The Drop Dynamics Module houses an acoustic positioning system which counteracts the effects of small accelerations of a spacecraft and thus allows long-term study of free-floating materials such as liquid drops. The acoustic positioning system provides an acoustic 'well' in the center of the experiment chamber. Data collection is by cinematographic photography. The module subsystems are discussed

Stephens, J. B.

English

NASA Technical Reports Server

N79 - 1.90 38
Paper No. 29
e
CANCELLATION OF RESIDUAL SPACECRAFT ACCELERATIONS
FOR ZERO-G SPACE PHYSICS EXPERIMENTS
James B. Stephens, ,let Propulsion Laboratory, California Institute
of Technology, Pasadena, California
ABSTRACT
The Drop Dynamics Module houses an acoustic positioning
system which counteracts the effects of small accelera-
" tions of a spacecraft and thus allows long-term study
of free-floating materials such as liquid drops. The
acoustic positioning s_stem provides an acoustic "well"
in the center of the experiment chamber. Data
-r collection is by cinematographic photography. The
mod_11e subsystems are discussed in this paper.
I. INTRODUCTION
t
The Drop Dyvami_s Module (DDM) is a Spacelab-
compatible acoustic positioning and control system for conduct-
ing drop dynamics and physics experiments in the nearly weight-
less environment of space. The use of acoustics for levitating
and manipulating materials counteracts perturbing effects
, caused by small accele_'ations of the spacecraft. The system
consists basically of a chamber, a drop injector subsysLem, an
i acoustic positioning subsystem, a control subsystem, and a
data collection subsystem. The principal means of data collec-
tion is by cinematographic cameras. A drop of a selected
liquid is positioned in the center 9f the chamber by forces
created by acoustic standing waves. By varying the phase and
amplitude of t.be acoustic waves, the drop can be spun or oscil-
lated up to fission. The module is designed to perform its
expeA'_ments unattended, except f_,r startup and shutdown events
and other unique events requiring the attention of the Spacelab
payload specialist.
The major modu]e subsystems are presented in the fol',ow-
ing discussion.
LI. MODULE SUBSYSTEMS
Figure I is a functional block diagram of the module,
while Figure 2 is an artist_s concept of the module in place on
Spacelab. The Spacelab-bornr eubsystems of the module include
the acoustic chamber, con:col electronics, and imaging and data
acquisition. The ground-based subsystems include the
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necessary hardware and software for generation of automatic
sequence programs and for data analysis from the imaging and
other data records.
6
A. Acoustic Chamber 4
The acoustic chamber is center stage for the experiment i
activities: it is the resonant cavity which provides the neces-
sary acoustic standing w_ves to position liquid 4rops and it is
the backdrop for viewing and imaging the drop , ction.
The chamber i_ a thick-walled (I. Z7 cm) lucite rectangular
parallelepiped unit (i, d. approximately 15.2 x 15.2 x 16. ? cm).
:, At the center of the chamber the imaging cl._ar field of view is
12 x 12 cm. Acoustic driver ports are located on thr_e ortho-
gonal walls; the other thr-.e walls are transparent for imaging
and viewing, and une of these is hin_ed for access to the chamber
interior. Injector ports at the center of two opposite corners
provide fol introduction of the liquid drop.
A separate frame acts as a mount structure for the
cameras, mirrors, lights, sensors, injecters, and acoustic
• drivers. This chamber frame is mounted on retractable support
_lides to provide access for adjustment and servicing.
The chamber mockup is shown in Figur_ 3, as it will be
used in zero-g aboard KC-135 _ircraft.
]3. Acoustic Positi 'ling
The DDM will provide sufficient acoustic forces to initia!ly
position and maintain the center of a 2.5 cm drop within 3.0 cm
of the center of the chamber during module accelerations up to
10"Tg. For a Z. 5-cm diameter drop of water, this force will be
approximately 80 dyr.es. At 300OK and I arm, the acoustic reso-
nant frequencies of these drivers will be 1141, I141, and 10Z7Hz.
The acoustic forces will be controlled so that the drop centers
(as defined above) within I. 0 minute after injection.
T._.e acoustic power level, relative phase, modulation fre-
quency, modulation aruplitude and modulation phase _re con-
trolled independently for each axis.
Introduction of phase shift will cause the X-Y signal to
rotate about the "Z", or long axis ' the cl._mber, while the
torqu,_ is controlled by varying either the amplitude or phase.
The nominal m_ximum drop rotation rate w_ll be IZ rad/sec for
a 7.5-cm drop, with a controllable angular acceler tion of up to
I. 0 rad/sec Z. The mmimum rate of chan£e of acc. ieration will
be 0.01 rad/sec3, and the minimum rise time for the torque on
the drop will be 0. I scc. For a 2.5-cm diameter water drop,
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the maximum acceleration of I. 0 rad/sec 2 will correspond to a
torque o_ 5.1 dyne-cm.
a
Modulation of the acoustic signal amplitude alone will ......
cause an oscillation force to be applied to the drop in any or all
of the t,':ee chamber axes. The nominal drop oscillation stimu-
lus frec,_.,ncies wil' be in the range of 0 to I00 Hz, with control-
lable in,'-¢ase or r' --lease at a maximum rate of change of
1 Hz/_e,,. The oscillation signal (acoustic amplitude modulation)
will be _ ;_ :iable in three phases: 0o, 90 ° , and 180o. The phase
, of the Z-,,xis modulation will be fixed. The X and Y a:_es may
; each be modulated with either the 0o, 90 o, or 180 ° signal.
In addition, removal of the acoustic power will allow the
dr_,_ to drift undisturbed within the chamber. A drop centerir q
system will maintain the drop within the imaging field of view
and prevent collision with the chamber walls by using optical
sensors to control the acoustic power level.
The power levels, sensor location and other paramete_'s
of the drop centering system wili be selected to prevent the drop
from contacting r_e chamber wall in the presence of a 10-2g _c-
coloration. The centering forces will be limited to assure t,hat
the drop does not fissi-,n unintentionally within the imaging fiel_
of view even if this results in a collision with the chamber wall.
C. Fluid Management
Apart from acoustically manipulating the drop within the
chamber, provisions have been made for storing, injecting, and
charging the fluids.
v
The main functio_ o," the injector subsystem is to place a
drop (up to I0 cm 3) at the center of the chamber with as little
residual motion as possible, at a rate of 0. I - I. 0 cm3/sec.
After injection, the residual drop velocity is 0.5 cm/sec or less.
The subsystem can accommodate any nonflammable, non-toxic,
reasonably chemically inert liquid which has a vapor pressure of
less than one atmosphere at the maximum module operating
temperature (55oC). The subsystem will be capable of multiple
injections and retrievals of liquid drops
Six different reservoirs of liquid will be provided. Each
reservoir will have two flexible plastic tubes (tygon) attached,
each with an attached probe (the probes resemble long blunt
hypodermic needles). The tips of the injectors will be changed
every time the liquid is changed. The injecter mechanisms
drive the probes into the center of the chamber where the liquid
is released. Once the drop is formed, the probes are abruptly
withdrawn from the chamber, leaving the drop in the center.
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After injection the drop may be electrically charged or dis-
charged by inserting the charging probe so that it penetrates the
drop. The voltage can be manually adjusted, the drop charged,
• and the probe withdrawn.
/
: The drop may be electrostatically charged to +I000 volts. _;
The drop charging voltage will be controllable to +IV up to 100V, ..... +
:_ and +5V up to 1000V. The charging mechanism wTll also be cap- _
+" able-of discharging the drop to within 10V of the chamber wall
potential. Provision will be made for maintaining the entire +_
interior surface of the chamber at moduie ground potential dur-
, ing charged drop experiments. This will require the chamber
interior to be coated with a conductive m_terial, so that the
J entire surface is one conducting surface.
./+
D. Viewing and Imaging
The chamber interior can be viewed directly by the opera-
_ tor through the transparent walls. With the chamber in its norm-
al operating position, the entire chamber interior is visible. The '
' direct viewing provision will allow the module operator to oper-
ate module controls comfortably while viewing the chamber ,_
+ interior.
For direct viewing, the DDM will provide steady (non-
pulsed) illumination of the chamber interior. The intensity and
* direction of illumination will be sufficiet_ so that a clear (undyed)
: water drop may be clearly seen against t _e chamber background,
with an apparent drop brightness of at lea_t ZOO ft-Lamberts.
_ The principal means of data collection during the experi-
ments is by three 16 mm cinematographic cameras mounted on
three mutually orthogonal sites of the acoustic chamber. In-
cluded in the field of view of each camera is an alphanumeric
film annotation display and a reseau pattern or grid for geometric
calibration of the cameras to an accuracy of 0.02 cm. One
camera images the chamber center directly, while the other two
: image it via mirrors.
The cameras will have a focal length of Z5 ram, aperture
: of f/8, and depth of field 16.09 crn for two views and 17.78 cm
for the third view. Practically any high-speed color or black-
and-white film :s usable.
• Imaging will be accomplished so that the size and shape of
the drop xr,_y be determined to +O. 0Z cm. The minimum resolu-
tion in the object pla_e will be 20 cycles/cm (line pair/cm)(When
using color film, the .;maging resolution requirements are
: reduced.) Images wil_ be recorded at rates up to 200 per
second for each of the three views.
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The imaging sample rate (frame rate) will be stable to
within +0.1 frame/see, and the images of each of the three axes
will be synchronized to within +0. 0005 sec of each other and of the
module clock.
The illumination subsystem utilizes three strobe lights
: which are mounted around the acoustic driver ports to illuminate
the drop from any of the three orthographic sides opposite the
camera imaging ports; i.e., the drop can be front, back or side
lit. The light can be diffused or filtered by a coating applied to
: the chamber wall as desired.
E. Control and Sequencing
The module may be controlled manually by the operator,
•, completely automatically, or in some combination of these modes.
The module basic control functions will be controlled
through software programs generated either by the DDM or at
remote locations (away from the module). To facilitate remote
"' programming, the program language and memory medium will
be cornpatible with commonly used general purpose computers.
The program memory will be non-volatile for the expected dura-
tion of a Spacelab mission.
The DDlvl will provide subroutine capability for program-
' ruing short, frequently used sequences. Typical sequences which
could be stored in subroutines will include the basic rotation and
oscillation experiment sequences described in Ref. 1. There
will be no limit on the size and number of subroutines other than
that imposed by total controller memory capacity The purpose
of the subroutines will be to simplify programming and to allow
manual commanding of simple operations. Subroutines will be
stored in read-only memories (ROMS) or similar storage media.
Subroutines may be accessed either manually or under software
Contr ol.
F. Data Analysis
The ground-based portion of the DDM will provide support
/ for the reduction and analysis of DDM imaging records and
engineering and status data records. The objective of the data
analysis will be to convert raw DDM data te a form usable by the
science users. Prior to analysis of imaging records, high-
quality copies will be made for storage and distribution to users.
In general, data analysis will consist of:
1) Formatting and tabulating all module engineering and
status data and correlating it to the imaging records
Z) Mathematical characterization of drop profiles as a
function of time, acoustic power, phase, and modula-
tion frequency
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3. Derivation from (Z) of drop oscillation resonant
frequencies (particularly the fundamental), rotation
rates, damping constants, arop radii, and line shapes.
J
The imaging records will be analyzed by digitizing the ....
coordinates of at least 32 points on the drop profile for a selected
set of images (see Ref. 1). In addition the location of tracer
particles, if any, will be digitized.
The digitizing of imaging records may be accomplished
manually with the assistance of a light table, or autornatical|y.
The digital imaging records will be on magnetic tape in a format
• compatible with standard general-purpose computers.
The DDM will provide software for analysis of the module
data records and the digitized imaging records. This software
' will be written in a commonly used language (such as Fortran).
HI. CONC LUSIONS
The design of the module meets the requirements of the
baseline experiment proposed by JPL; however, modifications
may be made as needed to accommodate other experiments,
providing funding is available. The baseline experiments on
rotation and oscillation of liquid drops are precursors to future
experiments in which the oscillation of rotating drops will be
studied. The experiments are also precursors to ones in which
the drops are electrically charged, electrically conducting, di-
electric, non-Newtonian, or superfluid; and where external
fields are applied (electric, magnetic, electromagnetic, acoustic,
or thermal). In addition, it is envisaged that multiple drop
experiments w!U be performed in which the interactions of free
drops can be observed. These and other studies in basic physics
will be greatly aided by the capabilities of the Drop Dynamics
Module.
REFERENC ES
1. Wang, T. G., Elleman, D. D., and Saffren, M. M., JPL
Drop D_rnamics Experiment, JPL Document 701-2Z4,
30 July 1975.
Z. Drop Dynamics Module Proicct Plan, JPL Document 701-
221, 16July'1976.
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Paper No. 30 ....
UNIQUE TEST FACILITY FOR EVALUATION OF MHD ELECTRODE
AND INSULATOR MATERIALS
- I.M. Grinberg, R. G. Lute, and A. A. Boiarski, Battelle's Columbus
• Laboratories, Columbus, Ohio
ABSTRACT
The development of central-atatlon, open-cycle,
coal-flred l_V power generators depends to a great
/._ extent on the ability of the crltlcal electrode and :
insulator components to perform satisfactorily. The
unique performance requirements for the materials
must be considered in terms of the long-duration
physical, thermal, chemical, and electrical environ-
i , meats in which reliable generator operation must be
maintained. Development of electrode and insulator
materials requires their evaluation in an environ-
meat that closely simulates expected central-statlon
channel operational conditions in order to adequately
: relate the effects of long-time material exposure
with those of high-temperatu_re, seed, coal-slag, end
electrical current transfer on critical material
properties. Such screening evaluations are difficult
to conduct economically under well-characterized con-
trolled conditions in an operational I_D generator.
This paper describes a unique MI_D test facility which
is capable of providing a simulated F_4D environment
over a broad range of gas temperature, pressure, fuel,
electric field, and combustion gas conditions and is
well suited for the conduct of materials evaluations.
The test facility utilizes a hybrid electric arc-
heated combustion-driven gas supply. The use of electric
arc-heated gas in conjunction with combustion-driven
flow is shown to provide the flexibility required to
independently assess relative effects of the important
gas side properties on material performance. It is
also shown that the important MI_D channel parameters
can be independently controlled without application of
a magnetic field with application of an applied voltage
to provide the desired current density in electrode
materials.
..... p/,., ,,
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, A brl_f d&s_rlptlon of each of the components
and operational envelope of the overall system is
given in terms of the attainable simulated test .:
channel conditions. Conditions achieved in tests
recently conducted to evaluate electrode materials
used in the U02 HHD facility are shown. Also in-
cluded is a brief description of diagnostics used
to characterize the gas environment.
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Cancellation of residual spacecraft accelerations for zero-G space physics experiments

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