Proper Way to Set Initial Orbit Time for Simulation?

[Jmiceli17]

Hi! I have a a few questions about simulation time in Basilisk.

Firstly, what is the assumed calendar start time of a simulation?

Second, when setting the initial conditions for an orbit, what is the proper way to set the initial time or "orbit epoch"? I have seen references to epochMsg when setting gravity bodies (like here ) but is that something that should be tied to the spacecraft objects as well? If so, how is that done?

In my current set up, adjusting timeInitString argument of createSpiceInterface does change the "Mission Time" that Vizard shows (so I at least have that connected properly), but that is not impacting the initial orbit conditions.

Thank you in advance for the help!

[schaubh]

The default simulation year, month, day, etc. are defined in

basilisk/architecture/utilities/ArchitectureUtilities/Header Files/simDefinitions.h

If you look at modules that depend on date and time (some magnetic field, atmospheric drag, etc.), you will see the use of EPOCH_YEAR, EPOCH_MONTH, ... that are defined in that class.

[schaubh]

Regarding setting the spice simulation time, that only impacts that module.

[schaubh]

To see how to make Vizard know what the mission time is, I recommend using a stand-alone epoch message as is done in the scenario script examples/scenarioHelioTransSpice.py. You see the line

viz.epochInMsg.subscribeTo(gravFactory.epochMsg)

which tells vizInterface what epoch date and time to share with Vizard.

[Jmiceli17]

Thank you! I think I was confused about what time the initial true anomaly corresponded to. My understanding now is that the timeInitString argument of createSpiceInterface essentially defines when true anomaly is 0.