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Propellant estimation by Thermal Gauging Method (TGM)

Propellant estimation by Thermal Gauging Method (TGM). Dr Boris Yendler. YSPM. Agenda. Introduction How Thermal Gauging Method (TGM) can help satellite operator How YSPM can help satellite manufacturer to make satellite TGM “friendly” Basic of Thermal Gauging Method (TGM)

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Propellant estimation by Thermal Gauging Method (TGM)

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  1. Propellant estimationby Thermal Gauging Method (TGM) Dr Boris Yendler YSPM

  2. Agenda • Introduction • How Thermal Gauging Method (TGM) can help satellite operator • How YSPM can help satellite manufacturer to make satellite TGM “friendly” • Basic of Thermal Gauging Method (TGM) • Requirements for using TGM • Comparison with book-keeping and PVT • Example of TGM estimation • Looking back • Past performance • Awards • Testimonial • Conclusion • References

  3. How TGM will help Satellite Operator

  4. Benefits to Operator • More accurate estimation of propellant remaining – TGM is more accurate than book-keeping and PVT at EOL • TGM is independent method – book-keeping (BK) and PVT methods are NOT independent (both use pressure transducer) • Increase confidence in accurate determination of EOL – use of independent methods increase reliability of estimation (BK and PVT methods are NOT independent) • TGM helps an Operator to make accurate business decision

  5. How YSPM helps Satellite Manufacturer

  6. Designing Satellite being TGM “friendly” • YSPM will work with satellite manufacturer to make satellite TGM “friendly” on design stage. We will help to determine an optimal designs of: • Heater • Position on a tank • Shape • Ground control • Power • Temperature sensor • Position on a tank • Accuracy • Telemetry A/D and D/A conversion • Tank thermal connection: • To s/c environment, e.g., optical properties of MLI, panels, etc • Between tanks (multi-tank system) • Allowable temperature rise

  7. Thermal Gauging MethodBasic

  8. Basics Measure a propellant tank load using temperature rise • Temperature rise can be induced by: Tank heaters; Sun load; Equipment (e.g. IRU unit on BSS 601); etc. • Thermal Gauging Method (TGM) accuracy improveswith load propellant load decreasebecause sensitivity of temperature rise to tank load is increasing when tank load drops • The method is capable of gauging: • individual tanks in multi-tank propulsion systems with no separation valve • Mono and bi propellant propulsion systems

  9. TGM Phases Regardless of spacecraft type, Thermal Gauging method follows the same phases Build integrated Thermal Model (Tank(s) and Spacecraft) Prepare and Conduct in-flight test (tanks heating and cooling) Calibrate integrated model per flight conditions Find propellant load of each tank Determine accuracy of the estimation

  10. Requirements for estimation • Spacecraft design – to build Tank and Spacecraft Thermal Models • Tank temperature – typically propellant tanks have thermistors • A mean of changing tank temperature – heater (tank, bus unit, payload, etc), sun NOT MUCH

  11. Comparison with other Propellant Gauging Methods

  12. Methods of Gauging • Bookkeeping- calculate consumed propellant (includes V, ranging, etc) • Accuracy worse over time due to accumulation of error • Pressure, Volume, Temperature (PVT) - calculate remaining propellant based on Gas Law (including variants like re-pressurization) • Accuracy worse over time due to lost of sensitivity of He pressure to volume change in tanks with low propellant load • Thermal Methods - calculate remaining propellant based on temperature rise (Including ESA TPGS, Comsat PGS, TGM, …) • Accuracy better over time

  13. Bookkeeping vs. Thermal Gauging Method Tank Initial Load = 500 kg • Bookkeeping accuracy is calculated based on consumed fuel Assuming accuracy of 2% ; uncertainty – 450 kg x 2% = 9 kg • TGM accuracy is calculated based on remaining fuel Assuming accuracy – 12%; uncertainty – 50kg x 12% = 6 kg 50 kg remaining 450 kg consumed

  14. PVT vs. TGM at BOL • Assuming: propellant tank ≈500 liter; accuracy of PVT – 2%; TGM – 12% Thermal PVT • Beginning of Mission (BOL) • gas volume 1 liter; using 1 liter of propellant doubles gas volume- pressure reduces 50% • 2% accuracy of gas volume is 0.2 liter • (≈ 0.2 kg) • Propellant load 499 kg; using 1 kg of propellant reduces mass by 0.5%; small change in slope of temperature rise • 12% accuracy is 60 kg

  15. PVT vs. TGM at EOL Thermal PVT • gas volume 480 liters; using 1 liter of propellant increases He volume by 0.2%- pressure reduces 0.2% • 2% accuracyof gas volume is 9.6 liters (≈ 9.6 kg) • Propellant load 20 kg; using 1 kg reduces mass by 5%; significant change in thermal response • 12% accuracy is 2.4 kg

  16. Comparison (example of generic spacecraft) High • Book-keeping, PVT • High accuracy at Beginning of Life (BOL) through Middle of Life (MOL) • Low accuracy at End of Life (EOL) • Thermal Gauging • High accuracy towards EOL Accuracy Low End Beginning

  17. Example of TGM Extimation

  18. Step 1a-Tank High Fidelity Model • 3-D propellant distribution in the tank using Surface Evolver • Grid for Finite Element Model (FEM) • high enough density to simulate temperature gradients • More then 20000 nodes • Detailed propellant and temperature distribution • Simulation run time (6 – 10 hours per run)

  19. Tank High Fidelity Model-cont’d Tank Model Temperature Distribution (heaters are on domes)

  20. West West North Radiator North Radiator South Radiator South Radiator East East Step 1b - Satellite Models BSS 601 (Ref.1) SpaceBus 2000 (Ref.2) StarDust (Ref.4) EuroStar 2000 (Ref.3)

  21. Step 2a- Test Procedure Operational Constrains • Avoid eclipse season (change of thermal condition) • No change in payload/Bus unit configuration (change of thermal condition) • No station-keeping maneuvers performed (change of propellant load, sloshing) • Enough time to cool-down for the tanks after turning heaters OFF • Tank temperature can not exceed qualification limit Get approval from Manufacturer before the test

  22. Step 2b- in-flight test Heaters ON (Fig.4 from Ref.2 )

  23. Step 3 - S/C Model Calibration • No ground calibration is required • Calibration is performed using current flight data • Calibration of satellite model to reflect current condition of the satellite

  24. Step 4 -Propellant Estimation Flight vs Simulation (Fig.5 from Ref.2)

  25. Error Analysis – Step 5

  26. Categories of Uncertainty • Two categories of uncertainty • A least squares curve fit and associated uncertainty • Uncertainties of specific model parameters • Physical parameters • Temperature measurement • Numerical model

  27. Error Analysis Starting Point • Satellite data: (Ti, ti) • Simulation curves: T(t, m, p1, p2, p3,…, q1, q2, q3,…) • Uncertainties for q parameters:σqi

  28. Least Squares Analysis Mismatch Function M Load is determined by Minimizing function M with respect to propellant mass (Fig. 4 from Ref.4)

  29. Uncertainty • Assuming that the model is a good fit apart from statistical errors, • These can all be calculated. The variance of Ti comes out of the least squares fit if we assume they are all equal.

  30. TGM Accuracy of Estimation • Bottom Line • Theoretical accuracy is determined by uncertainty analysis (Phase 5) • Theoreticaluncertainty is conservative • Actual accuracy can be determined ONLY after tank(s) depletion • Existing flight data indicate that Actualaccuracy of Thermal Gauging Method is about 12% - 15% of propellant remaining

  31. Typical Schedule of TGM estimation • paper work SOW, NDA, Contract – 3 weeks • Model development – 2 weeks • In-flight test – 2 weeks • Model Calibration – 2 weeks • Propellant Estimation – 2 weeks • Uncertainty Analysis – 1 week • Final Report • Total – 12 weeks

  32. Typical Deliverables • One summary report with test procedure • One summary report with propellant estimation • One summary with accuracy of estimation • One final report

  33. Looking Back • Past Performance • Awards • Testimonials

  34. Past Performance - S/C Platforms • My experience includes more than 45 thermal gauging estimations during last 7 years including the following platforms: • Alcatel/TAS France SpaceBus 2000, 3000A • Astrium/EADS EuroStar 2000 • Boeing SS 376, 601 • LM A2100, Ax2100, series 3000, 5000,7000 • US Government • SS/Loral FS1300 • NASA (StarDust)

  35. S/C Platforms – cont’ • Majority of spacecrafts have tank heaters and thermistors • Thermal gauging has being successfully used on spacecrafts not designed specially for the approach, like StarDust, SS/L FS1300, SpaceBus 2000, etc • Thermal gauging was even successfully used for BSS 601 which does not have tank heaters

  36. Customers and Awards My customers include but not limited to : USA (Loral Skynet); US Government (USAF, NASA); Japan SkyPerfect (JSAT, SCC); Turkey (Turksat); France (Thales); Canada (Telesat), Saudi Arabia (Arabsat); etc. COMSAT PGS group received 2006 US Air Force Chief of Staff Team Excellence Award

  37. Testimony from USAF "The DSCS program office's satellite life extension efforts help to save up to five million dollars per year," said Brig Gen Ellen Pawlikowski, MILSATCOM Systems Wing Commander. "By extending the life of the DSCS constellation and by sharing these innovative techniques with other space programs, the team's work will be felt for many years to come.“ Astro News, November 3, 2007 www.aerotechnews.com

  38. Conclusion • Thermal Gauging Method will provide accurate propellant estimation for satellites of different platforms • Thermal Gauging Method provides independent estimation of propellant remaining • Use of the TGM increase reliability of the estimation • TGM helps operators to make accurate business decision • YSPM will help manufacturers to design spacecraft “thermal gauging friendly”

  39. References T. Narita, B. Yendler, "Thermal Propellant Gauging System for BSS 601", 25th AIAA International Communications Satellite Systems Conference (organized by APSCC), September 18–20, 2007, Bangkok, Thailand, paper AIAA 2007-3149 B.Yendler, et all, "Thermal Propellant Gauging, SpaceBus 2000 (Turksat 1C) Implementation", AIAA SPACE 2008 Conference & Exposition, September 9–11, 2008, San Diego, California, paper AIAA 2008-7697 Apracio, B.Yendler,"Thermal Propellant Gauging at EOL, Telstar 11 Implementation", Space Operations 2008 Conference, May 12–16, 2008, Heidelberg, Germany, paper 2008-3375 B. Yendler, et all, "Fuel Estimation for StarDustNExT mission",AIAA Space 2010 Conference and Exposition, Aug 30–Sep 2, 2010, Anaheim, CA, USA

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