1. Preliminary Design Review
A&AE 490 Satellite
Purdue CubeSat
Preliminary Design Review
December 8, 2004
Good afternoon and welcome to the AAE 490 Satellite – Purdue CubeSat – Preliminary Design Review.

2. Project Engineer – George Pollock Faculty Advisor – Prof. David Filmer
My name is George Pollock and I am the Project Engineer for the CubeSat team. I would also like to introduce Prof. David Filmer, the team’s faculty advisor. On behalf of Prof. Filmer, myself, and the entire CubeSat team, welcome.

3. To begin today’s presentation, I will offer some background information about the CubeSat program. The CubeSat program is jointly coordinated by Cal Poly and Stanford Universities. It offers research institutions worldwide an unprecedented opportunity to develop and launch small picosatellites. The CubeSat program provides integration and launch coordination and uses a common Cal Poly-developed deployment platform. Participation in this standardized program removes many burdensome tasks from participating teams, allowing us to focus our energies on designing and building the satellite.

4. Poly Picosat Orbital Deployer (P-Pod)
Interface between CubeSat and LV
Reliable on-orbit deployment
Separation and low spin rate
The Poly Picosat Orbital Deployer (or P-Pod) has been developed by Cal Poly for use as the standard deployment platform for all CubeSats. The P-Pod is a square tube, which holds three CubeSats stacked upon one another. The satellites are spring-loaded and the door is latched until on-orbit deployment. The spring plunger and guide rails along the P-Pod’s length provide a predictable, linear deployment with low initial spin rate. Achieving adequate separation from the upper stage and minimizing spin rate are two critical tasks that the P-Pod reliably performs. The design of the Purdue CubeSat must satisfy P-Pod specifications as well as other CubeSat program requirements.

5. System Level Requirements
CubeSat Guidelines:
No interference
Space debris
Clean deployment
Power off for integration and launch
Mass ≤1kg
C.M. within 2cm of geometric center
Structure: P-Pod interfacing requirements
P-Pod cannot be used to constrain deployables
Operations requirements
This slide offers an outline of key system level requirements from the CubeSat program. The satellite may not interfere with other CubeSats or primary payloads. It may not generate any space debris and must be designed to deploy smoothly from the P-Pod without jamming. Power must remain off during all phases of integration and launch—to avoid RF or electrical interference with the launch vehicle and primary payloads. Total system mass can be no greater than 1 kg, and the center of mass must be located within 2cm of the satellite’s geometric center. The structure must comply with a list of P-Pod interface and size tolerances. Deployable systems such as antennae and gravity gradient booms may not be constrained by the P-Pod. Several requirements, including time delays for both the release of deployable devices and the power-up of communication systems will dictate mission operations.

6. System Level Requirements
PURDUE CubeSat MISSION OBJECTIVES
SCIENCE:
Measure radiation environment on orbit
Record and transmit radiation data
ENGINEERING:
Achieve passive attitude stabilization in nadir orientation
Demonstrate limited active attitude control (can be open loop)
In addition to the requirements given by Cal Poly, the Purdue CubeSat team has developed a list of mission objectives to focus the design effort. The science objectives are to sample the radiation environment on the satellite’s circular, polar orbit at km altitude and to record and transmit this data to a ground station at Purdue. As this is Purdue’s first satellite, the engineering objectives will pave the way for future satellites by accomplishing fundamental attitude control objectives. The two primary goals are to achieve passive attitude stabilization in a nadir orientation, and to perform limited active attitude control (which can be open loop in nature). These top-level science and engineering objectives have been flowed down to the subsystem level this semester, and each of six subsystems contribute to successfully accomplishing these goals.

7. Subsystems Structures Payload Attitude Dynamics and Control Systems
Communications
Computer
Power
The six CubeSat subsystems are listed here in the order they will present today. Structures, Payload, Attitude Dynamics and Control Systems, Communications, Computer, and Power. Following the presentation of the Power subsystem, we will open the floor to any questions the audience has for our team.
At this time, I would like to introduce the one-man structures team, Mr. Michael Carpenter.

8. Structures Overall Goal Model general structure, and components
Coordinate with other subsystems
Adjust structure, and components to meet design requirements

9. Structures Modeling Create a CATIA model of the structure
Create models of subsystem components

10. Structures Coordination with other subsystems
Component sizes and masses
Location of components
Met with members of each subsystem to determine where components could and couldn’t be placed

11. Structures Meet Requirements
Satellite center of mass, total mass, and volume requirement
Determined the best location and size of the different components
All structural frequencies must be greater than 20 Hz

12. Structures General Layout General sizes and shapes of components
Location of components

13. Mass Budget

14. Structures Further Work
Eliminate some of the assumptions in the center of mass code.
Create a more detailed structural model.
Verify that the structural frequencies are all above 20 Hz

15. Payload
Joshua Siler
Radiation Detector Selection
Charles Weaver

16. Overview Mission Criteria Detect number of charged particles
Detect power level of charged particles
Criteria
Particle Detection Range
Desired: 1keV to 15keV
Size (l x w x h)
Mass

17. Candidates Amptek MD-501 Stanford University CubeSAT system
Detection range: 0.1keV to 100keV
System size: 82.6 x 57.2 x 19 mm
Power Usage: .3 Watts
Stanford University CubeSAT system
Detection range: 4keV to 100keV
System size: 30 x 35 x 9 mm
Power Usage: 60 mW

18. Selection Stanford University System Pros Cons
Best particle detection range for our application
Smaller size
Lower power consumption
Better positioning flexibility in CubeSAT
Cons
Parts ordered separately
Build our own mounting structure

19. Picture

20. Picture
Signal Generator
Oscilloscope

21. Research Detector Selection started with Previous Semester's Work
Started By Familiarization with Aurora Formation and Earth’s Magnetic Field
Used The Exploration of the Earth’s Magnetosphere by Stern and Peredo as a valuable reference

22. Critical Issues Size Light rays swamping particle detector
Originally proposed system size was fixed
Our system has limited flexibility
Light rays swamping particle detector
Can be solved by placing an opaque barrier in front of detector
Alters lower bound of particle detection range

23. Future Goals Continue interfacing with computer team
Selection of light blocking barrier
Must meet CubeSAT structural standards
Must block out as little radiation as possible beyond visible light
Work with structures team to build mounts for CubeSAT

24. ADCS Subsystem The ADCS TEAM Team Member Responsibilities
Brienne Bogenberger
Team Leader
Whitney Jackson
Magnetic Field Model
Ryan Irwin
Attitude Determination/Simulation Code
Jackie Jaron
Sun Sensors
Angela Long
Gravity Gradient Boom Deployment

25. Overview Detailed look at the components of the ADCS subsystem
Magnetic Field modeling
Dynamical model
Attitude sensors
Will discuss
Current Status
Problems encountered and addressed
Work to be continued

26. Mission Plan Deployment from pod
Turn on electromagnets such that the satellite aligns with the Earth’s magnetic field
Deployment of communication antennas
Use sun sensor to determine which hemisphere the satellite is located above
Deployment of gravity gradient boom over magnetic north or south pole
Magnetic field strongest at poles
Magnetic field/electromagnet interaction will dampen effects of boom deployment torques
sun
+z face highlighted

27. Geomagnetic Field
Viewed as a dipole magnet with magnetic north pole deviating form north geographic pole by approximately 11 degrees

28. Geomagnetic Field Seven Parameters Declination, D Inclination, I
Horizontal Intensity, H (with north (X) and east (Y) components)
Vertical Intensity, Z
Total Intensity, F

29. Geomagnetic Field Geomagnetic Field significant to project because
Electromagnets aboard CubeSAT work to align with geomagnetic field, serving as an initial controller; electromagnetic field needed to do this is determined from knowing geomagnetic field intensities
Changes in declination of the field determines area over which gravity boom can be deployed
It provides significant torque that must be taken into account for CubeSAT’s attitude simulation
Data to acquire:
Declination: for use in determining proper location area for gravity boom deployment
Horizontal and Vertical Intensity components: for attitude simulation code and to find equivalent electromagnet currents

30. Methods to Determine Mathematical Model Online Calculator
International Geomagnetic Reference Field (IGRF)

31. Mathematical Model Several theses covering model as a dipole magnet
Benefits:
Approximation would be attained
Computer code would provide answers
Drawbacks:
Process exceptionally lengthy and tedious; much additional research is required for moderately accurate model
Other methods provide better accuracy

32. Online Calculator National Geophysical Data Center (NOAA) Benefits:
Exact (or nearly exact) data known within a certain timeframe
Drawbacks:
A complete data table would be too large for CubeSAT’s computer

33. IGRF International Geomagnetic Reference Field
Acceptable model created by International Association of Geomagnetism and Aeronomy, IAGA
Made up of set of Gauss coefficients provided by IAGA, updated every five years
Accurate to within 30 minutes; 200 nanotesla
Benefits:
Reasonable approximation
Easy to use in computer code when coefficients are known
Drawbacks:
Must update every five years

34. Geomagnetic Field Conclusions
IGRF most applicable for our purposes
Combined written code with mathematical functions coded by engineers at NASA Langley to provide field for given set of Keplerian elements

35. Geomagnetic Field Conclusions
Example:
Keplerian Elements:
a = km Ω = 45°
e = 0 ω = 30°
i = 80° M = 80°
Initial Condition: θ0 = 70°
Future Work:
Completely implement into attitude simulation code
Update Gauss coefficients in 2005

36. Purpose of Dynamics
Create tool that accurately simulates CubeSat dynamics for future design of boom and electromagnetic controllers
Establish a road map to allow evolution of simulation code to incorporate increasingly complex force and structural models
Assess means of determining attitude using various sensor systems

37. Motions of Interest Motion within orbit plane
Determine satellite orientation with respect to magnetic field
Motion with respect to sun
Determine CubeSat attitude
Motion with respect to ground station
Determine antenna pointing accuracy
Create necessary coordinate frames to evaluate these motions 1 3

38. Force Models Gravitational force Electromagnetic force
Distributed non-uniformly over CubeSat
Electromagnetic force
Interaction of current through coils with Earth’s natural magnetic field
Incorporate magnetic field model
Aerodynamic & solar disturbances
Neglect due to relatively small magnitudes

39. Predicting Dynamics Incorporate force models with attitude conditions
Incorporate inertial characteristics from structural model
Derive equations of motion of unsymmetrical satellite
Run simulations for given design and initial attitude conditions

40. Road Map Force Models Structural Models
Earth currently modeled as point mass
Need to account for oblateness
Only Earth magnetic field modeled
Need to account for on-board field due to electronics
Structural Models
Currently entire satellite modeled as rigid body
Need to account for flexibility of antennas and boom structures
Currently assuming principal directions coincide with planes of satellite casing
Need to update as CubeSat design changes

41. Attitude Sensors Magnetometer Initial concept from previous semesters
Measures magnetic field in three directions
Inappropriate for CubeSat needs
Used in the past for highly elliptical orbits to measure field variation with altitude
Purdue CubeSat in circular orbit
Magnetic variations too small for reliable attitude information
Requires storage of magnetic field ephemeris data

42. Attitude Sensor (con’t)
Position Sensitive Detector (PSD) & Diodes
Uses sunlight to directly determine orientation while magnetometer uses indirect field information
Used on previous satellites for similar purposes
Need to perform studies to determine number and placement of PSDs and diodes
Diodes
Pinhole
PSD
Film
CubeSat

43. Gravity Gradient Boom Boom Deployment Current Status Origin
Prototype built – 8.89 cm x 8.89 cm x .635 cm box
Testing deployment methods – release mechanism, boom material
Origin
Reduce torque produced by deployment
Try to create a spring-like force without using external hardware (motors, springs, etc.)
Other CubeSat’s used coil method (contingency plan)

44. Tape Measure Tape measure packed in a spring like form
Weight attached to the end and is held in place
Boom deployed when weight is released

45. Integration - Structure
Gravity Gradient Boom
Integration - Structure
Boom housing located in center of the satellite
Along z-axis
Critical Issues Addressed
Size of boom housing
Material to be used (measuring tape)
Self-contained deployment

46. Work To Do Remaining work Continued testing Length of boom
Permanent deformation (duration and temperature)
Spring constant (amount of torque produced)
Length of boom
Sizing of the weight
Integrating release mechanism with the computer team
Contingency plan

47. Communications Team Members Kyle Smith (Senior , AAE)
Anh-Thu Nguyen (Grad, AAE)
Kambiu Chan (Senior, EE)
Robert Fontaine (early resignation)

48. Communications Overview of entire system Component selection
Microcontroller
Transceiver
Operation of hardware & software
Link budget
Interfacing work
Issues resolved
Remaining work & Future goals

49. Communications Component Selection Microcontroller
Self-contained system with central processor
Easy to program
Reprogrammable

50. Communications Alinco DJ-C5T Dual Band Transceiver
Small dim. & light weight
Good frequency coverage
Low output power

51. Communications
Operation of Hardware

52. Communications Hardware TNC (Terminal Node Controller)
Modulates digital signals into analog signals and vice versa
Works like a human talking on a radio
Sending analog tone to mic in of the transceiver (Human talking to the mic)
Receiving analog tone from the speaker jack (Human listening to the speaker)
AX.25 communication protocol
Microcontroller based
2 separate TNC systems (1 for redundancy)

53. Communications Hardware Transceiver
Accepts analog signals from TNC and converts it into RF signals
Coordinates the input/output traffic in the system data bus.
Extracted from COTS 2 way radio product

54. Communications Hardware Duplexer Antenna
gives the antenna its dual band connectivity
144 Mhz (downlink) 440 Mhz (uplink)
Antenna
“Home made” dipole antenna from 4 pieces of measuring tape
Best choice for balancing reception power, size and price

55. Communications Hardware Antenna Turnstile operation
Dipole #1’s signal lags the diople #2’s signal by 90 degrees
Allow the satellite to have reliable communication with the station regardless of which side is facing the earth

56. Link Budget Spacecraft Transmitter Power Output: 0.3 watts In dBW:
-5.2
dBW
In dBm:
24.8
dBm
Polarization loss: -3 dB
S/C Connector, Filter or In-Line Switch Losses:
Very
Small
Spacecraft Antenna Gain:
16.8
dBiC
Spacecraft EIRP:
11.8

57. Link Budget Spacecraft Antenna Pointing Loss: Very Small
Antenna Polarization Loss:
Path Loss:
-133.8 dB
Atmospheric Loss:
Ionospheric Loss:
Rain Loss:
Isotropic Signal Level at Ground Station:
-124.7
dBW

58. Link Budget Ground Station Antenna Pointing Loss: Very Small
Ground Station Antenna Gain:
12.5
Ground Station Transmission Line Losses:
-1.6
G.S. Signal-to-Noise Power Density (S/No):
55.4
System Desired Data Rate:
1200
In dBHz:
30.8
Telemetry System Eb/No:
24.6
Telemetry System Required Bit Error Rate:
1.00E-06
Telemetry System Required Eb/No: 18
System Link Margin:
6.6

59. Communications Detail of current status Link budget draft complete
Components are selected
PIC ordered
Transceiver selected

60. Communications Critical issues that have been resolved Size Weight
Progress on link budget
Component selection

61. Communications Remaining Work Future Goals Finish up the firmware
Finalize the antenna Interfacing work
Data rate requirement
Allocating bandwidth for different modules
Determining the best sampling rate of different sensors and design & conduct RF power testing
Future Goals
Interfacing the module with the other systems

62. Computer Subsystem Computer Subsystem Team Members:
Avanthi Boopalan (AAE)
Kam Biu Chan (EE)
Guidance and Support:
Michael Maletich (ECE)

63. Computer Subsystem Overview Intra-Subsystem Communication
Attitude Control Chip
Sensors
Test and Debug

64. Computer Subsystem Intra-Subsystem Communication Subsystems use MCUs
MCUs need to Communicate
Ex. Time tracker
I2C Bus Protocol for Communication
I2C = Inter-Integrated Circuit
Basically two wires that connect chips
One data line, and one clock line
MCU = Microcontroller Unit or a Chip

65. Computer Subsystem Attitude Control Chip Chip with Autonomous Code
Very Important – Starts the Cubesat
Communicates with the sensors to determine attitude
Deploys Boom
Evaluates stability criteria
Based on conditions, deploys boom

66. Intra-Subsystem Communication
Computer Subsystem
Current Work
Intra-Subsystem Communication
Prototyping board with parts
Reading Material
Attitude Control Chip
Library Functions
Meeting with the team

67. Computer Subsystem Sensors Sun sensors, Temperature sensors Conversion
Calibration
Communication

68. Computer Task Accomplished Components selection
System Architecture re-design
Module Firmware design
Attitude Control Team
Sensor Team
Inter system communication testing
Hardware wiring

69. Computer
Components Selection
System Platform
Programming language

70. Computer PIC16F877 AT91R40807 PRO CON Components selection CPU
2 choices
PIC16F877 VS AT91R40807
PIC16F877
AT91R40807
PRO
Simple and user friendly
Designed for autonomous control
Better performance
CON
Size
No Analog to Digital Converter
Cost

71. Computer Basic C PRO CON Components Selection Programming language
PIC Basic VS PIC C
Basic C
PRO
User Friendly
Lots of sample code
Compiler provided
Team received more training in C
Popular among other cubesat projects
CON
Not as common as C
Free PIC C compiler has limitations

72. Computer
System UML diagram( Old VS New)

73. Computer Rearranging the computer architecture Module Based
Advantages over the old system
Smooth out design progress
Easy to program
Faster processing speed

74. Computer Future Work Board Layout More programming
Testing and debugging
System integration

75. Power Group Members: Tasks Accomplished:
Robert Manning (Bob the Builder)
Tasks Accomplished:
Establish and refine power budget
Define subsystem operating times and procedures
Selection and purchase of solar cells
Subsystem design and simulation
Large component selection
Satellite in loop simulation concept

76. Power
Power budget:
Communications
 Power
Science
  Power
Microcontroller
13 mW
Transmitter
1200 mW
Detector Circuitry
75 mW
Receiver
160 mW
Detector
2.5 mW
Dynamics
Power / Thermal
Power (W)
7 mW
Electro-magnet (2)
2100 mW
Power needed for beacon, heating, cooling, sun-sensors,
boom deployment, antenna deployment are not available.

77. Power Critical subsystems “Typically on” systems
Microcontrollers, receiver & sun sensors
260 milliWatts
“Typically on” systems
All critical systems plus science package
420 milliWatts
Transmitting over Lafayette
Transmitter plus critical subsystems
1.6 Watts
Electromagnetic attitude control

78. Power Solar Cell Decision Spectrolab’s Improved Triple Junction Cells
Trade-off between cost & efficiency
Contacted Emcore & Spectrolab
Spectrolab’s Improved Triple Junction Cells
26% efficiency at BOL
Will use two in series on each side of cube
1.95 Watts at maximum power point
5.1 Volts open circuit
$50 per CIC is a bargain!

79. Power Subsystem Design Principles Reliability over efficiency
Feast or famine
Solar
Panels
Primary
Battery &
Capacitor
Power
Distribution
DC/DC
Converters
Subsystem
Li Polymer
Battery

80. Power Battery, Capacitor & Solar Cell Interaction
2 350 Farad Double Layer Capacitors
Stores energy for 350 mW for 40 minutes.
Thionyl Chloride Lithium Battery (3.6 Volts)
Using this scheme, back-up power is stored without active devices or microcontroller intervention!
Power to
DC/ DC
Converters

81. Power Component selection & design concepts
Use standard buck-boost DC/DC ICs, such as LTC3441
Use COTS Schottky diodes in series-parallel configuration for redundancy
Use two UltraLife’s 930 mAh Lithium Polymer Battery for secondary battery
Unsure about charging and discharging schemes and circuitry

82. Power Satellite in loop testing
Allows complete testing of satellite before launch
C++ software currently being developed
Uses LM317 regulator and current sense amplifier
Electromagnet Voltages
Spacecraft
Solar Cell
Power
Control
board
w/ RS232
Computer
Sun Sensor
Digital Pot

83. Power
Future work
Verify work with Prof. Oleg Wasynczuk in ECE department
Test I-V characteristics of solar cells
Purchase double layer capacitors
Build DC/DC converters and test current draw
Build solar cell simulator
Finish writing C++ code with attitude simulation and umbra calculations (OpenGL might be nice)

84. Questions?

85. Students: see George Pollock or Prof
Students: see George Pollock or Prof. Filmer if interested in joining the CubeSat team next semester. AAE, ME, ECE students are especially encouraged to join the team.