2021-10-08, 05:18 PM
Hi Razvan,
I'll defer to BMD on the question of ephemeris calculations in HORIZONS since I only use ST4v to calculate the ephemeris. The trick with ST4v is to input the appropriate epoch for the osculating elements. If the epoch is too far off the ephemeris positions will be incorrect, as you're aware. Back in July 2021 (earlier in this thread) BMD & I tried to input elements from HORIZONS at fractional days, like Jul 9.75 with limited success. This would be the ideal way to deal with close approaches using ST4, enter osculating elements at for example, October 9.0, 9.25, 9.50 & 9.75, then have ST4 choose the closest epoch for the calculations. Currently ST4 doesn't seem to keep epochs that are too close together in time as this would require. I imagine having the program try to keep this all straight would really make things complicated, as if orbital mechanics aren't already complicated.
All this stuff is pretty niche, so I'm sure that Greg has more pressing & useful things to work on for the ST4 community. Perhaps with more users showing interest in this activity, it'll move up the scale in importance.
Phil S.
I'll defer to BMD on the question of ephemeris calculations in HORIZONS since I only use ST4v to calculate the ephemeris. The trick with ST4v is to input the appropriate epoch for the osculating elements. If the epoch is too far off the ephemeris positions will be incorrect, as you're aware. Back in July 2021 (earlier in this thread) BMD & I tried to input elements from HORIZONS at fractional days, like Jul 9.75 with limited success. This would be the ideal way to deal with close approaches using ST4, enter osculating elements at for example, October 9.0, 9.25, 9.50 & 9.75, then have ST4 choose the closest epoch for the calculations. Currently ST4 doesn't seem to keep epochs that are too close together in time as this would require. I imagine having the program try to keep this all straight would really make things complicated, as if orbital mechanics aren't already complicated.
All this stuff is pretty niche, so I'm sure that Greg has more pressing & useful things to work on for the ST4 community. Perhaps with more users showing interest in this activity, it'll move up the scale in importance.
Phil S.