Differences between Captive Aerostats and Tethered Drones and how they Complement each other

Mar 31, 2022 | Military Drones, Tethered Drones Applications

Tethered drones and captive aerostats are both excellent tools for conducting aerial surveillance. The unique characteristics of these platforms make each system perfect for some applications but less ideal for others. Technological innovations have provided peacekeepers with numerous tools to aid in intelligence gathering. Some of the most valuable tools come in the form of aerial surveillance platforms. Tethered drones and captive aerostats are two of the most useful platforms for this application. While it may seem like these systems are redundant, their optimal use case is a complementary one. 

Understanding what makes these platforms unique is vital to maximizing their use. With a clear sense of the benefits and limitations of tethered drones and captive aerostats, one can better appreciate their importance and optimal utilization. These assets provide one of the best aerial surveillance platforms currently available.  

 

What are Tethered Drones

Sometimes called captive drones, tethered drones are uncrewed aerial vehicles (UAVs) that utilize a physical link to provide power. In some cases, the physical link is also a conduit for communications and data transfer. Typically, the physical connection is in the form of a wire or fiber optic cable. This cable has the ground control station at one end and the drone at the other. In most cases, the drone is a multirotor system.  

Captive drones come into two varieties: classic drone with a tether module and tethered drones by design. Classic drones are off-the-shelf units that have been modified to use a ground power station. Tethered drones by design are systems built from the ground up to be fully integrated and compatible units. By design systems are optimal as engineers look to maximize compatibility and efficiency among all components during design and testing. Captive by design systems are more persistent and can remain flying for 24 hours. In comparison, classic drones with a tether module are typically limited to around 8 hours. 

Elistair’s ORION 2 is an example of a by design tethered drone system. These systems are portable and designed to provide continuous aerial surveillance. The setup time for tethered drone systems is less than 10 minutes and they can fly at an altitude of 100 meters. Additionally, utilizing a drone like the ORION 2 requires only a single operator to perform all functions.

Unlike free-flying drones whose batteries offer limited flight duration, tethered drones can stay airborne for many hours, even a full day. Generators are most often used as the fuel source, providing relatively limitless power. 

 

What are Captive Aerostats

Captive Aerostats, or captive balloons, are helium or hydrogen-filled balloons used for aerial surveillance and as a tactical communication relay. In general, these systems include the balloon, a tether, wench, and an array of sensors attached to the underside of the balloon. They are much larger than most drones, with lengths ranging from 1 to 75 meters.  

These systems are broken into tactical, operative, and strategic categories. Tactical balloons are the smallest, ranging in length from 1 to 20 meters and climbing to an altitude of 300 meters. Next are the operative balloons with a length between 20 and 50 meters and a max height of 1,000 meters. The largest balloons are the strategic class with lengths from 50 to 75 meters and max altitudes of up to 5,000 meters. 

As a result of their size, captive aerostats demand a much larger footprint on the ground and require an operational crew. Depending on the size of the balloon, some of the more extensive systems can demand up to 10 people. The support system on the ground is also significant. For this reason, captive aerostats are best employed for long periods of time in a single location. 

 

Benefits and Limitations of Tethered Drones

Aerial surveillance activities require intelligence gathers to maintain their focus. Missing the slightest detail in the data collected could have catastrophic consequences. For this reason, analysts greatly benefit from the autonomous nature of tethered drones. Tethered drones can operate up to 100 meters above the ground. The entire operation of the system only requires a single person.  

Elistair Orion 2 tethered UAS flight testIn addition to a low commitment of human resources, tethered drone systems have a minimal logistics footprint. Drones and ground control modules are small enough to fit into hardened mission cases. These units are lightweight and compactable, with swappable arms and legs, making it easy to transport them, even in small vehicles. Two cases and a portable generator are all that are required. 

With such a small logistics footprint, it should come as no surprise that tethered drone systems are rapidly deployable. Security personnel can quickly grab the two hardened cases and generator and move to where the drone is needed. If the system is already in a vehicle, the process is even faster. The speed at which one can deploy tethered drone systems is a significant benefit of the platform. Taking the system down when the mission is complete is just as easy as the setup. 

The design and size of tethered drone systems allow for better wind resistance. This is especially the case when compared to captive aerostats. Capability to fly in higher wind speed is important because it affects the stability of the drone. It also affects power consumption, but this is less important for a tethered system as it receives its power from a generator and not a LiPo battery. Tethered drones with a low wind resistance can fly in more substantial wind speeds without reducing data quality. As a consequence they offer a greater service continuity. 

A final advantage is the cost of these systems. Whereas captive aerostats can cost millions of dollars, tethered drone systems cost tens of thousands. The relatively low cost allows the technology to be within reach of most governments, militaries, and security forces. 

The primary limitations related to tethered drone systems are payload capacity and on-station time compared to captive aerostats. The payload options for UAVs are constantly benefiting from innovations and advancements in optics capabilities. That being said, there are payload weight limitations that prevent tethered drones from carrying more robust optics packages. For example, a standard tethered drone can carry up to 2 kilograms, whereas a strategic captive aerostat could carry up to 3,000 kilograms. 

Tethered drones can remain airborne for 24 hours. This is a substantial amount of time to collect information and conduct surveillance operations. Aerostats can remain airborne for several days allowing for even greater periods of uninterrupted ISR. 

 

Benefits and Limitations of Captive Aerostats

When comparing captive aerostats to other aerial surveillance platforms, balloons have two primary advantages. For end-users looking for long-term coverage of a position, captive balloons can remain on station for months at a time. This unmatched duration allows for continuous aerial surveillance. Given the height these platforms operate at, targets can be detected at a distance of over 50 kilometers.

Picture of an aerostat on the groundThe second advantage captive aerostats have is the ability to carry large payloads. Some of the larger platforms can carry payloads weighing up to 3,000 kilograms. Payloads can include radar systems, infrared cameras, video, and communications equipment. The payload weight limitations of captive aerostats leave planners plenty of room to develop custom aerial surveillance solutions that fit their specific needs.

An excellent example of captive aerostats is the Tethered Aerostat Radar System (TARS). These systems have been utilized for several decades and are employed in a wide range of applications worldwide. The payload capabilities of TARS allow for easy detection of targets in the air, on land, and on the water.

While the benefits of captive aerostats are noteworthy, they have three significant limitations to consider. First, these balloons require a considerable commitment of resources. In addition to the cost of these platforms, a complete TARS is nearly $9 million, the logistics footprint is substantial. Hangers, heavy equipment, vehicles, and storage tanks for lighter than air gases are essential to operating and maintaining captive aerostats.

Another disadvantage, particularly when conducting aerial surveillance, is the size of these platforms. The presence of a captive balloon will be no secret to anyone for many miles. In addition to being easy to spot, they are vulnerable to attack. This vulnerability, combined with their logistics footprint, limit their use outside protected areas such as large forward operating bases (FOBs), government installations, or large enclosed facilities.

Finally, the size of captive aerostats also causes their use to be weather dependent. The shape and size of these systems make them susceptible to weather conditions. Wind, air pressure, and rain often make using a balloon impossible.  

 

Tethered Drone Use Cases

The number of use cases for tethered drones is almost limitless. Many industries have found uses for captive drones to include defense, telecommunications, and public and private security sectors. While tethered drones like the ORION 2 are highly versatile platforms, three ideal use cases include border surveillance, FOB protection, and tactical communications.

Elistair Orion tethered drone and its Safe-T ground power stationBy their nature, borders are areas prone to conflict and criminal activity. The borders of many countries stretch for hundreds, if not thousands, of kilometers. The sheer magnitude of a country’s borders often encompasses varied terrain from mountains to water features making these boundaries challenging to monitor. Barriers in the form of fences and walls offer some protection and deterrence, but these obstacles are highly ineffective without monitoring.

The ability for tethered drones to rapidly deploy to an area, especially when mounted on a vehicle, makes them ideally suited for border security. Captive drones have seen successful implementation at high traffic areas like checkpoints and in remote and almost inaccessible locations. They are also very effective at monitoring large crowds.

FOBs allow militaries to project their presence beyond well-established and protected installations. While these locations enable force projection, they expose personnel to more significant dangers. Maintaining aerial surveillance in these locations is essential. Tethered drones are excellent at detecting and preventing attacks and intrusions.

Tethered drones offer secure communications in tactical situations. Because data is transferred between the drone and base station via the tether, it is a closed system reducing the risks of jamming. The tether is key to making these systems robust in modern combat and security environments. Users of captive drones can rest assured their aerial surveillance operations will remain operational and secure during even the most advanced cyber-attacks.

 

Captive Aerostat Use Cases

Captive aerostats are excellent in the same roles as tethered drones but at a much larger scale due to their size and cost. Border protection, FOB security, and providing tactical communications are valid use cases for captive aerostats.

Big aerostat on the ground in a desertic landscapeWhile tethered drones are excellent for small to medium FOBs, the payloads of these systems are not designed for significantly larger installations. An example from recent history can be found on Afghanistan’s most extensive airbase, Bagram.

In addition to the extensive runway and tarmac, the facility has a vast infrastructure covering over 70 square kilometers. There is too much area for tethered drones to effectively cover with multiple entry points and a long perimeter wall.

Captive aerostats are more than capable of monitoring such an extensive facility. Given the size of Bagram, there is no need for aerial surveillance assets to maintain stealth. With dozens of square kilometers of space on the base, the facility offers plenty of room for the logistical footprint aerostats require. The airbase is a textbook location for captive aerostat employment.

 

Combine Efforts

Tethered drones and captive aerostats complement each other well in the right situations. Each system can apply the beneficial attributes inherent in its design to aerial surveillance operations while the other makes up for its limitations. There are many situations where pairing these assets is advantageous, with two of the strongest cases represented in border security and FOB protection.

Border checkpoints are often the site of larger cities on both sides of the boundary. The number of crossings can be enormous in a given year.

Consider how the combined efforts of tethered drones and captive aerostats could aid in this gargantuan task. Captive balloons could be floating several kilometers away from the border, while tethered drones could be employed at checkpoints and inspection areas directly at crossing points.

This dual application of assets would allow border patrol agents to conduct aerial surveillance at great distances with the aerostat. Due to the ease of installing tethered drone systems on a vehicle, vehicle-mounted systems can move as needed to provide additional ISR services. This characteristic gives security forces enhanced flexibility as a complex situation changes.

If we look again at our example of Bagram airbase, we can see a case where the addition of tethered drones significantly improves force protection. With a captive aerostat already floating high above the base, threats can be identified at great distances. Suppose that the base is attacked along the perimeter wall during a given period of observation. The wall may obstruct the view of the captive aerostat. In order to gain a clear picture of the threat, another ISR asset must be employed.

Tethered drones mounted on QRF vehicles could quickly be sent to the location of the attack. Within minutes, the drones could be flying above the area and collect data for security forces. Given the long on-station time of tethered drones, the UAV’s cameras could monitor the situation for the duration of the attack even if it were to extend into the evening.

 

Conclusion

Tethered drone systems excel when end-users need mobility and rapidly deployable observation platforms. Captive balloons are best employed where the need for long-duration surveillance and heavy payloads is combined with locations that can support their logistics footprint. In many cases, combining these platforms provides the best coverage without sacrificing flexibility. Together, tethered drones and captive aerostats help to build one of the best ISR pictures possible. 

Author – David T. Daly

More information about Elistair solution 

News About Tethered Drone Applications