NASA Technical Reports Server (NTRS) 19990047388: MEMS Rate Sensors for Space

4 Pages·0.23 MB·English

by  NASA Technical Reports Server (NTRS)

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MEMS Rate Sensors for Space
Joel Gambino
NASA/GSFC, Guidance, Navigation and Control Center
Greenbelt, Md
Currently, MEMS Rate Sensor
ABSTRACT systems are being produced for
terrestrial and missile
Micromachined Electro Mechanical applications. Therefore they
System (MEMS) Rate Sensors offer have relatively coarse
many advantages that make them performance, a large rate range
attractive for space use. They (up to i000 deg/sec), and are
are smaller, consume less power, not radiation hardened. Before
and cost less than the systems this technology can be used for
currently available. MEMS Rate attitude control on spacecraft,
Sensors however, have not been design issues must be addressed.
optimized for use on spacecraft.
This paper describes an approach To address these design issues,
to developing MEMS Rate Sensors a program has been initiated at
systems for space use. the GSFC that seeks to optimize
the MEMS Rate Sensor for space
INTRODUCTION use and develop a MEMS based
Inertial Reference Unit (IRU)
Spacecraft designers are for space use. This paper will
striving to replace traditional summarize the results to date of
heavy, power-hungry mechanical the optimization effort and
gyro systems with lightweight describe two approaches for
and extremely reliable solid development of an IRU.
state rate sensing systems. One
such system is the micromachined MEMS GYROS
gyroscope. These systems offer
extremely small size (about 8 Advances in micromachining have
in^3), low weight (less than 3 enabled the fabrication of very
ibs.), low power (3 watts), and small, low cost inertial
much lower cost then the sensors. These MEMS "Gyros"
existing technology gyros used sense angular rates by measuring
in space applications. coriolis forces acting on a
vibrating mass. This vibrating
Many satellites of the future mass or sensing element is
will be much smaller than those typically etched in silicon or
currently being produced. quartz which is driven
Hundreds of "nano-satellites" electrostatically into
launched and released into oscillation. When a rate is
various orbits for space and applied to the sensor, the
earth science missions have been deflection of the sensing
proposed. The mass and power element due to coriolis forces
budgets for these satellites is capacitively sensed. This
will be less than what a single deflection signal is
ACS component now consumes. The proportional to the angular
potential for small size and low input rate of the sensor.
cost of the MEMS rate sensor
make it an attractive option for
these future satellites.
SYSTEMS AVAILABLE TODAY: encouraging organizations who
show interest in this area. Two
There are several microgyro manufacturers that have shown
based IRU systems available interest in developing space
commercially. They combine microgyros are Draper Laboratory
microgyros, accelerometers, and and Kear fott Corp. Both have
some even include GPS navigation extensive experience in
to provide position information. designing, building, and testing
The size of these systems is on qyro systems for space and both
the order of 25 to 40 in^3. are working with NASA/GSFC to
Their power consumption is less produce microgyro systems for
than i0 watts. space. Draper is studying ways
to optimize sensors for space
Several off the shelf units were while Kearfott is constructing a
obtained for testing and single axis sensor package with
evaluation at the GSFC. One of a dynamic range and bandwidth
the units obtained was the scaled for space use.
Systron Donner Motion Pak IMU.
This unit combines three quartz TOP VIEW ! vl_r_u
tuning fork gyros with three
quartz accelerometers. Also
LEFT SENSE _ RIGHT _N_£
obtained was a Boeing Digital
Quartz IMU (DQI) [I]. This unit
uses quartz gyros built by
Systron Donner that have better
performance than those used in
the Motion Pak IMU.
STRUCTURE _ _ SUPPORT
ANCHOR POINT
The most recent acquisition was OUT_T
that of the Boeing Beta Rate
VIBRATING MASSES
Sensor. It uses a silicon
SIDE VIEW
micromachined gyro developed by
Draper Laboratory [2][3]. These LEFT RIGHT
gyros which are packaged DRIVE DRIYE
individually, promise good MO_'R_MU'I_'R
performance and flexibility.
Also, Draper continues to 5£NS£ PLA TZ REBApLLAANTCEE
downsize and improve the Draper Microgyro
performance of these units which
will be used to produce a micro
Inertial Measurement Unit (IMU). MICROGYRO OPTIMIZATION FOR SPACE
The performance of microgyros is Most of the Microqyro systems
very coarse when compared to currently being produced are
systems currently used for space designed for automobiles and
applications. The market is ballistic missiles. They have
driven by military and very high dynamic ranges (up to
automotive customers where ultra i000 deg/sec) and high
low noise performance is not of bandwidths (greater than 50 Hz).
prime concern. This low market Spacecraft on the other hand,
demand and high performance typically require a relatively
requirement explains why few low dynamic range (5 to I0
microgyro manufacturers have deg/sec) and can live with lower
sought to provide space units. bandwidths (less than i0 Hz).
Also, the performance of
As a result, the GSFC has sought currently available units makes
to develop space microgyros by
them useable in very limited further increase performance as
applications. well as making the unit
radiation tolerant.
The Microgyro effort at GSFC
seeks to improve the performance
of Microgyro systems to a level
that would be useful for
_,,- _00 Hz MAX
spacecraft missions by
optimizing both the gyro sensing
element and the electronics. To
this end, we have teamed with
__ y
Kearfott to develop space
specific gyro sensors. Also, b OUTPUT _> RODTITAHTEIORN
ROTAT_N FREQUENCY
the GSFC is also exploring ways f*
to improve the performance of
"off the shelf" units. Current $UBSTRATE
ACCELEP_kTION
az
efforts involve rescaling the %-m;, _'c m(_x J_)
dynamic range of existing
sensors, optimizing the Kearfott Microgyro ]
electronics for low noise, and
filtering sensor output.
GSFC DEVELOPMENT
4A
(i) The GSFC is also working to
develop an IRU from commercially
o o available sensors. Two
approaches for IRU development
are presented. First, a 3 axis
Bandwidth
IRU packaged as a single unit is
(deg/hr) > 5Hz > 5Hz
being assembled from 3
individual Microgyro modules.
Angle Random
Second, one or more microgyro
Walk (deg/rt-Hz) 1 0.01
modules will be integrated onto
an industry standard (compact
Bias (deg/hr) 40 0.I
PCI) board to produce a building
block for a modular Attitude
Power (watts) 3 0.5 Control system (ACS).
Kearfott is producing an MODULAR ACS IRU CARD:
engineering model microgyro
scaled to +/- i0 degree/second With requirements for systems to
dynamic range. It is hoped that be smaller, cheaper, and lower
lowering the dynamic range will power, spacecraft designers are
improve the noise challenged to come up with
characteristics of the unit. innovative approaches to
spacecraft systems. One such
In the NASA/GSFC lab, we are approach is the Modular ACS.
experimenting with filtering the The idea is to construct ACS
gyro output to improve noise building blocks using a standard
performance. interface. Each board will
provide one or more ACS
In the future, redesign of the functions. This approach will
sensing element will be minimize the amount of redesign
investigated as well as reducing necessary for new spacecraft.
bandwidth in an effort to
MICRO IRU: Future work will be done to
characterize the effects of
A micro Inertial Reference Unit reducing dynamic range and
(IRU) will be fabricated from 3 bandwidth. Development will
single microgyro modules, a continue as advances are made in
power supply, and interface sensor design.
electronics. The overall size of
the IRU will be 27 in^3. The
unit will weigh about 1 lb. and
consume about 3 watts.
The first prototype IMU will be
constructed using gyro modules
built by Boeing. These units
operate from a single +5 volt
supply and provide a voltage
output which is linear over the
REFERENCES
input rate dynamic range.
Preliminary testing indicates
[i] R. P. Jaffe "DQI Technical
the need for filtering of this
Description and Performance
output to reduce high frequency
noise. Capability", AIAA 96-3711, July
29-31 1996.
CONCLUSIONS
[2] J. Bernstein, S. Cho, A. T.
King, A. Kourepenis, P. Maciel,
Due to low demand and high
and M. Weinberg, "A
performance requirements, few
vendors are interested in Micromachined Comb-Drive Tuning
Fork Rate Gyroscope", IEEE 0-
developing microgyro systems for
7803-0957-2/93.
space applications.
[3] N. Barbour , J. Connelly, J.
The performance of currently
Gilmore, P. Greiff, A.
available microgyro systems is
Kourepenis, M. Weinberg,
adequate for only a small number
"Micromechanical Silicon
of space applications but the
Instrument and Systems
advantages offered by this
Development at Draper
technology justify further
Laboratory", AIAA 96-3709, July
development.
29-31, 1996.