IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 10, 2015 | ISSN (online): 2321-0613
MEMS Technology & Its Application for Miniaturized Space System
Prosun Roy
B.Tech. Student
Department of Mechanical Engineering
Techno India College of Technology
Abstract— MEMS- Micro electro mechanical system. Over
the last decade Micro-Electro-Mechanical System (MEMS)
have evoked great interest in the scientific and engineering
communities. They are formed by integration of electronic
and mechanical components at micron level. MEMS has
gained acceptance as viable products for many commercial
and government applications. This paper will give an
introduction to these exciting developments of MEMS, the
fabrication technology used and application in various
fields. Future applications of miniaturized space systems
will have special needs on MEMS components. This paper
addresses the needs, status and perspectives of the MEMS
Technology for miniaturized space system from the
perspectives of a spacecraft developer. First, the needs of the
future space missions on MEMS components are discussed.
Then, the state-of-the-art MEMS technologies are reviewed
based upon these needs. Finally, perspectives of space-based
MEMS technology will be addressed based on the analysis
of both future mission needs and technological trends.
Lastly, it concludes saying that MEMS have enough
potential to establish a second technological revolution of
miniaturization.
Key words: MEMS, Space Systems, Miniaturization, MicroPropulsion, Satellite
I. INTRODUCTION
Micro-Electro-Mechanical System (MEMS) technology
promises to improve performance of future spacecraft
components while reducing mass, cost and manufacture
time. In the past two decades, MEMS technology has
significantly been advanced. The progress of MEMS offers
potentials and opportunities for miniaturized space system,
especially micro and nano satellites. By using this
technology, also small countries can play a strong role in
future space exploration and applications. On the other side,
future applications of miniaturized space systems have
demanding needs, which may call for MEMS components,
thus further boosting the developments of MEMS
technology.
This paper addresses the needs, status and
perspectives of the MEMS technology for miniaturized
space systems as seen by a spacecraft developer. Here,
„miniaturized space systems‟ denotes spacecraft with a mass
of less than 100kg, i.e. micro-, nano-, pico-, and even femtosatellites. It is noted that this paper will not cover MEMS for
other space systems, e.g. for large spacecraft or planetary
missions. This paper intends to answer three (3) questions:
What are the needs of developing MEMS
components for miniaturized space systems?
What is the state-of-the-art of MEMS components in
miniaturized space systems?
What are the perspectives of MEMS components for
future miniaturized space systems?
The paper is organized in three main parts. First,
past and expected future missions utilizing miniaturized
space systems are discussed, followed by an analysis of
mission needs on various aspects, such as performance,
reliability, cost and unique functionality of MEMS
components. Specific developments for sensors and
actuators will be presented.
The domain of MEMS, encompasses the processbased technologies which are used to fabricate tiny
integrated devices and/or systems that integrate
functionalities from various physical domains into one
devices. Such devices are fabricated using a wide range of
technologies, having in common the ability to create
structures with micro- and even nanometer accuracies. The
critical physical dimensions of MEMS products can vary
from a few micrometers to several millimeters. These
devices or systems have the ability to sense, control and
actuate on the micro scale, and generate effects on the macro
scale. The one main criterion of MEMS is that there are at
least some elements having some sort of mechanical
functionality whether or not these elements can move. The
term used to define MEMS varies in different parts of the
world. In the USA they are predominantly called MEMS,
while in some other parts of the world they are called
„Microsystems Technology‟ or „Micro Machined Devices‟.
While the functional elements of MEMS are miniaturized
structures, sensors, actuators, and microelectronics, the most
notable elements are the micro sensors and micro actuators.
Micro sensor and micro actuators are appropriately
categorized as „transducers‟, which are defined as devices
that convert energy from one form to another. In the case of
micro sensors, the device typically converts a measured
mechanical signal into an electrical signal.
II. HOW MEMS WORK
The sensors gather information by measuring mechanical,
thermal, biological, chemical, magnetic and optical signals
from the environment.
Fig. 1: MEMS Functional View
The microelectronic ICs act as the decision-making
of the system, by processing the information given by the
sensors. Finally, the actuators help the systems respond by
moving, pumping, filtering or somehow controlling the
surrounding environment to achieve its purpose.
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MEMS Technology & Its Application for Miniaturized Space System
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A. Interdisciplinary Nature of MEMS
The interdisciplinary nature of MEMS relies on design,
engineering and manufacturing expertise from a wide and
diverse range of technical areas including integrated circuit
fabrication technology, mechanical engineering, material
science, electrical engineering, chemistry and chemical
engineering, as well as fluid engineering, optics,
instrumentation and packaging. The complexity of MEMS is
also seen in the extensive range of markets and applications
that incorporate such devices. MEMS can be found in
systems ranging from consumer electronics, automotive,
medical, communication to defense applications as well as
satellites. Current examples of MEMS devices include
accelerometers for airbag sensors, microphones, projection
display chips, blood and tire pressure sensor, optical
switches, and analytical components such as lab-on-chip,
biosensors and many other products.
More recently, the MEMS research and
development communities have demonstrated a number of
micro actuators including: micro valves for control of gas
and liquid flows, optical switches and mirrors to redirect or
modulate light beams, independently controlled micro
mirror arrays for displays, micro resonators for a number of
different applications, micro pumps to develop positive fluid
pressures, micro flaps to modulate airstreams on airfoils, as
well as many others. Surprisingly, even though these micro
actuators are extremely small, they frequently can cause
effects at macro scale level; i.e. these tiny actuators can
perform mechanical feats far larger than their size would
imply.
B. Fabrication of MEMS Technology
MEMS, an acronym that originated in the USA, is also
referred to as Micro System Technology (MST) in Europe
and Micromachining in Japan. Regardless of terminology,
the uniting factor of a MEMS device is in the way it is
made. While the device electronics are fabricated using
„computer chip‟ IC technology, the micromechanical
components are fabricated by sophisticated manipulations of
silicon and other substrates using micromachining process.
MEMS fabrication is an extremely exciting endeavor due to
the customized nature of process technology and the
diversity of processing capabilities. MEMS fabrication uses
many of the same techniques that are used in the integrated
circuit domain such as oxidation, diffusion, ion implantation
etc. and combines these capabilities with highly specialized
micromachining processes. Processes such as bulk and
surface micromachining as well as high-aspect-ratio
micromachining (HARM) selectively remove parts of the
silicon or add structural layers to form the mechanical and
electromechanical components. While integrated circuits are
designed to exploit the electrical properties of silicon,
MEMS takes advantage of other material properties like
optical, mechanical etc. Within the wider field of MST we
also see processes like micro molding, laser ablation etc.
used to create Microsystems components.
III. OVERVIEW OF MISSIONS UTILIZING MINIATURIZED
SPACE SYSTEMS
There are already more than 200 modern miniaturized space
systems launched into orbit since 1980s. In addition to
existing systems, a significant number of miniaturized space
systems are under development worldwide and many
missions are expected to be launched in the following ten
years. Table 1 exhibits typical miniaturized space systems
that utilize or will utilize MEMS components.
Table 1: Typical Miniaturized Space Systems utilizing
MEMS
A. Needs for MEMS
The needs of miniaturized space systems on MEMS
technology can be obtained by analyzing „Table1‟.
First, it can be found from „Table1‟ that so far
MEMS components have been used for technology
demonstration only, although future science missions plan to
extensively utilize MEMS components. This is due to the
low technology readiness level (TRL) of space components.
On the other side, although there is a strong demand on
using mature Commercial-Off-the-Shelf (COTS) terrestrial
MEMS products, e.g. accelerometer, in space, the suitability
of these products in space environment is still doubtful.
Therefore, it is necessary to extensively validate the
reliability and performance of COTS MEMS components
before using them in operational missions. Furthermore,
space MEMS components developers must be aware of the
difference between terrestrial and space environments,
especially in relation to radiation and thermal aspects.
Second, there is an obvious trend that future
operational missions will utilize a cluster of miniaturized
spacecraft, which implies that cost will be a key driver.
Mass production could possibly reduce the manufacturing
cost of, e.g., the PAM mission. However, for most other
missions, the number of spacecraft will not be very high and
the benefit of mass production will not be significant. In this
case, a dedicated development of a MEMS component for a
mission might not be optimal. The need will be, in contrast,
developing low-cost and modular MEMS components that
can be utilized by a large range of space missions.
Modifying terrestrial MEMS components for a better
reliability and performance in space environment could be a
promising solution here.
Third, the strongest demand on MEMS components
is from the Attitude and Orbit Control System (AOCS). This
is due to two reasons: [1] The AOCS is one of the
bottlenecks of utilizing miniaturized space systems for
operational mission. Future mission typically require high
precision attitude control and orbit maintenance capability
within very limited mass. Power and volume budgets, which
cannot be realized by traditional technology [2] The AOCS
is the most typical system in a spacecraft bus that combines
mechanical system with electronics, where MEMS can play
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MEMS Technology & Its Application for Miniaturized Space System
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a very important role. Therefore high-precision, low-cost
and modular AOCS MEMS components will still be the
primary need of miniaturized spacecraft.
B. MEMS Sun Sensor
Different types of MEMS sun sensors have been developed
in Europe. The left side of Fig 2 shows the 2-axis sun sensor
originally developed for DTUsat-1. The sensor has the size
of 7mm 8mm and can achieve the resolution on the order of
1degree in the 40 degree range and 2.5 degree – 5 degree
from +40 degree - +70 degree and -40 degree to -70 degree.
Another interesting development is the digital sun sensor on
a chip (right side of Fig 2), which was developed by a
consortium led by Selex Galileo. The imager sensor,
processor, and interface electronics are placed on the same
chip. This sensor and interface „on a chip‟ results in low
mass (60 grams), low powering consumption (0.21W) and
small volume (30mm
30mm
25mm) with good
performance (resolution 0.02 deg, field of view 128 deg).
experiment unit (most right in Fig 4) has been flight on
Cyrosat-2 and exhibited moderate performance (bias
stability < 10 deg/hour).
Fig. 4: The silicon detector (left three) and the flight
experiment unit (most right) of the MEMS Gyro by SEA
E. MEMS Earth Sensor
Engineers from EPFL are developing a MEMS-based Earth
sensor that directly measures the gravity gradient vector
instead of optical information to provide the attitude
knowledge. As shown in Fig 5, the MEMS Earth sensor
measures the gravity gradient vector by measuring the
gravity gradient torque on a Si-pendulum. This approach
eliminates the need for multiple external access ports,
allowing a compact sensor to be situated anywhere inside
the spacecraft. It is expected that this MEMS Earth sensor
could achieve the accuracy of better than 5 degree.
Fig. 2: The MEMS 2-axis Sun Sensor of DTU (left) &
digital Sun Sensor on a chip of Selex Galileo (right)
C. Miniaturized Star Tracker
Under the ESA NEOMEx programme, a miniaturized star
tracker is under development by Selex Galileo. The casing
of the star tracker is shown in Fig 3. The star tracker also
utilizes the „System-on-chip‟ concept by placing imager
sensor, processor and interface electronics on the same chip.
It is expected that the star tracker could provide the accuracy
of 15 arcsec with the mass of 175 grams,power consumption
of 0.72W and the volume of 42mm 37mm 83mm.
Fig. 5: The MEMS-based Earth sensor of EPFL
F. Micro-Propulsion
Micro-propulsion is the most active area of space MEMS
developments in Europe. The first micro-propulsion system
to be introduced here is a cold-gas one developed by
NanoSpace and has been demonstrated on board the
PRISMA mission in 2010. The system is capable of
delivering accurate thrust ranging from tenths of microNewtons up to milli-Newtons. As shown in Fig 6, the
system consists of three types of MEMS components:
MEMS thruster module, MEMS pressure sensor and MEMS
isolation valve. The key component is the golf-ball sized
thruster module containing a silicon wafer stack with four
complete rocket engines with integrated flow controlled
valves, filters and heaters. Extremely small internal heaters
inside the thrust chamber increase the performance of the
system in terms of specific impulse. The propellant is
Nitrogen. The four thrusters are orthogonally distributed in
the equator plane of the golf-ball sized thruster module.
Fig. 3: The Miniaturized Star Tracker by Selex Galileo
D. MEMS Gyro
A space MEMS Gyro has been developed by a group of
British companies led by Systems Engineering &
Assessment Ltd (SEA). This MEMS Gyro uses a silicon
ring which is with a number of plates on the silicon
structures around its circumference that are capacitively
coupled to the ring (drive and sense plates). The physical
implementation of the silicon detector is shown in Fig 4,
which clearly shows the silicon ring and the associated
balance plates, as well as the external wires. The flight
Fig. 6: The cold-gas micro-propulsion system of
NanoSpace. (most left- System; second left- MEMS thruster
module; second right- MEMS pressure sensor; most rightMEMS isolation valve)
Another micro-propulsion system is a plasma-arcjet
micro-rocket (Fig 7) developed by Micro-Space in Italy.
This system ignites plasma inside the micro-nozzle for low
thrust range and microrocket for larger thrust range.
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MEMS Technology & Its Application for Miniaturized Space System
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Propellant consumption is reduced by 10 times; therefore it
is suitable for much longer nanosatellite missions.
Fig. 7: Plasma-arcjet micro-rocket of Micro-Space
With the support of the European and ESA, a
consortium led by EPFL is developing a micro Electric
propulsion (EP) system. The concept for this micro EP
system is a colloid thruster using electrostatic acceleration
of charged species for propulsion. In addition, this EP
system uses voltage-driven fluid handling with arrays of
individually addressed MEMS capillary emitters with
integrated extraction electrodes. This approach allows for a
simple architecture, since no pumps are required; all fluid
handling is done by capillary and electrostatic forces.
Hence, the complexity of the complete propulsion system is
radically reduced, leading to lighter, more compact, and
reliable design, as shown in Fig 8. The baseline propellant is
the ionic liquid, though other propellants are under
investigation.
As the enhancement of the role as an enabling
technology, it is expected by spacecraft developers that the
MEMS components could provide multiple functionalities.
For example, the nano-material could provide
multifunctional substrate and coating that combines the
functionalities of radiation shielding with ElectricalMagnetic (EM) transparent. The MEMS processing
technology also allows the realization of photovoltaic solar
cell in planner „antenna‟ structures. These multi-functional
capabilities could significantly reduce the required resources
of the components to the miniaturized spacecraft.
The final perspective is a system integrated
approach making use of space MEMS technology.
Currently, space MEMS products are developed as
standalone components to be integrated into miniaturized
spacecraft. Typically, the interconnection and coherence
between the MEMS components are not known at all. This
may lead to an extensive test and therefore loose the benefits
of utilizing MEMS technology. In order to solve this
problem, the „system-of-systems‟ approach shall be used.
An expected output of the system-of-systems approach is
the concepts of „satellite-on-chip‟ or „satellite-in-package‟,
which integrate the functionalities of different spacecraft
subsystems on a same chip or a same Printed Circuit Board
(PCB). The involvement of space craft systems engineers in
the development of space MEMS technology will be done of
the best solutions here.
V. CONCLUSION
Fig 8: The micro EP system. (top- MEMS EP module;
bottom left- The Principle; bottom right- The complete
system)
IV. PERSPECTIVE OF MEMS IN SPACE
From aforementioned existing or ongoing developments of
space MEMS components, it is apparent that the MEMS
technology allows developers to rescale traditional space
systems down to the microsystem level and, therefore,
provides tremendous opportunities for future missions
utilizing miniaturized space systems. However, this
downscaling is only a small part of the benefits that can be
brought by MEMS technology.
The first perspective is the role of MEMS as an
enabling technology for future miniaturized space systems.
„Enabling‟ means the MEMS technology will provide the
presently unavailable capabilities that are vital for long-term
missions. There are many unique physical phenomenon that
only happen in the micro world. For example, the
electrostatic force is not strong in the macro world but could
act as the actuator in a MEMS switch. An array of fine
pointing micromirrors or membrane mirrors can enable
inter-satellite optical communication or optical observation
with a nano-satellite or even a cubesat.
The reduction of mission costs requires substantial reduction
in mass, volume and power consumption. At the same time,
ever-more
ambitious
science
objectives
require
miniaturization without loss of performance. MEMS enable
this exploration of space by producing miniature science and
engineering devices that are potentially integral with
radiation-hardened electronics. Reliability, packaging and
flight qualification of MEMS and their related systems are
critical in fast insertion of these breakthrough EMS
technologies into space applications. The international space
and MEMS communities recognize this, and large efforts
are being created to produce an exciting new era in space
exploration.
ACKNOWLEDGEMENTS
Author Thanks Miracle Israel Nazarious, Studying Space
Science & Technology in „Luleå University of Technology‟,
SWEDEN, For Technical Support.
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