Celestia
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Orbital precession
Would be good to be able to specify orbital precession in ssc files. It would probably use a PrecessingOrbit
block, similar to PrecessingRotation
.
From @pedro-fixingstuff on Discord:
how I imagine it would work
PrecessingOrbit { Epoch SemiMajorAxis Period Eccentricity Inclination AscendingNode ArgOfPericenter MeanAnomaly NodePeriod PericenterPeriod }
From TTarrants on Discord, posting here because it's related
Remember when we talked about the possibility of Celestia displaying precessing orbits?
PrecessingOrbit { Epoch _float_ Period _float_ PrecessionAxisInclination _float_ PrecessionAxisNode _float_ MeanAnomaly _float_ }
^ Or something to that effect. It might also be interesting to have a block for decaying orbits.
DecayingOrbit { Epoch _float_ # Epoch of semi-major axis. DecayRate _float_ # dP/dt in seconds per year at epoch. DecayRateChange _float_ # d^2P/dt^2 in seconds per year. }
(of course negative decay rate values could produce expanding orbits) The WASP-12b paper got me thinking about this because eventually because the orbital period is evolving, there is going to be a mismatch between literature transit times and transit times as they are observed in Celestia. Granted, I haven't done the base amount of effort to determine how big an issue this is going to be over our lifetimes. Probably not much I suspect.
Another concern would be a need to modify the orbital period in some way. Perhaps that could be done automatically. The period at some time t _0 will be a certain ratio of what it was at t _1 regardless of what the user provides as the stated orbital period in
EllipticalOrbit
.... or maybe DecayingPeriod might be what we should define since that is usually the observed parameter.
From pedro again:
From the suggestions thrown here and on other channels about modelling orbital precession and evolution, I came up with the idea to add a one-size-fits-all
DynamicOrbit
block, which I think could look like this:DynamicOrbit { Epoch Period SemiMajorAxis Eccentricity Inclination AscendingNode ArgOfPericenter MeanAnomaly NodePeriod ApsisPeriod PeriodChange or SemiAxisChange LowerClamp UpperClamp }
Most of the names should be self-explanatory, but I imagine the
LowerClamp
andUpperClamp
as ways to limit the changes in semi-major axis/period to a certain range of values or a period of time.