Flight to Mars: How Long? Along what Path?

This site demonstrates how, with the use of orbital mechanics, a space mission to Mars can be planned. Using no more than algebra, Kepler's laws and the formula for the energy of an object in a Kepler orbit, it derives the time for an optimal flight to Mars, the timing of the flight, the thrust needed to enter the orbit and to leave it upon arrival, and details of the flight back to Earth, including the delay before the relative positions of Earth and Mars are appropriate. Educational levels: High school, Undergraduate lower division