I. Literature Review

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НазваниеI. Literature Review
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The organization and scheduling of this project is to fit within a two semester time frame. All work for the project will be shared equally, dependent upon each team members' strengths. The planned completion of this project is early April 2011 with allowances for extensions. The bulk of the scheduling is comprised of design and manufacturing. Procurement of materials should be minimal due to the simplicity in the design approach. The work breakdown structure of the project currently consists of ten tasks:

  1. Problem Definition – Define the task to be accomplished including constraints such as final product volume and mass, and project scope.

  2. Budget/Cost Analysis – Determine an estimate for the amount of capital necessary to develop and test the prototype.

  3. Finalization of Approach – Based on the background research and project scope, decide on the method of deorbiting, be it an inflatable or rigid structure.

  4. Software Development – Write software and code that will allow the mechanism to perform its intended function.

  5. Materials Sourcing – Obtain all of the materials necessary to construct and demonstrate the prototype deorbiting system.

  6. BUS Interfacing – Integrate the prototype hardware and software with the command and control computer of the CubeSat.

  7. Structural Design/Packaging – Finalize and construct the housing for the deorbiting device.

  8. Integration – Integrate the hardware, software, and controllers into the CubeSat payload.

  9. Testing

  10. Report and Summary

Care has been taken to allow for leeway in the scheduling, so that any difficulties encountered during a particular phase in the work breakdown structure will not cause the project to exceed the firm deadline of the end of the Spring 2011 semester. A Gantt chart has been developed of the project timeline, and is attached in the Secondary Material section of the Appendix.

Final Deployment Testing

After all of the materials and peripherals were gathered and integrated into a final product, deployment testing of the finished prototype was conducted. Initially it had been decided to use LabVIEW to communicate with the valve and initiate inflation. However, this project was identified as an ideal candidate to demonstrate the ability to communicate with the payload remotely. This added an extra depth of realism to the proof of concept demonstration because when actually deployed on a CubeSat inflatable deployment would have to be initiated either from the ground or from the main payload bus, and this initiation would occur remotely. The remote valve and controller are discussed in detail in a separate section. LabVIEW was maintained as a backup, in case the remote actuators malfunctioned. Remote activation was not originally prescribed in the project objectives, and is considered a bonus added on to the project.

Final testing was conducted in the Instrumentation Lab of the Physics Building. This location was chosen because of the proximity to the LabVIEW software. Several of the workstations within the Instrumentation Lab have the software loaded on them as well as the digital input/output interfaces. Supply air was available in the Physics Building as well, similar to that in the AE student lab. The Instrumentation Lab also housed the vacuum chamber, which was still in a condition of being retrofitted, discussed in a separate section.

Testing began by preparing the inflatable, folding it according to the prescribed corner technique and stowing it in the container. The bottom of the inflatable was secured to the container base with tape. Once the lid was installed and securely fastened the air line was installed in the supply valve from the Instrumentation Lab and inserted into the filling valve of the inflatable. This was then secured with tape to avoid leakage and ensure a proper seal. A 12-V power source was required for the valve, and a computer USB port was required to operate the microcontroller. Before installing the air line to the valve it was tested to verify proper opening and that air was flowing through it on cue. The inflation line was then connected to the outlet port of the valve.

Upon activation, the solenoid valve opened and allowed air to begin to flow into the inflatable. The lid initially resisted this inflation, as per its requirements, but gave way once a suitable pressure had been achieved. Failure of the lid occurred in two primary locations, and one secondary location as shown in Figure 20.

Primary failure

Secondary failure

Figure : Primary and secondary failure locations of container lid under inflation

Primary failure here alludes to the first failures that occur due to the inflatable pressure acting against the lid. Secondary failure occurred after inflation was well underway, and was caused by the inflatable displacing the torn lid. After tearing, the container lid did not inhibit inflation further, as it was easily displaced by the enlarged inflatable. Inflation continued until the balloon was fully inflatable and all surfaces stretched taut. The valve was then signaled to close with the remote and the test was terminated.

This test was declared successful because the objectives of the proof of concept were demonstrated. These objectives included packaging of the system within the container restraints, validation of the folding technique, deployment of a rupturable physical lid, and complete inflation. Additionally this test was able to demonstrate remote valve activation, which can subsequently be utilized for other projects and systems.

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