1
A Survey on Satellite Components and Services
Romain Gemble∗ , Michael Koch† , and Kingsley Yeboah‡
Department of Electrical Engineering and Information Technology
Technische Universität Darmstadt
Merckstraße 25, 64283 Darmstadt, Germany
∗ [email protected] † [email protected] ‡ kingsley [email protected]
Abstract—A satellite, in a wide sense, is an object orbiting
around a planet or a star. Here we only tackle satellites as manmade satellites orbiting around the Earth and aiming at providing
various services. The story of satellites begins at the end of 1960s.
At that time, satellites are very small with dimensions of less
than 1 m and weights not larger than few tens of kg. Hence,
signals sent to stations on Earth are very weak and the latter
need to have very large antennas and thus very large overall
dimensions. From 1960s up to now, satellites size has continued
to increase and so Earth stations receive antennas to be of order
of few centimetres. Nowadays, satellites are omnipresent above
our heads, they are bigger, reaching weights of few tons and
satellite systems are getting smarter and more powerful thanks
to research and development on advanced components. This
paper aspires to give a survey on recent satellite components and
services. We give an overview of the components (communication
system, power and thermal system, and propulsion system) and
services which are used today, show recent developments and
open research questions.
Index Terms—satellites, transponders, satellite antennas, satellite communication, satellite navigation systems, telecommunication services
I. I NTRODUCTION
When the first man-made earth satellite Sputnik 1 was
successfully launched by the Soviet Union in 1957 the
concept of geosynchronous satellites had already been around
for 12 years. In October 1945 Wireless World published
an article by Arthur C. Clarke which was titled “Extra
terrestrial relays – Can Rocket Stations Give World-wide
Radio Coverage?” [1] in which he proposed the usage of three
relay stations at an orbit of 42.000 km above earths equator
to ensure complete coverage of the globe. After analysing
the requirements to launch such relay stations, including the
rocket design, he came up with the theory that it would only
be a few years until his concept would become a reality.
Nowadays satellites are omnipresent. NASAs National
Space Science Data Centers Master Catalog lists hundreds
of active and thousands of abandoned satellites [2] orbiting
earth at various distances. Satellites are used for navigation,
telephony, Internet access, television, imaging, environmental
services, and many more.
In this paper we give an overview of the components used
in modern satellites, as well as the services provided by
satellites. The rest of this paper is organised as follows: In
Sec. II we present related work, in Sec. III we discuss the
components of modern satellites (namely the communication
system, power and thermal system, and propulsion system),
and in Sec. IV we give an overview of currently active
satellite services.
II. R ELATED W ORK
In [3] mobile satellite networks and services have been
surveyed. They focused on the specific characteristics of
systems which are unique in comparison to other systems
and presented important standards for mobile satellite
communications and services. Furthermore they surveyed
the main characteristics of operational and planned mobile
satellite systems and proposed an analytical framework
allowing their comparison, which they believe to be a good
tool for the design and market study of future mobile satellite
systems. To our best knowledge, this study from the year 2010
is the most recent one. Since then many new technologies
for satellite components as well as services have emerged.
In the following chapters we will summarise the existing
components and services and present more recent ideas for
technologies and services.
III. S ATELLITE C OMPONENTS
A satellite consists of many different subsystems [4, p.
284] like the power and thermal system, attitude and orbit
control system (propulsion system), communication system,
structural system, and many more. In the following section
we will describe the three main subsystems of a satellite,
namely the communication system, the power and thermal
system, and the propulsion system. We will give an overview
of currently used technologies and summarise recent research
activities and open research questions.
A. Communication System
The communication system of a satellite, which is called
the communication payload, is used for communication
between the satellite and earth stations as well as intersatellite communication. It consists of the antennas as well as
transmitter-receiver units which are called transponders.
In [5], the following types of communication payloads have
been identified:
2
•
•
•
•
Transparent “Bent-Pipe” transponder.
Regenerative repeater with routing capabilities.
Transparent repeater with analog routing capabilities.
Transparent digital repeater (“Digital Bent-Pipe”) with
routing and beamforming capabilities (also known as
“Translucent”).
We will refer to these as Bent-Pipe, Regenerative Repeater,
Transparent Repeater + Router, and Digital Bent-Pipe and
describe the concepts in the following paragraphs.
1) Bent-Pipe: The Bent-Pipe is the oldest and most
simple concept of a communication payload. A Bent-Pipe
simply receives a signal, does frequency conversion and
amplification, and then retransmits the signal.
2) Regenerative Repeater: In addition to the features of
a Bent-Pipe, a Regenerative Repeater can regenerate the
received signal before retransmitting it.
3) Transparent Repeater + Router: In addition to the
features of a Regenerative Repeater, a Transparent Repeater
+ Router can base his decision on which transponder he
retransmits the received signal based on analogue routing
techniques.
4) Digital Bent-Pipe: The Digital Bent-Pipe is the most
recent and most sophisticated type of communication payload.
As the Bent-Pipe, it does not regenerate the received signal.
However, it uses multiple access schemes, such as time division multiple access, frequency division multiple access and
code division multiple access.
In addition to these payload types there are some recent
research results regarding reconfigurable antennas [6], dual
polarisation per beam [7] [8], cognitive communications [9]
[10] [11], wide band amplifiers [12] [13] [14], and a proof
of concept model of a digital transparent processor [15]. We
will summarise this research in the following paragraphs.
5) Reconfigurable Antennas: Existing satellites have
their antennas fixed, i.e. the antennas are designed for one
application and deployed with the satellite. If different
applications or frequencies should be realised by a single
satellite, multiple antennas need to be deployed with the
satellite. Recently there have been approaches to design
antennas that can be reconfigured after the satellite has been
deployed to space.
In [6] a helical antenna is proposed which can tune its
operating frequency by mechanically changing its height
above the ground plane in a rotational matter. It is intended
for usage on small satellites and covers a frequency range of
240 MHz to 450 MHz. Due to the reduced size of the overall
satellite (one reconfigurable antenna instead of multiple fixed
antennas) fuel can be saved which in turn would lead to a
longer operational time of the satellite or reduced operational
costs.
6) Dual Polarisation per Beam: Traditionally satellites
use different polarisations on different beams to minimise
distortion between beams (e.g. use horizontal polarisation
on the upstream beam and vertical polarisation on the
downstream beam). The idea to use dual polarisation per
beam, i.e. use two polarisations on the same beam to transmit
two parallel streams of information simultaneously has been
extensively researched over the last years.
In [7] the results of recent studies have been summarised
and it has been shown that the use of two polarisations on
every beam of a satellites payload is indeed feasible. In [8]
the idea of dual polarisation per beam has been combined
with the approach of hybrid mobile satellite systems (systems
in which a mobile station can communicate with both a
satellite and a terrestrial base station). This scenario implies
four different polarisation schemes are being used on the
mobile station (e.g. two different linear polarisation schemes
for the communication with the terrestrial base station and
two different circular polarisations for communication with
the satellite). They concluded that these techniques could
indeed be used in the next generation of hybrid mobile
satellite systems. The implication of these results is that the
capacity of the satellites can be increased by transmitting two
independent information streams on every beam.
7) Cognitive Communications: Satellite spectrum is
becoming scarce due to the increased demand for broadcast,
multimedia and interactive services. This leads to the problem
of how to increase spectral efficiency in satellite networks.
One idea to conquer this problem is the method of cognitive
communications. In cognitive communications, one part of the
spectrum is shared by two satellite systems or by a satellite
system and a terrestrial system. In [10] the most common
techniques for cognitive communication have been identified
as spectrum sensing, underlay, overlay, and database related.
The spectrum sensing approach allows a secondary user to
transmit whenever the primary user is not occupying the
frequency band, the underlay approach allows the secondary
user to transmit as long as the interference requirements of the
primary user are fulfilled, the overlay approach uses advanced
coding and transmission strategies to mitigate interferences,
and the database related approach uses a database which is
queried by the cognitive users for free spectrum bands.
Another approach for cognitive communication has been
made in [11]. They propose a dual satellite system with a
primary satellite which uses larger beams and a secondary
satellite which uses smaller beams. To achieve cognitive
communication their system uses a signalling link between
the gateways of the two systems. This signalling link
is used to inform the secondary system of the primary
systems beamhopping pattern, as well as to exchange timing
information. They conclude that their proposed system can
significantly increase spectral efficiency over existing satellite
systems. In [9] they did interference modelling for these four
3
techniques and found that spectrum sensing and database
techniques provide best performance in high interference
regions while in low- or medium interference regions the
underlay technique provides better performance. The also
found that the overlay technique is only suitable for integrated
systems with a high level of interaction.
8) Wideband Amplifiers: Most satellites today use the
channelised approach, whereby the frequency band is divided
into multiple narrow band channels and each channel is
amplified separately. In [12] an alternative to this traditional
approach, the idea of wide band amplifiers, is presented. To
implement this approach, higher power, wider bandwidth,
and more linear travelling wave tube amplifiers need to be
developed. The results of using wide band amplifiers would
be higher bandwidth utilisation since the need for guard bands
between the narrow band channels is omitted, less hardware,
lower mass, and the possibility of new services which need
higher bandwidth.
In [13] the model 1693HD travelling wave tube amplifier is
presented. This amplifier produces 75 watts of CW saturated
RF power over bandwidths greater than 6 GHz in the V
frequency band. It provides better efficiency, better linearity,
lower noise, and lower mass than previous amplifiers. It
has been tested with multiple qualification tests, such as
random vibration testing, pyrotechnic shock simulation, and
cycling between thermal extremes in a vacuum. As a result
of those tests it has been flight qualified for space applications.
In [14] the KA-SAT satellite is described, which is a
high throughput satellite. The overall system capacity is 90
Gbit/s and up to a million users. This system still uses the
channelised approach, with a bandwidth of 250 MHz per
channel. Due to the drive for capacity, the next generation of
satellites will need high power amplifiers which can cover
2.9 GHz in V band.
Combining those results, there is both the need for wide
band amplifiers, as well as the implementation of one such
amplifier which has already been flight qualified. Hence, most
likely those wide band amplifiers will be used in the next
generation of high throughput satellites.
9) Digital Transparent Processor: In [15] an on board
digital transparent processor for a multi-beam satellite has
been proposed. This processor segregates uplink signals
coming from different earth terminals, switches them per user
requirements, and combines them for downlink transmission.
This results in inter-beam and intra-beam mesh connectivity
of user terminals without the need for a hub earth station.
Their processors consists of four main subsystems, namely the
frequency demultiplexer, the channel switch, the frequency
multiplexer, and the mesh network manager. They described
the architecture, algorithm, and implementation details of
the processor. Furthermore they presented simulation and
hardware test results. Their processor essentially serves as an
exchange-in-the-sky, providing hubless mesh connectivity of
user terminals.
B. Power and Thermal Systems
The [16] main source of power is sunlight which is
harnessed by the satellite’s solar panels. A satellite also has
batteries on board to provide power when the sun is blocked
by the Earth. The batteries are recharged by the excess current
generated by the solar panels when there is sunlight.
Satellites operate in extreme temperatures from -150 ◦ C to
150 ◦ C and may be subject to radiation in space. Satellite
components that can be exposed to radiation are shielded with
aluminium and other radiation-resistant material. A satellites
thermal system protects its sensitive electronic and mechanical components and maintains it in its optimum functioning
temperature to ensure its continuous operation. A satellites
thermal system also protects sensitive satellite components
from the extreme changes in temperature by activation of
cooling mechanisms when it gets too hot or heating systems
when it gets too cold.
C. Propulsion System
[16] Satellite propulsion system mainly includes the
rockets that propel the satellite. A satellite needs its own
propulsion system to get itself to the right orbital location
and to make occasional corrections to that position.
A satellite in the geostationary orbit can deviate up to a
degree every year from north to south or east to west of
its location because of the gravitational pull of the Moon
and Sun. A satellite has thrusters that are fired occasionally
to make adjustments in its position. The maintenance of a
satellite’s orbital position is called ”station keeping”, and the
corrections made by using the satellite’s thrusters are called
”altitude control”.
A satellite’s life span is determined by the amount of fuel
it has to power these thrusters. Once the fuel runs out, the
satellite eventually drifts into space and out of operation,
becoming space debris.
The papers [17] and [18] might be of interest for this
chapter.
IV. S ATELLITE S ERVICES
Satellites are used to provide a big amount of services.
The International Telecommunication Union (ITU) has listed
them in [19], we describe only few of them. Most of them
are provided by terrestrial or by satellite systems. Usually,
we define two different types of services :
•
The Fixed-Satellite Service (FSS), which is mainly used
for broadcast (television, radio stations) and broadband
Internet. This service sets up a radio communication link
between a satellite and a fixed earth station as defined in
[19]. The first generation of such FSS uses the C-band (
4
6 GHz for up-link (UL) and 4 GHz for down-link (DL)
) whereas recent FSS use the Ku-band (14 GHz UL –
12 GHz DL). Some FSS use also the Ka-band (30 GHz
UL – 20 GHz DL) to transmit, like KA-SAT and future
High Throughput Satellites (HTS) [14], [20] section 3.3.
•
The Mobile Satellite Service (MSS), which provides
information from satellite to mobile Earth stations such as
ships, aircraft, land vehicles and more and more handheld
devices. These services can be Internet on mobile (GSM,
UMTS standards), digital video, audio broadcasting,
radio-navigation and so on. The generally-used frequency
bands are L/S (1 to 4 GHz) and recently Ku- (11 to 17
GHz) and Ka-bands (20 to 30 GHz). More information
about the frequency allocation can be found in [19].
Some operational satellite systems for mobile services
are Globalstar, Iridium, Inmarsat BGAN and Thuraya [3].
Now, we are going into details by describing the satellite
services for the user. They can be either FSS or MSS.
Broadcasting Satellite Service (BSS): As defined in [19],
this service is able to broadcast digital TV (Standard/High
Definition TV, 3DTV) as well as radio programmes and
various audio, video or multimedia content. Recent broadcast
satellite systems provide services by utilising the Ka-band
at 21 GHz in down-link (DL). For satellite systems the
two following standards are mainly used: Digital Video
Broadcasting-Satellite (DVB-S and DVB-S2 for the second
generation [21]) and Digital Audio Broadcasting (DAB).
Most of broadcasting satellite systems are designed for direct
reception and fixed users. Nevertheless, with the growing
need of multimedia data for mobile terminals and the lack of
terrestrial infrastructures outside of cities, satellite systems
can be used as a complement or as an alternative to provide
video or multimedia data. That is why new standards like
DVB-SH (Satellite to Handheld) and Digital Multimedia
Broadcast (DMB) [22] based on DAB have been developed
for direct reception for mobile and handheld devices. More
information on these standards can be found in [21], [23] or
[16].
Radionavigation Satellite Service (RNSS): This service is
getting more and more important due to the growing demand
in radionavigation systems. Indeed, nowadays, radionavigation
devices are small, practical, intuitive, quite precise and getting
more and more inexpensive.
The Navigation System with Time and Ranging/Global
Positioning System (NAVSTAR/GPS) is probably the most
famous one, developed by the USA and operating at 1.6
GHz and 1.2 GHz. At least 24 operational GPS satellites
95% of the time are required to provide the navigation
service. The service is capable of guaranteeing an accuracy
between 3.5 m and 7.8 m. The second operational RNSS is
GLONASS, developed by Russia. For more than 10 years,
the European Space Agency (ESA) with the partnership
of the European Commission is also developing an RNSS
called Galileo. Note that the fore-mentioned systems can be
classified in Global Navigation Satellite Systems (GNSSs)
[24]. With their global coverage, excellent accuracy, and
lack of infrastructure requirements for the user, GNSS is the
main tool for navigation. The applications are numerous:
transportation (fleet management, en route navigation), civil
engineering (surveying and monitoring), agriculture (yield
mapping, monitoring of chemical distributions), and so on
[25], [26].
GPS and Galileo (as soon as it is going to be operational) not
only provide radio navigation services but can be considered
in wider sense as Radiodetermination Satellite Services
(RDSSs) because they collect data for other purposes than
navigation (Earth observation, mapping, search and rescue...).
For more information, see [25], [26].
Most of the radionavigation services are designed for outdoor
applications but for recent years, the need has been felt to
use the radionavigation services for indoor purposes [27], [28].
Earth exploration-Satellite Service: To quote [19], it gathers
data which give information to the characteristics of the earth,
its natural phenomena, the environmental situation and so on.
It can be utilised for meteorological, geological or mapping
purposes for example.
V. C ONCLUSION
The satellites are part of our daily lives even if we do
not see them since being thousands of kilometres above our
heads. Without them, telecommunications probably would not
be as developed, weather forecasts would not be as accurate,
and satellite guidance would not exist. Since the launch of
the first satellite, considerable advances in electronic systems,
in reducing the size of the satellites, and in increasing their
lifetime have been performed.
In this paper, we reviewed the systems and components
used in modern satellites by looking into research papers on
communication payloads, key components like antennas or
wide band amplifiers, and on power and propulsion systems.
We also gave an overview of some important services and
showed what they offer.
With the ever growing demand for bandwidth, one major
focus for the next generation of satellites will be the
implementation of wide band amplifiers and technologies
to increase the spectrum utilisation. On the other hand, the
users demand for higher mobility, smaller mobile stations,
and even the usage of one mobile station for both terrestrial
and satellite communication will lead to more research in this
area. To satisfy all those needs, one key technology will be
digital transparent processors which offer a huge flexibility in
comparison to traditional bent-pipe transponders.
To summarise all this, research in the area of satellite systems
is far from over and a lot of interesting challenges lie ahead.
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