The dust control group designed a system to restrict dust that is disturbed by the Enabler during its operation from interfering with astronaut or camera visibility. This design also considers the many different wheel positions made possible through the use of artinuation joints that provide the steering and wheel pitching for the Enabler. The system uses a combination of brushes and fenders to restrict the dust when the vehicle is moving in either direction and in a turn. This design also allows for each of maintenance as well as accessibility of the remainder of the vehicle

Hilton, Kevin

Karl, Chad

Litherland, Mark

Ritchie, David

Sun, Nancy

English

NASA Technical Reports Server

NASA-CR-192065
Kevin Hilton, Chad
9/9/0,9 3 7-c z./,¢d5 yJ- J
DUST CONTROL FOR ENABLER /_,_5'
Karl, Mark Litherland, David Ritchie, and Nancy Sun
ABSTRACT
The dust control group designed a system to restrict dust
that is disturbed by the ENABLER during its operation
from interfering with astronaut or camera visibility. This
design also considers the many different wheel positions
made possible through the use of artinuation joints that
provide the steering and wheel pitching for the
ENABLER. The system uses a combination of brushes
and fenders to restrict the dust when the vehicle is moving
in either direction and in a turn. This design also allows
for ease of maintenance as well as accessibility of the
remainder of the vehicle.
5. The device should keep at least 80 % of the dust
down.
6. The device should be independent of vehicle power
systems.
7. Parts of the device that may come in contact with
rocks should be extremely durable. Attachments
should be high-strength.
8. The device should be manufacturable on the moon
at a later date.
MATERIALS SELECTION
INTRODUCTION
The purpose of the Enabler project was to design a lunar
work vehicle. The Dust Control group was responsible
for the design of a device to restrict dust from interfering
with astronaut and camera visibility.
In a previous Apollo mission, the astronauts noticed
that lunar dust had a tendency to "rooster-tail" from the
wheels of the lunar rover. The dust was electrostatically
charged and thus stuck to almost everything, including the
astronaut, the lunar rover, and the lenses of cameras. This
presented a problem, especially for astronaut and camera
visibility.
This report presents a possible solution to this
problem.
PROBLEM STATEMENT
The objective of the Dust Control group was to devise a
system to keep dust down, so it would not interfere with
visibility of the astronaut and the cameras. The device
needs to satisfy the following criteria:
1. The device should not weigh more than 200 kg.
2. In the event of damage to the system, the
astronaut must be able to repair _ replace all damaged
parts easily.
3. All main parts of the device should last 10 years.
Replaceable parts should last a minimum of 2
months of continuous use.
4. The astronaut should have easy access to the sides
of the vehicle at all times. Any dust control device
should allow for this access.
Materials for the dust control device are a quintessential
component for the design of the device. The materials
must be able to withstand the harsh environment of the
moon.
High doses of radiation cause most man made polymers
to degrade, and they would therefore not be the optimum
choice. Radiation tends to cleave the Carbon-Carbon,
Carbon-Nitrogen, and Carbon-Oxygen bonds. Radiation
also has ill-effects on some metals causing embrittlement
in such metals as steel, and it may therefore lose
characteristics necessary for its intended purpose.
The vacuum pressure also has detrimental effects on
some materials. Some metals such as cadmium, zinc or
magnesium at greater than 125 degrees C sublimate and
some polymers degrade under vacuum.
Strength is a very important characteristic, because the
dust control parts must withstand the impact of the lunar
soil and small rocks. However, a low coefficient of
thermal expansion for the fender, a smaller Young's
Modulus for the brushes and sheet and weight are factors
to be considered in addition to strength. Since bolts hold
the fender in place the thermal coefficient should be as low
as possible and the material should also have the highest
strength and lowest weight possible. Young's Modulus
should be low enough for the material to flex but large
enough to remain horizontal and strong enough to
withstand the forces of the lunar soil coming off of the
wheel
Aluminum 356 was decided to be used for the support
structure of the brushes, the hinges, and the attachment
bracket because it is one of the lighter weight aluminums
(2.68 g/cm^3). It also has a respectable coefficient of
thermal expansion of 21.5 x 10A-6/C which is not the
least (19.0 x 10&6/C for A132) nor the most (25.0 x 10^-
6 for A1220) toward the lower end of coefficients of
aluminum alloys. It is 82.7% Al, .3% Mg and 7.0% Si
(NASA-CR-I92065) DUST
ENARLER (Georgia Inst.
5p
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and has a tensile strength of 230 MPa, a yield strength of
165 MPa and the ductility of 4% EL in 5.08 cm.
Radiation and vacuum pressure have little effect upon this
aluminum.
S glass is the material of the brushes and knit inner
sheet because it is stiff enough to remain horizontal when
five fibers are braided together. High performance glass
fibers could be used but they would be too stiff and would
break a lot easier than the S glass which will bend under
the same stress. The glass bristles are to be teflon coated.
This will increase the abrasion resistance of the bristles.
The teflon coating will also allow the bristles to last
longer, because it will reduce the abrasion and therefore
reduce flaws created by the lunar soil. Flaws in the glass
are the places where failure is most likely to occur. The S
glass contains 65 (wt. %) of SiO2, 25 (wt. %) of AIO3
and 10 (wt. %) of MgO and has the tensile strength of
4,500 MPa, Young's Modulus of 85,000 MPa, density of
2.48 g/cm^3 and a coefficient of thermal expansion of 3.0
x 10^-6/(2. The lower Young's Modulus is necessary
because the bending allows the force to be dissipated over
a greater distance. Since the distance is greater, the stress
is less than a stiffer fiber that does not bend as much.
Radiation and vacuum pressure have little effect on S
glass.
A moulded woven graphite fiber reinforced borosilicate
matrix is the material of choice for the fender. The carbon
fibers prevent micro cracks in the structure from
propagating and when the graphite is exposed it acts more
like a lubricant. Complex shapes can be made by
injection or compression moulding into shaped dies at
high temperatures. It has a density of approximately 2.25
g/cm^3 with an elastic coefficient 02) of 380 GPa, an
ultimate tensile strength of 2.2 GPa and a coefficient of
thermal expansion of -.6 x 10A-6/C. The low coefficient
of thermal expansion high strength and fairly low density
make this material the optimum one for the fender.
Radiation and vacuum pressure have little effect on this
material.
DETAILED DESCRIPTION OF PARTS
Hinge
The purpose of the hinge in the dust control device is to
attach and remove the brushes with great ease. It also will
make it easy to access the vehicle by being able to raise
the brushes up out of the way. Here the hinge will be
made from steel but on the moon it will be made from
Aluminum 356.
There are four different parts to this hinge:
1. The brush bar will be attached to the upper partof
the hinge by bolts and will use the three bolt holes at
the bottom in the triangular shape. There is also a
circular rod attached, it is used to attach the hinge to
the chassis. Refer to figure one below.
Top view Side view
Figure 1
2. The lower part of the hinge will fit into the
slotted part on the chassis. It has a hole in the center
so that the rod from the upper half of the hinge can
penetrate the lower half and keep the entire hinge in
place. Please refer to figure two below.
En_ for
rod {
Front view Side view
Figure 2
3. The spring will wrap around the pin of the hinge
in an effort to keep the hinge in the closed position.
Please refer to figure three below.
Hinge pin
through the K_ieepre_ure in this
Side view
Figure 3
4. The last part of the hinge is the pin that holds the
two halves of the hinge together. Please refer to
figure four.
D Hinge pin
Figure 4
Center Brush Assembly
The center brush assembly is the echanism to controol
dust between the front and center wheels and center and
rear wheels. Because of the large range of motion in these
areas, the interference of the assembly is very critical.
The center brush assembly consists of two major parts,
and some minor attachment parts.
Brushes
The brushes are the key to the mechanism. They are able
to accommodate a dual task. First, they are able to deflect
the dust downward and away from the chassis. More
importantly, the brushes do not interfere much in a full
near side turn and allow the vehicle to perform unhindered
movement.
The brushes are angled so that they are parallel to the
opposite side brushes when in a full 30 degree near side
turn. They are at an angle of 14 degrees to the chassis.
This allows the brushes to move back and forth with the
least amount of angle between them, when the maximum
amount of interaction of the brushes occurs. The
maximum forces between the brushes will be lessened by
this set up.
The brushes are connected to a brush bar to form
something like a comb. The brush barfits in a groove in
th solid piece framework. The brush bar slides into the
groove from the edge of the solid piece framework. The
straight brush bar slides in at the outer edge of the vehicle,
while the angled brush bar slides in at the inside. The
brush bars are held in place by a pre-threaded wing nut.
The angled brush bar is harder to replace, but should not
have to be replaced very often because it has shorter
brushes andis not the recipient of a large amount of dust.
Solid Piece
The solid piece is much sturdier than the brushes. The
solid piece is positioned so that it does not interfere with
the solid piece on the opposite side. Also, the solid piece
is designed so that it only interferes with the brushes on
the other side in a limited capacity. The solid piece
conforms very closely to the fender to minimize the dust
that escapes between them. As stated earlier, the solid
piece also serves as an attachment point for the brush bar.
The solid piece is a framework with a thin sheet in
between it. The framework gives both the strength and a
means of attachment for the brushes. The thin sheet
allows the assembly to stay light while still giving
complete dust protection.
The entire assembly is bolted to and supported by a
hinge. The hinge provides several useful functions. The
hinge allows the assembly to be lifted so that access to
the vehicle's chassis is not impaired. Also, the hinge will
allow the assembly to move if it is hit underneath by a
large rock that the vehicle might be trying to climb. The
hinge also can make it easier to attach the brush bars,
especially the angled bar.
Attachment Brackets
Purpose
The purpose of the attachment bracket is to provide hard
attachment points for the fender and brush arm assembly,
while allowing easy removal of the brush arm assemblies.
It also must avoid the bolts which attach the main wheel
bearings to the chassis, while providing for easy removal
of the wheel beating bolts. This must be accomplished
inside a distance of no greater than five (5) inches axially
on the lateral portion of the chassis. See Figure 1.
_tl_tml4at [tiVoli
Design Elements
The attachment clamp consists of two steel "boxes"
measuring approximately 300 x 120 x 80 mm. See
Figure 2. These boxes are welded to the chassis at
approximately the location shown in Figures 1 and 2. In
this position, they allow the brush arm assemblies to be
mounted above the center of the chassis and avoid the
wheel bearing mounting bolts.
Whed Being
O
F_um 2
Materials
To facilitate mounting the attachment brackets, the
material chosen is steel. This choice was dictated by the
factthathechassismaterial is already steel. By choosing
the same material, it is now possible the install the
brackets by welding them directly to the chassis. This
gives a very strong, solid attachment point for the brush
arm assemblies. A f'u'm attachment point was necessary
because the brush arms will be undergoing violent
displacements and should be able to return to the exact
point of rest that was intended by the designer. For a
more detailed description of the materials involved.
Fender
The fender's purpose is to prevent the dust from
covering the vehicle when it leaves from 0 degrees to 90
degrees from the wheel relative to the horizontal plane.
The dust goes around the fender and then back down to the
ground. The fender has 12.7 cm. of clearance to keep the
wheel from touching the fender when it is deformed from
various obstacles. The fender leaves the chassis at a 60
degree angle to keep space between it and the conical
wheel. The fender comes 5.08 cm. below the outside of
the wheel which is also at a 60 degree angle to prevent
dust from escaping and covering the vehicle with a thin
dust layer. Polyethylene is the material used on the earth
vehicle, but we recommend using a moulded woven
graphite fiber reinforced borosilicate matrix for the lunar
vehicle. The fender is .4 cm. thick because it would be
thick enough to withstand the stresses of impact of the
lunar soil and small rocks. Each fender would weigh 24.5
pounds and all six fenders would weigh 147 pounds.
Front & Rear Dust Brush Assembly
To aid in keeping dust below the chassis in front of and
behind the vehicle, a special dust brush assembly is
required. The front and rear dust brush assembly differs
from the center brush assembly used between the wheels
for the following reasons:
1. The center brush assembly is too low to be used
in front of and behind the vehicle. If the center brush
assembly is used in front of and behind the vehicle, it
would be subjected to impact from large rocks being
climbed by the vehicle.
2. The center brush assembly would interfere with
the seat if used in the front of the vehicle.
The dust brush assembly consists of four main parts:
1. The Base Sup_tmrt. This aids in supporting the
dust brushes. It is welded at the base to the hinge.
On the other end, it is welded to the arm support.
The base support is hollow and the walls have a
thickness of 4 mm along the entire length of the
piece. The base support is made of steel in the earth
model, but aluminum is recommended for use on the
moon.
2. The Arm SuDt_ort. This also aids in supporting
the dust brushes. This piece is angled at 30 degrees
to horizontal, and is welded on both ends. At the
lower end, it is welded to the base support. At the
upper end, it is welded to the brush holder. This
piece is also made of steel, and is hollow with a wall
thickness of 4 mm along the entire length.
3. Brush Holder. This holds the removable brushes.
The brush holder is 60 mm x 60 mm x 410 mm.
The housing is made of the same type rectangular
steel tubing as used for the support arm, but one
"long" face is cut open for brush attachment.
4. Brushes. These replaceable brushes are each
composed of 6000 staggered bristles, held together by
a steel "clamp", which can easily be slid into the
brush housing, and are easily removed for
replacement. Staggered bristles are used to reduce the
total number of bristles needed to function properly.
These nylon bristles are 1 mm in diameter and 808
mm long.
Teflon coated fiberglass bristles are reccomended for
use on the moon.
The total weight of four assemblies needed for the
vehicle, using the materials chosen for the moon, is 115
pounds. All materials chosen and reasons why they were
chosen are discussed in the materials section of this report.
CONCLUSIONS
The objective of this project was to design a 6 wheeled
lunar work vehicle. The Dust Control group was to
design a device to restrict lunar dust from interfering with
astronaut and camera visibility. Astronauts noticed that in
previous missions, that lunar dust kicked up by the
wheels of the lunar rover would hover for long periods of
time, thus interfering with visibility. Also, the
electrostatically charged dust stuck to almost everything,
including the camera lenses, which hindered filming.
In order to maintain astronaut and camera visibility, a
device was designed to reduce the amount of dust thrown
up by the vehicle's wheels. The total weight of the dust
control system does not exceed 200 kg, while still
providing the strength necessary to stand up to impact
with rocks when the vehicle is traveling at speed. The
design allows for occasional replacement of parts that will
see a great deal of wear and tear. This replacement can be
easily accomplished by the astronauts while wearing
pressure suits. In the event that access to the vehicle is
required, the brush assemblies rotate upward, allowing the
astronautso reachthe interior of the vehicle with a
minimum of effort. The dust control system will keep
approximately 80% of the dust below the chassis while
not interfering with the line of sight of the astronaut and
the cameras. It does not require power from the vehicle
drive motors and is extremely durable. All parts of the
design will be manufacturable on the moon.
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ACKNOWLEDGEMENTS
We wish to acknowledge Dr. Stephen Liang, who helped
us with our decision matrix and Dr. Desal, who helped us
with material selection.


Dust control for Enabler

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