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Propellant estimation using the
Thermal Gauging Method (TGM)
Dr. Boris Yendler
YSPM, LLC
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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
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How TGM helps Satellite Operators
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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
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How YSPM Benefits Satellite Manufacturers
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Accuracy Analysis – Phase 5
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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
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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)
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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
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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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