The Evolutionary Mission Trajectory Generator (EMTG) is a global trajectory optimization tool for designing interplanetary missions that perform multiple flybys and either low-thrust or high-thrust propulsive maneuvers on the way to destinations in the solar system. Some targets, such as Mars and Venus, are reachable using direct flights with chemical propulsion technology. Others, such as Mercury, main-belt asteroids, and comets are not easily accessible. One way to mitigate this problem is by using more efficient propulsion systems, such as low-thrust solar electric propulsion. Another is to find more efficient paths to the destination, possibly including gravity assist maneuvers, or planetary flybys.

The EMTG works with minimal user oversight. The user must input only the starting location, the destination, the allowable range of launch dates, the allowable flight time, and minimal information about the spacecraft hardware. EMTG then autonomously searches for the optimal sequence of planetary flybys and propulsive maneuvers that delivers the most payload to the destination.

The EMTG mission design process first decomposes the general trajectory design problem into two nested optimization problems. The outer-loop problem solver chooses the number of planetary flybys and the identities of the flyby planets. Each possible choice of flyby planet is assigned an integer code, and an integer-valued genetic algorithm (GA) is used to choose the optimal flyby sequence. A novel null gene method is used to allow the GA to control the length of the flyby sequence.

The small amount of information that must be supplied by the user is supplied through either a scripting interface or a graphical user interface (GUI). The GUI is used to post-process results from the EMTG. The EMTG runs on a standard desktop computer. It is best deployed as a force multiplier, allowing a single analyst to explore a wide variety of mission design options in a short period of time.

This work was done by Jacob Englander of Goddard Space Flight Center. GSC-16824-1

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This article first appeared in the September, 2014 issue of Software Tech Briefs Magazine.

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