1. University of Arizona Student Satellite Project “UASat”
Spring 2000 Formal Review
April 27, 2000

2. 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

3. 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

4. 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 self-confidence & 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
Perhaps we could mention something relating to the “GTEC Vision” right here?

5. UASat Mission Sprite & Lightning Detection Photometry of Bright Stars
Laser Communication Experiment

6. 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 self-confidence & 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
Perhaps we could mention something relating to the “GTEC Vision” right here?

8. 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 self-confidence & 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
Perhaps we could mention something relating to the “GTEC Vision” right here?

9. SSP needs the support from the four vertices:
UA, Local Community, Industry, & Gov’t
Human resources
Space & facilities
Operational Support
SpaceGrant UA
SSP
Internship.
Components
Sub-systems
Technical expertise
Testing facilities
HES launch
NASA
NSF
Industry
Curriculum development
Local Community
Scholarships, Mentorships, Donations
KCH21.VI.1998

10. Criteria for Success Minimum Criteria Ultimate accomplishment
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.

11. 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

12. Management (Cont.) Project Mentors SI Mentor Administrative Mentor
Dr. K. C. Hsieh, Physics
Dr. Hal Tharp, ECE (sabbatical)
SI Mentor
Dr. Terry Bahill, SIE
Administrative Mentor
Susan Brew, SpaceGrant

14. 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)

15. 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)

16. 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?

17. 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)

18. 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?

19. How to Contact SSP SSP HQ Phone Email: World Wide Web
Physics and Atmospheric Sciences, Room 569
Phone
(520)
World Wide Web

20. “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.
Endorsement from Peter Likins, President of the University of Arizona.

21. 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

22. UASat: Guidance, Navigation, and Controls Presented by Brian Shucker and Martin Lebl

23. GNC Team Members Team Members: Greg Chatel (AME) Marissa Herron (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)

24. 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 ability to perform groundstation tracking slew maneuver
Power Generation
requires attitude knowledge with respect to Sun
Three axis control required

25. Sensors Sensors Used Sensor Measurement Rates
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

26. Extended Kalman Filter Block Diagram
-- Discrete Measurement Updates
-- Continuous Dynamic Propagation Models t k
In from
instruments u
Out to
controller
State
Model t
State
Update
i.c.
Gain
Update t k
Covariance
Update u
Covariance
Model t
i.c.

27. The Kalman Filter State Variable: Measurement Updates
Gain Matrix:
State Update:
Covariance Update:
Dynamic Propagation Between Measurements
Data from rate gyros will be numerically integrated
Equations of motion are excluded to simplify the analysis

28. Magnetometer Advantages: Disadvantages:
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

29. GPS board – Space Rated Space rated board Advantages:
Proven Heritage Design
Radiation Hardened
Disadvantages:
Expensive

30. 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.)

31. 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

32. Coarse Sun Sensor Advantages: Disadvantages: Inexpensive design
Very low power
Disadvantages:
Only works on the sun side
Only useful for determining the sun vector for power generation

33. Current Status Theory Sensor models are not complete Matlab Code
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

34. 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.

35. 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

36. 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

37. Kinematics Satellite x y W w n z i h Direction of Perigee
Vernal equinox
Line of Nodes
Satellite x y W w n z i h

38. Attitude Control: Reaction Wheelsx
e1,rw
e2,rw
e3,rw
e4,rw z
Set of 4 miniature reaction wheels used for primary control y

39. Controller Block Diagram
Dynamics and
State Estimation
Wheel Speed
Management
Model-based
Compensation
Viscous
Term
Pseudo
Inverse
Elastic +

40. 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

41. Coil Design Formulae Moment equation: Mass and wire size:
Power, current, voltage and resistance:

42. Total Mass vs. Power Consumption
Design Optimization
Total Mass vs. Power Consumption
Specifications
Dipole moment of Am2
Power consumption of 0.3 W
16 mA at 20 V
Uses 32 gauge square magnet wire
Total mass of 3 kg
mass [kg]
Power [watts]

43. Mounting Possibilities
Two ideas
Designed to fit within side beam
Wrapped into groove on exterior of satellite
Three coils form mutually perpendicular axes

44. 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.

45. Theory
Dipole moment calculations
Need and efficiency calculations

46. Conditions for Torquer Activation
Need
Start Conditions
Detumbling
HMax
Start
Stop Condition
HStop
Stop H0
Velocity Restriction
BStop
BMax
Efficiency

47. 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.

48. 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).
Explain that the simulations are realistic

49. Ground tracking maneuver

50. Telescope axis pointing error
200
400
600
800
1000
1200
0.5 1
1.5 2
2.5 3
3.5 4
4.5 5
x 10 -3
Pointing error (degrees)
Time (s)

51. Reaction wheel torques-3
200
400
600
800
1000
1200 -1 1
x 10 1
Reaction Wheel Torques (Nm)
Time (s)

52. Reaction wheel speeds Reaction Wheel Speeds (rpm) Time (s) 1000 900
800
700
600
Reaction Wheel Speeds (rpm)
500
400
300
200
100
200
400
600
800
1000
1200
Time (s)

53. 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,

54. Magnetic Moment X Y Z Time(s) -5 5 -5 5 -5 5 12000 6000 8000 100005 X -5 5 Y -5 5 Z
Time(s)
12000
6000
8000
10000
4000
2000

55. Reaction Wheel Momentum
Time(s)
12000
6000
8000
10000
4000
2000
HRWA
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9

56. Spacecraft Body Momentum
Time(s)
12000
6000
8000
10000
4000
2000
Hbody
0.2
0.4
0.6
0.8
1.0
1.2
1.4

57. Total Momentum Htotal Time(s) 12000 6000 8000 10000 4000 2000 0.2 0.4
0.6
0.8
1.0
1.2
1.4

58. Questions? Comments?

59. 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