Radio frequency mass gaging technique model for particular spacecraft fuel and tank configuratio

Loftus, T. A.

English

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IPOSITIVE GAGING SYSTEM
FEASIBILITY STUDY
SUMMARY REPORT
PERIOD, May 15, 1967 to November 15, 1967
Contract No. NAS 9-6751
Prepared for
NASA - MANNED SPACECRAFT CENTER
HOUSTon, Texas
by
THE BENDIX CORPORATION
INSTRUMENTS b LIFE SUPPORT DIVISION
Davenport, Iowa
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PUBLICATION NO. 3914.1-68-3
April 17, 1968
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FOREWORD
This Summary Report was prepared by the Instruments and Life Sunnort Division of
the Bendix Corporation under Contract NAS 9-6751, "To Investigate and Desi gn a
Radio Frequency (RF) Mass Gaging Technique Independent of Gravity". The work
was administered under the direction of the National Aeronautics and Space
Administration Manned Spacecraft Center.
This report covers work conducted from May 15, 1967 to November 15, 1967.
Prepared by 7. 4- L-ont c
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Project Engineer
Reviewed y
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Manager Fluid Measurernents
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Paustian
Administrative Fnnineer
Approved by /!:^,2 V 
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I. INTRODUCTION
The Bendix Corporation,	 Instrument & Life Support	 Division,	 respectfully
submits this Summary Report to the Manned Spacecraft Center (MSC) to docu-
ment the progress made during the period	 15 May	 1967,	 to	 15 November	 1967,
on NASA Contract NAS 9-6751	 "To	 Investigate and Design a Radio Frequency
Mass Gaging Technique	 Independent of Gravity".	 The work performed under
this contract	 is based on the proposed program plan submitted as a portion
of Bendix Publication No. 	 3564-66,	 Revision	 "A",	 "Technical	 Proposal	 For
Positive
	
Gaging System Feasibility Study",	 pl; , s 	 the subsequent	 revision,
dated 3 February	 1967.
II. STUDY OBJECTIVES
- Under the proposed program,	 the work was	 divided	 into two phases.	 During
the
	 first phase,	 a theoretical	 analysis was	 to be performed to detail 	 the
measurement of	 fuel	 dielectric properties,	 and define the performance of
characteristics	 for several	 RF Fuel	 Mass Measurement Systems	 relative to
a "worst" Apollo or LEM Spacecraft fuel 	 and tank configuration.	 Experi-
mental	 work was then to be conducted on a	 limited basis to verify the
theoretical	 predictions or to evaluate the measurement techniques. 	 The
experiments to determine system performance were to be performed using
scale model	 SPS tanks,	 propellant simulants and	 laboratory type hardware.
Predictions of	 full	 scale system performance were to be made by scaling
the results obtained from the model
	
study to the actual	 tank and fuels
	
for
which the model	 was made.	 The performance of the system with  other fuels
in	 the particular tank configuration was 	 then	 to be	 included to enable a
r choice of a best gaging technique for a particular tank and	 fuel	 combina-
tion.
During the second phase, 	 an analysis was	 to be made of	 potential	 failure
areas and their effect on the system performance. 	 This analysis was	 to
be of a
	
limited scope because of the theoretical	 nature of this study,
concerned only with the major sources of 	 failure predicted for a system
component of	 a particular class or principle of operation.
Conclusions were to be made on the performance of the systems	 investigated
and recommendations	 for future evaluation or design and development ^ro
based on the	 results of	 the analysis and experiments conducted 	 in Phase	 I.
!II. RELATIONSHIP TO OTHER NASA EFFORTS
A study was conducted by the Instruments & Life Support Division for the
National Aeronautics and Space Administration _ George C. Marshall Space
Flight Center under Contract NAS 8-18039, "Studies to Determine the
Feasibility of Various Techniques for Measuring Propellant Mass Aboard
Orbiting Space Vehicle".
The contract, NAS 8-18039, bears similarity to Contract NAS 9-6751 ins -
far as advantages taken of the uniform illumination of the fuel interior
by the RF methods to render the measurement independent of propellant
position within the tank. Three RF based miss gaging techniques were
studied for the latter contract, while one of these was studied for the
former contract due to differences in the properties of the fuels for the
two contracts.
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IV,	 METHOD OF APPROACH b PRINCIPAL ASSUMPTIONS
The basis of a mass gaging system that is to be Independent of propellent
location within a spacecraft tank is that the propellent measurement must
be Independent of any geometric property of the propellant. In order for
this to be true, the interior of the propellent tank must be uniformly
Illuminated with some form of energy. The radio frequency band of tl^s
electromagnetic spectrum was chosen as being the most physically realizable
portion for obtaining uniform illumination. In this portion, the material
properties of dielectric constant and loss tangent provide the connection
between propellent mass and the electromagnetic field for the establishment
of a gage Independent of propellent geometry and location.
Basic Theory
Three basic techniques were evaluated which made use of the uniform illumina-
tion of the tank interior with RF energy, In all techniques, the output
was a function of mass content In the tank, Figure 2 shows the response
	 +
obtained from an exact calculation made to determine the uniformity of the
RF illumination for 'ractional filling with a given dielectric. The linear
form of the response shows that the electromagnetic Illumination of the
tank Interior is uniformly dependent on tank content. The form of the
response was also ma'ntained for three mutually perpendicular orientations
of the propellent surface, These two facts can be combined to show that the
electromagnetic illumination will remain uniform regardless of tank content 	 j
or distribution.
V.	 BASIC DATA GENERATED AND SIGNIFICANT RESULTS
Technique A
The experimental system was set up as shown in Figure I. A static loading
test was performed, and the data obtained for the horizontal, vertical and
Inverted positions of a tank is shown. The response is shown In Figure 3.
SINGLE ANTENNA EXPERIMENTAL SYSTEM
F I SIRE
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rTechninue
The experimental setu p was similar to the one used in Technicue
exce p t the data p rocessor rin g+ I yWd a different  output character , r i n. The
data obtained is shown, and the response is shown in Floure A.
TechninuA C
In this system the data processor was i.e only difference on comnar-son
j	 with the other exnerimental systems. Th p data obtained i =or a static
1	 loading test is shown, and the res ponse is shown In Fi g ure 5.
Experiments were also conducted in the Meld of li q uid dielectric measure-
ments. The method used was that of Von Hinnel, which Is the most versa+;le
4	 method of dielectric measurement. Based on a oaner by Roberts and Vor
Hippel, the method utilized the measurement of impedance at the SUrTaCe
of the liquid when p laced at the end of a short-circuited wavnriuide. The
!	 apparatus is shown in Figure 6. By measuring the voltake star` n n_ wave
ratio (VSWR), and position of the minimum of the standing wi. ,e natters,
•-	 the surface impedance may be calculated. From this, and the v.r.own th;c%-
ness of liquid, the die l ectric constant and loss tangent of the 11 m 4ic Mav
be calcuiated.
VI,	 LIMITATIONS
Techni q ues A and 3 both produced responses similar in nature, show:nq a
high sensitivity at low fillin gs and a total loss of sensitivity a' h"cn
fillings, This suggWs that these two tec_hninues are p robabl y sultebw
for detec t ion up to the 40% filling.
Technicue C p roduced a response of a more satisfactory nature, without
any loss of sensitivity for =illings from 0 - 100%.
VII.	 IMPLICATIONS FOR RESEARCH
The response oroduced from Technicue C had a disconti ni:in in i;s *ri..
This was attributed to the effect of the	 ruld around the antenna. F --nor
study is necessary to formulate an antenna system which would not be &— acted
by the presence of the liquid. Pesearch is necessary in areas or data
^-	 processing and dielectric properties. Knowled ge of the dielectric nrorc:
f	 ties is essential since these p roperties determine the sy-;t pm sensitivity,,
accuracy and temperature dependence.
Vill. FURTHER EFFORTS
L
On the basis of the study programs accom p lished by Bendix, the use of nr
techniques to ga pe propellent mass ahoard orbitin g space vehicles has icon
p roven feasible. The Bendix Cor p oration recommends thal a hardware
development program be initiated that will result in the imnlemente! on
of Technique	 as a treanheard system.
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The development of a breadboard system is recommended in order to assure
that a physicall y realizable RF Gaging System can be implemented. Although
subassemblies have Leen fabricated and tested during the feasibility study,
a complete system has not been fabricated. Fabrication and test of a
complete breadboard system will allow adequate definition of a flight
prototype, and will provide a test bed for the solution of any unforeseen
problem areas.
The followin g tasks are recommended in order to provide further development
of a Radio Frequency Gaging System for orbiting space vehicles:
Task 1 - DESIGN BREADBOARD SYSTEM
The dasign of a breadboard Radio Frequency Gaging System will be
based on the design parameters established from the feasibility
study. The breadboard system will use all of the components or
their functional equivalents required for a prototype system. Tte
breadboard system will not include packaging to a final configura-
tion; however, it will be packaged to a level sufficient to allow
testing with scale model propellant tanks. The following tasks
w II be performed in the design phase:
A. Des i gn
The tank probes, electronic circuits, mechanical parts, and
interconnecting elements required for signal conditioning
and data processing will be designed. Any mechanical parts	 -j
required for the system will be selected to meet the environ-
mental requirements. Special attention to compatibility re-
quirements will be given to any components which will come
into contact with the propellant. All mounting hardware re-
quired will be defined.
B. Propellant Measurements
The Roberts-Von Hippel technique should be perfected for
measuring the properties of liquids such as glycol, benzene,
etc., before being applied to the propellants in question.
The properties of the propellants N 0 , Aerozine 50 and MMH
should then be measured over the frequency range of interest.
This should include the determination of the effects of 	 j
-temperature on the propellants in order to decide whether
temperature compensation methods are needed for the gaging
systems.
C. Theoretical & Experimental Studies
Further study will be made to better Define the theoretical
basis for Technique C as a means of mass measurement
with respect to the propellants in q uestion. Experiments,
up to date, have not indicated any further problems besides
the liquid effect on the antenna. The theoretical study
should also be used to determine whether any major hardware 	 I
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problems will be encountered in implementing the techniques.
Methods of overcoming these problems will be outlined which
may be evaluated by experimentation.
Task 2 - FABRICATE EXPERIMENTAL HARDWARE
On the basis of the design studies, the necessary hardware will
be fabricated for experimentation. These experiments will be
conducted in order to verify the system characteristics predicted
by the design studies. These characteristics would include sensi-
tivity, accuracy and response time under the expected environmental
conditions. These experiments will be conk cted with and without
tank internal perturbations in order to study their effect on the
accuracy and sensitivity of Technique C.
Task 3 - EVALUATE SIGNAL PROCESSING DE=SIGN
The electronic means of signal processing necessary to achieve a
mass readout will be evaluated, on the basis of system accuracy
and sensitivity.	 Invariance to propellant position will be veri-
fied by experimentation with scale model propellant tanks.
Task 4 - SPECIFY SYSTEM COMPONENTS
A specification of the system components required for a total
mass gaging system will be made. 	 This specification will include
system operational characteristics relative to the worst tank,
propeilant and environmental conditions. Components will be
chosen that are suitable for flight hardware.
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Positive gaging system feasibility study Summary report, 15 May - 15 Nov. 1967

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