Project Design Review Project Design Review DIABLO DIABLO De-rotated Imager of the Aurora Borealis in Low- De-rotated Imager of the Aurora Borealis in Low- earth Orbit earth Orbit Nicole Nicole Demandante Demandante Laura Fisher Laura Fisher Jason Gabbert Jason Gabbert Lisa Hewitt Lisa Hewitt Image taken from Space Shuttle over South Pole: http://www.geo.mtu.edu/weather/aurora/imag Lang Kenney Lang Kenney Nick Pulaski Nick Pulaski Matt Sandoval Matt Sandoval Tim Sullivan Tim Sullivan
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Project Design Review DIABLO De-rotated Imager of the Aurora Borealis in Low-earth Orbit Nicole Demandante Laura Fisher Jason Gabbert Lisa Hewitt Image.
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assemblyassembly Spinning test bedSpinning test bed Control loopControl loop
Goal: Goal: Achieve the least amount Achieve the least amount
of smear in the imageof smear in the image Model final fight Model final fight
spacecraftspacecraft
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System Level Design-to-System Level Design-to-SpecsSpecs
The system shall The system shall ……
Optical SystemOptical System Take pictures at Take pictures at
9090°° Pointing within 3Pointing within 3°° Field of view Field of view
minimum of 6minimum of 6°° Earth
12°
Spin Axis
3°
Optical Axis
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System Level Design-to-System Level Design-to-SpecsSpecs
Control LoopControl Loop Pixel smear - Images can be resolved to better Pixel smear - Images can be resolved to better
than 1 pixel per kilometer than 1 pixel per kilometer ** Sun-shading AssemblySun-shading Assembly
No direct sunlight between 60No direct sunlight between 60°° and 90 and 90°° latitude latitude Test SystemTest System
Test bed range: 2 – 20 rpmTest bed range: 2 – 20 rpm Offset Test – Tilt 1Offset Test – Tilt 1° relative to test bed° relative to test bed Test camera resolution to shutter speed ratio Test camera resolution to shutter speed ratio
similar to flight camerasimilar to flight camera
*Changed from PDD, customer approved
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System DesignsSystem Designs
Optical and Spin Axis AlignmentOptical and Spin Axis Alignment Design will be used by customerDesign will be used by customer
System Level Design System Level Design ComparisonComparison
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 StabilizationRail Car Parallel Plate Axis Allignment
For more detail see slides 41 - 46
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SubsystemsSubsystems
OpticalOptical RotationRotation StructureStructure Electronics & SensorsElectronics & Sensors Controls & Data AcquisitionControls & Data Acquisition PowerPower
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Optics
Sizing Camera
Transfer picturesDo not limit FOV
Rotation StructuresElectronics/
SensorsControls Power
Take mutiplepictures
Adjustable shutter speed
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SizingSizing Actual spacecraft will use two de-rotated assembliesActual spacecraft will use two de-rotated assemblies
R = 0.75 – 1 m
R = 0.75 – 1 m
h
RTest
6°
“Design-To”Radius
r
R=0.75-1m
Actual test platform does not need to be this large so long as the height Actual test platform does not need to be this large so long as the height is sufficient to meet above requirementis sufficient to meet above requirement
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ArrangementArrangement
Requirements on flight Requirements on flight cameracamera Long focal length (~10cm)Long focal length (~10cm) Thermal shieldingThermal shielding Radiation shieldingRadiation shielding
Moment of InertiaMoment of Inertia Camera Choice: COTS Camera Choice: COTS
“point and shoot”“point and shoot”
MirrorMirror
For more detail on camera choice, see slide 47
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Resolution Resolution
Operating Range: -90 ° to -60° and 60° to 90°
Depends on Orientation of Orbit
0
2
4
6
8
10
12
14
16
-100 -80 -60 -40 -20 0 20 40 60 80 100
Latitude
Res
olu
tion (pix
els/
km) sg
df
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Optics Rotation StructuresElectronics/
SensorsControls Power
Test Bed Motor
De-Rotated Motor
Match test bed rotation with precision of
0.075rpm
Angular velocity range of
2 to 20 rpm
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Precision Motor OptionsPrecision Motor Options
Direct Drive Servo MotorDirect Drive Servo Motor Stepper Motor Stepper Motor Brushless Servo Brushless Servo MotorMotor
Stepper/Servo Motor Stepper/Servo Motor MountingMounting
Motor does not support Motor does not support axial loadsaxial loads
Structure must be Structure must be supported by test bedsupported by test bed
Direct Drive Motor MountingDirect Drive Motor Mounting Motor supports axial loadsMotor supports axial loads Structure can be mounted Structure can be mounted
Possible SolutionsPossible Solutions Slip Rings:Slip Rings:
Mercotac Rotary Electrical ConnectorsMercotac Rotary Electrical Connectors Conductix R Series Slip RingsConductix R Series Slip Rings Moog 6300 Series Slip RingsMoog 6300 Series Slip Rings
BatteriesBatteries Nickel CadmiumNickel Cadmium Nickel Metal HydrideNickel Metal Hydride Lithium IonLithium Ion
Motor does Motor does not work as not work as specifiedspecified
UnderestimatUnderestimate Vibratione Vibration
Behind in Behind in schedulingscheduling
Over budgetOver budget
Parts are Parts are delayeddelayed
Fabrication Fabrication errorerror
Control Control software is software is inaccurateinaccurate
Compression Compression in camera in camera imageimage
Mounting Mounting inaccuracyinaccuracy
Probability
Con
sequ
ence
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ConclusionConclusion System design and subsystem design options will System design and subsystem design options will
fulfill customer requirements and expectationsfulfill customer requirements and expectations System design is feasible within the budget, time, System design is feasible within the budget, time,
and expertise leveland expertise level
Image – FAST satellite artist sketch: http://sprg.ssl.berkeley.edu/fast/
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ReferencesReferences
Fundamentals of mechanical vibrations, S. Fundamentals of mechanical vibrations, S. Graham Kelly, McGraw-Hill, Inc. Graham Kelly, McGraw-Hill, Inc.
Pros and ConsPros and ConsFixed CameraFixed Camera
Pros:Pros: Mechanically less complicated, no moving partsMechanically less complicated, no moving parts Control system not requiredControl system not required Proven technologyProven technology
Cons:Cons: Complete coverage would require 30 cameras with a 12° Complete coverage would require 30 cameras with a 12°
field of view.field of view. For the given camera shutter speed (100ms), resolution For the given camera shutter speed (100ms), resolution
(1Meg), and field of view (12°) and assuming only a 1 (1Meg), and field of view (12°) and assuming only a 1 pixel smear, the maximum rotation rate would be pixel smear, the maximum rotation rate would be 0.11718°/s. Actual rotation rate is ~72°/s.0.11718°/s. Actual rotation rate is ~72°/s.
Back to system level choice
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Pros and ConsPros and ConsPassive StabilizationPassive Stabilization
Pros:Pros: Simple design, easy to constructSimple design, easy to construct No de-spun motor requiredNo de-spun motor required Aligns camera with magnetic field lines without help Aligns camera with magnetic field lines without help
from main satellitefrom main satellite No control loop neededNo control loop needed
Cons:Cons: Difficulty with verificationDifficulty with verification Potential interference with the science hardwarePotential interference with the science hardware Possible pointing and stability issuesPossible pointing and stability issues Can’t point camera off of magnetic field lines if desiredCan’t point camera off of magnetic field lines if desired
Back to system level choice
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Passive Stabilization Passive Stabilization CalculationsCalculations Assuming that the de-rotated section is a solid cylinder of radius 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: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 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 velocity ω of 72 degrees/s (the speed of the satellite) within 1 second in a frictionless environment, the required torque τ will be:in a frictionless environment, the required torque τ will be:
To get the desired torque with a magnetic field strength of B=20,000 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 nT (the field strength from orbit) the magnet must have a linear dipole moment μ of:moment μ of:
Using the magnetic torquers found at Using the magnetic torquers found at http://http://www.smad.com/analysis/torquers.pdfwww.smad.com/analysis/torquers.pdf a torque rod which can generate a torque rod which can generate a linear dipole moment of 80 Am2 has a length of 0.5m, 2 coils, and 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 draws 4.7W of power at 28V. This gives a turn density n and current i of:of:
At the center of a long solenoid the magnetic field strength B=μni 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 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:is about k=8000, so the field strength generated by this magnet is:
Pros:Pros: A small movement in the motor will not result in a large deviation in A small movement in the motor will not result in a large deviation in
pointing accuracypointing accuracy Not as stringent requirements on motor sensitivity as other suggested Not as stringent requirements on motor sensitivity as other suggested
designs.designs. Cons:Cons:
Thermal expansion would cause large errorsThermal expansion would cause large errors Radius could expand by up to 5% (depends on material)Radius could expand by up to 5% (depends on material)
Momentum balancing requirements would require additional masses Momentum balancing requirements would require additional masses and precise balancingand precise balancing
Scaling with actual satellite would not be a feasible size, requiring an Scaling with actual satellite would not be a feasible size, requiring an unreasonably large trackunreasonably large track
Changing moment of inertia would result in scaling issue for the control Changing moment of inertia would result in scaling issue for the control looploop
Electrical system very complicated and expensive – would require large Electrical system very complicated and expensive – would require large slip ringslip ring
Cons:Cons: Masses not evenly balanced would create Masses not evenly balanced would create
precession in the top plate.precession in the top plate. Requires the addition of excess massRequires the addition of excess mass May not be able to meet the sun shading May not be able to meet the sun shading
requirementrequirement
ScalingScaling
Back to system level choice
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Optical and Spin Axis Optical and Spin Axis Allignment CalculationsAllignment Calculations
Pros:Pros: Easiest to balance massEasiest to balance mass Lots of space and flexibility in mounting cameraLots of space and flexibility in mounting camera Smallest amount of mass (lack of ballast)Smallest amount of mass (lack of ballast) Less susceptible to thermal expansion issuesLess susceptible to thermal expansion issues Scalable to actual flight instrumentScalable to actual flight instrument
Cons:Cons: Complicated attachment to testbedComplicated attachment to testbed Stability issuesStability issues
Jitter, vibrationJitter, vibration
Back to system level choice
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CameraCameraLevel 1 Trade StudyLevel 1 Trade Study
Features: Zoom, Wireless, Timers
Adjustability: Shutter, Aperture, Flash
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
Point and Shoot (PS) 2.5 3 3 3 2 80
SamplesSamples
Back to optics
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RotationRotation Test Bed MotorTest Bed Motor
Simulates the rotation of spinning satelliteSimulates the rotation of spinning satellite Does not require precise controlDoes not require precise control No size, weight or power constraintsNo size, weight or power constraints
OptionsOptions AC or DC motorAC or DC motor
InexpensiveInexpensive Single voltage inputSingle voltage input Simple manual controlSimple manual control
Electronic Requirements on Electronic Requirements on Angular Position and Angular Angular Position and Angular
VelocityVelocity Requirement from OpticsRequirement from Optics
Maximum of 6 pixels smeared per lineMaximum of 6 pixels smeared per line 1595 pixels in 121595 pixels in 12° field of view – 0.0075 °/pixel° field of view – 0.0075 °/pixel 6 pixels = 0.045 °6 pixels = 0.045 ° Shutter Speed ~ 0.1 secShutter Speed ~ 0.1 sec Only can smear 0.045 ° per 0.1 sec Only can smear 0.045 ° per 0.1 sec
Encoder and Resolver MatrixEncoder and Resolver MatrixEncoderEncoder ResolverResolver TotalTotal
Low speed operationsLow speed operations
AccuracyAccuracy
Minimal ComplexityMinimal Complexity
CostCost
ModificationModification
Motors/Sensor Motors/Sensor packagepackage
AvailabilityAvailability
Absolute PositionAbsolute Position
Back to electronics
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Electronic Requirements on Electronic Requirements on VibrationsVibrations
ResolutionResolution aa = ω x (ω x r)= ω x (ω x r) ωω = 1/3 rev/sec =2.09 rad/sec = 1/3 rev/sec =2.09 rad/sec r = 6.13 cm r = 6.13 cm a = 26.79 cm/sa = 26.79 cm/s22
Acceleration = 27.3 mg => resolution is 27.3 mgAcceleration = 27.3 mg => resolution is 27.3 mg BandwidthBandwidth Shutter speed = 0.1 secShutter speed = 0.1 sec Frequency due to camera = 10 HzFrequency due to camera = 10 Hz f = 1 kHz f = 1 kHz