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DRAFT-Sat Preliminary Design Review. 2003-2004 Senior Projects University of Colorado Aerospace Department. Objective. Provide a low budget system that can remove orbital perturbations from a satellite trajectory.
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DRAFT-SatPreliminary Design Review 2003-2004 Senior Projects University of Colorado Aerospace Department
Objective • Provide a low budget system that can remove orbital perturbations from a satellite trajectory. • System must compensate for perturbations in 3 axes causing the satellite to move 1cm or more from an orbital trajectory. • System must be self contained. • System must be testable both in microgravity aboard the KC-135 and in 1g of gravity on the surface of the Earth. • Applications in preventing orbit decay and improving satellite position knowledge.
Background • 2002/2003 Drag Free Team • Tested a 2-D prototype. • Verified the prototype could hold the position of the system to within 1cm for 10 seconds on an air table. • CO2 propulsion system with a thrust of 0.7 N to control the prototype. • Data processing done on a PC in MATLAB. • Bang-Bang control law with derivative gain. • Powered by external source.
STRUCTURE Chris Erickson
Structural Design Structural Design Drivers: • High strength / weight • Minimize mass for air table testing. • Robust enough for handling • Safely below yield strength during handling and assembly. • Meet G-loading and drop requirements for KC-135 • -Meet KC-135 flight requirements of: • 9 g forward loading. • 3 g aft loading. • 6 g downward loading. • 2 g lateral loading. • 2 g upward loading. • Sustain 4ft drop in 0.75 g environment. • Ease of Machining
Architecture Comparison -Compare architectures using structural design drivers. Due to unknowns with component weight, g-load and drop tests will not yield sufficient comparisons between structures at this point of the design. Instead, the structures will be compared by their robustness to crushing, a good measure of overall strength and handling robustness. -Use FEM models of structures for comparison. Load Models with 200 lb on their upper surfaces. Constrain vertical movement of lower surface.
Comparison: Study is done using 6061-T6 Al Comments: Minimum FOS Weight Machining Complexity 0.063 0.88 lb Complex 0.58 0.91 lb Simple Octagonal Ring is nearly 10x stronger. (based on yield strength) Nearly identical weight. Octagonal Ring is much simpler to machine.
Structural Materials Material Design Drivers: • High strength & stiffness to weight ratio. • Easy to machine. • Readily available. • Low cost. The options to choose from are: • Aluminum Alloy • Plastic • Steel • Titanium Alloy
Structural Risks * *
Octagonal Ring Assembly Conceptual Assembly of Proposed Design
SENSING Ryan Olds
Requirements 5V DC Power Supply. Draws 200mA. RS-232 or TTL serial communication with a microcontroller. Needs to be 2 inches from the object it is tracking. Tracked object must have a sharp contrast with surroundings (ex. Red on White). Specifications 4 - 17 frames per second. 2.25" wide x 1.75" high x 2" deep. Up to 160 x 288 Resolution. B/W Analog video output SX52 Processor (33% faster than previous system). Can operate between 1200 and 115200 baud. Wide angle lens can increase FOV to 55. CMUcam2 • Heritage • CMUcam1 used by 2002-2003 Drag Free team to successfully control a 2-D plate to within 1cm. • Much of the software is already written and tested.
Proof Mass Needs to be visible to the camera. Contrasts with Background. Must be at least 5% of camera FOV. Must be capable of movement in 3 axes. Cannot be perturbed. Cavity Needs to be transparent so that the proof mass is visible. Must provide adequate light so the proof mass is visible. Must allow the proof mass to displace more than 1cm. Proof Mass / Cavity Requirements
Proof Mass Bright Color (Red) to contrast with cavity. 1cm diameter (allows proof mass to be 10%-20% of camera FOV) Cavity 5cm sided cube. Allows proof mass to displace as much as 2cm. Clear plastic walls allow the camera to see the proof mass. LEDs Proof Mass / Cavity 2cm 5cm 2cm Transparent Walls 5cm Error Box
z y x Camera Orientation for 3-D Color Tracking CMUcam2 resolution (160 x 288) 55 55 5cm 5cm 5cm Zres = 92 pix/cm 55 Zres = 4 pix/cm Yres =51 pix/cm Yres =51 pix/cm Xres = 92 pix/cm Xres = 92 pix/cm
DATA ACQUISITION Mike Cragg
Microcontroller Requirements • Data Rate • 128-544 Hz • Processor Speed • 1280-5440 Hz • Memory • 13600 bytes • Interface • RS-232 • TTL
Control Flow Chart CMOS Image Array CMOS Image Array CMUcam2 (2) Buffer Buffer CMUcam2 Vision Board CMUcam2 Vision Board RS-232 or TTL RS-232 or TTL Microcontroller Microcontroller RAM PC RS-232 TTL TTL Solenoids (6)
Microcontroller Options • Motorola • Expensive • Complicated • Atmel AVR Microcontroller • Inexpensive • Microchip PIC Microcontroller • Inexpensive • Firsthand knowledge
Not enough RAM Will need umbilical to download data directly to PC Not self contained Will still be able to function, but no verification Insufficient Processor Speed Slow reaction time Limited control Interface Unable to download data to PC RAM Umbilical Processor Lower data rate Interface Utilize RS232 and TTL connections Risks/Off Ramps
PROPULSION Katie Dunn
Propellant Piping Piping Piping Fluid Regulation Device Fluid Release Device Power Data Nozzle Thrust Propulsion Flow Chart X 6 X 6
Propulsion System Requirements • Provide enough thrust to control the system • Provide control in three axis • Build to KC-135 requirements • Must be able to withstand the pressure needed to obtain the required thrust
Thrust must be able to counter a 1 cm/sec initial velocity Structure mass is 5kg or less Model thrust using kinematics physics equations Graph of force vs time Steve Graph Range of thrust the system must produce 0.1 N – 0.7 N Choose batteries to supply power Choose solenoid based on thrust range Characterize power of solenoid Pick material to hold specific pressure The Solution Thrust must be able to control the position of the system to within 1 cm
Miscalculation of thrust range Drives many components of system Use regulator on apparatus so it can be adjusted (within a certain range) Inability to meet specified power consumption requirement for solenoids OFF RAMP-use external power Basic model did not include Friction of air table Pressure losses in piping Risks and Outstanding Issues
POWER Stephen Levin-Stankevich
Cameras(2) 5V @ 200mA 5V Regulator Batteries COTS V >~ 8V I < ~ 1A Data Acquisition System 5V @ 200mA On/Off Switch High V High I Regulation Circuit Propulsion Solenoid Actuators
Batteries • AA rechargeable batteries • Provide simple interface • Low cost, lightweight, and easily obtainable • Easily adaptable if system requirements change • Propulsion design may require alternative • If high current and voltage cannot be supplied through a capacitor circuit to the solenoids a Li-Ion battery may be required for high current draws.
SOFTWARE Stephen Levin-Stankevich
Control System Block Diagram Camera Sensors X,Y,Z pos File on microcontroller Error Estimation In Software Control Law (trade study) Thrust Feedback Loop Courtesy of 2003 DFS Team
Control System • Last year’s results show the bang-bang controller provides accurate results. • Primary work will be developing the control software for use with the microcontroller • Goal is to reduce dead-band size by implementing smaller thrust • Analog control of pressure for a P-D controller will be a project on-ramp.
Testing and Verification Chris Erickson
Testing Options • Pendulum Setup • Suspend the structure from a tether and verify position control. • Spring Mass Setup • Attach the structure to a spring system in all 3 axes and verify position control. • Air table Setup • Test position control 2 axes at a time on the air table (test 2 axes and flip structure) • KC-135 • Test position control in a micro-gravity environment.
Project Management Plan William Lumbergh
Drag Free Spacecraft Project Manager Ryan Olds Prof Penina Axelrad Office: ECAE 159Phone: (303) 492-6872 Prof Steve Nerem Office: ECAE 100Phone: (303) 492-6721 Professor Advisory Board Safety Engineer Stephen Stankevich Mechanical Design Engineer Chris Erickson Instrumentation Engineer Mike Cragg Chief Financial Officer Mike Cragg Software Stephen Stankevich Katie Dunn Mike Cragg Ryan Olds Structure Chris Erickson Data Acquisition Mike Cragg Propulsion Katie Dunn Mike Cragg Power Stephen Stankevich Sensing Ryan Olds
DRAFT-SatWork Breakdown Structure 1.0 Management 2.0 Systems 3.0 Testing 4.0 Software 5.0 Structure 6.0 Data Acquisition 7.0 Propulsion 8.0 Power 9.0 Sensing 1.1 Schedule 2.1 Integration of subsystems 3.1 Test planning 4.1 Extend existing code to 3 dimensions 5.1 Select materials 6.1 Select microcontroller 7.1 Select propellant and solenoids 8.1 Select power source 9.1 Select sensors 1.2 Task management 2.2 Design requirements 3.2 System and subsystem testing and verification 4.2 Improve performance of PD controller 5.2 House all subsystems 6.2 Program microcontroller 7.2 Thruster model 8.2 Supply power to all subsystems 9.2 Proof mass and cavity 1.3 Financial 2.3 Trade Studies 3.3 Technical reports 4.3 Translate MATLAB to C language 5.3 CG placement 6.3 Interface with sensors and propulsion 7.3 Propellant piping system 9.3 Interface with microcontroller 1.4 Team organization 3.4 Conform to all KC-135 requirements and regulations. 5.4 Machine structure 6.4 Store data in memory
Open Issues • Propulsion System Thrust Sizing and Part Selection • Microcontroller Setup • Battery Selection
Sensors and Actuators Sensors • Control System • Camera • Propulsion • Fluid regulation device • Power • Voltage monitor Actuators • Propulsion • Fluid regulation device • Fluid release device