INSIGHT INTO THE REQUIREMENTS OF SELF-AWARE,
ADAPTIVE AND RELIABLE EMBEDDED SUB-SYSTEMS
OF SATELLITE SPACECRAFT
Rajeev Kumar Kanth, Pasi Liljeberg, Hannu Tenhunen
Turku Centre for Computer Science, University of Turku, Joukahaisenkatu 3-5 B, Turku, Finland
Qiansu Wan, Waqar Ahmad, Li-Rong Zheng, Harish Kumar
1
Royal Institute of Technology, Kista, Sweden
1
DOECE, BIT, Muzaffarnagar, India
Keywords: Self-aware System, Satellite Sub-System, Telemetry Tracking and Command, Embedded Sub-Systems,
Adaptive Antenna, Satellite Spacecraft, Adaptive Space Hardware, On-Board Data Handling.
Abstract: This position paper gives an insight for self-aware and adaptivity requirements of the sub-systems
embedded in a satellite spacecraft. The most signicant and considerable issues of self-aware and adaptive
systems that are necessary in present and future on-board satellite spacecraft are illustrated in this paper. An
attempt has been made to discuss several embedded sub-systems and space environment scenarios of the
spacecraft. As a case study, an adaptive sierpinski based dual band antenna has been devised. The adaptive
nature of this antenna provides a foundation of longer and more reliable mission life of a spacecraft.
Through this paper it will be shown that adaptive, recongurable and reliability issues are the most
prominent and potential area of research for outer space communication technology.
1 INTRODUCTION
A sub-system or system in a satellite spacecraft is
called space hardware. Space hardware consists of
several parts (electronics and mechanical) and
materials with suitable surface treatment for
withstanding environmental effects while on ground
and on space. As maintenance in space during
mission life is impossible, so the parts, materials and
the processes used for making spacecraft sub-
systems must be highly self-aware, adaptive and
reliable.
This position paper describes different self-
aware and adaptive issues that spacecraft sub-
systems encounter during its useful life period. The
nature of the spacecraft sub-systems are supposed to
be extremely insensitive to the external environment.
The need for achieving mass efficient adaptive
designs, selection and control of parts, materials and
processes of the sub-systems are the major
challenges in structuring a satellite spacecraft.
Structure also plays an important role in the thermal
control of the spacecraft by providing conductive
paths, radiating surfaces and acting as heat sinks.
A spacecraft sub-system begins its life in ground
and usually long storage time is envisaged in
different environmental conditions. While on
ground, the spacecraft materials and components
encounter all classical aging problems like oxidation
and corrosion, effect of variable humidity, biological
attack, losses due to evaporation, metal migration
etc. The launch environment encompasses a range of
simultaneous applied energy loads created due to
random vibration, acoustical noise, pressure
variations and acceleration. Space hardware
including their components and materials are
assessed by different mechanical and environmental
tests for their suitability in the launch environment.
When a satellite is positioned in the parking slot
in space, its mission life starts (Maral and
Bousquet). During this period, sub-systems of
satellite spacecraft encounter environment which is
made of vacuum, extreme high and low temperature
(+80
0
C to -180
0
C in GEO) and radiation of different
dose levels. The embedded onboard sub-systems of
603
Kanth R., Liljeberg P., Tenhunen H., Wan Q., Ahmad W., Zheng L. and Kumar H..
INSIGHT INTO THE REQUIREMENTS OF SELF-AWARE, ADAPTIVE AND RELIABLE EMBEDDED SUB-SYSTEMS OF SATELLITE SPACECRAFT.
DOI: 10.5220/0003406706030608
In Proceedings of the 1st International Conference on Pervasive and Embedded Computing and Communication Systems (SAAES-2011), pages
603-608
ISBN: 978-989-8425-48-5
Copyright
c
2011 SCITEPRESS (Science and Technology Publications, Lda.)
spacecraft must follow the space qualication. The
activity by which it is ensured that the parts and
materials used in satellite sub-system will be able to
withstand effects of the above three environments
without degrading performance is known as space
qualication.
Motivated by the evidence of adverse space
environment for satellite spacecraft, our aim is to
develop an understanding the issues and importance
of self-aware, recongurable and adaptive designs
for the onboard spacecraft sub-systems. Through this
paper, we are aiming to grab the reader’s attention at
self-aware and adaptive sub-systems of satellite
spacecraft are the most potential and prominent area
of research.
Our paper is structured as follows. Section II
describes the existing literature in context with our
research work. The next two sections provide the
practical underpinnings of satellite sub-systems and
space environment respectively. Section V describes
a list of self-aware and adaptability issues related to
satellite spacecraft. The development of adaptive
dual band antenna is discussed in section VI,
conclusion and future works are presented in Section
VII.
2 RELATED WORKS
Substantial research has been conducted on several
key areas related to the self-aware and adaptive
space hardware sub-systems. The recent existing
literatures (Maral and Bousquet), (Vassev et al.,
2010), (Striemer and Akoglu, 2010), (Kang et al.,
2010), (Lee and Choi, 2010), (Jung, 2010),
(Santambrogio et al., 2010), (Cheng et al., 2010),
(Stauffer, 2009) of adaptive systems for space
applications include self-congurable swarm-based
space exploration systems, low density parity check
(LDPC) engine for space based communication
systems and several papers on recongurable and
self-aware computing architectures for onboard
spacecraft embedded sub-systems. In the same way,
a number of papers can be found for recongurable
multi core architectures, built-in self-test and self-
repair, adaptive signal processing, image data
compression and power amplier.
The most available literature do not focus on
recongurable, adaptive and self-aware issues for
each of the embedded onboard satellite sub-systems
and satellite payload. Therefore here our work is to
enlighten those several issues that spacecraft
encounters during its mission life. We also make an
effort to describe several problems that takes place
in on-board spacecraft concerning adverse space
environment.
3 SATELLITE SUB-SYSTEM
Communication satellites are very complex and
extremely expensive to construct & launch.
Currently communication satellites are designed and
developed for 12 to 15 years of life time during
which the communication capability of the satellite
earns revenue, to recover the initial and operating
costs. Since the satellite has to operate over a long
period out in the space, the sub-systems of the
satellite are required to be very reliable. Major sub-
systems of a satellite are bus sub-systems and
payload. The satellite-bus-sub-systems include
mechanical structure, attitude and orbit control
system (AOCS), propulsion system, electrical power
system, tracking telemetry and command (TTC)
system and thermal control system. Similarly
satellite payload comprises of communication
transponder and antennas. Since a communication
satellite earns revenue, the satellite must carry as
many communications channels as possible.
However, a large communication channel capacity
necessitates large electrical power from large solar
arrays and battery, results larger mass and volume of
the satellite. Parking a heavy satellite in
geosynchronous orbit is very expensive; therefore it
is logical to keep the size and mass of the satellite
small. Lightweight materials optimally designed to
carry the load and withstand vibration and large
temperature cycles are considered to be signicant
parameters for the structure of the satellite.
Attitude and orbit control system (AOCS) (Yoon
and Tsiotras, 2002), (mackunis et al., 2008)
maintains the orbital location of the satellite and
controls the attitude of the satellite by using different
sensors and ring small thrusters located in different
sides of the satellite. Liquid fuel and oxidizer are
carried in the satellite as part of the propulsion
system for ring the thrusters in order to maintain
the satellite attitude and orbit. The amount of fuel
and oxidizer carried by the satellite also determines
the effective life of the satellite.
The electrical power in the satellite is derived
mainly from the solar cells. The power is used by the
communication payload and also by all other
electrical sub-systems in the satellite for
housekeeping. Rechargeable battery is used for
supplying electrical power during eclipse of the
satellite spacecraft. Telemetry, tracking and
command (TTC) system of the satellite works along
PECCS 2011 - International Conference on Pervasive and Embedded Computing and Communication Systems
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with its counterparts located in the satellite control
earth station. The telemetry system collects data
from sensors on board the satellite and sends these
data via telemetry link to the satellite control centre
which monitors the health of the satellite. Tracking
and ranging system located in the earth station
provides the information related to the range and
location of the satellite in its orbit. The command
system is used for switching on/off of different sub-
systems in the satellite based on the telemetry and
tracking data.
The thermal control system maintains the
temperature of different parts of the satellite within
the operating temperature limits and thus protects
the satellite sub-systems from the extreme
temperature conditions of the outer space.
4 SPACE ENVIRONMENT
Space environment consists of zero gravity
condition, vacuum with thermal cycling (high and
low) and diverse solar radiation. Zero gravity
condition does not impose considerable effects on
space hardware except loose conductive and non
conductive particles entrapped in the spacecraft.
These particles can move freely inside creating
blockage or shorting of sensitive electrical circuits
resulting damage in few sub-systems. Precautions
are taken to prevent such entrapment during
hardware fabrication using clean room fabrication
and associated protection.
Vacuum of the order of 10
-13
Torr or higher
exists at geosynchronous orbit. Any sliding and
rubbing of surfaces as in bearing and for rotating
movements tend to get vacuum welded. Use of dry
lubricant material is a solution to this problem.
Outgassing of polymeric substances, sealing and
potting compound etc create total weight loss and
condensable volatile mass in thermo vacuum
environment in space.
The outgassing products can cause low voltage
corona of the electrical circuit and change the
physical properties of optical surfaces inside
spacecraft. It is a practice to screen these materials
before using in space hardware so that total mass
loss (TML) and collection volatile condensable mass
(CVCM) are less than a predetermined level.
5 SELF-AWARE AND
ADAPTIVE ISSUES
This section describes the potential self-aware and
adaptive issues which need to be considering while
designing a spacecraft. The most prominent issue is
to supply a regulated electrical power to each of the
sub-systems of the spacecraft. Embedded solar cells
are the primary source of energy during the mission
life of a satellite. During eclipse period the
electrochemical batteries are the most appropriate
means of secondary energy source. Nickel-cadmium
and Nickel-hydrogen cells have been normally used
for the storage of electrical energy since the advent
of communication satellites. A number of self-aware
and adaptive issues have been devised in electrical
power supply sub-system of the spacecraft. They are
as follows:
The solar generator consists of small groups
of cells arranged in series or in parallel. The
choice of combination is such that it
maximizes the relative adaptability and
reliability, taking into account of failure rates
of the cells.
The solar generator wings of the satellite are
rotated in order to maintain the apparent
movement of the sun. Hence it must employ
self-aware solar sensors and adaptive control
circuits so as to check out the proper
dimensioning of the power at the time of
summer solstice and equinoxes.
The design of secondary energy sources must
be adaptable in varying temperature
conditions. The key issues for battery energy
sources are dimensioning, depth of discharge
(DOD), protection against overcharging and
several battery technologies.
In the same way the potential self-aware and
adaptive designs are required in attitude control of
the satellite spacecraft. Maintaining attitude is
fundamental for the satellite to fulll its function.
The embedded self-aware sensors measure the
orientation of the satellite axes with respect to
external references. Embedded sun, earth, star, radio
frequency and laser detector sensors should be
adequately designed so as to adapt in adverse space
environment and to provide the accurate orbit
attitude and alignment errors.
Telemetry, Tracking and Command (TTC) and
On Board Data Handling (OBDH) are another two
important mutual sub-systems in satellite spacecraft.
Adaptive electronic systems should be employed in
TTC and OBDH sub-systems so that they ensure
enduring availability of the links with the ground
stations. One of the important characteristics of the
command link is security. Hence the embedded sub-
systems are not only supposed to be self-aware and
INSIGHT INTO THE REQUIREMENTS OF SELF-AWARE, ADAPTIVE AND RELIABLE EMBEDDED
SUB-SYSTEMS OF SATELLITE SPACECRAFT
605
adaptive but also adequately secured so that the
system is insensitive to the signals transmitted by
intruders.
The purpose of the thermal control is to maintain
the sub-systems and equipments within the
temperature ranges which enable it to operate
reasonably. A self-aware temperature sensor adjusts
the thermal conductivities among various parts of
the satellite. The thermal reliability of the on-board
equipments and sub-systems depend on adaptability
of the components in different temperature
conditions.
6 ADAPTIVE ANTENNA- A
CASE STUDY
The payload is one of the most important sub-
systems of satellite spacecraft. Antenna is a part of
the payload. We have chosen development of an
adaptive multi-layered antenna as a case study. Here
the emphasis has been given to explore the self-
aware and adaptability issues of the developed dual
band, self-tunable and sierpinski based fractal
antenna. The detail design methodologies, result
analysis and development mechanisms are
demonstrated in (Kanth et al, 2010), (Kanth et al.,
2010), (Kanth et al., 2009). The major challenges
during the development of this adaptable antenna
were selection of space qualied materials and meet
the required specications. The work was performed
satisfactorily using the materials copper, duroid,
foam, glass epoxy and coaxial probe to achieve the
required specications in terms of return loss, gain
radiation and coverage area. The multi-layered
layout of the proposed adaptive antenna is shown in
Fig. 1.
Figure 1: Multi-Layered Layout.
The adaptive nature (dual band self-tunable) of
the proposed antenna has been described in (Kanth
et al., 2009). The adaptability of the on-board sub-
systems must qualify space adverse ranges of the
temperatures, outgassing properties in vacuum, zero
gravity and random vibration resistance. The
selection of the materials for fabricating this antenna
is such that it surpasses all the space qualication
tests and ensures the required performance as per the
specications. The return loss of the developed
adaptive dual band self tunable antenna is presented
in Fig. 2. Several iterations and new optimizations
techniques were involved to achieve the desired
performance. The developed multi-layered,
sierpinski based adaptable dual band antenna is
shown in Fig. 3.
Figure 2: Return Loss Diagram- Adaptive Nature.
Figure 3: Dual Band Adaptive Satellite Navigational
Antenna.
7 CONCLUSIONS AND FUTURE
WORKS
This position paper explicitly introduces, analyzes
and reflects on important issues and problems
PECCS 2011 - International Conference on Pervasive and Embedded Computing and Communication Systems
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related to the topic. Obvious practical implications
of these investigations illustrate that adaptive and
self-aware issues are the potential research areas for
outer space communication technology. We have
developed a space qualied payload antenna which
is adaptive in nature. Undoubtedly, the realization of
adaptive, self-aware and recongurable sub-systems
of the spacecraft not only enhances the reliability but
also lengthen the mission life of spacecraft. The list
of self-aware and adaptive issues of the embedded
sub-systems of satellite spacecraft, mentioned in this
paper gives guidelines to a designer to ensure
corrective actions before it is launched. Here we
conclude that self-aware and adaptive designs are
the most important issues in developing a successful
satellite spacecraft.
There are many avenues for further research.
The rst important future work is to measure the
degree of reliability considering the self-aware and
adaptive design issues for the embedded sub-
systems of the spacecraft. One should focus on
related parameters of these issues and explore the
significances in terms of reliability and mission life
enhancement. Another imperative future work is to
consider the adaptive designs in realization of high
power amplier, attitude control systems, TTC,
propulsion sub-system and on-board processing
systems. Finally, it would be worthwhile to examine
the role of self-aware and adaptive designs in
minimization of failure rate of the sub-system in its
mission life.
ACKNOWLEDGEMENTS
The authors would like to thank Indian Space
Research Organization (ISRO) satellite centre, India
and Computer System Laboratory, University of
Turku, Finland for providing necessary support to
carry out these investigations.
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