro platforms, the MicroBAT meets the complex challenges presented by surveillance, reconnaissance, and observation missions.
The company says the MicroBAT is ideal for use in a wide range of small size applications.
Sharing capabilities with MicroBAT 275, Aqua MicroBAT adds immersion to the already impressive performance envelope.
Successfully tested at depth of two meters, Aqua MicroBAT can be installed on a variety of vessels and including ability to land on water, UNVs (Unmanned Naval Vehicles), and on both manned and unmanned platforms intended to land on water.
All MicroBAT systems offer a high-resolution stabilization control board, remarkably accurate geared motors, and an EO zoomed sensor for monitoring.
Last November, Bental announced that its MicroBAT 275 stabilized camera system for light weight UAVs is being tested by the German Armed Forces.
As ADM was going to press, Bental announced that it had trialled the system for senior Italian MoD officials, including Chief of Staff of Italy's armed forces and its defence minister.
The demonstration took place earlier this year with OtoMelara featuring MicroBAT installed onboard its Ibis UAV platform as well as onboard a ground robot.