Observing Fluid Flows in
Microgravity using DDPIV
The Caltech Student Microgravity Initiative 2010
Caltech
1200 E. California Boulevard
Pasadena, CA 91125
Designated Team Contact: Erin Zampaglione, [email protected], 626-395-XXXX
Faculty Supervisor: Dr. Morteza Gharib, [email protected], 626-395-4453
Additional Support: Dr. Eugene Trihn, [email protected], 818-354-5359
Team:
Eric Chin
John Forbes
W. Max Jones
Calvin Kuo
Daniel Obenshain
Erin Zampaglione
Flyer
Flyer
Flyer
Flyer
Flyer
Flyer
Sr, CNS*
Sr, Physics
Sr, Physics
Jr, MechE
Sr, CS, English
Jr, Biology
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
*Computational and Neural Systems
I, Morteza Gharib, approve of this proposal. X___________________
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Table of Contents
Cover Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Flight Week Preference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Test Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Test Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Experiment Safety Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Outreach Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Institutional Letter of Endorsement
From Caltech President Dr. Jean-Lou Chameau . . . . . . . . . . . . . . . . . . . . . . . . . 20
From Caltech Dean of Students Dr. John Hall . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Statement of Supervising Faculty
From Dr. Morteza Gharib, Caltech Professor . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
From Dr. Eugene Trinh, JPL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Funding/Budget Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
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Flight Week Preference
We would prefer to fly in Flight Week 2 (7/08/2010 – 7/17/2010), rather than Flight
Week 1 (06/17/2010 to 06/26/2010), but we’re flexible.
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Abstract
We will examine the fluid flow caused by the coalescence of a droplet onto the top of a
flat surface of a fluid. When the droplet has a large surface tension and minimal velocity
as it contacts the surface, corresponding to a low Weber number, a vortex ring is formed
upon coalescence. The three dimensional velocity field of the drop and the surface during
this process will be quantitatively determined using defocusing digital particle image
velocimetry (DDPIV). When this experiment is done under 1 G conditions, it is
impossible to separate out the effects of surface tension and gravity. Performing this
experiment in microgravity allows us to observe this process in a regime where the
influence of surface tension dominates that of gravity.
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Test Objectives
We aim to quantitatively describe fluid flows created when a drop of fluid coalesces with
a flat surface of the same liquid, particularly in the vortex-forming regime. In doing so,
we hope to demonstrate the effectiveness of DDPIV in a microgravity environment.
This experiment is not a follow-up to a previous RGSFOP experiment, although it is
closely related to Dooley 1997, in which a drop of water is observed as it coalesces with a
surface at zero velocity in 1 G. Dimensional analysis of that situation, with the goal of
describing the time scale of vortex ring formation, yields three dimensionless quantities.
These quantities respectively correspond to the effects of viscosity, gravity, and surface
tension. Assuming that surface tension effects dominate gravity and viscosity, one can
conclude that the time scale is related to the surface tension by a simple power law. The
results of the 1997 experiment nearly adhere to this, but there is a clear systematic
deviation. We hypothesize that in a microgravity environment, the power law would
describe this relation much more precisely.
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Test Description
We're planning on observing the fluid flow caused by the coalescence of a droplet onto a
flat surface of the same fluid. In order to accomplish this in the microgravity
environment, the flat surface will be at the interface between two immiscible liquids. The
liquids will be contained in one of five relatively small plexiglass containers, filled nearly
completely. The composition of these liquids has yet to be decided, but they are likely to
be composed of some combination of water, glycerin, corn oil, and isopropyl alcohol.
The oil would be immiscible with any mixture of the other liquids. Using the same fluid
contained in the lower stratum, drops will be formed from a pipette tip fixed to the top of
the container. These will be
attached via tubing to a separate
box containing plungers, one per
plexiglass cell (Figure 1).
The precise method of
controlling the plungers has not yet
been determined. In all cases, we
would have a single button or
switch that would trigger the
formation of a drop, and the
recording of its coalescence with
the DDPIV system (see below).
Possibilities include experimentally Figure 1: This is a wire frame picture of the assembly.
The camera and holes for tubing are not included, as
determining a set length of time
necessary for each motor to run to we are unsure of their dimensions. The camera will go
produce a drop that will just touch on the block suspended on the two bars and the tubing
will go in holes on the top of the containers. Slots
the interface between the two
may also be added to the main base for the cargo
immiscible fluids. This method
would require the height of each straps for take off and landing.
stratum to be precisely calibrated in all trials, which may prove rather difficult. Another
possible method is to complete a circuit by the contact of the drop with the lower stratum.
The velocity field of the fluids will be mapped using a technique called
defocusing digital particle image velocimetry (DDPIV) in which small reflective particles
are placed in the fluid, illuminated with a laser, and filmed with a high-speed camera.
From this we can reconstruct the 3-D velocity field using commercially available
software. This method is remarkable in that it is able to view the situation in three
dimensions with only one camera. Ideally the camera will be able to interface with a
laptop via USB, which will allow in-situ analysis after each trial.
The work of Dooley 1997 examined the coalescence of water drops onto a flat
surface formed by a water-air interface. In that situation, the authors assert that the
potentially important physical parameters in the problem are surface tension σ, density ρ,
time scale of vortex-ring formation τ*, the gravitational acceleration g, the viscosity ν,
and a characteristic length scale of the drop L. From these, one can form three
dimensionless parameters: (ν τ* / L2), (gτ*2/L), and (σ τ*2 / ρ L3). For the experiment
described in Dooley 1997, one may well expect that the effects of surface tension
dominate both gravity and viscosity. As such, one could theoretically relate surface
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tension and time scale by a power law, assuming constant density and drop size. The data
(figure 4 of Dooley) fits approximately, but suggests that the other parameters have a
non-negligible influence.
In our experiment, we will be able to directly compare results between 1G and
microgravity environments, leaving everything else in the experiment unchanged –
namely surface tension, densities, drop sizes and viscosities. Not only will we be able to
observe the effect of gravity on the relation between surface tension and time scale, but
also we will be able to directly observe the difference in velocity fields.
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References
Anilkumar, AV, et al. “Surface-Tension-Induced Mixing following Coalescence of
Initially Stationary Drops.” Phys. Fluids A 3(11) (1991): 2587-91
Dooley, BS, et al. "Vortex Ring Generation Due to the Coalescence of a Water Drop at a
Free Surface." Experiments in Fluids 22.5 (1997): 369-74.
Graff, EC, and M Gharib. "Performance Prediction of Point-Based Three-Dimensional
Volumetric Measurement Systems." Measurement Science and Technology 19.7
(2008): 75403-500.
Lu, J, et al. "Three-Dimensional Real-Time Imaging of Cardiac Cell Motions in Living
Embryos." Journal of Biomedical Optics 13 (2008): 014006.
Pereira, F, et al. "Microscale 3d Flow Mapping with DDPIV." Experiments in Fluids 42.4
(2007): 589-99.
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Experiment Safety Evaluation
Flight Manifest
Primary Fliers:
Eric Chin
John Forbes
W. Max Jones
Calvin Kuo
Daniel Obenshain
Erin Zampaglione
Experiment Description / Background
We will examine the fluid flow caused by the coalescence of a droplet onto the top of a
flat surface of a fluid. When the droplet has a large surface tension and minimal velocity
as it contacts the surface, corresponding to a low Weber number, a vortex ring is formed
upon coalescence. The three dimensional velocity field of the drop and the surface during
this process will be quantitatively determined using defocusing digital particle image
velocimetry (DDPIV). When this experiment is done under 1 G conditions, it is
impossible to separate out the effects of surface tension and gravity. Performing this
experiment in microgravity allows us to observe this process in a regime where the
influence of surface tension dominates that of gravity.
Equipment Description:
The proposed fluid experiment will require one independent test per microgravity
experience during a flight. The equipment was thus designed to contain several
independent test chambers that could be switched out instead of having one test chamber
that would have to be reset and recalibrated for each test. One benefit of having multiple
independent test chambers were that recalibrating a single test chamber for a multitude of
different tests would be time consuming, and given the short periods between
microgravity experiences during a flight, such long recalibration times would reduce the
number of tests that we would be able to complete during one flight. Another benefit for
having independent test chambers was that if one test chamber became contaminated or
malfunctioned, then it would not comprise me entire experiment (just that one trial),
whereas with one test chamber, if there was a mechanical problem or contamination, then
it would potentially jeopardize the entire experiment.
Our experiment is also sensitive to vibrations from the aircraft, so the equipment
needed to be designed in order to minimize such unwanted flight movements. Thus, the
experimental apparatus is designed on top of a platform designed to minimize movements
in the plane parallel to the floor of the aircraft. Thus full test apparatus is shown in figure
1. Each component of the proposed apparatus will also be explained in more detail.
Figure 1 depicts the entire apparatus for our experiment
The experimental apparatus is split into three distinct sections. The first section is
the suspension system described earlier (figure 2). The suspension system will support
the base plate and all the experimental components and damp the vibrations of the
aircraft. The suspension is comprised of two sets of parallel bars set perpendicular to
each other. Each set is designed to provide suspension in one axis (the x or the y axis
parallel to the floor of the aircraft) in order to minimize vibrations from the aircraft. The
sets of bars are connected by sliders that will slide along the x-directional suspension bars
while supporting the y-directional bars as shown. The suspension system has four feet
that are designed to be bolted to the aircraft floor using the 3/8 inch diameter bolts
provided. Each foot has two legs where a bolt will be secured to the aircraft floor, and
each foot will be bolted 40 inches away from its closest neighbors as shown in figure 2.
The springs used to provide the damping for the vibrations of the aircraft as of now are
12 inches in length. The springs will be further constrained in order to ensure that the
edges of the base plate will not go beyond the perimeter defined by the feet of the
apparatus (for safety reasons, the entire apparatus will be confined to the area defined by
the feet of the apparatus). The final pieces in the suspension system are the base plate
holders, which will support the base plate. The base plate holders will also be able to
slide along the y-directional suspension bars, thus allowing the entire system to provide a
2-dimensional suspension solution for the base plate and the experimental apparatus.
Figure 2: 2-dimensional suspension system
The second part of the experimental setup is the base plate that sits on top of the
suspension system (figure 3). The base plate will have #8-32 tapped holes spaced 6
inches apart in a 36 inch square grid. We decided upon such a configuration so that the
apparatus could be as versatile as possible. The base plate will be able to support a wide
variety of experimental components that we can switch out in order to perform different
experiments, instead of switching out the entire apparatus. This allows us to perform
experiments that might require different hardware components while in midflight, so long
as the components are compatible with the base plate. The entire base plate will be 42
inches square and will be constrained by the suspension system to remain within the 54
inch square perimeter set by the suspension feet. During take-off and landing procedures,
the base plate will be strapped down further in order to keep it stable. The straps will
also provide extra support during the periods of increased accelerations that are expected
during the take-off and landing procedures. Handles for the straps will be placed at the
midpoint along the sides of the base plate.
Figure 3: Base plate
The final piece of the system comprises all of the experimental components that
will be used for the flight. Specifically modeled here are the fluid containers and the
camera support. We expect to also add components to control the droplets in each
container and an interface for user input. The container component (figure 4) is actually
series of 5 fluid containers at 7 inches cubed each. Each container will also have an input
on the top where the syringe mechanisms that will create the droplets can be applied.
The camera apparatus (figure 5) will allow the camera to traverse from container to
container in order to provide data for each experiment as they are done. Notice that each
of these components are designed to fit onto the base plate with screw holes placed in line
with those on the base plate. Other components will be designed similarly.
Figure 4: Fluid Container
Figure 5: Camera Apparatus
As a final note, all the components for our experimental setup were designed in
Solidworks 2005 under a California Institute of Technology license.
Structural Design:
We will be constructing the experimental setup out of cast alloy steel, 1060 alloy
aluminum, and medium-high impact acrylic. These materials were defined in Solidworks
2005 and the properties that the program lists are in table 1:
Material:
Elastic Modulus
(lb/in^2)
Poissons Ratio
Shear Modulus
(lb/in^2)
Thermal Expansion
Coefficient
Density (lb/in^3)
Thermal
Conductivity
(W/mK)
Specific Heat
(J/kgK)
Cast Alloy Steel
1060 alloy
Aluminum
Medium-High impact
Acrylic
2.76E+07
1.00E+07
348091
0.26
0.33
0.35
1.13E+07
3.92E+06
129084
1.50E-05
2.40E-05
5.20E-05
0.263729
0.0975439
0.0433527
38
200
0.21
440
900
Table 1: Properties of proposed materials
1500
The cast alloy steel will mostly be used in the suspension system, which takes the
highest loads because it has to support the entire experimental apparatus. The acrylic is
used for the base plate as well as in experimental components that require a transparent
material (fluid containers). The aluminum is also mostly used in experimental
components as well. The setup will also require a variety of steel screws. The design
thus far only implements #8-36 and #10-32 screws. The properties for these screws are
provided in table 2 from McMaster Carr assuming a 1 inch length screw.
Screw Type:
#8-36
#10-32
Rockwell
Minimum Tensile
Hardness
Strength (psi)
Thread Fit
Minimum C39
180,000
Class 3A
Minimum C39
180,000
Class 3A
Table 2: Properties of screws used
ASTM Specification
ASTM A574
ASTM A574
The entire apparatus will be bolted to the aircraft floor using the 3/8 inch bolts
that are specified by NASA. We will also use 4 cargo straps to further secure the base
plate and keep it stable during take-off and landing because of the higher expected
accelerations.
Electrical System
We will use a motorized injection system to produce drops. Appropriate signals (either
preprogrammed or according to a feedback system) will be generated using a PIC
microcontroller signaling a PWM motor driver. Feedback system (if used) may rely on
changes in resistance across a drop-surface liquid bridge as in Dooley 1997. Both
initiation of drop formation and image acquisition may be triggered either manually or
via accelerometer.
Microcontrollers will run on 5VDC; motor drivers will run off of the supplied 28VDC.
Computers and cameras will either run on 120VAC provided or internal batteries.
Pressure / Vacuum System
No Pressure/Vacuum Systems included in this experiment.
Laser System
We plan to use one laser, class 3a or lower rating, for the purpose of illuminating the
particles used for DDPIV.
Crew Assistance Requirements
The experiment is fairly self-contained and we expect the operation to be mostly digital.
Thus, we will probably not need any help from the in flight crew. The flight crew might
be required to help us switch out some of the experimental components on the base plate.
We will need the ground crew to help us install the apparatus in the aircraft.
Institutional Review Board (IRB)
No human test subjects, animal test subjects, and/or biological substances will be used in
this experiment.
Hazard Analysis:
We will design the experimental apparatus to the best of our ability such that it
will not fail. However, we have conceived two failure scenarios that would compromise
experimental integrity and safety of the cabin crew. The first scenario involves a fluid
leak in one of the compartments. If such a leak does occur, then we will lose the data for
that particular test; however the remainder of the test can still be performed. The free
liquid could; however, compromise on board systems unless it is contained properly and
prove to be a mild safety hazard for the cabin crew. We do not plan to use toxic fluids in
any of our experiments, however, the fluids might make conditions in the cabin more
slippery.
The second scenario we have envisioned involves the failure of a part in the
suspension system. Such a scenario would result in the entire experimental apparatus
becoming unstable and potentially separating from the base parts that hold the suspension
to the aircraft floor. Such loose equipment would prove to be a hazard to both the aircraft
and the cabin crew, as the base plate and the experimental apparatus are expected to be
over 100lbs and could either damage the aircraft or injure the in-flight crew.
Again, we will be designing the experimental apparatus with as much structural
integrity as possible to ensure that neither scenario will occur and to ensure the general
safety of the in flight crew and the aircraft.
Tool Requirements
We expect to be using many off the shelf tools in order to secure mechanical devices. We
will require hex screwdrivers to secure the screws in the device and wrenches to secure
components in the device. We will also require a drill to make adjustments to the
apparatus if necessary and a soldering iron to make electrical adjustments.
Ground Support Requirements
We would ask Ground Support for storage space for the liquids that we will be loading
onto our experiment, which will possibly include water, glycerin, and corn oil.
Hazardous Materials
It is possible that we could use standard fluorescing dye, such as fluorescein, in order to
perform the DDPIV. Fluroescein is hazardous if it comes in contact with skin, or is
ingested. However, there are alternative (and highly preferred) possibilities for DDPIV
tracking, such as Molecular Probes ® FluoSpheres.
Procedures:
Ground Operations: While on the ground, we propose to construct the designed
apparatus and then perform the tests that we will be performing in flight to ensure that the
mechanisms work in the allotted 20 seconds of microgravity. The apparatus as it is
designed will lower a pipette to the fluid interface and then release a small droplet onto
the interface. This process is completely automated and should not take longer than 10
seconds. The remaining 10 seconds will be used to observe the interactions between the
droplet and the fluid layer using a high speed camera that will record data from the
DDPIV particles suspended in the fluids. The droplet coalescence should take no more
than 5 seconds and thus, one droplet test can be conducted within the time frame of the
microgravity experience in flight.
Once we have repeatedly tested the system to ensure that it will consistently
operate in the time frame given, we will perform the several test regimens with different
fluids in order to obtain 1g data that we can use to compare to the microgravity data and
to determine which fluid combinations will be best to test in a microgravity environment.
With 30 parabolic arcs in a single flight, we will plan on having at least 25 fluid
combination tests to perform in microgravity.
Pre-Flight: During the pre-flight stage, we will first fill all of the fluid containers with
the fluid combinations that we have determined during ground testing. These fluid
containers will be stored in the larger container (46.5 x 22.5 x 17.5 as specified in the
Interface Control Document AOD 33912) in preparation for take-off so that the base
plate will not have as great a load during the high acceleration period. We will then
secure the apparatus to the base of the aircraft and also attach the straps that will be used
during take-off. Other experimental components will also be attached to the base plate
once the suspension system is secured and ready for take-off.
In-Flight: There are 4 phases that were specified during the parabolic flight. For the
purposes of this proposal, the first part of the parabolic flight will be the apex of the
curve, where the aircraft will begin its freefall back to earth. During this period, the in
flight crew will prepare to initiate the experiment while the ground crew ensures that all
the systems are operational. Experimental data cannot be obtained during this section of
the flight curve because the gravity will vary between 0 and 1.8g's ("dirty air") and will
not provide any useful data.
The second phase of the parabolic flight path will be defined as the free fall back
to earth, where microgravity is experienced. During this time, the experiment will be
initiated. The syringe within thee fluid container will be lowered to the fluid interface
and a droplet will be released. The coalescence will then be recorded by the camera and
the data will be transmitted to storage by either an onboard computer or a ground based
linked computer. One test should take no longer than 20 seconds, which is the amount of
time that microgravity is expected to last.
The third phase of the parabolic flight will be defined as the bottom of the arc,
where the aircraft will begin its climb back to the top of the parabola. During this time,
the ground crew of the flight crew will confirm the success or failure of that particular
test and ensure that the data collected is properly stored.
The final stage of the parabolic arc is the climb back to the top. During this time,
a period of approximately 1.8g's is experienced, and thus experimental data will not be
collected. This time will be used to set up the next test for the next period of
microgravity. To do this, the commands for the next fluid test container will be initiated
and readied while the camera will move to the appropriate container in order to collect
data. This time will also be used by the flight crew to switch out test container apparatus
if necessary in order to perform the next set of tests. The ground crew meanwhile will
briefly analyze the data in order to advise the flight crew as to which tests should be
performed and what adjustments, if any, to either the hardware or the software needs to
be made. Once the aircraft has completed its climb, the next test should be set up and
ready to go.
The aircraft will undergo 30 parabolic flights, so the above-mentioned procedure
will be repeated 25-30 times depending on how many tests we are able to setup (we
presume that a majority of the flight crew will be trying to cope with the changes in
acceleration during the first few parabolic arcs).
Outreach Plan
We have a blog, currently hosted at http://csmi2010.wordpress.com/. This will
provide a means for students who are interested in following our progress to do so.
Our main target audience for outreach will be local high school students. We
have contacted Arcadia High School, Maranatha High School, Polytechnic School, and
Pasadena High School. We have also contacted the California Science Center Museum.
We will be working with the Caltech Educational Outreach office to find even more
opportunities for outreach.
Our objective is to provide the students with a more concrete understanding of
basic scientific principles, such as free fall, intermolecular forces in polar and nonpolar
liquids, and the importance of observation and the scientific method.
We plan to accomplish this by small-scale presentations at multiple schools and
other venues. We would have three potential presentations, which we would give at
times that would be convenient for the teachers involved.
From January to February, we would provide the students with a discussion of
gravity and free fall. This is a very common area for misconceptions, and is the focus of
a number of the California State science content standards in physics. The discussion in
this case could follow a pattern wherein a team member poses a question which may be
the source of some confusion (e.g. “Why do objects on Earth fall with the same
acceleration?”, “How does that acceleration compare to objects near the moon?”, and
“Why do objects in free fall feel weightless, despite still feeling a gravitational force?”).
From February to March, we would present the students with a demonstration of
fluid dynamics. The general setup would include a container of some sort – likely the size
of a small fishtank, and a high-speed camera. The phenomenon of vortex-ring generation,
which is the object of our scientific study, can be qualitatively demonstrated with a drop
of milk and a container of water. The vortex ring could be viewed in slow motion,
thereby showing an analog of the experiment we would actually be carrying out. If the
fluid is sufficiently viscous (e.g. corn oil or a water-glycerin mixture), the phenomenon of
terminal velocity could be easily demonstrated. This is a prime application of Newton's
Second Law – namely that an object experiencing no net force will experience no
acceleration, yet may have a nonzero velocity. With the addition of a small amount of
dye or a small number of tracer particles, it may be possible to view turbulent flows, the
effect of various-size objects traveling through the fluid, or convective flows.
From March to May, we would bring our finished experimental apparatus to the
schools in order to demonstrate collection of the 1 G control data. We would discuss the
importance of the scientific method, in particular the ideas of control, repeatability, and
designing an experiment to test a hypothesis.
Institution’s Letter of Endorsement
From the President
Institution’s Letter of Endorsement
From the Dean
Statement of Supervising Faculty
From Dr. Morteza Gharib
Statement of Supervising Faculty
From Dr. Eugene Trinh
Funding/Budget Statement
Mechanical Parts
Plexiglass - $200
Aluminum - $100
Machine Shop - $1000
Misc. parts and labor - $700
Electrical Parts
Laser - $200
Computer - $1000
Optics - $1000
Camera - $5000
Misc. parts - $500
Travel and Expenses
Plane tickets? - $3000
Alternatively: Car and gas - $1000
Shipping - $500
Lodging - $1500
TOTAL - approx. $13000
Potential Funding Sources
Caltech EAS Division
Space Grant