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DTUsat-1: Computer
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DTUsat uses a pure star configuration for simplicity. All modules are directly connected to the computer and perform no autonomous functions except comparator-type safeguards. To reduce the wiring complexity and improve performance, some functions are decentralized. All analog interfaces are connected to the computer by a common SPI-bus, while the temperature measurements are done in direct-to-digital Dallas 1-wire temperature sensors. The rest of the functions are controlled from the parallel ports of the CPU, while the radio communication data stream uses an on-chip UART. A spare UART is available for the payload module, but as our camera did not get ready in time for the launch, it is not used in this satellite.

The on-board computer is based on an Atmel AT91M40800 32 bit RISC processor running at 16 MHz with 2 Mb Flash, 1 Mb RAM, and 16 kb ROM for radiation- and fault resistant boot software. The software in the flash can be changed by ground station command. The computer runs the free operating system eCos and a packet handler system to communicate between processes. The ROM contains a boot- and failsafe mode programmed directly in c, capable of safeguarding the satellite in failure modes and receiving software updates via the radio link.

The computer is constructed on a single board that will constitute one layer of the internal of the satellite. The demands to the onboard computer are a little different than they are to an ordinary computer:

  • There will be very little power available in the satellite. This means that power consumption of the computer system has to be very low.
  • It has to be able to cobe with the radiation in space.
  • Replacement of all software must be possible from earth, as it might be corupted in space.

Please have a look in the files section for more information.

The picture below shows a prototype of the OBC: