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TCOM 598 Independent Study of Telecommunications

Unmanned Aerial Vehicles (UAVs)

Enabled by Technology

Renee Puels

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By definition, Unmanned Aerial Vehicles (UAVs) are “remotely piloted or self-

piloted aircraft that can carry cameras, sensors, communications equipment or other

payloads”. 1 The first UAVs introduced in the early 1900s were rudimentary in design

with limited operational use. UAVs have now evolved into complex and extremely

advanced autonomous systems capable of exploiting time and space due to the rapid

technological revolution that continues today. This transformation is a direct result of

significant advances to navigational systems, data links, computer processing, and sensor

technologies. With the continued advances of these technologies, UAVs will be on the

forefront of our globally integrated world impacting our daily lives as well as national

security operations. UAVs have already altered how certain military operations and

business are currently conducted. Therefore, it is imperative to detail these key

technological innovations and breakthroughs thrusting UAVs to the forefront of the

modern era. Evaluating how these capabilities are applied and their impacts will

illustrate the dramatic effect UAVs play in our daily lives as well as military operations.

2

UAVs were first designed and employed in the early part of the twentieth century

and developed for use with military applications. Elmer Ambrose Sperry is known as the

father of unmanned aircraft with ideas and innovations ahead of his time. Sperry

partnered with the Navy and in 1918 demonstrated the first powered unmanned flights

via a naval aerial torpedo. The torpedo launched into the air, flew 1,000 yards and dove

into the sea at a predetermined location.2 This successful test would lead to further

development in unmanned flight. In the 1920s, the U.S. military made further progress

by demonstrating control of an unmanned aircraft via remote radio control.2 During

1930s and 1940s, UAVs were primarily produced as target drones in training scenarios

for anti-aircraft gunners and applied in various other training environments.2

Conceptually, unmanned target drones were simple in design since the technology of the

time limited their capabilities. Drones are still used today in training environments to test

current and next generation air-to-air missile technology and are valuable U.S. military

training assets.

During the 1950s, technological breakthroughs and innovations led to the

development of reconnaissance UAVs equipped with advanced navigational systems.2

The SD-1 Observer was the first tactical reconnaissance UAV developed by Northrop

Gruman. The SD-1’s configuration was based on existing UAV designs with the addition

of externally mounted cameras.2 The U.S. military took this basic configuration to

further develop UAV target drones into effective surveillance and reconnaissance aircraft

during the 1950s and 1960s.

The United States Air Force made a significant leap in UAV development during

the 1960s by introducing the “Lightning Bug.” The Lightning Bug’s design was based

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on the BQM-34 Firebee target drone previously developed by the Ryan Aeronautical

company.3 The Firebee demonstrated early success as a photo-reconnaissance aircraft

during development.3 Slight modifications enabled the Firebee to sustain longer flights at

higher altitudes suitable for reconnaissance tasks. The Lightning Bug flew its first

mission in Southeast Asia during the summer of 1964 and later completed over 3,400

tactical surveillance and reconnaissance missions during the Vietnam War. The UAV

collected valuable imagery on enemy surface-to-air missile sites, prison camp locations

and other significant military targets.3 Despite these successful operations, the U.S.

decided not to expand its UAV research and development programs after the conclusion

of the Vietnam conflict. At the time, the U.S. evaluated UAV applications as limited

with little future relevance in military operations.4 Therefore, UAVs were not

significantly used in U.S. military operations until the 1990s where they played a crucial

role during Operation Desert Storm.

The U.S. was not the only nation experimenting with and employing early UAVs.

UAVs significantly impacted military operations in several countries over a relatively

short period of time. The primary reasons for their increased applications were “the

development of lightweight composite structures, reliable digital flight control systems,

miniaturized sensors and robust data links.”6 In the early 1970s, the Israeli government

invested heavily in UAV research and design resulting in the Israeli Aircraft Industry’s

“Scout” UAV for their military.5 The Scout was developed from scratch and the first

genuine remotely controlled UAV prototype with adequate sensors and stable electro-

optic systems required for functionality on a small platform.5 The Scout possessed

4

modest surveillance and reconnaissance capabilities and operated at altitudes of 15,000

feet for six hour flight missions.6

The Scout provided the Israelis intelligence gathering and decoy capabilities in

successful military operations during the 1982 Lebanon War. Scout surveillance and

reconnaissance missions enabled the Israeli Defense Force (IDF) to lull then destroy

Syrian air defense systems through successful Israeli air strikes in a major air battle over

the much disputed Bekaa Valley. 5 The IDF successfully used the Scout to locate Syrian

air defense assets and aircraft while collecting the electronic signatures and frequencies

of Syrian radar systems. 5 Prior to the massive Israeli air assault, the IDF launched

Scouts emitting electronic signatures to disguise the UAVs as attack aircraft to force an

The INS is a core part of all aerial platforms which determines the position,

velocity and altitude of an aircraft using gyroscopes operating on fundamental laws of

physics.8 At the heart of the INS are gyroscopes in the form of mechanical or optical

devices that maintain orientation based on angular momentum while in motion.9

Gyroscopes are sufficiently accurate initially but orientation tends to drift over time due

to external forces exerted on the gyroscope.9 Precession, as this is called, results is an

unreliable reading of position over time. To combat precession, scientists have

developed new types of gyros that minimize its effects. The implementation of ring laser

gyros have dramatically reduced precession.9 Ring laser gyros utilize two laser beams

that rotate around the gyroscope axis. Forces on the gyroscopic rotation cause resonant

frequencies of the two optical beams to change. These changes are subsequently sent

through refracting mirrors which then hit a detector.9 Measurement of the changes

determine external rotation rate and direction.9 The precision of these measurements

5

determine gyroscopes accuracy and level of precession. Although ring laser gyros

dramatically increased INS accuracy over time, it still didn’t eliminate precession

altogether. UAVs were in need of a more consistent navigational system if they were to

become a viable military resource. The answer came in the form of embedded GPS and

INS developed for redundancy which proved extremely reliable while minimizing

inaccuracies.

The United States Department of Defense (U.S. DOD) developed the GPS based

on a “three dimensional, time difference of arrival position finding system.”10 One of the

driving forces behind GPS was the need for a guidance and location tracking system for

the U.S. DOD Mobile System Accurate for ICBM Control during the 1960s.11 The U.S.

Navy and Air Force invested in research and design for a navigation system capable of

meeting this task. Contracted as highly classified by the U.S. government during the

Cold War, the Aerospace Corporation played a critical role in engineering and designing

what we now know as GPS.11 The GPS was first launched in 1978 and originally

comprised of 10 developmental satellites.12 Today, GPS has expanded to a constellation

of 24 Medium Earth Orbit satellites plus spares that are operating approximately 11,000

miles above Earth. 12 With an orbit of 12 hours, each satellite is spaced 120 degrees apart

allowing 6 satellites to be acquired at any location at any given time.10 At least four

satellites are required to determine location with a GPS receiver.

The GPS satellite constellation is known as NAVSTAR and is currently

maintained by the United States Air Force. 13 NAVSTAR requires a master control

station and five other ground monitoring systems located worldwide for adequate

operations and accuracy. 12 The master control system is responsible for monitoring and

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controlling the NAVSTAR satellite constellation. Since timing is critical to ensure

accurate GPS readings, each satellite is equipped with an atomic clock. 12 The atomic

clocks are monitored by the ground stations. A GPS signal takes three nanoseconds to

transmit from a satellite to a receiver since the radio signal travels at the speed of light. 12

Originally, GPS was designed for use with two L-band frequencies, L1 and L2.

L1 and L2 transmit at frequencies 1575.42 MHz and 1227.6 MHz respectively.15

Embedded on these bands are two codes transmitting data known as Coarse/Acquisition

(C/A) ranging code and the Precise (P(Y)) ranging code. These codes were designed to

segment usage of the satellite system between commercial and military applications. The

C/A code is modulated at a chipping rate of 1.023 MHz with a wavelength of 300

meters.14 The C/A code was designated to support commercial applications and is

transmitted on L1. The P(Y) code, transmitted on L2, is restricted to military use and

modulates at a chipping rate of 10.23 MHz with a 30 meter wavelength.14 Both the P(Y)

and C/A codes are modulated with binary phase shift keying onto the carrier frequency

using a spread spectrum pseudo noise (P/N) sequence. Each satellite has a unique P/N

sequence used to identify itself from other GPS signals.15 Figure 1 depicts modulation of

the C(A) and P(Y) codes onto the GPS signals.15

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Figure 1 GPS Signal Modulation (L1 and L2)

Prior to the year 2000, the U.S. military intentionally degraded the GPS signal on

the C/A code of the L1 link used by commercial applications using selective

availability.15 The result was a signal accurate to only 100 meters for commercial use.15

The U.S. military degraded the signal due to concerns that adversaries could use the

NAVSTAR to their advantage. Selective availability applied a randomly generated time

difference that was added to the L1 link to purposely provide a less reliable GPS

reading.15 As a result, precise GPS location readings were not available for commercial

aviation or maritime navigation.

Selectively availability is a significant factor for error but is not the only factor

attributed to GPS location inaccuracies. Time delays naturally occurring with respect to

the Earth’s ionosphere also contribute to error. The level of interference in the

ionosphere experienced on a GPS signal is dependent upon the density of ions in the

atmosphere and the distance the signal travels.15 The number of ions that exist in the

atmosphere are dependent on time, magnetic latitude, and sunspot cycle.15 Delays caused

by interference in the ionosphere can result in up to a 70 nanosecond delay. This time

delay translates to approximately a 10 meter error in GPS navigation. 15 Although the

difference may appear small, a 10 meter error could spell the difference between success

and failure with respect to military, aviation, and sea operations.

Other environmental factors such as troposphere effects, multi-path, geometric

dilution of precision (GDOP), and ephemeris errors also affect the accuracy of GPS.15

GDOP is a mathematical calculation used in GPS readings. GDOP is calculated using

the geometric shape of the receiver position relative to the position of the satellites.15 The

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location of the GPS satellites relative to the receiver affects accuracy when using GDOP

triangulation calculations methods. The most accurate GPS readings occur when a

receiver uses signals from GPS satellites that are positioned furthest apart.15 GDOP is

carefully considered in U.S. military target planning. Ephemeris errors are the calculated

differences between the expected positions versus the actual orbital position of a GPS

satellite. 15 The orbital position of the satellite is therefore a critical component to

determining a receiver’s position and if inaccurate, provides a less reliable GPS reading.

Many GPS applications, including UAV navigation, left little room for the margin

of error these inaccuracies caused. As a result, it became necessary to improve the

accuracy of GPS. Maritime and air navigation organizations needed a more accurate

system to safely navigate the waterways and airways. To meet commercial and military

demand for a more accurate product, Differential GPS (DGPS) was developed during the

late 1980s and early 1990s. 16 DGPS increases the accuracy of today’s GPS systems to a

couple of meters, even in moving applications.16 The best cases showcased accuracy

under 10 centimeters.16

DGPS uses a ground station in addition to the GPS satellites to determine a more

precise location. DGPS requires a GPS ground station with a receiver set up at a

precisely known location.16 By comparing the timing difference of the signal received by

the GPS receiver to the known position of the ground station, a more exact reading is

acquired. Over the last decade, the U.S. has developed a national DGPS system that is

currently maintained by the U.S. Coast Guard. It consists of 84 fixed ground stations

covering approximately 87 percent of the continental U.S.17 Future expansion will

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increase the number of ground stations to 128.17 Figure 2 below shows a current picture

of the coverage that DGPS provides within the U. S. as of February 2006.17

Figure 2: DGPS ground station locations as of February 2006

Ground station coverage is significant as the accuracy of DGPS is dependent on

the distance from the GPS receiver to the fixed ground station. Distance affects time

required for a signal to reach a given satellite and receiver. As distance increases,

accuracy decreases. Based upon a U.S. Department of Transportation study on DGPS

accuracy, error is estimated to increase at a rate of 0.67 meters per 100 kilometers.18 As

mentioned earlier, selective availability was turned off in 2000 since DGPS became

widely available and accurate. Therefore, embedded GPS errors in the communications

link were no longer justified for sole use of the U.S. military.

The improvements to GPS make it a powerful navigational tool, enabling global

reach and power. It is important to note that GPS not only provides navigational data but

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also supports targeting and surveillance applications. Innovative mathematical methods

and techniques have been developed to increase the precision of UAV targeting and the

surveillance of areas by using GPS related data. These advances have significantly

impacted UAV operations. For example, a technique called Multiple Image Coordinate

Extraction (MICE) was developed for rapid targeting of precision guided munitions.

MICE further corrects the position error related to GPS accuracy and provides near

perfect coordinates for targeting, surveillance, and other operations.

Using imagery gathered by UAVs, MICE can pinpoint target coordinates to

within a 5 meter circular error probability (CEP).19 This is significant because previous

geolocation methods were accurate to only 100 meters which is unacceptable for precise

targeting. 19 MICE techniques use basic principles of photogrammetry to determine the

precise target location and size of an object. 19 MICE has been successfully implemented

on UAV platforms including the Predator and proves adaptable since it is not platform or

sensor specific.19 Previously, UAV target location error was a result of poor knowledge

of camera pointing angles and ground elevation, as well as GPS. 19 MICE overcame these

problems using detailed plotting and specific data. No less than three noncollinear

images with associated support data are required for precise MICE calculations. 19

Supporting data include the GPS latitude, longitude and altitude of the UAV. 19 The

imagery is used in a complex MICE algorithm that interpolates target locations defined

on a three dimensional Euclidean space onto a two dimensional image plane as

represented in Figure 3 below. 19 Per MICE methodology, “points A, B, and C are

mapped onto points a, b, and c in the image plane. The light rays from A to a, B to b, and

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C to c are straight lines that all intersect at a single point, corresponding roughly to the

center of the camera lens.”19

Figure 3 MICE interpolation technique

The precise location of an object is then determined using standard nonlinear

matrix solution techniques.19 Simulations show GPS only target accuracy was

approximately 14 meters CEP. DGPS increased accuracy to 3-4 meters CEP. 19 As

discussed, GPS combined with other advanced technologies such as MICE is paramount

to continued successful UAV operations.

To ensure the U.S. maintains a robust GPS system, modernization efforts are

underway to guarantee its continued lifespan over the next 30 years. When complete,

these efforts will more than double the number of existing navigational signals. It costs

the U.S. military approximately 750 million dollars annually to maintain NAVSTAR.13

This multi-million dollar budget includes funding for operating and maintaining the

satellite constellation, research and development for future launches, and procurement for

replenishment satellites. 13 As part of the modernization effort, a commercial signal was

added to the L2 data link known as the L2C link. L2C was added to replacement GPS

satellites launched in 2003.20 The L2C link is constrained to a single bi-phase signal

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component to deconflict with the other codes transmitting on the L2 link.21 The L2C

signal is designed using two codes known as CM and CL. CM is a moderate length code

with 10,230 chips and is modulated with message data. 21 CL is a long code with 767,250

chips and has no message data. CL is primarily used for tracking and acquiring the L2C

signal. 21 L2C advantages include flexibility, low power requirements, small design, and

low consumer cost applications. 21 L2C also has the best cross-correlation performance.21

These advantages will make L2C the most popular commercial GPS band used over the

next decade. 21

Future components for GPS modernization include a new L5 link, designed to

meet the growing civil demand for GPS. The L5 signal is transmitted on 1176.45 MHz

with a binary offset carrier of a 10.23 MHz square sub-carrier wave. This signal is

modulated at a chip rate of 5.115 Mbps using two bi-phase components in quadrature

phase shift keying (QPSK). 21 This modulation design enables the L5 link to transmit

significantly more data since QPSK incorporates three bits per symbol. The L5 link is far

more advanced and advantageous than current communications links, boasting data rates

ten times greater than the L1 and L2C links. 21 The L5 link is more powerful then the L2

signal by 6 dB which gives it greater immunity and security. 21 The L5 signal includes

increased security features utilizing next generation cryptography and a newly designed

keying structure. It will be utilized on fourth generation Block IIF GPS satellites. 22

These satellites are scheduled for launch in 2007.22 The three main benefits of the L5

design are 1. precision approach navigation, 2. increased worldwide availability, and 3.

improved interference mitigation.20 Below is a table that shows comparative

characteristics of the L2, L2C, and L5 links.

13

Civil SignalCarrier Freq

(MHz)

Code

Length

(chips)

Code Clock

(MHz)Phases

Bit Rate

(Bps)FEC

L2 1575.42 1023 1.023 Bi-phase 50 No

L2C 1227.6010230

7672501.023 Bi-phase 25 Yes

L5 1176.4510230

1023010.23

Quad-

phase50 Yes

Table 1: L-Signal Characteristics (L1, L2C, L5)

The table shows that each link has similar fundamental frequencies with unique

attributes. Both the L2C and L5 links use forward error correction which improves

transmission reliability and efficiency. A distinct modulation spectrum allows the L5

link to receive high powered signals without affecting the performance of Y or C/A code

receivers. 21 This attribute gives L5 immunity to anti-jamming measures directed at C/A

signals. 21

Table 2 below shows more comparative characteristics of the L-signals.21

Although L2 is the weakest signal, it is the least susceptible to ionosphere delays and

errors because ionospheric refraction error is inversely proportional to frequency

squared.21 Comparatively, the L2C and L5 link have a respective 65% and 79% higher

incidence of error.21 This is significant because the ionosphere is the single largest

14

contributor to GPS inaccuracies. L2C strength is that it has the best correlation value due

to increased power levels, decreasing susceptibility to the signal’s interference.

Civil Signal Fully Available Ionoshperic Error Ratio Correlation Protection

(dB)

L2 Now 1.00 > 21

L2C ~ 2011 1.65 > 45

L5 ~ 2015 1.79 > 30

Table 2: L-Signal Characteristics (continued)

The military also plans to implement a new military only signal on the L1 and L2

bands by 2012. Called the M code, this signal will have more power and less

susceptibility to frequency jamming. 20 The original GPS signals lack sufficient power

causing a concern with respect to anti-jamming threats. These used only -160 dbW of

power for transmission.14 The M code will transmit at a power level of -158 dBW which

will improve many attributes of the signal. The Block IIF satellites will broadcast two M

coded signals on L1 and L2. 22 The M5 attributes include much greater immunity to

jamming, more robust acquisition, better security features and an improved data message.

The M code will be transmitted on a subcarrier frequency of 10.23 MHz with a spreading

code rate of 5.115 Mbps. 23 The signal will be protected for worldwide commercial use

and designated for aeronautical radio navigation as well as aviation safety of life

applications.20 This will be done by increasing the power without interfering with

existing C/A and Y code receivers. 23 Figure 4 below illustrates the GPS signals power

spectral densities at 1W of power showing each signal has a unique spectrum and varying

15

signal strengths across the bandwidth.23 The M signal is represented by the red “BOC”

spectrum.

Figure 4: “Fingerprints” of GPS Signals

Analysis of Figure 5 below illustrates comparative spectrum outputs of GPS

signals. The graph shows that the M code utilizes the same frequencies as the original

signals but has the strongest power output over the entire bandwidth of the signal. 23 As

explained earlier, this will not interfere with existing signals since the modulation

techniques of each signal gives each link unique signatures for identification. 23 The

cumulative modernization efforts that result in the newly acquired GPS signals will

greatly enhance the GPS system capacity and will continue to provide critical

navigational data for UAV operations and targeting capabilities.

16

Figure 5 GPS Spectrum and Frequency Allocation

The data link is another critical UAV communications component that serves

three important functions. First, an up-link allows the ground station and satellite to

control the UAV system and payload.25 Second, a downlink transmits UAV telemetry

and sensor data back to the ground station. 25 Third, the data link allows the ground

station to measure the azimuth and range to the UAV from the ground antenna and

satellite to ensure successful communications between the UAV and command and

control. 25 The physical portion of a UAV data link consists of an air data terminal (ADT)

and antenna. 25 The ADT includes the RF transmitter and receiver. 25 Modems interface

with the other sensors and communications equipment on the UAV to process and

compress the data. 25 Each component of the data link provides a critical function for

conducting UAV communications.

Many considerations went into designing the data link for UAVs including

operating range, anti-jamming margins, data rate, and cost.25 Operating range is defined

by mission requirements and is non-negotiable making it the easiest parameter to

determine.25 When considering line-of-sight ranges, ground and space antennas’ gain can

be substituted for processing gain between 30 and 40 dB with reasonable cost. 25 This

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allows higher data rates without degrading anti-jamming measures. 25 For beyond line of

sight ranges, increasing antenna gain yields little benefit without the unrealistic use of

airborne relay vehicles. Higher frequencies are generally required when requirements

call for higher anti-jamming margins. 25 This subsequently increases cost as increasingly

sophisticated hardware and technology are required. 25 Therefore, careful thought and

consideration must go into designing and implementing a successful data link component

for UAV platforms.

Data links have always been a major limitation to UAV operations. According to

a 2004 study by the U.S. Defense Science Board, “current data link requirements range

from a few kbps for launch and recovery to in excess of 250 Mbps for the transmission of

output of sophisticated sensors.”26 Data link requirements continually exceed what

current UAV data links can realistically support. The U.S. military surmises that the

“principal issue of communications technologies is flexibility, adaptability and cognitive

controllability of the bandwidth, frequency, and information/data flows” with respect to

UAV communications.7 A frustration within the UAV community is that data links are

limited by constrained bandwidths, technological limitations, and usable frequency

availability. Over the last 20 years, the military has experienced the bottle-neck effects of

UAV data links and is focusing on improving its infrastructure, frequency management,

and technology. In the near term, data compression methods developed by military

initiatives will alleviate saturated communications links. 7 Radio frequency technologies

within line of sight ranges are being replaced by satellite communications links to meet

high data rate requirements. Optical data links are being developed to improve existing

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capabilities. Following is a synopsis of the communications currently used for data links

and what lies ahead.

The majority of UAVs currently operate using line of sight and satellite data link

communications. For example, the Pioneer which was developed in the 1980s was the

first generation of UAVs using RF technology. The Pioneer’s uplink used C-band and

UHF line of sight communications. 7 The downlink was also C-band line of sight. 27 The

data link modulation scheme included direct sequence spread spectrum methods also

known as direct sequence code division multiple access.27 Direct sequence spread

spectrum divides the information to be transmitted into small segments.28 Each segment

is digitally combined with a higher data rate bit sequence called a chipping code using a

spreading ratio. Redundancy and error checking are advantages to the chipping code. In

other words, if the transmitted signal succumbs to interference, the original data may still

be recovered. The Pioneer’s data rate was limited to 7.317 kbps which is extremely slow

compared to data rates available today.29 The data rate limitations were a constrained

spectrum and the basic physical UAV requirement of small lightweight vehicles with

limited power.25

Current UAVs, including the widely successful Predator, incorporate significantly

improved data links using advanced technology and satellite communications. The

Predator requires 25 to 30 amps to operate the onboard Sensor Processor Modem

Assembly used for data link communications. 46  This aircraft sustains power using two

alternators that provide the 28 volts necessary for flight. 46  If the engine or both

alternators fail, the Predator has two batteries that can provide a nominal twenty to thirty

minutes of backup power. 46

19

Like the Pioneer, the Predator uses C-band frequencies for line of sight

operations, but with an increased data rate capacity supporting a 4.5 Mbps analog data

signal.30 The line of sight link is primarily used for launch and recovery and is capable of

operating within 100 nautical miles of the ground control station. 30 The Predator’s

takeoff is conducted and controlled by a Launch and Recovery Element (LRE) through

UHF line of sight communications. 46  Once airborne, the LRE powers up the satellite link

which gets relayed from space to a satellite dish at a deployed location.46  The Predator is

capable of over-the-horizon operations through a Ku-band commercial satellite

communications link. 30 The satellite link supports up to 1.544 Mbps and is used

primarily for command and control and imagery. A limitation to satellite operations is

that the Predator can only operate within the satellite’s 1500 nautical mile spot beam.30

The signal is transmitted via satellite and then through fiber optics until it reaches the

Predator command and control centers back in the U.S. 46  It takes less than 2 seconds for

a bit to travel from the command and control center to the aircraft and back.46 

The Trojan Spirit II systems are the deployed command and control centers that

monitor and execute Predator operations through satellite communications. These

systems are ruggedized and consist of two highly mobile multi-purpose vehicles with

integrated equipment shelters, two trailer mounted satellite antennas and two diesel

powered generators with onboard environmental control units. 31 The Predator operation

teams have full reachback capability due to the advanced communications the Trojan

Spirit II provides. The Trojan Spirit II also links the Predator communications system to

other centralized intelligence centers within the U.S. military network and is extremely

adaptive to today’s expeditionary warfighter needs. 31

20

The Predator was first employed by the U.S. Air Force in 1994 and was a key

asset during Bosnian operations in 1995. 44 Since 1995 it has flown missions over Iraq,

Bosnia, Kosovo, and Afghanistan as well as domestic boarder patrol. 44 The Predator

reached its 100,000 flight hour mark in 2004 and was declared “operationally capable” in

2005. 44 The first operational Predator missile launch occurred in 2002 where it destroyed

a civilian vehicle carrying suspected terrorists. 44 During Operation Iraqi Freedom,

missions were flown where U.S. Air Force F-16 fighter aircraft flew protection and escort

for the Predator as it launched and destroyed enemy targets with Hellfire missile.45

A standard Predator mission is approximately 20 hours long. 46 A pilot, sensor

operator, intel mission coordinator, and mission commander are the minimum personnel

required to conduct a mission. 46 Total manning depends on mission length and

availability as a great deal of coordination, teamwork, and expertise are required to

conduct a successful sortie.46 The operations team flies the aircraft to the target and

usually conducts traditional intelligence, surveillance, and reconnaissance (ISR) while

supporting ground troops.46  In certain cases, ground troops contact the Predator squadron

operations team directly to request support from the Predator’s onboard Hellfire

missiles.46  The Hellfire missiles are almost identical to those employed by Apache

helicopters. 46  Although Predator capabilities are impressive, future UAVs will operate

with significantly greater data link bandwidth and agility.

The Global Hawk is the next current generation of UAVs with significantly

greater data communications capabilities. Like the Pioneer and Predator, the Global

Hawk uses line of sight and over-the-horizon satellite communications. Command and

control and sensor information is transmitted on the Ku-band through satellite

21

communications. Line of sight communications primarily operate on the X-band

Common Data Link (CDL).29 The CDL was defined by the military as a “full duplex,

jam resistant spread spectrum, point to point data link.”27 The CDL is the U.S. military’s

interoperability standard for imagery and signal intelligence enabling compatibility

between all military services in order to communicate and disseminate information

efficiently.27 UHF is also available for Global Hawk satellite and line of sight

communications but is limited to 19.2 kbps.29 A majority of Global Hawk

communications use INMARSAT satellite links operating under the aforementioned X

and Ku-band spectrum. Redundancy is the major advantage of INMARSAT.

Using the advanced capabilities detailed above, the Global Hawk has become the

premier surveillance and reconnaissance aircraft for military operations. Prior to the

Global Hawk, the manned U-2 aircraft was the primary source for collecting worldwide

intelligence, surveillance, and reconnaissance. The Global Hawk is well on its way to

replacing the U-2 altogether for several reasons. First, the Global Hawk is capable of

flying 3000 nautical miles and loitering for 8 hours before returning to base. 42

Comparatively, the U-2 can fly the same distance but retains no loiter time.42 Second,

Global Hawk pilots simply swap out when fatigue becomes a factor on long missions

while the U-2 pilot must obviously remain put. Finally, the U-2 can provide the same

capabilities when deployed from an in-theater location but takes 5 days to set up whereas

the Global Hawk can launch immediately.42 Therefore, the Global Hawk is more

advantageous when considering time sensitive targets.

Since the Global Hawk’s first flight in 1998, the UAV has flown thousands of

hours in support of combat operations worldwide. 42 The Global Hawk made history in

22

2001 by completing the first unmanned powered flight across the Pacific Ocean.47

Militarily, the Global Hawk was initially used to assist NATO commanders in identifying

targets during the Bosnian-Kosovo conflict.47 Later, the Global Hawk acquired 55

percent of time sensitive targets generated during the first year of Operation Iraqi

Freedom (OIF) while only flying five percent of all high altitude missions.48 These

targets included 13 surface-to-air missile batteries, 50 SAM launchers, 300 canisters and

70 missile transporters, and 300 tanks constituting 38% of Iraq's armored force.47 The

Global Hawk also collected valuable reconnaissance on hundreds of targets in

Afghanistan during Operation Enduring Freedom (OEF) and continues to successfully

support current global operations.32 The Global Hawk flew over 4,300 hours supporting

OIF and OEF utilizing only six aircraft. 42 Due to the overwhelming success of this UAV,

the U.S. Air Force plans on expanding the Global Hawk fleet to over 50 systems

operating out of Beale AFB, California.42 The Global Hawk’s dominance has had far

reaching effects across a wide spectrum of military operations and will continue to

provide a wealth of information for years to come.

Researchers and developers forecast remarkable advances in data links for the

next generation of UAVs. The U.S. military is continually developing methods to utilize

higher GHz range radio frequencies capable of supporting 10 Gbps data rates.7 However,

a constrained RF spectrum, particularly in the 1 to 8 GHz range, is a drawback to radio

frequency technologies.7 GHz range frequencies are also susceptible to the same

propagation effects that impact GPS signals. As a result, other technologies are being

tested. One of the most promising alternatives are optical/laser data links.

23

Optical/laser communications technologies are proving to be a viable option for

UAV data links. The benefits of optical based systems are large usable bandwidth, low

probability of intercept, weigh 30 to 50 percent less than comparable RF systems, and

offer immunity from interference or jamming.33 They also consume less power allowing

easy adaptability for light weight UAVs with limited power sources.33 Optical data link

tests have shown the ability to support two to three times greater data rates compared to

the best RF systems.7 For example, in 1996 a ground based laser communications system

demonstrated data rates of 1.1 Tbps at a range of 140 km.33 Following are case studies

that have shown success with optical communications.

In 2000, the U.S. Naval Research Laboratory completed extensive testing of an

optical based data link system on a small rotary wing UAV using a modulating retro-

reflector (MRR). An MRR uses an optical retro-reflector, such as a cube, and an electro-

optic shutter operating as a two way communications link consisting of a laser, telescope,

and pointer-tracker. 34 The optical retro-reflector is a passive optical system which reflects

light back exactly along its point of incidence.34 A common retro-reflector is made of

three mirrors mounted in a shape similar to the inverse corner of a cube. 34 The electro-

optic shutter is used to turn the laser “on” and “off” and supports signal modulation. 34 In

laboratory tests, this system was capable of producing data rates of 6 Mbps made possible

through the use of a semiconductor based on a multiple quantum well (MQW) shutter.34

The MRR concept in not new, however its applications were limited due to lack of

existing support technology.34 Recent advances have allowed retro-reflectors to be used

in satellite systems as they are incredibly accurate to a few millimeters.34

24

The advantages of an electro-optical system is its compact lightweight design and

low power requirements. 34 These systems also boast low probably of intercept since the

retro-reflected laser beam’s divergence is equal to the diffraction-limit of the retro-

reflector which is only 200 micro-radians. 34 They are also extremely efficient and

support high data rates. To support Mbps data rates, a semiconductor optical switch was

developed using GaAS Multiple Quantum Wells (MQW) technology. 34 Although MQW

technology is somewhat complex, it has been used in many applications including laser

diodes. 34 The advantages of these semiconductors are a low 1 Watt or less power

requirement and high switching speed. 34 MQW modulators were successfully tested at

impressive 40 Gbps data rates.34 However, the current lack of technology to support this

high data rate is the limiting factor for practical optical communication applications.

Existing technology can only support data rates in the tens of mega bits per second.34 The

maximum data rate depends on range and laser transmitter type on the ground station.34

The test performed by the Naval Research Laboratory used a 600 Kbps data link

at a range of 100-200 feet. The MRR system was mounted on a small UAV platform to

transmit/receive data from a ground based laser interrogator. 34 The large ground based

laser platform illuminated the UAV platform with an unmodulated continuous laser

beam.34 The laser beam then hit the modulating retro-reflector which passively reflected

the laser back to the ground platform.34 The electro-optic shutter turned on and off using

an electrical signal that carried the small platform’s data.34 Laser beam accuracy was not

an issue due to the field of view’s hundred degree tolerance.34

In early 2006, another successful test was completed using satellite laser

communications.35 A Northrop Grumman/Lockheed Martin Transformational Satellite

25

Communications System (TSAT) ground terminal successfully supported data rates

between 10 and 40 Gbps. 35 The test used a single-access optical aperture mounted on the

front end of a communications terminal and a laser to send and receive data between the

terminal and satellite.35 The communications terminal was designed to be spacecraft

mountable and required precise tracking for data communications.35 These tests proved

optical systems are plausible and can meet future requirements of next generation UAV

systems.

More data link research and development is required for different types of UAV

platforms. Data links for much smaller systems, such as mini-UAVs, require unique

composition due to the platform’s size, weight, and power limitations. A system

specifically designed to support mini-UAVs is the Starlink developed by Tadiran

Spectralink. The Starlink “Mark II” was finalized in August 2006 and is the latest data

link system. Starlink has a high spectrum efficiency and wireless features immune to

jamming and frequency interference.36 The previous version of Starlink, the Mark I, was

adopted by over 13 countries with over 200,000 operational flight hours. 36 The Mark I

used frequency division duplexing for digital modulation. 36 The Mark II improves upon

Mark I efficiency through the application of time division duplexing (TDD).36 The major

advantage of TDD is its efficiency as it divides a data stream into frames and assigns the

transmitted and received signals to specific time slots. 36 TDD is highly spectrum

efficient since it utilizes the same frequency for both downlink and uplink and requires

only one antenna.36

A mini-UAV currently using the Starlink communications system is the Skylark.36

The Skylark is a compact UAV that can fit in two backpacks. The UAV weighs about 12

26

pounds, has 12 hours of endurance, and can operate within a 3-6 mile radius.37 The

Skylark was designed for tactical close range surveillance and reconnaissance, providing

artillery fire adjustments, improving force protection, and enforcing perimeter security. It

is easy to assemble and operate and can be launched by hand.37 The Skylark system

consists of three air vehicles, a ground control system, and day or night sensor/camera

payload.37 In 2004, the IDF bought Skylark systems that are currently being used by it’s

military forces.37 Coalition forces used Skylark in support of operations in Afghanistan

and Iraq and the UAV has currently been selected by the Australian military as their

primary mini-UAV system.37 Micro technology advances have allowed mini-UAVs to

become a common tool currently used by soldiers on a daily basis. Advances to the

system’s data link are critical for the mini-UAV’s continued success.

While scientists concentrate on improving data link communications, others are

focused on improving UAV capabilities which require less human control and

intervention. Autonomous UAV operations may be possible with the advent of future

advances utilizing highly sophisticated network centric technologies.7 Current forecasts

predict chip manufacturers will be able to place a billion transistors on a single silicon

chip around 2010. This chip technology would allow 20 times current chip capacities.33

Micro-fabrication of a billion transistors will undoubtedly lead to faster processor speeds

and ultimately the ability to automate the UAV decision making process.33 Scientists

hope to develop a “silicon” based pilot to replace the human intervention currently

required for Unmanned Combat Air System decision making.33 Again, data link

technology will continue to play a critical role with any autonomous system.

27

Advances in micro technology and the computer revolution have allowed the U.S.

to begin development of Unmanned Combat Air Systems capable of “smart” autonomous

operations. The Joint Unmanned Combat Air System (J-UCAS) testing phase began in

2002. The J-UCAS is being designed to revolutionize the basic construct of air warfare

and is the first major step towards unmanned aircraft combat systems.38 The J-UCAS

program started as a joint endeavor between the Defense Advanced Research Project

Agency (DARPA), Air Force, and Navy.38 The J-UCAS primary missions include

Suppression of Enemy Air Defenses (SEAD), surveillance, and precision strike. SEAD

requires aircraft to suppress enemy radar missile defense systems ensuring air and space

superiority and safe passage of other aircraft.39 These missions are currently performed

by aircraft like the manned F-16 Fighting Falcon.

The first J-UCAS system, the X-45, completed its first successful flight in May

2002. Developed by Boeing, the X-45 demonstrated seamless operations for command

and control, communications, and navigation.39 In March 2004 the X-45 successfully

dropped a 250 pound inert bomb over the Edwards Air Force Base ranges.40 This

milestone marked the first time an unmanned aircraft dropped live weapons at a high

speed and altitude.40 In February 2003 the Northrop Grumman X-47 successfully

performed low speed handling qualities and simulated carrier landings suited toward

naval operations.40 These stealthy systems hold a great deal of promise for the future of

J-UCAS development. However, due to other priorities and budget constraints, the Air

Force pulled out of the J-UCAS program in January 2006.41 Speculation on Air Force

withdrawal focused on funding requirements to support a long range bomber initiative.41

The J-UCAS program is now under Navy control with an uncertain future.41

28

Unmanned aircraft initiatives like the J-UCAS are established by the Joint

Requirements Oversight Council (JROC) and overseen by the Vice Chairman of the Joint

Chief of Staff under the Department of Defense. The Joint Unmanned Combat Aerial

Vehicle Center of Excellence, established by the JROC in July 2005, is focused on setting

the strategic roadmap for joint programs. Their primary focus is to ensure

interoperability of all UAVs amongst the services, develop tactics, techniques, and

procedures, and establish an overall concept of operations for future joint unmanned

systems. Although there is a great deal of uncertainty regarding the future employment

of the J-UCAS X-45 and X-47 models, their development yields promise for joint UAV

initiatives.

Technologically advanced onboard sensors are another key component to

continued success of UAV intelligence, surveillance, and reconnaissance applications. A

myriad of sensors including thermal, video, infrared, and optical have enhanced imagery

to pinpoint accuracy. According to the Department of Defense, “sensors now represent

one of the single largest cost items in an unmanned aircraft.”7 For example, sensors

currently used on the Predator cost as much as the original aircraft.7 The three main

categories of sensors include 1. Video, Electro/Optic, and Infrared 2. Synthetic Aperature

Radar with moving target indicators, and 3. Signal Intelligence focusing on electronic

data collection.7 Sensors aboard current UAVs today are powerful. The sensors are

usually direct from development and testing so when fielded, require a significant amount

of training for effective operation. 46 Following is an in-depth look at Predator and

Global Hawk advanced sensor systems.

29

  The Predator uses both Electrical Optical (EO) and Infrared (IR) sensors.  EO

systems consist of daylight video cameras transmitting basic TV imagery to controllers.46 

EO image quality depends on the camera’s distance from the target and amount of

available light.46  Predators predominantly rely on IR sensors due to their day or night

compatibility.46  IR sensors detect differences in surface temperature so controllers can

identify items such as a hot car engine that cannot be seen using EO.  Command and

control operators then select either white hot or black hot to enhance polarity on the black

and white IR image.46  Another IR application currently being used in Iraq is aimed at

identifying improvised explosive devices (IED).  Operators can detect a temperature

differential in the disturbed soil along roads where insurgents have recently buried IEDs. 

Although EO cannot be seen at night it has the daytime advantage of discerning color.46 

For instance, if a terrorist is driving a green land rover then controllers can look for a

green land rover.  These sensors operate like advanced targeting pods on fighter aircraft.

Fused IR with EO sensors combines the advantages of both systems.46 

The Global Hawk makes use of a sophisticated integrated sensor system (ISS) that

includes synthetic aperture radar (SAR) and a third generation fused

electro-optical/infrared system. According to Raytheon, the SAR operates on the X-band

and has a 600 MHz bandwidth requiring 3.5 kW of peak power.42 The SAR includes a

sophisticated moving target indicator which enables the UAV to operate 24 hours a day

in all types of weather.42 The ISS can capture 3 foot resolution in wide area search mode,

and 1 foot resolution in spot mode.42 An Enhanced Integrated System Suite is being

developed to upgrade the current radar resolution by 50 percent and will be introduced in

the near future.42 The electro-optical/infrared sensor operates in the micron waveband

30

and is able to collect 1,900 spots per day, equivalent to a 2 km by 2 km area, with an

accuracy of 20 meters.42 A wide area search mode covers an 10 km wide area.42 Using

these sensors, the Global Hawk is capable of providing surveillance over an area of

40,000 square nautical miles at an altitude of 60,000 feet during a 24 hour timeframe.42

Sensor data is transmitted via the CDL line of sight X-band and beyond line of sight Ku

band via satellite communications. 42 All sensor data is distributed to the Global Hawks

mission control element/ground station who transmits the imagery back to operation

centers.

Other emerging sensor technologies have potential applications to military UAV

operations. Multispectral and hyperspectral imagery (HSI) produce spectral bands that

are unique to materials and objects. Future military applications using HSI include

detecting biological and chemical agent particles. Passive HSI imaging can help detect

unconventional attacks. HSI could also use spectral sensors to counter concealment and

other enemy denial tactics. HSI is just one example of new UAV sensor technologies on

the cutting edge. These newly developed sensors can glean vast amounts of information

and will continue to evolve to meet future requirements.

A look at recent aviation history will give true appreciation of what UAVs offer

and are able to accomplish with technological innovation. Since the 1980s, the United

States invested significant resources to expand UAV operations because of their ability to

accomplish the “dirty”, “dull” and “dangerous” missions without putting a flight crew at

risk. An example of a relatively “dull” yet dangerous mission was documented during

the recent 34-day Bosnia-Kosovo conflict. To carry out airstrikes, B-2 crews flew 30

hours roundtrip creating crew fatigue that culminated during the most dangerous portions

31

of the mission.7 A post conflict assessment recommended increasing the two two-man

crew ratio to four crews. However, this option requires increased training and flight

hours flown by the limited B-2 inventory or reducing the number of operational sorties

compromising pilot proficiency.7 Forward basing B-2 assets was also suggested to

decrease mission length but proves unrealistic with a decreased U.S. overseas footprint

and political pressures. Currently the Predator demonstrates robust crew endurance

flying continuous 24 hour missions over Afghanistan and Iraq using multiple stateside

crews.7 In fact, a specific crew may begin a mission, fly eight hours, swap out and go

home for the night and return the next morning to take over the same mission. An

unmanned long range bomber would overcome the aforementioned risks and operational

limitations.

Potential exposure to “dirty” nuclear and biological hazards presents another risk

taken by aircrews of manned aircraft.7 Between 1946 and 1948, unmanned B-17s were

flown directly into nuclear test clouds immediately following detonation to collect air

samples.7 Unmanned aircraft of the time were extremely limited in operational use

prompting the military to conclude the risks of manned flight in these environments were

allowable to ensure mission completion.7 Unbelievably, manned flight through nuclear

fallout testing commenced into the 1990s.7 Current and future UAVs capable of mission

completion are the obvious alternative for these “dirty” missions.

Finally, airborne reconnaissance has always been considered a “dangerous”

mission better suited for UAVs. For example “25 percent of the 3rd Reconnaissance

Group’s pilots were lost in North Africa during World War II compared to 5 percent of

bomber crews flying over Germany”.7 During the Cold War, 23 manned aircraft and 179

32

airmen were lost during reconnaissance missions. The aforementioned Global Hawk is

an overwhelming reconnaissance UAV success story proving an unmanned aircraft can

complete the mission without endangering the aircrew.

Technology will continue to revolutionize how the military employs UAVs. The

United States Department of Defense set a vision for the future by developing core

competencies required for UAV operations in the twenty-first century. This vision,

released in the Department of Defense’s UAV roadmap, defined the UAV’s role within

the military construct by outlining far reaching objectives to be met by the year 2030.

Technology is the enabler for a majority of these objectives. Five operational goals have

been defined for successful future joint UAV operations. The first is to acquire more

multi-mission UAVs that can perform intelligence, surveillance, and reconnaissance as

well as offensive combative roles.7 Today’s conflicts are more difficult to segregate than

the past and a multi-role UAV is required to meet today’s challenges. Increased number

of multi-role UAVs will give the military the flexibility it needs in today’s global

conflicts. The second objective is to provide greater bandwidth and frequency agility for

UAV operations.7 Data links have been a significant bottle-neck to supporting critical

military requirements during conflicts of the modern era. Robust systems and

infrastructure are absolutely necessary for successful operations during the information

age. The third objective calls for the implementation of a file and fly a process in

military and Federal Aviation Administration regulations to allow UAVs to operate in

national airspace.7 This will allow the development of autonomously operated UAVs

with a combative or other multi-faceted role such as securing our national borders. The

fourth objective calls on the military to define parameters for small UAVs allowing them

33

to fly in national airspace.7 Finally, the fifth objective outlines requirements for a new

class of UAVs for urban operations. As seen in the Iraqi conflict, urban warfare is

difficult to successfully neutralize with significant risk to military missions and lives.

Urban operations will require UAVs to operate at low altitudes in congested and

“obstacle rich” airspace.7 Operating in urban environments require extremely precise

navigational systems that can function in mini-UAVs with abilities to operate building to

building or street to street. Following are illustrations of futuristic UAVs required for

meeting these goals. Some of these systems are already impacting military operations.

Mini-UAVs are very small, lightweight, and portable. The Buster, which stands

for a Backpack Unmanned Surveillance Targeting and Enhanced Reconnaissance UAV,

is a mini-UAV successfully employed in the field. The Buster is in it’s fourth year of

development, weighs only 10 pounds, and is just 41 inches long.7 This UAV is capable

of 10,000 feet altitudes with a four hour flight endurance time and is able to provide

soldiers with critical real time battlefield intelligence.7 The complete Buster system

includes four air vehicles, one ground control station, a launcher, color cameras and

thermal imaging payloads.48 The ground control station communicates with Buster using

a 225-395 MHz military navigation signal. Real time video and sensor readings are also

sent over this channel. Live video is transmitted over C-band data links to the ground

station terminal. The Buster is currently being tested by the Army Night Vision

Laboratories as a testbed for night vision sensors.7 Special Operations Forces also

currently field this small UAV.7

The FQM-151 Pointer developed by AeroVironment in the late 1980s is another

mini-UAV currently in use.7 One hundred hand launched battery powered FQM-151

34

Pointers have been employed by the U.S. Army, Marines and Air Force since 1989.7

Approximately 60 of these systems are currently utilized in Iraq and Afghanistan

operations.7 The Pointer is a small nine pound, low cost, remotely piloted drone that

carries a forward looking camera and uses GPS for navigation.49 It can be carried in two

backpacks and fly for approximately 90 minutes.49 The RQ-11 Raven is already slated to

fully replace the Pointer due to the fast pace of innovation.

The Raven, developed by AeroVironment, is a four pound next generation mini-

UAV currently used by Army Special Operation Forces.50 The Raven is essentially a

smaller version of the Pointer. In November 2005, the RQ-11 Raven was designated the

Army’s official small UAV and over 1,000 units costing $25,000 per system were

purchased.50 Each system consists of three aircraft, a ground control station, and a remote

video terminal.7 The Raven provides “over the hill” intelligence at the tactical level.7

Launched like a “paper airplane,” the Raven has a range of approximately ten miles

constrained by line of sight, command and control, and communication.50 It is capable of

broadcasting live video or providing images using two color infrared night cameras.50

The Raven has been extensively used in Afghanistan and Iraq over the last few years. In

Iraq, a Raven was able to spot an insurgent road block preventing locals from reaching a

polling location.50 As a result, U.S. forces cleared the intersection to ensure safe passage

for the voters.50 The Raven also aided in IED identification before they could inflict

damage. On average, a Raven can land approximately 200 times before required

maintenance.50 The Army has an annual $9 million contract with Aerovironment

Corporation to maintain these systems. 50

35

Even smaller than mini-UAVs, Micro-Aerial Vehicles (MAVs) are the next

generation of small UAVs able to fly undetected in hard to breach areas. Funded by the

DARPA, the MAV is defined as a micro-reconnaissance aircraft with no dimension

larger than six inches. Developed by AeroVironment, the Wide Area Surveillance

Projectile (WASP) MAV, weighs only six ounces. The WASP is capable of flying

approximately 60 minutes with a 5 mile range.7 It has successfully flown from sea level

up to 5,000 feet and can withstand 105 degrees Fahrenheit.51 The WASP’s payload

consists of fixed, forward, and side looking color daylight cameras with a real time video

downlink.51 It also uses the same ground control unit as the Raven.51 The WASP was

designed for use over land and sea. Its purpose includes organic squad-level

reconnaissance and surveillance for Naval support and light infantry military operations

on urban terrain.51 The WASP is relatively cost efficient at 5,000 dollars per unit.7

Prototype WASP vehicles have been flown by the U.S. Navy and plans are in progress

for full production.7 On the cutting edge, the WASP recently won the 2006 Best of

What's New Award from Popular Science in the Aviation and Space category.51

Although military has been the primary UAV focus, they also offer commercial

benefits as well. Research and development teams have diligently concentrated on

enabling UAV platforms to support future internet and mobile communications services

for both military and commercial use. According to a market study conducted at the

University of Sydney, Australia, some of the most lucrative potential commercial markets

for UAVs include mineral exploration, media resources, environmental control and

monitoring, telecommunications, crop monitoring, and unexploded ordinance detection.52

Others studies have shown that UAVs can also play a critical role during disaster

36

management crises.53 UAVs are ideally suited to support disaster after action teams as

they have long loitering flight times, pose minimal safety of flight risks, and provide

information and video instantaneously.53 Disaster management teams rely heavily on

data to make critical decisions on how to mitigate disasters, where to send aid and

assistance, and placing measures for damage control.53 For example, UAVs could have

provided valuable intelligence and prevented much of the chaos and damage seen by

Hurricane Katrina. Part of the problems experienced with Hurricane Katrina was the lack

of information as the majority of communications infrastructure was destroyed. Existing

UAV platforms such as the Predator and Global Hawk are being considered to support

important disaster management functions. A limitation to the collection of data lies with

existing sensors. Sensors currently in use would tax existing bandwidths as imagery over

vast disaster areas would overload the system and the customers looking for specific

imagery and other information.53 There are many untapped markets that UAVs can have

a significant impact on in the near future grossing billions in profit while improving our

way of life.

Extensive research within the UAV community is focused on developing systems

for use as high altitude platforms to support throughput of high data rates and mobile

services for short and long term applications. Recent interest in using high altitude

platforms such as UAVs to support mobile telephony or broadband services has become

possible due to technological breakthroughs. UAVs as high altitude platforms, HAPs,

can broadcast radio services including multimedia, deploy as stand alone two way tactical

data links, act as surrogate services for existing military terrestrial and airborne systems,

and possibly provide civil mobile services by flying as a base station. Benefits include

37

their rapid and flexible deployment capabilities, increased line of sight coverage, and

closer range. A closer range is advantages to link budgets and time delay of

transmitted/received signals.53 The ITU has designated frequency spectrum at 47 GHz

HAPs communications links. 53 However, there is a lot of technical standardization and

protocols that need to be determined to ensure future functionality. Challenges to

overcome in developing HAPs are cost, reliability and service ability, network

configuration and interoperability, and skepticism and confidence. As with any new

system, HAPs are currently very costly but developmental costs should drop significantly

as the industry stabilizes and prototypes are benchmarked. There are a lot of unknowns

with operating HAPs at these altitudes for any length of time, so reliability and service

potential is yet to be determined. The weather at these extreme altitudes is very active.

Skepticism also exists as HAPs are not widely accepted or known to be able to support

commercial applications and successful entrepreneurs must demonstrate its feasibility for

HAPs to be employed worldwide.

HAPs offer many advantages in emergency preparedness, and disaster

management and mitigation. As high altitude long endurance (HALE) systems, they

would be able to augment critical functions that include remote sensing and surveillance,

search and rescue, navigation, and radiolocation.54 It could also support a wide range of

civil applications. With highly sophisticated sensors these UAVs would be able to cover

remote regions of the world.54 The U.S. military has developed plans to employ similar

unmanned airships that would be free-flying and tethered. The endurance of these

airships ranges from 5 days to 1 month. 54 Examples of airships currently deployed

around the world are the Tethered Aerostat Radar Systems (TARS),

38

the Joint Land Attack Elevated Netted Sensor (JLENS), the High Altitude Airship

(HAA), and the Marine Airborne Re-Transmission System (MARTS).7 Following is a

detailed synopsis of these systems.

The TARS provides low level radar surveillance data for the nation’s drug

interdiction program. Maintained by the Air Force, it was developed in the 1980s. 7 It

also provides the North America Aerospace Defense Command with low level

surveillance in support of air sovereignty over the Florida Straights. 7 One of the TARS

currently in use has a unique mission as it broadcasts American television signals to Cuba

for the Office of Cuba broadcasting. 7 Due to weather, TARS is operational only 60

percent of the time. 7 It can stay airborne for as long as 30 days. 7

Another airship in research and development to support homeland security is the

JLENS. 55 The JLENS is designed to provide over the horizon surveillance to primarily

counter cruise missile threats using advanced sensor and networking technologies. 7 The

JROC approved its operational requirements and mission in 2004.55 This program has

had approximately 355 million dollars allocated for its research and development over the

last decade.55 Since then, an additional 2.1 billion dollars has been approved for future

procurements of the JLENS system.55 A JLENS system is made of two aerostats.56 One

aerostat has radar for surveillance and the other aerostat has precision track illuminating

radar.56 Both aerostats are able to fly 15,000 feet above sea level and are tethered to a

ground monitoring station. 55 The surveillance radar provides initial target detection and

the precision track illuminating radar determines a fire control quality track based on the

initial detection. 55 It is designed to have an endurance of 30 days. 56 The first JLENS

system is expected to be operational by 2010. 55

39

Still in its research and design phase, the High Altitude Airship, HAA, will

demonstrate the military potential of an unmanned, untethered, solar powered airship that

can operate at 65,000 feet for one year.7 At this altitude it will have a large footprint of

the ground for surveillance and reconnaissance operations. However, operating at such

an high altitude will require a very large volume of helium to support even modest

payloads. For example, a HAA may need to be 500 feet long with over five million cubic

feet of helium to sustain operations for flight.56 It is intended to self-deploy the HAA

from the U.S. to any worldwide location and remain in a geo-stationary position for a

year before requiring to return for servicing.7 It will also be capable of carrying a multi-

mission payload while continuously in flight for a month. 7 AeroVironment is developing

a High Altitude Airship called the Global Observer that will use a liquid hydrogen fuel

propulsion system, taking advantage of its specific energy.51 It will be capable of

carrying multiple surveillance payloads to include electro-optic/infrared, synthetic

aperture radar, communications intelligence, and signals intelligence. 51 Existing

communications compatible with the HAA can support several Gigabit per second data

links. 51 Using high altitude airships as communications platforms has already been

demonstrated by Japan, NASA, and AeroVironment flight tests. During their tests “the

world’s first high definition TV and 3G-high altitude relay applications from 65,000 feet

were demonstrated using payloads from Toshiba and NEC and commercial-off-the-shelf

TV sets and mobile handsets.”51 As detailed, there are many benefits of employing a high

altitude airship supporting commercial and military applications.

Another airship currently in use by the U.S. Marine Corps is the MARTS.7 Per

its name, MARTS is a communications relay for secure, reliable, over-the-horizon

40

communications.7 MARTS provides continuous communications coverage over a 160

mile footprint.7 Its outer lining is robust, as it was designed to be able to operate even

with punctures from small arms fire, lightning strikes, and high winds up to 85 miles per

hour. 7 As a communications relay its payload only consists of simple, highly reliable

transponders that are connected to a fiber optic cable to the ground equipment. 7 To

minimize its exposure to hostile forces, it requires a gas boost every 15 days.7 The first

MARTS system was moved to Iraq in February 2005 and there are plans to deploy a total

of 6 which will cost the Marine Corps an additional 14 million dollars.57 The most

significant challenge to these airships is its limited mobility.

There is extensive research and funding that is being invested in HAPs and its

future appears to be very promising. There are over 30 companies that are involved in

designing or manufacturing airships and other aerostats in North America, Europe and

Asia.56 The increased attention to airships like the ones just detailed are due to several

factors. Because of U.S. domination in air power, threats to high altitude airships is

virtually nonexistent. 56 This has led to serious consideration in using airships to support

daily and strategic endeavors. Second, the U.S. military continues to demand “persistent

surveillance” as “network-centric warfare approaches, increased emphasis on homeland

security, and growing force protection demands in urban environments all call for

‘dominant battlespace awareness’”.56 Finally military requirements, budget cuts, and

other necessities have led teams to consider HAPs in future requirements and

operations.56 Per the Department of Defense, existing and planned communications

capabilities will meet only 44 percent of forecasted requirements. HAPs can help bridge

41

this gap by augmenting satellite data links and supporting regional and tactical

communications and connectivity.7

UAVs have been developed primarily to support military endeavors, but

commercial UAV applications are worthy of pursuit as well. The application of

developing UAV technologies continues to change the face of traditional aerospace

power capabilities and commercial activities. Technology is the catalyst for new

endeavors in the UAV evolution making the possibilities limitless. From the first

remotely controlled drone to the autonomously operated X-47 JUCAS, it is truly amazing

what the power of technology has enabled for unmanned aerial systems. The future is

bright and unpredictable and it will be exciting to see what the world of UAVs looks like

in 2030 and beyond.

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Bibliography

1 John Pike, “Unmanned Aerial Vehicles”, http://www.fas.org/irp/program/collect/uav.htm (Aug 05)2 “Unmanned Aerial Vehicles and Precision Guided Munitions at the Centennial”, http://www.uavforum.com/library/defnews.doc (Aug 05)3 Christopher A. Jones, Maj, USAF, “Unmanned Aerial Vehicles (UAVs) An Assessment of Historical Operations and Future Possibilities” (Mar 97)4 “Unmanned Aerial Vehicle”, http://en.wikipedia.org/wiki/Unmanned_aerial_vehicle, (Aug 06)5 Ralph Sanders “An Israeli Military Innovation UAVs”, Joint Force Quarterly, Winter 02-036 “New Dawn for UAVs”, http://www.global-defence.com/2000/pages/uav.html (Aug 06)7 “Unmanned Aircraft Systems Roadmap 2005-2030”, http://www.acq.osd.mil/usd/Roadmap%20Final2.pdf (Aug 05)8 Dr John K. Fawcett, “Additional Topics: Inertial Navigation”, (Mar 05)9 “Gyroscopes”, Science and Technology Encyclopedia, http://www.answers.com/topic/gyroscope10 Mary Bellis, “”History of the Global Positioning System – GPS”, http://inventors.about.com/od/gstartinventions/a/gps.htm 11 Steven R. Strom, “Charting a Course Toward Global Navigation”, Crosslink Satellite Navigation Volume 3, Number 2 (Summer 02)12 The Aerospace Corporation, “GPS Primer”, http://www.aero.org (2003)13 NAVSTAR Global Positioning System Joint Program Office, “GPS Overview” http://www.navcen.uscg.gov/gps (Aug 06)14 M.Hernández-Pajares, J.M.Juan, J.Sanz , “GPS Data Processing”, http://maite152.upc.es/~manuel/tdgps/tdgps1_article.html (Aug 06)15 Peter H. Dana, “Global Positioning System Overview”, http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html (May 00)16 “Differential GPS”, http://www.answers.com/topic/differential-gps17 David Wolfe, “Systems of Interest”, U.S. Coast Guard Engineering, Electronics and Logistics Quarterly (Summer 06)18 Luís Sardinha Monteiro, Terry Moore, and Chris Hill, “What is the accuracy of DGPS?”, University of Nottingham19 Thomas B. Criss, Marilyn M. South, and Larry J. Levy, “Multiple Coordination Image Extraction (MICE) Technique for Rapid Targeting Precision Guided Munitions”, John Hopkins APL Technical Digest, Volume 18, Number 4 (1998)20 “GPS Modernization”, http://gps.faa.gov (Aug 06)21 LCDR Richard D. Fontana, Wai Cheung, Paul M. Novak, Thomas A. Stansell Jr, “The New L2 Civil Signal, http://www.navcen.uscg.gov/gps/modernization (Aug 06)22 Defense Science Board Task Board “The Future of the Global Positioning System”, http://www.acq.osd.mil/dsb/reports/2005-10-GPS_Report_Final.pdf (Oct 05)23 Capt Brian C. Barker, John W. Betz, John E. Clark, et, “Overview of the GPS M Code Signal”, http://www.mitre.org/work/tech_papers/tech_papers_00 (May 00)

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24 Dan Nobbe, “Highly Integrated GPS Receiver Overcomes Jamming,, Pinpoints Location”, Defense Electronics, http://www.rfdesign.com (Feb 04)25 Hamid R. Saeedipour, Md., Azlin Md. Said, and P. Sathyanarayana, “Data Link Functions and Attributes of An Unmaned Aerial Vehicle (UAV) System Using Both Ground Station and Small Satellite”, University of Science Malaysia (Apr 05)26 “Defense Science Board Study on Unmanned Aerial Vehicles and Unmanned Combat Aerial Vehicles”, Office of the Undersecretary of Defense (Feb 04)27 “Common Data Link”, http://www.globalsecurity.org (Sep 06)28 “An Introduction to Direct-Sequence Spread-Spectrum Communications“,http://www.maxim-ic.com/appnotes.cfm/appnote_number/1890 (Sep 06)29 “UAV Annual Report FY 1996”, http://www.fas.org/irp/agency/daro/uav96/content.html (Nov 96)30 “Air Combat Command Concept of Operations for Endurance Unmanned Aerial Vehicles”, http://www.fas.org/irp/doddir/usaf/conops_uav/part06.htm, (3 Dec 96)31 “AN/TSQ-190 TROJAN / TROJAN SPIRIT II”, http://www.globalsecurity.org, (Sep 06)32 “Global Hawk”, http://www.af.mil/factsheet (Sep 06)33 Wang Jong Chin and Victor Chua Yung Sern, “Unmanned Aerial Vehicle: Development Trends and Technology Forecast”, DSTA Horizons, http://www.dsta.gov (Sep 06)34 W.S. Rabinovich, G.C. Gilbreath, Chris Bovais, et, “Infrared Data Link Using a Multiple Quantum Well Modulation Retro-reflector on a Small Rotary-Wing UAV”, US Naval Research Laboratory35 “Major Milestone Reached for High Data Rate Laser Communications”, http://www.spacewar.com/communications.html (3 Apr 06)36 Elisra Group, “Tadrian Spectralink debuts its new high spectrum efficiency ‘StarLink Mark II’ FH/TDD Digital Data Link for Mini-UAVs”, http://www.auvsi.org/media/pressreleases/2006/Tadiran2.pdf (Aug 06)37 “Australia Deploys Skylark UAVs to Iraq”, http://www.defenseindustrydaily.com/2005 (4 Nov 05)38 David Axe, “Clouds on the horizon for pilot-less bombers”, http://www.nationaldefensemagazine.org/ (Aug 06)39 “Joint Unmanned Combat Air Systems”, http://www.darpa.mil/j-ucas, (31 Mar 04)40 http://www.darpa.mil/j-ucas/ (Sep 06)41 David Axe, “JUCAS takes another hit”, http://www.defensetech.org, (Aug 06)42 “RQ-4A/B Global Hawk High Altitude, Long Endurance, Unmanned Reconnaissance Aircraft, USA”, http://www.airforce-technology.com/projects/global (Sep 06)43 “Mini-UAV launched from Predator”, General Atomics Aeronautical Systems, Inc, http://www.ga.com (Sep 2006)44 “Predator RQ-1 / MQ-1 / MQ-9 Unmanned Aerial Vehicle (UAV), USA”, http://airforce-technology.com (Sep 06)45 Interview Eric Puels46 Interview Geoffrey Fukumoto47 Northrop Grumman RQ-4A Global Hawk, http://www.northropgrumman.com/unmanned/index.html (Oct 06)

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48 Angel Rivera Jr and Victor Murray, “Friendly Skies, Hostile Skies”, Technology Today (Summer 2006).49 Andreas Parsch, “Aerovironment FQM-151 Pointer”, http://www.designation-systems.net/dusrm/m-151.html (Sep 06)50 “Raven UAV Draws Raves from the Field”,http://www.defenseindustrydaily.com/mt/mt-search.cgi?IncludeBlogs=2&search=raven (Sep 06)51 Aerovironment UAVs, http://www.avinc.com (Sep 06)52 Dr K.C. Wong, “Aerospace Industry Opportunities in Australia Unmanned Aerial Vehicles (UAVs)”, http://www.aero.usyd.edu.au/wwwdocs/uav.html (Sep 06)53 Steve Wegener , “UAV Over-the-Horizon Disaster Management Demonstration Projects”, NASA Ames Research Center (Feb 00)53 Tim Tozer, David Grace, Jon Thompson and Peter Baynham, “UAVs and HAPs potential convergence for military communications”(Jun 00),54 Milebrook Technology Inc, “Application of High-Altitude Long Endurance (HALE) Platforms in Emergency Preparedness and Disaster Management and Mitigation”55 Mickey McCarter, “Boost for Cruise Missile Defense” http://www.military-aerospace-technology.com/article.cfm?DocID=521 (Sep 06)56 Christopher Bolkhom “Potential Military Use of Airships and Aerostats” (May 2005)57 Defense Industry Daily, “$14M+ for Blimps in Iraq”, http://www.defenseindustrydaily.com/ 2005/04/14m-for-blimps-in-iraq/index.php (Apr 05)

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Figures

Figure 1 GPS Signal Modulation (L1 and L2). Peter H. Dana, “Global Positioning System Overview”, http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.html (May 00)Figure 2 DGPS ground station locations as of February 2006. David Wolfe, “Systems of Interest”, U.S. Coast Guard Engineering, Electronics and Logistics Quarterly (Summer 06)Figure 3 MICE interpolation technique. Thomas B. Criss, Marilyn M. South, and Larry J. Levy, “Multiple Coordination Image Extraction (MICE) Technique for Rapid Targeting Precision Guided Munitions”, John Hopkins APL Technical Digest, Volume 18, Number 4 (1998)Figure 4: “Fingerprints” of GPS Signals. Capt Brian C. Barker, John W. Betz, John E. Clark, et, “Overview of the GPS M Code Signal”, http://www.mitre.org/work/tech_papers/tech_papers_00 (May 00)Figure 5 GPS Spectrum and Frequency Allocation. Capt Brian C. Barker, John W. Betz, John E. Clark, et, “Overview of the GPS M Code Signal”, http://www.mitre.org/work/tech_papers/tech_papers_00 (May 00)

Tables

Table 1 L-Signal Characteristics (L1, L2C, L5). “GPS Modernization”, http://gps.faa.gov (Aug 06)Table 2 L-Signal Characteristics. 21 LCDR Richard D. Fontana, Wai Cheung, Paul M. Novak, Thomas A. Stansell Jr, “The New L2 Civil Signal, http://www.navcen.uscg.gov/gps/modernization (Aug 06)

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