Project Design Review
DIABLO
De-rotated Imager of the Aurora Borealis in Low-earth Orbit
Nicole Demandante
Laura Fisher
Jason Gabbert
Lisa Hewitt
Lang Kenney
Nick Pulaski
Matt Sandoval
Tim Sullivan
Image taken from Space Shuttle over South Pole: http://www.geo.mtu.edu/weather/aurora/images/space/
Agenda






Background, objectives, requirements
System Design Alternatives
System Design-To-Specifications
Subsystem Design Alternatives
Project Feasibility and Risk Assessment
Project Management Plan
2
Background


Initial Idea: LASP Monitor Proposal
Scientific Purpose:
Visible light images
and in-situ
observations
3
Objective


Objective: Provide a
spinning satellite with a
de-rotated imaging
system
Deliverables:




De-rotated imaging
assembly
Spinning test bed
Control loop
Goal:


Achieve the least amount
of smear in the image
Model final fight spacecraft
4
System Level Design-to-Specs


The system shall …
Optical System



Take pictures at 90°
Pointing within 3°
Field of view
minimum of 6°
Optical Axis
Spin Axis
12°
3°
Earth
5
System Level Design-to-Specs

Control Loop


Sun-shading Assembly


Pixel smear - Images can be resolved to better than 1
pixel per kilometer *
No direct sunlight between 60° and 90° latitude
Test System



Test bed range: 2 – 20 rpm
Offset Test – Tilt 1° relative to test bed
Test camera resolution to shutter speed ratio similar
to flight camera
*Changed from PDD, customer approved
6
System Designs

Optical and Spin Axis Alignment

Design will be used by customer
7
System Designs

Fixed Cameras

Passive Stabilization
Spin axis
Spin
direction
Cameras
Cameras
Booms
8
System Designs

Rail Car

Parallel Plate
9
System Level Design Comparison
Image Clarity
(22%)
Complexity
(15%)
Fabrication
(15%)
Ease of Verification
(15%)
Moment
of Inertia
(10%)
Mass
(10%)
Comparable to
Actual Satellite
(13%)
Total
Score
Fixed
Camera
1
10
9
7
2
2
1
4.64
Passive
3
8
9
1
9
10
1
5.47
Rail Car
7
3
5
7
5
6
6
5.66
Parallel Plate
7
6
6
7
5
6
4
6.00
Axis
Alignment
8
7
7
7
7
8
8
7.45
Fixed Camera
Passive Stabilization
Rail Car
Parallel Plate
Axis Allignment
For more detail see slides 41 - 46
10
Subsystems






Optical
Rotation
Structure
Electronics & Sensors
Controls & Data Acquisition
Power
11
Optics
Rotation
Sizing
Structures
Electronics/
Sensors
Controls
Power
Camera
Transfer pictures
Do not limit FOV
Take mutiple
pictures
Adjustable shutter
speed
12
Sizing

Actual spacecraft will use two de-rotated assemblies
R=
0.75 –
1m
r
“Design-To”
Radius
R = 0.75 – 1 m
h
RTest
6
°
Actual
test platform does not need to be this large so long as the height
is sufficient to meet above requirement
13
Arrangement
Mirror

Requirements on flight camera
Mirror





Long focal length (~10cm)
Thermal shielding
Radiation shielding
Moment of Inertia
Camera Choice: COTS “point
and shoot”
For more detail on camera choice, see slide 47
14
Resolution
sgdf
16
14
Resolution (pixels/km)
12
10
8
6
4
2
0
-100
-80
-60
-40
-20
0
20
40
60
80
100
Latitude
Operating Range: -90 ° to -60° and 60° to 90°
Depends on Orientation of Orbit
15
Optics
Rotation
Test Bed
Motor
Structures
Electronics/
Sensors
Controls
Power
De-Rotated
Motor
Angular velocity
range of
2 to 20 rpm
Match test bed
rotation with
precision of
0.075rpm
16
Precision Motor Options
Direct Drive Servo Motor
Stepper Motor
Brushless Servo Motor
Static Torque
Mass
Max Power
Consumption
Accuracy
LV341 Stepper
Motor
550 oz-in
3.85 lb
250 W
350 steps/rev
BE232D Servo
Motor
476 oz-in
3.1 lb
190 W
NA
DM1004B Direct
Drive Motor
566 oz-in
6.6 lb
300 W
1,024,000
steps/rev
17
Motor Mounting Designs
Stepper/Servo Motor Mounting

Motor does not support
axial loads

Structure must be
supported by test bed
Direct Drive Motor Mounting

Motor supports axial loads

Structure can be mounted
directly to motor
For bearing options, see slide 49
18
Optics
Rotation
Structures
Bending
Electronics/
Sensors
Controls
Power
Stiffness
Bending < 6 microns
(6 pixels)
Vibration Frequencies
Bending < 0.3°
(6 pixels)
ωn > Launch Vibration
Frequency=50hz
Forcing Frequency ≠ Resonance
Frequency (ωn)
19
Structural Design
Option #1
Option #2
Requirement:
•Bending < 6 microns (pixel smear req.)
•Bending < 0.3° (pixel smear req.)
•Stiffness of structure
Judgment criteria: Lest mass, Moment of inertia, Deflection
Option #3
Structural design: Sunshade
Periscope Dimensions

Requirements


12° Field of View
Shade lens from direct
sunlight
Total Height = 17 cm
Inner diameter = 7cm
Outer diameter = 8cm
Height from support plates = 5 cm
Sunshade opening = 6 cm
Sun shade thickness = 0.5 cm
Support plate thickness = 1cm
21
Structure design: deflection requirement feasibility
Approximation: cantilever beam
Requirement:
•Bending < 6 microns (pixel smear req.)
•Bending < 0.3° (pixel smear req.)
•Stiffness of structure
Meets Requirement
For more detail, see slide 50
Fails Requirement!
Solution: substitution of support
rods with truss structure
22
Structural design: Material selection
Design to goal: Highest Mass/Stiffness
Mass/Stiffness
AISI 4130 Steel
9.562E-06
Aluminum 1350-H16
9.770E-06
Aluminum 2024-T3
9.434E-06
Aluminum 5182-O
9.475E-06
Aluminum 6061-T6
9.750E-06
Aluminum 7075-T6
9.808E-06
Titanium 6-4
9.697E-06
Other Considerations:
Good Selections
• Availability
• Aluminum 2024-T3
• Cost
• Aluminum 5182-O
• Fatigue Strength
• Steel 4130
• Coefficient of thermal expansion
For more detail on material selection, see slide 51
23
Optics
Rotation
Structures
Angular Position
Electronics/
Sensors
Angular Velocity
Controls
Power
Vibrations
Range: ±360°
Range: 2 and
20 rpm
3 Axes
Resolution:
0.045°
Resolution:
0.075 rpm
Bandwidth:
1 kHz
Microprocessor
Compatible
Microprocessor
Compatible
Resolution:
27.3 mg
24
Sensors

Encoder option preferred
over Resolver










Low speed operations
Accuracy
Minimal Complexity
Cost
Ability to Modify
Motors/Sensor package
Availability
Absolute Position
Encoders can measure
angular position and
velocity
Tachometer or Rate Gyro
may be used in conjunction
with Encoder

Accelerometers will be
used to measure the
vibrations
For more detail on electronics, see slides 52, 53, 54
25
Optics
Rotation
Structures
Simulation
Electronics/
Sensors
Controls
Power
Microcontroller
Determine
Environmental
Torques
Input velocity & position
Determine
Δposition
Process
Control algorithm
Determine
Motor Torque
Within 0.075 Nm
Output motor current
26
Simulation and Software Algorithms
Environmental
Applied Control
Torque
Torques
Angular
Velocity
Sensor
Position
Sensor
Dynamics
(calculate angular
rate)
Dynamics
Kinematics
Kinematics
Control
(calculate angular
position)
Law
Control Law
Motor
(PID)
Torque
27
Test Set Up
•Verification:
• ωDe-rotated= ωRotated
• ractual=rdesired
• Lflight=Lmodel
•Validation
•Image analysis
For more detail on controls, see slide 57, 58 28
Optics
Rotation
De-Rotated
Motor
Sensors
Provide Power:
Dependant on
Motor Selection
Low Mass:
Reduce
Required
Torque
Structures
Electronics/
Sensors
Structures
Camera
Provide
Power:
200mA at 6V
Low
Volume:
Fit Within
Available
Space
Controls
Power
Microcontroller
Powered by
Internal
battery
Provide Power:
4mA at 5.5V
Transfer
power
across
rotating
sections
29
Power

Design Criteria





Complexity
Cost
Mass
Volume
Possible Solutions

Slip Rings:




Batteries




Mercotac Rotary Electrical Connectors
Conductix R Series Slip Rings
Moog 6300 Series Slip Rings
Nickel Cadmium
Nickel Metal Hydride
Lithium Ion
Slip Ring/Battery Combination
For more detail on power, see slide 55, 56
30
Work Breakdown Structure
DIABLO
Systems Engineer
Management
Optics
Laura Fisher
Jason Gabbert
Scheduling
Camera Selection
Task Management
Testbed Sizing
Group Management
Define Pixel Smear
Risk Management
Geometry Design
Structures
Tim Sullivan
Laura Fisher
Lang Kenney
Imaging Platform
Design
Sunshade Design
Testbed Design
CAD Model
FEM analysis
Rotation
Matt Sandoval
Jason Gabbert
Power
Verification
Nick Pulaski
Nicole Demandante
Controls
Lisa Hewitt
Tim Sullivan
Nick Pulaski
Rotation Design
Identify Power Needs
Identify Verification
Needs
Software Diagrams
Motor Selection
Hardware Selection
Hardware Selection
Test Set Up
Data Acquisition
and
signal conditioning
Testbed Simulation
Bearing Selection
Integration with
Sensors
Software Algorithm
Final Testing
Fabrication
31
Schedule through CDR
For rest of detailed schedule, see slide 59
32
Schedule for Spring Semester
More detailed schedule, see slide 61
33
Cost Estimates
Team
Component
Optics
Camera
Power
Structures
Approx Cost
Margin
Total Cost
1
$500
20
$600
$50
1
$50
25
$62.50
$100
1
$100
25
$125
Encoders
$50
2
$100
25
$125
Rate Gyro/Tachometer
$50
2
$100
25
$125
Accelerometer
$12
2
$24
20
$28.80
Miscellaneous
$100
1
$100
25
$125
Motor
$600
1
$600
20
$720
Drive
$1,500
1
$1,500
20
$1,800
Controller
$1,000
1
$1,000
20
$1,200
Testbed Motor
$200
1
$200
20
$240
Bearings
$150
2
$300
20
$360
Slip Rings
$85
2
$170
25
$212.50
Batteries
$20
1
$20
15
$23
Miscellaneous
$30
1
$30
15
$34.50
Bulk Material
$150
1
$150
20
$180
Mirror Mount
Rotation
Quantity
$500
Mirror
Electronics and Sensors
Unit Cost
$4,944
$5,961
34
Mass Estimates
Mass
kg
sun shade
0.437
Periscope
15
Test Bed
6.09
4 Support Rods
7.09
1 Support Plate
0.574
Camera
0.5
Motors
7.5
Electronics/Sensors
0.3
Power system
0.5
Total Rotating
23.401
Total + Test bed
37.99
Total with 25% margin
47.49
35
Risk Matrix
Consequence
Inaccurate
Sensors
Motor does not
work as
specified
Underestimate
Vibration
Behind in
scheduling
Over budget
Parts are
delayed
Fabrication
error
Control
software is
inaccurate
Compression in
camera image
Mounting
inaccuracy
Probability
36
Conclusion


System design and subsystem design options will fulfill
customer requirements and expectations
System design is feasible within the budget, time, and
expertise level
Image – FAST satellite artist sketch: http://sprg.ssl.berkeley.edu/fast/
37
References








Fundamentals of mechanical vibrations, S. Graham Kelly,
McGraw-Hill, Inc.
Engineering Mechanics Dynamics, Bedford/Fowler,
Prentice Hall, 2005
http://www.mercotac.com/html/products.html
http://www.conductix.com
http://www.polysci.com
http://www.onlybatteries.com
http://www.panasonic.com/industrial/battery/oem/
http://www.bbma.co.uk/batterytypes.htm
38
BACKUP SLIDES
Pros and Cons
Fixed Camera

Pros:




Mechanically less complicated, no moving parts
Control system not required
Proven technology
Cons:


Complete coverage would require 30 cameras with a 12° field
of view.
For the given camera shutter speed (100ms), resolution (1Meg),
and field of view (12°) and assuming only a 1 pixel smear, the
maximum rotation rate would be 0.11718°/s. Actual rotation
rate is ~72°/s.
Back to system level choice
40
Pros and Cons
Passive Stabilization

Pros:





Simple design, easy to construct
No de-spun motor required
Aligns camera with magnetic field lines without help from main
satellite
No control loop needed
Cons:




Difficulty with verification
Potential interference with the science hardware
Possible pointing and stability issues
Can’t point camera off of magnetic field lines if desired
Back to system level choice
41
Passive Stabilization Calculations





Assuming that the de-rotated section is a solid cylinder of radius R=15cm
with mass m=0.5kg the moment of inertia I is:
If we want to be able to accelerate the despun portion to an angular
velocity ω of 72 degrees/s (the speed of the satellite) within 1 second in a
frictionless environment, the required torque τ will be:
To get the desired torque with a magnetic field strength of B=20,000 nT
(the field strength from orbit) the magnet must have a linear dipole
moment μ of:
Using the magnetic torquers found at
http://www.smad.com/analysis/torquers.pdf a torque rod which can
generate a linear dipole moment of 80 Am2 has a length of 0.5m, 2 coils,
and draws 4.7W of power at 28V. This gives a turn density n and current i
of:
At the center of a long solenoid the magnetic field strength B=μni where
μ=μ0*k. The relative permeability of a nickel alloy for the core is about
k=8000, so the field strength generated by this magnet is:
Back to system level choice
42
Rail Car Calcuations

Pros:



A small movement in the motor will not result in a large deviation in pointing
accuracy
Not as stringent requirements on motor sensitivity as other suggested designs.
Cons:

Thermal expansion would cause large errors





Radius could expand by up to 5% (depends on material)
Momentum balancing requirements would require additional masses and precise
balancing
Scaling with actual satellite would not be a feasible size, requiring an
unreasonably large track
Changing moment of inertia would result in scaling issue for the control loop
Electrical system very complicated and expensive – would require large slip ring
Back to system level choice
43
Parallel Plate Calculations

Pros:


Cons:




Simple construction
Masses not evenly balanced would create precession
in the top plate.
Requires the addition of excess mass
May not be able to meet the sun shading requirement
Scaling
Back to system level choice
44
Optical and Spin Axis Allignment
Calculations

Pros:






Cons:



Easiest to balance mass
Lots of space and flexibility in mounting camera
Smallest amount of mass (lack of ballast)
Less susceptible to thermal expansion issues
Scalable to actual flight instrument
Complicated attachment to testbed
Stability issues
Jitter, vibration
Back to system level choice
45
Camera
Level 1 Trade Study
Ease of
Alignment (7%)
Cost
(31%)
Features
(17%)
Required
Skill (24%)
Adjustability
(21%)
Total
Component Level
1
1
1
1
1
29
Single Lens Reflect (SLR)
3
1.5
2
2
3
61.5
2.5
3
3
3
2
80
Point and Shoot (PS)
Features: Zoom, Wireless, Timers
Adjustability: Shutter, Aperture, Flash
Samples
Back to optics
46
Rotation

Test Bed Motor




Simulates the rotation of spinning satellite
Does not require precise control
No size, weight or power constraints
Options

AC or DC motor



Inexpensive
Single voltage input
Simple manual control
47
Bearing Options
Thrust Ball Bearings
Ball Bearings
Cylindrical Roller
Bearings
Tapered Roller
Bearings
Radial Load Support
Axial Load Support
Thrust Bearings
No
Yes
Ball Bearings
Yes
No
Roller Bearings
Yes
No
Tapered Bearings
Yes
Yes
Back to rotation
48
Structural design
Periscope
S/C Configuration:
ω
L
F =mrω²
Satellite
r
Modeled As Cant. Beam:
v
θ
m = ¼ Total
System Mass
Back to structure
49
Material Selection
Feasibility Matrix
Material
Modulus of
Elasticity (ksi)
0.7
CTE, linear 250°
(µin/in-°F)
0.3
0.337
29700
0.7
1
7
0.3
0.331
0.7
0.979
10000
0.7
0.336
14.2
0.3
0.163
0.1
0.7
0.957
10600
0.7
0.356
13.7
0.3
0.169
Aluminium 5182-O
0.0957
0.7
1
10100
0.7
0.340
14.4
0.3
0.16
Aluminium 6061-T4
0.0975
0.7
0.982
10000
0.7
0.336
14
0.3
0.166
Aluminium 7075-T6
0.102
0.7
0.938
10400
0.7
0.350
14
0.3
0.1658
Titanium 6-4
0.16
0.7
0.598
16500
0.7
0.55
5.11
0.3
0.45
Invar 36
0.291
0.7
0.3298
20500
0.7
0.69
2.32
0.3
1
Cost
0.9
density (lb/in³)
0.7
AISI 4130 Steel
0.284
0.7
Aluminium 1350-H16
0.0977
Aluminum 2024-T3
AISI 4130 Steel
Aluminium 1350-H16
Aluminum 2024-T3
Aluminium 5182-O
Aluminium 6061-T4
Aluminium 7075-T6
Titanium 6-4
Invar 36
Fatigue Strength
(psi)
Shear Strength
0.8
0.9
130,000
0.8
1
13.48
0.9
0.353
0.9
0
2.153113
11000
0.8
0.084
11.25
0.9
0.423
0.9
0
1.418867
41000
0.8
0.315
12.53
0.9
0.379
20000
0.9
0.862
2.340604
21800
0.8
0.167
4.76
0.9
1
20000
0.9
0.862
2.796396
24000
0.8
0.184
5.91
0.9
0.8054
14000
0.9
0.603
2.38815
48000
0.8
0.369
11.37
0.9
0.4186
23000
0.9
0.991
2.516004
79800
0.8
0.613
41.25
0.9
0.115
23200
0.9
1
2.438711
0.8
0
59.93
0.9
0.079
0.9
0
1.084855
Back to materials
Total
50
Electronic Requirements on Angular
Position and Angular Velocity

Requirement from Optics






Maximum of 6 pixels smeared per line
1595 pixels in 12° field of view – 0.0075 °/pixel
6 pixels = 0.045 °
Shutter Speed ~ 0.1 sec
Only can smear 0.045 ° per 0.1 sec exposure
Thus smear => 0.451 °/sec = 0.075 rpm
Back to electronics
51
Encoder and Resolver Matrix
Encoder
Resolver
Total
Low speed operations
Accuracy
Minimal Complexity
Cost
Modification
Motors/Sensor package
Availability
Absolute Position
Back to electronics
52
Electronic Requirements on
Vibrations

Resolution

a = ω x (ω x r)
ω = 1/3 rev/sec =2.09 rad/sec
r = 6.13 cm
a = 26.79 cm/s2
Acceleration = 27.3 mg => resolution is 27.3 mg

Bandwidth







Shutter speed = 0.1 sec
Frequency due to camera = 10 Hz
f = 1 kHz
Back to electronics
53
Power
Slip Rings
Size (in^3)
Weight
Cost
Mercotac
2.6
~4 oz
$170
Conductix
71
~10 lbs
$700
Polysci
4.3
~8 oz
$440
NiCd
0.65
1 oz
$5
total w/ motor
84.5
8.6 lbs
$690
total w/o motor
5.2
8 oz
$40
NiMH
0.65
1 oz
$6
total w/ motor
84.5
8.6 lbs
$828
total w/o motor
5.2
8 oz
$48
Li-Ion
1.5
1.5 oz
$15
total w/ motor
69
4.3 lbs
$690
total w/o motor
4.5
4.5 oz
$45
Batteries
Back to power
54
Batteries and Slip Rings
Cost
Complexity
Mass
Size
8
7
9
10
Conductix SR 4
7
3
5
Moog SR
6
7
9
10
NiCd
4
8
5
4
NiMH
3
8
5
4
Li-Ion
4
8
7
5
Combination
10
6
8
8
Mercotac SR
Back to power
55
Functional Block Diagram
•Torques
•Environmental (E1 & E2)- drag
•Friction (F1 & F2)
•Spinning Platform Motor (M2)
•Applied Torques
•De-rotated Platform Motor (M1)
•Equations of Motion
I1   net1   E1   F 1   M 1
I 2   net2   M 2   F 2   E 2   F 1   M 1
Back to controls
56
Microcontroller



Input: position and
velocity sensor data
Output: signal to derotating motor
Process PID or PI control
law
Back to controls
57
Schedule
58
Back to fall schedule
Schedule
Back to fall schedule
59
Schedule for Spring Semester
Back to spring schedule
60
Schedule for Spring Semester
Back to spring schedule
61