P16102: RIT-SPEX Structure
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Detailed Design

Table of Contents

Pre-Approval

We are looking to provide a systems architecture for RIT SPEX to deploy solar cells to maximize the area of solar cells exposed to the sun during orbit and flight of a 1U CubeSat

Stationary

We have decided to design a solar cell array that deploys two wings on opposites sides of the vehicle. In conjunction with the three panels already in place and assuming a constant solar angle flight, which is common, it will expose three panels to the sun constantly. This design also needs to meet flight readiness, minimize mass and reduce cost for the SPEX research group.

Hot Knife

To deploy the solar cells, the elements should rotate around a hinge point integrated into the structure with springs also installed in there. To fully stow these components, a hot knife mechanism, common in space applications will be employed through the use of fishing line to hold the wings shut. On demand, a length of high resistance Nichrome wire heats up, forcing the nylon to break. The springs will then deploy the wings to be exposed to the sun.

Major Questions to Answer

Before this presentation there were many questions:

After this presentation:

Material Choice

We have chosen Polyetherimide, better known by its commercial name: Ultem 9085, as the material out of which to print our components. This choice was made based on numerous advantageous material properties which are detailed in the next section.

For the rails, we are planning on using 6061, which is allowed by section 3.2.15 of the CubeSat design standard.

We are planning to tap and connect using M3x0.5 screws to connect most hardware and low-profile rivets if necessary.

Metal, glass, or fractured solar cells will be used as boilerplates for the actual solar cell devices mounted on five faces of the CubeSat.

A volume fitting mass analog to be made later will occupy the remainder of the 1.33 kg mass budget for the CubeSat as internal electronics.

Design Questions From Last Review

  1. Eigenfrequencies and Strengthening
  2. Boilerplates
  3. Machinability and Manufacturing Changes
  4. Thermal Analysis (with vibration)
  5. Acoustic Vibration

Changes to Final Design

Material Selection

Material Selection Matrix (12/2/15)

Material Selection Matrix (12/2/15)

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Several 3D printable materials were compared across several properties. Upon analysis and comparison, we found Ultem to be the best choice for our design. Ultem offers the following advantages to our project:

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Ultem Properties (12/2/15)

Ultem Properties (12/2/15)

Mechanical Design and Drawings

Assembly

Deployed CubeSat Assembly Isometric View (12/2/15)

Deployed CubeSat Assembly Isometric View (12/2/15)

Undeployed CubeSat Assembly Isometric View (12/2/15)

Undeployed CubeSat Assembly Isometric View (12/2/15)

Side Rails

Rails Isometric View (12/2/15)

Rails Isometric View (12/2/15)

Top Plate

Top Plate Isometric View (12/2/15)

Top Plate Isometric View (12/2/15)

Side Plates

Side Plate Isometric View (12/2/15)

Side Plate Isometric View (12/2/15)

Bottom plate feature dimensions

Bottom Plate Isometric View (12/2/15)

Bottom Plate Isometric View (12/2/15)

Wire Routing

View of modified wire retention system (12/14/15)

View of modified wire retention system (12/14/15)

View of restraining line in system (2/9/16)

View of restraining line in system (2/9/16)

Hole placement

A standard hole size of M3 was chosen for all screw attachments in the assembly. This allows the selected solar panels to be attached and eliminates the need for multiple varieties of screws. Screw holes were added to the top plate and the top solar panel was rotated 90 degrees from the previous design so that the screws would not interfere with the hinges.
Screw Hole Placement (12/3/15)

Screw Hole Placement (12/3/15)

Bill of Materials

Our Bill of Materials has been updated to reflect the change in printing material from carbon fiber to Ultem and actual production quotes.

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B.O.M. (12/2/15)

B.O.M. (12/2/15)

Design for Manufacturing

3D Printing of Ultem

Ultem 9850 was recently made 3d printable, supplied in a filament form, the material must be heated to a high temperature in order to make it melt. Ultem selection meets a variety of selection criteria for ductility, heat transfer, and strength, and 3D printing the material allows us to make and design complex internal geometry which allows this project to capitalize on the technology and save a great deal of weight and volume.
Hyrel 3D Printing-AM Institute
On campus, a Hyrel 3D printer was recently purchased, and it features a high temperature head capable of reaching 350 degrees C. This printer is designed for industrial applications, and features a higher resolution and printing quality than most commercial printers at 0.1 mm layer resolution (0.4 to 1 mm resolution). Hyrel will be able to provide a professional quality print in house and at the same time, its use is restricted to projects like P16102, meaning that the opportunities to print would be often.

Buying filament from a company such as Fisher Unitech would cost approximately $650 and be sufficient for 6 to 10 CubeSats in full based on testing and potential breakage.

Incept3d Outsourcing
The opportunity to outsource the printing is possible. Quotes filed through Incept3d indicates that it would cost upwards of $250 to set up for a few prints of the base plate. The turnaround time is unknown currently and the total cost of all printing would be approximately $500.
Analysis
Ultimately, we are planning to purchase the Ultem filament from an industrial supply company and then use it in the Hyrel Printer here. So far with printing, out of the seven elements we've printed and the ten total components needed to print have failed, indicating a potential print failure rate of approximately 25%.

If we were to print on campus, we'd have an upfront cost of $650, and then the ability to reprint as necessary, in light of the fact that the printed mass of the CubeSat is under 100 grams and that future projects could use the material.

Outsourcing the printing, valued at potentially $500 with a 25% chance of failure and reprint not including failure through testing leads to the following potential costs, $500 + 25%($500) = $625 + shipping, handling, and leadtime.

Machining

The rails will be machined out, and designed for it. A bar stock of 6061, which is permissible in the CubeSat design standard will be cut to net length. The pieces will be surfaced finished on two sides, then the end sections will be machined. After this, the part will be clamped from the end rails and machined out. Once the machining is complete, holes will be drilled and tapped. The process could be automated with Prototrak or done by hand. It will take 3 to 4 hours per rail to machine.

Assembly

To assemble the system, the baseplate and hinge assembly will be made and then meshed to the rails along with the top plate that houses the wire path.

Ideally, we'd use screws at this level to allow us to assemble and disassemble easily, but could use rivets to finalize the assembly.

Dis-Assembly/ER 12 Time Requirement

As it stands right now, there are two methods to removing the circuitry core of the CubeSat design. The insides are designed to meet the Pumpkin CubeSat PCB specification and there is space for mounting.

Method 1- Fall Apart Method In this case, the screws connecting the side rails are removed, allowing the sides to fall away, exposing the core with the top and bottom plates still attached with the deployables still attached. This requires only 8 fasteners to be removed.

Method 2- Core Extraction A top or bottom plate could be removed, along with the supports connecting the core to the bottom or top plates, allowing the entire core to be removed independent of the frame housing.

Qualification of Design

Systems Architecture Chart

System Architecture and Interconnect (October 2015)

System Architecture and Interconnect (October 2015)

Simulation/COMSOL

Launch Thermal Analysis

Launch-Steady State Temperature Distribution (12/2/15)

Launch-Steady State Temperature Distribution (12/2/15)

In Orbit Thermal Analysis

 Thermal Simulation: Front face sun exposure

Thermal Simulation: Front face sun exposure

Vibration Analysis

P16103
 First Natural Frequency from Preliminary Design

First Natural Frequency from Preliminary Design

 First Natural Frequency Final Design

First Natural Frequency Final Design

 Second Natural Frequency Final Design

Second Natural Frequency Final Design

 Third Natural Frequency Final Design

Third Natural Frequency Final Design

Other Orientations
 2g Load 100 Hz Off Axis Direction (12/2/15)

2g Load 100 Hz Off Axis Direction (12/2/15)

 Von Mises Stress for a Stationary 6g Load Applied in the Z-Direction

Von Mises Stress for a Stationary 6g Load Applied in the Z-Direction

 Von Mises Stress for a Stationary 6g Load Applied in the X-Direction

Von Mises Stress for a Stationary 6g Load Applied in the X-Direction

 Von Mises Stress for a Stationary 6g Load Applied in the Y-Direction

Von Mises Stress for a Stationary 6g Load Applied in the Y-Direction

Acoustic Coupling

System Operations Flowchart

In Flight Operations (December 1st, 2015)

In Flight Operations (December 1st, 2015)

Prototyping

Prototype Development

To this point, the specificity of our tests as well as visualization of the overall design have been somewhat restricted. We sought to free ourselves from this restriction by making a full structural prototype. As all of our structural components have CAD models, this was accomplished using RIT's "The Construct". All parts were printed out of PLA which is free to us as students. Printing the sample parts also prepared us for the type of lead times we are likely to experience. In addition, we were able to verify the feasibility of our planned assembly method by assembling the prototype.
Prototype Top View (12/7/15)

Prototype Top View (12/7/15)

Prototype Bottom View (12/7/15)

Prototype Bottom View (12/7/15)

Creep Analysis

Previously conducted creep tests have the geometry and loading to properly reflect the conditions that the actual restraining line will experience. Using a 3D model of the CubeSat bottom plate and weights based off of the tension the actual springs will provide, a more relevant creep test was performed.

Printed Bottom Plate
As part of our plan to print a full prototype of the CubeSat, a bottom plate was printed out of PLA at RIT's "The Construct". This plate gives us a better idea of how friction and bending will effect creep.
Printed Bottom Plate (12/7/15)

Printed Bottom Plate (12/7/15)

Tension
Each deployable solar panel is pushed open by two 0.05 in*lb (.0056 N*m) springs. The two springs pull on the restraining line with a lever arm of approximately 0.1 m. This provides a total of 0.1 N of tension on the line. In addition, the restraining line will intentionally be tensioned after installation for added security. A total tension of 1.6 N is assumed to incorporate this added tension. 1.6 N represents the amount of tension require to pull the fishing line taut. This tension is accomplished by hanging a 160 g mass from either side of the restraining line.
Bottom Plate Creep Test Setup (12/7/15)

Bottom Plate Creep Test Setup (12/7/15)

Results
A 15.5 cm section of the restraining line was marked prior to the test. After leaving the setup at room temperature for four days, the marked section remained 15.5 cm in length. This shows a complete lack of creep and suggests that the creep we see on the final product will not exceed the 6.5 mm clearance between the resting state of a deployable panel and the PPOD wall. Although more testing will be needed next semester to further verify this result, this test suggests that the current restraining line design is acceptable and we are justified to move forward with it.
Bottom Plate Creep Test Results(12/7/15)

Bottom Plate Creep Test Results(12/7/15)

Lessons Learned from Assembly

We decided to print out the entire structure and practice putting it together. Through this experience, a lot was learned about how this assembly could be made better when released to manufacturing. Changes would include:

Risk Analysis

Our risk assessment has been updated to reflect the following developments:
Updated Risks (12/7/15)

Updated Risks (12/7/15)

Final Customer Requirements

When traced back to customer requirements, we show that our design meets the needs of our customer.
Customer Requirement Validation (12/2/15)

Customer Requirement Validation (12/2/15)

ER Table

ER and Description Minimum Ideal Current Status?
1 Min Undeployed Area Time (cm2-orbit) 100 100 100 Satisfied
2 Deployed Area Time (cm2-orbit) 150 300 300 Satisfied
3 System Mass (grams) 420 300 ~360 Satisfied
4 CubeSat Clearance (mm) 1 1 >1 Satisfied
5 Time from Command (s) 2<t<8 2<t<8 ~ 7 Satisfied
6 Operating Temperature (deg C) (-40,40) (0,20) Material Selection Satisfied
7 Available Interior (mm) 96 90 85 100 100 100 96 90 ~80 Satisfied
8 Exterior Protrusion Space (mm) 6.5/face 6.5/face CAD Satisfied
9 Change in COM (mm) 50 >10 Simulation Satisfied
10 Constant Launch Acceleration (g) 6 8 Simulation Satisfied
11 Cost of Prototype ($USD) 500 400 $100-$500 Satisfied
12 Time to Remove Blank (s) 8 6 <8 ?
13 Launch Vibration Test (Pass/fail) Pass Pass Simulation Satisfied
14 Full Documentation Pass Pass Pass Satisfied

MSD II Plans

Gantt Chart

MSDII Work Plan

MSDII Work Plan

Ordering Plans

Supplier Line Items Status Order Form
McMaster Carr
  • Spring
  • Metal Stock for Rails
  • Rail Ends
  • Screws
  • Helicoils
  • Fishing Line
  • Transistors and Electronics
Waiting Approval
Aerocon Systems
  • Nichrome Wire
Waiting Approval
Fisher Unitech
  • 3D Printing Filament
Waiting Approval Link

Test Plan

Table Top Deployment

Facilities Required: None.

Engineering Requirements Tested: ER5-Time from command to deploy, ER11-Cost of prototype.

Timetable for Testing: 1/26/16 - 2/1/16.

Temperature Deployment

Facilities Required: Oven and Freezer.

Engineering Requirements Tested: ER5-Time from command to deploy, ER6-Operating temperature.

Timetable for Testing: 2/2/16 - 2/8/16.

High Altitude Balloon

Facilities Required: High altitude balloon.

Engineering Requirements Tested: ER2-Maximum deployed area time, ER5-Time from command to deploy, ER6-Operating temperature.

Timetable for Testing: 2/9/16 - 3/7/15.

Bottom Plate Creep

Facilities Required: Oven.

Engineering Requirements Tested: ER8-Available exterior protrusion space.

Timetable for Testing: 2/9/16 - 2/15/16.

Full System Creep

Facilities Required: Oven.

Engineering Requirements Tested: ER6-Operating temperature, ER8-Available exterior protrusion space.

Timetable for Testing: 2/29/16 - 3/10/15.

Fit Check

Facilities Required: None.

Engineering Requirements Tested: ER4-PPOD-CubeSat clearance, ER8-Available exterior protrusion space.

Timetable for Testing: 2/16/16 - 2/22/16.

P16103

Facilities Required: P16103 test table. Shop Air.

Engineering Requirements Tested: ER13-Launch vibration test from 16103.

Timetable for Testing: 3/25/16 - 4/7/16.

Imagine RIT Plans

Due to the linked nature of our projects, out group will share a booth with P16103. At least one member from each group will occupy the booth at all times throughout the day. Our part of the display will include the final CubeSat, a descriptive poster and PLA printed CubeSat parts that visitors can handle.
Sketch of Imagine RIT Layout (December 2015)

Sketch of Imagine RIT Layout (December 2015)

Approval

As we come to the end of MSD I, we seek approval from our guide for the following:
 Project Package Structure

Project Package Structure

Gate Review


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