Stage immersion report .pdf



Nom original: Stage immersion report.pdf
Titre: Modèle mémoire SI
Auteur: Aubin GOUMIN

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Design and development of
the mounting between
Astrobee and RINGS
Florida Institute of Technology

Relations industrielles ENSMM – service des stages

Melbourne – États-Unis

Goumin Aubin - Parisi Lucas

Stage d’immersion
2ème année

Année scolaire 2017-2018
Groupe B

École Nationale Supérieure de Mécanique et des Microtechniques
26, rue de l’Épitaphe
25030 Besançon cedex – France
+33 381 40 27 32
http://www.ens2m.fr

Mémoire de stage d’immersion

Goumin Aubin

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Goumin Aubin

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Acknowledgments
I look back on a great time I have experienced here in Florida. First of all, I would like to thank
professor Hector Gutierrez for the opportunity he has given me to come to FIT. It was a chance and
honor for me to work on such project. Thanks for the trust and freedom you have given me during
this internship, it makes me feel like I have brought something useful to this wide project.
Furthermore, I would like to thank Nasir Hariri for his trust, the discussions and explanations he
kindly gave me to achieve my tasks. I really enjoy working together and I have learnt many useful
things with you.
In addition, I would like to thank all my colleagues from the lab for the pleasant time we had. We
have experienced many beautiful moments at FIT and more generally in Florida, I will never forget
it.
Finally, I would like to thank my supervisor at ENSMM, Joël Imbaud, for his advices throughout
my internship.
It was a great experience to see how things are going at an American university, I have experienced
more than I hoped for. Everyone, once again, many thanks!

At Besancon, the 19/09/2018
Aubin Goumin.

Goumin Aubin

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Table of contents
Acknowledgments ............................................................................................................................... 4
Table of contents ................................................................................................................................. 5
Table of figures ................................................................................................................................... 6
Glossary .............................................................................................................................................. 7
Introduction ......................................................................................................................................... 8
1- Introduction................................................................................................................................. 8
1-1. School presentation ........................................................................................................... 8
1-1. SPHERES, RINGS, SVGS and Astrobee projects ........................................................... 8
1-2. History of the RINGS project ......................................................................................... 11
1-3. Context leading to my missions ...................................................................................... 12
1-4. First mission: Motion Platform ....................................................................................... 14
1-5. Second mission: Mounting interface between Astrobee and RINGS ............................. 15
1-6. Planning .......................................................................................................................... 15
1-7. From 3D design to prototype .......................................................................................... 16
1-8. Conclusion: Motion platform project ............................................................................. 19
2- Astrobee-RINGS interface ........................................................................................................ 20
2-1. Design Constraints relative to Astrobee features ............................................................ 20
2-2. Constraints and requirements ......................................................................................... 22
2-3. Overview of the design ................................................................................................... 22
2-1. Remark on the clutter and lack of room – Choices leading to final design .................... 24
2-2. Metal parts strength ........................................................................................................ 26
2-2.1.

Framework of the study: simplifications and limitations ........................................ 26

2-2.2.

FEA simulations ...................................................................................................... 28

2-2.2.1. Not critical loads ............................................................................................... 28
2-2.2.2. Torque load Y axis ............................................................................................ 28
2-2.2.3. Torque load Z axis ............................................................................................ 29
2-2.2.4. FEA simulation conclusion ............................................................................... 29
2-3. Weight, inertia and Mass balance ................................................................................... 29
2-4. Screws dimensioning ...................................................................................................... 30
2-4.1.

Non-removable parts – Inserts and nylon patch screws .......................................... 31

2-4.1.1. Bottom and top support on payload fastening .................................................. 31
2-4.2. Helicoil inserts with captive fasteners – removable screws .................................... 34
2-4.2.1. Fasteners for payload-Astrobee connection ...................................................... 34
2-5. Assembly sequence by ISS crew .................................................................................... 37
2-6. Additional technical documents ..................................................................................... 37
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2-7. Conclusion: Interface between Astrobee and RINGS .................................................... 38
3- Personal conclusion .................................................................................................................. 39
Online Resources .............................................................................................................................. 42
Attachments ...................................................................................................................................... 43

Table of figures
Figure 1. : latest version of the SPHERES satellite ............................................................................ 9
Figure 2. : RINGS and mounting hardware interface ....................................................................... 10
Figure 3. : SPHERES-RINGS system............................................................................................... 10
Figure 4. : Astrobee 3D model (Front view) ..................................................................................... 11
Figure 5. : Astrobee 3D model (Back view) ..................................................................................... 11
Figure 6. : Concept of operation for formation flight of RINGS using SVGS ................................. 12
Figure 7. : Implementation of the concept of operation for formation flight of RINGS (Figure 6) on
the glass table .................................................................................................................................... 13
Figure 8. : Different iterations of the motion platform leading to the one I designed ...................... 14
Figure 9. : Last implemented version when I arrived at FIT ............................................................ 16
Figure 10. : 3D model of the new version mounted on RINGS ........................................................ 17
Figure 11. : 3D model of the new version mounted on RINGS - Side view .................................... 17
Figure 12. : Support plates ............................................................................................................... 18
Figure 13. : (left) Column (right) Fan side support........................................................................... 18
Figure 14. : Top supports .................................................................................................................. 18
Figure 15. : (left) Top plate support (right) Fan holder .................................................................... 19
Figure 16. : (left) 3D model (right) Real system assembled ............................................................. 19
Figure 17. : Main Astrobee features [w5] ......................................................................................... 20
Figure 18. : Astrobee front panel ...................................................................................................... 20
Figure 19. : Astrobee top panel ......................................................................................................... 20
Figure 20. : Astrobee’s camera clearances [w5] ............................................................................... 21
Figure 21. : Astrobee back panel ...................................................................................................... 21
Figure 22. : Astrobee fans and side view with impeller.................................................................... 21
Figure 23. : Mechanical Interface between RINGS and Astrobee – Version 1 ................................ 22
Figure 24. : . (left) The skin and top cover of Astrobee. (right) Bumper attachment points. ........... 23
Figure 25. : . (left) Payload with quick-release system. (right) Payload with captive fasteners ....... 23
Figure 26. : Final 3D design of the mounting between Astrobee and RINGS ................................. 24
Figure 27. : 1st solution where batteries fit in the design (the ring is not shown) ............................. 24
Figure 28. : 2nd solution (right) global view (left) zoom on battery adapter ..................................... 25
Figure 29. : 3nd solution for batteries configuration .......................................................................... 25
Figure 30. : (left) Payload with quick release system (right) Payload with captive fasteners .......... 26
Figure 31. : (left) Mounting hardware. (right) Simplified mounting parts for simulation purposes. 27
Figure 32. : Fixtures in green and screws tightening forces in purple .............................................. 27
Figure 33. : Simulations showing loads, Torque on Y axis and fixtures. (left)Von-Mises Stress
(right) Displacement (not to real scale)............................................................................................. 28
Figure 34. : Stress convergence function of element size (mm) with Torque on Y axis ........... Error!
Bookmark not defined.
Figure 35. : Stress with maximum value on the bottom bracket – minimum element size: 0.25mm 29
Figure 36. : (left) The mass of brackets and battery payload (shown in blue) is approx. 6.2 kg, and
its center of mass relative to the geometric center is X =-2.97 mm, Y =-0.65 mm, Z =-52.41 mm.
(right) The mass of brackets, payload and RINGS (all shown in blue) is approx. 12.862 kg, with
center of mass: X = -1.14 mm, Y = -0.36 mm, Z = -0.48 mm .......................................................... 30
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Figure 37. : Position of the screws. (left) Top payload. (right) Bottom payload .............................. 31
Figure 38. : Characteristics and 2D drawing of the ¼ button head screw ........................................ 31
Figure 39. : Parameters for the calculation of torque (T).................................................................. 32
Figure 40. : Sum up table of appendix 11: Recommended MAXIMUM tightening torque for
Stainless Steel 18-8 (type 304) screws (1 ≤ Grade ≤ 2) .................................................................... 32
Figure 41. : Thread shearing distribution .......................................................................................... 33
Figure 42. : Table : Locking fasteners additional torque needed ...................................................... 33
Figure 43. : Bottom support fastened on bottom payload showing friction zone ............................. 34
Figure 44. : Characteristics and 2D drawing of the 8-32 captive Socket head screw ....................... 35
Figure 45. : Force applied to the top module .................................................................................... 35
Figure 46. : Zoom on the captive fasteners between Astrobee and the payloads ............................. 35
Figure 47. : Parameters for the calculation of torque (T).................................................................. 36
Figure 48. : Sum up table of appendices 11: Recommended MAXIMUM tightening torque for
Stainless Steel 18-8 (type 304) screws (1 ≤ Grade ≤ 2) .................................................................... 36
Figure 49. : Ribbon Cable (orange) from RINGS avionics to payload bay connector ..................... 37
Figure 50. : Concept Astrobee-RINGS in the International Space Station ....................................... 38
Figure 51. : . (left)Total displacement. (right) Von Mises equivalent stress. ................................... 48
Figure 52. : Stress convergence function of element size (mm) with force on X axis ..................... 49
Figure 53. : . (left)Total displacement. (right) Von Mises equivalent stress. ................................... 49
Figure 54. : Stress convergence function of element size (mm) with force on Y axis ..................... 50
Figure 55. : . (left)Total displacement. (right) Von Mises equivalent stress. ................................... 50
Figure 56. : Hypothetic load on Astrobee ......................................................................................... 51
Figure 57. : (left)Total displacement. (right) Von Mises equivalent stress. .................................... 51
Figure 58. : Stress convergence function of element size (mm) with torque on X axis ................... 52
Figure 59. : Hypothetic load on Astrobee ......................................................................................... 52
Figure 60. : . (left) Von Mises equivalent stress (right) Zoom on the hot point ............................... 53
Figure 61. : Stress convergence function of element size (mm) with torque on Z axis .................... 53
Figure 62. : (left) Payloads out of Astrobee (right) Top payload slides into Astrobee ..................... 55
Figure 63. : (left) Bottom payload slides into Astrobee (right) Payloads in place ........................... 55
Figure 64. : Astrobee and RINGS before assembly .......................................................................... 56
Figure 65. : Astrobee slides into the RINGS with this specific orientation ...................................... 56

Glossary
ENSMM : École Nationale Supérieure de Mécanique et des Microtechniques
NASA: National Aeronautics and Space Administration
ISS: International Space Station
3D: 3 Dimensions
RINGS: Resonant Inductive Near-Field Generation System
SPHERES: Synchronized Position Hold Engage Re-orientated Experimental Satellites
EMFF: ElectroMagnetic Formation Flight
SVGS: Smartphone Video Guidance Sensor
BOM: Bill Of Materials
CAD: Computer-Aided Design
CW: Clock Wise
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CCW: Counter Clock Wise

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Introduction
This report is based on my work and on the previous work of my colleague Goumin Aubin at
Florida Institute of Technology from April 1st 2019 until August 21th 2019. During this 5 months’
internship I have been assigned to two different projects, both for NASA. First one is about update
the Simulations and 3D design of the previous work of Aubin for machining purpose, and the second
one is about building the assemblage of a project called RINGS. The first one is about interpreting
the test results from the simulations to make sure that the assemblage is resistant enough. The second
is about building the assemblage from aluminums parts thanks to the engineering drawings of the
RINGS. It’s a request from NASA to adapt their new Astrobee robot to a system/project called
RINGS.
the project and the second is more of an entire design and dimensioning project.
The first one is necessary to improve tests results on a system in the lab and the second is a request
from NASA to adapt their new Astrobee robot to a system/project called RINGS.

1- Introduction
1-1. School presentation
The Florida Institute of Technology [w1] is one of the closest universities to the Kennedy Space
Center where aeronautics and aerospace bring dynamism to the region. Florida has a lot of companies
in these fields and is the second state in the US. The school not only provides teaching courses in
aeronautics and aerospace but also in other general scientific subjects and fields such as biology, civil
engineering, materials, IT, etc…
About 11800 students come every year to FIT. The university also has a large amount of labs
where students, interns and PhD students work on school projects, on research or company projects
such as the one I worked on.
The school is equipped with a machine shop, a 3D printing lab and other fabrication shops.
In the lab, Nasir Hariri, preparing for a PhD, was working mainly on electronics, automation and
control on the same project (RINGS-SVGS).
1-1. SPHERES, RINGS, SVGS and Astrobee projects

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SPHERES, which stands for "Synchronized Position Hold Engage Re-orientated Experimental
Satellites" is the name of the project for the first flying robot (satellite) we will be talk about. [w2][w3]
Each satellite is an 18-sided polyhedron that is 0.2 meter in diameter and weighs 3.5 kilograms.
Individual satellites contain an internal propulsion system, power, avionics, software,
communications, and metrology subsystems. The propulsion system uses carbon dioxide (CO2),
which is expelled through the cold gas thrusters. SPHERES satellites are powered by AA batteries.

Figure 1. : latest version of the SPHERES satellite
RINGS is the name of the project concerning coiled rings. They are not meant to work on their
own, one of the SPHERES satellite is placed in the center. SPHERES-RINGS unique hardware
consists of two RINGS Assemblies each consisting of resonant coils, coil housing with fans, power
electronics/batteries and RINGS/SPHERES support structure hardware. Each RINGS Assembly has
a diameter of 77 cm with a height of 13.5 cm and weighs 8.9 kilograms. Each RINGS Assembly is
powered with two 18V 2.0Ah DeWALT batteries. [w4]

≈ 0.2 m

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Figure 2. : RINGS and mounting hardware interface
Figure 3. : SPHERES-RINGS system
SVGS is a project meant to improve guidance of the SPHERES-RINGS system using a
smartphone camera. Astrobee is a free-flying robot which can be considered as an improvement of
the SPHERES satellite. The Astrobee will achieve tasks to help the crew, can be controlled from the
ground and will take part in experiments. In my case what matters is that it will replace the SPHERES
satellite in the SPHERES-RINGS system to become the Astrobee-RINGS system. [w5]

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Figure 4. : Astrobee 3D model (Front view)

Figure 5. : Astrobee 3D model (Back view)
1-2. History of the RINGS project
The project has already built up a wide history. In the year 1998, the Massachusetts Institute of
Technology was chosen to develop a new tool to be able to test and investigate different techniques
within space technology. Soon after, in 2001, the first model of a new satellite (robot) was released.
This new small satellite was given the name SPHERES.
In 2003 the first SPHERES launch to the International Space Station (ISS) was planned, but
unfortunately, due to the tragic incident with the Space Shuttle Atlantis, it was delayed until 2006. In
the meantime, the SPHERES has become the most used payload ever in the ISS.
In 2009 an idea came up to test a new experiment. The idea was to place an electromagnet coil
around the SPHERES in order to propel the satellites through EMFF. Other ideas came up such as
achieving wireless power transfer in a microgravity environment which could increase the lifetime

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of the satellite, but also to switch to a propellant-free technique which is less dangerous. In the years
that followed, major steps were taken in the RINGS project and eventually in 2013 the first
experiments of the RINGS project were done in the ISS. Some of them were not completed because
of issues with the localization system (IR Transceivers).
After having tested many new techniques and developments, in the year 2017 it was decided to
replace the SPHERES and improve the localization system with the new robot called Astrobee.
1-3. Context leading to my missions
SPHERES was the first project to be developed, and as it has been previously said, the RINGS
project came to existence to achieve EMFF and wireless power transfer at first in the ISS and then
implement if possible this technology outside the ISS. This type of “small” satellite (compared to
usual ones) would be convenient to achieve complicated missions without causing too many issues
if one of the “squadron satellite” was to be inoperative. Moreover, this type of multi-satellite mission
can improve space photography thanks to multiple photographs being shot at the same time from
different known locations. SPHERES and RINGS were previously equipped with IR transceivers
used among other things to locate the RINGS+SPHERES system (called satellite). Two satellites are
used during experiments. With the problem of localization, the crew was not able to perform
conclusive experiments. The goal at FIT lab is to prove that with a new type of localization system it
will be possible to control the satellite. It is important to do so before the RINGS system is sent back
to the ISS to reduce the chances of failure. In basic experiments SPHERES are used to propel and
achieve the initial position where the RINGS are coaxial to one another but at FIT lab we use our
own propelling system. Then the goal is to bring the two RINGS closer/further using the magnetic
field.

Figure 6. : Concept of operation for formation flight of RINGS using SVGS
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Figure 7. : Implementation of the concept of operation for formation flight of RINGS (Figure 6) on
the glass table
In a case of wireless power transfer the position maybe not be that critical but during a photography
mission it is critical that every satellite is precisely positioned relative to others. That is where the
SVGS comes in, this project has a precise goal, providing position data thanks to vision. Around the
same time NASA wanted to replace the outdated SPHERES with their long years of use and because
they were starting to be obsolete. The Astrobee’s first goal is to help the crew and increase their time
spent on experiments by automating inventory and time-consuming tasks. But this free-flying robot
could also replace the SPHERES in the SPHERES-RINGS system and complete more diversified
tasks. Astrobee will be equipped with cameras and one of them is similar to smartphone cameras,
that is why the SVGS project was launched. At FIT the aim is to perform experiments to validate,
improve and to report to NASA about the implementation of this technology.

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1-4. First mission: Motion Platform
The first mission I was assigned to was to update the motion platform of the RINGS system. In
the lab we don’t have access to neither the SPHERES nor the Astrobee which is still in development.
So we must create and build our own motion platform. We need to be able to initially position the
two RINGS coaxial and maintain it during the experiment. In the lab we cannot achieve a 6DOF
motion but only a 3DOF motion. The lab is equipped with a glass table and each RINGS has 3
“frictionless” air bearings to simulate microgravity (see Figure 7). Previous versions of the motion
platform have already been implemented and tested but it still does not match with the requirements.
Important oscillations are still present and rapidity must be improved. The previous system is
composed of 4 fans, each one is mounted on a servomotor. By rotating the servos, they have been
able to move the RINGS forward/backward, sideways and rotate it. My task is to think jointly with
Nasir Hariri how to improve the motion platform and then make the 3D design, to produce the BOM,
to assemble and to provide help in the implementation and to test of the new platform.

First motion platform

Second motion platform

Last motion platform

Figure 8. : Different iterations of the motion platform leading to the one I designed

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1-5. Second mission: Mounting interface between Astrobee and RINGS
The second mission is a clear request from NASA. The goal is to change the interface between
RINGS and SPHERES into an interface which can welcome the new free-flying robot: Astrobee.
This is the main mission of my internship, I worked around 15 weeks on this project. I was
asked to make a 3D model of the assembly, design the new parts, verify that it matched the
requirements and write a report on this concept design. Every other week, we had, my tutor and I, a
conference call with NASA AMES Research Center to get feedback on my work. Because this was
Phase 1 of the project, the report of the concept design was necessary to convince NASA that this
design is the best and that every parameter has been taken into account. The deadline for the technical
report was initially set for early-mid June. Finally, the report was done by June 10th and updated
substantially in the following weeks. What they needed was not a really detailed technical report but
I tried to make it as comprehensive and detailed as possible to save time for Phase 2 when the details
and machining of the parts will append if the concept is validated.
1-6. Planning
At the beginning of my internship I was assigned two projects, the first one had to be done
immediately and the second one at the time of Mr. Gutierrez’s first conference call from NASA
Ames.
I read reports and documentation about the RINGS, Astrobee and SVGS project, and then I
designed the motion platform. Throughout the internship, I soldered, assembled and mounted the
motion platforms on the RINGS when what we ordered was delivered and depending on what was
needed.
I started the second task as soon as we had more information. Every other week we had, my tutor
and I, a conference call with NASA for feedback and for design follow up. At the end of the internship
I planned to write the technical report on the concept design requested by NASA and work on more
detailed calculation and design if I had time (2D drawings detailed bill of materials and other
documents may be useful if and when the concept is accepted by NASA).
I added and adjusted the title of each task throughout the internship to make it more clear.
The planning is shown below but also with bigger scale in appendix 1.

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1-7. From 3D design to prototype
The new platform had to be designed to improve the response time of the system. When the
RINGS have to move to a position it needs to be non-oscillating. The easiest solution was two
duplicate each fan to provide thrust in both directions.

Figure 9. : Last implemented version when I arrived at FIT

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The fans are not cheap and I proposed to reduce the number of fans to 6 instead of 8. The fans on
the middle platform can provide thrust force for the forward/backward movements (x axis). The 4
fans on the sides provide the torque needed to turn around the vertical axis (z axis) if they work by
pair. If we change the pair working together we can achieve sideways movements too (y axis).

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Figure 10. : 3D model of the new version mounted on RINGS

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3

2

4

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Figure 11. : 3D model of the new version mounted on RINGS - Side view
Removing the fans on top, we could have used fan 1 and 3 for CCW rotation around z axis, 2 and
4 for CW rotation around z axis. And we can achieve sideways movements by using 1 and 4 (+y) or
2 and 3 (-y).
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The code had to be radically changed. Nasir and I, decided to use 8 fans so we can control easily
each axis of motion without changing the code too much. The goal was to implement this solution as
quickly as possible and the cost was not very critical so I kept the design we can see on Figure 10.
The support plates, the columns and the side supports for the fans were machined out of raw
aluminum plates and beams.

Figure 12. : Support plates

Figure 13. : (left) Column (right) Fan side support
Because this was rapid prototyping we decided jointly with Nasir how to build the parts. The
machined parts bring rigidity. The other parts are going to be 3D printed to allow some compliance
and because of their shape. The top supports, the top plate and the fan holders are 3D printed.

Figure 14. : Top supports

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Figure 15. : (left) Top plate support (right) Fan holder
I assembled the parts when everything was ready.

Figure 16. : (left) 3D model (right) Real system assembled
Then we needed to do all the electronics connections and soldering. There were 8 fans, 8 speed
controllers, 8 opto-isolators (not shown on the electrical diagram), relay module, an Arduino DUE
board, a 9DOF IMU sensor, a Bluetooth board and other interfacing boards for RINGS-Motion
Platform communication. (appendix 2)
1-8. Conclusion: Motion platform project
The motion platform design and assembly including electronics was not really time consuming,
but really interesting to get close to the RINGS project. I talked a lot with Nasir, not only about the
3D design, but also about the electronics and control of the motion platform. I did not get into the
details but that was really interesting.
It was a really good introduction to the main project I worked on: the new mounting system for
Astrobee-RINGS interface.

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2- Astrobee-RINGS interface
2-1. Design Constraints relative to Astrobee features

Figure 17. : Main Astrobee features [w5]


Front/Top Panel

The mechanical interface between RINGS and Astrobee must ensure that nothing on the front
panel is blocked (NavCam, SciCam, Speaker / Microphone, Laser Pointer, HazCam, Touch Screen,
Power Switch, Forward Flashlight, Wake Button and Status LEDs). For this reason, the front panel
will be on the open side of the assembly. The astronauts will have access to the front panel at all
times after ASTROBEE is connected to RINGS.

Figure 18. : Astrobee front panel

Figure 19. : Astrobee top panel
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Figure 20. : Astrobee’s camera clearances [w5]


Back panel

The back panel includes the PerchCAM, DockCam and Aft Flashlight. In the proposed interface
with RINGS, the back panel will be on the other open side of the assembly. Even though the
ASTROBEE-RINGS assembly does not have to dock during experiments it was decided to keep it
clear.

Figure 21. : Astrobee back panel


Fans and impellers

Astrobee has twelve thruster fans for propulsion. The RINGS assembly cannot block or impinge
on any of the fans. Two impellers (air intakes for the thruster fans) are located on opposite faces of
Astrobee. The proposed design must provide minimal blocking of air flow to the impellers.

Figure 22. : Astrobee fans and side view with impeller
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2-2. Constraints and requirements
Here is a list of the main requirements the mounting had to respect:


Structural parts have to be made of Aluminum (type 18-8) T6-6061 (Yield Stress of
275MPa);



Other parts have to be non or mildly-magnetic;



The structure must be able to withstand a 125lbf (560N); [w6]



Safety factors for metallic structures have be at least 1.4; [w7]



Batteries previously used have to fit in with the new design;



The system must be well balanced on the Y and Z axis.

Details about these requirements will be given when the corresponding part of the design will be
detailed in the report.
2-3. Overview of the design
When I arrived, a design of the Astrobee had been created based on the early released 2D drawings
sent by NASA. The Astrobee’s 3D model was designed to show the main features and dimensions in
order to create a mounting as close as possible to a feasible solution. The first version of the
mechanical interface between RINGS and ASTROBEE was based on friction brackets (this design
was already done by a previous student). The proposed attachment method is shown in Figure 14,
and is based on spring-loaded clips that can be hand-tightened by the astronauts.

Figure 23. : Mechanical Interface between RINGS and Astrobee – Version 1
This approach had certain advantages but also several problematic issues. The solution is based
on clamping the assembly to Astrobee’s outer cover – the attachment force is therefore given by

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friction. The friction forces required to meet impact requirements become very large, which result in
large clamping force on Astrobee’s skin. To avoid damage to Astrobee’s cover would have required
to remove the skin and the top cover to access firm attachment points such as the bumper attachment
points (See Figure below). This would have required significant crew time and effort on ISS, and
exposed internal components of Astrobee that are protected by the covers. Version 1 would also have
led to partial thruster obstruction (with RINGS batteries) and partial obstruction of other Astrobee
features. Therefore, after the first feedback we concluded that this was not a good solution.

Figure 24. : . (left) The skin and top cover of Astrobee. (right) Bumper attachment points.
It became clear that the best attachment method to Astrobee for a payload of the size and mass of
RINGS would imply using bolted connections whilst avoiding removal of Astrobee’s skin or cover
if possible.
Astrobee is equipped with 3 payload bays – one on top and two at the bottom - that are used to
add measurement systems, sensors or an arm for example. [Appendix 3] Throughout the discussions
with NASA it appeared that these 3 payload bays are not going to be used during the RINGS-Astrobee
experiments. Therefore, an attachment to the payloads bays seemed possible. What motivated us to
design the attachment on the payload is that it can be mounted on Astrobee with a quick release
system using levers or with 4 fasteners for each payload (See next Figure). The mounting with
fasteners will provide a more rigid assembly and we have chosen to develop this solution.

Figure 25. : . (left) Payload with quick-release system. (right) Payload with captive fasteners
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Relying on feedback the final concept design has been presented to NASA and I will detail the
choices in the next pages.
Ring bracket
Link Ring-plate
Top plate
Top support
Top payload frame

Bottom payload frame

𝑍Ԧ
𝑍Ԧ

𝑋Ԧ

ሬԦ
𝑌

𝑋Ԧ

Bottom support
Triangle support

ሬԦ
𝑌

Figure 26. : Final 3D design of the mounting between Astrobee and RINGS
2-1. Remark on the clutter and lack of room – Choices leading to final design
At the beginning of the project I had to propose multiple configurations and emphasize the
advantages and default of each one. I had a hard time figuring out where I can place and fix the
removable batteries and their adapters (in grey in the figures) keeping in mind that they could not
block any airflow or features and that they had to be easily accessible by the crew. In the figure below
the yellow transparent shapes shows where the area must be clear because of cameras, buttons, etc…
With this first solution (see figure below), the batteries fits in the design but in terms of balance it
is not convenient. It may not be safe either because the batteries are too close to one another. Finally,
it does not seem easy to design a plate to fasten battery adapters.

Figure 27. : 1st solution where batteries fit in the design (the ring is not shown)
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This other configuration is more balanced than the previous one but if we zoom in the battery
adapter does not fit. I could have changed the shape of the battery adapters to make it possible but
the goal was to keep the same electrical system (such as battery adapters) because they have been
tested and therefore will not need to be tested again by NASA, saving time and money.

Figure 28. : 2nd solution (right) global view (left) zoom on battery adapter
The third configuration I design was convenient regarding the balance and more simple to design
a support to attach the battery adapters. But in this configuration the batteries are barely touching the
skin of the Astrobee and cannot be remove easily by the crew.

Figure 29. : 3nd solution for batteries configuration
I presented all the configuration at one of the first conference call and they suggested that we use
the payloads as I previously enlightened. They sent me 3D models and 2D drawings of the frames
and of the typical payload they use for other purposes so I can change it to my needs. [Appendix 4]
The first version was the payload equipped with the quick release system but I used a simpler shape
with captive fasteners to fit my needs (see next Figures).
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Figure 30. : (left) Payload with quick release system (right) Payload with captive fasteners
At the end I asked about the safety distance required between batteries (of Astrobee and of the
RINGS). I move them apart from the center in order to have at least the same distance there is between
Astrobee batteries.
2-2. Metal parts strength
2-2.1. Framework of the study: simplifications and limitations

The Astrobee-RINGS system is meant to go into the International Space Station, therefore the
interface will not be subjected to loads during its normal use. This type of experimental hardware
needs to be able to sustain 125lbf (≈560N). [w7] This situation could appear in case of a collision or
if the RING is fixed on the international space station and one of the crew members tries to get the
Astrobee out while it is mounted. In the requirements, the force has to be focused on a 0.5inch
diameter zone, but in our case, we are not trying to verify that the Astrobee can sustain such force
but that the mounting can. In that case we assume that the Astrobee is rigid and the whole load is
routed to the mounting system. A safety factor of 1.4 is also recommended for the design of metallic
flight structures [w7].
All metal parts are made of aluminum 6061 (T6) which is the same material as the frame of the
Astrobee where the payloads are fastened. NASA recommended the use of this material with its
interesting ratios between weight, strength and machinability. The simulations performed with
SolidWorks FEA feature are meant to show that the mounting can sustain the worst scenario.
The Astrobee and RINGS 3D models are not shown in the simulation. They can’t be changed and
are considered non-deformable. In order to be able to apply the forces and the torques in the
simulation another part is needed, we do not use the Astrobee for technical purposes due to
simulation. First the Astrobee 3D model does not allow us to apply the load exactly where we want

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because of the software. Secondly, the Astrobee has too much detail and it hugely increases the time
to perform simulations. Sometimes the meshing process could not be achieved because of certain
geometric aspects of the Astrobee. Moreover, we simplified the geometry and the number of contacts
which are highly time consuming. The payloads were adding a lot of elements increasing simulation
duration; they have been changed to a barebones version.

Figure 31. : (left) Mounting hardware. (right) Simplified mounting parts for simulation purposes.
The top (respectively bottom) parts are reduced to 1 unique part. The contact dimensioning will
be done separately.
The part which replaces the Astrobee during the simulation is considered non-deformable. The
RING (i.e. the 3 supports on the ring) are considered fixed (in blue on the picture). In purple this is
the force from the tightening of the brackets. Simulation with forces on the three axes are not really
restrictive, whereas torque simulations, which are less likely to happen in real life and not specifically
requested, are more restrictive. Below is an overview of the results. See appendices 5 to 9 for more
details.

Figure 32. : Fixtures in green and screws tightening forces in purple

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2-2.2. FEA simulations
2-2.2.1.

Not critical loads

Axial loads are not critical and aluminum yield stress is way above the stress we computed with a
factor of 7 at least. More detailed information can be found in the appendices 5 to 7. The X axis
torque load is not critical either and will be described in appendix 8.
2-2.2.2.

Torque load Y axis

It quickly transpired that the weakest point overall is on the brackets that are clamped on the ring
- I have chosen to keep them from the previous design with SPHERES.

Figure 33. : Simulations showing loads, Torque on Y axis and fixtures.
(left)Von-Mises Stress (right) Displacement (not to real scale)

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Figure 34. : Stress with maximum value on the bottom bracket – minimum element size: 0.25mm
The stress converges around 41MPa which is way under the yield stress of aluminum (275MPa).
The displacement is about 0.2mm and did not change when reducing elements which is expected.
There is no specific requirement on the displacement and I considered that below one millimeter I
did not have to perform more simulations.
2-2.2.3.

Torque load Z axis

Simulation with a torque on the Z axis is very similar to the Y axis. The details can be found in the
appendices. [appendix 9]
The stress converges to 166MPa 96MPa and that is the most critical axis. On this axis we can
guarantee – according to the simulation - that the 1.4 safety factor is respected (already taken into
account when applying the force) but there is no extra margin.
2-2.2.4.

FEA simulation conclusion

Torque simulation are really less likely to occur and are the ones that are more restrictive. The
load the flying system has to be able withstands is a collision or kick load and the mounting system
will most probably be able to withstand it. The Astrobee is probably what can be damaged in that
situation and this study does not rely on FIT lab testing.
2-3. Weight, inertia and Mass balance
The guidelines known at the moment the project was done were:


Astrobee has to be well balanced on the Y axis;



Astrobee has to be well balanced on the Z axis;



Balance on the X axis is not really important compared to the other two.

The previous weight of the Spheres Mounting was around 2kg. The weight of the mounting
including the payloads is about 3.2kg (top payload weighs around 0.4kg and bottom payload around
0.75kg). There are no guidelines concerning the mass of the mounting but the previous one gives an
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idea of how much it was. Reducing weight is important, to save money and energy for the launch
into space station for example. But during the experiments a heavier system may not be bad.
Increasing the inertia could help to keep the system stable and less sensitive to disturbances such as
air movements produced by the crew during the experiment.
NASA AMES did not know exactly about the inertia of Astrobee and told us to consider that is
was a cube with a center of mass centered on the geometric center. What I had to verify is that the
mounting system, batteries and ring were balanced.

Figure 35. : (left) The mass of brackets and battery payload (shown in blue) is approx. 6.30kg, and
its center of mass relative to the geometric center is X =-3.36 mm, Y =-0.82 mm, Z =-51.34 mm.
(right) The mass of brackets, payload and RINGS (all shown in blue) is approx. 12.92 kg, with
center of mass: X = -1.33 mm, Y = -0.45 mm, Z = -0.60 mm
The final adjustments to inertia and mass will be based on measurements on the final assembly.
With the current design and available estimates (see appendix 10 for RINGS characteristics), the
center of gravity of the RINGS-Astrobee assembly is within a few mm of its geometric center in all
three axes. Ballast mounting points on the payloads can be used to further improve mass and inertia
mass distribution.
2-4. Screws dimensioning
There are two guidelines regarding fasteners on ISS. First, all screws not meant to be removed by
the crew must be secured by another method such as locking nuts, nylon patch screws, Loctite thread
locking or thread locking inserts. I have chosen the nylon patch screws because NASA already
performed tests and validated their use it these conditions. Secondly, screws that need to be removed
by the crew must be fixed to a larger component to avoid losing hardware during assembly - captive
fasteners are used for this purpose. Screws had to be chosen with imperial system characteristics but
the dimensioning is done in the SI base units.
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2-4.1. Non-removable parts – Inserts and nylon patch screws

There is a total number of 12 new screws which won’t be removed. 3 bolted connections will be
kept from the previous mounting as well as 3 ring brackets.
6 screws are going to be used to fix the batteries to the bottom payload, 4 screws are going to
fasten each support (top and bottom) to the respective payload, the 2 last are going to fasten the plate
to the top support.
All the parts that are being machined are made of aluminum, in order to prevent the threads to be
damaged the use of inserts is recommended and used for all tapped hole. All the screws are made of
18-8 Stainless Steel (type 304). Unless specified a 1.4 safety factor is taken into account.
Only one fastening connection will be detailed, the other connections are very similar. The
screw type is the same.
2-4.1.1.

Bottom and top support on payload fastening

The two supports (see below for clarification) are fastened to the payloads with two 1/4-20 screws
each. They will be the same as those used to fasten the batteries adapters.

Figure 36. : Position of the screws. (left) Top payload. (right) Bottom payload
We need to verify if the screw can sustain the tension if a kick force of 125lbf (560N) is applied
axially.

𝐷𝑚𝑖𝑛 = 0.185𝑖𝑛 ≈ 4.70𝑚𝑚
𝐷𝑡ℎ𝑟𝑒𝑎𝑑 = 0.25𝑖𝑛 ≈ 6.35𝑚𝑚
𝑆𝑎𝑓𝑒𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 = 2
𝑌𝑖𝑒𝑙𝑑 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 215 𝑀𝑃𝑎

Figure 37. : Characteristics and 2D drawing of the ¼ button head screw
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With these characteristics, one screw can sustain a tensile load of:
𝐹𝑚𝑎𝑥

215
𝜋 ∗ 4.72
=
∗(
) = 1865 𝑁
2
4

If the load is evenly divided between the 2 screws each screw will face

560
2

= 280 𝑁. It means

the axial force resulting from the tightening torque must not exceed 𝐹 = 1865 − 280 = 1585 𝑁.
We can estimate the axial force knowing the torque and vice versa thanks to Kellerman and Klein
formula.
𝑝

𝐷

𝑇 = ( 2𝜋 + 0,583 × 𝑑 × 𝜇𝑓 + 2 × 𝜇𝑡) × 𝐹 ()
In that case we have:
𝑝𝑖𝑡𝑐ℎ 𝑝 = 1.27 𝑚𝑚
𝑑 = 6.35 𝑚𝑚
𝐷 = 7.938 𝑚𝑚 (average diameter of the contact between the screw and the part or between the
washer and the part)

Friction
Coefficient μ

Aluminum

Stainless
Steel
(304/303)

Stainless Steel
(304/303)

0.4

0.9

Figure 38. : Parameters for the calculation of torque (T)
µt is the friction coefficient between the washer (SS) and the frame (Aluminum).
µf is the friction coefficient between the thread (SS) and the insert (SS).
The screws must not be tightened more than 𝑇 = 8.12 𝑁𝑚. Recommended maximum tightening
torque for this type of screw is around 7 Nm. [Appendix 11] [w8]
Screw size /
Diameter
# 8-32 /
4.16mm
# 10-32 /
4.83mm
# 1/4-20 /
6.35mm

Load F
(lb)

Load F
(N)

Torque
(in-lbs) dry

Torque
(Nm) dry

Torque
(in lbs) lubed

Torque
(Nm) Lubed

580

2580

19.5

2.2

15

1.7

820

3647

31.5

3.6

25

2.8

1320

5871

70

7.9

55

6.2

Figure 39. : Sum up table of appendix 11: Recommended MAXIMUM tightening torque for
Stainless Steel 18-8 (type 304) screws (1 ≤ Grade ≤ 2)
Then we need to verify that the internal and external thread can sustain the load, it is even more
important because we are using aluminum.
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We can calculate the area of the threads (Internal and external). The first thread usually faces 50%
of the total load (See next Figure). If the first thread can sustain 50% of the shear load with a 1.4
safety factor (Sf) the design is satisfactory. In addition, all threaded holes will be equipped with
inserts which improves distribution of stress. (See figure below)

Figure 40. : Thread shearing distribution
2
2
𝐴1𝑠𝑡 thread = 𝜋 (𝑅𝑡ℎ𝑟𝑒𝑎𝑑
− 𝑅𝑚𝑖𝑛
)

st

1 thread area:
With R thread =

𝐷𝑡ℎ𝑟𝑒𝑎𝑑
2

0.5×𝐹𝑚𝑎𝑥

Stress: 𝑆𝑓 × 𝐴

1𝑠𝑡 thread

et R min =

𝐷𝑚𝑖𝑛
2

(See figure 26)

0.5×1865

= 1.4 × 𝜋 (3.1752 −2.352 ) ≈ 91 𝑀𝑃𝑎, Fmax is the maximal traction load the

screw can sustain.
Knowing that the Shear Strength ≈ 0.6*Yield Strength we have:
Aluminum 6061 Shear Strength (External part material) = 165 MPa
Stainless Steel 18-8 Shear Strength (Screw material) = 129 MPa
The screw threads will be damaged first if the load is excessive and will not damage the external
thread. Adding the inserts and using the screw traction load due to tightening instead of the maximal
traction load (125lbf = 560N) provides an extra safety factor.
Now that we have verified that the screw can axially face the load, the last thing we need to verify
is that the friction between the supports and their respective payload is higher than the 560N kick
force so as to avoid applying any shear load to the screw.
With Nylon patch screws the effective torque is lower than the one you apply on the screw (seen
on torque sensor for example). According to the supplier’s recommendation it needs more torque to
have the same effect. [w9]
Size
# 8-32
# 10-32
# 1/4-20

Torque to add in-lb
4
6
12

Torque to add Nm
0.45
0.68
1.36

Figure 41. : Table : Locking fasteners additional torque needed
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Assuming a torque of 2 Nm we can have an axial force of 587.5N using the Kellerman and Klein
formula – see page 26 ().
Aluminum/Aluminum friction coefficient is between 1.05 and 1.2, depending on sources. The
most restrictive value is taken into account in the calculus.
The friction Tangential force for 1 screw is 293N taking into account the safety factor. 2 screws
will be able to produce 586 N. On its own each support with only 2 screws can sustain the 125lbf
(560N) load. The screw will have to be tightened between 3.36 (=2+1.36) Nm and 7 Nm.

Friction zone

Figure 42. : Bottom support fastened on bottom payload showing friction zone
2-4.2. Helicoil inserts with captive fasteners – removable screws

All parts that are being machined are made of aluminum, in order to prevent the threads to be
damaged, and the use of inserts is recommended. Another requirement is to use captive fasteners
when they need to be removable so that the crew cannot lose any screw from the assembly because
it is attached to a bigger part.
Every threaded hole will be equipped with an insert.
All the screws are made of 18-8 Stainless Steel (type 304).
Unless specified a 1.4 safety factor is taken into account.
2-4.2.1.

Fasteners for payload-Astrobee connection

The payload screws cannot be chosen so we will verify if the screws we have to use can sustain a
125lbf traction force.

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𝐷𝑚𝑖𝑛 = 0.12𝑖𝑛 ≈ 3.04 𝑚𝑚
𝐷𝑡ℎ𝑟𝑒𝑎𝑑 = 0.164𝑖𝑛 ≈ 4.166 𝑚𝑚
𝑆𝑎𝑓𝑒𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 = 2
𝑌𝑖𝑒𝑙𝑑 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 215 𝑀𝑃𝑎

Figure 43. : Characteristics and 2D drawing of the 8-32 captive Socket head screw
With these characteristics, one screw can sustain a tensile load of:
𝐹𝑚𝑎𝑥

215
𝜋 ∗ 3.042
=
∗(
) = 780 𝑁
2
4

𝑭
Ԧ = 560 N

Figure 44. : Force applied to the top module

Figure 45. : Zoom on the captive fasteners between Astrobee and the payloads
In the worst case it is the top payload screw pattern which will face the load with only 4 screws.
If the load is evenly divided between the 4 screws each screw will face

560
4

= 140 𝑁. It means the

axial force resulting from the tightening torque must not exceed 𝐹 = 780 − 140 = 640 𝑁.
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We can estimate the force knowing the torque and vice versa thanks to Kellerman and Klein
formula.
𝑝

𝐷

𝑇 = ( 2𝜋 + 0,583 × 𝑑 × 𝜇𝑓 + 2 × 𝜇𝑡) × 𝐹 ()
In that case we have:
𝑝𝑖𝑡𝑐ℎ 𝑝 = 0.794 𝑚𝑚
𝑑 = 4.166 𝑚𝑚
𝐷 = 5.461 𝑚𝑚 (average diameter of the contact between the screw and the part or between the
washer and the part)

Friction
Coefficient μ

Aluminum

Stainless
Steel
(304/303)

Stainless Steel
(304/303)

0.4

0.9

Figure 46. : Parameters for the calculation of torque (T)
µt is the friction coefficient between the washer (SS) and the frame (Aluminum).
µf is the friction coefficient between the thread (SS) and the insert (SS).
The screws must not be tightened more than T=2.18 Nm which is convenient because these screws
have to be tightened by the crew and the average maximum tightening torque with a screw driver is
between 2.5 and 3.0 Nm. [w10] Recommended maximum tightening torque for this type of screw is
around 2.2Nm.
Screw size /
Diameter
# 8-32 /
4.16mm
# 10-32 /
4.83mm
# 1/4-20 /
6.35mm

Load F
(lb)

Load F
(N)

Torque
(in-lbs) dry

Torque
(Nm) dry

Torque
(in-lbs) lubed

Torque
(Nm) Lubed

580

2580

19.5

2.2

15

1.7

820

3647

31.5

3.6

25

2.8

1320

5871

70

7.9

55

6.2

Figure 47. : Sum up table of appendices 11: Recommended MAXIMUM tightening torque for
Stainless Steel 18-8 (type 304) screws (1 ≤ Grade ≤ 2)
The calculation for thread shearing and friction is very similar and the characteristics are given in
the appendices for more details. Every screw connection has been verified with the same calculation
process. The concept design can easily integrate the screw connections proposed based on the
calculation.

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2-5. Assembly sequence by ISS crew
RINGS Batteries: The payload batteries need to be connected to RINGS using a cable and Molex
connector.
Ribbon Cable to Payload: Astrobee’s payload connector is connected to the RINGS avionics using
a ribbon cable shown in the next Figure. The cable is first plugged to RINGS; during assembly the
cable has to be routed between Astrobee and the top plate to avoid damage to the wires. Finally, the
other end of the ribbon cable is plugged to Astrobee’s payload connector – See next Figure.

Figure 48. : Ribbon Cable (orange) from RINGS avionics to payload bay connector
The design was not easy to do with the lack of space and the requirements of no obstruction of
Astrobee features. First, to place all components - especially the batteries – and secondly to design
parts that could sustain the kick load. Another goal was to design it so the crew can assemble Astrobee
and RINGS easily and quickly. The crew will need:


two screwdrivers: one standard hexagonal, size #8 (

5
32

inch) and one standard

hexagonal, size #1/4 (¼ inch). The screws have to be tightened to the maximum value
possible by the crew (i.e. around 2.5 Nm for an average human and standard
screwdriver);


To perform the sequence in the right order to be able to assemble the system – see
appendix 12 for clarification.

2-6. Additional technical documents
At the end of the internship I spent a bit of time on the 2D drawings for the parts that may have to
been machined if the project is accepted. It was not requested for the concept design but I had time
to make 5 out the 7 parts which need to be machined. The main requirements for functional
dimensioning was to have a precise position of the screw patterns and positioning pins between the
frame of the Astrobee and the payload. The 2D drawings can be found in appendix 3.

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2-7. Conclusion: Interface between Astrobee and RINGS
The technical report on the concept design for the interface between Astrobee and RINGS have
been delivered to NASA on time. Based on the results from the RINGS-SVGS experiments and my
work on the mounting system NASA will decide if they want to pursue and go to the next phase:
detailed design, order the parts and machine the parts needed. The first steps of the project were not
easy, especially before we knew we could use the payload bays to fit the batteries. Then I design and
dimensioned as much mechanical connections and parts to validate the design. FEA simulation have
been the hardest thing because I needed to simplify the design in order to perform the tests. The time
between two conference call was convenient, I had time to work on the project before the follow up
presentation every other week and at the same time I had feedbacks very quickly if I asked Mr.
Gutierrez or when we sent emails to NASA.

Figure 49. : Concept Astrobee-RINGS in the International Space Station

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3- Personal conclusion
My internship was hugely rewarding. I had the opportunity to use what I have learnt throughout
my studies and I also acquired knowledge and autonomy during these 5 months. Working in a lab
was something I wanted to experience, and it was even better to be able to do it abroad. I met foreign
interns in the lab and I really enjoyed talking to them, either about the project or on other everyday
issues. It has strengthened my will to go abroad, to work and to visit other countries. I will probably
look for an internship in a country with a different culture; an Asian or Scandinavian country would
be a good opportunity for me.
As regards the technical aspects of my internship, I was able to rely on my general knowledge of
CAD software to use the one available at FIT. However, a tricky aspect was the use of both the
imperial and metric system. I had to deal with these two systems of units in both everyday life and
during the project.
Working in a lab was, from my experience, more of an individual task rather than a team project.
This said, it has allowed me to improve my language and technical skills on a very interesting project
— I was already interested in the aeronautics and aerospace sector; this project has confirmed that I
want to pursue in this field. I am now looking forward to do my next internship in a private company,
which will offer me the opportunity to improve my communication and management skills.

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Online Resources
[w1]: Florida Institute of Technology (FIT) web site : https://fit.edu/
[w2]: NASA SPHERES documentation:
https://www.nasa.gov/mission_pages/station/research/experiments/2021.html
[w3]: NASA SPHERES news
https://www.nasa.gov/spheres/home
[w4]: NASA RINGS documentation:
https://www.nasa.gov/mission_pages/station/research/experiments/311.html
[w5]: NASA Astrobee documentation: https://www.nasa.gov/astrobee and
https://www.nasa.gov/sites/default/files/atoms/files/irg-ff029-astrobee-guest-science-guide.pdf
[w6]: NASA Safety Requirement Document:
https://mmptdpublic.jsc.nasa.gov/mswg/Documents/SSP%2050021.pdf, page 63.
[w7]: Structural design requirements and factors of safety for spaceflight hardware (NASA):
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023499.pdf, page 26.
[w8]: Recommended tightening torque, Fastenal:
https://www.fastenal.com/content/feds/pdf/Torque%20of%20Stainless%20Steel,%20Non%20fer
rous%20Torque.pdf and
https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/08/20-Fasteners.pdf
[w9]: Additional torque recommended by nylon patch screw supplier, Longlok:
http://www.longlok.com/site/pdf/handbook.pdf
[w10]: Master’s theses on Effects of Bit Type on Maximum Torque and Axial Force Using Manual
Screwdrivers, Marquette University:
https://epublications.marquette.edu/cgi/viewcontent.cgi?article=1226&context=theses_openPage

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Attachments
Appendix 1: Planning........................................................................................................................ 44
Appendix 2: Electrical diagram ........................................................................................................ 45
Appendix 3: View of the bottom payload bays on the Astrobee and 2D design of the frame .......... 46
Appendix 4: Standard payload with fasteners................................................................................... 48
Appendix 5: Load on X axis ............................................................................................................. 48
Appendix 6: Load on Y axis ............................................................................................................. 49
Appendix 7: Load on Z axis .............................................................................................................. 50
Appendix 8: Torque on X axis .......................................................................................................... 51
Appendix 9: Torque on Z axis .......................................................................................................... 52
Appendix 10: Mass and inertia characteristics of the RINGS .......................................................... 53
Appendix 11: Two different sources which shows recommended tightening torques ..................... 53
Appendix 12: Mounting sequence .................................................................................................... 55
Appendix 13: 2D Drawings of all the parts ...................................................................................... 57
Appendix 14: Pictures of all the parts made at the machine shop at FIT…………………………...62

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Appendix 1: Planning

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Mémoire de stage d’immersion

Appendix 2: Electrical diagram

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Appendix 3: View of the bottom payload bays on the Astrobee and 2D design of the frame

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Appendix 4: Standard payload with fasteners

Appendix 5: Load on X axis

The load is on the X axis with a force of 740𝑁 = 560𝑁 ∗ 1.4 (i.e. 1.4 is the safety factor and
560𝑁 = 125𝑙𝑏𝑓)
The displacement is minor, about 0.2mm.
Stress is also not really high with an additional safety factor of 7 compared to aluminum strength.

Figure 50. : . (left)Total displacement. (right) Von Mises equivalent stress.
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Stress (Mpa)

42.00
41.00
40.00
39.00
38.00
37.00
36.00
35.00
2.5

2

1.5

1

0.5

0

Figure 51. : Stress convergence function of element size (mm) with force on X axis
Appendix 6: Load on Y axis

The load is on the Y axis with a force of 740𝑁 = 560𝑁 ∗ 1.4 (i.e. 1.4 is the safety factor and
560𝑁 = 125𝑙𝑏𝑓)
The displacement is minor, less than 10−1 𝑚𝑚.
Stress is also not really high with an additional safety factor of 16 compared to aluminum strength.

Figure
52. : . (left)Total displacement. (right) Von Mises equivalent stress.

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