Fast node-gyp reader for JPL planetary ephemeris

Currently only 440 version is supported, tested with linux_p1550p2650.440 and works fine. Last time I downloaded the eph file it was available under this link: https://ssd.jpl.nasa.gov/ftp/eph/planets/Linux/de440/linux_p1550p2650.440

How to use

First, be sure to call loadEph440 globally with path to linux_p1550p2650.440 before doing anything else with the library

Planetary mapping is as follows:

1 = mercury barycenter
2 = venus barycenter
3 = earth
4 = mars barycenter
5 = jupiter barycenter
6 = saturn barycenter
7 = uranus barycenter
8 = neptune barycenter
9 = pluto barycenter
10 = moon
11 = sun
12 = solar-system barycenter
13 = earth barycenter

After that, following functions are available:

getBulk

getBulk(input: GetBulkInput[], output: number[]): void

Gets positions of elements in relation to other elements. The result is stored in the output parameter as series of 3d vectors, interleaved position and velocity, which are stored as 3 numbers, so the output array must have size equal to input.length * 6. For example in case of input having 2 inputs A and B, the output format will be:

[
  A.position.x, A.position.y, A.position.z,
  A.velocity.x, A.velocity.y, A.velocity.z,
  B.position.x, B.position.y, B.position.z,
  B.velocity.x, B.velocity.y, B.velocity.z
]

The format is clear, but it's pretty strange, it's all because of performance, as the main reason of this library existence is performance. The position returned is in AU and velocity in AU/Day, to have the most raw data.

getGravityFlux

getGravityFlux(where: ephvec3, whenTimestamp: number, output: ephvec3): void

• output must be an array of 3 numbers and result stored in it will be in format:

[
  acceleration.x, acceleration.y, acceleration.z
]

• where is expected to be in meters, acceleration returned is in meters/seconds^2,
• whenTimestamp is a unix timestamp with fractions support

integrateGravity

integrateGravity(startPosition: ephvec3, startVelocity: ephvec3, startTime: number, endTime: number, timeStep: number, outputPosition: ephvec3, outputVelocity: ephvec3): void

• outputPosition must be an array of 3 numbers and result stored in it will be in format:

[
  position.x, position.y, position.z
]

outputVelocity must be an array of 3 numbers and result stored in it will be in format:

[
  velocity.x, velocity.y, velocity.z
]

• startPosition and startVelocity are expected to be in meters
• startTime and endTime are unix timestamps with fractions support
• timeStep is the time resolution to use in seconds, higher means faster but lower precision
• outputPosition is saved as meters
• outputVelocity is saved meters/second

generateTrajectoryForecast

generateTrajectoryForecast(startPosition: ephvec3, startVelocity: ephvec3, startTime: number, endTime: number, timeStep: number, outputPositionArray: number[]): void

• outputPositionArray must be an array of numbers with count equal ((endTime-startTime) * 3) / timeStep and result stored in it will be in format:

[
  position.x, position.y, position.z,
  ...
]

• startPosition and startVelocity are expected to be in meters
• startTime and endTime are unix timestamps with fractions support
• timeStep is the time resolution to use in seconds, higher means faster but lower precision
• outputPositionArray is saved as meters