The structure subsystem is responsible for providing a robust body for the satellite which can house all the components and protect them from the harsh conditions of space.
- Materials selection, characterization and treatment
- Structure design
- Internal decking
- Vibration simulations and testing
- Antenna deployment mechanism
- Thermal management and control
1. Material selection, characterization and treatment: Considering the mass budget and the severe conditions in space, Al 6061-T6 and Al 7071-T6 were tested for universal tensile strength, density, machinability and anodizing response. The comparative studies revealed that Al 6061-T6 is better suited. Hence it has been used for the main frame of the satellite. Other materials like ABS, FR4 have also been used as per the specific requirements. All these materials were first tested for their properties before being put into use.
2. Structure Design: Swayam is a Pico satellite having dimensions 100x100x113.5 mm and mass less than 1 kg. The main structure of the satellite consists of four rails and two frames. These Al-6061 rails hold the two milling units in position and its extended part restricts rotational degree of stud. Three PCB’s are arranged in a U deck, with the battery pack in the middle. The design underwent a number of revisions, each incorporating minute improvements from its predecessor. Pro Engineer and AutoCAD are the software used for designing.
3. Internal decking: The arrangement must ensure optimum utilization of internal volume. The basic requirements are:
- To provide maximum area for PCBs
- To minimize concentration of hot spots
- To meet the center of gravity requirements (within 2 centimeters of the geometric center)
- To provide sufficient room for batteries
Considering dissipation of power and thermal restraints, the PCBs have been arranged in a U deck, and the battery pack has been placed in the middle.
4. Vibration simulations and testing: During launch, the satellite undergoes intense vibrations. It must be able to sustain these. For the same, simulations have been run in Ansys software. They have been validated by performing tests on both the qualification and flight models.
5. Antenna Deployment mechanism: Nylon- Nichrome method is used for antenna deployment. A nylon wire passed through a nichrome coil restrains the antenna until deployment. Electric pulses passed through the nichrome coil generate heat which melts the nylon, resulting in deployment.
6. Thermal management and control: Temperature of the satellite has to be maintained within a particular range in order to ensure proper functioning. A passive thermal system has been employed in Swayam. Insulating materials like kapton, white paint, low emittance tape, black tape and optical solar reflector are used. The thermal system has been put to test in the thermo vacuum test (on QM and FM) and hot and cold test (on QM). Simulations have been performed by creating a finite element model of the satellite in Siemens UG NX and solving for various low earth orbits as well as thermo vacuum profile.