DEATH BY A THOUSAND CUTS:

Micro-Air Vehicles in the Service of Air Force Missions 
 
 
 

by

Arthur F. Huber II, Lieutenant Colonel, U.S. Air Force 
 
 
 

July 2002

Occasional Paper No. 29

Center for Strategy and Technology

Air War College 
 

Air University

Maxwell Air Force Base, Alabama 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

DEATH BY A THOUSAND CUTS:  
 

Micro-Air Vehicles in the Service of Air Force Missions 
 
 
 

Arthur F. Huber II, Lieutenant Colonel, U.S. Air Force 
 
 

July 2002 
 
 

The Occasional papers series was established by the Center for Strategy and Technology as a forum for research on topics that reflect long-term strategic thinking about technology and its implications for U.S. national security.  Copies of No. 29 in this series are available from the Center for Strategy and Technology, Air War College, 325 Chennault Circle, Maxwell AFB, Alabama 36112.  The fax number is (334) 953-6158; phone (334) 953-6460. 
 
 
 

Occasional Paper No. 29

Center for Strategy and Technology 
 
 

Air University

Maxwell Air Force Base, Alabama 36112 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Contents

Page

Disclaimer…………………………………………………………….…...i 
 

Tables and Illustrations………………..………………………………….ii 
 

Preface and Acknowledgements…………………………………………iii 
 

Author…………………………………………………………………….iv 
 

Abstract……………………………………………………………………v 
 

I.  Introduction…………………………………………………………….1 
 

II. Why Micro Air Vehicles?………………………………….…………..3 
 

III. The State of Micro-Air Vehicle Technologies…………………...…..13 
 

IV.  Micro Air Vehicle Support to USAF Functions…...………………..31 
 

V.  Summary and Concluding Thoughts…………………………………47 
 

Notes……………………………………………………………………..51 
 
 
 
 
 
 
 
 
 
 
 
 

Disclaimer

      The views expressed in this publication are those of the author and do not reflect the official policy or position of the Department of Defense, the United States Government, or of the Air University Center for Strategy and Technology. 
 
 
 
 
 
 
 
 
 
 
 

i 
 
 
 
 
 

Tables and Illustrations

Page

Table 1.  UAV Classifications, Characteristics, and Examples……….…..4 
 

Figure 1.  Comparison of Micro-Air Vehicle Flight Regime …………….5 
 

Table 2.  Baseline MAV Weight Distributions …………………………14 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

ii

Preface and Acknowledgments

   What are the potential Air Force applications of emerging micro-air vehicle (MAV) systems and supporting technologies and what are the implications of this potential for the execution of military operations?  These are the central questions that motivated the development of this research paper.  As an Air War College (AWC) student in an elective class sponsored by the Center for Strategy and Technology (CSAT), I was afforded the chance to delve into this area, one that I have been watching with interest for several years.   I have found this area to be of personal and professional interest, because it harks back to the aerodynamics research I conducted as a graduate student at the University of Notre Dame.  Also, it opens up possibilities for enhancing the asymmetric advantages of air power enjoyed by the United States as compared with the rest of the world. 

   While I am solely responsible for the work represented by this research paper, it could not have come to fruition without the key contributions of several people.  At the top of the list are my wife, Beth, and daughter, Juliann, who endured many late nights during which I worked away on this research.  I am pleased to acknowledge the sage guidance and key insights provided by my CSAT advisors, Dr. Grant Hammond and Colonel (Ret., USAF) Ted Hailes.  Several professionals in the field of micro-air vehicle development also deserve praise for reviewing this manuscript and they include Dr. William Davis and Mr. David Johnson of MIT Lincoln Laboratory, Dr. Thomas Mueller of the University of Notre Dame, and Dr. Steven Walker of the Air Force Office of Scientific Research.  Lastly, I thank my fellow CSAT and AWC Seminar 3 classmates for their genuine interest in this research topic and their constructive comments to make it a better product.

iii 

The Author 
 

      Lieutenant Colonel Arthur F. Huber, II, is a flight test engineer whose career has spanned various assignments within the weapon systems acquisition process.  He holds Bachelor degrees in Aerospace Engineering and Government & International Relations as well as a Master of Science degree in Aerospace Engineering, all from the University of Notre Dame.  He is a distinguished graduate of the Air Force Reserve Officers Training Corps and Squadron Officer School.  He has served as an Air Force Fellow at RAND for in-residence Intermediate Service School, and is a recent graduate of the Air War College.

   Lieutenant Colonel Huber started his military career assigned to the Air Force Space Technology Center as a staff plans officer, space-based surveillance technology program manager, and executive officer to the commander.  While there, he was selected to attend Air Force Test Pilot School and graduated in June as a flight test engineer.  He was then assigned to the 46^th Test Wing where he was a branch chief while managing flight test activities for technology demonstrations, air-to-air missile development, safe separations, and avionics integration. While assigned to RAND, Lieutenant Colonel Huber performed policy research on military acquisition reform, counter-proliferation of weapons of mass destruction, laboratory quality measurement, and “reachback” operations.  Subsequently, he transferred to the Pentagon where he performed duties as a Program Element Monitor for electronic warfare and air-to-air missile programs within the Office of the Assistant Secretary of the Air Force for Acquisition.  Thereupon, he was selected to command the 413^th Flight Test Squadron during its busiest period ever accruing over 2000 test hours per year in support of electronic warfare systems development and testing. 

   Lieutenant Colonel Huber has flown in multiple aircraft systems accruing approximately 100 hours in utility class planes and another 425 hours in high-performance aircraft to include the F-4, F-15, F-16, and T-38.   
 
 
 
 

iv

Abstract

   Technological progress in a number of areas to include aerodynamics, micro-electronics, sensors, micro-electromechanical systems (MEMS), and micro-manufacturing, is ushering in the possibility for the affordable development and acquisition of a new class of military systems known as micro-air vehicles (MAV).  MAVs are a subset of uninhabited air vehicles (UAV) that are up to two orders of magnitude smaller than the manned systems that permeate our contemporary life.  Recent advances in miniaturization may make possible vehicles that can carry out important military missions that heretofore were beyond our reach or could only be attained at great risk or resource expenditure.  These missions will be possible if MAVs can fulfill their potential to attain certain attributes to include: low cost, low weight, little to no logistical “footprint,” mission versatility, range, endurance, stealth, and precision.

   A review of the literature in this area indicates that the military potential of this emerging field remains on the “technological push” side of the equation with little to no “requirements pull” from the user community.  Accordingly, concepts of operations deriving from the war fighting community – particularly the United States Air Force (USAF) – are sparse.  At a higher level, the potential of micro-air vehicles opens up new possibilities in the formulation of military strategies that require investigation.  This paper provides an outline of the contemporary technological dimension of MAVs and contemplates how they might be used to enhance Air Force operations. 
 
 
 
 
 
 
 
 
 
 

v 
 
 
 
 

I.  Introduction

A two-ship of enemy fighters taxies to the end of the runway to conduct their last checks before take-off.  Just as the aircraft rev their engines a handful of aircraft a bit smaller than model airplanes dive down from an altitude of 300 feet.  Unseen by airfield observers because of their small size, these innocuous vehicles home in on the fighters’ engine intakes using a combination of imaging infrared and acoustical sensors.  Darting into the intakes they quickly cause foreign object damage and engine shutdown.  There will be no glory in aerial combat for these fighters today.

—A possible wartime scenario in the not too distant future 
 

   There are many pressures on today’s U.S. military.  The variety and the nature of threats and other challenges expands daily.  Potential adversaries get smarter all the time and their access to modern weaponry appears uninhibited.  There is no reduction in operations tempo. The lag between cutting edge technologies and those installed in newly fielded military systems appears to be worsening, and efforts to contain costs meet with limited success at best. 

   That the U.S. continues to exercise its unqualified leadership in military matters around the globe in the face of such pressures is a tribute to its leaders’ vision as well as the hard work and ingenuity of its people.  The soundness of such leadership and its underpinnings are attested to by the preeminence of our nation’s air forces, which more and more are being pushed to the “front lines” of conflict.  They have become the weapons of choice for handling difficult duties throughout the world.  Without taking anything away from the military people who make this preeminence a daily reality, it is no less founded on the superior war fighting capabilities inherent in our systems and technology.  These advanced technologies provide an asymmetric advantage to U.S. forces, at least to the extent the U.S. acquires them first, and forges their incorporation into concepts of operation.

   One area of technological advancement that holds promise to help the U.S. maintain its military leadership is the emerging field of micro-air vehicles (MAV).  Technological progress in a number of areas including, but not limited to, aerodynamics, microelectronics, sensors, micro-electromechanical systems (MEMS), and micro-manufacturing, is ushering in the possibility for the affordable development and acquisition of this new class of military systems.  MAVs are a subset of uninhabited air vehicles (UAV) that are roughly two orders of magnitude smaller than the manned systems currently in use.  Recent advances in miniaturization may make it possible for very small vehicles to carry out important military missions that are either too risky or too expensive to conduct today.  These missions should be possible if MAVs achieve the characteristic attributes of being low cost, low weight, having little to no logistical “footprint,” mission versatility, range, endurance, stealth, and precision.  Micro-air vehicles may represent a pioneering advancement providing the U.S. a new asymmetric advantage.

   A review of the literature in this area indicates that the military potential of this emerging field remains on the “technological push” side of the equation with little to no “requirements pull” from the user community.  Accordingly, concepts of operations deriving from the war fighting community – particularly the United States Air Force – are sparse.  At a higher level, the potential of MAVs opens up new possibilities in the formulation of military strategies that require investigation.  This paper undertakes to ask and provide answers to two essential questions: What are the potential Air Force applications of emerging micro-air vehicle systems and supporting technologies and what are the implications of this potential for the execution of military strategy? 

   To answer these questions this paper will start with a generic overview of what is unique about MAVs that makes their development inviting and how they compare to other UAV systems.  Then, it will assess their potential and the interest in them and their applications within the Air Force, the other military services, and the civilian arena.  Subsequently, a thorough review of MAV technologies will be presented followed by investigation of military functions they might fulfill and potential contexts in which they might be employed.   
 
 
 
 

II. Why Micro-Air Vehicles?

What Makes Micro-Air Vehicles Unique?

   MAVs are a subset of UAVs characterized by their relatively small size.  With wingspans in the fifteen-centimeter range, MAVs have a number of advantages including the following: 
 

• MAVs may be more amenable to a “faster, better, cheaper” approach to their development, procurement, and fielding
• It should be possible to design MAVs to have a small (even negligible) logistics footprint
• MAVs may afford a “commodity” approach to mission accomplishment either by enabling a variety of payloads to be manufactured for a single airframe or by proving flexible enough to permit payload variation in the field
• MAVs may prove a cost-effective augmentation to existing, low-density, high-demand systems
• MAVs may bring mission capabilities to smaller units that heretofore were not large enough to justify possession and operation of traditional systems providing such capabilities
• MAVs may afford the U.S. asymmetric avenues in the conduct of warfare

   While the diminutive nature of micro-air vehicles makes possible their employment in a variety of military settings, it also comes with constraints that must be acknowledged and taken into account for proper tactical use. Likewise, the fact that MAVs can be found within a spectrum of UAV capabilities provides an onus to avoid redundancy and to optimally focus use on applications that leverage their unique characteristics.

   Table 1 below provides a listing of the spectrum of UAVs and the relative place of micro-air vehicles within it. 
 

Table 1.  UAV Classifications, Characteristics, & Examples

Source: adapted from Peter Van Blyenburgh, “UAVs – Where Do We Stand?” Military Technology, March 1999, 29-30.  Used with permission from Monch Publishing, Bonn, Germany. 
 

   As can be seen from this table, micro-air vehicles occupy a niche very near the bottom run of UAV systems.  MAVs possess wingspans in the range of fifteen centimeters (about six inches) as compared to the high end UAVs, which can have wingtip-to-wingtip measurements of up to 3500 centimeters, as in the case of Global Hawk.  This represents over two orders of magnitude difference in size.  Figure 1 below provides some perspective for this difference in scale.  The horizontal axis in the figure uses “Reynolds Number” which is an aerodynamic scaling function directly proportional to size and speed.  As shall be discussed later, the small size of MAVs has profound consequences for their design with regard to aerodynamics and systems integration as well as for their mission utility.  The example missions listed for MAVs in Table 1 are verbatim from the table’s source, but as shall be seen later, are only a partial listing of the possible mission set.   
 
 
 

Figure 1.  Comparison of the Micro Air Vehicle (mAV) Flight Regime with Others¹ 
 

What Is the Basis for an Air Force Interest in MAVs?

   From a military point of view, micro-air vehicles are attractive for a number of reasons.  The leading motive would appear to be the promise they hold in the realm of information operations, particularly support for intelligence, surveillance, and reconnaissance (ISR) before, during, and after events of interest.  These functions will be executed through carriage and operation of miniaturized sensors, a key element of Joint Vision 2020.²

   The goal here is greater battlespace awareness and reduced decision cycle times.  To the extent MAVs contribute favorably to these goals, compared to other alternatives, their use in military contexts will appear inviting. 

   The USAF is fully on board with this Joint Staff vision.  In America’s Air Force Vision 2020, the Air Force leadership states, 
 

[W]e’ll provide the ability to find, fix, assess, track, target and engage anything of military significance, anywhere. . . . Information superiority will be a vital enabler of that capability. . . . Capitalizing more fully on a set of revolutionary technologies – like stealth, advanced airborne and spaceborne sensors and highly precise all-weather munitions – we’ll operate with greater effectiveness . . . With advanced sensors and a range of precise weapons, from large to very small, we’ll be able to strike effectively wherever and whenever necessary with minimum collateral damage.³ [emphasis added] 
 

With this statement, the central importance of information superiority is acknowledged, while the solution space is left open to systems of any size that can get the job done.

   Though such vision statements are necessarily broad in scope, the Air Force has made a limited number of pronouncements that are more specific in their endorsement of systems and technologies similar in kind to MAVs.  In New World Vistas Air and Space Power for the 21st Century, published in 1995, the Air Force Scientific Advisory Board laid out predictions for technologies relevant to the future of the Air Force.  To their credit, the Study Board members prefaced their predictions with an assumption on what the future combat environment will look like.  To summarize, the Scientific Advisory Board foresees a smaller Air Force having to fight a long way from home, in urban and jungle terrain, against adversaries from the nation-state level down to terrorist cells, attacking a wide variety of targets from conventional weapons to information systems, and having to deal with nuclear, Biological, and chemical (NBC) weapon threats.  In order to help address these challenges, the study asserts that it should be a “goal” of the Air Force to “know at all times the relevant global military situation,” and ensure “such awareness should be in near real time.”

   In addition to “Global Awareness,” the study goes on to outline five other “capabilities” that it sees as necessary for the Air Force “to continue into the 21st century as the world's best and most respected” aerospace power and posits a number of system concepts to provide such capabilities.  One “Global Awareness” system mentioned is a “miniature UAV” (itself carried aboard a “larger UAV”) that could deploy ground sensors.  Of the other five “capabilities,” one has some relevance to MAVs, that being “Projection of Lethal and Sublethal Power.”  A system proposed in this vein is a “robotic micro munition” designed “to attack deeply buried hard targets.”  The study also identifies key technologies for development that will support its vision.  Among those worth highlighting are micro-sensors having “novel readout methods” and “low probability of intercept” as well as “[m]icro-electromechanical systems for sensing and manipulating.”⁴

   One other official document which speaks to MAV-like systems resulted from an effort directed by the Chief of Staff of the Air Force known as Air Force 2025.  This study outlined several “alternate futures” or environments to facilitate its strategic planning methodology and defined them as “an array of [possible] future worlds in which the U.S. must be able to survive and prosper.”  Within this context the study team identified ten “top systems” among forty-three envisioned, including a concept known as “attack microbots.”  This concept is described as 
 

. . . a class of highly miniaturized (one millimeter scale) electromechanical systems capable of being deployed en masse and performing individual or collective target attack. Various deployment approaches are possible, including dispersal as an aerosol, transportation by a larger platform, and full flying and crawling autonomy. Attack is accomplished by a variety of robotic effectors, electromagnetic measures, or energetic materials. Some sensor microbot capabilities are required for target acquisition and analysis. Microbots could provide unobtrusive, pervasive intervention into adversary environments and systems. The extremely small size provides high penetration capabilities and natural stealth. 
 

In assigning this concept a role in future interdiction missions the study said, “Penetrating sensors and designators, coupled with micro-technology, will permit weapons to have the processing power required to ‘touch’ targets in the right spot.”⁵ 

   While not one of the “top 10,” the Air Force 2025 study also identified a concept known as “miniature unattended ground sensors” to support the intelligence, surveillance, and reconnaissance function.  These devices would be air-dropped as a “swarm” in the vicinity of a “supply chokepoint and become a remote sentry reporting on enemy activity.”  In this capacity, miniature unattended ground sensors would help guide munitions as well as report on munitions effects.  Predicting just how far the technology might advance, the study asserted that miniature unattended ground sensors of 2025 with a complete suite of communications and power capabilities, camouflage, and either motive or adhesive systems would be one centimeter square by one millimeter thick.”  It further stated that miniature unattended ground sensors would be “ideal for detecting weapons of mass destruction and operating in urban environments.”⁶

   To enable these and other concepts to become a reality, the Air Force 2025 study identified six “high leverage technologies,” which “stood out because they are important to a large number of high-value system concepts.”  Among these were “micro-mechanical devices” which has already been alluded to above as MEMS.⁷  Such devices are sized on the order of hundreds of microns and represent fully functional mechanical machines – sometimes combined with electronic devices – and manufactured through lithography or similar techniques used in computer chip production.  Given the centrality of micro-electromechanical systems to MAVs and other micro-robotic systems, their development should be viewed as a “critical path” item.

   Another organization expressing interest in micro systems for Air Force application is RAND. While not an “official” source of Air Force opinion, RAND has nonetheless proven itself a significant influence over Air Force thinking in the realms of technology and policy.   In Technology Trends in Air Warfare senior RAND analyst, Benjamin Lambeth, envisions “[m]icrosensor-directed micro-explosive bombs . . .able to kill moving targets with just grams of explosive.”  Additionally, he sees a time when “[g]round weather sensors can be delivered by small UAVs aboard larger UAVs.”⁸   Another RAND study, Military Applications of Microelectromechanical Systems (MEMS), posited a number of concepts to demonstrate how MEMS could have military utility.  While none of them was specifically a micro-air vehicle type system in itself, each could be married up to a MAV to enable a useful mission.  These concepts included the following: 
 

• Chemical sensor for the soldier
• Identification friend or foe
• Active surfaces
• Distributed sensor net
• Micro-robotic electronic disabling system

The first concept, if carried aloft by a MAV, would allow remote sensing of noxious battlefield agents such as nuclear, biological, and chemical products.  The second could be delivered by MAVs to facilitate targeting of enemy resources and avoidance of fratricide.  The third could be a means at the subsystem level to enhance MAV aerodynamic performance.  The fourth MEMS concept would “allow the commander to blanket an area [with micro-sensors] with a single shot, or to use micro-sized UAVs for seeding.” 

   The micro-robotic electronic disabling system concept involves target attack and disabling via infiltration of the target’s electronics.  It would be dispensed in the general neighborhood of the target via carrier vehicle such as an UAV.  The micro-robotic electronic disabling system would be contained within small canisters that would fly or glide (via “aerobot,” parafoil, etc.) to within a short distance of their target(s).  From there they would then move on their own to infiltrate and deliver the kill mechanism.  Targets vulnerable to micro-robotic electronic disabling systems would include: power plants and relay stations, transportation grid nodes, airports, seaports, switching yards, major freeway intersections, television and radio stations, telephone exchanges, computer based research centers, and electronics at key industrial sites.⁹

   As can be seen from this limited set of sources, the Air Force certainly has reason to be interested in micro-air vehicles.  They hold potential to provide military worth by supporting “global awareness” and power projection operations.  Despite such potential, there is only one dedicated research and development (R&D) program under Air Force sponsorship known to the author that is looking at how MAVs could be optimized for Air Force missions.¹⁰  Instead, interest appears to be greater in other military circles.

Who Else Is Interested in MAVs?

   The Army, Navy, and Marines currently appear to be showing much greater interest in micro-air vehicles than the Air Force.  Interest in these aircraft has also appeared from civilian quarters as well.

Military

   Currently, the bulk of U.S. R&D sponsored by the military in micro-air vehicle technologies comes from the Defense Advanced Research Projects Agency.  They are now in the third year of a $35 million four-year program in which MAVs and supporting technologies are being developed and demonstrated.¹¹   This program can trace its roots back to two workshops hosted by RAND in the early 1990s in which several technologies were identified “warrant[ing] greater U.S. defense R&D investment.”  Among these promising program areas was development of “miniature (e.g., fly-size) flying and/or crawling systems capable of performing a wide variety of battlefield sensor missions.”¹² Later, in the mid-1990s, the Massachusetts Institute of Technology Lincoln Laboratory did some technical analyses which pointed to the feasibility of MAVs.  Not stopping there, they devised a conceptual design and presented it to then Vice Chairman of the Joint Chiefs of Staff, Admiral William Owens.  Upon being asked if he saw potential utility in such a machine, the Admiral was impressed enough to encourage the Lincoln Laboratory researchers to continue their work in the field and to challenge his brethren in the naval R&D community to do the same.¹³

   According to the Defense Advanced Research Projects Agency (DARPA) micro-air vehicle program representatives, a shift toward a more diverse array of military operations, often involving small teams of individual soldiers operating in non-traditional environments is already evident in the post-cold war experience.”  As a result, there is a need for small reconnaissance sensors to provide “greatly enhanced situational awareness for the small unit or individual soldier.”¹⁴

   The focus of thinking within DARPA is support for the “over-the-next-hill” and “around-the-corner” reconnaissance needs of foot soldiers either individually or in small units.   Special operations units also function in small groups, often performing missions of extreme sensitivity and imminent danger.  Thus, it is no surprise that the U.S. Special Operations Command saw fit to draft a “first operational requirements document for an MAV” in June, 1998.¹⁵  The U.S. Army’s Armor Center and the United States Marine Corps are also reportedly in the midst of drawing up requirements documents for MAV (or slightly larger mini-UAV) systems.¹⁶

   The Naval Research Laboratory has cooperated extensively with DARPA on micro-air vehicle work, receiving funding from the latter, but has focused MAV payload work in a direction different than intelligence, surveillance, and reconnaissance.  Instead, the Naval Research Laboratory has looked to MAVs to act as a means to carry out the suppression of enemy air defenses mission.¹⁷  Their concept of operations has either foot soldiers or larger UAVs carrying the MAV to within several kilometers of the target.  Then, it would fly autonomously with its miniature jammer package to a landing on the threat radar whereupon it would commence interfering with the radar signal.  What the jammer lacks in power, would be compensated for by reduction in distance to the victim receiver.¹⁸

Civilian

   It is difficult to gauge how much R&D is being conducted by commercial firms, insofar as almost all the literature dealing with the subject relates to military sponsored work.  Even for efforts paid for by the military, the developers are quick to point out civilian applications for MAV systems.  Dr. Samuel Blankenship at the Georgia Tech Research Institute (GTRI) foresees use of MAVs by police and fire officials, scientists, and farmers.  Tasks might include killing harmful insects, measuring smokestack emissions, monitoring concentrations of chemicals in agricultural or industrial spills, surveying wildlife, and providing recreation as toys.¹⁹   Still other possibilities mentioned include: traffic monitoring, border surveillance, forestry, power-line inspections, real-estate photography,²⁰ hostage crisis monitoring,²¹ search and rescue (such as maneuvering through damaged buildings looking for survivors after a disaster), locating illegal drugs or weapons,²² surveillance of criminal activities,²³ replacing weather balloons, serving as temporary antennas,²⁴ crowd monitoring and control,²⁵ home security, and the entertainment industry.²⁶  

   In the aftermath of the terrorist attacks of September 2001, other uses of MAVs have come to the forefront.  MAVs may be useful for homeland security and anti-terrorist applications to include detection of weapons, and tracking targets of interest such as personnel or shipments. 

   It appears that unlike other trends in defense related R&D, the tide has not yet turned for micro-air vehicle technologies.  As a result, the military cannot yet depend on commercial interests to lead the way in development as has occurred in the microelectronics industry.  Instead, the military will have to continue to provide the “seed” resources and leadership to promote advances in this area.  Still, as shall be seen, enough progress may have been made over the past decade that more of the R&D burden can be shared between these communities in the future. 
 
 
 
 
 
 
 
 
 
 
 

III.  The State of Micro-Air Vehicle Technologies

We’re at the Wright Brothers stage.²⁷

—Richard Wlezen

DARPA’s Acting Program Manager for MAVs 
 

   The quote above from Richard Wlezen says a lot about the state of the art of micro-air vehicles, but it should not be misinterpreted to mean that useful military applications for MAVs are a long way away.  Even in the case of the Wright Brothers, aircraft were flying military missions within a decade after their first flight in 1903.  Despite the many technical challenges remaining for MAV development, “many people working on micro air vehicles . . . assert that the necessary technology is rapidly becoming available.”²⁸

   If size is the driving parameter in micro-air vehicle development, what sorts of requirements exist in this vein?  As it stands now, no “Analysis of Alternatives” has been conducted by any military department to provide a bounded trade space for mission performance requirements versus cost and technological feasibility.  Lacking such guidance, the development community has had to make their best guess as to what this trade space should be.  Accordingly, DARPA, in its current program, has set out the following goals: 
 

• A dimensional limit of fifteen centimeters in length, width, and height
• An approximate vehicle weight of fifty grams²⁹
• A useful payload weight of about twenty grams
• An endurance of twenty to sixty minutes
• An operating range out to ten kilometers
• A cruising speed of between ten and twenty meters per second³⁰
• A unit production cost of $5,000 (near term) down to $1,000 (far term)³¹

The dimensional limit chosen by DARPA “was no accident” as both physics and technology considerations come into play.³²  As shall be discussed below, aerodynamic characteristics begin to diverge from the norm at this size and miniaturization of components becomes hard pressed as well.  Furthermore, DARPA desired “to push the technology involved, on the grounds that this value [fifteen centimeters] ‘is half a foot, and a foot looked too easy.’”³³

   It is self evident that a micro-air vehicle is a system composed of constituent subsystems.  It is at this subsystem level that many of the technology challenges present themselves.  That said, it is very important to realize that unlike many other, larger systems, MAVs present a rather difficult systems engineering challenge.  This is because for MAVs to be successful, they will require “high degrees of system integration with unprecedented levels of multifunctionality, component integration, payload integration, and minimization of interfaces among functional elements.”³⁴ Additionally, extremely constrained weight and volume limits and high surface-to-volume ratios mean the traditional practice of “stuffing more” into the airframe shell will probably not suffice.  Instead, each of the MAV’s components must perform as many functions as possible.³⁵  An example of this might be antennas embedded in the surface skin of the MAV providing signal reception as well as bearing structural loads.  Beyond the surface, weight, and volumetric concerns; close coupled, dynamic electromagnetic and thermal interactions will be even greater issues than they are for larger systems.³⁶

Table 2.  Baseline MAV Weight Distribution

Source: Adapted from W. R. Davis, et al., “Micro Air Vehicles for Optical Surveillance,” The Lincoln Laboratory Journal 9 (1996): 197-214. 
 

   Despite the high level of integration and multi-functionality required, it is still useful to break out each major aircraft subsystem to discuss the progress made by and issues facing micro-air vehicle designers.  Table 2 above provides an example breakout that reflects mid-1990s technological limitations in which propulsion weight (and most likely energy storage/conversion as well) dominates.

   While this “component” or subsystem listing is a somewhat representative one, the discussion here will use a slightly different breakdown.  To this end the following areas will be treated individually: aerodynamics, propulsion, energy generation and storage, guidance and navigation, communications, and finally payloads.