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Propellant estimationby Thermal Gauging Method (TGM)

Dr Boris YendlerYSPM

AgendaIntroductionHow Thermal Gauging Method (TGM) can help satellite operatorHow YSPM can help satellite manufacturer to make satellite TGM friendlyBasic of Thermal Gauging Method (TGM)Requirements for using TGMComparison with book-keeping and PVTExample of TGM estimationLooking backPast performanceAwardsTestimonialConclusionReferences

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**Tank temperature rises with time when heat is applied to the tank. Heat can come from different sources

How TGM will help Satellite Operator

Benefits to OperatorMore accurate estimation of propellant remaining TGM is more accurate than book-keeping and PVT at EOLTGM 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

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*Tank temperature rises with time when heat is applied to the tank.

How YSPM helps Satellite Manufacturer

*Designing Satellite being TGM friendlyYSPM 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 tankShapeGround controlPowerTemperature sensor Position on a tankAccuracyTelemetry A/D and D/A conversion Tank thermal connection:To s/c environment, e.g., optical properties of MLI, panels, etcBetween tanks (multi-tank system)Allowable temperature rise


Thermal Gauging MethodBasic

BasicsTemperature rise can be induced by: Tank heaters; Sun load; Equipment (e.g. IRU unit on BSS 601); etc.Thermal Gauging Method (TGM) accuracy improves with load propellant load decrease because 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 valveMono and bi propellant propulsion systems

*Measure a propellant tank load using temperature rise

**Tank temperature rises with time when heat is applied to the tank. Heat can come from different sources

TGM PhasesBuild integrated Thermal Model (Tank(s) and Spacecraft)Prepare and Conduct in-flight test (tanks heating and cooling)Calibrate integrated model per flight conditionsFind propellant load of each tankDetermine accuracy of the estimation

Regardless of spacecraft type, Thermal Gauging method follows the same phases*


Requirements for estimationSpacecraft design to build Tank and Spacecraft Thermal ModelsTank temperature typically propellant tanks have thermistorsA mean of changing tank temperature heater (tank, bus unit, payload, etc), sun

NOT MUCH*


Comparison with other Propellant Gauging Methods

Methods of GaugingBookkeeping- calculate consumed propellant (includes V, ranging, etc)Accuracy worse over time due to accumulation of errorPressure, 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 loadThermal Methods - calculate remaining propellant based on temperature rise (Including ESA TPGS, Comsat PGS, TGM, )Accuracy better over time

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Bookkeeping vs. Thermal Gauging MethodBookkeeping 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

450 kg consumed50 kg remainingTank Initial Load = 500 kg*

*Book-keeping 2-3% of USED, BUT PGS method accuracy 10-15% of Remaining. Were ahead of the game because remaining is much smaller than used at EOL (see picture)

PVT vs. TGM at BOLBeginning of Mission (BOL)*Assuming: propellant tank 500 liter; accuracy of PVT 2%; TGM 12%

*PVT vs. TGM at EOL

gas volume 480 liters; using 1 liter of propellant increases He volume by 0.2%- pressure reduces 0.2%

2% accuracy of 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

PVTThermal

Comparison (example of generic spacecraft)*Book-keeping, PVTHigh accuracy at Beginning of Life (BOL) through Middle of Life (MOL)Low accuracy at End of Life (EOL)Thermal GaugingHigh accuracy towards EOL

*This is generic example fuel mass could be different for different satellites and for different situations.

Example of TGM Extimation

Step 1a-Tank High Fidelity Model3-D propellant distribution in the tank using Surface EvolverGrid for Finite Element Model (FEM) high enough density to simulate temperature gradientsMore then 20000 nodesDetailed propellant and temperature distribution Simulation run time (6 10 hours per run)

Tank High Fidelity Model-contd Tank ModelTemperature Distribution(heaters are on domes)

Step 1b - Satellite ModelsStarDust (Ref.4) SpaceBus 2000 (Ref.2)BSS 601 (Ref.1)EuroStar 2000 (Ref.3)*

Step 2a- Test Procedure

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 OFFTank temperature can not exceed qualification limit

Operational ConstrainsGet approval from Manufacturer before the test

Step 2b- in-flight testHeaters ON(Fig.4 from Ref.2 )

Step 3 - S/C Model CalibrationNo ground calibration is requiredCalibration is performed using current flight dataCalibration of satellite model to reflect current condition of the satellite

Step 4 -Propellant EstimationFlight vs Simulation (Fig.5 from Ref.2)

Lines simulation results; Markers Temperature Sensor readingTank heaters were turned ON at t=0

Error Analysis Step 5

Categories of UncertaintyTwo categories of uncertaintyA least squares curve fit and associated uncertaintyUncertainties of specific model parametersPhysical parametersTemperature measurement Numerical model

Error Analysis Starting PointSatellite data:(Ti, ti)Simulation curves: T(t, m, p1, p2, p3,, q1, q2, q3,)Uncertainties for q parameters:qi

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*T represents temperature, either measured or simulated, depending on whether there is a subscript.t represents time, again, subscripted representing data, unsubscripted representing an independent variable.m represents the one parameter of real interest, the mass of the tank contents.The p parameters represent parameters that are not known, and therefore must be fit to the data. There are usually very few of these as fitting parameters decreases confidence in the model.The q parameters represent parameters that are known, but only to within a (known) uncertainty.Sometimes the uncertainties for T and t can be estimated, which allows a measure of goodness of fit, or systematic error.

Everything is known about the simulation function in principle, but in practice it is costly to evaluate.

Least Squares Analysis

*(Fig. 4 from Ref.4)Load is determined by Minimizing function M with respect to propellant massMismatch Function M

*Note that m does not depend on the p parameters, as they have been fit along with m. In principle each p is also a function of the data points and q parameters.

One simplification has been made here implicitly: the time data points have been ignored. Generally these are assumed known absolutely, but they can be treated as statistical data without much added complicatios.

UncertaintyAssuming 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.

*

*It is assumed here that all the data points have the same variance.More details of this calculation are given in an in-house document which we can provide.

TGM Accuracy of EstimationBottom LineTheoretical accuracy is determined by uncertainty analysis (Phase 5)Theoretical uncertainty is conservativeActual accuracy can be determined ONLY after tank(s) depletion Existing flight data indicate that Actual accuracy of Thermal Gauging Method is about 12% - 15% of propellant remaining

Typical Schedule of TGM estimationpaper work SOW, NDA, Contract 3 weeksModel development 2 weeksIn-flight test 2 weeksModel Calibration 2 weeksPropellant Estimation 2 weeksUncertainty Analysis 1 weekFinal Report

Total 12 weeks*


Typical DeliverablesOne summary report with test procedureOne summary report with propellant estimationOne summary with accuracy of estimationOne final report

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Looking Back Past Performance Awards Testimonials

Past Performance - S/C PlatformsMy 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, 601LM A2100, Ax2100, series 3000, 5000,7000 US Government SS/Loral FS1300 NASA (StarDust)

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S/C Platforms contMajority of spacecrafts have tank heaters and thermistorsThermal gauging has being successfully used on spacecrafts not designed specially for the approach, like StarDust, SS/L FS1300, SpaceBus 2000, etcThermal gauging was even successfully used for BSS 601 which does not have tank heaters

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Customers and AwardsMy 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*

"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, 2007www.aerotechnews.comTestimony from USAF*

Conclusion Thermal Gauging Method will provide accurate propellant estimation for satellites of different platformsThermal Gauging Method provides independent estimation of propellant remainingUse of the TGM increase reliability of the estimationTGM helps operators to make accurate business decisionYSPM will help manufacturers to design spacecraft thermal gauging friendly

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References T. Narita, B. Yendler, "Thermal Propellant Gauging System for BSS 601",25th AIAA International Communications Satellite Systems Conference (organized by APSCC),September 1820, 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 911, 2008, San Diego, California, paper AIAA 2008-7697 Apracio, B.Yendler,"Thermal Propellant Gauging at EOL, Telstar 11 Implementation",Space Operations 2008 Conference, May 1216, 2008, Heidelberg, Germany, paper 2008-3375 B. Yendler, et all, "Fuel Estimation for StarDust NExT mission",AIAA Space 2010 Conference and Exposition, Aug 30Sep 2, 2010, Anaheim, CA, USA

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**Tank temperature rises with time when heat is applied to the tank. Heat can come from different sources*Tank temperature rises with time when heat is applied to the tank. *Tank temperature rises with time when heat is applied to the tank. **Tank temperature rises with time when heat is applied to the tank. Heat can come from different sources*Tank temperature rises with time when heat is applied to the tank. *Tank temperature rises with time when heat is applied to the tank. *Book-keeping 2-3% of USED, BUT PGS method accuracy 10-15% of Remaining. Were ahead of the game because remaining is much smaller than used at EOL (see picture)*This is generic example fuel mass could be different for different satellites and for different situations.*T represents temperature, either measured or simulated, depending on whether there is a subscript.t represents time, again, subscripted representing data, unsubscripted representing an independent variable.m represents the one parameter of real interest, the mass of the tank contents.The p parameters represent parameters that are not known, and therefore must be fit to the data. There are usually very few of these as fitting parameters decreases confidence in the model.The q parameters represent parameters that are known, but only to within a (known) uncertainty.Sometimes the uncertainties for T and t can be estimated, which allows a measure of goodness of fit, or systematic error.

Everything is known about the simulation function in principle, but in practice it is costly to evaluate.*Note that m does not depend on the p parameters, as they have been fit along with m. In principle each p is also a function of the data points and q parameters.

One simplification has been made here implicitly: the time data points have been ignored. Generally these are assumed known absolutely, but they can be treated as statistical data without much added complicatios.*It is assumed here that all the data points have the same variance.More details of this calculation are given in an in-house document which we can provide.*Tank temperature rises with time when heat is applied to the tank. *Tank temperature rises with time when heat is applied to the tank. [

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