satellite ground station emulator

1. 1
Abstract: The need to train satellite ground station operators is of critical importance for the success of a space mission. An operator is
responsible for monitoring the health of a spacecraft and recording of payload data. This paper proposes an architecture that uses an existing
ground station for training purposes in the form of emulation. Telemetry is simulated and transmitted to a ground station from a remote
location, thus allowing the use of all the available physical equipment. In addition, means are provided for the simulator to inject noise and
incorrect telemetry that test the operator’s understanding not only of a satellite mission, but also their ability to react to anomalies that may
occur. The paper also suggests incremental modes of training that guide an operator through different scenarios leading to communicating with
an amateur satellite.
1.INTRODUCTION1
.
Power Unit - Composed of at least one rechargeable battery and
solar cells.
Command and Data Handling Unit - Composed of at least one
microprocessor to handle data flow within the satellite, monitoring
the health of the satellite over time, and coordinating the
operations of the satellites.
Atitude Control Unit - A control unit responsible for aligning the
satellite in space.
Payload - At least one scientific experiment, commercial service,
or military units.
As a result of these common components for satellites, a ground
station receives similar categories of information pertaining the
health of the satellite. These include temper-ature readings,
information about the status of the batteries, key register values,
and many self-test results. Therefore, the training of a base station
operator must include a basic un-derstanding of how to analyze
such data to determine if the satellite is functioning properly.
2.2 Groundstation
A ground station is a system composed of a receiver, a transmitter,
and antennas to receive/trasmit radio frequencies from/to space
and convert the signal into data that can be interpreted and
analyzed by a computer. Figure 1 shows a block level diagram of a
ground station. Absent from this diagram are power systems and
control systems required to align the antenna to maximize the
signal received from the satellite. In the past, large satellite
projects had dedicated ground stations to track the spacecraft and
transfer data received. This approach is not only expensive, but it
also limited the communications time to those periods where the
satellite is within a line of sight from the ground station [3]. There
is now a trend to developing a network of ground stations that can
provide effective 24 hour connectivity to satellites [4].
SATELLITE GROUND STATION EMULATOR:
AN ARCHITECTURE AND IMPLEMENTATION PROPOSAL
SUDHIR KUMAR
Dept. of Electronics and Telecommunication Institute of Technology NIRMA UNIVERSITY
Email: 15mecc24@nirmauni.ac.in
Many diverse industries have an increasing demand for real-time
simulators. Such simulators provide the real-time environments
for spacecraft simulations to verify the readiness of ground
facilities prior to launch, including the validation of the mission
control system, spacecraft procedures, and the training of
spacecraft operators. For example, SIMSAT is a simulator
developed by the European Space Agency (ESA) and the
European Space Operations Centre (ESOCC) [1]. This paper
describes an architecture of such a simulator, and attempts to
extend its functions to include emulation. The communication
with a satellite and a ground station can be generalized as the
uplink and downlink of telemetry, payload data and commands to
execute. On the ground, an operator is responsible for receiving
the information and scheduling future tasks to be performed by
sending new commands to the satellite. After launching a satellite,
the operation of a ground station is critical for the success of a
satellite mission. The station is responsible for receiving,
validating, interpreting and sending data to and from the
spacecraft. The operator of the station must be trained not only to
operate the equipment, but also to be able to interpret data
received in order to spot ir-regularities that could jeopardize the
mission. In order to train operations, a ground station emulator
could be used that would address both the operator’s abili-ties to
operate the equipment as well as their knowledge of the mission
that would minimize human errors and maximize the chances of
mission success.
2. BACKGROUND
2.1. Satellite
A satellite is an orbiting spacecraft that carries at least one payload
that can be used for scientific research, commercial use, and/or
military tactics. Despite the wide variety of pay-loads, satellites
share a similar architecture consisting of:
Communication Unit - Composed of atleast one antenna and a
modulator/demodulator to communicate with the base stations.

2. Fig. 1 Block diagram of ground station
The shift to ground station networks makes the design of a ground
station emulator for training purposes a priority Any ground
station joining the world network needs to be able to train
personnel efficiently to offer reliable services to satellite
designers. In addition, offering on-demand access to satellites 24
hours a day is of great importance to pico-satellite missions that
have a shorter mission lifetime. The ability to track satellites 24
hours a day, provides a never before seen on-demand access to
satellites. This is of particular importance for pico-satellite
missions with a shorter life than commercial or military satellites.
Instead of connecting to the satellite a few times a day to retrieve
data, one can have a continued flow of data, thus maximizing the
throughput.
2.3. Example of a Ground Station
A ground station for low Earth orbiting (LEO) satellites has been
installed and made operational at the University of Manitoba by
the end of October 2008. The ground station includes a roof-top
tracking cross-polarized Yagiuda antenna system (as shown in Fig.
2), connected to a transceiver with a tracking software (SatPC32)
and many other pieces of support equipment. The ground station
is connected to other radio facilities and packet networks, as well
as to the Internet and digital and analog telephone networks. The
primary objective of the ground station is to provide a facility for
data and voice communications with LEO satellites through
amateur radio bands (2 m and 70 cm). The station is intended to
serve as a vital link in various projects.
2.3.1. ARISS Telebridge
The ground station can provide voice communications with
astronauts on the International Space Station (ISS). Such contacts
are done under the umbrella of Amateur Radio on the
International Space Station (ARISS), and have been available for
a number of years to high schools and other educational
institutions to encourage students to get involved in space-related
projects.
Fig.2. Antennas used by UOFM ground station
2.3.2. GENSO
The ground station can provide a near global telemetry facility for
the Global Educational Network for Spacecraft Operations
(GENSO). GENSO is aimed at Cubesat operators and Amateur
Satellite (Amsat) users to provide worldwide opportunities for
telemetry recovery by error correction (multiple data streams).
GENSO is an initiative sponsored by the International Space
Education Board (ISEB), consisting of the education departments
of the European Space Agency (ESA), the Canadian Space
Agency (CSA), Centre National detudes Spatiales (CNES), the
Japan Aerospace Exploration Agency (JAXA), and the National
Aeronautics and Space Administration (NASA).
2.3.3. High-School Balloon Launches
The ground station can track balloons launched by Manitoba high
schools and other institutions. The latest launch was done by
Maples Collegiate at the end of October 2008.
2.3.4. Prairie Near-Space Exploration Laboratory
The ground station can track payloads to be launched by the Near-
Space Exploration Laboratory at the University of Manitoba that
is being developed. The payloads will carry various experiments
related to the Wincube projects. There is also interest from
industries to test their electronic components and subsystems in
near-space conditions (e.g., temperature, pressure, radiation).
2.4. Emulation as a Training Tool
Emulation is defined as the act of imitating the behaviour of a
component to make a system appear to be functioning in its
entirety. This allows a person to be trained to operate a satellite
ground station in a real environment without the inherited risks of
using real satellites.

3. 3
2.5. Training Ground Station Operators
During the design phase of a satellite, all testing of
communications between the satellite and the ground station is
performed by technical personnel working on the project.
However, once the satellite is launched, those designers may no
longer be involved in the project, and as a result the operation of
the ground station falls upon the responsibility of other
individuals who had been likely involved in the design of the
payload for the satellite [4]. Thus, it is critical to train such an
individual not only to operate the ground station, but also to be
able to react to possible anomalies. Training must, therefore, be
divided into two parts: the normal operations and the special
scenarios to deal with anomalies [1].
2.5.1. Normal Operations
The designers of the satellite must make the satellite behave within
expected parameters at all times. This means that all components
must be functioning. These parameters determine the accepted
range of values for both the execution of payload and gathering of
telemetry to the ground station. Training an operator to work
within the normal operations of the satellite involves learning to
analyze and log information pertaining to the operation of the
system and to confirm the satellite is operating normally.
3. PROPOSED ARCHITECTURE
Figure 3 shows the proposed architecture for a ground station
emulator to train personnel and at the same time verify the
operations of the ground station’s equipment.
Fig.3. Proposed emulator architecture
The proposed architecture is composed of three nodes: a ground
station, a controller, and a simulator.
3.1. Ground Station Node
In this proposal, the ground station is not modified, but rather
additional components are added to assist in the training process.
This assumes the ground station is non-mission specific Thus, it
can be used for multiple missions by reconfiguring the station
using Ground Station Markup Language (GSML) [4] or other
similar means.
3.2. Controller Node
The node is composed of a workstation attached to two
subcomponents: a repeater/transceiver and a noise generator. The
workstation is connected to the Internet to communicate with the
Simulator node. This unmanned station acts as a proxy link
between the simulator and the ground station. Its purpose is to
allow the operator and the trainer to interact during the training
process while having the benefit of communicating with a remote
object. In addition, the repeater may contain a logger to keep track
of all communications going through this channel. This tool would
be a useful measuring tool to estimate data flow rates and error
rates.
3.2.1. Repeater/Transceiver
The repeater node is composed of an antenna, a transmitter, and a
receiver. The transmitter and receiver must be customizable in
order to work within both amateur and commercial frequency
bands. This node receives radio waves from the ground station,
demodulates them and transfers them to the simulator via the
controller’s Internet connection. Similarly, telemetry and payload
data is sent from the simulator to the transmitter node so that it
can be modulated and set to the ground station.
3.2.2. Noise Generator
The noise generator node is composed of a workstation connected
to an Internet connection. The machine uses an arbitrary
waveform generator, a frequency synthesizer, a mixer and an
amplifier as described in [3] to generate broadband noise. This
station receives commands from the simulator that control the
type and magnitude of noise to generate.
3.3. Simulator Node
The simulator node is composed of a workstation connected to an
Internet connection. This machine receives telemetry and payload
data sent from the ground station through the repeater node, and
can send information to the repeater to be transmitted to the
ground station. Simulation is often used as part of the design,
testing and development of satellite to verify the operations of the
components. The simulator software must be customizable in
order to be programmed with the appropriate simulated telemetry
and payload data to use. The system starts by transmitting a
beacon signal until a communication link is established with the
ground station.
3.4. Communication Between Nodes
The proposed architecture requires different types of
communication protocols to transfer information to and from the
various nodes in the system. The Ground Station and Controller
Nodes use Amateur Radio Bands (with the understanding that
expansion to commercial bands is possible with the appropriate
licenses). All data exchanges are frequency modulated where
different frequencies can used for uplink and downlink channels.
Payload and telemetry data sent to and from the Ground Station to
the Simulator use a protocol that satisfies the transfer rates for the
satellites modeled. In the case of OSCAR-51, the requirement is
as high as 76.8 kbps while the usual rates are at 1.2 kbps or 9.6
kbps and rarely 38.4 kbps [3]. The protocol selected is Simple
Object Access Protocol (SOAP) which is normally used for web
services and can handle large data transfers.

4. 4. MODES OF OPERATIONS
The training consists of five units where the operator is ex-posed
to both the workings of the ground station and the specific details
of a satellite mission. Each new unit builds on the knowledge
from the previous stage. The units are de-scribed below. It is
important to note that for each new mission, an operator needs to
go through the Rehearsal and Scenario training again to learn the
specifics of that mission.
1. System Test - This mode sends a predefined set of
telemetry data to the ground station to verify operations of
the ground station, and reply with an acknowledge
command.
2. Playback - In this mode, the simulator reads a file
containing the telemetry data and sends that information to
the ground station. This mode is intended to allow the
operator learn how to tune into the frequencies for the
satellite and compare the received information to the
expected data.
3. Rehearsal - In this mode, the simulator generates real-time
telemetry and payload data to send to the ground station.
This extends the Playback mode adding a layer of
complexity by not being able to verify the data with
expected values, but rather having to analyze it life to
ensure it is valid.
4. Scenario - The scenario mode is the most important in
training the operator. In this mode, the operator controls the
ground station while a trainer controls the satellite
simulator. The trainer can inject errors into the transmission
and/or turn off components to force the operator to react by
transmitting the proper command sequences to salvage the
mission.
5. Live - In this mode, the operator can connect to an amateur
satellite from AMSAT such as AMSAT-OSCAR 51 [4].
This would be the last training step that will allow the
operator to put their skills to the test by receiving data from
a real satellite.
.
5. LIMITATIONS
This architecture is not a substitute for communications with a
satellite in orbit. There are two areas that cannot be simulated
accurately: noise and Dop pler Shift. Interference due to
electromagnetic radiation will not be present in this design.
However, depending on the location of the repeater and ground
station nodes, the effects of other types of noise may be more
prominent than electromagnetic noise would be in space. Thus,
for the purposes of training an operator to use the ground station,
the existence of noise (regardless of the type) will be sufficient.
The Doppler effect cannot be simulated with a stationary repeater
station. As such, the operator will need to use the Live operating
mode to connect to an amateur satellite in order to experience
signal variations as the satellite orbits around the Earth. In order
to alleviate the problems, the next phase in the development of
the emulator will include uploading messages to AMSAT
satellites and then downloading them to the ground station, as
illustrated in Fig. 4. The uploading can be done from the same
ground station or from another ground station located at a remote
location.
Fig.4. Extended emulator architecture
6. SUMMARY
This paper has outlined an architecture for a training facility and
procedure to teach a person to operate a satellite ground station.
This layout can be utilized with any existing ground station as
implemented at our site. The proposal added a simulator node to
generate satellite telemetry, a repeater node to force transmissions
over long distances, and a noise generator to create anomalies in
data communications that replicate the space environment. In
addition, the system outlined five modes of operation for training
that build the operator’s knowledge of the equipment and the
specifics of a mission.
7. ACKNOWLEDGE
I am grateful to Prof. Manisha Upadhyay and Prof. Aarti Gehani
who inspired and gave me support to write this term paper. In
addition I would also like to thank my friends for their valuable
time and constant support in preparing this paper.
8. REFERENCES
[1] D. Innorta and A. Williams, “New simulation approach for the
training of satellite mission control teams,” in Proc. IEEE Asia
Conference on Modeling and Simulation, AMS07 (Phuket; March
27-30, 2007)
[2] J. Puig-Suari and B. Twiggs, “Cubesat design specifications,”
October 2008, Available as of December 17, 2008 from
http://cubesat.atl.calpoly.edu/pages/documents/developers.php.
[3] K. Farzaneh, L. Mohamady, and A. Eidi, “Designing high
available satellite ground stations,” in Proc. IEEE Confer-ence
on Innovations in Information Technology, IIT07 (Madi-nat
Jumeirah, Dubai; November 18-20, 2007), pp. 267 – 271.
[4] Schor, D. kinsner, W.thore- satellite ground system emulator-
IEEE conference_ Canada_2009.