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Mission Statement

The mission of the Command and Data Handling System (C&DH) is to receive and execute commands; collect, store, and transmit house-keeping data; and support SERB approved payloads.

The primary mission of the flight computer is to control the satellite and manage telemetry and experiment data for a minimum of two years.

Mission Requirements

The mission requirements are first listed by originating sources and then compiled into a single list of final requirements

Requirements due to MidSTAR-1 Mission Requirements

  1. Support the Linux Operating System
  2. PC based using an open hardware architecture

Requirements due to CFTP

  1. 10 MBytes of storage
  2. Support RS-422 asynchronous serial connections

Requirements due to ICSAT

  1. 50 MBytes of data files
  2. Support serial connections up to 1 Mbps
  3. Support RS-422 synchronous serial connections
  4. Support RS-232 asynchronous serial connections

Requirements due to Main Communications

  1. Support serial connections up to 100 Kbps
  2. Support RS-422 asynchronous serial connections
  3. Support RS-232 asynchronous serial connections

Requirements due to Electrical Power System

  1. Support digital output
  2. Support analog input
  3. Support temperature sensors
  4. Support voltage sensors
  5. Support current sensors

Requirements due to Structures

  1. Support temperature sensors

Collected Requirements

  1. Support the Linux Operating System
  2. PC based using an open hardware architecture
  3. Support RS-422 asynchronous serial connections
  4. Support RS-422 synchronous serial connections
  5. Support RS-232 asynchronous serial connections
  6. Support serial connections up to 1 Mbps
  7. Support digital output
  8. Support analog input
  9. Support temperature sensors
  10. Support voltage sensors
  11. Support current sensors

Specifications

Hardware Specifications

Based on the requirements in the previous section the following hardware was selected. The individual components were selected by power usage if there were multiple components that fulfilled the requirements.

Origin of Hardware Specifications

The decision to use the PowerPC based MIP405 over an x86 based board was based solely on the low power consumption of the board combined with the feature set. The choice was limited to x86, PowerPC, and ARM processor architectures because of support for the linux kernel. The MIP405 integrates ethernet, serial ports, and Disk-on-Chip interface on a single board while providing 128MB of ECC memory and a powerful processor for under 2 watts. The closest x86 based system with comparable features found consumed 5 watts of power.

The M-Systems Disk-on-Chip was chosen because it was the defacto standard flash memory harddisk replacement. The decision to use flash memory over a traditional harddisk was to increase reliability and reduce power. The 384 MByte version was chosen to provide for the required storage with room for growth and the operating system.

The Commtech Fastcom ESCC-104-ET was chosen as the synchronous serial interface board based on advice from our technical advisor Dr. Ron Parise from Computer Sciences Corporation. Dr. Parise has had previous experience with the board.

The Diamond Systems Emerald-MM-8 was chosen for the asynchronous serial board based on its innate flexibility with any of the 8 ports capable of being configured as RS-232, RS-422, RS-485.

RMV's IO485 data acquisition and control board was chosen for the distributed telemetry system because of built in support for daisy chaining and handling a large number of boards. The integrated expandability is fundamental to addressing future telemetry issues later in the satellite line.

Software Specifications

From the requirements the C&DH will run Linux. In order for the long term support of the operating system (most likely a 2.4 series) Linux kernel will be selected. There remains the possibility that a 2.6 series kernel could be chosen, but it will remain doubtful until the new kernel series has stabilized and shows a significant benefit of switching.

To create the open software architecture the IP protocol stack was chosen to provide inter process, intra-satellite, and satellite-ground communications. This allows programs to be created at different facilities on different hardware and integrated with minimum difficulties.

 

  1. Design
    1. Hardware Design Summary
      1. Block Diagram
      2. Power Usage
      3. Layout Diagram
      4. Cabling Diagram
      5. Wiring Diagram
      6. Serial Port Assignments
      7. Telemetry Assignments
      8. Pin-Outs
      9. Components
        1. Single Board Computer
        2. Asynchronous Serial Card
        3. Synchronous Serial Card
        4. Telemetry and Control Card
        5. Cables
        6. Inventory
      10. Software Design Summary
        1. Detailed Class Diagram
        2. Control Packet Layouts
        3. Operating System
    2. Mass Properties Table