Fall 2006
TCOM 598 Independent Study of Telecommunications
Unmanned Aerial Vehicles (UAVs)
Enabled by Technology
Renee Puels
By definition, Unmanned Aerial Vehicles (UAVs) are “remotely piloted or selfpiloted 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.
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
2
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
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
3
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 electrooptic systems required for functionality on a small platform.5 The Scout possessed
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
4
early Syrian’s reaction.5 Syria proceeded to launch most of their air defense missiles
against the UAVs leaving the country temporarily defenseless . 5 By ingeniously
programming Syrian radar system frequencies into anti-radiation missiles, Israeli aircraft
were able to seek and destroy Syrian defenses effortlessly without facing a significant
missile threat. 5 As a result, the IDF was able to pinpoint Syrian anti-air defense systems
and aircraft without suffering a single casualty in the largest air assault since the Korean
War. 5 Nineteen enemy battery systems and twenty-two Syrian aircraft were destroyed. 5
Although a smaller nation, Israel successfully used UAVs to their advantage to defeat a
much larger force.
Based on the Scout’s success, the United States and other nations followed
Israel’s lead in developing their own UAV programs. Today, UAVs are a universal
weapon of the twenty-first century with over twenty nations developing their own next
generation strike systems spawning a multi-billion dollar industry.2 The U.S.
government alone has allocated 1.6 billion dollars between 2005-2009 for UAV research
and development.7 However, industrialized nations are not alone in embracing UAV
potential. As witnessed in the recent 2006 Israeli-Lebanon crisis, terrorists and other
rogue organizations are also utilizing UAVs during planned terror attacks. Hezbollah
reportedly attempted several attacks on Israeli cities using low flying UAVs armed with
explosives. Apparently, UAVs will play a critical role in many future combative
operations involving nation-state and guerilla/terrorist warfare.
The continued advancement of UAVs relies heavily on technological innovation.
As new standards and technologies emerge, communications integration and
interoperability are critical to ensuring the advancement of UAV capabilities. For
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instance, the technological feats that enabled the U.S. based Global Positioning System
heavily influenced UAV navigational and targeting functions. New techniques and
standards based upon GPS continue to improve UAV accuracy and support capabilities.
Radio frequency applications are the primary means by which data links and sensor
communications are conducted. However, other technologies on the horizon may be the
next generation solutions to support these functions. For example, promising
optical/laser research can bring huge bandwidth advances to the UAV spectrum of
operations. Also, network and computer technologies are playing a critical role in the
autonomous development of UAV platforms. Continued improvement in computer
processing will enable network-centric operations between UAVs, manned aircraft, and
ground support. At the forefront of many efforts is the development of “smart” UAVs
capable of making autonomous decisions without human intervention. Currently,
computer processing technologies lack the sophistication needed to mimic the human
brain but is forecasted to be plausible in ten to fifteen years.7 Along with all of these
technological advances comes limitations. The challenge is seamlessly integrating each
technological piece in an effort to further exploit UAV applications. Some successful
integration of advanced navigational systems, data links, and sensors have already been
realized. The following detailed analysis of each component will illustrate its significant
impact on UAV capabilities.
Communications equipment is one of the most critical UAV components enabling
global reach. Today, global reach is largely possible due to the enhanced navigational
capabilities of the Global Positioning System (GPS). The advent and growth of the GPS
in the later half of the twentieth century has allowed UAVs to be guided and controlled
6
from anywhere at any time. Currently GPS receivers are accurate to within meters. 15
This is crucial because precision and accuracy are paramount for executing military
operations. The application of GPS in UAV operations is critical to current and future
navigation and control. Due to GPS accuracy, military commanders are able to precisely
determine where, when, and how to employ UAV capabilities to meet a specific military
objectives. Prior to GPS, Inertial Navigation Systems (INS) alone enabled airborne
navigation.
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
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
7
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
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
8
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
Figure 1 GPS Signal Modulation (L1 and L2)
9
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
location of the GPS satellites relative to the receiver affects accuracy when using GDOP
10
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
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
11
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
also supports targeting and surveillance applications. Innovative mathematical methods
and techniques have been developed to increase the precision of UAV targeting and the
12
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
C to c are straight lines that all intersect at a single point, corresponding roughly to the
center of the camera lens.”19 13
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
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
14
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.
15
Carrier Freq
Code Length
Code Clock
Civil Signal
Bit Rate
Phases
FEC
(MHz)
(chips)
(MHz)
(Bps)
L2
1575.42
1023
1.023
Bi-phase
50
No
L2C
1227.60
1.023
Bi-phase
25
Yes
50
Yes
10230
767250
10230
L5
1176.45
Quad10.23
10230
phase
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
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.
16
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
signal strengths across the bandwidth.23 The M signal is represented by the red “BOC”
spectrum.
17
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.
Figure 5 GPS Spectrum and Frequency Allocation
18
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
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.
19
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
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
20
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
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
21
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
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
22
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
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
23
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
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
24
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.
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
25
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 retroreflector (MRR). An MRR uses an optical retro-reflector, such as a cube, and an electrooptic 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
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 retroreflector 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
26
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
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
27
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 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
28
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.
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
29
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
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
30
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.
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.
31
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 electrooptical/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
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
32
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
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
33
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
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
34
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
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
35
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
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
36
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 miniUAV 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
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
37
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
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
38
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
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
39
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),
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
40
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
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
41
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 multimission 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
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
42
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
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
43
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.
44
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47
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
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Levy, “Multiple Coordination Image Extraction (MICE) Technique for Rapid Targeting
Precision Guided Munitions”, John Hopkins APL Technical Digest, Volume 18, Number
4 (1998)
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Clark, et, “Overview of the GPS M Code Signal”,
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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)
48