Tethered Drones: A Persistent Capability for Situational Awareness and Communications

By Ben Gross | May 11th, 2023

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One of the biggest design challenges for many drone manufacturers is the maximization of the aircraft’s range, and how to squeeze every last bit of efficiency from the battery and aerodynamics. Many drone applications, from delivery to precision agriculture, need unmanned aircraft platforms that can cover as much ground as possible in a single flight. Given this, it may seem counter-intuitive to put a drone on a leash and restrict its movement.

Tethered drones, however, have a number of advantages that enable them to serve particular applications that require a persistent capability in one specific locale. They can be attached to a mains power source, a portable generator, or a vehicle power supply, giving them effectively unlimited flight time as long as the parent power supply holds out. The tether can also be used to transfer data as well as power, and this communications link is much harder to jam, intercept or otherwise interfere with compared to a wireless RF (radio frequency) connection.

As fixed-wing drones cannot hover in place, tethered drone systems utilize multirotor aircraft. By themselves, battery-powered quadcopters and hexacopters typically achieve from around 20 to 45 minutes of free flight. With the addition of a tether system, their endurance can be multiplied significantly. Tethered drone solutions may be sold as just a base station that is compatible with leading commercial off-the-shelf drones such as the DJI Mavic platforms, or provided as part of a complete UAS (unmanned aerial system) that includes an aircraft.

Tethered drone system capabilities

The tether itself is a flexible cable that is typically constructed with an outer cladding made from a lightweight synthetic  material such as aramid, with a core consisting of copper for power conduction and optical fiber for data transfer. Even the most weight-optimized construction will eventually add up over a long enough cable, so the maximum length of tether and hence the operating altitude of the drone is typically around a couple of hundred meters, with the limiting factor being the weight that can be balanced by the upthrust of the rotors.

The base station of many tethered drone systems is designed with an auto-tensioning mechanism that continuously monitors the force on the cable and adjusts the tension to prevent slack. This allows the system to be used in windy conditions and even on moving platforms such as land vehicles or boats.

With a permanent connection that stops “flyaway” accidents as well as crashes due to drained batteries, tethered drone systems are generally much safer for operations over people compared to free-flying unmanned aircraft. As such, it may be easier to apply for authorization such as the FAA (Federal Aviation Administration) Part 107 waiver for a tethered drone.

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Applications for tethered drones

Tethered drones are commonly used by the military as a quick and efficient way to launch an “eye-in-the-sky” capability that can gather video and data for ISR (intelligence, surveillance and reconnaissance) purposes. However, there are also a variety of civilian applications for these systems. These include:

Public safety and law enforcement – Tethered drones can provide critical situational awareness and aerial intelligence for first responders. Using both visual and thermal imaging cameras, they can track suspects, find casualties and missing persons, monitor fire hotspots, and more.

Broadcasting – With long flight times and low latency, tethered drones are ideal for live-streaming concerts and sports events as well as providing footage for news broadcasting.

Security – providing persistent watch over important areas and facilities as well as large crowds and events, streaming the footage back to a central control room.

Monitoring and data gathering – Drones can be used to mount a sensor at greater heights than a tree or mast, providing an excellent monitoring platform for traffic, atmospheric and weather conditions, wildlife and other applications.

Infrastructure and facilities inspection – Flying a drone around structures such as bridges and wind turbines can be tricky, especially under windy conditions. Tethered systems enable visual inspections to be carried out with fewer risks and without the need for a highly skilled pilot.

Tethered drones and cellular communications

Many of the tasks suited to tethered drone systems are likely to take place in urban or suburban environments with good cellular coverage. This makes 4G and 5G cellular communications ideal for the base station, which can then be deployed an unlimited distance from an organization’s command center as long as a cell tower is within range.

Cellular communications provide a number of advantages over traditional RF datalinks. With the number of connected devices constantly on the rise, many portions of the RF spectrum now suffer from crowding issues. 5G has the potential to support up to a million devices per square kilometer, thus preventing drone performance from suffering due to spectrum crowding while also not contributing further to the problem.

5G also provides data rates of up to 10 gigabits per second with latency as low at 1 millisecond, making it highly suited to data-intensive and real-time applications such as security and broadcasting.

Tethered drone systems are also often used to provide cellular connectivity in austere communications environments. Acting as a flying cell site, they can be quickly deployed by emergency services in disaster zones and remote locations, providing cellular service for mobile phones, tablets and other devices carried by personnel in the field. This connectivity could also be used by free-flying drones, thus enabling operations to be extended even further.
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Halo – an ideal connectivity solution for tethered drones

Elsight’s Halo platform is ideal for incorporation into tethered drone base stations, providing a carrier-agnostic cellular connectivity solution that can be deployed anywhere with the right SIM cards. The compact and lightweight unit can accept up to four SIMs from one or multiple network providers.

This multi-SIM capability can be used to provide essential redundancy for mission-critical applications, seamlessly switching to a backup link should the primary connection experience issues. Halo can also use advanced secure bonding technology to aggregate all active datalinks together into one channel, allowing you to maximize available bandwidth.

Halo is fully cybersecure, using advanced algorithms to split video and sensor data from the drone into encrypted packets and then sending this data stream via a secure VPN tunnel either to Elsight’s proprietary cloud platform or a selected server, where the packets are decrypted and recombined.

To find out more about making Halo’s connectivity capabilities part of your tethered drone system, please get in touch.


What is situational awareness?

Situational awareness involves perceiving and gathering information from the environment, using this process to inform decision-making. For UGVs (unmanned ground vehicles), UAVs (unmanned aerial vehicles) and other unmanned systems, this may be done by the operator through observation of cameras and other sensors, or carried out autonomously by the system.

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