2. Executive Summary
This report explores the preliminary design process needed to design a coring device for
NASA’s Asteroid Redirect Mission (ARM). One of ARM’s objective is to put an asteroid into
the moon’s orbit. From there, astronauts will travel to the moon and extract samples from the
asteroid to study its composition. With the help of NASAprovided guidelines and parameters,
the problem was defined, a handful of concepts were generated, and eventually an Encased
Auger was decided upon. Known calculations from a screw auger conveyor system were used to
calculate the torque and force necessary to power the system in a low gravity system. After
comparing to the human capabilities in space, the Encased Auger was determined to be able to
perform the required duty of extracting a small core sample. It is comprised of a ratchet, drill
chuck, multiple bearings, and the auger with a casing surrounding it. The ratchet will power the
drill chuck, which is gripping and driving the stem of the auger into the asteroid regolith. At the
bottom of this double helix auger will be two flaps through which the material will flow through.
Using spring hinges, the flaps will close once the astronauts pull up and release the pressure on
the springs. A solid model assembly has been created ao prototyping and test plans are the next
steps. It is imperative to begin coordinating with the machine shop staff to finish necessary steps
in order to acquire machine shop access.
1
4. Introduction
NASA is known as the United States government agency responsible for the civilian
space program as well as aerospace research. NASA wants to improve and expand the space
program, so NASA created the MicroG NExT 2016 Design Challenge various challenges
which teams of students can choose to partake in. The goal of these challenges is to take humans
past the Earth’s orbit and gain knowledge of the Solar System. Our team has chosen to partake in
the second challenge to design a coring device capable of obtaining a sample of regolith, loose
pieces of rock and unconsolidated sand, near the surface of an asteroid.
Detailed in the report is the entire design process complete at this point. Beginning with a
statement of the problem and resources provided by NASA, a set of specific design criteria were
created. Next brainstorming sessions were held to create possible design solutions; these
solutions were turned into a few possible design concepts. Using various methods a final concept
was selected to move forward with. After extensive modeling and analysis, a detailed design of
the prototype, the manualpowered Encased Auger, was created. The most suitable materials for
the main parts of the design were chosen and minor adjustments were made to the final concept
from the conceptual design report. These individual parts were modeled on SolidWorks and were
assembled together. Then, extensive calculation were made to support the design feasibility. By
these models and analysis, a preliminary design was created that is feasible, efficient, and
effective.
Background Information
One of the greatest contemporary concerns is the possibility of a major catastrophe
caused by an asteroid. NASA’s goal is to perfect a strategy to deflect these large objects using
3
5. the asteroids themselves. The Asteroid Redirect Mission (ARM) uses the gravitational force
between a large asteroid and a smaller counterpart taken from the surface. The spacecraft
carrying the smaller counterpart, or Asteroid Redirect Vehicle (ARV), performs a series of
circles, creating an Enhanced Gravity Tractor to deflect the large asteroid from its path[1]
. After
the redirection, the smaller asteroid is transported to the moon’s orbit where it can be studied.
Using a secondary vehicle such as NASA’s Orion, scientists will dock to the ARV and go on to
analyze the asteroid and its regolith[1]
. Perfecting this process will help NASA in their aspirations
to eventually send humans to Mars.
Asteroids can be classified into three different types: the Ctypes, the Stypes, and the
Mtypes. The most common type of asteroid is the Ctype, representing over 75% of all
asteroids. The composition of Ctypes is very similar to the sun, consisting of large quantities of
carbon molecules with smaller quantities of hydrogen and helium molecules.[2]
They are mostly
coalblack, although they can also be found grey as they are made mostly of rocks and metals.
The importance of the Ctypes comes from the fact that some of them contain water. Scientists
believe this can be the key for inspace fuel for rocket ships and energy needed to unlock more
complex asteroid resources. However, they are difficult to spot because they are coalblack.
Nevertheless, due to their water content, Ctypes are of utmost interest to scientists of outer
space.
The second type of asteroid is the Stype, making up about 17% of all asteroids. The
composition of Stypes is mostly stony magnesiumsilicates, mixed with iron and metallic iron.[3]
While they are less likely to contain hydrated materials, the silicates of the Stypes represent a
potential source of building material and radiation protection for commercial and government
4
6. space operations. Stypes tend to be relatively bright, making them much easier to spot than the
Ctype asteroids.
The last type of asteroid is the Mtype, the third most common asteroid that can be
classified. They are rich in metals as they consist mostly of metallic iron with refinery grade
nickel and iron.[4]
Although they are not known to contain hydrated materials, their metallic
content can be useful in the future as more spacebased projects take place. Because all asteroids
contain useful resources within their composition, it is important to develop methods to be able
to obtain these resources.
Coring devices are regularly used in geological surveys to determine the composition of
the Earth at places of interest. These devices come in many different varieties ranging from a
diamond drill to piston corers. Diamond drills work by cutting around a solid core sample which
is placed into a core tube as the drill cuts deeper.[5]
The core tube is then hoisted up the drill pipe
by a winch or other lifting mechanism.[5]
Water is usually pumped into the hole to aid in cooling
the system because the drill must be cooled by a fluid to prevent overheating due to friction.[5]
Another type of coring device is the reverse circulation (RVC) device.[5]
RVC works by creating
small chips in the rock that are forced up the drill pipe by pressurized air. Then, they are
collected via a cyclone mechanism.[5]
RVC uses two types of drill bits depending on the moisture
present. For dry rock, a hammer bit is used to smash the rock into small pieces.[5]
Once the rock
begins to soften due to moisture a tricone bit is used to grind the rock into smaller pieces.[5]
Piston and gravity corers both use gravity to sink into soft sediments on the ocean floor.[6]
The
difference between the two is that a piston corer uses a piston to drive the core pipe deeper into
the sediment, whereas the gravity corer uses the effect of gravity.[6]
5
7. Since gravity does not exist in outer space, NASA needed a way to simulate
microgravity conditions on Earth. Thus, NASA conceived the idea of constructing the world’s
largest indoor pool, the Neutral Buoyancy Laboratory (NBL), to mimic weightlessness and
practice interstellar flight procedures. The neutral buoyancy pool measures 202 feet (62 m) long,
102 feet (31m) wide, and 40 feet (12.34 m) deep (20 feet above sea level and 20 feet below)[7]
.
The walls of the NBL are reinforced with 645 tons of steel, while the floor is reinforced with 689
tons of steel. The pool has a capacity of 6.2 million gallons of water, maintained at 86°F, while
filtering 5,400 gallons per minute. Even at this size, the world’s largest pool can not
accommodate the entire International Space Station, which measures 305 feet by 240 feet.
However, the NBL was sized with the intentions of performing two spacewalk simulations
simultaneously.
Astronauts rehearse spacewalk missions at the NBL; while underwater, a person is
subjected to hydrostatic pressure and buoyancy. To solve this, astronauts would don a spacesuit
in which weight could be adjusted so that it neither sinks nor floats, hence, the term “neutral
buoyancy”[8]
. Everything needs to be neutrally buoyant to the replicate microgravity conditions
of outer space, from the astronaut’s tools to the lifesize mockup of the space station,
The NBL still has a couple of technical challenges to overcome. The first challenge of the
neutral buoyancy pool is the effect of drag due to water[9]
. Drag is a friction force that opposes an
object’s direction of motion relative to the surrounding fluid. Drag is nonexistent in outer space,
therefore it is easy to set an object in motion, while difficult to keep it stationary. To overcome
this, astronauts generally move slowly to minimize the effects of drag, which is directly
proportional to the squared velocity of a moving object. The second problem is that astronauts
6
8. are not weightless in the suit and will press down against the suit depending on body
orientation[9]
. This can be problematic and uncomfortable if the astronaut is upside down or in
another difficult position. Therefore, precise sizing of the suit is critical to overcoming this
challenge.
Problem Statement
The objective of this project is to design a coring device prototype for NASA that will
obtain a sample of regolith off the surface of an asteroid in microgravity. Accordingly, NASA
created the Microg NExT 2016 Design Challenge; the device is intended for use solely by
NASA. This coring device should be able to penetrate the regolith, collect its samples, and
maintain its stratigraphy. By doing so, an analysis of the asteroid’s history and internal structure
would become possible. NASA imposed very specific constraints on the prototype design as
stated in the Microg NExT 2016 Design Challenge on NASA’s website[10]
.
Problem Definition
The device should perform the following actions while in use: the device shall collect a
core sample that must be 1inch in diameter and 6inches in length, the device shall obtain a core
from a bin of regolith containing a mixture of unconsolidated sand and rock fragments less than
0.25 inches in diameter, and the device shall maintain the stratigraphy of the core during
collection, containment, and transportation.
The device may be operated manually or pneumatically. In the case the device is driven
pneumatically, the following will be supplied by NASA: pressure of 125 psig, NBL Shop Air
Connector, and the umbilicals. The following details of the NBL Shop Air Connector are
provided:
7
9. i. Grainger: Coupler Plug, (M)NPT, Item# 1HLZ8, Mfr. Model#
A73440BG (Note: the female P/N is 1HLZ9)
ii. Quick Coupler Body, (F)NPT, Steel Item# 1HUK7, Mfr. Model#
A73410BG
The physical dimensions of the device must meet the following constraints as set by
NASA in the design requirements[11]
: The device may have multiple parts that attach and detach,
the device (all parts) shall fit within an 8in x 8in x 18in volume for stowage; the device (all parts)
shall have a dry weigh less than 15 pounds, the device shall have a tether attachment point 1 inch
in diameter, and the mockup components shall not contain sharp edges or items capable of
cutting or puncturing because of the potential for personal injury due to contact.
While the ultimate goal will be to use the device in future space missions, for testing
purposes the device will be tested in the NASA Microg pool[11]
. Accordingly, the device must be
operable in a chlorine water environment. The device must also be designed with drain holes or
designed with geometry to allow the free flow of air or water as required, to support submersion
and removal to and from the NBL pool.
The operation of the device will by handled by a single astronaut who will have both
hands available[1]
. The astronaut must be able to operate the device with Extravehicular Activity
(EVA) gloved hands (similar to ski gloves). There must not be any holes or openings in the tool
that will cause the astronaut’s fingers to become entrapped[10]
. The hardware of the device must
be able to withstand normal handling and kick loads while not presenting a safety hazard[10]
. Kick
loads are reactive burst of motion resulting from other instruments’ motion. For every action
there’s a reaction and in outer space these reactions can be exponentially dangerous
8
10. Design Solution
The manual powered Encased Auger was chosen as the coring device for NASA’s
Microg NExT 2016 Design Challenge. This design consists of a helical auger encased inside of
a cylindrical tube. The helical auger has a stinger bit attached at its end designed to disturb the
material. The helical auger also has integrated flaps which opens as material travels up the flights
of the auger and closes as a certain amount of material enters the auger. The other end of the
helical auger has a drill shank that is connected to a keyed chuck, that is connected to a
cylindrical housing. A ratchet lever is used to power the device. The device also contains a
tethering point and a stabilizing handle. To power the device, the astronaut rotates the ratchet
lever while holding on to the stabilizing handle for support.
Figure 1: Exploded view of coring device with bill of materials
9
11.
Figure 2: Full assembly of the encased auger
The main part of the prototype is the helical auger. At one end of the helical auger is a
stinger bit and two integrated flaps; at the other end is a shank which connects to the keyed
chuck. The two flaps are attached to the auger via two flap pins. The helical auger is then
encased inside of a cylindrical tube. A bearing is placed at the end of the tube on the shaft
connecting to the keyed chuck. The auger has a length of 7.21 inches, a pitch of 0.75 inches, a
helical diameter of 1 inch, and a shaft diameter of 0.25 inches. The cylindrical tube has an inner
diameter of 1 inch and outer diameter of 1.25 inches. This ensures the proper amount of core
samples will be collected inside the cylindrical tube. The auger will be attached to the housing
using an off the shelf chuck.
10
12. The cylindrical housing is another main part of our prototype. The housing encloses the
shaft of the drill chuck and remains stationary while the device is powered. It also stabilizes the
astronaut; it includes an attached stability handle and a tether point. The housing consists of two
half cylinders held in place by four housing screws. The length of the cylindrical housing is 4
inches while the length of its attached stability handle is 4.49 inches. Its housing screws are .15
inches in diameter, with ¼”20 machine threads.
The ratchet lever used to manually power the device is attached to the chuck adapter. An
astronaut simply rotates the ratchet lever to transmit power to the helical auger. The chuck
housing also has two bearings where it meets the drill chuck. The ratchet lever can be detached
from the rest of the assembly once sample collection is complete. When the astronaut is done
collecting samples, the cylindrical tube with the helical auger can also be detached from the
device. Flaps on the bottom of the auger will keep material from falling out until the auger can
be removed and rubber stoppers installed.
Modeling and Analysis
To proceed with the manual powered Encased Auger, it must be determined that the
design is feasible. In order for the design to be feasible, the total torque of the auger must be
within reasonable limits of human power. To derive the total torque of the auger, the auger is
modeled as a screw conveyor with a fully enclosed tubular casing. First, the effective radius of
the screw conveyor is defined as
Re = 3
2
(R −Ro
2
i
2
R −Ro
3
i
3
) (1)
where Ro is the outer radius of the screw flight and Ri is the inner radius of the radius of shaft[3]
.
The helix angle of the screw flight corresponding to the effective radius is then
11
13. an αe = t −1
[( p
πD)(Ri
Ro
)] (2)
where p is the pitch length of the screw conveyor and D is the screw flight diameter[12]
.
The fullness efficiency must now be defined, the measure of how much material is inside
of the encased screw conveyor. This can be given as
ɳf = p
hav
(3)
where hav is the average height of material on the screw surface and p is the pitch length of the
screw conveyor[12]
.
With the fullness efficiency, it is possible to determine the weight of the bulk material
retained on each pitch. The weight is
⍴gɳ W = π R( o
2
− Ri
2
)p f (4)
where is the density of the material and g is the gravitational constant.⍴
The weight of the material per pitch at an arbitrary inclination angle must be accounted
for.
F cos(θ))Δ ra = W (sin(θ) + μe (5)
where is the equivalent friction coefficient to allow for drag of the casing walls during μe
motion. This is defined by
μe = μc (1 ɳ)+ K F (6)
where is the friction coefficient for bulk material on the casing surface and is the pressure μc K
ratio ranging from 0.4 to 0.6.
From this we can determine the Torque of the screw per pitch
ΔF R tan(α )Tsp = 3
2
p
L
ra e e + Φs (7)
12
14. where s is the friction angle for bulk solid on screw surface; Re is effective radius; is Φ αe
effective helix angle; L is length of screw conveyor; p is pitch.
Next the torque of the shaft on the material must be found. First the pressure of the bulk
solid on the shaft must be determined.
ρgpησn = K f (8)
where K (K=0.4) is the pressure distribution around the shaft, is the density of the bulk solid, p ρ
is pitch, g is acceleration due to gravity, and is fullness efficiency.ηf
Finally torque on the shaft is
πR σTsh = 2 i
2
np
L
(9)
where Ri is the inner radius, L is length of the screw conveyor, p is pitch and is the pressure of σn
the solid on the shaft.
The total torque is found by taking the sum of the torque on the shaft and torque of the
screw
T = Tsp + Tsh (10)
After plugging in values, it is seen that the torque is heavily dependent on the weight of
the material and the gravitational constant in microgravity. The maximum torque of the screw
conveyor comes out to approximately 3 footpounds, which is within the capabilities of humans
in outer space. The mean maximum torque strength of an astronaut is shown to be between 121.5
to 153.9 footpounds with a standard deviation of 3.41 to 5.08 footpounds[13]
. By modeling the
encased auger as an encased screw conveyor and by assuming the astronaut has two available
hands, a manually driven auger device in microgravity is very feasible. Engineering drawings
and solids models for each part can be found in appendix 2 & 3 respectively.
13
15. Approach to Solution
Concept Generation
Our team created many different concepts for a coring device through a series of
individual and team brainstorming sessions. For each brainstormed concept, feedback was
provided on basis of feasibility and performance. Then each concept was either improved or
scrapped; eventually, a morphological chart was created and this morphological chart gave us
four concepts we considered as our final design. The concepts generated are: the Dome Drill, the
Post Hole Digger, the Conical Bit, and the Encased Auger.
The Dome Drill is our first concept. It contains notches in the head intended to disturb the
ground. This leaves a circular hole for the material to pass through. To capture the material, the
astronaut pulls up after reaching the required depth. This assumes the weight of the material,
along with an upward jerkmotion, effectively closes the levers.
Figure 3: Domed Drill bit with spring loaded closure flaps Figure 4: Handheld means of power for Domed Drill
14
16. Our second concept is the Post Hole Digger Design, similarly powered with a handheld
device as shown in Figures 3 & 4 . The Post Hole Digger Design also uses springs; however, the
springs are compressed rather than wound. Once the material fills the separate container, it
effectively shifts the container up, releasing the springs and closing the latches.
Figure 5: Side view of post hole digger. Figure 6: Top view of post hole digger
Our third design is the Conical Bit. This design is similar to Dome Drill because it
employs the flapspring concept except with more frequency. The regolith flows through the
flaps, and the flaps close themselves once the maximum sample size is obtained. This design is
heavily dependent on downward, parallel force, much like the Dome Drill and the PostHole
Design.
15
17.
Figure 7: Conical Drill Bit with flaps
Our final design is the Encased Auger. This design uses a helical auger encased in a
cylindrical tube. This tube has a removable circumferential drill bit on the end that aids in the
coring. The regolith is captured inside of the auger as it rotates upward. Once the material is
collected, an integrated flap closes the cylindrical container. By placing an auger within a
cylinder, along with the use of flaps, we believe this effectively captures the material and stores
it.
16
18.
Figure 8: Encased Auger Concept
Concept Selection
These four concepts were seen as the most feasible; therefore we used a weighted
decision matrix to help make our choice. We completed the decision matrices using different
concepts as the datum to ensure consistent results. For our decision matrix we decided that
stratigraphy was the most important design criteria. Next we gave power, material transport, and
17
19. manufacturing the same weighting factor; the least important factors were durability, stability,
ease of maintenance, and weight.
Table 2: Weighted decision matrix with the Dome Drill as the datum
Criteria Weights Dome Drill Post Hole
Digger
Conical Drill Encased Auger
Power 1.5 D S S S
Material Transport 1.5 A S S S
Manufacturing 1.5 T - - +
Durability/Reliability 1 U S - +
Stability 1 M S S +
Ease of Maintenance 1 - - +
Weight/Size 1 S S S
Stratigraphy 2 S S -
Table 3: Morphological Chart with the Encased Auger as the datum.
Criteria Weights Domed
Drill
Post Hole Digger Conical Drill Encased Auger
Power 1.5 S S S D
Material Transport 1.5 S S S A
Manufacturing 1.5 - - - T
Durability/Reliability 1 - - - U
Stability 1 - - - M
Ease of Maintenance 1 - - -
Weight/Size 1 S S S
Stratigraphy 2 + + +
18
20.
The results of the decision matrices show the Encased Auger is the best coring device
Concept. The Encased Auger possesses advantages in manufacturing, durability/reliability, and
ease of maintenance. The Encased Auger has the advantage of manufacturing because the other
designs consists of more parts, parts that would be more complex to manufacture.
For example, the Dome Drill consists of many notches in the head and springloaded
levers dependent on the weight of the sample materials to close the levers. The many notches in
the head are tedious to manufacture, along with the springloaded levers. The Post Hole Digger
consists of springloaded latches that are dependent on the shifting volume of the material;
manufacturing this design requires extreme precision. The Conical Drill Bit consists of many
springloaded flaps, which are tedious to manufacture. Since the Encased Auger only consists of
the auger and cylindrical drill bit, it is easier to manufacture than the other designs. Given that
the Encased Auger is easiest to manufacture, it is also the most durable, most stable, and most
effective at extracting the sample of regolith.
The only advantage the Encased Auger does not possess is the advantage of maintaining
stratigraphy. This is the one minor concern of the Encased Auger. The helical auger must rotate
out while the device is collecting regolith and when the cylindrical case is unscrewed from the
device; as a result, there is minor interference with the stratigraphy of the regolith sample.
However, this interference should not ruin the stratigraphy of the regolith sample. The Encased
Auger should be able to collect regolith samples without fear of compromised stratigraphies.
The Encased Auger also meets the specifications and constraints set by NASA in the
problem statement. The problem statement sets a specific volume of core samples which must be
19
21. collected with consistent stratigraphies; the Encased Auger accomplishes this task. As far as the
device itself, it must fit within an 8” x 8” x 18” volume, weigh less than 15 pounds, have a tether
point 1” in diameter, contain no sharp edges, and be operable in chlorine water environment.
After detailed design and modeling, we designed the Encased Auger to meet these requirements.
Finally we are given a choice between manual or pneumatic powered for the device. Using the
morphological chart, we chose manual powered as the device consists of less moving parts than a
pneumatic device; this increases the device’s reliability and manufacturing. The Encased Auger
meets all the problem specifications both effectively and efficiently.
Plan for Future Work
Table 3: Project Timeline for remaining steps
Task Name Start End Duration (days)
Design Verification 1/4/16 1/13/16 9
Prototype
Construction
1/13/16 2/17/16 35
Prototype Testing 2/17/16 2/28/16 11
Design Evaluation
Report
2/20/16 3/2/16 11
Design Presentation 3/8/16 3/8/16 1
Final Design Report 3/16/16 3/16/16 1
20
22.
Now that detailed design is complete the project will move into design verification and
prototype construction. Off the shelf parts will need to be ordered and custom parts will be
machined during the next three months. The design may be subjected to multiple iterations until
satisfaction. By May, a working prototype should be built and all steps of the design process will
have been completed. The Gantt chart has been updated to show only the remaining parts of the
design process that need to be completed.
Figure 9: Gantt chart of remaining design processes
21
