P16104: Microfluidic Spectroscopy for Proteins within CubeSats
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Subsystem Design

Table of Contents

Team Vision for Subsystem-Level Design Phase

As a team, our goal for this phase was to divide our device into subsystems and then divide our team members amongst those subsystems. We intended on further each of the individual systems by designing and beginning to determine which materials we would need. Our goals as a team were broad, but among subsystems additional goals would be set.

During this phase, we divided our device into four subsystems: electrical, mechanical/structural, microfluidic, and spectroscopy. We then divided our seven team members amongst the four subsystems so each would have two people. Each of the subsystems were able to reach small goals which are showcased in the reports below. Electrical was able to begin ordering materials, mechanical/structural 3D printed preliminary designs, microfluidic determined materials and design of the bio-assay, and spectroscopy determined which light source would be best to use.

Feasibility: Prototyping, Analysis, Simulation

Electrical Subsystem

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Temperature sensors (T) will monitor the experiments and board status. The current sensors (C) monitor the power consumption of all major components. The position sensor (P) verifies proper solenoid operation.

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The UV LED illuminates the Bioassay, with the photons passing through an optical filter to add isolation from unwanted external sources (i.e. Sun). The output filter eliminates the UV LED output and provides additional filtering against unwanted light. The photodiode output will be filtered for noise and amplified to a readable voltage for the MCU.

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The majority of sensors were chosen from Adafruit due to the available development boards. Our selections were based on the components ability for rapid prototyping and testing.

The UV light sensor can measure wavelengths at 350 nm. The current sensor is able to log power consumption and report back to the CubeSat. This will aide in detecting issues and failures. The UV LEDs have been selected to test the light sensor for proper operation. That is, the UV LEDs will simulate the florescent proteins.

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Teensy 2.0 Development Board

This board allows for quick software development through the Arduino library. The board also matches our current hardware requirements of sensors and outputs.

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Breadboard testing will confirm operations. Testing will also allow for quick transition to custom hardware if confirmed that the test is successful.

Structural Subsystem

Chassis Selection:
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1U Skeletized Chassis by Pumpkin Inc. Meets required NASA standards for CubeSats as well as different launchers 5052-H32 Aluminum, Walls - 1.27mm thick, Bases - 1.5mm thick, Rated for -40 to +85 °C, 97.46mm X 97mm interior

The chassis itself is alodyned while the walls are hard anodized. This allows for the chassis to remain conductive creating a Faraday cage. If the chassis were completely hard anodized, it would become an electrical insulator. Able to easily integrate solar panels Price - $925.00. Unable to manufacture in house due to specialized material treatments. Rapid prototyping was utilized to create a mockup.

Structural Prototyping

Project Requirements:

The bioassay must fit into a 1U CubeSat. The components and sensors of the bioassay are supported by a surrounding structure. As our bioassay develops and changes, so too will the design of the surrounding structure.

Solution:

Rapid prototyping techniques such as CNC machining, laser cutting, and 3D printing could potentially allow us to make quick and detailed changes to our CubeSat structure. Currently there have been several uses of additive manufacturing techniques in Cubesats.

Use of Rapid Prototyping in Cubesats

Pros:

Cons:

Considering our project’s scope does not require a launch capable structure, the use of 3D printing and other rapid prototyping techniques will meet our needs.

Initial Testing: CAD Files

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1st printed mockup

Vibrations - Model Analysis

Model Analysis: Using the overall mass and stiffness of a structure model analysis is used to find the periods at which the structure will naturally resonate. NASA CubeSat requirements prohibit 1st resonance frequency to be above 100 Hz

Modeling: Assumptions: Specifics regarding internal components unknown. Shapes and sizes were estimated to serve as placeholders CubeSat launched from PicoSatellite Orbital Deployer (P-POD) P-POD is constrained along the rails (sides), but it allowed slight movement in the vertical direction. Constrained in both x and y directions and allowed slight freedom in z.

Results: Mode 1:

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Mode 1: 56.271Hz, Mode 2: 152.1Hz, Mode 3: 156.3Hz, Mode 4: 157.75Hz, Mode 5: 171.79Hz,

Mode 1 is significantly lower than 100 Hz. Changes to internal components should not result in drastic changes.

Thermal: 4 heat sources- Direct Solar radiation, Albedo (Radiation from sun bounces off earth), Earth Infrared, Internal heat generation.

Experimenting with different ways to incorporate all sources into model

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Spectroscopy Subsystem

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The document containing the rationale, calculations, and sources can be found here: Spectroscopy Math.

Microfluidic Subsystem

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The document containing the rationale, calculations, and sources can be found here: Protein Concentration and Reagents.

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Schematic of channel and well.

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Diagram of PDMS layer design. The channel will be built up by thin layers of PDMS bonded together.

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The document containing the rationale, calculations, and sources can be found here: Microfluidic Channel Design.

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The document containing the rationale and sources can be found here: Solenoid Valves.

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Hydrophobic surfaces promote protein adsorption. The following table shows benchmarking for different surface modification techniques.

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The document from which this information was gathered can be found here: Wong, Ieong and Ho, Chih-Ming.

Polyethylene glycol is the path we are choosing to take. It will be a liquid layer that is thermoset to the PDMS surface.

Drawings

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Bill of Materials (BOM)

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Updated Engineering Requirements

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Risk Assessment

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The working document can be found here:P16104 Risk Assessment.

Design Review Materials

The following presentation was given on October 22, 2015: Subsystems Level Design Review

Plans for next phase

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Individual Plans

August Allen's Three Week Plan: August's Goals.

Mallory Rauch's Three Week Plan: Mallory's Goals.

Anna Jensen's Three Week Plan: Anna's Goals.

Andrea Mazzocchi's Three Week Plan: Andrea's Goals.

James Lewis's Three Week Plan: James's Goals.

Matthew Glazer's Three Week Plan: Matthew's Goals.

Darin Berrigan's Three Week Plan: Darin's Goals.


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