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Cassini: MEA Cover Commanding
07.14.2009 11:00 AM
Ruwan Somawardhana

By Ruwan Somawardhana
Spacecraft Thermal Engineering

The Cassini spacecraft operates on sequences of commands that control every function the spacecraft executes. These commands are a combination of science and engineering requests designed to follow through on the mission. The engineering commands are in support of the science commands and they ensure the spacecraft operates correctly, stays on orbit, and is protected from any hazard.

One set of commands that I am in charge of as a member of the Thermal/Devices team are the Main Engine Assembly (MEA) cover articulations. The MEA cover is designed to encapsulate the nozzles of the MEA which are susceptible to micrometeroid damage. During critical dust hazard crossings I need to make sure that there are commands to close the cover and before any main engine burn I have to ensure there are commands to open the cover with enough time to verify it opened correctly.

There are times when the cover needs to be closed soon after a burn, so flight rules need to be checked to make sure the cover isn’t closed too soon after a burn because the hot engine nozzles can harm the cover materials. This can involve extensive pre-planning with the various subsystems in order to ensure there is enough timing to execute the necessary articulations in relation to orbit trim maneuvers.

In general, once the time of an articulation is settled upon, I can create the spacecraft commands, ensuring they do not violate any flight rules and then give the commands to a systems engineer so that they can merge my commands with all the other commands to create a complete sequence for the spacecraft to follow.

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