search

neuoy / KSPTrajectories

A Kerbal Space Program mod to display trajectory predictions, accounting for atmospheric drag, lift, etc.
GNU General Public License v3.0
144 stars 47 forks source link

Imprecise prediction in high altitudes without cache #103

Open fat-lobyte opened 7 years ago

fat-lobyte commented 7 years ago

At high altitudes, prediction seems to be off.

While above 67 km, the calculated impact marker drifts westwards, implying that the calculated force is stronger than the actual experienced force. After going below 67 km, the prediction stabilizes. The cutoff is relatively sharp (boundary of about 66500m-67000m).

This is especially bad for very flat trajectories, since a lot of time is spent at the outer edge of the atmosphere with a high velocity, amplifying even minor errors. In the quicksave below, the error from the initial prediction to the final crash point was about 35km.

Quicksave for testing: kerbin-flat-entry.sfs.txt

Telemetry data file: kerbin-flat.csv.txt

fat-lobyte commented 7 years ago

Forces seem to be off by like 20% in high altitude:

kerbin-flat-forces_high-alt

kerbin-flat-forces-ratio_high-alt

Haven't found the reason yet

fat-lobyte commented 7 years ago

Doing silly things like changing the simulattime interval improves the situation.

I changed dt from 0.1 to 0.05, and an improvement in Error from 40km West to 19km East. So while it's not that much better, it sure does something.

jcart commented 3 years ago

Was this addressed?