Patched conic approximation
In Astrodynamics, the Patched Conic Approximation or Patched Two-body Approximation[1] is a method to simplify trajectory calculations for spacecraft in a multiple body environment.
Method
The simplification is achieved by dividing space into various parts by assigning each of the n bodies (e.g. the Sun, planets, moons) its own sphere of influence. When the spacecraft is within the sphere of influence of a smaller body, only the gravitational force between the spacecraft and that smaller body is considered, otherwise the gravitational force between the spacecraft and the larger body is used. This reduces an unsolvable n-body problem to multiple solvable two-body problems, for which the solutions are the well-known conic sections of the Kepler orbits.
Although this method gives a good approximation of trajectories for interplanetary spacecraft missions, there are missions for which this approximation does not provide sufficiently accurate results.[2]
Example
On an Earth to Mars transfer, a hyperbolic trajectory is required to escape from the gravity well of the Earth, then an elliptical or hyperbolic trajectory in the Sun's sphere of influence is required to transfer from Earth's sphere of influence to that of Mars, etc. By patching these conic sections together the appropriate mission trajectory can be found.
See also
References
- ^ Bate, R. R., D. D. Mueller, and J. E. White [1971], Fundamentals of Astrodynamics. Dover, New York.
- ^ Koon, W.S., Lo, M.W., Marsden, J.E., Ross, S.D. (2008) Dynamical Systems, the Three-Body Problem and Space Mission Design. Marsden Books. ISBN 978-0-615-24095-4.