SPECTRE
(Solar-sail Pitch Enabling Controller Through Root Excitation)
Michael Andrews, Brendon Barela, Austin Cerny, Corinne Desroches,
Kyle Edson, Conrad Gabel, Chris Riesco, Justin Yong
● SPECTRE seeks to design and prototype a sail blade controller for a
proposed heliogyro cubesat mission
● SPECTRE is a continuation of last year’s GHOST senior design
project which focused on designing the deployment system of the
sail blades
Customer:
Keats Wilkie
NASA Langley
Advisor:
Dr. Xilin Li
LASP
Content Breakdown
Project Overview
Blade Behavior and Controller
Requirements
Vacuum Chamber Requirements
Summary
1.0 Project Overview
•Background
•Requirements and Design Considerations Overview
•CONOPS
•Functional Block Diagram
2.0 Blade Behavior and Controller Requirements
3.0 Sensors
4.0 Actuators
5.0 Vacuum Chamber Requirements
6.0 Summary
●
A heliogyro is a solar sail satellite
propulsion concept with spinning sail
blades held in place by centrifugal forces
●
Concept first proposed in 1970’s for a
rendezvous with Halley's Comet
●
Heliogyros offer major advantages over
traditional solar sail designs
o
Deploy large surface areas of sail
material with very little support
structure
o
Blades can be pitched to initiate
potential orbital maneuvers
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Illustration of heliogyro solar sail rendezvous with Halley’s Comet
(source: NASA/JPL)
Actuators
Vacuum Chamber
Requirements
Summary
●
HELIOS is a proposed heliogyro that have been
researched by the CU aerospace department and
our customer at NASA Langley
●
NASA would like a smaller low-cost heliogyro
demonstrator suitable for a standard CubeSat
platform
●
Last years GHOST team demonstrated a
deployable heliogyro CubeSat platform but
failed to incorporate a successful blade control
system
●
SPECTRE will design, prototype, and test a
proof-of-concept blade damping augmentation
system for a heliogyro CubeSat mission
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
6 blade HELIOS satellite
GHOST team heliogyro platform.
Vacuum Chamber
Requirements
Summary
●
●
●
●
●
●
●
Satellite must incorporate 2 sail blades with aspect ratios of at least 100:1
Blades must pitch over a range of ± 90° to within ± 5° of a desired angle
The controller must demonstrate the ability to damp the first mode of inplane (pitching) and out-of-plane (flapping) oscillation
Blade areal density including tip mass shall be comparable to other NASA
designs and not exceed 6 g/m2
The blade and controller subsystem must fit within a 6U CubeSat volume of
which a minimum of 2U are assumed to be allocated for other subsystems
10 Watts of power is allowed the blade control subsystem
○ We are currently negotiating this requirement with our customer
Design of the CubeSat bus and other mission systems is not required
Blade Behavior
and Behavior and Controller
Blade
Sensors
Project Overview
Controller Requirements
Requirements
Project Overview
Vacuum
Actuators Chamber
Requirements
Vacuum Chamber
Requirements
Summary
Summary
● Design is not necessarily going to be spaceworthy, though parts used
will have spaceworthy alternatives
● Although preliminary designs incorporate sensing within the
spacecraft, a working controller can still be validated if sensors are
located external to the spacecraft
● Design will have to be tested in a 1 g Earth environment. The effects
of air damping will need to be accounted for
● Ultimately, our customer wants a physically deliverable blade
controller that he can show off to his NASA colleagues
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
●
Two Main tests will validate controller
o
Perform a 90 degree pitch
maneuver and damp resulting
oscillations and measure
performance
o
Excite flapping and pitching
modes with actuators, then use
controller to damp the resulting
oscillation and measure
performance
Testing will need to be performed in
a vacuum chamber
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
Blades will be spooled up and housed in the sides
of the CubeSat in a housing that occupies roughly
2U on either side of the 6U CubeSat
●
The blade will pitch by moving the entire housing
with a rotary actuator connected to the CubeSat bus
●
High resolution LEPD sensors will be used to
calculate blade blade mode and amplitude based
high resolution measurements of deflected blade
angle near the root.
●
Linear and rotary actuators will move the blade and
housing to damp flapping and pitching oscillation
from the blades
Blade Behavior
Blade and
Behavior and Controller
Sensors
Project Overview
Controller Requirements
Requirements
Project Overview
Vacuum
Actuators Chamber
Requirements
of d d
in
w
Vacuum Chamber
Requirements
Summary
Summary
1.0 Project Overview
2.0 Blade Behavior and Controller Requirements
•Time Requirements
• Blade Behavior
• LEPD Sensor
• Actuators
3.0 Sensors
4.0 Actuators
5.0 Vacuum Chamber Requirements
6.0 Summary
Sun
Blades pitched perpendicular to solar
pressure. Orbital velocity increases
● Time to damp requirements stem
from a typical heliogyro mission
profile
● Two 90° pitch maneuvers are
performed during 1 LEO orbit to
maximize increase in velocity
Earth
● Research has suggested 12
minutes or 1/8th a LEO orbit as a
reasonable settling time
(REFERENCE)
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Blades pitched 90° to avoid
deceleration. Orbital velocity remains
constant
Vacuum Chamber
Requirements
Summary
● First flapping mode behaves linearly, the mode shape resembles
that of a swinging pendulum
● For earth test conditions,
(Roark, pg 766)
For 0.15m X 15m blade, f = 0.228 Hz
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
Controller is being designed so that at least 95% of the blade’s surface area is exposed
to the sun at all times
●
Blades may still oscillate, but amplitude must be low enough that the cross sectional
area exposed to the sun is >95% of blade surface area
●
Deflection angle α may not exceed 18.2 degrees, Note that this angle is independent
blade aspect ratio
Overhead View
Profile View
α
α = cos-1(0.95) = 18.2 degrees
Project Overview
Blade Behavior and
Controller Requirements
Nominal Cross Sectional Area
Minimum Cross Sectional Area
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
● Blade twists along lengthwise axis, with the tip oscillating and the
root remaining in place
● On Earth, twisting frequency
(Roark, pg 767)
o For 0.15m X 15m blade, f = 0.727 Hz
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
A trapezoidal area is perpendicular to solar pressure during twisting. Twist angle
cannot exceed 25.8 degrees (cos-1(.9)) for this area to remain 95% of the nominal area.
●
Blade will be deflected in opposite directions on opposite sides of the blade. The
deflection angle α will depend on the blades aspect ratio. For an aspect ratio of 100:1
will approximately equal 0.03 degrees
Overhead View
Profile View
0.05 * blade
width (W)
α
blade length (L)
Nominal Cross Sectional Area
Minimum Cross Sectional Area
α = tan-1( .05 W / L) = tan-1(.05/AR)
For AR = 100, α = 0.03 degrees
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
1.0 Project Overview
2.0 Blade Behavior and Controller Requirements
3.0 Sensors
•Basic Sensor Requirements
•LEPD Sensors and configuration
•LEPD Accuracy
4.0 Actuators
5.0 Vacuum Chamber Requirements
6.0 Summary
Sensor requirements stem from small deflection angle of torsional mode (α = 0.03
degrees)
● Sensing must be non-contact to conform to blade mass requirements
o Optical sensing options proved to be the most viable
● Sensing requirements depend on whether measurements are made at the root or tip
Sensing at the Tip
Sensing at the Root
● Blade is displaced furthest at the tip
● Higher resolution needed due to smaller
● Optical measurements must travel further
blade deflections
and are more susceptible to noise
● Twisting and flapping behavior both
● Measurement of the torsional behavior
correspond to deflection in the same
computationally expensive and involves
direction
image processing
● Deflection due to solar pressure is
minimal
●
Optical measurements can miss the tip entierly
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
Radiation is reflected off a surface and hits
the sensor
●
Quadrant Bi-Cell Photodiodes produce four
currents from incoming light, separating the
signal into transverse and lateral
components.
●
By reflecting a beam of light off of the blade
and onto the active area of the photodiode,
we can measure the position of the blade at
the point of reflection.
●
Resolutions of 1 μM are typical. Grid areas
typically have a radius of 2.5 mm
Project Overview
Blade Behavior and
Controller Requirements
Sensors
http://www.globalspec.com/FeaturedProducts/Detail/OptoDiode/255
014/New_Quadrant_Photodiode_5_mm2
http://www.aptechnologies.co.uk/support/ph
otodiodes/bi-cell-a-quadrant-photodiodes
δx=(B+D-(A+C))/(A+B+C+D)
Actuators
Vacuum Chamber
Requirements
Summary
●
The photodiode and laser diode will
be attached an inner blade housing.
●
Measuring the difference in the
nominal light angle, and current
incidence angle will provide the
blade’s deflection angle
●
Sensors will not move relative to the
blade when the blade is being pitched
●
2 LEPD sensors placed on the edges
of the blade can detect both the
pitching and the flapping modes
Project Overview
Blade Behavior and Controller
Requirements
Vacuum Chamber
Requirements
Summary

Resolution of the measurement of the deflection angle depends on the incidence angle
theta. The laser beam will be placed roughly 5 cm from the root of the blade and 5 cm
underneath the blade based on CubeSat geometry. If the theta is within 47 to 49
degrees, the a light source
Sensor measurement at maximum allowable
deflection angle vs sensor incidence angle.
The radius of the sensor is bounded in red.
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Effective LEPD resolution of the
measurement of the deflection angle
Actuators
Vacuum Chamber
Requirements
Summary
1.0 Project Overview
2.0 Blade Behavior and Controller Requirements
3.0 Sensors
4.0 Actuators
• Actuator Design and Integration
• Requirements for actuator and Piezoelectric Motors
• Damper Frequency
• Microcontrollers
5.0 Vacuum Chamber Requirements
6.0 Summary
● The actuator configuration
consists of a linear sliding
actuator “stacked”on top of a low
profile rotary actuator.
● Actuator configuration is placed in
between the blade housing unit
and the CubeSat bus.
● This configuration allows for ±90
degree pitch control as well as
damping for blade flapping.
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
The actuators must be capable of moving the blade at frequencies greater
than the mode frequencies of the blade
● The response times of the actuators must be faster than the periods of
the blades
● The linear or angular velocity the actuators are capable of do not necessarily
need to be the same as the linear or angular velocity of the tip of the blade
● The rotary actuator must be able to pitch the blade ±90° and provide
torsional damping. Requires torque of 0.013 mN.m for a 1 minute 90° pitch
manuever, based on estimated housing interia of 7.37 gM2
●
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
Y = Maximum root amplitude
ω = frequency of the root movements
ωn = natural frequency of the solar sail
Xp = The amplitude of the tip
To achieve a lower amplitude at the tip, the
root must have a frequency higher than the
natural frequency of the solar sail
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
Benifits
● High resolution and accuracy ( <0.01 μm)
o Allows for small angular velocity to minimize blade
perturbations
● Direct drive motor virtually eliminates backlash and hysteresis
● Lightweight and small volume
● Low voltage requirements ( <12VDC)
● No power needed for holding torque
● Fast Response (10-50 μs)
● Vacuum Versions available
Drawbacks
● Angular/Linear velocity is limited
● Much more expensive than traditional motors
● Require extra controller/amplifier circuits
Project Overview
Blade Behavior and
Controller Requirements
Sensors
http://www.directindustry.com/prod/micos/single-shaft-linear-stagesmanual-7412-1553626.html
Actuators
Vacuum Chamber
Requirements
Summary
Rotary Stage: RPS-32
Linear Stage: LPS - 65
•Continuous 360 degree motion
•Travel range 52 mm
•Mass 0.035 kg
•Mass 0.6 kg
•Max speed 45 deg/sec
•Max Speed 10 mm/s
•Resolution 0.002 micrometers
•0.0005 micrometers
•Load capacity 1 kg
•Load capacity 2 kg
•Voltage 0 to 48 V
•Current 0.2 Amps
•Dimensions 36x32 mm
•Dimensions 160x65x20 mm
http://www.pimicos.com/web2/en/1,
6,350,rps32.html
http://www.pimicos.com/web2/en/1,
6,350,rps32.html
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
● Ideally will require < 5W
Inputs (~5)
Outputs (4)
Photodiode sensors (2)
● Sample current input (~74mA)
● Resistor required to convert to
voltage
Actuators (2)
● Varying Voltage up to roughly
12V
● Analog or Digital
Encoder (2) for actuators
● Bit rates depend on
resolution/range
Laser Diodes (2)
● Operating voltage 2-2.5V
● Constant output
Computer/Bus Input (1)
● Commanded angle
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
● PIC18F87K22 Microavionics
PICboard and baseboard
o Borrow or buy, ~$200
o 5.5 µA run mode, 1.8 to 5.5V
 ~30 µW
o 24 A/D input channels
o 9 Multi-pin I/O Ports
o Headers for external
connections
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
1.0 Project Overview
2.0 Blade Behavior and Controller Requirements
3.0 Sensors
4.0 Actuators
5.0 Vacuum Chamber Requirements
•Vacuum Testing Overview
•Test Chamber set up
•Past research with Blade Damping
6.0 Summary
● Early experimentation has shown air viscosity is too high for the blade
controller to be tested accurately
o Vacuum chamber will be required to test the controller
● Test blade will need to be scaled, full scale 15 vacuum chambers are
not feasible with the projects budget or time frame
● Our research has indicated a chamber that simulates atmospheric
conditions at 40,000 ft (p = 18.8 kPa, ρ = 0.3016 kg/m3) will reduce air
damping enough to test our controller properly
o These values are derived from the approximate altitude where
cooling fans cease to function due to the inability for air to
circulate
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
●
●
●
●
Currently to achieve the necessary aspect ratio, the dimensions of the blade
are 0.15m X 15m but will need to be scaled to 0.03m X 3m
Flapping mode frequency will increase 5x to 1.14 Hz
Torsional mode frequency will increase 5x to 1.60 Hz
o Based the following equations (Roark, pg 766-767):
Though the frequency of the modes will increase they will still can be
matched by the actuators. The deflection angles that need to be measured are
unchanged as they depend solely on the aspect ratio of the blade
Blade Behavior
Blade and
Behavior and Controller
Sensors
Project Overview
Controller Requirements
Requirements
Project Overview
Vacuum
Actuators Chamber
Requirements
Vacuum Chamber
Requirements
Summary
Summary
Power &
Commands
●
Pressure vessel constructed from 25.4 cm (10in)
diameter PVC pipe that is 3 m in length for a scaling
ratio of 1:5.
o
o
o
●
Large enough to house an entire 6U CubeSat
E ≈ 3.3 GPa (engineering toolbox)
Wall thickness 0.927 cm (0.365 in) (flexpvc)
10” PVC
3m
Assuming an internal pressure of 18.8 kPa
o
Critical buckling pressure given by
o
Safety factor of 2.24
Actuator
Housing
Solar
Sail
(Roark, pg 736)
Blade Behavior
Blade and
Behavior and Controller
Sensors
Project Overview
Controller Requirements
Requirements
Project Overview
Pump
Vacuum
Actuators Chamber
Requirements
Vacuum Chamber
Requirements
Summary
Summary
Standard Atmosphere:
760 Torr
Source: Heliogyro Solar Sail Structural Dynamics, Control and Experimentation
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
1.0 Project Overview
2.0 Blade Behavior and Controller Requirements
3.0 Sensors
4.0 Actuators
5.0 Vacuum Chamber Requirements
6.0 Summary
• Status Summary
• Budget
• Testing to be Done
●
●
●
●
Blade remains in a housing that rotates with the blade. Sensors remain stationary to the
blade while the blade pitches. The blade and housing will have a combined mass of
approximately 1.1 Kg and
2 sets of LEPD sensors measure both edges of the blade near the root. High resolution
measurements of blade deflection are possible by optimizing the sensor incidence
angles
Flapping modes will be damped with a linear piezoelectric actuator, twisting with the
pitching motor, stacked on each other
Blade to be scaled to ⅕ its original length and tested with the controller in a vacuum
chamber to reduce air damping.
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Actuators
Vacuum Chamber
Requirements
Summary
11%
18%
Sensors
Actuators
21%
Project Overview
Blade Behavior and
Controller Requirements
Sensors
Vacuum
50%
Actuators
Remainder
Vacuum Chamber
Requirements
Summary
● FEM analysis (2-3 weeks, ongoing)
o Specifically blade behavior in response to a movement of the
actuators needs to be investigated, blades are not rigid bodies
o Establish the amplitudes of oscillation that are to be expected
during a pitching maneuver
o Determine acceptable levels of angular acceleration during
pitch manuevers
● Positioning of LEPD diodes will need to be optimized based on the
expected amplitudes (~2 weeks)
● Control system needs to be designed based on FEM response
analysis (~3 weeks)
o Demonstrate a working Simulink model of controller that
encorporates blade dynamics
Project Overview
Blade Behavior and Controller
Requirements
Vacuum Chamber
Requirements
Summary
● Selection of a pump and appropriate means of mounting the
controller for the vacuum test chamber (1 week)
● Detailed design of blade housing, including deconstruction into
machinable parts (1-2 weeks)
Project Overview
Blade Behavior and Controller
Requirements
Vacuum Chamber
Requirements
Summary
● Modeling techique from Daniel
Guerrant and Dale Lawrence
● Assumes no material/structural
damping
● The membrane in between the
elements are mass-less
● Experimental results have shown
good correlation with this FEM
theory
Source:Heliogyro Solar Sail Blade Twist Stability Analysis of
Root and Reflectivity Controllers
● CubeSat deployed after
launch
● Blades are deployed
● Blades are pitched to a
commanded angle by an
actuator for a maneuver
● Sensors detect the
current mode of the
solar sail
● Actuators move in order
to dampen the blades

𝐹 = 𝑚𝑎


𝑚 = 𝑚ℎ𝑜𝑢𝑠𝑖𝑛𝑔 + 𝑚𝑏𝑙𝑎𝑑𝑒 = 810 + 282 = 1092 𝑔
𝑣 𝑡 = 𝑣 0 + 𝑎𝑡

𝑎=


𝑣 𝑡
𝑡
Find t using frequency given since f = 1/sec
𝑎 = 𝑣 𝑡 𝑓 −1

𝜏 = 𝐼𝛼

Ι𝑡𝑜𝑡𝑎𝑙 = Ι1 + Ι2 + Ι3 + Ι4 = 73760

𝜃 𝑡 = 𝜃 0 + 𝜔 0 𝑡 + 𝛼𝑡 2

𝜋
4

𝛼 = 0.001745

Type equation here.
𝜏 = 73760 ∗ 0.001745 = 0.01287 𝑚𝑁 ∙ 𝑚

𝑔
𝑐𝑚2
1
2
1
2
= 𝛼(30)2 (rotate 45 degrees in 30 seconds)
rads
sec
Need to select motor with v >= fd
● The rotary actuator must be able to pitch the blade ±90 degrees
and provide torsional damping. Requires calculation of rotational
torque: τ = Ια
● I is the moment of inertia about the the blades pitching axis. This
inertia is composed of the aluminum housing,the deployed blade,
its spool, and tip mass.
o Ιtotal=Ι1+I2+Ι3+Ι4
● α is the angular velocity needed from the motor in order to provide
sufficient damping in the required time frame. Function of blade
mode frequency.
Expect to see oscillations with frequency 𝑓 = 0.23 𝐻𝑧
Frequency is a function of actuator velocity and traveled distance 𝑓 =
𝑣
𝑑
Need to select motor with v >= fd
=
𝑐𝑦𝑐𝑙𝑒
𝑡𝑖𝑚𝑒
How LEPD’s Work (cont.)
•
•
•
•
Pitching and flapping modes are vertical
displacements
Change vertical displacement into a parameter to
sense
Make sure sensor chosen has a large enough
active area
SPOT-4D, 1.61 mm2; 9D, 19.6 mm2; UDT 4x4
Array 1.96 mm2
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDoQFjAC&url=http%3A%2F%2Fwww.osioptoelectronics.com%2FLibraries%2FProduct-DataSheets%2FQuadrant-Bi-Cell-Photodiode.sflb.ashx&ei=DFk3VO6aEYityASoqILwDg&usg=AFQjCNESjr7cFeEAVMDHuVhearmslzNZqw&bvm=bv.77161500,d.aWw
Density vs. Height
7
x 10
4
Density vs Height
Pressure vs Height
1
0.8
5
Density (kg/m3)
Pressure (N/m2)
6
4
0.6
0.4
3
0.2
2
1
0
0.5
1
Height (m)
1.5
2
x 10
4
0
0
0.5
1
Height (m)
1.5
2
x 10
4
● Maximum deflection of 1 to 1.25mm
● High level of precision, dependent on
voltage divisions, on order of nm
● Rise time on order of milliseconds
● Weight of 10g, volume of 300 mm3
● Cost from $200 to $500, depending on
included wiring, mounting, displacement,
etc.
● Require ±60-100V
● Displacement tolerance of ±15-20%
Piezoelectric bending actuators
(source: piezo.com)
●
●
●
●
●
●
●
●
Rotational motor would not provide damping
Bending actuators move in phase to damp flapping
Actuators move in opposite phase to damp twisting
Use LEPD to sense disturbances
Benefit of being less massive than stacked actuators
Similar cost
Less possible displacement
Increased complexity










Pump
10” Clear PVC Pipe (probably needs adjusted down)
GoPro or other camera to put inside to take video if “clear” is not
enough to see the blade’s behavior
LED’s to put inside to light chamber, if needed, to take video
PVC cap, used to mount SPECTRE
PVC Cement (UNI 1500-08)
Reducer from 10” to 4”
4” Suction hose
Second reducer from 4” to 3/4”
Additional fittings if needed to interface with the pump
● Epoxy can be used to seal holes needed for wiring.
o Various epoxies capable of 10-9 torr (less than 1 Pa) (Lesker)
● Adds ~$100 to vacuum chamber cost
● Removes need for wireless control and battery power, reducing cost
● Either clear PVC in sections, or use camera and lighting within
chamber
● Pressure gauges
Source:Heliogyro Solar Sail Blade Twist Stability
Analysis of Root and Reflectivity Controllers
Source: Wilkie, William K., et al. "Recent Progress in Heliogyro Solar Sail Structural Dynamics." (2014).