Tethered Drones

Tethered drones (or uncrewed aerial systems - UAS) offer a potential solution to the Achilles heel of the vast majority of small UAS, their endurance.
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Tethered drones (or uncrewed aerial systems – UAS) offer a potential solution to the Achilles heel of the vast majority of small UAS, their endurance.

Getting up high to take a look…

Whilst there are a number of specific use cases such as facility inspection and broadcasting, most will use UAS as a means of lofting a sensor higher than a mast, or standing in a tree. Calculating the distance to the horizon requires the use of some fairly complex equations, explained at this link and expressed as the image below

A 2m high person can see another 2m tall person at about 10km (assuming artificial optics). Raise the 2m to 6m, a typical elevating mast, that 2m high person can now be detected at 14km. Put that same sensor on a UAS at 30m and those observed areas start to increase dramatically. At 30m, the same 2m targets can be observed at just under 25km. The world is not perfectly obstruction-free of course, and at those ranges, a simple optical sensor would need some augmentations but I think you can see the obvious benefits of standing on a very tall hill, metaphorically, as did Samuel Cody and the Royal Engineers all those years ago.

Small UAS, therefore, provide the military user with a range of advantages before we start getting into the realms of arming them.

This is not free though, most small UAS have limited endurance and payload, and the higher the payload, usually, the smaller the endurance. The Proteus from UAV Tek in Cheltenham, just as one example, with an endurance of about 45 minutes.

Tethered drone

Users can always carry spare batteries and there are even hydrogen fuel cell solutions, the video below shows one such example from ISS Aerospace in Berkshire, flight times of up to 120 minutes.

Another problem with conventional UAS is their training requirement, developing and maintaining the skill set is not easy and needs constant maintenance. Whilst in use, they will also require an operator.

Tethered Drones

The CAA describes tethered UAS as;

A tethered UAS is one where the unmanned aircraft remains securely attached (tethered) via a physical link to a person, the ground or an object at all times while it is flying. The tether normally takes the form of a flexible wire or a cable and may also include the power supply to the aircraft as well.
Operations with a tethered UAS can be used as an efficient solution in a number of cases, for example where an operating area is restricted, or when the required flight time exceeds the normal endurance of a free flying battery powered aircraft.

Tethered drones replace or supplement the onboard battery with a DC umbilical cable, sensor feeds can also be routed onto the cable to avoid transmitting using radio signals if required. The tether is payed out from a drum and electromechanical devices ensure tension is maintained if the base station moves. With a tether, endurance is measured in hours or even days. Systems can stay aloft with little or no user intervention and provide 24/7 coverage for surveillance, convoy overwatch, base protection and other applications. Many now also allow the base station to move at speeds of up to 25mph or more.

This video provides a good overview of such a readily available system

One of the greatest challenges for tethered UAS designers is the weight of the tether cable itself, too heavy and the UAS will simply be unable to fly. Most designs now use high voltage DC signals that can utilise thinner conductors. This article provides a good background on these power challenges.

Systems can be networked together to create a wide-area view, Logos Technology in the US have released a version of their wide-area surveillance system specifically for tethered UAS, called the MicroKestrel 

A miniaturized version of the Kestrel aerostat-based system, MicroKestrel delivers wide-area motion imagery (WAMI) from tethered Group 1 unmanned aircraft systems (UAS). This micro-WAMI system provides 180- or 360-degree coverage of an area up to 20 square kilometers in size. Available in short- and long-range versions, MicroKestrel supports the user with uninterrupted monitoring of live and recorded imagery. Powerful and portable, MicroKestrel delivers unparalleled situational awareness at a moment’s notice.

The video below provides an overview

Other manufacturers include

Volarios

Dragonfly Pictures

Hoverfly

Lifeline

Elistair

Fotokite

In addition to sensor payloads, a number of manufacturers have demonstrated signals intelligence, communications and even counter UAS capabilities with tethered systems, an example of the latter shown in the image below

 

Both the British Army and Royal Navy have been experimenting with British made tethered UAS., Drone Evolution with the former and Tethered Drone Systems for the latter. Evolve Dynamics also have a similar system.

 

O2 and Fotokite have also teamed up to offer a fire and rescue tethered system

The obvious problem with tethered UAS is that they pretty much only go up and down, and this might be an obvious indicator to a smart and technically able enemy to where to land a missile or artillery shell, but if these limitations are accepted, an operational procedures adapted, tethered systems can offer defence users a seriously impressive capability, whether at sea, in a city or other land environment.

The market is still evolving, but there is no shortage of choice, what are we waiting for?

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