Both tower-mounted and helium aerostat platforms have demonstrated the importance and capability of sustained multi-day and/or multi-week-long surveillance from height, but both platforms have inherent limitations. Towers as fixed assets have significant financial, ground access, and maintenance requirements. In addition, once known, blind spots and alternative paths to avoid the surveillance capability of the tower sensors can be developed. Helium aerostat platforms inherit the financial, infrastructure, staffing, and maintenance requirements of their military origins, and, like towers are, by ground support requirements, fixed assets that can be avoided. Even as they have remarkable down-look capability, the aerostats are also susceptible to the limitations of flight conditions. Recent developments in commercial-off-the-shelf (COTS) unmanned aerial systems (UASs) and power tether systems point to a cost-effective potential tactical alternative to towers or helium aerostat platforms.
Tethered drones are quad, hex - and/or octa-copters that are tethered to a base station and receive power via the tether. By virtue of the tether, the size, payload, and the flight time of the drone are not restricted by the on-board power supply. Very large sensor arrays can be deployed for hours/days at a time so long as a reliable power supply is provided to the tether. The external power also allows the drones to maintain position in relatively high winds that would exhaust the power reserves of free-flight drones and would threaten aerostat platforms.
As a tethered device, the drones fall under the same FAA restrictions for aerostats (under 500’), but unlike aerostats, the drones have a significantly smaller profile. By virtue of their small profile, they are less intrusive and a less overt surveillance platform. Leveraging COTS quad-, hex-, and/or octa-copter platform components, the tethered drones are low in cost and require minimal maintenance.
Typically carried and launched from a “Pelican”-like or larger cases, the drones are a single-button launch and retrieve system using COTS flight control software for a tethered platform. The tether is spooled out and retrieved automatically from the base station. As a safety precaution, the drones carry a battery to allow a controlled landing in the event of a power failure.
The size and capability of the platforms are defined by the mission and can include electro-optical sensors, thermal, and other sensors. The platforms can either feed the control and sensor data up and down the tether or use radio and/or Wi-Fi transmission. By virtue of available power and altitude, Wi-Fi can be transmitted over a large area providing ground assets with live feeds from the ground platform to cell phones and tablets.
The best practices and methods for tethered drone use are in circumstances requiring ad-hoc sustained surveillance from a controlled base with minimal cost and minimal observable profile. Although the platforms can operate at higher than FAA approved altitudes, they are a “best fit” for low-level, semi-covert surveillance over a sustained period of time. The drones can also be used over water or in desert areas and have a “follow” capability to allow them to be used from a moving platform in unobstructed areas. This gives the platforms superior littoral and desert capability.
It should be emphasized a tethered drone surveillance platform is a tactical asset that can complement existing land/sea monitoring capabilities with a low-risk, low-cost, rapid acquisition-to-deployment cycle protocol. Even as an equivalent capability does not exist in conventional technical/sensor inventories, this technology can be acquired and deployed in weeks rather than months or years, and at a lower cost than any airborne equivalent sensor platform. In the pragmatic, that translates to immediate enhancement of tactical surveillance capability with a minimum acquisition or logistic footprint. This is possible by the use of lightly modified existing UAS platforms and COTS tethering systems designed to accommodate a variety of UAS designs and capabilities.
Tethered drone advantages include:
Capability for sustained (multi-hour/day) flights with significant payloads – as power is passed up the tether, tethered platforms can employ larger motors, and in turn, can fight higher winds. This also allows larger payloads, including advanced electro-optics, thermal imaging, etc.
Lower visibility profile – unlike tethered aerostats, quad/hex/octa-copters have a much smaller form factor making them difficult to detect at a distance.
Simple single-button launch and recovery – COTS tether systems now feature a level of onboard intelligence for tether and platform management to allow for automatic launch and recovery.
Lower cost by leveraging COTS drone components – although there are dedicated specifically built tethered platforms, the use of COTS UASs equipped with tethers allows for the use of lower cost, mass-produced platforms, and associated components.
Faster acquisition to deployment cycle – COTS components allow off the shelf acquisition, simple configuration, and immediate deployment.
Less restrictive FAA regulations – the legal interpretation of a powered tethered platform is the equivalent of a kite. This exempts tethered UASs from requirements for a COA.
We would welcome the opportunity to discuss tethered drones for land and ship-borne persistent surveillance.
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