Small unmanned airships for remote perception

8th International Airship Convention, Bedford, 2010

Climate-1 Paper 20

Small unmanned helium airships with electric power plant as low cost remote-sensing platforms

Adrian Peña Cervantes

UAS (Unmanned Aerial Systems) Consultant, Mexico City, Mexico.

Abstract As long as developing nations in Latin America make efforts to mitigate climate changes in their regions, the economic factor plays a major role in the implementation of affordable solutions. In the next years, mitigating climate change programs in Latin America will employ in larger scale aerial vehicles to collect, analyze and making modeling for biomass and soil carbon in community-level agricultural, agro forestry, or forestation/reforestation projects. In this case, unmanned remote sensing platforms could substantially change the costs and reliability of monitoring mitigation projects and enable greater participation even from small-scale agriculture in local communities across the region, where the use of satellite mapping or manned aircrafts could represent a prohibitive use because of the costs implied. The primary tool to map and estimate land cover or land use at the regional and local level could be a low-cost, unmanned helium airship under development by institutes and company partners in Mexico, Spain, Ecuador, Canada and USA which represents a better cost effective platform not needing specialized airfields, including energy efficient electric power plant with a photovoltaic envelope generator for auxiliary power storage devices, dependable new soil-analytical techniques that use visible-near-infrared reflectance (VNIR) spectroscopy and the most important: better training and operation qualities for farm and agro forestry operators.

Paper 20 Adrian Peña Cervantes

8th International Airship Convention, Bedford, 2010 2

1 INTRODUCTION According to the National Forest and Soil Inventory of Mexico 2004-2009 [1], In Mexico have evolved some 15,000 different plant species (between 50 and 60 percent of known species of Mexico so far) that are Mexico’s endemic. This means that half or more of Mexico’s flora cannot found anywhere else in the world. If one species becomes extinct in Mexico, it disappears completely from the world. This is an example of critical biodiversity issue that faces not only Mexico but most of the countries across Latin America region, fig 1. [2]

Fig.1: Forests at Risk in Latin America, with Assessment of Level of Threat. Image taken from the United Nations Environment Program through its global environment outlook (GEO) website [2]. Although over the past two decades, Sustainable Forest Management (SFM) has become an environmental issue worldwide, there is a widespread concern about high rates of forest loss and degradation in many areas. This states the need for new efforts by local agro-forestry communities and governments to collect new field data for

model parameterization, as existing forest inventory data are few and in constant change. In recent years, Mexican and Latin American Biologists have indicated that forests in the region may be subjected to a variety of different activities simultaneously, which may have interactive effects on ecological processes and the exploration of such interactions remains a significant modeling challenge in environment protection in the region [3]. A key current challenge for SMF is to develop adequate cost/benefit methods for mapping the value of different ecosystem services on which livelihoods depend so this information may be incorporated in a high rate in spatial planning. Such analyses obtained in a big scale could potentially be integrated with spatially explicit models of forest dynamics, providing a tool for exploring provision of ecosystem services under different scenarios of environmental change. The research outputs obtained are also requested to support the development and implementation of policies relating to SFM, through the development of decision-support tools and management recommendations. Actually, the Satellite and Manned aircrafts mapping is a widely used tool to obtain statistical models of the spatial dynamics of forest cover, species distribution data, and other GIS (Graphical Interface Systems) information among Latin America countries, in order to identify areas of actual or potential biodiversity loss, and thereby helping to identify priorities for conservation actions. As another widely used tool, the local surveys and mapping by forest and agriculture technicians are performed



today through a combination of conventional, manned aircraft fly-overs and foot patrols. Manned aircraft have a high cost rate, very high greenhouse gas emissions, are dangerous, intrusive in ecosystems and are not very good platforms for long and detailed imagery aerial photography due their normal high speed - high altitude above ground level flight conditions. In the other hand, conventional patrols are obviously very labor intensive, and thus slow and dangerous for human beings. These decision-support tools mentioned before permit the adequate production of map-based research outputs using survey techniques and GIS (Graphical Interface Systems) and greatly facilitate data integration and presentation in a form that can be understood by decision makers and provide a tool for exploring the potential impacts of different policy interventions. However, it is desirable to find decision-support tools that perform the same mapping activities, but with better cost-benefit conditions for the FSM challenges previously mentioned in this introduction. According to the previous assessment, it is the purpose of this paper to propose the embrace of airship technology as an affordable remote perception and mapping platform in accordance with Latin American boundary conditions given by the economic and ecological circumstances. The use of small unmanned helium airships for remote perception in forest and agriculture industry can represent a viable option capable to efficiently complement satellites, offering an excellent reactivity and a more permanent availability to the relevant environment specialists. These unmanned airships will bridge the gap between what can be measured by

satellites and what is measured at static ground-based, research stations. They are easy to transport, relatively simple to deploy in forest or remote geographic areas as well as easy to launch and recover by on-field operators and agro-forestry specialists. They provide real advantages in terms of modularity, silence, substantial autonomy and high degree of controllability during normal and scheduled day and night hours. Most of Its missions will take place within visual line-of-sight and at altitudes ranging from 150 to 500 feet and are therefore outside airspaces used by manned aircraft. Consequently, a significant number of remote perception applications could rapidly be fulfilled with this UAV Lighter-than-air technology. Additional to technological benefits, these systems reduce human life exposure in long, dull, intrusive and dangerous air missions for forestry and agriculture use. They provide potential economic savings and environmental benefits with less fuel consumption, less greenhouse gas emission, and less disruptive noise than for manned aircraft. Given the economic constrains, the procurement of an unmanned airship system is facilitated by the low required financial outlay and the less sophisticated payload requirements (when compared to military and manned aircraft) despite the lower training burden for forestry and agro-forestry operators. These Small Unmanned airships can be widely used for additional monitoring of wildlife and nature observation, and reveal excellent capabilities in support of the SFM policies and actions by the use



of hyper-spectral imagers ranging the VNIR (Visible and Near Infrared 400 - 1000 nm) and SWIR (Short-Wavelength Infrared 900 - 1700 nm) spectrum. These cameras have a world-wide use in various manned and unmanned environment projects. They represent the most growing technology tools in remote perception techniques to identify spectral features that are related to water stress, nutrient deficiency and pest infestation, among many other biophysical characteristics. Relaying the experience gained in Mexico during the last years with RPV Small Airships, Unmanned Aerial Vehicles and GNC (Guidance, Navigation and Control) techniques, it was decided to create in a true interdisciplinary spirit, a teaming with biologists, agriculture researchers, environmental engineers, airship experts, forestry technicians, renewable energy experts, institutes, companies and UAV professionals in different countries as Mexico, Spain, USA, Canada and Ecuador to create an airship technology test-bed demonstrator in the next years serving the agriculture and forestry community in Latin America region with commercial and industry standards. This airship project is believed to be a successful technology development consortium that brings recent advances in ultra-lightweight fabrics, composites, thin-film solar cells and unmanned control techniques, to create a small unmanned airship as outlined in this paper to become a viable decision-support tool for agro-forestry communities and environment protection organizations in Latin America.

2 DESIGN In order to conduct highly dependable flight operations in harsh forestry environments at different altitudes ranging from 0 – 9000 feet above sea level, the technical characteristics of the small unmanned airships are planned as follows:

• 3 small airships versions ranging 7.8 m – 14m long, 3.0m, maximum diameter.

• Equipped with 4 control rudders in a ``X shape'' configuration.

• 2 electric motors power plant as main thrusters providing a maximum speed 45 km/h, decreasing in wind gusts to 25 km/h. One Electric motor as stern propulsion thruster for Yaw control at low speeds is optional depending upon versions and missions requirements.

• Flight endurance: 1- 2 hours with 25Km/h cruising speed.

• Maximum available payload prospected to 8 kg (18 lb).

• Two envelopes in the airship hull body. Inner envelope works as pressure-resistant gas helium bag.

• Semi rigid configuration with outer envelope engineered to maintain rigidity necessary for the integration of solar cell array, gondola, stern thruster and rudders in the airship.

• Flight range according to electrical propulsion system (25Km/hr cruise speed) and autopilot capabilities is calculated for 5Km (3 Miles).

Figure 2 overviews the main Systems in the small unmanned airship vehicle design.



Fig.2: Small airship main systems and airship design. The operational requirements for the unmanned small airship will be designed under a logistic hierarchical plan executed under a mandatory flight operations center, considered to be implemented in the GCS (Ground Control Station) System. This system will provide coordination, monitoring and control of all systems of the UAVs small airship versions as well as weather forecast, computerized strategies and emergency operations [4]. 3 OPERATIONAL FEATURES 3.1 GNC Guidance, Navigation and Control. The GNC (Guidance, Navigation and Control) system provides an autopilot capability to the airship, so that its flight path meets the high-level objectives commanded by the forestry and agriculture operators. This system also gathers state and flight conditions information from itself and all other sub-systems, and transmits that data in a telemetry stream back to the GCS (ground control station). When the telemetry data is received by the GCS, it is displayed to the operator via user-configurable, customized displays. This feedback loop enables the operator to monitor the overall airship performance and then issue commands as necessary according to the pre-programmed flight mission.

The onboard GNC (guidance, navigation and control) system will work autonomously to perform station keeping in the presence of varying winds and rising/falling atmospheric density. The GNC will be designed under a R&D program starting with the creation of control algorithms for the unmanned airship in accordance to efficient operational qualities for agro-forestry operators and portable Ground Control Stations. These control algorithms will be tested using dynamic simulations through MATLAB – SIMULINK software. These simulations will identify potential errors before carrying out any hardware development, and therefore reducing greatly development costs [5] Some of the simulations activities will be the following: • Dynamics of the aircraft • Guidance and navigation • Control System • external disturbances (wind, etc ...) The research outputs from these simulations will be the following:

• Determine primary control equations.

• Autopilot dynamics simulations and control system response to perturbations.

• Response of different versions platforms to changes in the control system.

Previous experience in Unmanned Aerial Vehicles platforms by the Spanish and Mexican research companies and partner institutes in the consortium have allowed the input of new control theories in airship technology giving a GNC (Guidance, Navigation and Control) system project enrichment. Other



engineering partners in Ecuador have gained in recent years valuable experiences in airship projects, GNC systems as well as unmanned vehicles. They will provide many on-site tests and research outputs at different altitudes above sea level in their region and will take a design in the simulation loop for the electric propulsion management algorithms. The entire GNC system and Payload management control system will be embedded in an on-board rugged high performance “node” PC from the Nematron Corporation Company showed in fig. 3.

Fig. 3: Rugged High Performance "Node" Industrial PC model nc100 Photo courtesy of Nematron Corporation, Michigan, USA. 3.2 GROUND CONTROL STATION Since the small unmanned airship development intended must be practical and easy to operate, the operator’s interface will have a custom design based in portable and rugged Ground Control Stations. The design and development of the ground control station is carried out under the graphical programming language LABVIEW to display the following control and status data from the airship’s autopilot, sensors and basic instrumentation telemetry:

• Latitude, longitude and altitude from the GPS system on board.

• Latitude, longitude and altitude from the Kalman filter.

• Airship’s Euler angles. • Acceleration. • Angular velocity. • Airship’s magnetic bearing. • Static Pressure. • Dynamic pressure (Pitot-Tube)

according to airship’s performance at low speeds.

The GCS also provides for the creation of the following parameters for transmission to the airship:

• Configuration parameters control system

• Static pressure in the ground station.

• Operation Mode. • Points of programmed path on

the route or planned mission It has been agreed that a condition of up to 2 hours endurance is required. Therefore, for the final system, larger capacity batteries will be required and designed in a strategic plan for Solar Cells chargers and local electrical power when available at mission’s localities. In order to obtain the best energy budget control in an automated version, the Ground Control Station and on-board energy management system will be designed under the most advanced hardware and HMI (Human Machine Interface) in the industry. The Red Lion and Nematron Corporation companies from USA were selected to provide the entire SCADA (Supervisory Control and Acquisition) system), PLC (Programmable Logic Controllers), PC embedded Main processors and Resistive touch screens panels. Figures 4 and 5 show the display monitors and HMI hardware interfaces.



Fig. 4: Energy Management SCADA monitors. Photography courtesy of Red Lion, Inc.

Fig. 5: Roughed portable PC system with touch screen monitor for use in portable Ground Control Stations. Photography courtesy of Nematron Corp. 3.3 PROPULSION – ELECTRIC POWER PLANT The propulsion will be provided by a group of electric brushless motors (2 motors) attached to each side of the gondola below the center line of the airship and controlled by a dedicated DSP controller module that takes part of the GNC design. A third electrical motor will be installed in the stern portion of the hull to provide Yaw control under specific maneuvers at low speeds. This motor will be driven by the GNC system as well as the other power plant equipment and will have a control algorithm defined under software simulations and energy management. The power for these motors is supplied by a bank of Lithium-Polymer batteries (14.8V 4-6 cells 1600mAh X 2) carried at the gondola’s compartment with

1250W maximum electric consumption for each motor as well as associated wiring with low current waste cables along the entire electrical system. The propeller (14” x 7”) and motors are protected by a plastic ducted fence mounted at the end of a bar, which rotates driven by a servomotor and a gear system to provide plurality of controllable pitch thrust vector, in order to ascend, descend or gain speed in level flight. The reason to opt for electric motors even when they do not weight more than fuel engines was mainly the clean energy factor they provide and Control qualities for the autopilot system. In comparison with fuel engines they are less powerful, meaning reduction in the maximum reachable speed and the small possibility to fly in wind gusts. Anyway, the missions foreseen for remote perception missions in forestry and agriculture lands do not require fast operation speeds but quite and low vibration flights. Their main drawback is the weight of the required batteries, which considerably reduces the available payload onboard. Even when battery technology has reached amazing weight loss options, it is even a major factor to overcome in the present outlined airship project. 3.4 SOLAR POWER ARRAYS “Solar energy is attractive in an environmentally conscious age. Sunlight is a renewable, free non-polluting and non-inflammable fuel” (G. Khoury, Airship Technology, Chapter 16) [6]. Under this concept, the solar power system and cell arrays to be installed in the upper external surface of unmanned airship’s envelope, will be designed and constructed in Spain and Mexico by a couple of private research centers, taking a screening of the most promising



technologies in photovoltaic solar cell arrays based on requirements for the harsh environments where the Small unmanned airship will be operating. An analysis of costs and market conditions for selected photovoltaic technology is associated to this screening program to meet the requirements of the intended tasks, considering possible locations of the solar cells in the unmanned airship that could be consistent with the specific regional maps of radiation in the forest regions where agro-forestry remote perception operations will be executed. The target in mind in the research group for solar cell arrays is energetic efficiency under limited energy consumption for essential telemetry, payload and GNC (Guidance, Navigation and Control) Systems, but not including the electric power plant which as previously stated in this paper, will require a large amount of electrical power only guaranteed by battery systems. Progress toward the implementation and encapsulation of photovoltaic materials and their integration into the envelope in final unmanned airship system assembly has been slow but the first research outputs found viable application solutions. One of them would be the thermoplastic or thermosetting polymeric materials applied under different manufacturing processes as thermoforming, resin infusion and bonding. The cell arrays development program considers in a step-by-step procedure the study results provided by structure and stress analyst engineers in the research group for the selection of photovoltaic cells mechanical properties as following:

• Stiffness / flexibility and resistance.

• Low weight. • General operating conditions as

temperature, pressure, cycles of work, mode of operation, environmental conditions, etc.

• Permeability / leakage materials. • Service Lifetime. • Maximum costs (cost/benefit).

3.5 DATA LINK The Small Unmanned Airship missions require the use of a dependable data link to control and command the unmanned GNC (Guidance, Navigation and Control) system. A second data link will be installed on-board to down-link the real-time hyper spectral camera, as well an optional gyro-stabilized payload video streaming with a telemetry wireless sensor network. This WSN (Wireless Sensor Network) could pick-up sensor status signals across the forest and agriculture lands under monitoring. Appropriate high speed Data Link will be designed by institutes and companies in Mexico, Spain and USA to ensure that maximum benefits shall be provided to the unmanned airship operations with a high level of safety. Previous experiences in unmanned aerial systems and High Altitude Platforms telecommunications programs have lead the research group to envision and propose highly dependable wireless technology to be integrated as Data link system on board the small unmanned airship [7]. Standardization and compatibility with broader telecommunications strategies according to the Unmanned Aerial Systems trends in the world will be considered as main design criteria from the start point. Data Link necessary



connectivity exists, and the required frequency and bandwidth to control the unmanned aircraft are available, but the main fact from this point is to design the entire unmanned system in a worldwide wireless normalization and standardization format. According to general operational terms, the Data Link will operate mainly in the line-of-sight of the unmanned airship and in continuous presence of radio coverage. The knowledge of all flying parameters (down-linked to the control station by telemetry) is essential to ensure the appropriate handling of the airship. In addition, when automatic phases of flight are conducted, the pilot must be able to take over direct control of the unmanned airship during take-off and landing stages as well as in the case of unexpected or emergency situations along the mission path with radio coverage availability. An outside line-of-sight operation or radio coverage lost strategy will relay to the autopilot’s GNC (Guidance, Navigation and Control) system to autonomous command the airship for a “back home” maneuver and tracking the aircraft position in real time under emergency RF signal beacons. This will help the operators in the GCS (Ground Control Station) to track and maintain command of the aircraft under different emergency conditions. Figure 6 shows an overview of the entire Data Link system and a WSN (Wireless Network System) system. 3.5.1 WIRELES SENSOR NETWORK As mentioned before in the Data Link description, there is a practical approach for a type of forest monitoring system solution in a telemetry format to improve the presence of the monitoring

equipment and to introduce wireless sensor networks technology. This WSN system could enable on-field biologists to unobtrusively collect new types of data, providing a new decision-support tool for static mapping of physical conditions along the forest or agriculture lands. The flight operations across forestry and agriculture lands additional to obtain imagery and mapping through GIS photogram, could become a sensor’s status collector in areas previously prepared with sensor nodes in trees, soils, waterways, rivers and any other biophysical status sensor necessary. The hardware design of sensor network nodes and network protocols for forest monitoring will be conducted by Biologists and telecommunication engineers in research institutes in Mexico, Canada and Spain in order to obtain a specialized custom technology test-bed with wide applications capabilities. The principle of operation of this system is based under the assumption that the small unmanned airship operations along the mission corridors established in environment monitoring programs will provide the opportunity to collect through wireless telemetry, sensed data and re-transmit to the field biologists this information during flight visits to its coverage areas. Collected data also will be stored in the on-board database server, which will serve the user's management software queries. Users will be able to access a real-time display of forest information and also dynamically interact with the wireless sensor network through the Ground Control Station Mission management software.



The sensing devices that can be installed on individual trees or agriculture and forestry soils are the following:

• CO2 sensor. • Humidity and temperature

sensors. • Pressure sensor. • Soil moisture sensors.

Figure 6 shows the wireless sensor network and its associated displays through the Data Link system.

Fig. 6: Data Link and Wireless Sensor Network. 3.6 PAYLOAD - HYPERSPECTRAL CAMERA The small unmanned airship will employ spectral imaging techniques to identify spectral features that are related to surveys of forest and agriculture land, obtaining high spatial, spectral, and temporal resolution imagery from biophysical parameters as water stress, nutrient deficiency, pest infestation in woodland and soils as many others. In order to obtain this data acquisition and image sequence into the system’s payload port, the research group conducted an evaluation trial for the selection of a very small, lightweight, and robust hyper spectral imaging

instrument capable of being deployed in harsh environments such as those encountered in the forest monitoring activities. This hyper spectral imaging instrument, built by the company Headwall Photonics Inc. (Fitchburg MA, USA), has a totally-reflective, aberration-corrected concentric imager design with an f/2.8 optical aperture, covering spectral ranges in the VNIR- Visible and Near-Infrared (400 - 1000 nm) and in the SWIR-Short-Wavelength Infrared (900 - 1700 nm). The aberration-corrected, concentric imager design delivers extremely low distortion over an exceptionally large Field of View, a large aperture for high signal to noise ratio (SNR), and very low stray light for accurate radiometric measurements, all very critical specifications in a spectral imaging instrument. The fully-integrated Micro-Hyperspec™ (Fig 7) Imaging Spectrometer model weighs 2.2 lbs including fore optic lens and 2-D camera. In the other hand, the weight of the additional technical equipment mounted on the payload port is a critical constraint expected to become around 10 lb including shock resistant fanless Industrial PC built by the Nematron Corporation Company, the Data Link equipment as well as associated power supplies and batteries for the support of the hyper spectral payload tasks.



Fig 7: Micro-Hyperspec™ Imaging Spectrometer. Photography, courtesy of Headwell Photonics, Inc. 4 CONCLUSIONS

The small unmanned helium airship could be considered as a “flying robot”. However, we are far from being able to design actual lighter-than-air autonomous flying machines with highly developed and reliable artificial intelligence. This project in terms of unmanned aerial vehicles systems is a new opportunity to increase autonomous tasks for airships platforms. Despite, “unmanned” term might give the wrong idea that there is no “flight crew” or “no man in the loop”, the human part of the operation will be the main aspect in the flight/mission tasks. Furthermore, the “man in the loop” for remote perception activities will be mainly the field biologists, the agriculture and forest technicians and the ecologists that know really “what to see” in environmental terms and “what to look for” in spectral imagery terms. The autonomous ability inherent to the small airship through its autopilot system and GNC system will assist mainly the operators to conduct easer and more precise operations and to reduce work load activities in a highly dependable control loop from the Ground Control Station.

Another important aspect to solve in this project will be the legal and regulatory implications with civil authorities like FAA (Federal Aviation Administration), DGAC (Dirección de Aviación Civil, in spanish –General Direction of Civil Aeronautics, in English) in Mexico and other aviation regulatory organisms as ICAO (International Civil Aviation).

Generally speaking, if we want to get airborne the small unmanned airship in a commercial sustainable mode, first we need to get the corresponding certificates and/or permits, and one of them is the one that certifies the airworthiness of the system for the intended unmanned operations.

Unmanned Aerial Vehicles (or UAVs) can fly in segregated air space as well as in non-segregated air space. When flying in non-segregated air space, they shall do so with the same safety guarantees as manned aircraft. This is therefore an issue with multiple dimensions, such as legal, regulatory and certification, which need to be addressed globally therefore not in isolation one from the others. [7]

In Latin America, UAV/AUS regulations are a very unclear subject, but the project outlined in this paper means an opportunity to open discussions about the way to introduce new standardizations for lighter-than-air unmanned aerial vehicles in the region.

Despite technical, administrative and budgeting issues, the proposed small unmanned airship project under consortium model in different countries is a great opportunity to expand the lighter-than-air technology knowledge in Latin America with an environmental, technological and social deep impact.

“If you have built castles in the air, your work need not be lost; that is where they

should be. Now put the foundations under them” -

Henry David Thoreau, American author, poet, naturalist, historian and

philosopher.



5 ACKNOWLEDGEMENTS

• I express my gratitude to the National Council for Science and Technology (CONACyT) of Mexico [9] for its funding and technical support to airships and unmanned vehicles programs in previous years. Without the Mexican government policies to support science, technology and innovation, this research project could not be possible.

• I acknowledge with gratitude the valuable help of biologists from the Institute of Ecology AC of Mexico, INECOL [10] for their valuable engagement, advice, and review of various materials to help me understand the environmental problems faced in Mexico and Latin America and to help me take my project involved in the environment conservation.

• I want to express sincere appreciation for the intense and dedicated work performed by the funders, members and collaborators of the International Airship Association to promote the airship technology. Their advice and enthusiasm are invaluable for Latin American airship researchers.

• I would like to express my gratitude to the Western Hemisphere Information Exchange, especially to Ricardo Arias from the Science & Technology Stability directorate of the U.S. Southern Command for their support to my research activities thorough the invitation to join conferences and forums devoted to unmanned vehicles systems and environmental projects in Latin America [11].

6 REFERENCES

[1]National Forestry Commission

http://www.conafor.gob.mx/biblioteca/Inventario-Nacional-Forestal-y-de-Suelos.pdf El Inventario Nacional Forestal y de Suelos de México 2004-2009. Una herramienta que da certeza a la planeación, evaluación y el desarrollo forestal de México.

[2]http://www.unep.org/geo/. United

Nations Environment Programme. Global Environment Outlook.

[3]Toward Integrated Analysis of Human Impacts on Forest Biodiversity: Lessons from Latin America. Copyright © 2009 by the author(s). Published here under license by the Resilience Alliance.Newton, A. C., L. Cayuela, C. Echeverría, J. J. Armesto, R. F. Del Castillo, D. Golicher, D. Geneletti, M. Gonzalez-Espinosa, A. Huth, F. López-Barrera, L. Malizia, R. Manson, A. Premoli, N. Ramírez-Marcial, J. Rey Benayas, N. Rüger, C. Smith-Ramírez, and G. Williams-Linera. 2009. Toward integrated analysis of human impacts on forest biodiversity: lessons from Latin America. Ecology and Society 14(2): 2. [online] URL: http://www.ecologyandsociety.org/vol14/iss2/art2/

[4]Jurgen Bock, Airships to the Arctic V

Symposium, Calgary, Canada, 2009. “Lay-out of an LTA cargo carrier for autonomous operation”, p 12-21.



[5]Roy Langton, “Stability and Control of Aircraft Systems Introduction to Classical Feedback Control”, Aerospace Series-Wiley.

[6]Airship Technology, Edited by

Gabriel A. Khoury and J. David Gillett, Cambridge University Press 1999

[7]Cuevas Ruiz-José Luis, Aragón-

Zavala Alejandro, Delgado-Penin Jose Antonio. “High-Altitude Platforms for Wireless Communications”, Wiley, first Edition 2008

[8]International Civil Aviation

Organization – Information paper www.icao.int/anb/panels/acp/wg/f/.../acp-wgf18ip08_eads_rev%201.doc

ACP-WGF 18/IP08 12/05/08. [9] The National Council for Science

and Technology of Mexico (CONACyT) URL: http://www.conacyt.gob.mx/

[10]INECOL Institute of Ecology AC,

Mexico. http://www.inecol.mx/index.php/english

[11]Latin America Fuel and &

Unmanned Vehicles Conference. Panama City, December 2009. http://www.arc.fiu.edu/WHIXConference/Default.aspx