Engineering topics
Clancy, Susan C.
Publications and source records attributed to Clancy, Susan C..
SpaceWire as a Cube-Sat Instrument Interface
SpaceWire is used in the control and data interface for an instrument on a pair of small satellites, one of which was launched in summer 2017. The instrument SpaceWire interface is implemented in a Field Programmable Gate Array as an instantiated core controlled by a LEON3FT CPU, which is also implemented as an instantiated core. The UT699 processor in the flight computer provides the spacecraft side’s SpaceWire interface. A simple message based protocol consisting of four message types was defined, based on existing SpaceWire standards. One was for passing commands to and responses from the instrument in the form of text strings similar to those from a system console where each line of text is passed in a SpaceWire message. Another was for passing spacecraft time to the instrument. The third was for transferring files using a subset of the Remote Memory Access Protocol (RMAP). The fourth was for retrieving science data from the instrument. A set of user application programming interface (API) routines provided an abstracted interface to both the serial console (used during debug) and the SpaceWire device interface. Early instrument development and testing was done with a set of utilities that controlled a Star-Dundee USB-SpaceWire brick providing a user interface similar to a serial console terminal emulator with the addition of file and data transfers. Later in the integration and test process, these utilities were integrated with the COSMOS ground systems software used for spacecraft control, providing a seamless transition from standalone instrument tests to benchtop flat-sat test and full spacecraft level tests.
Using SpaceWire Time Codes for Spacecraft Time Synchronization
This paper describes how SpaceWire Time Codes can be used for synchronizing time within various subsystems of a spacecraft as well as, maintaining a common time reference needed for coordinating operations within a spacecraft. The algorithms to account for inaccuracies in the time distribution method were based on the NASA-4009 Space Telecommunication Radio System (STRS) standard [1], which defined an interface for synchronizing clocks running at different tick rates and tick resolutions.
Cassini remote terminal interface units as part of instrument test bed operations during the tour of Saturn
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