Cubesat Frame Mount, Design Specifications

This document serves to collect all of the electrical and mechanical design constraints in one place. The constaints are broken up into mechanical, electrical, and Misc. requirements. Mechanical refers to any structural restrictions as well as the physical forces that the assembly will endure. The electrical constraints are any EM restrictions, wiring location requirements, and any other requirements that do not directly translate to a mechanical requirement. Misc. requirements are meant for anything that does not fall into either category, since there might be something I am forgetting.

Ideally, the requirements are broken up into 'must' and 'should'. The 'must' requirements will be prioritized, while the 'should' requirements are relegated to quality-of-life improvements and anything that is not a main priority.

Please feel free to populate the useful links and contact information.

If the design constraint was met, it is marked with a [Y], and if it was not met it is marked with a [N]. If they are not met, a note is added.

Useful links:

• CubeSat Design Specification, Rev. 13
• CAD models

Contact Information:

• Ian Zabel: ian.b.zabel@gmail.com, ibz@pdx.edu
• Alex Farias: afarias@pdx.edu
• Joe Shields: shields6@pdx.edu
• Glenn LeBrasseur: glenn.lebrasseur@gmail.com

Mechanical Design Constraints

Regarding the mechanical constraints, specific values and dimensions are desired. If a requirement is something like 'must be easy to access 'tuna can' connections', please place those in misc. design requirements.

Enclosure and Rails:

• [N] Volume between rails must accommodate 6.5 mm normal from the CubeSat side walls (plane of rails).
  • Due to the available volume within the module, the rails must be L-brackets instead of individual rails.
• [Y] Overall length must be above 376.8 mm to accommodate CubeSat rails and 'tuna can'.
• [Y] Distance between parallel rails must be 100 mm along both the X and Y walls.
• [Y] Enclosure should accommodate 80 mm long (Z) and 72.5 mm wide (X and Y) access ports
• [N] Rails width must be above 8.5 mm.
  • Due to the available volume, the rails are restricted to contacting 6.5 mm of the CubeSat corners.
• [ ] Rails should have a surface roughness less than 1.5 micro-meters.
• [Y] P-Pod rail contact area must be at least 75 % total contact.
• [N] Rail material must be Al. 6061, 7075, 5005, 5052
  • The material cannot be conductive to ensure radio transparency
• [N] Rail material should be Al. 6061
  • The material cannot be conductive to ensure radio transparency
• [N] Rails must be anodized Al.
  • The material cannot be conductive to ensure radio transparency

CubeSat and 'Tuna Can':

• [ ] Must have maximum 3U CubeSat mass be 4 kg.
• [ ] CubeSat COM must be located within 2 cm from the geometric COM in the X and Y directions.
• [ ] CubeSat COM must be located within 7 cm from the geometric COM in the Z direction.
• [ ] Geometric tolerance must be: 0.X +- 0.1; 0.XXX +- 0.001.
• [ ] Spacing between access ports must be above 27 mm.
• [ ] Length must be below 36 mm normal to the Z- face.
• [ ] Should be centered on the Z- face.
• [ ] 'Tuna Can' radius must be below 64 mm.

Electrical Design Constraints

Enclosure and Rails:

• N/A

CubeSat and 'Tuna Can':

• [ ] Must have Z- inserted first, no/minimal wired connections at base.
• [ ] Should have magnetic field below 0.5 Gauss above Earth field.
• [ ] Should have all wired connections contained within the 'tuna can'.

Misc. Design Constraints

Enclosure and Rails:

• [Y] Should accommodate 3 access ports on one side.
• [Y] Must leave room for electronics between the rail mount and the airframe cylinder.
• [N] Should have a total of 8 rails, 2 for each CubeSat rail.
  • Due to the available volume, the rails are restricted to contacting 6.5 mm of the CubeSat corners.
• [Y] Must allow the CubeSat to slide in and be mounted without needing screws.

CubeSat and 'Tuna Can':

• [ ] Z- face must be inserted first.
• [ ] CubeSat deployables must be constrained within CubeSat.
• [N] Width, height, standoffs, and protrusions must comply with 3U+ CubeSat acceptance checklists.
• [N] Access ports must be referenced on the X+ side.
  • The rail to module mounting restricts access to the CubeSat without unscrewing the assembly prior to removal.

Dimension Notes

These are notes regarding the physical dimensions of the airframe section and rings. All dimensions from the design specifications.

# Mounting Ring Geometry

Di = 6     # Diameter, inner, female/male ring (in.)
Dm = 0.12  # Diameter, mounting holes (in.)
N  = 6     # Hole count (#)
Lm = 0.285 # Mounting hole length (in.)

# CubeSat Geometry (3U)

Wr = 8.5   # Minimum rail width (mm)
Fr = 1     # Minimum rail fillet (mm)
Wc = 100   # CubeSat width, X+ Y+ (mm)
Lc = 340.8 # CubeSat length, Z+ (mm)

La = 86.5 # Access port length, Z+ (mm)
Wa = 72.5 # Access port length, Y+ (mm)
Lb = 27.  # Access port seperation, Z+ (mm)
ov = 6.5  # Access port overhang, Z- (mm)

# Tuna Can Geometry
# Centered on Z- face

Rt = 64 # Max tuna can diameter (mm)
Lt = 36 # Max tuna can length (mm)

Design Notes

The overall design, shown in figure 1, consists of four main components. The rail system is what houses the 3U+ CubeSat, along with all other electronics surrounding the CubeSat. The rail to ring interface serves to mount the rail carriage to the rings. The two rings serve to carry all connections to the rest of the rocket, along with the interface to the other modules. The six plates that surround the rails serve to add torsional strength and mark the location of the 1U and 2U CubeSat locations. All components besides the rail to ring interface are made out of acrylic laser cut using the MELT 60W.

Mounting Plates:

The aluminum mounting discs are screwed into the six radial holes already present on the module rings. The 'closed' acrylic plates are screwed to the aluminum rings using the eight mounting holes. These holes also allow the entire center assembly to be screwed to the end mounting plates as well as the laser cut plates to be bolted together for easier alignment when making small changes.

Rail System:

The rails themselves are made of acrylic ahered together using this adhesive. The rails contact the CubeSat rails across the entire length of the CubeSat, while also being adhered to the plates with the square openings shown in figure 1. The four plates located at the 1U and 2U distances from the base are adhered as well to ensure improved torsional strength.