NASA Suborbital Flight Communication and Fire Box

=Problem Definition= This project continues the work completed by the previous University of Idaho capstone teams who have partnered with NASA Ames Research Center on developing a communications system for a Tube Deployed Re-entry vehicle (TDRV). Previous teams have done a variety of groundwork such as building a guided parafoil system that can move a returning payload in order to reach a pre-determined GPS location during its descent. Other work, accomplished by the most recent team, includes creating a carrier module capable of controlling and housing the Iridium 9523 modem in order to help integrate into future returning cube satellites. Lastly, a previous team developed the initial codebase for communicating over the Iridium satellite network utilizing the Iridium 9523 via SBD (short burst data) messages. They also attempted to implement dial-up capabilities but were unsuccessful. Our team is building off of these previous groups and creating a fully functional communication system through an Iridium 9523 connected to a carrier module that is powered by Canon BP-955 batteries in a fireproof containment unit. The end product will be a cheap, reliable, and physically safe system capable of real-time data communication with a returning satellite. The project can be broken down into 3 main components:  The software necessary to provide communication through the Iridium network. The carrier module re-design necessary to host the Iridium-9523 module in a smaller form factor. The battery box to store the Lithium-ion batteries necessary to power the system in a safe way. 

=Deliverables=   Software:   An Arduino compatible software library written in C++ for a microcontroller capable of using an onboard Iridium-9523 modem to allow for SBD (short burst data) and dial-up communication via the Iridium satellite network.  This software must properly power the carrier board the Iridium modem on startup.</li> It must also parse data from TechEdSat (TES) and forward the message to the Iridium-9523.</li> Incoming data that is received by the Iridium-9523 modem must be parsed by the microcontroller and forwarded to TES.</li> The microprocessor must keep track of which state the Iridium-9523 modem is in and be capable of switching based on the input from TES.</li> Encryption and decryption capabilities should be added to increase the security during data communication.</li> </ul> A server capable of receiving and parsing transmitted information from the Iridium modem and storing the messages locally.</li> </ul>  Carrier Module: </li>  Fully functional Iridium Carrier Module confined to the PC-104 form factor.</li>  Report on the effect of vacuum and orbit temperatures on the functionality of various types of capacitors and resistors, and the performance differences between typical and high-performance resistors. </li> </ul>  Battery Box: </li>  A lightweight “firebox” capable of containing a fire as a result of thermal runaway caused by batteries used to power the reentry module.</li> </ul> </ul>

=Specifications= The requirements as outlined by our client are shown below:  </ul>

=Project Learning=

Software:
The initial hurdle that the CS subteam had to research and overcome was getting the carrier module to power on correctly and provide proper communication between all possible ports. This includes the microcontroller, Iridium-9523 modem, and TES ports. To learn how the board was built and how to use it, we had to reach out to the previous design team creator, Avery Brock, for plenty of questions and advice on how to fix the board and ultimately get it working. This also required the aid of our Electrical engineers to read over the Eagle schematics and determine which jumpers needed to be moved in order to fix problems with power so we could move on with our project and actually develop code for a board that works. The helpful files we used as research for this carrier board can be found here: Carrier Board Files In order to develop the software library, we decided to first research what previous University of Idaho capstone CS subteams completed to give us a reference for how to move forward. We quickly learned that although some of these teams accomplished SBD functionality, they did so on different hardware platforms under different restraints. For instance, they used NAL specific hardware (the black box) to communicate with the Iridium modem while we are developing for a microprocessor (SAMD21) on a custom carrier board designed by a previous design team. This indicated to us that we have to go about our software design differently, but can still use specific commands called by their code within our own since we learned that the Iridium modem responds to general AT (ATtention) commands. Also, we were given the goal of implementing dial-up communication which no previous teams were able to successfully achieve so this had to be researched separately. Most of this helpful information was found in Iridium AT reference guides and general Iridium manuals. The link to previous design team information can be found here: Previous Team Information The link to Iridium specific information and AT commands can be found here: Iridium Information Late Research: We discovered in February 2020 that in order to utilize the dial-up connection we establish, the board must have a TCP/IP stack in order to send and receive messages. Upon initially looking into a solution, we found a lightweight implementation for embedded systems called lwIP that seems promising at the expense of system resources and programming effort. An alternate option to implementing our own stack would be to bypass it altogether by switching the data plan from a dial-up connection to a RUDICS (Router-based unrestricted digital internetworking connectivity solution) connection. According to the NAL website, RUDICS is an enhanced gateway that connects a call to a pre-defined IP address that allows for an end-to-end IP connection between the host application and ISU. The three main benefits of RUDICS over dial-up would be: The elimination of analog modem training time.</li> An increased call connection quality.</li>  Protocol independence: This eliminates the need for a TCP/IP stack implementation! </li> </ol> This third benefit is the main reason switching to RUDICS over dial-up is the best option for NASA ARC (Ames Research Center) moving forward. This reduces the stress on the board by eliminating the need for an internet stack and provides all the other benefits listed and more. As of the design EXPO, NASA has not been able to switch their data plan to RUDICS due to an expensive upfront fee required, but we have advised them of our research and recommendation to switch in this area and they are in the process of switching for either future design teams or their own internal software development on this project.

Carrier Module:
<ul> <li>The carrier module subteam is re-designing a carrier module that was created by a previous senior design team so much of the project learning for this section includes viewing and studying previously created schematics created in EAGLE.</li> <li>Experience with this software is limited among team members so the early struggle on this project includes learning the software and how to make it usable for future re-design.</li> </ul>

Battery Containment Unit:
As outlined in the design specifications, the battery insulation box must withstand the mechanical and thermal shock of an explosion resulting from thermal runaway of Canon BP-955 batteries. Since thermal runaway produces hydrogen gas at a temperature exceeding 500oC and flames we must design a ventilation system that will vent the hot gasses while containing the flames. A potential material to fulfill these requirements are open-cell metal foams. Metal foams are metals with built-in pores, where 25% of the volume is occupied by air. Several of the chemical and physical properties are left unaffected. Namely Thermal/electrical conductivity, melting point, corrosion resistance, and reactivity. However, The addition of porosity creates a larger surface area. The major effect we would see is the increase in heat absorbed during contact. The large surface area makes metal sponges great heat sinks where energy is transferred energy away from the batteries in the event of thermal runaway. The absorption of energy is effective enough to make metal foams an effective material to quench flames. Since the box is designed to contain four batteries and prevent thermal runaway we must thermally isolate each battery. To do this and maintain within the weight and size constraints an aerogel or aerogel like material is needed. Aerogels are ultralight porous ceramic materials that are typically 98% air. The high distribution of the nano-sized pores inside the Aerogel creates excellent thermal and electrical insulation. However, the silica skeleton is incredibly brittle and the quantity of the pores limit airflow. Aerogel insulation blankets are produced by submerging a polymer, typically polyethylene terephthalate (PET), felt with silica gel before creating the aerogel. The polymer-stabilized aerogel insulation blankets are flexible with an operating temperature of 350oC and a density of 0.15g/cm3. High-temperature insulation blankets are produced by stabilizing the aerogel with fiberglass instead of PET. Pyrogel XT-e, is an example of a high-temperature aerogel insulation blanket. It has a density of 0.2g/cm3 and an operating temperature of 650oC. Initial learning consisted of reaching out to Mechanical and Material Science Engineering professors, listing possible materials, conducting a literature review, then narrowing down the selection so a design can be constructed.

=Final Design= <ul> <li> Software: </li> <ul> <li>General Details: <ul> <li>Power up carrier board - Consists of code running on the MCU. It will set pins on the carrier module to provide power to the Iridium-9523. <li>Serial communication over RS-232 - Can utilize an external raspberry pi to manually read/write from the Iridium modem to easily test AT commands and develop our code. <li>SBD transmission - SBD packets can be sent via AT commands over the Iridium network and arrive in an email inbox. <li>Establish dial-up connection - The Iridium Gateway number allows for data connections and acts as an Internet Service Provider (ISP). <li>The final codebase will transition control from our Raspberry Pi setup to the MCU on the carrier module instead. <li>Final code library - The library will contain classes and methods for sending and receiving SBD packets as well as establish and maintain a dial-up connection automatically. <li>TCP/IP stack - We will develop and implement a lightweight TCP/IP stack to utilize the network connection and stream data to a ground server. <li>Server - The server will act as a listener with a provided port and IP address to record all incoming TCP packets sent from our Iridium modem. </ul> <li>UML Class Diagram: <li>UML Activity Diagram: </ul> <li> Carrier Module: </li> <ul> <li>General Details: <ul> <li>Component Testboard: <ul> <li>The design is finalized, ordered, and assembled. <li>It has been shipped for testing and we are waiting to see how the components performed under near space conditions to ensure a final re-design uses components compatible with these conditions. </ul> <li>The new flight ready carrier module with be a 4-layer board (2 signal planes, power, and GND). <li>Iridium modem will need completely uninterrupted ground plane beneath it. </ul> <li>The re-designed carrier board will follow the block diagram seen below: <li>The schematic for the new boost converter can be seen below: <li>The re-design will conform to the 104 form factor and appear like the diagram below: <li>The test board design and final build can be seen in the images below: </ul>

Battery Containment Unit:
The Battery box design must conform to a PCB-104 form factor, 3.4in x 3.15in. Additionally, the box must weight less than 500g, ideally 300g. Due to the tight size constraints, the batteries must be packed in the following configuration:

The box will be made out of 3/16in thick 1100 1H4 aluminum with an integrated ventilation system on the top surface. Aluminum is used as the basis for the box due to its stable phase at cryogenic/pyrogenic temperatures and weight. The vent will be made by welding open-celled aluminum foam to the center of the metal sheet. The vent will have an internal lining of pyrogel XT-e. A silica aerogel blanket was originally intended but was later determined not viable due to a maximum operating temperature of 300 Celsius, half of the temperature released during thermal runaway. Instead, Pyrogel XT-E is being considered due to its operating temperature of 650 Celcius. Proof of concept is still required and two experiments have been designed to test the material's flame quenching, thermal resistance, and airflow properties. However, the literature available on these materials supports the current design.

The vent prototype is shown below:

</ul>

=Validation=

Software:
<ul> Successfully Completed </ul>

<li>Interfaced with the Iridium-9523 modem. <li>Validated Iridium network signals and achieved usable signal level and data integrity. <li>Transmitted short burst data messages and received them through an associated email account. </ul>

Future Validation: The software team plans to fly with VAST (Vandals Atmospheric Science Team) to test and validate that the communication from the Iridium-9523 is functional and performs the intended actions.

Carrier Module:
<ul> Successfully Completed </ul>

<li>Re-designed components: <li>New Boost Circuit: <li>Designed with the Texas Instruments Power Designer <li>Validated that it performs as expected with LTSpice and allows for worst case (~1A) current draw <ul> <li>New PCB Layout: <li>Form factor design with 4-layer technology built overseas. <li>Upgraded SAMD51 chip: </ul> <li>Microchip provides 15 page checklist to help with the building and test against. <li>Created the power supply requirements.

Future Validation: <li>After assembling the PCB, we will test the components onsite. <li>Testing will work with the Software subteam to ensure that code working on the initial carrier module will work on the re-designed board. </ul>

Battery Containment Unit:
<ul> Incomplete due to COVID-19 </ul> A series of experiments were designed to fail li-ion batteries, determine the approximate energy released during thermal runaway, and show how thermal runaway is transferred from cell-to-cell/module-to-module. A full list of the experiments is shown below. <ul> </ul> Initial testing was conducted with a two-cell Zippy brand Li-ion batteries. To fail the battery we connected two external leads and recorded the temperature of the battery with a thermal camera. Hydrogen gas production and temperature of 135oF were observed but extreme failure was not observed due to safety measures built into the batteries. Different Li-ion batteries with fewer built-in safety measures are required in order to observe extreme failure. As a result, we ordered several single 18650 Li-ion cells from Samsung. Experiment one has four procedures where thermal runaway will occur; short circuit, overcharge, external heat, and mechanical failure. The objective of this experiment is to determine the most reliable way to fail the li-ion cell for future experiments. Experiment two would look at how thermal runaway transfers from cell to cell and module to module. One cell would e forcibly failed and data would be collected with the thermal camera. This experiment will allow us to better understand how thermal runaway transfers between the modules and will determine the critical transfer temperature. Additionally, different lining materials will be tested for their effectiveness to halt the transfer of thermal runaway between the modules. The flames produced during thermal runaway are produced by hydrogen gas burning, not oxygen/nitrogen. As a result, the flames burn hotter and may not be as effectively quenched by the metal foam as oxygen-based flames are. Experiment number three would force a li-ion cell into a thermal runaway with the metal foam placed within the produced flames. Images collected with the thermal camera would be used to measure the flame propagation through the foam. From these images, the critical flame quenching distance can be measured. Should the foams effectively quench the flames they can be utilized in the final design. To determine the amount of energy released by a single Li-ion cell during thermal runway we would have built and calibrated a "coffee cup" calorimeter. A sealed powder coated junction box would hold the cell and be submerged inside another box with room temperature water. The cell would be forced into thermal runway and the change in water temperature would be used to determine the energy released by the cell. To calibrate the calorimeter, hot water would be poured into the junction box to determine the energy absorbed by the steel. The airflow test would determine how effectively the materials would ventilate pressurized gasses. The junction box would be sealed with a burst disk calibrated to a specified pressure. The materials of interest would sit next to the burst disk. Once the disk popped the pressurized air would escape through the material of interest. The time it would take for the air inside the box to return to atmospheric pressure would be recorded. Materials with shorted depressurization time would be better at ventilating the gasses built up during thermal runaway. The ventilation prototype consisting of the metal foam and pyrogel/silica fabric will be validated with this experiment. </ul> </ul>
 * 1) Forced Failure of 18650 Li-ion cells: </i>Development for Reproducible Failure Procedures</i>
 * 2) Transfer Mechanism of Thermal Runaway
 * 3) Flame Quenching Properties of Pyrogel and Al metal foam
 * 4) Determination of Energy Released during Thermal Runaway of Li-ion cells via Calorimetry
 * 5) Flowthrough Properties for Battery-Box Ventilation Materials

Future Validation: The experimental results from experiments two, three, and five would validate the selection of the materials for the final product. The final firebox prototype will be sent to Johnson Space Center for destructive testing to test it's resistance to mechanical failure.

=Team Members=

=Additional Documentation=

Project Schedule

Meeting Minutes