The CanX-7 Nanosatellite ADS-B Mission: A Preliminary Assessment

Abstract

The development of space-based Automatic Dependent Surveillance-Broadcast (ADS-B) will allow surveillance of aircraft in areas not covered by radar or ground-based ADS-B systems. In September 2016, the Canadian Advanced Nanospace eXperiment-7 (CanX-7) satellite was launched into a 690 km sun synchronous orbit with an ADS-B receiver payload. The first phase of ADS-B data collection took place over the North Atlantic between 4 and 31 October. A preliminary assessment of the data indicates that the average ADS-B signal strength is close to the calculated receiver detection threshold of �D94.5 ± 0.5 dBm. The pattern of received ADS-B reception appears to be consistent with a signal propagation model developed for the CanX-7 mission. Future work includes the comparison of coincidental flight plan data for the operations area and an analysis of the payload antenna pattern.

Full text

Positioning, 2017, 8, 1-11
http://www.scirp.org/journal/pos
ISSN Online: 2150-8526
ISSN Print: 2150-850X
DOI: 10.4236/pos.2017.81001 February 28, 2017
The CanX-7 Nanosatellite ADS-B Mission:
A Preliminary Assessment
Ron Vincent, Richard Van Der Pryt
Department of Physics, Royal Military College of Canada, Kingston, Ontario, Canada
Abstract
The development of space-based Automatic Dependent Surveillance-Broad
-
cast (ADS-B) will allow surveillance of
aircraft in areas not covered by radar
or ground-based ADS-
B systems. In September 2016, the Canadian Advanced
Nanospace eXperiment-7 (CanX-
7) satellite was launched into a 690 km sun
synchronous orbit with an ADS-B receiver payload. The first phase of ADS-
B
data collection took place over the North Atlantic between
4 and 31 October.
A preliminary assessment of the data indicates that the average ADS-
B signal
strength is close to the calculated receiver detection threshold of −94.5 ± 0.
5
dBm. The pattern of received ADS-
B reception appears to be consistent with a
signal propagation model developed for the CanX-7 mission. Future work i
n-
cludes the comparison of coincidental flight plan data for the operations area
and an analysis of the payload antenna pattern.
Keywords
ADS-B, Space-Based ADS-B, CanX-7, Air Traffic Control
1. Introduction
Automatic Dependent Surveillance-Broadcast (ADS-B) is an air traffic surveil-
lance technology in which aircraft transmit identification, position, velocity and
status on 1090 MHz. The transmissions may be received by other aircraft or by
ground stations for relay to Air Traffic Services to augment traditional surveil-
lance radars. The ADS-B message is 120-bits in length and broadcast at random
intervals between 0.4 and 0.6 seconds with pulse position modulation to help
prevent signal collisions between aircraft. Signal power varies between 75 W and
500 W, depending on aircraft category [1]. The vertically polarized ADS-B trans-
mission alternates between top- and bottom-mounted quarter-wave monopole
antennas.
How to cite this paper:
Vincent, R
. and
Van Der Pryt
, R. (2017) The CanX-7 Na-
nosatellite ADS
-
B Mission: A Preliminary
Assessment
.
Positioning
,
8
, 1-11.
https://doi.org/10.4236/pos.2017.81001
Received:
February 5, 2017
Accepted:
February 25, 2017
Published:
February 28, 2017
Copyright © 201
7 by authors and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access

R. Vincent, R. Van Der Pryt
2
Currently only 30% of the Earth is covered by the combination of radar and
ADS-B. In the absence of aircraft surveillance, existing air traffic procedures use
standardized routes and large inter-aircraft spacing to provide aircraft separa-
tion. ADS-B coverage is limited by the placement of ground stations, which
cannot be installed in mid-ocean and are difficult to maintain in remote areas. A
potential solution for the surveillance of aircraft anywhere in the world is
through the monitoring of ADS-B transmissions using orbital platforms. The
first space-based ADS-B receiver flew on Proba-V in 2013, followed by the
GOMX-1 (2013) and GomX-3 (2015) nanosatellites. The Canadian Advanced
Nanospace eXperiment-7 (CanX-7) satellite was launched with an ADS-B re-
ceiver in September 2016. In January 2017, the first ten Iridium NEXT satellites
carrying hosted ADS-B payloads were placed in low Earth orbit (LEO) as part of
a 66-satellite constellation that is projected to provide full Earth coverage for
ADS-B signal reception.
The ADS-B payload onboard CanX-7 was developed at the Royal Military
College of Canada (RMCC). ADS-B research has been conducted at RMCC since
2009, which includes the first ADS-B receiver in near space and extensive signal
propagation modelling [2]-[8]. This paper gives a preliminary assessment of the
CanX-7 ADS-B mission. Section 2 describes the satellite and payload parameters;
Section 3 outlines the first phase of operations; Section 4 discusses the prelimi-
nary findings and Section 5 includes a summary and future work.
2. CanX-7 Satellite and ADS-B Payload
Funded by the Natural Sciences and Engineering Research Council of Canada,
Defense Research and Development Canada-Ottawa, COM DEV and the Cana-
dian Space Agency, CanX-7 was developed and built by the University of To-
ronto Institute of Aerospace Studies-Space Flight Laboratory (UTIAS-SFL). The
primary payload consists of four deployable drag sails that will demonstrate pas-
sive de-orbiting from LEO. The Inter-Agency Space Debris Coordination Com-
mittee recommends de-orbiting of spacecraft in LEO within 25 years of mission
completion, which is problematic for small satellites without propulsion systems.
The drag sail, with a total area of 4 m2, is scheduled for activation approximately
six months after launch. Deployment of the sail will be captured with onboard
cameras. The secondary payload is an ADS-B receiver that will collect transmis-
sions prior to drag sail initiation. Raw ADS-B data will be stored onboard
CanX-7 and downlinked later to the UTIAS ground station. Attitude determina-
tion is accomplished with a magnetometer, while a set of three magnetic tor-
quers provide 2-axis attitude control by aligning a primary axis with the local
magnetic field. Solar cells generate power with a lithium ion battery used for
energy storage. Thermal tapes provide passive temperature control for the
spacecraft. Table 1 lists specifications of CanX-7, while Figure 1 and Figure 2
show the major components of the satellite.
The ADS-B payload consists of an ADS-B receiver, low-noise preamplifier,
payload computer and a microstrip patch antenna. Payload electronics are lo-

R. Vincent, R. Van Der Pryt
3
Figure 1. The CanX-7 satellite with major components indicated (Courtesy of UTIAS-
SFL).
Figure 2. CanX-7 satellite with drag sails deployed (Courtesy of UTIAS-SFL).
Table 1. CanX-7 specifications.
Element Description
Primary Payload Drag Sail
Secondary Payload ADS-B Receiver
Size 10 × 10 × 34 cm
Mass 3.6 kg
Communication Downlink S-Band
Communication Uplink UHF
Attitude Determination Magnetometer
Attitude Control 3 Magnetic Torquers (2-axis)
Primary Power Solar Cells
Energy Storage Lithium Ion Batteries
Thermal Control Passive
Propulsion None
Boom Camera
Solar Panels
UHF Antenn as
ADS-B Patch
Antenna
Drag Sail Modules
S-band
Antenna

R. Vincent, R. Van Der Pryt
4
cated within an aluminum enclosure to reduce electromagnetic interference with
other satellite components. The receiver is a commercially available unit (88 mm
× 53 mm, 60 g) with a throughput of 1700 messages per second. Upon demodu-
lation, each message is tagged with a Received Signal Strength Indicator (RSSI)
value and time of arrival before being saved by the payload computer. ADS-B
messages are subsequently transferred to the spacecraft computer for storage
and downlink. The right hand circularly polarized conformal antenna is 75 mm
in diameter and features a 35 MHz bandwidth, 4.5 dBic gain and a broad uni-
form main lobe with a half power beam width of 95˚ [9]. A schematic of the
ADS-B payload is shown in Figure 3 [9].
3. ADS-B Operations
CanX-7 was launched into a sun synchronous orbit of 690 km on 28 September
2016, resulting in approximately 15 orbits per day. Following a satellite-com-
missioning period, the first phase of operations began on 04 October and ended
on 31 October. During this time, the ADS-B receiver was activated for 18 mi-
nutes in the Northern Hemisphere during each orbit, representing a latitudinal
coverage between 12˚N and 78˚N. There were 381 collection periods in which a
total of 776,584 call sign, position and velocity messages were received. Status
messages were not decoded and are not included here. Overall statistics for the
first phase of the mission are shown in Table 2.
Figure 3. Exploded view of the CanX-7 ADS-B payload.
Table 2. ADS-B mission statistics for the Northern Hemisphere, 4 to 31 October 2016.
Property Value
Total Collection Periods 381
Total Messages Decoded 776,584
Call Sign Messages 7.9%
Position Messages 46.4%
Velocity Messages 45.7%

R. Vincent, R. Van Der Pryt
5
Although ADS-B data collection was planned for every orbit, the primary
analysis concentrated on the North Atlantic over the Shanwick and Gander
Oceanic Control Areas (OCAs). This region was selected for the first phase of
the experiment since it is relatively quiet with respect to non-ADS-B 1090 MHz
transmissions. Additionally, NAV Canada has access to historical flight plan in-
formation for the region. As a result of the sun synchronous nature of the orbit,
CanX-7 flew over the operations area at approximately the same local time each
day. There were as many as four passes over the operations area per day, but
typically a descending pass between 1100 UTC and 1300 UTC and an ascending
pass between 2100 UTC and 2300 UTC provided the best coverage. Figure 4
shows the CanX-7 ground track for a 24-hour period, with favorable descending
and ascending passes identified. Data provided by NAV Canada indicated that
air traffic in the Ganderand Shanwick OCAs experience two peaks every day. As
seen in Figure 5 there is a maximum of about 220 aircraft at 0300 UTC repre-
senting the eastward flow of aircraft and a similar peak at 1400 UTC repre-
senting the westward flow of aircraft [6]. During CanX-7 passage the number of
Figure 4. CanX-7 ground track for a typical 24-hour period with descending and as-
cending passes over the operations area highlighted. The operations area is indicated in
red (Satellite Tool Kit Software).
Figure 5. Number of aircraft in the Gander and Shanwick OCAs is shown for a 24-hour
period. Expected number of aircraft in the operations area is indicated in the boxed areas
for the ascending and descending pass for a typical day.

R. Vincent, R. Van Der Pryt
6
aircraft expected in the operations area ranges between 150 and 200 aircraft for
the descending pass and 50 to 75 for the ascending pass. Data collected over the
operations area accounted for approximately 13% of the first phase data.
4. Data Assessment
4.1. Spacecraft Pointing
The magnetic torquer on board CanX-7 aligns the ADS-B antenna Boresight
with the local magnetic field. While this is a simple method to achieve Earth
pointing objectives in the region, the absolute accuracy and rate of change of ro-
tation as the satellite transits from either the north or south through the opera-
tions area is problematic. Travelling at 7.5 km/s it takes the spacecraft approx-
imately five minutes to pass over the operations area. If CanX-7 enters the re-
gion from the north on a descending pass the spacecraft begins with a pointing
direction closer to nadir than if it enters from the south. The rotation vector
during a pass is dependent on local magnetic field conditions and satellite re-
sponse to changes in the field. Figure 6 shows a sequence of aircraft contacts in
Figure 6. A sequence of four images (a) to (d) is shown as CanX-7, denoted by the orange
circle with UTC time, transits southward through the operations area for selected
10-second intervals on 29 October. Red dots represent ADS-B messages received during
the entire pass, while aircraft symbols indicate signal reception during the shown
10-second interval. Aircraft symbol does not indicate heading.
(a)
(c) (d)
200 km
Greenland
200 km
Greenland
(b)
200 km
Greenland
200 km
Greenland

R. Vincent, R. Van Der Pryt
7
the operations area during a descending pass on 29 October. The satellite posi-
tion is shown in 10-second increments with red dots representing ADS-B mes-
sages received during the entire pass, while aircraft symbols indicate signal re-
ception during the shown 10-second interval. In Figure 6(a) the satellite,
represented by the orange symbol, did not detect any of the aircraft. As the satel-
lite transits southward in Figures 6(b)-(d), an increasing number of contacts is
evident. The sequence, which is typical of the descending passes, implies a bias
of the satellite antenna to the northwest because of the pointing vector. Contacts
to the east of the satellite track do not appear until the satellite is near the south-
ern boundary of the operations area. Figure 7 shows the local magnetic field for
the 29 October descending pass in one-minute increments based on the Interna-
tional Geomagnetic Reference Field (IGRF). The theoretical offset of the nadir
point is shown to the northwest of the satellite ground track.
4.2. Signal Levels
ADS-B signals received by the payload are given an integer RSSI value between 0
and 255. The average RSSI value for all signals received was 28, which is close
the calculated −94.5 ± 0.5 dBm Minimum Detectable Signal (MDS) of the payl-
oad receiver. In accordance with Van Der Pryt and Vincent [8], Figure 8 shows
the ADS-B signal propagation model for a satellite altitude of 690 km based on a
500 W transmitter and a typical aircraft antenna radiation pattern for ADS-B
transmissions. Taking into account the calculated payload MDS, represented by
the dashed line in Figure 8, the model implies that aircraft 5˚ to 8˚ and 42˚ to
60˚ from nadir should be detected. There is a null 0˚ to 5˚ because of the aircraft
quarter-wave monopole radiation pattern, while signals between 8˚ and 42˚ are
Figure 7. The IGRF local magnetic field is shown in one-minute increments for satellite
passage through the operations area for the descending pass on 29 October. The Bore-
sight of the antenna points to the northwest (Satellite Toolkit Software).

R. Vincent, R. Van Der Pryt
8
Figure 8. Expected ADS-B signal strength at an altitude of 690 km is shown in relation to
degrees from nadir for a 500 W transmitter and a typical aircraft radiation pattern for
ADS-B transmissions. The dotted line is the calculated −94.5 ± 0.5 dBm MDS of the
ADS-B payload.
predicted to fall below the payload detection threshold.
Spurious contact was observed for all passes. This is likely because signal
strength may be near the threshold of payload sensitivity depending on air-
craft-satellite orientation. While there are many instances of single message
contact in the database, there are also examples of hundreds of messages re-
ceived from the same aircraft in a single pass. With respect to multiple message
contact, the data stream could be near continuous or experience significant in-
tervals between messages. For the descending pass of 29 October (Figure 6)
there were 60 different aircraft detected in the operations area, representing 996
position messages. During this pass, there were seven instances of 40 or more
position messages received from a single aircraft with a maximum of 106 mes-
sages from the same aircraft. Figure 9(a) illustrates the breakdown of the posi-
tion messages received for each aircraft in the operations areas during the 12
UTC descending pass on 29 October. Figure 9(b) offers a comparison to the 12
UTC descending pass of 16 October to demonstrate the observed consistency
between similarly timed passes. The average RSSI value for 40-plus multiple
message contact shown in Figure 9(a) and Figure 9(b) is not significantly dif-
ferent from the overall average RSSI value of 28 and remains close the payload
MDS. This implies that the disparity between the number and consistency of re-
ceived signals from individual aircraft may be a function of aircraft antenna rad-
iation pattern rather than transmitter power. For 16 and 29 October, the greatest
number of received messages originated from a Boeing 777 (KLM) and a Boeing
767 (Delta) respectively, which could indicate a superior antenna configuration
for space-based ADS-B surveillance.
4.3. Signal Propagation Model
The tilt of the antenna boresight as a function of the magnetic field may result in
contact at extended ranges from the satellite. Figure 10 shows the beginning (a)
and end (b) of a 23 UTC ascending pass on 16 October. During this pass there
Nadir Angle –Satellite to Aircraft (degrees)
5º to 8º from nadir 42º to 60º from nadir
10 20 30 40 50 60
-105
-100
-95
-90
Received Power (dBm)
Payload MDS

R. Vincent, R. Van Der Pryt
9
Figure 9. Number of position messages per aircraft is illustrated for 12 UTC descending
passes on (a) 29October and (b) 16 October. The integer value of the average RSSI is
shown in parenthesis for aircraft with more than 40 position messages.
(a)
(b)
Figure 10. A sequence of two images (a) and (b) is shown as CanX-7, denoted by the
orange circle with UTC time, transits northward through the operations area for selected
10-second intervals on 16 October. Red dots represent ADS-B messages received during
the entire pass, while aircraft symbols indicate signal reception during the shown 10-
second interval. Aircraft detected at extended ranges on the coast are highlighted in the
yellow box to the bottom left of each panel. Aircraft symbol does not indicate heading.
52 (29)
29 October, 12 UTC Pass
60 Aircraft
996 Position Messages
(b)
(a)
42 (33)
16 October, 12 UTC Pass
59 Aircraft
965 Position Messages

R. Vincent, R. Van Der Pryt
10
are few contacts in the operations area, however a grouping of aircraft are de-
tected on the east coast of North America. The slant range to these aircraft is
2500 to 3000 km. During this timeframe, there is evidence that the payload did
not detect a number of aircraft between CanX-7 and the coastal region. Figure
11 shows flights reported during the satellite pass by
Flightradar
24, a flight
tracking application that combines data from several sources including ground-
based ADS-B and radar. Considering the calculated MDS of the payload, the
signal propagation model in Figure 8 predicts the potential of missed contacts in
the medium range as suggested by Figure 11.
5. Summary and Future Work
The CanX-7 ADS-B receiver collected data over the Gander and Shanwick OCAs
from 4 to 31 October 2016. The average signal strength for 776,584 decoded
messages detected was close to the calculated receiver MDS of −94.5 ± 0.5 dBm.
ADS-B transmissions appear sporadic at times because the average signal
strength is near the threshold of payload sensitivity depending on aircraft-satel-
lite orientation. Aircraft contacts vary from single transmission receptions to
hundreds of near continuous messages. The disparity in message reception is
likely a function of aircraft antenna radiation pattern since there was no ob-
served increase in power for continuously received messages. The distribution of
aircraft contacts, including long-range signal reception, appears consistent with
a signal propagation model developed for the CanX-7 mission. Precise mapping
of the radiation pattern of the satellite antenna is complicated by the magnetic
torquer attitude control method. A complete data analysis will be carried out
over the next several months, including a rigorous approach to the satellite
pointing characteristics and the comparison of NAV Canada flight data for the
operations area.
In November 2016 the polarity of the magnetic torquers of the satellite was
reversed to allow the observation of ADS-B transmissions in the southern he-
misphere. In December, operations commenced once again in the Northern
Hemisphere to collect data over the Polar region. Following a successful software
update of the ADS-B receiver, CanX-7 was re-tasked to collect ADS-B data over
Figure 11. Aircraft reported by flightradar24 during the time of satellite pass at 2342
UTC on 16 Oct. 2016. Some aircraft may not be ADS-B equipped.

R. Vincent, R. Van Der Pryt
11
high-density air traffic areas. The drag sail is scheduled for deployment at the
beginning of May 2017, at which time ADS-B operations shall be terminated.
References
[1] RTCA DO-260B (2009) Minimum Operational Performance Standards for 1090
MHz Extended Squitter Automatic Dependent Surveillance-Broadcast (ADS-B) and
Traffic Information Services-Broadcast (TIS-B).
Radio Technical Commission for
Aeronautics
.
[2] Francis, R., Vincent, R., Noël, J.M., Tremblay, P., Desjardins, D., Cushley, A. and
Wallace, M. (2011) The Flying Laboratory for the Observation of ADS-B Signals.
International Journal of Navigation and Observation
, 2011, Article ID: 973656.
[3] Francis, R., Noël, J. and Vincent, R. (2011) Orbital Monitoring of Automatic De-
pendent Surveillance-Broadcast (ADS-B) Signals for Improved Air Traffic Surveil-
lance in Remote and Oceanic Airspace.
Proceedings of the
62
nd International As-
tronautical Congress
, IAC-11.
[4] Cushley, A. and Noël, J.M. (2014) Ionospheric Tomography Using ADS-B Signals.
Radio Science
, 49, 549-563. https://doi.org/10.1002/2013rs005354
[5] Van Der Pryt, R. and Vincent, R. (2015) A Simulation of Signal Collisions over the
North Atlantic for a Spaceborne ADS-B Using Aloha Protocol.
Positioning
, 6, 23-
31. https://doi.org/10.4236/pos.2015.63003
[6] Van Der Pryt, R. and Vincent, R. (2015) A Simulation of the Reception of Auto-
matic Dependent Surveillance-Broadcast (ADS-B) Signals in Low Earth Orbit.
In-
ternational Journal of Navigation and Observation
, 2015, Article ID: 567604.
[7] Vincent, R. (2015) The CanX-7 ADS-B Mission: Tracking Aircraft from Space.
Ca-
nadian Space Society
:
Canadian Space Summit
, Vancouver, 19-20 November 2015.
[8] Van Der Pryt, R. and Vincent, R. (2016) A Simulation of Reflected ADS-B Signals
over the North Atlantic for a Space-Borne Receiver.
Positioning
, 7, 51-62.
https://doi.org/10.4236/pos.2016.71005
[9] Bennett, I., Paris, A., Cotton, B. and Zee, R. (2016) Nanosatellite Aircraft Tracking:
Simulation and Design of the CanX-7 ADS-B.
The Canadian SmallSat Conference
,
Toronto, 2-3 February 2016.
Submit or recommend next manuscript to SCIRP and we will provide best
service for you:
Accepting pre-submission inquiries through Email, Facebook, LinkedIn, Twitter, etc.
A wide selection of journals (inclusive of 9 subjects, more than 200 journals)
Providing 24-hour high-quality service
User-friendly online submission system
Fair and swift peer-review system
Efficient typesetting and proofreading procedure
Display of the result of downloads and visits, as well as the number of cited articles
Maximum dissemination of your research work
Submit your manuscript at: http://papersubmission.scirp.org/
Or contact pos@scirp.org