Propellant estimationby

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)• Requirements for using TGM• Comparison with book-keeping and PVT• Example of TGM estimation• Looking back

– Past performance– Awards– Testimonial

• Conclusion• References

2

How TGM will help Satellite Operator

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

4

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

Thermal Gauging MethodBasic

Basics

• Temperature 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 valve- Mono and bi propellant propulsion systems

8

Measure a propellant tank load using

temperature rise

TGM Phases

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

2. Prepare and Conduct in-flight test (tanks heating and cooling)

3. Calibrate integrated model per flight conditions

4. Find propellant load of each tank

5. Determine accuracy of the estimation

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

9

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

10

Comparison with other Propellant Gauging Methods

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

12

Bookkeeping vs. Thermal Gauging Method

• 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

450 kg consumed 50 kg remaining

Tank Initial Load = 500 kg

13

PVT vs. TGM at BOL

Beginning of Mission (BOL)

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

14

Assuming: propellant tank ≈500 liter; accuracy of PVT – 2%; TGM – 12%

15

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

PVT Thermal

Comparison (example of generic spacecraft)

16

• 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

EndBeginning

Acc

urac

yHigh

Low

Example of TGM Extimation

Step 1a-Tank High Fidelity Model

• 3-D propellant distribution in the tank using 3-D propellant distribution in the tank using

Surface EvolverSurface Evolver

• Grid for Finite Element Model (FEM)Grid for Finite Element Model (FEM)

− high enough density to simulate temperature gradientshigh enough density to simulate temperature gradients

• More then 20000 nodesMore then 20000 nodes

• Detailed propellant and temperature distribution Detailed propellant and temperature distribution

• Simulation run time (6 – 10 hours per run)Simulation run time (6 – 10 hours per run)

Tank High Fidelity Model-cont’d

Tank Model

Temperature Distribution(heaters are on domes)

Step 1b - Satellite Models

StarDust (Ref.4)

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

EuroStar 2000 (Ref.3)20

East

West

North

Rad

iato

r

South

Rad

iato

rEast

West

North

Rad

iato

r

South

Rad

iato

r

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 OFF• Tank temperature can not exceed qualification limit

Operational Constrains

Get approval from Manufacturer before the test

Step 2b- in-flight test

Heaters ON

(Fig.4 from Ref.2 )

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

Step 4 -Propellant Estimation

Flight vs Simulation

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

(Fig.5 from Ref.2)

Error Analysis – Step 5

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

Error Analysis Starting Point

• Satellite data:(Ti, ti)

• Simulation curves: T(t, m, p1, p2, p3,…, q1, q2, q3,…)

• Uncertainties for q parameters:σqi

27

Least Squares Analysis

i

ii qqppmtTTM 22121 ,...),,...,,,,(

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

mat

ch F

un

ctio

n

Load [kg]

(Fig. 4 from Ref.4)

Load is determined by Minimizing function M with respect to propellant mass

Mismatch Function M

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.

2

2

2

2

2

jqj j

Ti i

m q

m

T

m

29

TGM Accuracy of Estimation

Bottom Line• Theoretical accuracy is determined by uncertainty

analysis (Phase 5)

• Theoretical uncertainty is conservative

• Actual 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 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

31

Typical Deliverables• One summary report with test procedure

• One summary report with propellant estimation

• One summary with accuracy of estimation

• One final report

32

Looking Back• Past Performance• Awards• Testimonials

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)

34

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

35

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 COMSAT PGS group received 2006 US Air Force Chief of Staff Team Excellence AwardChief of Staff Team Excellence Award

36

"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

Testimony from USAF

37

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”

38

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

39