Added an optional `atmosphereAlt` paramater in bodies's descrptions.
The flyby calculation now prevents a periapsis altitude below
the atmosphere limit.
- `ChunkedEvolver` has been moved to a namespace `Evolution` to avoid
useless member functions.
- The DE algorithm now uses a dynamic CR coefficient, which increases
exponentially from `minCrossProba` to `maxCrossProba` at a rate
defined by `crossProbaIncr`.
- The 3D physics functions have been moved into a `Physics3D` namespace
- The `TrajectoryCalculator` has been completely recoded and commented
- The `TrajectoryOptimizer` has been recoded accordingly
- Various optimizations focusing on reducing the number of costly
function calls
- Reimplemented 2D orbital mechanics functions in physics-2d.ts
and encaspulated inside a `Physics2D` namespace.
- Deleted physics.ts and moved the required functions into physics-3d.ts
Further cleaning and reimplemntation will be done on the physics-3d.ts
content.
- Forced consistency on error handling : every raised error throws
an `Error` object.
- Commented sections relative to 2D physics and sequence generation.
