Flight Dynamics System Manfred Bester THEMIS FDMO CDR
Flight Dynamics System Manfred Bester THEMIS FDMO CDR Peer Review − Flight Dynamics 1 June 1 -2, 2004
Flight Dynamics System Overview • • Coordinate Systems Flight Dynamics Software User Training Product Generation Orbit Determination Attitude Determination Issues, Concerns and Risks THEMIS FDMO CDR Peer Review − Flight Dynamics 2 June 1 -2, 2004
Inertial Coordinate Systems Earth Centered Inertial Coordinate Systems • Defined by Intersection of Equator and Ecliptic Motions of Defining Planes • Equator (Celestial Pole) – Gravitation Attraction of Sun and Moon on Equatorial Bulge – Two Components: Lunisolar Precession and Nutation • Ecliptic – Gravitational Attraction of Other Planets – Planetary Precession: Includes Eastward Movement of Equinox and Decrease of Obliquity Related Coordinate Transformations • General Precession – Includes Both Lunisolar and Planetary Precession • Nutation – Includes Nutation in Longitude and in Obliquity THEMIS FDMO CDR Peer Review − Flight Dynamics 3 June 1 -2, 2004
Inertial Coordinate Systems Mean Equator and Mean Equinox • AKA Mean-of-date – Includes Precession Only and Neglects Nutation • B 1950. 0 – AKA B 1950. 0 Inertial – AKA Mean-of-date B 1950. 0 • J 2000. 0 – AKA J 2000. 0 Inertial – AKA Mean-of-date J 2000. 0 True Equator and True Equinox • AKA True-of-date – Includes Precession and Nutation True Equator and Mean Equinox • AKA TEME – Includes Precession and Nutation, Ignores Equation of Equinoxes – Used with Two-line Elements THEMIS FDMO CDR Peer Review − Flight Dynamics 4 June 1 -2, 2004
Coordinate Transformations Between Inertial Coordinate Systems • Mean-of-date to Mean-of-date (Different Dates) – Involves Rotation Around Three Axes – Described by Time Dependent Precession Parameters – Rotation Angles ζ, θ and ξ • Mean-of-date to True-of-date (Same Date) – Correct for Nutation – Described by Time Dependent Nutation Parameters – True Obliquity ε – Nutation in Longitude δψ • Mean-of-date to True-of-date (Different Dates) – Apply Combined Precession and Nutation Transformation • TEME to True-of-date – Disregard Equation of the Equinoxes, i. e. Use Mean Sidereal Time • B 1950. 0 and J 2000. 0 – Use Different Sets of Precession and Nutation Parameters THEMIS FDMO CDR Peer Review − Flight Dynamics 5 June 1 -2, 2004
Flight Dynamics Software Tool Version Platform Heritage Function Method of Verification GTDS 96. 03 Delta 4, 09/11/1997 (Source Code, Compiled on SPARC / Solaris) NASA/GSFC, Multiple Missions Ephemeris Generation, Mission Design, Orbit Determination Testing Against Heritage Code and Other Software GMAN Version 94. 03 PC (Source Code, Compiled on SPARC / Solaris) Version 96. 01 PC (i 386 / Windows XP) NASA/GSFC, Multiple Missions Maneuver Planning Testing Against Heritage Code and Other Software Free. Flyer Engineer Version 5. x (Windows XP) NASA/GSFC, TERRA, EO-1, AQUA Maneuver Planning Testing Against Heritage Code and Other Software Sat. Track Version 4. 5 (SPARC / Solaris, i 386 / Linux) FAST, RHESSI, CHIPS, IMAGE, SPEAR Orbit Analysis, Pass Scheduling, Automated Product Generation, Networking, 3 -D Visualization, Ground Station Control Testing Against Heritage Code and Other Software THEMIS FDMO CDR Peer Review − Flight Dynamics 6 June 1 -2, 2004
Flight Dynamics Software Tool Version Platform Heritage Function MSASS Latest to Be Delivered in 12/2004 (SPARC/Solaris, I 386/Windows XP) Requires Matlab NASA/GSFC, SMEX, EO-1 Attitude Determination Testing Against Heritage Code and Other Software, Comparison with Attitude Vector Input to Virtual. Sat MTASS Latest to Be Delivered in 12/2004 (SPARC/Solaris, I 386/Windows XP) Requires Matlab NASA/GSFC, SMEX, EO-1 Attitude Determination Testing Against Heritage Code and Other Software, Comparison with Attitude Vector Input to Virtual. Sat THEMIS FDMO CDR Peer Review − Flight Dynamics 7 Method of Verification June 1 -2, 2004
Software User Training GTDS • • Upgrade to Latest Version Orbit Determination GMAN • • • Configuration of Spacecraft Definition Files Maneuver Planning Generation of Thruster Command Sheets Free. Flyer • • • Alternate Commercial Solution for Maneuver Planning Determine if Free. Flyer Meets Mission Requirements Consulting Agreement with AI Solutions Under Development MSASS / MTASS • • • Configuration of Resource Files Real-time Attitude Determination Post-pass Attitude Determination for Science Data Analysis THEMIS FDMO CDR Peer Review − Flight Dynamics 8 June 1 -2, 2004
Ephemeris Products • • • Ephemeris, Special Vectors and Two-line Elements Attitude and Beta Angle Predicts Ground Station and TDRSS View and Link Access Periods Earth and Lunar Shadows Region Crossings Orbit Events Antenna Track Files Solar Interference Mutual RF Interference Analysis Approach Analysis Maneuver Timelines Coordinate Systems and Units • • True-of-date Used Consistently for All Ephemeris Products Metric Units Only THEMIS FDMO CDR Peer Review − Flight Dynamics 9 June 1 -2, 2004
Product Generation Product Frequency Product Usage Software Method of Verification Ephemeris Daily Mission Planning, Orbit Analysis, Product Generation GTDS Test Cases Run at GSFC, Comparison with Ephemeris Generated by Other Software Extended Precision Vectors (EPVs) Daily Provided for Completeness Sat. Track Comparison with Original Ephemeris Improved Interrange Vectors (IIRVs) Daily Scheduling of Passes at NASA/GN Stations, Generation of Acquisition Data at NASA/GN Stations Sat. Track Comparison with IIRVs Generated by Other Software Orbit Parameter Messages (OPMs) Daily Provided for Completeness Sat. Track Comparison with Original Ephemeris Two-line Elements Daily Quick Look Orbit Analysis, Back-up for THEMIS OD Download from NASA Compare Ephemeris Generated with SGP 4 Model Against GTDS Ephemeris Attitude Report Daily Mission Planning, Attitude Verification Sat. Track Testing and Comparison Against Heritage Products Beta Angle Report Daily Mission Planning Sat. Track Testing and Comparison Against Heritage Products Shadow Report Daily Mission Planning Sat. Track Comparison with IDL-based Shadow Predicts Duration Events Daily Command Load Generation with MPS Sat. Track Testing and Comparison Against Heritage Products THEMIS FDMO CDR Peer Review − Flight Dynamics 10 June 1 -2, 2004
Product Generation Product Frequency Product Usage Software Method of Verification Orbit Events Daily Command Load Generation with MPS Sat. Track Testing Contact Schedule Daily Mission Planning Sat. Track Testing against multi-mission pass schedules Multi-mission Pass Schedules Daily Mission Planning Sat. Track Testing SMEXSS Schedules Daily Command Load Generation with MPS Sat. Track Testing against multi-mission pass schedules Predicted Site Acquisition Tables (PSAT) Daily NASA/GN Pass Scheduling Sat. Track Testing View Periods Daily Command Load Generation with MPS Sat. Track Testing against multi-mission pass schedules Link Access Periods Daily Pass Scheduling Based on Dynamically Modeled Link Margin Sat. Track Testing TDRSS Schedules As Required TDRSS Scheduling Sat. Track Testing Track Files Daily BGS Antenna Acquisition Angles, Real-time Monitoring of Two-way Doppler Shift During Maneuvers, Determination of Range Delay for Setting Probe Clock Sat. Track Testing with BGS for Acquisition, Testing with ITOS for Setting of Probe Clock in Real-time THEMIS FDMO CDR Peer Review − Flight Dynamics 11 June 1 -2, 2004
Product Generation Product Frequency Product Usage Software Method of Verification Solar Interference Report Daily Inhibit of Autotrack Lock on the Sun (BGS Only) Sat. Track Testing and Comparison Against Heritage Products Event Timelines Daily MOC Automation Sat. Track Testing with Other Operating Missions and THEMIS Simulations Approach Analysis Daily Collision Avoidance Sat. Track Testing Against IDL-based Code Mutual RF Interference Analysis Daily Pass Scheduling with Interference Avoidance Constraint for Multiple Probes at Each Ground Station Sat. Track Testing and Comparison Against Heritage Products Maneuver Command Sheets As Required Maneuver Execution GMAN, Free. Flyer Test on Flat. Sat; Compare GMAN Output Against Free. Flyer Propellant Usage Summary As Required Maneuver Planning Excel Spreadsheet Careful Bookkeeping Tracking Data Daily Orbit Determination Tracking Data Formatters at the Ground Stations Comparison with Predicted Acquisition Data, Post-pass Analysis, Data Quality Checking THEMIS FDMO CDR Peer Review − Flight Dynamics 12 June 1 -2, 2004
Ground System Automation Berkeley Flight Dynamics System • Hardware Configuration – Multiple Redundant Systems (2. 8 GHz Pentium IV, Linux) • Software Tools – Sat. Track Suite V 4. 5 • Automated Product Generation – Generates All Required Products Every Night for All Missions Via Autoproducts Scripts • Sat. Track Gateway Server (Sat. Track/GS) – – – – Central Scheduling and Event Distribution System Control of Various Ground System Elements Network Monitoring Event Messaging Anomaly Notification Interfaced Via TCP/IP Network Socket Connections BGS Automation Accomplished by Integration of Sat. Track/GS and Sat. Track/MCS THEMIS FDMO CDR Peer Review − Flight Dynamics 13 June 1 -2, 2004
Product Utilization Berkeley Ground Data System THEMIS FDMO CDR Peer Review − Flight Dynamics 14 June 1 -2, 2004
Orbit Determination REQUIREMENT DESIGN M-58. Probe orbits shall be known to an accuracy of 10 km at perigee and 100 km at apogee. Compliance. Number of tracks and ground stations, and accuracy of equipment and software selected to achieve required performance. Orbit Determination Based on Two-way Doppler Tracking • Ground Stations Provide Two-way Doppler Tracking Data in Universal Tracking Data Format (UTDF) – One Station Sufficient to Provide Required Accuracy (10 km at Perigee, 100 km at Apogee) Over Multiple Passes (GNCD Analysis) – Data from Multiple Stations Plus Angle Tracking Yield Better Solution • UTDF Files – Converted to 60 -byte Format by Sat. Track – Processed with GTDS to Obtain New Orbit Solutions – New State Vectors Used to Generate Updated Planning Products Digital Range Measurement System (DRMS) • OD Technology Demonstration During Second Year – DRMS Measures Round-trip Delay of Digital Data Stream THEMIS FDMO CDR Peer Review − Flight Dynamics 15 June 1 -2, 2004
Doppler Accuracy Tests Rationale for Doppler Accuracy Tests • Prediction of Orbit Determination Accuracy – Two-way Doppler Accuracy Difficult to Predict for THEMIS Ground System Configuration – Use Telemetry Receivers Instead of Dedicated Track Receivers – Microdyne 700−MR (WB) with 758−D (W) Multi-mode Demodulator – Different Modulation Schemes Used, Dependent on Probe Range – Determination of Potential Error Sources • Generate Baseline for Expected Accuracy – Predict Accuracy of Range Rate Measurements as Function of CNR for BPSK and PCM/PSK/PM Modulation – Test Results Will Tell How Many Tracking Arcs Are Required to Perform Orbit Determination for THEMIS • Tests Performed with WFF Equipment on Loan to UCB – Functional Check-out of Equipment (CDMS, TDF and GPS Clock) – Long Loop RF Tests with Modulated Carrier & Telemetry Playback – On-orbit Tests with FAST and RHESSI Spacecraft THEMIS FDMO CDR Peer Review − Flight Dynamics 16 June 1 -2, 2004
Test Equipment Setup • Wallops Flight Facility Kindly Loaned Equipment to UCB – Apogee Labs Model 7701 Carrier Doppler Measurement System (CDMS) – Apogee Labs Model 2208 Tracking Data Formatter (TDF) – True. Time Model XL-DC GPS Time and Frequency Receiver • Test Timeline – CDMS and TDF Equipment Arrived at Berkeley on 09 -Oct-2003 – GPS Receiver Arrived on 31 -Oct-2003 – Purchased 2 Mini-Circuits Amplifiers (ZRL-400) to Match LO Signal Power Levels Between Microdyne 700 -MRB Receiver Outputs and CDMS Inputs – Installation in Berkeley Ground Station Completed on 17 -Oct-2003 – Preliminary Functional Checks Completed by 17 -Oct-2003 – Initial Doppler Tracking Tests Performed on 01 -Nov-2003 – Ground Based Loop-back Tests and On-orbit Tests with FAST and RHESSI Completed on 24 -Dec-2003 THEMIS FDMO CDR Peer Review − Flight Dynamics 17 June 1 -2, 2004
Doppler Test Schematic Diagram for Loop-back Doppler Accuracy Tests THEMIS FDMO CDR Peer Review − Flight Dynamics 18 June 1 -2, 2004
CDMS & TDF Interface Tests Performed • Verified CDMS Input Signal Levels – 2 nd LO from Receivers: RHCP: -0. 1 d. Bm; LHCP: +0. 9 d. Bm – 5 MHz Reference from True. Time Clock: +2. 6 d. Bm – Sync Pulses from True. Time Clock: 10 ppm, 0 - 3. 3 V, TTL • Verified TDF Input Signal Levels – IRIG-B Time Code from True. Time Clock: 4. 8/1. 4 Vpp • Configured TDF – – – Network Configuration Two-way Doppler Mode Transmit Frequency Sample Rate Support ID Tracker ID THEMIS FDMO CDR Peer Review − Flight Dynamics 19 June 1 -2, 2004
CDMS & TDF Functional Tests Performed • Verified 2 nd Local Oscillator Signal Frequency – Used Agilent Frequency Counter to Verify 180 MHz Frequency • Verified CDMS Lock – Green LEDs on CDMS Front Panel Lit Continually • Verified TDF Operation – Displayed Doppler Shift and Range Rate • Compared Reference Signals from GPS Receivers – Compared 10 MHz Reference Signals from Trak Systems and True. Time GPS Receivers – GPS Antennas Installed on Roof of Building – Observed Lissajous Figures on Oscilloscope – Phase Drift Between 10 MHz Signals of Order 10° / min – True. Time XL-DC Receiver Provides Much Cleaner Reference – Trak Systems Model 9000 B: – True. Time Model XL-DC: THEMIS FDMO CDR Peer Review − Flight Dynamics 20 3. 10 ± 0. 10 Vpp 2. 89 ± 0. 01 Vpp June 1 -2, 2004
Sources for Doppler Errors Determined Potential Sources for Doppler Errors • Synchronization of Timing Signals – All Reference Signals Need to Be Generated by the Same Source – 5 MHz RF Reference for Phase-lock Loops – 10 pps Clock for Triggering Measurements – IRIG-B Time Code for Time Tagging Measurements – Lack of Time Synchronization Causes Doppler Bias and Large Fluctuations in Doppler Signal – Lack of Accuracy in IRIG-B Time Code Causes Doppler Bias • Tuning of Receivers and Transmitters – Receiver Loop Stress Due to Finite Tuning Resolution Causes Bias – Mismatch Between Transmit Frequency and TDF Configuration • Imperfect Receiver Lock – Receiver Firmware Can Cause False or Imperfect Lock Under Certain Conditions Leading to Large Doppler Bias – Loop Bandwidth in Demodulator Critical to Avoid Spikes THEMIS FDMO CDR Peer Review − Flight Dynamics 21 June 1 -2, 2004
Loop-back Doppler Tests Doppler Accuracy Test Procedure for Loop-back Tests • Prepare Ground Station Configuration Files for Loop-back Tests – – – • Transmit Frequency: S-Band Antenna Feed: RHCP and LHCP Receive Modulation: BPSK and PCM/PSK/PM Loop Bandwidth: 3 k. Hz, 1 k. Hz and 0. 3 k. Hz IF Bandwidth: 3. 3 MHz Set Up Ground Station for Facility Self-test in Loop-back Mode – Configure and Calibrate Receivers – Configure Exciter, PTP, Matrix Switch, CDMS and TDF • Record UTDF Data Files with CDMS and TDF – Sample Rate: 10 Hz, 1 Hz and 0. 1 Hz • Analyze Recorded Data with Sat. Track UTDF Processing Tool – Assess Data Quality – Determine Average Range Rate (Bias) – Determine 1 -σ Range Rate Error THEMIS FDMO CDR Peer Review − Flight Dynamics 22 June 1 -2, 2004
Doppler Analysis Software Sat. Track UTDF Processing Tool • • • Reads and Decodes UTDF Files in 75 -Byte Format Performs Data Quality Checking Allows Filtering of Spikes Allows Elimination of Bad Data (e. g. Acquisition Sweeps) Allows Merging with Calculated Data from Track File, Including Application of Time Bias Performs Post-pass Averaging Performs Statistical Analysis Generates Output File Compatible with Sat. Track Graphics Visualization Tool Generates Output File in 60 -Byte Format for Input to GTDS (Not Yet Implemented) THEMIS FDMO CDR Peer Review − Flight Dynamics 23 June 1 -2, 2004
Loop-back Doppler Test Results Loop-back Test Objective #1 • Determine Standard Deviation of Range Rate as Function of Demodulator Loop Bandwidth for Various CDMS Sample Rates for BPSK Modulation at a Fixed Signal Strength Modulation Data Rate [kbps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] (RHCP) Test Duration [min] CDMS Sample Rate [Hz] Average Range Rate [m/s] Standard Deviation of Range Rate (1 -σ) [m/s] 2281. 5 BPSK 1000 3 3. 3 13. 7 5. 7 10 -0. 097420 0. 333542 * 2224 2281. 5 BPSK 1000 3 3. 3 13. 6 8. 4 1 -0. 088940 0. 081412 * 3 2234 2281. 5 BPSK 1000 3 3. 3 13. 5 9. 8 0. 1 -0. 087510 0. 028704 * 4 2309 2281. 5 BPSK 1000 1 3. 3 13. 4 11. 2 10 -0. 020158 0. 169810 5 0102 2281. 5 BPSK 1000 1 3. 3 16. 9 1 -0. 015545 0. 014186 6 0015 2281. 5 BPSK 1000 1 3. 3 13. 3 32. 3 0. 1 -0. 017164 0. 002843 7 2122 2281. 5 BPSK 1000 3 3. 3 12. 3 7. 2 10 -0. 091085 0. 253976 * 8 2259 2281. 5 BPSK 1000 1 3. 3 12. 3 11. 7 10 -0. 022182 0. 082642 Test ID File Name Transmit Frequency [MHz] 1 2216 2 * Discovered that Spikes Appear with BPSK Modulation when Demodulator Loop Bandwidth Is 3 k. Hz. Calculated Standard Deviation Includes Spikes. Root Cause for Spikes Needs to Be THEMIS FDMO CDR Peer Review − Flight Dynamics 24 June 1 -2, 2004 Investigated.
Loop-back Doppler Test Results Loop-back Test Objective #2 • Check for Spikes in Range Rate as Function of Demodulator Loop Bandwidth for BPSK Modulation in Both Receive Channels (RHCP, LHCP) at a Fixed Sample Rate – Spikes Do Typically Occur in Either Channel with Demodulator Loop Bandwidth of 3 k. Hz, But Do Not Occur with 1 k. Hz – Finding Suggests This Is Not a Receiver Malfunction – Need to Limit Demodulator Bandwidth to 1 k. Hz with BPSK Modulation Data Rate [kbps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] Test Duration [min] CDMS Sample Rate [Hz] Average Range Rate [m/s] Standard Deviation of Range Rate (1 -σ) [m/s] 2281. 5 BPSK 1000 3 3. 3 12. 4 RHCP 5. 8 10 -0. 112052 0. 288177 * 1859 2281. 5 BPSK 1000 3 3. 3 9. 4 LHCP 5. 8 10 -0. 168171 0. 359822 * 24 1908 2281. 5 BPSK 1000 1 3. 3 12. 4 RHCP 3. 8 10 -0. 019483 0. 085714 25 1913 2281. 5 BPSK 1000 1 3. 3 9. 3 LHCP 4. 8 10 -0. 019796 0. 090464 Test ID File Name Transmit Frequency [MHz] 22 1852 23 * Spikes Appear with BPSK Modulation Only when Demodulator Loop Bandwidth Is Larger than 1 k. Hz. Calculated Standard Deviation Includes Spikes. Root Cause for Spikes Needs to Be THEMIS FDMO CDR Peer Review − Flight Dynamics 25 June 1 -2, 2004 Investigated.
Loop-back Doppler Tests #22: Downward Spikes Appear with 3 k. Hz Demodulator Loop Bandwidth for BPSK Modulation. CDMS Rate Is. Review 10 Hz. − Flight Dynamics 26 THEMISSample FDMO CDR Peer June 1 -2, 2004
Loop-back Doppler Tests #22: Downward Spikes Do Not Appear with 1 k. Hz Demodulator Loop Bandwidth for BPSK. CDMS Rate Is. Review 10 Hz. − Flight Dynamics 27 THEMISSample FDMO CDR Peer June 1 -2, 2004
Loop-back Doppler Test Results Loop-back Test Objective #3 • Determine Standard Deviation of Range Rate as Function of Signal Strength for BPSK Modulation at a Fixed Demod Loop Bandwidth of 1 k. Hz and a Fixed Sample Rate of 10 Hz Modulation Data Rate [kbps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] (RHCP) Test Duration [min] CDMS Sample Rate [Hz] Average Range Rate [m/s] Standard Deviation of Range Rate (1 -σ) [m/s] 2281. 5 BPSK 1000 1 3. 3 4. 4 5. 0 10 -0. 027535 0. 049128 2317 2281. 5 BPSK 1000 1 3. 3 5. 4 4. 3 10 -0. 023569 0. 047458 11 2328 2281. 5 BPSK 1000 1 3. 3 6. 2 4. 7 10 -0. 22578 0. 055022 12 2334 2281. 5 BPSK 1000 1 3. 3 7. 4 4. 3 10 -0. 23338 0. 080044 13 2339 2281. 5 BPSK 1000 1 3. 3 8. 4 4. 4 10 -0. 026023 0. 069639 14 2343 2281. 5 BPSK 1000 1 3. 3 9. 4 3. 5 10 -0. 023743 0. 071078 15 2347 2281. 5 BPSK 1000 1 3. 3 10. 5 4. 2 10 -0. 022699 0. 064317 16 2352 2281. 5 BPSK 1000 1 3. 3 11. 7 4. 3 10 -0. 023067 0. 076080 17 2357 2281. 5 BPSK 1000 1 3. 3 15. 2 3. 8 10 -0. 025531 0. 082685 18 0002 2281. 5 BPSK 1000 1 3. 3 18. 7 4. 2 10 -0. 022995 0. 088737 19 0006 2281. 5 BPSK 1000 1 3. 3 22. 0 3. 5 10 -0. 022867 0. 080763 20 0011 2281. 5 BPSK 1000 1 3. 3 25. 5 4. 5 10 -0. 025189 0. 076162 21 0015 2281. 5 BPSK 1000 1 3. 3 28. 9 3. 5 10 -0. 022708 0. 067238 Test ID File Name Transmit Frequency [MHz] 9 2322 10 THEMIS FDMO CDR Peer Review − Flight Dynamics 28 June 1 -2, 2004
Loop-back Doppler Test Results Loop-back Test Objective #4 • Determine Standard Deviation of Range Rate as Function of Signal Strength for PCM/PSK/PM Modulation at a Fixed Demod Loop Bandwidth of 0. 3 k. Hz and a Fixed Sample Rate of 10 Hz Modulation * Data Rate [kbps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] (RHCP) Test Duration [min] CDMS Sample Rate [Hz] Average Range Rate [m/s] Standard Deviation of Range Rate (1 -σ) [m/s] 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 17. 6 10. 2 10 -0. 020201 0. 043129 2326 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 17. 8 5. 3 10 -0. 003799 0. 061474 41 2332 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 19. 1 6. 0 10 -0. 002619 0. 053407 42 2340 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 20. 2 6. 2 10 -0. 02722 0. 061164 43 2347 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 21. 5 6. 0 10 -0. 003041 0. 068596 44 2353 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 22. 8 5. 3 10 -0. 002931 0. 068514 45 2359 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 24. 2 5. 5 10 -0. 002722 0. 066684 46 0005 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 25. 6 5. 3 10 -0. 002410 0. 056723 47 0011 2281. 5 PCM/PSK/PM 64 0. 3 3. 3 26. 9 5. 6 10 -0. 002693 0. 046787 48 0017 2281. 5 PCM/PSK/PM 64 0. 3 31. 0 5. 6 10 -0. 001507 0. 043506 Test ID File Name Transmit Frequency [MHz] 39 ** 2242 40 * Subcarrier Frequency: 1. 024 MHz; Modulation Index: 1. 35 rad **Test #39 Performed on 04 -Dec-2003, All Others on 14 -Dec-2003. THEMIS FDMO CDR Peer Review − Flight Dynamics 29 June 1 -2, 2004
Loop-back Doppler Tests Test #39: PCM/PSK/PM; Subcarrier Frequency: 1. 024 MHz; Modulation Index: 1. 35 rad; Data Rate: 64 kbps; AGC Level: 17. 6 d. B; RHCP Channel; Video Averaging: 2 s; Spectrum Represents THEMIS FDMO CDR RF Peer. Signature. Review − Flight Dynamics 30 June 1 -2, 2004
Loop-back Doppler Test Results Loop-back Test Objective #5 • Determine if Longer Integration Times in CDMS Are Equivalent to Post-pass Averaging – Recorded Data with 3 Different CDMS Sample Rates and Averaged Samples Post-pass over 10 s – Investigated Behavior for PCM/PSK/PM and BPSK Modulation * Data Rate [kbps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] (RHCP) Test Duration [min] CDMS Sample Rate [Hz] Standard Deviation of Range Rate (1 -σ) [m/s] Standard Deviation of Range Rate (1 -σ) in 10 s Post-pass Integration Time [m/s] 2282. 5 PCM/PSK/PM 64 0. 3 3. 3 17. 5 22. 7 10 0. 041900 0. 001140 0357 2282. 5 PCM/PSK/PM 64 0. 3 3. 3 17. 5 20. 0 1 0. 008304 0. 001026 53 0418 2282. 5 PCM/PSK/PM 64 0. 3 3. 3 17. 5 20. 8 0. 1 0. 001130 54 0514 2282. 5 BPSK 1000 1 3. 3 13. 9 21. 3 10 0. 041036 0. 001214 55 0536 2282. 5 BPSK 1000 1 3. 3 13. 9 22. 4 1 0. 012341 0. 001309 56 0559 2282. 5 BPSK 1000 1 3. 3 13. 9 21. 3 0. 1 0. 001377 Test ID File Name Transmit Frequency [MHz] 51 0333 52 * PCM/PSK/PM: Subcarrier Frequency: 1. 024 MHz; Modulation Index: 1. 35 rad THEMIS FDMO CDR Peer Review − Flight Dynamics 31 June 1 -2, 2004
Loop-back Doppler Test Results of Loop-back Doppler Tests • Range Rate Accuracy as Function of Demod Loop Bandwidth – Demodulator Loop Bandwidth in Receivers Is Critical – Range Rate Error Scales With Loop Bandwidth as Expected – Spikes Occur When Loop Bandwidth Is Too Large – BPSK Modulation – Downward Spikes in Range Rate Occur with 3 k. Hz LBW – Clean Measurements without Spikes at 1 k. Hz LBW – PCM/PSK/PM Modulation – Downward Spikes in Range Rate Occur with 3 and 1 k. Hz LBW – Clean Measurements without Spikes at 0. 3 k. Hz LBW • Range Rate Accuracy as Function of Signal Power – Measured Range Rate Accuracy (1−σ) – Ground Based Loop-back Tests Typically Provide < 1. 5 mm/s with a Sample Rate of 10 Hz and a Post-processing Integration Time of 10 s – Range Rate Accuracy Appears to Be Independent of Signal Power – Applies to Both BPSK and PCM/PSK/PM Modulation – System Performance at Low Signal Levels – Quality of Telemetry Data Is Degraded at Low Signal Levels, But Range Rate Accuracy Is Not, as Long as Receivers Remain Locked THEMIS FDMO CDR Peer Review − Flight Dynamics 32 June 1 -2, 2004
FAST On-orbit Doppler Tests First BGS On-orbit Doppler Test Performed with FAST on 06 -Nov-2003 Transmit Frequency: 2039. 645830 MHz; Polarization: RHCP; Modulation: PCM/PSK/PM; Loop Bandwidth: 3 k. Hz; CDMS Sample Rate: 10 Hz; Spikes Filtered Out ± 0. 02 km/s Calculated Range Rate Based on 2 -Day Old TLE Set − No Time Bias Applied. THEMIS FDMO CDR Peer Review − Flight Dynamics 33 June 1 -2, 2004
FAST On-orbit Doppler Tests Doppler Accuracy Test Procedure for FAST On-orbit Tests • Prepare Ground Station Mission Configuration File for FAST – – – • Transmit Frequency: Transmit Power: Antenna Feed: Receive Modulation: Loop Bandwidth: IF Bandwidth: 12 MHz 2039. 645830 MHz 25 W RHCP PCM/PSK/PM 3 k. Hz, 1 k. Hz and 0. 3 k. Hz Set Up Ground Station in Automated Mission Support Mode – Configure and Calibrate Receivers – Configure Exciter, PTP, Matrix Switch, CDMS and TDF • Record UTDF Data Files with CDMS and TDF – – – Link Mode: Coherent Two-way Sample Rate: 10 Hz Analyze Recorded Data with Sat. Track UTDF Processing Tool Apply Time Bias to Calculated Range Rate to Minimize Residuals Determine Doppler Bias and 1 -σ Range Rate Error THEMIS FDMO CDR Peer Review − Flight Dynamics 34 June 1 -2, 2004
On-orbit Doppler Test Results On-orbit Two-way Doppler Test Objective #1 • Determine Two-way Doppler Accuracy with Orbiting Spacecraft for PCM/PSK/PM Modulation – Record Range Rate Data During 5 FAST Passes at BGS – FAST Has a Coherent Transponder Modulation Data Rate [ksps] Demod Loop Bandwidth [k. Hz] IF Bandwidth [MHz] Average Receiver AGC [d. B] Test Duration [min] CDMS Sample Rate [Hz] 2039. 64583 PCM/PSK/PM 4500 3 12. 0 38. 2 9. 8 10 +0. 778 ± 0. 1* 184153 2039. 64583 PCM/PSK/PM 4500 3 12. 0 29. 6 6. 5 10 +0. 850 ± 0. 1* 102 030900 2039. 64583 PCM/PSK/PM 4500 1 12. 0 50. 8 4. 3 10 +0. 410 ± 0. 1* 103 013857 2039. 64583 PCM/PSK/PM 4500 0. 3 12. 0 35. 2 2. 7 10 +0. 445 ± 0. 1 104 021640 2039. 64583 PCM/PSK/PM 4500 0. 3 12. 0 51. 4 4. 3 10 -0. 272 ± 0. 01** Test ID File Name Transmit Frequency [MHz] 100 163149 101 Optimum Range Rate Time Error Bias (Peak-to-Peak) [s] [m/s] * Spikes > 0. 1 m/s Were Removed and Were Not Included in Range Rate Error. **FAST Spacecraft Spin Rate of 12 rpm Clearly Visible in Plot of Residual Range Rate after Removing Largest Part of Residual Range Rate by Applying Time Bias to Calculated Data. Calculated Range Rate Is Based on 1. 5 -d Old TLE Set with Time Bias of -0. 272 THEMIS June 1 -2, 2004 s. FDMO CDR Peer Review − Flight Dynamics 35
FAST Doppler Track Analysis of On-orbit Doppler Tests with FAST Spacecraft Geometry: Spinning Platform: 12 rpm 4 Spin Plane Wire Booms, 2 Axial Stacer Booms, 2 Magnetometer Booms Spin Axis Pointed Perpendicular to Orbital Plane Cylindrical Antenna, Mounted on Body Axis Coherent Transponder Allows Two-way Ranging Post-launch Analysis of Mass Properties: (Provided by D. Pankow) One of the Spin-plane Wire Booms Did Not Deploy Completely Spin Axis Offset from Center of Mass: 49 mm Tilt Angle Between Body Axis and Spin Axis: 0. 37° Resulting Antenna Offset from Spin Axis: 43 mm THEMIS FDMO CDR Peer Review − Flight Dynamics 36 June 1 -2, 2004
FAST Doppler Track Analysis Test #104: Observed Range Rate of FAST at BGS. THEMIS FDMO CDR Peer Review − Flight Dynamics 37 June 1 -2, 2004
FAST Doppler Track Analysis Test #104: Observed − Calculated Range Rate; No Time Bias Applied to Calculated Range Rate. THEMIS FDMO CDR Peer Review − Flight Dynamics 38 June 1 -2, 2004
FAST Doppler Track Analysis Test #104: Time Bias of -0. 272 s Applied to Calculated Range Rate, Reduces Residuals by Factor of 60. CDMS Sample Rate 10 Hz; 10 Samples Averaged During Post-pass Analysis. Spacecraft Spin Rate of 12 FDMO rpm Clearly Visible. THEMIS CDR Peer Review − Flight Dynamics 39 June 1 -2, 2004
FAST Doppler Track Analysis Test #104: Time Bias of -0. 272 s Applied to Calculated Range Rate, Reduces Residuals by Factor of 60. CDMS Sample Rate 10 Hz; Only 4 Samples Averaged During Post-pass Analysis, Revealing More Complex Doppler Modulation. THEMIS Spin FDMO CDR Peer Review − Flight Dynamics 40 June 1 -2, 2004
FAST Doppler Track Analysis • Radius r of Circle on Which Antenna Moves Given by: r = v / (ω × cos β) v: Measured Doppler Velocity Associated with Antenna Motion [mm s-1] ω: Spin Rate [s-1] β: Elevation Angle of Line-of-sight Above Spin Plane [deg] • Measurement with BGS at 2003/347 02: 19: 00 UTC: v = 60. 2 ± 10. 8 mm s-1 (Range Rate Data − See Red Lines in Above Plot) ω = 2 π × 12. 0 / 60 s-1 (Attitude Sensor Data) β = 14. 3 deg (Orbit Analysis) r = 49. 4 ± 8. 9 mm • Measurement Agrees within Error Bars with Mass Properties Obtained from Post-launch Analysis: r = 43 mm THEMIS FDMO CDR Peer Review − Flight Dynamics 41 June 1 -2, 2004
FAST Doppler Track Analysis FAST Spacecraft Geometry Antenna Rolls Around Spin Axis Top View Antenna Shown Spin Every 90° of Axis Rotation Displacement of Spin Axis Is Almost Identical to Radius of Cylindrical Antenna, i. e. Antenna Rolls Around Spin Axis (See Above Drawing) Inner and Outer Parts of Antenna Move at Different Linear Velocities, Giving Rise to Differential Doppler Shift (Red and Blue Circles) THEMIS FDMO CDR Peer Review − Flight Dynamics 42 June 1 -2, 2004 Associated Phase Shifts May Cause
RHESSI Doppler Track Analysis of On-orbit Doppler Tests with RHESSI Spacecraft Relevant Spacecraft Features: Sun-pointed Spinning Platform: 15 rpm 4 Patch Antennas – 2 Forward, 2 Aft Non-coherent Transceiver with BPSK Modulation at 4 Mbps THEMIS FDMO CDR Peer Review − Flight Dynamics 43 June 1 -2, 2004
RHESSI Doppler Track Analysis Test #110: RHESSI One-way Doppler Track on Aft Antenna. CDMS Sample Rate 10 Hz; 5 Samples Averaged During Post-pass Analysis. Red Lines Indicate where Spin Doppler Modulation Was Measured. Rate 15. 0 Review rpm. − Flight Dynamics 44 THEMIS Spin FDMO CDRIs. Peer June 1 -2, 2004
RHESSI Doppler Track Analysis • Measurements with BGS at 2003/358 04: 47: 00 − 04: 49: 00 UTC: Forward Antenna: Aft Antenna: v = 372 ± 53 mm s-1 ω = 2 π × 15. 0 / 60 s-1 β = 38. 4 deg v = 566 ± 53 mm s-1 ω = 2 π × 15. 0 / 60 s-1 β = 10. 7 deg r = 302 ± 43 mm r = 367 ± 34 mm • Known Spacecraft Geometry: Forward Antenna: Aft Antenna: r = 285. 8 mm r = 368. 3 mm • Measurements and Spacecraft Geometry Agree Well within Error Bars • Interesting Comment: If RHESSI had a coherent transponder the spin Doppler modulation would be canceled out because the transmit and receive antennas are mounted 180° out of phase with respect to the spin axis! THEMIS FDMO CDR Peer Review − Flight Dynamics 45 June 1 -2, 2004
Doppler Test Summary of Ground Based and On-orbit Doppler Tests • Ground Station Configuration – Doppler Tests Demonstrated that BGS Microdyne 700 -MR (WB) Telemetry Receivers Can Be Used to Provide Accurate Range Rate Measurements with BPSK and PCM/PSK/PM Modulation – BGS Equipped with WFF Equipment Provides Doppler Tracking Data with Accuracy Comparable to NASA Ground Stations • Ground Based Loop-back Test Results – Range Rate Accuracy (1−σ) Obtained in Ground Based Loop-back Tests Is Typically < 1. 5 mm/s with a Sample Rate of 10 Hz and a Post-processing Integration Time of 10 s – Accuracy Essentially Independent of Signal-to-noise Ratio Down to the Receiver Lock Limit for BPSK and PCM/PSK/PM Modulation • On-orbit Test Results – On-orbit Tests with FAST Verified Range Rate Accuracy – On-orbit Tests with FAST and RHESSI Provided Information on Mass Properties and Spacecraft Geometry Based on Spin Doppler Modulation from the Relative Motion of the Spacecraft Antennas THEMIS FDMO CDR Peer Review − Flight Dynamics 46 June 1 -2, 2004
Implications for THEMIS • Operational Aspects – Record All Doppler Tracking Data at Rate of 10 Samples per Second to Allow for Detailed Post-pass Analysis • Orbit Determination – Above Results Used as Input to OD Covariance Analysis – Average Over Spin Doppler Modulation for Orbit Determination • Determination of Probe Mass Properties – Short Integration Times of 0. 1 s Allow for Analysis of Probe Spin Modulation – Determination of Displacement of Center of Mass from Body Z-Axis as Well as Precession Cone Angle – Observation of Coning and Nutation Damping After Probe Release and After Orbit and Attitude Maneuvers Appears Feasible – Verification of Symmetrical Wire Boom Deployment THEMIS FDMO CDR Peer Review − Flight Dynamics 47 June 1 -2, 2004
OD Covariance Analysis Tracking Arc Analysis for Orbit Determination • OD Covariance Analysis Performed by Code 595 (M. Beckman) – Provides Details on How Many Tracking Arcs per Orbit Are Needed to Determine Probe State Vectors with Required Accuracy • Accounted for Variety of Errors Sources – – – Solar Radiation: 30% Earth, Sun and Moon Gravity Model Station Location: 3 m in Each Axis Ionospheric and Tropospheric Refraction 3. 5 mm/s Accuracy (3 -σ) for Doppler Measurements in 10 -s Integration Time after Post-pass Processing – No Change in Doppler Noise as Function of Range • Various Station Scenarios – One Station (BGS) – One 30 -min Pass Per Day – Two Stations (BGS, WGS) – One 30 -min Pass Per Day, R < 10 RE – Three Stations (BGS, WGS, AGO) – 35 Passes Over 12 Days THEMIS FDMO CDR Peer Review − Flight Dynamics 48 June 1 -2, 2004
OD Covariance Analysis THEMIS FDMO CDR Peer Review − Flight Dynamics 49 June 1 -2, 2004
OD Covariance Analysis THEMIS FDMO CDR Peer Review − Flight Dynamics 50 June 1 -2, 2004
OD Covariance Analysis THEMIS FDMO CDR Peer Review − Flight Dynamics 51 June 1 -2, 2004
OD Covariance Analysis THEMIS FDMO CDR Peer Review − Flight Dynamics 52 June 1 -2, 2004
OD Covariance Analysis Summary • • • Planned THEMIS Approach Feasible One Ground Station (BGS) Can Support Basic OD Functions Data from Multiple Stations Needed for Orbit Solutions with High Accuracy Required to Support Small Delta V Maneuvers OD Covariance Analysis Results Probe Stations Passes / Arc Length [d] P 1 P 1 P 1 P 5 P 5 BGS BGS BGS, WLP, AGO BGS BGS 4 / 5. 5 d 5/7 d 12 / 14 d 18 / 21 d 5 / 21 d R < 10 R E 35 / 12 d 4 / 5. 5 d 5/7 d 12 / 14 d 18 / 21 d THEMIS FDMO CDR Peer Review − Flight Dynamics 53 Max. Position Error at Apogee / Perigee (3–σ) [km] 21. 0 / 3. 5 16. 0 / 3. 0 6. 9 / 1. 7 4. 0 / 0. 8 22. 5 / 6. 5 0. 4 / 0. 1 3. 4 / 1. 5 2. 6 / 1. 5 2. 2 / 0. 7 2. 3 / 1. 2 Max. Velocity Error at Apogee / Perigee (3–σ) [m/s] 0. 25 / 2. 5 0. 20 / 2. 0 0. 05 / 1. 5 0. 03 / 0. 58 0. 20 / 4. 75 0. 002 / 0. 056 0. 15 / 1. 15 0. 12 / 1. 0 0. 05 / 0. 53 0. 08 / 0. 76 June 1 -2, 2004
Tweak Maneuver Requirements Minimum Delta V Requirements for Tweak Maneuvers • • • Typical Orbit Tweak: ~ 5 m/s Small Tweaks: ~ 50 cm/s Smallest Tweaks: See Table Below Automated Mission Design Procedure Calls for Very Small Tweaks – Not Executed Maneuver Schedule Allows for Sufficient Tracking Time to Perform Orbit Determination with Required Accuracy Delta V Requirements Probe P 1 P 2 P 3 P 4 P 5 Smallest Required Delta V [cm/s] 8. 2 58 40 50 40 Orbital Period [h] 93. 232 47. 707 23. 931 23. 930 19. 145 THEMIS FDMO CDR Peer Review − Flight Dynamics 54 Corresponding Period Change [s] 191 479 11 14 9 June 1 -2, 2004
Orbit Determination Process THEMIS FDMO CDR Peer Review − Flight Dynamics 55 June 1 -2, 2004
DRMS Implementation DRMS Hardware Implementation • • • Uplink Uses Two Subcarriers at 16 k. Hz and 128 k. Hz Downlink Uses Two Subcarriers at 1024 and 128 k. Hz PRN Sequence of 216 -1 Bits Transmitted at Rate of 32 kbps Allows Unique Range Determination to 300, 000 km or 47 RE Round-trip Link Margin Allows Measurements Out to 40, 000 km DRMS Software Development • • Read Outgoing and Incoming Data Streams Simultaneously Perform Automated Shifting of Delay to Maximize Correlation BGS System Upgrades for DRMS • • DRMS Hardware (Linux Computer) for Signal Analysis Upgrade of Existing Back-up PTP (Demod/Bit Synch/Viterbi Card) Additional Matrix Switch for Baseband Signal Routing DRMS Software for Determination of Range Delay THEMIS FDMO CDR Peer Review − Flight Dynamics 56 June 1 -2, 2004
DRMS Design THEMIS FDMO CDR Peer Review − Flight Dynamics 57 June 1 -2, 2004
Attitude Determination REQUIREMENT DESIGN M-60. The THEMIS Ground System shall calculate and propagate all orbit and attitude parameters necessary for orbit maintenance and attitude control of each Probe. Compliance. Software systems to perform orbit and attitude determination and propagation will be employed at the MOC/SOC. Real-time, Ground-based Attitude Determination • • • Data Provided by Miniature Spinning Sun Sensor (MSSS), Flux Gate Magnetometer (FGM) and Inertial Reference Units (IRUs) Sensor Data Processed on the Ground in Real-time Slew Monitoring During Attitude and Orbit Maneuvers for Fault Protection Post-pass, Ground-based Attitude Determination • • Required for Science Data Analysis Data Provided by Sun Sensor and FGM Software Tools • Attitude Solution Obtained with MSASS, MTASS & UCLA Code THEMIS FDMO CDR Peer Review − Flight Dynamics 58 June 1 -2, 2004
Real-time Attitude Determination THEMIS FDMO CDR Peer Review − Flight Dynamics 59 June 1 -2, 2004
Attitude Determination Required Accuracy of Attitude Determination • Probe Spin Axis Inertial Orientation – Science: < 1° (3 -σ) (GS. SOC-12) – Prior to Maneuvers: < 5° (3 -σ) • • FGM to Spin Axis: < 0. 1° on Hourly Basis (GS. SOC-13) Probe Spin Axis to Body Z Axis: < 0. 5° (GS. SOC-14) Attitude Determination Error Analysis • Error Sources – Random Errors (Additive White Gaussian Noise) • Performed with ADEAS Code by Code 592 (Rick Harman) THEMIS FDMO CDR Peer Review − Flight Dynamics 60 June 1 -2, 2004
Issues, Concerns and Risks Issues • None Concerns • None Risks • None THEMIS FDMO CDR Peer Review − Flight Dynamics 61 June 1 -2, 2004
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