Propellant estimation using the

Thermal Gauging Method (TGM)

Dr. Boris Yendler

YSPM, LLC

1

Agenda

• Introduction

• How Thermal Gauging Method (TGM) can help satellite operators

• How YSPM can help satellite manufacturers to make satellite TGM

“friendly”

• Basics of the Thermal Gauging Method (TGM)

• Requirements for using TGM

• Comparison with bookkeeping and PVT

• Example of a TGM estimation

• Propellant estimation in connected tanks

• Looking back

– Platforms

– Past performance

• Conclusion

• References

2

How TGM helps Satellite Operators

3

Benefits to Operators

• More accurate estimation of propellant

remaining – TGM is more accurate than bookkeeping and PVT at EOL

• TGM is an independent method – bookkeeping (BK)

and PVT methods are NOT independent (both use pressure transducer)

• Increased confidence in accurate determination

of EOL – use of independent methods increases reliability of estimation (BK and PVT methods are NOT independent)

• TGM helps Operators to make accurate and well-

informed business decisions

4

How YSPM Benefits Satellite Manufacturers

5

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Designing a Satellite to be TGM “friendly” YSPM will work with a satellite manufacturer during the design stage to make satellite TGM “friendly.” We will help to determine the 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

Thermal Gauging Method Overview

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Basics

• Temperature rise can be stimulated by different heat sources:

e.g. propellant tank heaters; Sun flux; heat rejection from s/c

equipment (e.g. IRU unit on BSS 601); etc.

• Thermal Gauging Method (TGM) accuracy improves with

mission life due to the increase of sensitivity of temperature

rise to tank load when tank load reduces

• TGM is capable of gauging:

- individual tanks in multi-tank propulsion systems with no

separation valve

- Mono and bi propellant propulsion systems 8

TGM uses tank temperature

rise to gauge propellant load

Phases of TGM development

1. Build integrated Thermal Model (Tank(s) and Spacecraft)

2. Prepare and conduct flight test (tanks heating and cooling)

3. Calibrate integrated model per flight conditions

4. Calculate propellant load of (each) tank

5. Determine accuracy of the estimation

TGM follows the same path regardless of the

spacecraft platform

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Information needed for TGM

• Spacecraft design – to build Tank and Spacecraft Thermal

Models

• Flight tank temperature – typically propellant tanks have

thermistors

NOT MUCH

10

Comparison with other Propellant Gauging Methods

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Methods of Gauging

• Bookkeeping - calculate consumed propellant based on

rocket equation/ flow equation

– Accuracy worse over time due to accumulation of

error

• Pressure, Volume, Temperature (PVT) - calculate

remaining propellant based on Gas Law

− Accuracy worse over time due to loss 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 with time

12

Thermal Gauging Method vs. Bookkeeping

• TGM accuracy is calculated based on remaining fuel Assuming accuracy – 12%; uncertainty – 50kg x 12% = 6 kg

• Bookkeeping accuracy is calculated based on consumed fuel Assuming accuracy of 2% ; uncertainty – 450 kg x 2% = 9 kg

450 kg consumed 50 kg remaining

Tank Initial Load = 500 kg

13

TGM vs. PVT at BOM

Beginning of Mission (BOM)

PVT

– 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

Thermal

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Assuming: propellant tank ≈500 liter; accuracy of

PVT – 2%; TGM – 12%

Fuel

He

He volume

Change of

He volume

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TGM vs. PVT at EOM

– 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

PVT Thermal

He

Fuel

End of Mission (EOM)

He volume

Change of

He volume

Comparison (example of generic spacecraft)

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• Bookkeeping, 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

End Beginning

Accura

cy

High

Low

Example of a TGM Estimation

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Phase 1a-Tank High Fidelity Model

Input

• Propellant distribution in the tank (Surface

Evolver)

• Exact position of heaters and temperature sensors

• Thermal and optical properties

• High density grid - around 9000 nodes

Result

• Knowledge of temperature at temperature sensor

location due to detailed temperature distribution

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Tank High Fidelity Model-cont’d

Tank Model

Temperature Distribution

(heaters are on domes) 19

Phase 1b - Satellite Models

StarDust (Ref.4)

SpaceBus 2000 (Ref.2) BSS 601 (Ref.1)

EuroStar 2000 (Ref.3)

East

West

East

West

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Phase 2a- Test Procedure

• No change in payload/Bus unit configuration during

test (avoid change of thermal condition)

• No significant station-keeping maneuvers

performed (avoid change of propellant load,

sloshing)

• Enough time for tank cool-down after turning

heaters OFF

• Tank temperature can not exceed “yellow” limit

Operational Constrains

Get approval from Manufacturer before the test

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Phase 2b- flight test

Heaters ON

(Fig.4 from Ref.2 )

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Phase 3 - Model Calibration

• Satellite model calibration is performed using

current flight data

• Satellite model reflects current condition

• Ground calibration is not needed

23

Phase 4 -Propellant Estimation

Flight vs Simulation

Lines – simulation results; Markers – Temperature Sensor reading

Tank heaters were turned ON at t=0

(Fig.5 from Ref.2) 24

Accuracy Analysis – Phase 5

25

26 26

Accuracy of Estimation

• Theoretical Accuracy - error is calculated based

on employed model

Bookkeeping method – error is calculated using flow

model for thruster

PVT method – error is calculated using the Gas Law

TGM – following slides

• Actual Accuracy – error is calculated as difference

between predicted and actual consumed propellants

Tank should be completely depleted

Bookkeeping method is used to calculate consumed

propellant between time of prediction and time of

depletion

Categories of Uncertainty

Two categories of uncertainty • Uncertainty related to propellant estimation, σfit

• Uncertainty σp of different parameters of the model, such as:

― Physical parameters (e.g. optical properties of the tank

surface, heater power, etc.)

– Telemetry data (e.g. error introduced by Analog to Digital

and Digital to Analog conversions, temperature sensor

accuracy, etc.)

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Propellant Estimation

i

ii mtUTM2

),(

28

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 1 2 3 4 5 6 7 8 9 10 11 12

Mis

matc

h F

un

ctio

n

Load [kg]

(Fig. 4 from Ref.4)

Load is determined by minimizing Mismatch Function M with respect

to propellant mass m

Mismatch Function M

where: Flight Telemetry data: Temperature Ti determined at given time ti Simulation curves: Temperature U is function of time t and

propellant mass m (function of all model parameters)

Uncertainties

• The model uncertainty σfit is based on curve fit

• The uncertainty of model parameters pi :

• The total uncertainty:

2

2

2

ip

i i

parp

m

29

222

parfittot

TGM Accuracy of Estimation

Bottom Line

• Theoretical accuracy is determined by Accuracy

Analysis (Phase 5)

• Theoretical accuracy is conservative

• Actual accuracy can be determined ONLY after tank

depletion

• Our experience indicates that the actual accuracy of

the Thermal Gauging Method should be about 12% -

15% of propellant remaining

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Typical Schedule of TGM estimation

• Documentation: Contract, NDA – 3 weeks

• Model development – 2 weeks

• Flight test – 2 weeks

• Model Calibration – 2 weeks

• Propellant Estimation – 2 weeks

• Accuracy Analysis – 1 week

• Final Report

Total – 12 weeks

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Typical Deliverables

• One summary report with test procedure

• One summary report with propellant estimation

• One summary with accuracy of estimation

• One final report

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Propellant Gauging in Connected Tanks

• Book-keeping method can determine only total propellant in

connected tanks, not propellant load of each tanks

• If one tank has low load or depleted, the other tank with higher load can NOT be used — propellant wasted — mission life is reduced

• Only Thermal Method can determine propellant load of each

tank when tanks are connected

• Examples of a such event: Anik E1 and E2, etc.

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Looking Back • Platforms

• Past Performance

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Experience with S/C Platforms

• Dr. Yendler’s experience during last 8 years includes working with the following spacecraft 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)

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S/C Platforms – continued

• The majority of spacecraft have tank heaters and thermistors

• The majority of spacecraft have not been designed specifically

for thermal gauging, like StarDust, SS/L FS1300, SpaceBus 2000,

etc

• BSS 601 platform does not have tank heaters [Ref.1]

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Performed Work in Past

Dr. Yendler has performed work for the following entities, among others: USA (Loral Skynet; EchoStar); US Government

(USAF, NASA); Canada (Telesat); Japan SkyPerfect (JSAT, SCC); Korea(KT); Luxembourg (SES); Mexico(SatMex); Turkey (Turksat); France (Thales); Saudi Arabia (Arabsat); etc.

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Conclusion

• Using the Thermal Gauging Method provides

accurate propellant estimation for satellites of

different platforms

• The Thermal Gauging Method provides

independent estimation of propellant remaining

• Use of the TGM significantly increases the

reliability of the estimation

• The TGM helps operators to make more

accurate and cost effective business decisions

• YSPM can assist manufacturers in designing

“thermal gauging friendly” spacecraft

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References

1. 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

2. 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

3. Apracio, B.Yendler,"Thermal Propellant Gauging at EOL, Telstar 11 Implementation", Space Operations 2008 Conference, May 12–16, 2008, Heidelberg, Germany, paper 2008-3375

4. B. Yendler, et all, "Fuel Estimation for StarDust NExT mission", AIAA Space 2010 Conference and Exposition, Aug 30–Sep 2, 2010, Anaheim, CA, USA

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