The newest concept in spacecraft propulsion, designed to replace chemical propulsion, is xenon ion propulsion. While typical chemical propulsion systems produce a large amount of thrust, they are often less efficient than desired, which results in the spacecraft having to carry large amounts of heavy fuel. For longer duration missions, scientists are looking towards ion propulsion to reduce the mass of fuel necessary, as ion propulsion is about 6 times more efficient. However, the efficiency comes at a cost. Generally, the choice is either efficiency or thrust, but not both. Therefore, in order to get the same velocity change in a space craft (same amount of thrust), ion engines must run longer than a comparable chemical engine.

Relevant to Scientific Computing are the calculations needed to predict flight characteristics with ion engines. When using traditional chemical engines, burn time is assumed to be negligible (or small compared to other orbital periods). This assumption allows accurate calculations to be made by assuming the change in velocity happens instantaneously. For typical engine burns, this is true. However, because ion thrusters produce significantly less thrust, the ‘burn time’ is significantly longer. This implies that velocity changes occur over a long time relative to other orbital periods. Because the changes in orbital elements are difficult, if not impossible to define explicitly, the resulting motion must be numerically integrated to determine the result of a ion propulsion burn. While this may seem trivial with modern computers, it must be extremely precise. A slight miscalculation could put the spacecraft in a position where it does not have enough fuel to reach its destination, thereby jeopardizing a multi-million dollar mission.

XIPS Xenon Ion Propulsion Drive