Structures (STR)

Subsystem Top Level Requirements
-- Manage the mass, volume, and center of gravity (CG) of the spacecraft
-- Build a structure to support all spacecraft hardware
-- Build an antenna deployment system for the Communications and Science antennas

Subsystem Functional Requirements
The system shall not exceed a mass of 300 grams and a volume of 150 cm^3
-- The system shall adhere to all requirements set forth by the CubeSat Design (CDS) Document
-- The system shall maintain a thermal environment within the operating ranges of all components
-- The center of mass of the CubeSat shall be within two centimeters of the geometric center
-- The external structure shall be constructed of Aluminum 7075-T73 or 6061-T6

The CubeSat structure includes all necessary mounts and support structure, such that the other subsystems are safely housed. The external structure provides the only protection from the space environment, and provides critical radiation shielding to sensitive components. The solar cells are mounted upon a PCB substrate and are attached to each side of the structure.

An access port is located on one side of the structure as seen in the image to the right. This port will allow for the satellite batteries to be charged after assembly and/or integration to the P-POD. The port will also contain access to the In-Circuit Serial Programming (ICSP) lines for the PIC microcontroller allowing code to be modified even after assembly if necessary.

Antenna Deployment
The Structures subsystem is also responsible for designing the system that stows and deploys the antennas. Per the CDS, the antennas must be stowed such that they cannot accidentally shift or deploy during launch. The antennas will be lashed to the satellite prior to launch with nylon fishing line. Nichrome burn wire is used to melt through the nylon fishing line when the command to deploy is given. Should the nichrome fail to burn, the nylon fishing line will eventually outgas sufficiently causing it to break, therefore deploying the antenna. This system provides a level of redundancy for the critical antenna deployment should the primary nichrome wire system fail.

Because the CubeSat is very small, and therefore does not have excess weight or power available for an active thermal control system, an accurate thermal model was designed. The model separates the 1000 cm^3 cube into 83 different components, providing fine details in the temperature gradients throughout the structure. The model also takes into account solar heat flux, Earth Infrared Radiation, albedo, and the heat generation of high power components such as the PCOMM transceiver. Based on this model, the internal and external components may need to be painted or moved, to maintain allowable temperatures throughout.



Links & Downloads

CubeSat Design Specifications (CDS) Document

CubeSat Specification Drawing

CalPoly Test Pod User Guide

Technical Drawings (contains PDF and Solid Works Drawings)