University of Arizona
Student Satellite Project
“UASat”
Spring 2000 Formal Review
April 27, 2000
Purpose of Spring 2000 Review
• End of Semester Review of SSP
• Preparation for UASat Preliminary Design
Review (PDR)
– Gathering Team-Level Information
– Provide System-Level Overview
– Seek Advice and Guidance
Presentation Schedule
•
•
•
•
•
•
•
•
•
5:00- Project Manager Overview & Introduction
5:20- Science
5:50- Laser Communications
6:10- Guidance, Navigation & Control
6:30- Break
6:40- Systems Integration
7:00- Mechanical, Structures & Analysis
7:20- Data & Command Handling
7:40- Power Generation & Distribution
Purpose of SSP
1. A hands-on experience through team work on a complex
system with an objective
2. A needed channel for many students to gain selfconfidence & employable skills
3. An example of intercollegiate, inter-departmental, and
interdisciplinary collaboration
4. An avenue to enhance beneficial interactions among
university and community
5. A test-bed for innovative ideas in a wide variety of areas
UASat Mission
• Sprite & Lightning
Detection
• Photometry of Bright
Stars
• Laser Communication
Experiment
Purpose of SSP
1. A hands-on experience through team work on a complex
system with an objective
2. A needed channel for many students to gain selfconfidence & employable skills
3. An example of intercollegiate, inter-departmental, and
interdisciplinary collaboration
4. An avenue to enhance beneficial interactions among
university and community
5. A test-bed for innovative ideas in a wide variety of areas
S TUDE NT DIS TRIB UTION C HART
S ummary
as of D ecember 20, 1999
Total
Uns pecified
Fres h
Aeros pace E ngineering
1.0
2.0
As tronomy
-
Atmos pheric S ciences
S oph
P ercentage
Junior
S enior
Grad (by major) (of total)
-
2.0
3.0
-
8.0
11.3
6.5
0.5
1.0
1.0
-
9.0
12.7
-
2.0
-
-
-
-
2.0
2.8
Biomedical E ngineering
-
-
-
-
-
1.0
1.0
1.4
C hemis try
-
-
-
-
1.0
-
1.0
1.4
C omputer E ngineering
-
-
-
2.0
1.0
-
3.0
4.2
C omputer S cience
-
0.5
-
1.5
2.0
-
4.0
5.6
E lectrical E ngineering
-
-
2.0
1.0
2.0
-
5.0
7.0
E ngineering P hys ics
-
2.0
1.0
-
-
-
3.0
4.2
Materials S cience and E ngineering
-
-
-
-
1.0
-
1.0
1.4
Mathematics
-
-
-
0.5
-
-
0.5
0.7
Mechanical E ngineering
-
1.0
-
3.0
1.0
2.0
7.0
9.9
Media Arts
-
1.0
-
-
-
-
1.0
1.4
Nondegree
-
-
-
-
-
1.0
1.0
1.4
O ptical E ngineering
1.0
-
-
1.0
3.0
1.0
6.0
8.5
P hys ics
-
7.0
0.5
1.0
1.0
-
9.5
13.4
S ys tems and Indus trial E ngineering
-
-
-
-
-
1.0
1.0
1.4
Uns pecified
5.0
2.0
-
-
1.0
8.0
11.3
Total (by clas s s tanding)
7.0
24.0
4.0
13.0
17.0
6.0
P ercentage (of total)
9.9
33.8
5.6
18.3
23.9
8.5
s tudents
active in S S P
71.0
Purpose of SSP
1. A hands-on experience through team work on a complex
system with an objective
2. A needed channel for many students to gain selfconfidence & employable skills
3. An example of intercollegiate, inter-departmental, and
interdisciplinary collaboration
4. An avenue to enhance beneficial interactions among
university and community
5. A test-bed for innovative ideas in a wide variety of areas
SSP needs the support from the four vertices:
UA, Local Community, Industry, & Gov’t
Human resources
UA Space & facilities
Operational Support
SpaceGrant
SSP
HES launch
Internship.
Components
Industry Sub-systems
Technical expertise
Testing facilities
NASA
NSF
Curriculum development
Local Community
Scholarships, Mentorships, Donations
KCH21.VI.1998
Criteria for Success
• Minimum Criteria
– Continuous flow of graduates with experience.
• Ultimate accomplishment
– Delivery of UASat for NASA launch and
successful operation in flight, followed by
scientific and technological return.
Management
• Project Manager- Jon Alberding, BME
• Recruiting, Fundraising, Resources, Administration,
Systems Integration & Intra-Team Communication
• Project Assistant- Ether Adnan, MIS
• Project Communication, Administration,
Account Management
• System Engineer- Christiano Adabi, SIE
• System Documentation
• Interfaces
• Budgets
• Design Database
Management (Cont.)
• Project Mentors
– Dr. K. C. Hsieh, Physics
– Dr. Hal Tharp, ECE (sabbatical)
• SI Mentor
– Dr. Terry Bahill, SIE
• Administrative Mentor
– Susan Brew, SpaceGrant
Project Manager
J. Alberd ing
Evaluation & Selection Panel
R. Lorenz & members
Systems Mentor
T. Bahill
Systems Engr.
C. Abadi
Project Mentor
K. C. Hsieh
Admin. Assistant
Ether Adnan
Admin. Mentor
S. Brew
Mission Advisory Pool
L.Broadfoot & members
Leader
M. Hay
Mentor
C.Weidman
SC1
Team
Leader
D. Sing
Mentor
U. Fin k
SC2
Team
Leader
A. Valenzuela
Mentor
W. Wing
LCS
Team
SSP org chart as of 26 April 2000
Leader
K. Chugh
Mentor
J. D.
Carothers
DCH
Team
Leader
B. Shucker
Mentor
E. Fasse
GNC
Team
Leader
D. Klea.
Leader
W. Chee
Mentor
L. Schooley
Mentor
A. Witulski
TTC
Team
PGD
Team
Leader
W. Null
Mentor
W. Chen
MSA
Team
Current UASat Schedule
• Requirements Review (Completed 8/18/98)
• Preliminary Design Review (Late ‘00,
Early ‘01)
• Critical Design Review (Spring ‘02)
• Mission Readiness Review (Fall ‘03)
• Delivery to NASA (Spring ‘04)
UASat PDR Preparation
• Program Management
group works with Teams
• Program Management
group forms Preliminary
Gantt chart
• Negotiate Final Schedule
(TL, Mentor, PM, SE)
• Teams review IMAGE
PDR
• Teams review PDR
outlined by System
Engineer/Project Manager
• Negotiate Final Schedule
(TL, Mentor, PM, SE)
Management-Level PDR
Requirements
• Risk Management
– Schedule Control
• No real means of control
– Need for Risk Mitigation Strategy
• Technical Oversight Group
• Better Communication about Schedule Slip
• Quantitative Evaluation of Schedule
Performance
• What To Do If Slippage Occurs?
Management-Level PDR Requirements
• Cost Control
– Inherent Controls
• Student Project
• Students Build Some
Components/Subsystems
– Knowledge of Actual Costs for Bought Items
– Cost Tracking Strategy & Plan for When Reserves
Utilized
• Descoping
– Decision Tree, Options & Consequences
• Performance Assurance Implementation Plan
(PAIP)
Questions on Management
• How to retain Lower-Division Students?
• How to have a Risk Mitigation Strategy
with limited resources & maintaining
Educational Requirements?
• How to acquire needed resources?
• How to formulate a plan to cost-effectively
acquire needed components?
• How to implement a PAIP?
How to Contact SSP
• SSP HQ
– Physics and Atmospheric Sciences, Room 569
• Phone
– (520) 621-2574
• Email:
– ssp-admin@uasat.arizona.edu
• World Wide Web
– http://uasat.arizona.edu
“The Student Satellite Project at the University of Arizona is the best evidence
I have discovered anywhere of the creative initiative of Americans committed
to the Space Program, which has been an important part of my life for forty
years.
When I joined JPL as a young engineer in 1958, soon after the launch of
America's first satellite, the adventure of space exploration had captured the
imagination of young people all over America, and there was no bureaucracy
to slow us down. The new NASA in 1998 recognizes the importance of
youthful energy and innovative capacity, and welcomes such initiatives as the
SSP. This is a very exciting development, heralding as new day for both
NASA and our students. They have done their part, with the encouragement of
the University of Arizona. Now it is time for the community to step up to the
challenge of demonstrating that all of Arizona stands behind this incredible
initiative of the young men and women of the SSP who are reaching beyond
the skies.”
Peter Likins, June 17, 1998.
Presentation Schedule
•
•
•
•
•
•
•
•
•
5:00- Project Manager Overview & Introduction
5:20- Science
5:50- Laser Communications
6:10- Guidance, Navigation & Control
6:30- Break
6:40- Systems Integration
7:00- Mechanical, Structures & Analysis
7:20- Data & Command Handling
7:40- Power Generation & Distribution
UASat: Guidance, Navigation,
and Controls
Presented by Brian Shucker and Martin Lebl
http://uasat.arizona.edu/gnc
GNC Team Members
Team Members:
• Greg Chatel (AME)
•
• Barry Goeree (AME)
•
• Andreas Ioannides (Phys) •
• Gregg Radtke (ME)
•
Team Mentor:
• Dr. Fasse (AME)
Marissa Herron (AME)
Martin Lebl (CSc)
Brian Shucker (CSc/Math)
Roberto Furfaro (AME)
GNC Subsystem Requirements
• Science and Technical Objectives
– Lightning and Sprite observation
• requires attitude knowledge with respect to Earth
• requires horizon pointing
– Stellar Photometry
• requires attitude knowledge with respect to the stars
• requires inertial pointing
– Laser Communication System
• requires attitude knowledge with respect to Earth
• requires ability to perform groundstation tracking slew
maneuver
– Power Generation
• requires attitude knowledge with respect to Sun
• requires inertial pointing
• Three axis control required
Sensors
• Sensors Used
– Attitude Sensors:
Magnetometer, Coarse Sun
Sensor
– Spatial Sensor: GPS
– Rate Sensor: Integrating Rate
Gyros
• Sensor Measurement Rates
– Power vs. Accuracy Trade-Off
– Optimization Technique TBD
Extended Kalman Filter Block Diagram
-- Discrete Measurement Updates
tk
-- Continuous Dynamic Propagation Models
z
In from
instruments
x
x ()
Gain
K
P () Update
k
( )
State
Update
x
k
( )
u
t
State
Model
x
x
k
( )

Out to
controller
i.c.
k
k
tk
k
x ()
P ()
k
k
Covariance  ( )
Pk
Update
u
t
Covariance 
P
Model
P
k
( )

i.c.
P
k
x
k
The Kalman Filter
• State Variable:
• Measurement Updates
T
T
– Gain Matrix: Kk  Pk ( ) H k [ H k Pk ( ) H k  Rk ]
– State Update: xˆk ()  xˆk ()  K k [ zk  h( xˆk ())]
– Covariance Update: Pk ()  [ I  K k H k ]Pk ()
• Dynamic Propagation Between Measurements
– Data from rate gyros will be numerically integrated
– Equations of motion are excluded to simplify the analysis
Magnetometer
• Advantages:
– Can be used throughout orbit (sunside and
darkside)
– Low power
– Relatively affordable sensor
• Disadvantages:
– Cannot be used with the magneto torquers on
– Only so much precision can be achieved using
it
GPS board – Space Rated
• Space rated board
– Advantages:
• Proven Heritage Design
• Radiation Hardened
– Disadvantages:
• Expensive
GPS board -- Terrestial
• Terrestial board
– Advantages:
• Relatively Inexpensive
– Disadvantages:
• Needs modification to the firmware by
manufacturer
• May need Radiation shielding depending on
where it is mounted
• Obviously still non-heritage design (only
flew on ASUSAT, but never been turned on
before ASUSAT expired.)
Coarse Sun Sensor
• Sensor implemented using the solar panels,
and additional photo diodes to give
complete coverage.
• Only a course sensor for the power
generation mode
Coarse Sun Sensor
• Advantages:
– Inexpensive design
– Very low power
• Disadvantages:
– Only works on the sun side
– Only useful for determining the sun vector for
power generation
Current Status
• Theory
– Kalman Filtering is understood
– Main reference: Lefferts, Markley and Shuster (1982)
• Sensor models are not complete
• Matlab Code
– Most equations are coded
– Integration with other modules
• Documentation
– Tech. Note
Current Endeavors
• Finish sensor modeling (h(), H)
• Further develop & test Matlab code
– Get it running and integrated with other systems
– Refine estimates to get more realistic numbers
– Generate plots and graphs to obtain pointing
accuracy
• Look into what would deployable solar
panels allow us to do in terms of additional
sensors, and what changes to the current
design would it necessitate.
Open Issues & Concerns
• Can we meet the accuracy requirements?
– We won’t know until the simulation is complete.
– Possibilities for improving accuracy
• Add sensors: GPS attitude estimation system
(GPS Compound Eye), low power Star tracker
• Adjust sensor rates
• Change the dynamic model to include
equations of motion
What if we go to deployable solar
panels ?
• Need the Coarse Sun Sensor to be
implemented solely by photo diodes
• Have enough power for additional sensors:
– GPS compound eye:
• Works both sunside and darkside
– Low Cost Start Tracker
• Greatly increases our pointing accuracy
Kinematics
frame
Earth-Centered Inertial (ECI)
Earth-Fixed Frame (ECF)
Orbit Frame (ORB)
Spacecraft Frame (SCF)
Desired Frame (D)
origin
center of Earth
center of Earth
center of Earth
c.m. of satellite
c.m. of satellite
z-axis
celestial pole
celestial pole
orbit normal
telescope axis
h
Inclination
Altitude
Right ascending node
Argument of perigee
Eccentricity
Orbit period
i
51.6º
407 km
W TBD
w 0
e 0
92.7 minutes
i
x-axis
mean equinox
prime meridian
ascending node
first side panel
z
Satellite
n
W
x
Vernal equinox
w
Direction
of Perigee
Line of
Nodes
y
Attitude Control: Reaction Wheels
• Set of 4 miniature reaction
wheels used for primary
control
e2,rw
e4,rw
z
e3,rw
x
y
Rotor inertia
Max speed
Max torque
Electr. losses
Viscous friction
Coulomb friction
Motor efficiency
Torque gain
RW1
0.6387
8000
7.4
1.7708
0.3305
0.3045
0.9
0.95
RW2
0.6710
8000
7.4
1.7708
0.3827
0.2896
0.9
1.08
RW3
0.6194
8000
7.4
1.7708
0.3653
0.2747
0.9
0.91
RW4
0.6581
8000
7.4
1.7708
0.3131
0.3195
0.9
1.09
e1,rw
-3
2
10 kg m
Rpm
-3
10 Nm
W
10-6Nms/rad
-3
10 Nm
Controller Block Diagram
A
A
eci
d
eci
sc
wscf
d
w
scf
sc
Elastic
Term
Viscous
Term
 scf
w
d
 scf
el

+
+
 scf
sc
rwf

Pseudo sc
Inverse
+
 rw
Dynamics and
State Estimation
wrw
 wsm
scf
visc

scf
mdl
Model-based
Compensation
wscf
sc
Wheel Speed
Management
wrw
w rw, d
A sceci
Magnetic Torquers
• Student designed and built
• Used for momentum dumping and
detumbling
• Free-air coil design selected
– Simplest, least costly design
– Linear response to input current simplifies
control requirements.
– Possible issues with stray magnetic fields
• Three required
Coil Design Formulae
• Moment equation:
• Mass and wire size:
a  Na0
2 3

M  Na0
  4

• Power, current, voltage and resistance:
m2   
2
P  i R  
 
M  A
i
m a 0   
 
M  A
2
V
m   
 
a0  A 
N
R
a0
Design Optimization
Total Mass vs. Power
Consumption
• Specifications
30
20
mass [kg]
– Dipole moment of
5 Am2
– Power consumption
of 0.3 W
• 16 mA at 20 V
– Uses 32 gauge square
magnet wire
– Total mass of 3 kg
10
0
0
0.5
1
1.5
Power [watts]
2
Mounting Possibilities
• Two ideas
– Designed to fit within
side beam
– Wrapped into groove on
exterior of satellite
• Three coils form
mutually perpendicular
axes
Momentum Dumping Control
Algorithm
• The approach is to consider both the need
and efficiency of dumping at a particular
time.
• Use change in angular momentum to
estimate direction of the earth’s magnetic
field in the absence of magnetometer
reading.
Theory
• Dipole moment calculations
• Need and efficiency calculations
Conditions for Torquer Activation
• Start Conditions
Need
HMax
• Stop Condition
Detumbling
Start
HStop
Stop
• Velocity Restriction
H0
BStop BMax
Efficiency
Current Status
• Have opted for a torque coil design
• Remaining hardware work is in mounting
details.
• Need to purchase or build amplifiers
• Some fine tuning of momentum dumping
control constants may be necessary.
Attitude Control Simulations
•
•
•
•
Attitude dynamics and orbital kinematics are simulated.
Magnetic field is modeled
The control laws are sampled at 4Hz.
The aerodynamic drag torques are modeled. Solar pressure,
gravity gradient and residual magnetic moment are not
modeled.
• The reaction wheels models include: Coulomb and viscous
friction, limited torque capability (7.4·10-3 Nm),
misalignment (4o), uncertainty in gain (10%) and
uncertainty in inertia (4%).
• The satellite core model includes: uncertainty in the
moments of inertia (5%) and principal axes of inertia (4o).
Ground tracking maneuver
Telescope axis pointing error
x 10
-3
Pointing error (degrees)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0
200
400
600
Time (s)
800
1000
1200
Reaction wheel torques
Reaction Wheel Torques (Nm)
x 10
-3
1
0
-1
1
0
200
400
600
800
1000
1200
0
200
400
600
800
1000
1200
0
200
400
600
800
1000
1200
0
200
400
600
800
1000
1200
0
-1
1
0
-1
1
0
-1
Time (s)
Reaction wheel speeds
Reaction Wheel Speeds (rpm)
1000
900
800
700
600
500
400
300
200
100
0
0
200
400
600
Time (s)
800
1000
1200
Detumbling/Momentum Dumping
Detumbling Algorithm:
• Want K.E. to decrease,
which happens when
• This condition is satisfied
with
• Since change in B is due to
spacecraft rotation,
Magnetic Moment
5
X
0
-5
5
Y
0
-5
5
Z
0
-5
2000
4000
6000
Time(s)
8000
10000
12000
Reaction Wheel Momentum
0.9
0.8
0.7
0.6
HRWA
0.5
0.4
0.3
0.2
0.1
2000
4000
6000
Time(s)
8000
10000
12000
Spacecraft Body Momentum
1.4
1.2
1.0
Hbody
0.8
0.6
0.4
0.2
2000
4000
6000
Time(s)
8000
10000
12000
Total Momentum
1.4
1.2
1.0
Htotal
0.8
0.6
0.4
0.2
2000
4000
6000
Time(s)
8000
10000
12000
Questions? Comments?
Presentation Schedule
•
•
•
•
•
•
•
•
•
5:00- Project Manager Overview & Introduction
5:20- Science
5:50- Laser Communications
6:10- Guidance, Navigation & Control
6:30- Break
6:40- Systems Integration
7:00- Mechanical, Structures & Analysis
7:20- Data & Command Handling
7:40- Power Generation & Distribution