DayStar: Balloon-borne Star Tracking and Attitude Determination

1. DayStar Diurnal Star Tracking for Balloon-borne Attitude Determination Preliminary Design Review October 12, 2011 University of Colorado Aerospace Engineering Sciences

2. Briefing Overview and Content Purpose: The Preliminary Design Review will introduce the DayStar system options and demonstrate the feasibility of the chosen design solutions.

3. Objectives Overview Michael Skeen

4. Background [1] • Balloon-Borne Observatories: • Eventual goal: Operate 1-meter telescope from a balloon platform with Hubble Space Telescope performance • Sunrise: Sun-imaging 1-meter UV telescope, 0.05 arcsecond angular resolution[1] • Attitude Determination: • ST5000 (University of Wisconsin)[2] commonly used on sounding rocket • 0.5 arcsecond RMS accuracy • Saturated 20 minutes before sunrise on high-altitude balloon flight • Needed: • Increased accuracy • Operation in daytime conditions [2]

5. Project Goals and Requirements • The DayStar team will develop a prototype star tracking system capable of providing pointing knowledge to a diurnal, lighter-than-air platform. DayStar will improve on current attitude determination devices used on balloon payloads by providing daytime operational capabilities and an improved nighttime accuracy of 0.1 arcseconds RMS. Nighttime: Ambient sky brightness ≤ 2 kilo-Rayleighs Daytime: Ambient sky brightness ≤ 86,000 kilo-Rayleighs

6. Flight Concept of Operations

7. Development and Assessment of System Design Options Nick Truesdale

8. System Architecture System architecture is defined by customer to be a star tracker.

9. Trade Space Diagram (TSD) Star Tracker Centroiding Optics Imaging CDH Center of Gravity (CoG) CCD Refractor Telescope Camera Star Detection Robust CoG (roboCoG) CMOS Reflector Average Plus STD Intensity Weighted Centroiding (IWC) CCD Array Catadioptric Robust IWC (roboIWC) Median Absolute Deviation (MAD) Parabolic Fit Robust MAD (roboMAD) Gaussian Fit Static Flight Configurable

10. Functional Block Diagram (FBD) Memory CDH Optics Processor Structure External Baffle Filter Reimaging System Field Stop Objective Lens Storage Power Management Imaging Micro-Controller Interfaces CMOS Sensor Flash Memory Key Power Data Light FPGA

11. System Design-To Specifications Nick Truesdale

12. Accuracy Requirements • Project requirements: • System requirements:

13. Accuracy Modeling • Key values: • Minimum number of stars per frame • 8 at daytime, 20 at nighttime • Required by CDH statistical accuracy test • Minimum signal to noise ratio • 6.0 for daytime and nighttime • Required by CDH identification and centroiding accuracy tests

14. Accuracy Modeling • How many stars do we see? • Nighttime • ~78 stars • Daytime • ~18 stars • Both satisfy requirements Data from [3], [4]

15. Interface Requirements • Project requirements: • System requirements:

16. Interface Analysis • Key Values: • ICD Specifications • 40kg, 150W at 30V, and 9600 baud downlink • Easily met • Telescope mass < 10 kg • Computer power < 80W • Minimum data output rate • 10 Hz is the ST5000 operating speed • Encompasses frame rate, image transfer and processing

17. Development and Assessment of Subsystem Design Options Andrew Zizzi Jed Diller Sara Schuette

18. Algorithms – Design-To Specs Subsystem Requirements: Verification of Requirements: “At a given SNR, how well do we know our attitude?” “How well do we know our attitude from our centroids?” “How well can we locate what we detect?” “What SNR stars can we detect?” = × ×

19. Algorithms – Software Flow Minimum requirements for success Output Centroid Vectors Image Star Detection Centroid Stars Output Inertial Coordinates Star Catalog Search Stretch goals / ST5000 interface

20. Algorithms – Trade Study Results

21. Algorithms – Star Detection Percent of 7th Magnitude Stars Detected During the Day Purpose: Test algorithm’s ability to define the star detection intensity limit Define min/max blurring factor and min/max exposure time for best star detection performance Method: Results: 7th magnitude stars are detected 90% of the time with an exposure between ~30 and ~70 ms blurred over 16 to 36 pixels Overexposed Region Target Region Underexposed Region

22. Algorithms – Centroid Accuracy Purpose: Choose the most suitable centroiding method Define min/max blurring factor and min/max exposure times for best centroiding performance Method: Results: Robust IWC method chosen Star needs to be subtended over 16 – 36 pixels to achieve < 0.5” RMS accuracy 7th Magnitude Star During the Day Target Region Generated Star Subtended Over 25 pixels, SNR of 7 Intensity (raw counts)

23. Algorithms – Attitude Accuracy • Purpose: • Define how centroiding accuracy influences attitude accuracy • Define how number of stars in FOV changes attitude accuracy • Method: • Results: • 0.1” RMS attitude accuracy is attainable at various centroiding accuracies: • 6 stars at 0.5” RMS accuracy • 15 stars at 0.9” RMS accuracy • 25 stars at 1.1” RMS accuracy 10,000 Monte Carlo trials 0.1” Requirement Actual Star Vectors Perturbed Star Vectors ST5000Attitude Transformation Algorithm[14] LSF Attitude

24. Algorithms – Hardware Solutions Requirements: Minimum Data Transfer Rate From sCMOS: 664 bits/s Maximum CPU Power Dissipation: ~40 W Minimum Data Storage: ~10 GB Minimum Onboard Memory: ~6 GB Maximum Price: $1,840.0 • Consumer Grade Desktop Hardware • Pros: Simplicity, Computation Speed, Memory, Price • Cons: Power Draw, sCMOS Interface Options • Low Power Desktop Hardware • Pros: Simplicity, Power Draw, Price • Cons: sCMOSInterface Options, Computation Speed, Memory • Embedded Computer Hardware (PC/104 or AVR) • Pros: Power Draw, sCMOS Interface Options, Rugged • Cons: Complexity, Price, Computation Speed, Memory

25. Imaging Subsystem star light algorithms computer sensor electronics • Light to voltage to digital output • Will not saturate during daytime (unlike ST5000) • Sense enough stars for algorithms • Light to digital output at 10Hz 1001101 voltage digital output imaging subsystem

26. Imaging Requirements

27. Imaging Trade Results • CCD vs. CMOS vs. CCD Array • Historical knowledge says CCD • Modern CMOS wins for implementation and speed • sCMOS likely candidate • 5.3 megapixel • 100 fps in camera • Low read noise • Increased red spectrum performance

28. Best Case Scenario  Worst Case Scenario Night Day 6th Magnitude Star 4th Magnitude Star sCMOS Signal To Noise Ratio > 10 for 4th-6th Magnitude Stars Total Signal + Noise < Saturation (30,000 e- per pixel)

29. Imaging Model: SNR • Purpose: • Make sure sensor can detect enough stars during day • Sense 4th-6th magnitude stars (1.IMG.3) • Method: • SNR modeling • Signal: star - background • Noise: star, background, sensor • sCMOS sensor assumed • Blurring vs. megapixels (5.5 Mpknown to work) • Blurring vs. exposure time (shown) • Results: • Can sense 4th-6thmagnitude stars with SNR > 10 • Exposure time minimum found to be 30ms

30. Imaging Model: Saturation • Purpose: • Make sure sensor does not saturate for 4th-8th magnitude stars (1.IMG.1) • Method: • Signal from 4th magnitude star, back ground, sensor noise [e-] • 30,000 e-/pixel well depth • sCMOS sensor assumed • Blurring vs. megapixles(5.5 Mpknown to work) • Blurring vs. Exposure time (shown) • Results: • Do not saturate for exposure times less than 0.1 s.

31. Optics - Components • Optics subsystem will consist of three parts: • Telescope – designed by Equinox Interscience, built by Equinox and DayStar • External light baffle – designed and built by DayStar • Sensor Container – designed and built by DayStar baffle telescope Sensor container

32. Optics – Design-To Specs

33. Optics – Telescope Type Best Option: Refractor

34. Optics – Refractor Type • Two possible designs getting from objective lens to first focal plane: • One objective lens bends light onto focal plane • Long design • Easier to build • Step down design with multiple lenses • Shorter • Much more complicated, out of scope of class • Chosen design: One objective lens [15] Nikkor 300mm f/2.0 EDIF [16]

35. Optics – Telescope Design • Field stop limits field of view • Reimaging system demagnifies image to match sensor size at second focal plane Objective Lens Field stop Second focal plane Filter Possible intermediate lenses Reimaging system

36. Optics – External Light Baffle • Reduce the incident light on the objective lens • Will be placed in front of the objective lens • Amount of light allowed through objective lens determined by length and diameter of baffle design

37. Project Feasibility Analysis and Risk Assessment Andrew Zizzi Jed Diller Sara Schuette

38. Technical Risks

39. Algorithms – Feasibility Through Analysis Requirement Attitude Accuracy Centroiding Accuracy Star Detection 0.1” RMS attitude accuracy with 20 stars Worst case attitude of 0.05” accuracy with 20 stars Centroid stars up to 0.5” accuracy Detect 100% of stars up to 8th magnitude > × × Nighttime Centroid stars up to 0.5” accuracy 1.0” RMS attitude accuracy with 8 stars Detect 90% of stars up to 7th magnitude Worst case attitude of 0.1” accuracy with 8 stars × > × Daytime “At a given SNR, how well do we know our attitude?” “How well do we know our attitude from our centroids?” “How well can we locate what we detect?” “What SNR stars can we detect?” = × ×

40. Algorithms – Feasibility Through Research and Experience Research: • All algorithms weighed in trades are based on methods utilized in astronomical image analysis • The chosen algorithms have been proven on other startracking devices Experience: • Team experience in various multi-processed, multi-threaded embedded satellite software designs and implementations • Team experience in data structure formation, computer systems, robotics, and algorithms analysis [17] [14]

41. Prototyping: Imaging Sensor Imaging Interface Microcontroller • Breadboard: • Package Converter • 168 pin LCC to DIP package • PowerSupplies • 5 DC Voltage Supplies • 82 Pins • Control Signals • Integration with chosen CDH system • 9 Digital Signals • Data Product • 12 Image Signals FPGA USB to personal computer Key Power Data Light Imaging Board Power Management Engineering Grade CMOS Sensor

42. Imaging Feasibility

43. Optics – Lenses • Telescope designed for COTS lenses • Objective lens from Istar Optical [18] • Anastigmatic, achromatic • TALL POLE: Lens may take too long to get • MITIGATION: Backup 127 mm f/8 lens can be substituted with limited design changes • Intermediate lenses and relay lenses from Edmund Optics [19] • Achromatic doublets of various sizes • Standard lenses available for immediate shipment

44. Optics – Facilities • Telescope design contracted through Equinox • Equipment at Equinox • Machining • Knee mill x2, engine lathe, band saw, lathe, drill press • Optical alignment tools • Collimator, 1951 USAF resolution test chart • Gimbaled test setup • Can match Earth’s rotation • Test FOV, aberrations [20]

45. Testing/Verification

46. Project Management Plan Including Personal Health and Safety Michael Skeen

47. Team Organization Customer Dr. Eliot Young Advisors Dr. Palo, Dr. Kroehl, Russ Mellon, Kim Ennico Project Manager Mechanical/Electrical Systems Michael Skeen Electrical/Software Systems Nick Truesdale CFO Tyler Murphy Lead Safety Engineer Aaron Holt Lead Testing Engineer Zach Dischner Optics Lead: Sara Schuette Aaron Holt Tyler Murphy Electronics Embedded Systems Lead: Zach Dischner Jed Diller Aaron Holt Power Electronics Lead: Nick Truesdale Structures CAD/ Fabrication Lead: Tyler Murphy Aaron Holt Michael Skeen Software Lead: Kevin Dinkel Firmware Lead: Jed Diller Algorithms Lead: Andrew Zizzi

48. Team Composition

49. Work Breakdown Structure * Stretch Goal Responsibility

50. Fall Schedule October 2011 Detailed Subsystem Design Prototype Hardware Sourcing November 2011 Prototype Assembly CDR Preparations FFR Writing December 2011 Hardware Sourcing ‘Flight’ Software Development