Autonomous Aerial Fire-fighting (AAF) – A System for Fire Suppression by Autonomous Air and Ground Vehicles

By Brien Seeley M.D., President, Sustainable Aviation Foundation
Senior Fellow of UC Berkeley’s Institute of Transportation Studies (ITS)

Executive Summary

The feasibility, concept of operations and importance of a future system of autonomous aerial fire-fighting (AAF) are presented as an effective way to end wildfires and their major adverse impact on the climate crisis. The technical details of the facilities, air and ground vehicles and capacities of an extensible reference design for an AAF system capable of providing effective and pervasive aerial control of wildfires are described, along with its many benefits. These findings support a conclusion that urges the immediate launch of AAF as a comprehensive government-funded program.

Background

Wildfires, which are defined herein as an unplanned, uncontrolled, and unpredictable fire in an area of combustible vegetation, are increasing around the globe in a trend that is predicted to worsen in the coming years. The CO2 released by wildfires substantially increases global warming, which, in turn, increases the incidence and severity of wildfires, making them another of the tipping points that could make the climate crisis unstoppable. First-order calculations of the cumulated global losses of CO2 sequestration due to wildfires over the 20-year span from 2000 to 2020 find that they likely accounted for an increase of 101 Gigatonnes of atmospheric CO2 in just one year (2020), indexed to the year 2000.¹ This 101 Gigatonnes exceeds by two and a half times the nearly 40 Gigatonnes of CO2 emitted in the year 2020 from the global use of fossil fuels. This may explain why the one-year increase in atmospheric CO2 in March, 2024 was the largest ever.²  

The US EPA cites a figure of $190 billion dollars as the global cost in loss and damages of emitting 1 Gigatonne of CO2³ With the 101 Gigatonnes of CO2 attributable to wildfires in 2020, this EPA metric computes to a yearly global cost of over $19 trillion dollars. Added to this are the inestimable costs of the health damaging effects of wildfire smoke. 

The extant problems in wildfire suppression with aircraft include the following:

1. Shortages of trained and qualified fire-fighting pilots
2. Shortages of air-tanker aircraft due to their high cost (~$24M each)
3. Shortage of air attack bases, owing to their large runway size and cost
4. Remoteness of the too few air attack bases from some wildfire-prone areas
5. Excessive time intervals for air tankers to reach the scene of a fire
6. Inability for most air tankers to fly at night or in smoke and fog
7. Difficulties in achieving effective pattern application of fire-retardant, especially in conditions such as high winds, smoke, fog and darkness.

Agencies and officials are increasingly reluctant to authorize the necessary prescribed burns because of limited resources for control and because of the liability that attends having said burns erupt into wildfires⁴. Together, these findings indicate a clear need for a more effective system to suppress and contain wildfire and to ensure that controlled burns are controlled. The technology for early detection of wildfires already exists in the form of remote sensing systems, including shared networks of satellites with higher-resolution thermographic cameras, high altitude long endurance aircraft (HALE) and accurate GPS mapping and positioning. Said technology needs to be coupled with a more responsive aerial wildfire suppression system. 

The extant problems in wildfire suppression with ground vehicles are analogous to those with aircraft and include limited resources, limited trained crew, lack of proximity and access that is limited due to conventional fire engines that are often too large to pass on narrow unimproved trails enroute to a fire. The limited access by ground vehicles to promptly reach and attack wildfires in remote areas means that the initial attack must be an aerial attack. 

1. Introduction

The global threat of wildfires, coupled with their increasing frequency and intensity and the inherent dangers of combating them with conventional methods, necessitates the development of an innovative new system to fight them and prevent their devastating impacts. The challenges to conventional firefighting methods, as described above, can be overcome with a new type of aerial fire suppression system that use a combination of interoperable uncrewed, electric-powered vehicles, facilities, hardware, and software. This system offers a concerted, multi-modal approach to delivering fire suppressing liquid onto fires. The system leverages early detection and automated dispatch of uniquely capable, ultra-quiet, robotic aircraft (“eTankers”) from a highly distributed network of small facilities (“airparks”). This comprehensive system aims to revolutionize firefighting by providing a safer, lower cost, more effective, and environmentally friendly method for suppressing wildfires, while enhancing response times, and minimizing the risk to human life. The system, called Autonomous Aerial Fire-fighting (AAF), is designed to be scalable and adaptable to different environments and fire scenarios, making it a valuable and extensible tool in the ongoing global fight against wildfires.

2. System Components

2.1 eTankers: Autonomous Aerial Firefighting Units

eTankers are at the heart of this innovative fire suppression system. These electrically-powered, ultra-quiet, autonomous robotic aircraft are specifically designed for the precise delivery of fire suppressing liquids. Uncrewed eTankers are equipped with advanced technology including GPS navigation, LiDAR-based obstacle avoidance sensors, high-resolution thermographic cameras for real-time fire assessment, and secure communication capabilities, allowing them to fly precise trajectories. They are expressly designed to perform ultra-quiet, extremely short take-offs and landings (ESTOL) from small 3-acre airparks. To be able to use such tiny airparks, which is crucial to projecting fire control everywhere, the eTankers have to be of limited size yet large enough that a bucket brigade of them can be highly effective at dousing wildfires. Their low-drag, low span-loaded design and high lift-to-drag ratio enable them to have sufficiently long range to reach and return from remote fires. Their ultra-quiet, large diameter, slow-turning propellers with relatively modest power requirements eliminate noise emission problems. Their double-slotted, propeller-blown wing flaps provide extremely high lift coefficients and agile slow flight capabilities highly useful over steep terrain and in gusty winds. These unique design features allow them to operate safely and efficiently in diverse environments, from suburban residential and dense urban areas to remote mountainous wilderness areas with steep canyons, and even in challenging flight conditions such as smoke, fog, darkness and high winds.

The eTankers are also equipped with a modular payload system that can carry various types of fire retardant, including water, foam, and gel. The system can be easily configured to carry other payloads depending on the specific needs. The retardant is released through a precision delivery system that can be optionally controlled remotely by ground crews, allowing for targeted application and minimizing waste. The aircraft are also equipped with flame-hunting thermographic cameras that can detect hotspots and provide valuable information to ground crews about the fire’s behavior and spread. A reference design for the eTanker is shown in Figures 1a and 1b., below:

Figure 1a The high L/D ESTOL dual pod eTanker reference design makes a drop with flaps down.

Figure 1b The single and dual pod eTanker reference designs shown with fire suppression modules (FSM) onboard. Pod’s rear hatch opens to admit the electric payload cart (EPC).

Figure 1c The low-drag, single pod eTanker reference design shown with ultra-quiet propellers.

The utilization of electric propulsion systems on eTankers offers several advantages. Firstly, combined with its ultra-quiet propellers, it significantly reduces their noise emissions compared to traditional firefighting helicopters and very large air tankers (VLATs), which often rely on loud gas turbine engines. This noise reduction is crucial to making AAF operations universally acceptable at airparks in residential communities that are close to the Wildland Urban Interface (WUI). Secondly, electric propulsion is inherently more environmentally friendly, having zero tail-pipe emissions during operation and thereby reducing the carbon footprint of firefighting activities. Unlike conventional air tankers, eTankers carry no flammable fuel when flying low over wildfires. Additionally, electric motors require far less maintenance than traditional combustion engines, reducing downtime and operational costs. The eTankers are powered by high-capacity swappable battery packs that can be quickly exchanged and recharged at the airparks, enabling quick turnaround times between missions and encouraging greater development of renewable energy resources.

2.2 Airparks: Strategic Infrastructure for Fire Suppression

Airparks are roughly three-acre, short-runway, standardized facilities strategically distributed so as to enable AAF eTankers to initiate fire-fighting operations at any wildfire location. These facilities serve as hubs for fire retardant storage, vehicle maintenance, and communication. The standardized design of airparks ensures compatibility and seamless interoperability with eTankers, enabling rapid and continuous deployment and effective fire suppression operations. Each airpark is equipped with battery charging stations for the swappable eTanker battery packs, ensuring they are always ready for deployment. The charging stations use standard-sized, high-capacity battery packs and fast-charging technology to minimize the time eTankers spend on the ground, maximizing their availability for firefighting missions.

Each airpark is equipped with the necessary infrastructure to store and replenish fire retardant, maintain and repair eTankers, and facilitate communication between the aircraft and ground crews. The facilities are designed to be self-sufficient, with renewable energy sources like solar panels and battery storage systems reducing their reliance on the grid and ensuring uninterrupted operation during emergencies. The airparks also house weather stations and other monitoring equipment that provide real-time data on environmental conditions, which are used to inform the deployment and operation of the eTankers. A reference design for an airpark is shown below.

Figure 2. The 3-acre AAF airpark with central (pink) tank of fire suppressant on the crosshatched dock area along with multiple tiny green electric payload carts (EPCs), red robotic delivery carts RDCs). ESTOL flight paths for take-off and landing are shown.

The strategic distribution and number of airparks is determined through a combination of fire risk assessment models, historical fire data, and geographic considerations, ensuring optimal coverage of high-risk areas and minimizing response times to fire incidents. The system’s software continuously analyzes data from various sources, including weather patterns, vegetation density and moisture content, and human activity, to dynamically adjust the placement of eTankers at airparks and optimize their preparedness. This data-driven approach ensures that the system is always prepared to respond to fire incidents in the most prompt and effective manner.

2.3 Payload and Delivery Carts: Crucial To Effective High Capacity Operations

In addition to eTankers and airparks, the system incorporates versatile, autonomous robotic electric payload carts (EPCs) and electric-powered autonomous robotic delivery carts. These carts play a crucial role in streamlining the loading and delivery of fire retardant from airparks by eTankers. By automating these processes, the system ensures a continuous and effective supply of fire retardant for the eTankers, enabling them to quickly reload and return to their firefighting mission without delays. For AAF, each payload cart carries a fire-suppression module (FSM) comprised of a standard-size tank with valves that enable it to be gravity-filled from a dispensing silo at the airpark’s Fire Suppression Station (FSS) in just 10 seconds. See Figure 3, below. This minimizes turnaround time and maximizes the system’s capacity in terms of gallons dropped per hour.

Figure 3. The AAF Fire Suppression Station (FSS) with 6 siloes can simultaneously fill 6 Fire Suppression Modules (FSM) by gravity feed. Each FSM is latched onto a dock operable electric payload cart (EPC). Fluid transfers are made through electric swing-knife gate valves. Tank water is pre-treated with correct amounts of non-toxic additive surfactants and/or gelling agents, fed from small tanks into an upstream manifold to obtain the desired viscosity, adhesion and cling properties in the water-based suppressant used.

After the FSM latched onto an EPC is filled while parked under a silo, it autonomously rolls along the dock and through the open rear hatch of the docked eTanker, to be latched to its cabin floor, as shown in Figure 4, below.

Figure 4. The EPC (blue) with its silo-filled Fire Suppression Module (FSM) can autonomously roll along the dock through the open rear hatch into the cabin of the docked eTanker and be latched to its cabin floor, allowing, after swinging closed the eTanker’s rear hatch, immediate taxi for take-off.

The EPC is designed to be payload agnostic by virtue of its surface deck having a standardized array of latching rails that enable it to latch and haul not just a tank of fire suppressant but instead any of a wide array of other attachments. See Figure 5, below.

Figure 5. The electric payload cart (EPC) has a surface deck with a standardized array of latching rails to which can be attached a number of different payloads, including the Fire Suppression Module (FSM).

Those attachments include passengers seats, cargo bins, medevac litters, building materials, etc., each of which can latch to the standard pattern of latching rails on the surface of the EPC. The EPC itself has an automatic electric pin latching system by which it latches securely onto a standard pattern of latching rails on the cabin floor of an eTanker. That standard latching pattern on the cabin floor of the eTanker for latching the EPC is exactly the same pattern as is used on the robotic delivery cart (RDC).  

The RDC is an autonomous electric ground vehicle that is larger than the EPC and is designed to carry an EPC that is pin-latched onto its deck surface, regardless of the type of payload on the EPC. RDCs are roughly the size of a golf cart and comply with the specifications of a neighborhood electric vehicle or NEV. RDCs can autonomously haul a payload cart at 25 mph on neighborhood streets to deliver it to various ground destinations. These destinations could be the docks at other airparks, repair shops, residences or even to the location of a neighborhood house fire, where the payload cart’s fire suppression tank, coupled to a pump and spray nozzle, could autonomously and robotically spray its full liquid capacity onto the flames of a house fire. Figure 6., below shows a green RDC at the airpark dock with a docked eTanker ready to have the under-dock robot arm swap its battery pack.

Figure 6. The surface deck of the dock fits flush with both the top deck of the green RDC and the cabin floor of the docked eTanker, to allow easy autonomous transfer of payloads carried by the EPCs (blue), including the liquid carried in the tank of the Fire Suppression Module (FSM). The robot arm that autonomously performs battery pack swapping for the eTanker is shown under the dock with its two stacks of charged battery packs.

The integration of autonomous carts not only enhances operational efficiency but also reduces the workload on ground crews, allowing them to focus on other critical tasks such as fire monitoring, communication, and coordination with other firefighting resources. Furthermore, the electric-powered nature of these carts aligns with the system’s commitment to environmental sustainability, minimizing the overall impact of firefighting operations on the environment. The carts are equipped with sensors and navigation systems that allow them to safely and autonomously navigate the airpark facility, avoiding obstacles and optimizing routes for maximum efficiency. 

3. System Operation: A Coordinated Response to Wildfires

AAF operates through a well-coordinated system that synchronizes its various components, integrating cutting-edge technology with strategic infrastructure and operational procedures. Upon detection of a fire, whether through satellite imagery, ground sensors, or reports from the public, the AAF system initiates a rapid response. The nearest airpark is alerted, and a squadron of eTankers are immediately launched to the fire location. The system’s software analyzes real-time data from multiple sources, including weather conditions, terrain information, and fire behavior models, to determine the optimal 4D (3D + time) flight trajectory and fire retardant release points for each eTanker. This data-driven approach ensures that the eTankers are deployed in the most effective manner, maximizing the squadron’s capability to make nearly-continuous drops of fire suppressant onto the fire and minimizing the risk of collateral damage.

Guided by advanced software algorithms and real-time data, eTankers fly directly to the fire, adjusting their flight paths as needed to avoid obstacles and account for changing conditions. eTankers use a combination of GPS, LiDAR, and visual sensors to maintain situational awareness and avoid collisions with other aircraft or obstacles in their path. Upon arrival at the fire location, they drop fire suppressing liquid in a targeted manner on the areas most critical to dousing the flames. The precision delivery system allows for accurate placement of the drops, minimizing waste and maximizing fire suppression effects. The swappable EPCs at the airpark are each loaded with a tank of fire suppressing liquid and provide the returning eTankers with a nearly-continuous supply of retardant, allowing them to quickly reload and return to their mission. The eTankers make six to ten drops per minute until the fire is under control. Throughout operation, ground crews monitor the progress of the eTankers and the effectiveness of the fire retardant, providing feedback to the system and making adjustments as necessary. The system’s software continuously learns from each operation, refining its algorithms and improving its decision-making capabilities over time. 

Figure 7., below, shows the calculated effectiveness of AAF operations relative to that of the very large air tankers (VLATs).

Figure 7. Frequency of aerial fire suppression drops matters in effectiveness. The graph above is based on coverage level 2 with initial attack on the Cal Fire LNU complex fire using the actual data from https://graphics.reuters.com/CALIFORNIA-WILDFIRE/AIRCRAFT/bdwpkzmyyvm/ 

Fire detection is 4.5 minutes after ignition. The graph presumes 500 airparks for eTankers with local wind speed of 10 fps and flame spread at 10% of wind speed with a 24° spread angle on each flank. A squadron of eTankers operates with either 6 drops/minute (d/min) or 10 d/min. Minutes from take-off to 1st drop are: 35.4, 26.4, 4.5 for VLATs, S-2T and eTankers, respectively. VLATs are DC-10 and B-747. Drop intervals in minutes after 1st drop are: 20, 20, 18 for DC-10, B-747 and S-2T, respectively. B-747 data is hypothetical for 17,964 gallons per drop. NOTE: The graph does not account for slowing of flame spread by drops. The main message of this graph is shown by the green line trace that indicates the rapid and effective dousing of the fire achieved by 10 drops per minute with each of the squadron’s eTankers making a drop of 300 gallons. Even the smaller 150 gallon eTankers, when dropping 10 times per minute, are shown by the red dotted line with # legend to douse the fire within the first 30 minutes. Note the much less effective burn area suppression achieved with conventional VLATs.

4. Advantages of the System: A Paradigm Shift in Firefighting

The proposed AAF system offers a multitude of advantages over traditional firefighting methods, representing a paradigm shift in how we combat wildfires:

• Enhanced Access: The eTankers can access and operate in hazardous environments, such as in darkness, smoke or toxic fumes, and where it may be unsafe for human firefighters to enter. The ESTOL eTankers’ ability to maneuver in slow flight allows them to excel at terrain-following passes at low level over treetops. This enables them to access remote or difficult-to-reach areas, overcoming the speed and height limitations of very large air tankers (VLATs) and ground-based vehicles and enabling directly effective fire suppression in challenging terrains such as steep slopes, canyons, and dense forests. This enhanced access is crucial to promptly dousing small wildfires in wilderness areas where conventional air attack cannot reach.
• Increased Capacity: Small AAF airparks could blanket the nation to ensure that squadrons of eTankers can address any wildfire within minutes. The large available fleet of eTankers making frequent drops as often as every 6 seconds could deliver at least 20 times more liquid fire suppressant per hour than the present system. These massive volume drops would directly and effectively douse the wildfire rather than merely slow down the advance of its flame propagation front. 
• Rapid Response Time: A highly distributed network of airparks, combined with autonomous operations allows the AAF system to enable a swift and effective initial attack on nearly every fire incident, while the fire is small and manageable. Early initial attack limits the property damage and CO2 emission from the fire and can save lives. The system’s ubiquity and ability to operate 24/7, regardless of weather or visibility conditions, is its key to providing substantially greater effectiveness than conventional system. The use of squadrons of auto-refilled, autonomous vehicles with swappable battery packs also eliminates time lost to mobilization, filling, fueling and deployment procedures, potentially providing a 3-4 times faster initial attack on the fire.
• Improved Human Safety: By utilizing autonomous vehicles, the system significantly reduces the risk to human firefighters, who are often exposed to dangerous conditions during firefighting operations, such as extreme heat, smoke inhalation, and falling debris. This enhancement of safety can protect the lives of those on the front lines of wildfire operations.

5. Benefits of Fully Implemented AAF

• Ending wildfires could be the single fastest and most effective way to reduce atmospheric CO2 and thereby enable us to limit global warming to 1.5°C
• Reduce the frequency and severity of future extreme weather events
• Maintain and improve air quality to save millions of people from suffering serious lung damage
• Help restore affordable home-owners insurance
• Rejuvenate the civil aerospace and autonomous electric vehicles industries
• Encourage the development of more renewable energy 

6. Conclusion

The AAF system represents an urgently needed transformative advancement in firefighting technology. It is not only complementary to conventional methodologies, but by combining autonomous vehicles, interoperable facilities, and advanced software, the AAF system can provide an effective and sustainable approach to ending wildfires. The discovery that the cumulated damage from wildfires now accounts for the largest annual increase of atmospheric CO2 urges the immediate development and implementation of AAF as crucial to protecting our planet’s environment. The reach, capacity and applicability of AAF to nearly any environment combined with its focus on safety and sustainability qualify it as a global solution that can help all nations curb the climate crisis.

References

• ¹The data from Chen at https://essd.copernicus.org/articles/15/5227/2023/essd-15-5227-2023-discussion.html and the data from Zhuravlev: https://doi.org/10.3390/rs14215529 were combined to calculate the cumulated losses of CO2 sequestration: We applied these latest, most accurate data on the mean global wildfire burn areas over the 20-year period from 2000 to 2020 to the most recent compilation of the respective net ecosystem exchange values (NEE) for the main land-cover types of those burn areas (forest, grasslands, savannah, etc.) to obtain a first-order calculation of annual global atmospheric CO2 attributable to wildfires. We chose the period from 2000 to 2020 for our calculations to align with the data available in the studies linked above, and because it forms a representative and conservative sample of the modern era in which global wildfires have rapidly increased in size and frequency. Our findings are stark: When the losses of global CO2 sequestration are accumulated for the 20 years ending in 2020, they sum to over 95 Gigatonnes of CO2, and when combined with the 6 Gigatonnes of CO2 directly resulting from fire smoke in 2020, they comprise an annual CO2 emission of 101 Gigatonnes.
• ²https://keelingcurve.ucsd.edu/2024/05/08/largest-year-over-year-gain-in-keeling-curve-set-in-march/
• ³https://www.eenews.net/articles/epa-floats-sharply-increased-social-cost-of-carbon/
• ⁴https://extension.okstate.edu/fact-sheets/prescribed-fire-understanding-liability-laws-and-risk.html#:~:text=Liability%20concerns%20are%20often%20cited,reluctant%20to%20use%20prescribed%20fire.