lamberthub.universal_solvers.gooding#

A module hosting all algorithms devised by Gooding

Module Contents#

Functions#

gooding1990(mu, r1, r2, tof[, M, prograde, low_path, ...])

Lambert's problem solver using the method proposed by R. H. Gooding in 1990.

tlamb(m, q, qsqfm1, x, n)

Auxiliary routine for computing the non-dimensional time of flight as

xlamb(m, q, qsqfm1, tin, maxiter, atol, rtol)

Auxiliary routine for finding the independent variable as function of the

vlamb(mu, r1_norm, r2_norm, dtheta, tof, low_path, ...)

Auxiliary routine for computing the velocity vector components, both
lamberthub.universal_solvers.gooding.gooding1990(mu, r1, r2, tof, M=0, prograde=True, low_path=True, maxiter=35, atol=1e-05, rtol=1e-07, full_output=False)#

Lambert’s problem solver using the method proposed by R. H. Gooding in 1990.

Parameters:

  • mu (float) – Gravitational parameter, equivalent to \(GM\) of attractor body.

  • r1 (numpy.array) – Initial position vector.

  • r2 (numpy.array) – Final position vector.

  • M (int) – Number of revolutions. Must be equal or greater than 0 value.

  • prograde (bool) – If True, specifies prograde motion. Otherwise, retrograde motion is imposed.

  • low_path (bool) – If two solutions are available, it selects between high or low path.

  • maxiter (int) – Maximum number of iterations.

  • atol (float) – Absolute tolerance.

  • rtol (float) – Relative tolerance.

  • full_output (bool) – If True, the number of iterations and time per iteration are also returned.

Returns:

  • v1 (numpy.array) – Initial velocity vector.

  • v2 (numpy.array) – Final velocity vector.

  • numiter (int) – Number of iterations.

  • tpi (float) – Time per iteration in seconds.

Notes

This module holds the Lambert’s problem solver devised by R. H. Gooding in his technical report [1] originally published in 1988. However, the implementation corresponds to the one proposed by the author a couple of years later in his article [2] from 1990. Some improvements to the originally algorithm were also made by Klumpp in his performance comparison [3] between Lamberts problem solvers. Those have been added to this code to prevent failures for particular inputs. The result is a fully working algorithm for both single and multi-revolution orbits.

The code has been kept as close as possible to the original FORTRAN-77 one. However, some statements (like “goto line” ones) have been deprecated as they introduce “spaghetti code”. Since the original implementation imposed a relative tolerance together with the number of iterations, these parameters have been modified so the user can freely choose their values.

References

lamberthub.universal_solvers.gooding.tlamb(m, q, qsqfm1, x, n)#

Auxiliary routine for computing the non-dimensional time of flight as function of the number of revolutions, the transfer parameter and the independent variable.

Parameters:

  • m (float) – Number of revolutions.

  • q (float) – The transfer angle parameter.

  • qsqfm1 – Equivalent to \(1-q^2\).

  • x (float) – The independent variable.

  • n (float) – Number of output parameters to be returned.

Returns:

  • t (float) – Non-dimensional time evaluated at \(x\).

  • dt (float) – First derivative of the non-dimensional time evaluated at \(x\).

  • d2t (float) – Second derivative of the non-dimensional time evaluated at \(x\).

  • d3t (float) – Third derivative of the non-dimensional time evaluated at \(x\).

lamberthub.universal_solvers.gooding.xlamb(m, q, qsqfm1, tin, maxiter, atol, rtol)#

Auxiliary routine for finding the independent variable as function of the number of revolutions, the transfer angle parameter and the non-dimensional time of flight.

Parameters:

  • m (float) – Number of revolutions.

  • q (float) – The transfer angle parameter.

  • qsqfm1 (float) – Equivalent to \(1-q^2\).

  • tin (float) – The actual non-dimensional time of flight.

  • maxiter (int) – Maximum number of iterations.

  • atol (float) – Desired absolute tolerance.

  • rtol (float) – Desired relative tolerance.

Returns:

  • n_sol (int) – Number of solutions.

  • x (float) – First solution.

  • xpl (float) – Second solution, if available.

  • numiter (int) – Number of iterations.

lamberthub.universal_solvers.gooding.vlamb(mu, r1_norm, r2_norm, dtheta, tof, low_path, maxiter, atol, rtol)#

Auxiliary routine for computing the velocity vector components, both radian and tangential ones.

Parameters:

  • mu (float) – Gravitational parameter, equivalent to \(GM\) of attractor body.

  • r1_norm (float) – Norm of the initial position vector.

  • r2_norm (float) – Norm of the final position vector.

  • dtheta (float) – Transfer angle between initial and final vectors.

  • tof (float) – Time of flight between initial and final position vectors.

  • low_path (bool) – If two solutions are available, it selects between high or low path.

  • maxiter (int) – Maximum number of iterations.

  • atol (float) – Absolute tolerance \(abs(x_{i+1} - x_{i})\)

  • rtol (float) – Relative tolerance \(abs(\frac{x_{i+1}}{x_{i}} - 1)\)

Returns:

  • n_sol (int) – Number of solutions

  • vri (float) – Radial velocity component at the initial position vector.

  • vti (float) – Tangential velocity component at the initial position vector.

  • vrf (float) – Radial velocity component at the final position vector.

  • vtf (float) – Tangential velocity component at the final position vector.

  • numiter (int) – Number of iterations required to compute solution.