Transcript Attitude Determination and Control System

Attitude Determination
and Control System
Peer Review
December 2003
Introduction
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Main purpose of ADCS is controlling the orientation of
the s/c for mission and science objectives.
Spacecraft face disturbance torques in space causing
the s/c to spin. ADCS senses these disturbances and
corrects the error in the attitude.
Includes the necessary sensors for determining the
attitude of the s/c.
Includes necessary actuators for controlling the s/c.
Includes software for attitude determination from the
sensors and a control algorithm for the actuators.
Requirements
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Maintain nadir attitude for communication and imaging
objectives.
Perform onboard attitude determination and control.
Maintain roll and pitch control using a gravity gradient
boom.
Maintain attitude knowledge to 2° in every axis.
Maintain attitude control to +/- 10 ° in each axis.
Mass
2.25 kg
Power
4 W operating
These requirements constitute a fairly coarse ADC
system thus the design driving requirements are the
mass and power limitations.
Imposed System Requirements
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Placement of torque rods
 Rods must lie in right hand orthogonal system
 Preferably along the s/c body axis.
 The rods shall be placed such that the ends are at the edge of the s/c
structure thereby eliminating strong fields effecting equipment.
Data conversion will be performed by C&DH.
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Bx,By,Bz (.5V – 4.5V analog) input
phidot, thetadot, psidot (.25V – 4.75V) input
0-5V analog output x 3
TTL high/low analog output x 3
Need a 5V and 12V line from PWR.
S/C c.g. shall be located along the z-axis (boom) axis.
Magnetometer shall be located as individual component outside of attitude
interface board box.
Remaining electronics will be placed on the attitude board.
Imposed System Requirements
Component
Dimensions
(inches)
Mass (kg)
Location of
Mounting
Bolts
Standoff
height
Sockets
1’’ – 2’’ from
all other
Components
TBD
Torque Rod X
15'' X 1/8'' Rod
0.1
Aluminum
incasing,
Horseshoe
Mounting
Torque Rod Y
16'' X 1/8'' Rod
0.15
Same
same
TBD
Torque Rod Z
12'' X 1/4'' Rod
0.25
Same
same
TBD
ADC PCB
4’’ x 4’’
Corners
TBD
DB-9 or DB15
Magnetometer PCB
2’’ x 2’’
Corners
TBD
DB-9
ADCS Electronics
Magnetometer
Flight Computer
(3) 0-5V analog
Honeywell HMC2003
12V@20mA w/ 40μG resolution
Sensor Analog
Inputs
Sensor
ADC
Controller
Att. Det.
Likely a P-D or LQR
IGRF Magnetic Model
Orbit Propagator
Rate Gyros
3 single-axis MEMS gyros
+5V input @ 6mA
(3) 0-5V analog
Current Control
Circuit
Output cmds to turn rods
on/off and current direction
Possibly use multiple voltage
levels requiring a D/A
Converter
0-300mA
Torque Rods
(3) 3/4’’ x 10’’ @ max 150mA nominal
12V and 5V supply to board
POWER
Compare Expected
And actual
B Fields
Damp rates
Magnetometer
Honeywell HMC2003
• 20mA @ 12V
• mass < 100g
• -40 to 85 C operating temp.
• 40 μGauss Resolution
• $200
• 3 Analog Outputs (Bx, By, Bz)
• Set/Reset Capabilities
Rate Gyros
Analog Devices ADXRS150EB
 Single
axis rate gyros provide the rotational rate of
the s/c about the output axis
 Microchip operating at 5V and 6mA.
 Single analog output
 -40 to 85°C operating temp
 $50 each
Magnetic Torque Rods
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Electrical current is passed through wire wound around a
ferrous material creating a magnetic dipole moment.
Torquer dipole moment interacts with Earth’s magnetic
field to create the desired torques. T = MxB
3 orthogonal torque rods can produce torques
perpendicular to magnetic field vector
Unbiased momentum
Design
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Material
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Ferromagnetic material
Magnesium Zinc Alloy
Approximate density: 5000 kg/m3
Magnetic permeability
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Wire
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μ = 800 W/(A m)
24 Gauge
Copper
Output
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3 Am2 @ 300mA input
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Counteract max drag disturbance torque
Internal Placement
Magnetic torque rods create interference
 Magnetic fields emanate from ends only
 Rods sized to span entire length of
satellite
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Possible configuration
Sizing
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Design to obtain 5
Am2 @ 500mA
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Counteract max
drag torques
Provide detumbling
capacity
Tradeoffs
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Weight
Power
Output Moment
Sizing - Mass
Budget
1.5 kg
Estimate
.6kg
Sizing - Power
Budget
Estimate
2.5W
1W
Electronics Design
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Magnetometer and rate gyros require basic
circuit design
Torque Rod control requires more
complicated circuit.
 Control
current input
 Control current direction through torquer
Sensor Circuits
Y-axis
Rate Gyro
X-axis
Rate Gyro
47n
47n
22n
C P1
R ATEOUT
2
20
C P2
TEMP
9
18
C P4
22n
7
2.5V
ST1
SUMJ
12V DC
19
C P1
R ATEOUT
2
20
C P2
TEMP
9
18
C P4
17
C P3
2.5V
7
13 12 8
4
5VDC
13 12 8
AVCC
C MID
C MID
PDD
1
AVCC
AGN D
C P3
PGN D
17
AGN D
22n
PDD
22n
ST2
C P5
ST1
SUMJ
19
22n
14 10 11 3
PGN D
22n
ST2
C P5
14 10 11 3
4
100n
100n
1
HMC2003
5VDC
100n
100n
100n
1
100n
2
3
Z-axis
Rate Gyro
Xout
Xout
Yout
47n
Zout
22n
14 10 11 3
4
5
Yout
SR-
Zoff+
Xoff-
Zoff-
Ztrim
Xoff+
Xtrim
Yoff-
6
Zout
SR+
Yoff+
Zout
Ytrim
Xout
Yout
Vref
Vbias
GND
Vbridge
V+
Vsense
22n
SUMJ
ST1
ST2
C P5
7
GNDout
19
C P1
R ATEOUT
2
20
C P2
TEMP
9
18
C P4
17
C P3
2.5V
9
10
7
13 12 8
AVCC
C MID
AGN D
PDD
PGN D
22n
1
19
100k
18
17
16
15
22u
10k
13
12
11
10V DC
4
5VDC
100n
100n
100n
Rate Gyro Circuit
22u
ZTX605
14
8
GNDout
20
Magnetometer Circuit
Reset In
Torquer Control Circuit
Torque Rod Control Preliminary Schematic
Direction-TT L
1
1
2
Vin-Analog
+
2
Rbias
Out+
In+
O UT
-
20
O P AMP
1
1
T or que Rod
2
Out2
In-
Software Design
Control system design
 Hardware control functions
 Functional test software
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Software Design Overview
Orbit data update
Propagate orbit
Obtain expected
B field vector
from model in
orbit frame.
Euler Angles and
Rates
Compare the s/c
frame to the orbit
frame
Obtain B field
and rates in s/c
frame
• The Euler angles and rates will provide and
attitude error to the control algorithm.
Software Design Overview
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Onboard magnetometer data and rotational rate
information.
Software-based orbit propagation and magnetic
field model.
Partial error analyses has been completed.
 Sensitivity
of the magnetometer provides negligible
attitude knowledge errors on the order of 0.01°.
 Tracking data must be uploaded periodically to
correct propagation errors.
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Bdot data derivations could also be used for
comparison between s/c and orbital attitude
frames.
Control Design
Based on research paper by Cornell
University faculty member.
 Simple control law/code
 Analysis not yet performed.
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 Primary
control design work to be completed
during spring semester.
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Control design, analysis, simulation, flight code
development.
Hardware Control Functions
Control D/A converter for torque rod
current control circuit input.
 Control of TTL line for current flow
direction through torque rod.
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Prototype Report
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The hardware has been
purchased and prototyped
with a circuit.
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Rate gyro
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Magnetometer
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Prototyped and functioning
Still needs to be tested to
be sure output is correct
Prototyped and functioning
Still needs to be tested to
be sure output is correct
Torque Rods
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Prototyped in house
Functionality not yet tested
Commands
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Torquer On/Off
 Inputs
X,Y, or Z rod
 amount of current
 Direction of current
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 Outputs
digital signal to D/A to vary output voltage of D/A.
 TTL high/low for control of direction of current.
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Commands
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Control on/off
 Either
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Attitude Board on/off
 This
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run the control system or do not.
will provide/cut power to the attitude board
Attitude determination and control will be completely off
Read data
 Need
to read data from sensors and store to
variables.
Test Plans-Hardware
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Magnetometer
 Successfully
tested to
be sure it functions
 Verify the output is
correct with rated
magnets
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Rate Gyros
 Successfully
tested to
be sure it functions
 Verify the output is
correct by spinning
each rate gyro up on
spinning apparatus
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Compare angular rate
output value to known
angular rate value
Test Plans-Hardware
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Torque Rods
 Use
magnetometer to
test the amount of
torque produced
 Graph relationship
between current input
into current driver
circuit and amount of
torque produced
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Electric Circuits
 Torque
rod current
driver
 Magnetometer reset
circuit-functions with
hardware
 Rate Gyro circuitfunctions with
hardware
Test Plans - Software
Verify orbit propagation vs. STK HPOP
 Simulate feedback control loop
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 Provide
input torque to simulator
 Model will predict s/c reaction to torque
 Control loop will provide response
 Model can predict time domain responses to
input torques based on control design.