The OBDH subsystem is the responsible of giving communication between every subsystem in HumSAT and also is responsible of control the overall functioning of the satellite.
It is divided in two main components:
- OBC, which corresponds to the hardware and
- OBSW, which corresponds to the HumSAT Software.
This board was designed in collaboration with INTA (Instituto Nacional de Técnica Aeroespacial) and its original design is a heritage from Optos and Xatcobeo cubesats.
In addition to the aforementioned communication functionalities, the OBDH will be in charge of managing the power provided to other parts of the satellite like the TTC or the payloads.
The OBC is the hardware part of the OBDH in charge of giving support for all tasks to be performed by the OBSW. There are several electronic components, here there is a list of the most representative ones:
- FPGA: It is a VirtexII model. This model was already tested and validated for high doses of radiation.
- Memories: There are some memories for data storage (Flash memory), software execution and FPGA programming.
- Clock: There is an oscillator that can withstand high radiation doses and operate with a minimum time drift.
- External interfaces: There are several connectors placed all over the board to help debugging task and facilitate external communication with the entire satellite (EGSE).
The OBSW (OnBoard Software) is in charge of controlling the satellite in all aspects. Among others, the main characteristic of the OBSW is its modularity. This OBSW was designed to withstand a number of different interfaces, a number of varied payloads, etc, without having a major impact in its design.
Since this OBSW was designed for an FPGA, there is an small piece of code, named Bootloader, in charge of managing which version of the OBSW will be loaded into the execution memory. This Bootloader gives the flexibility to load the final OBSW or certain pieces of code focused in testing activities and also allows to update the software when the satellite is in orbit.