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Satellite toolkit for Elixir with SGP4 propagation, coordinate transforms, GNSS positioning, orbit determination, conjunction assessment, pass prediction, and a Rust NIF backend.

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sidereon lib sidereon lambert.ex
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lib/sidereon/lambert.ex 

defmodule Sidereon.Lambert do

  @moduledoc """

  Lambert problem solver (Battin's method).



  Given two position vectors and time of flight, find the transfer orbit

  velocities. Algorithm 61, Vallado 2022, pp. 505-510.

  """



  @type vec3 :: {number(), number(), number()}



  @doc """

  Solve Lambert's problem using Battin's method.



  ## Parameters



    * `r1`, `r2` - initial and final ECI position vectors in km

    * `v1` - initial velocity in km/s (needed for 180° transfers)

    * `dm` - direction of motion: `0` = short way, `1` = long way

    * `de` - direction of energy: `0` = low, `1` = high

    * `nrev` - number of revolutions (0, 1, 2, ...)

    * `dtsec` - time of flight in seconds



  ## Returns



  `{v1t, v2t}` - transfer velocity vectors at r1 and r2 in km/s.

  """

  @spec solve(vec3(), vec3(), vec3(), integer(), integer(), non_neg_integer(), number()) ::

          {{float(), float(), float()}, {float(), float(), float()}}

  defdelegate solve(r1, r2, v1, dm, de, nrev, dtsec), to: Sidereon.NIF, as: :lambert_battin

end