To send a mission to Mars requires launching a space probe into an elliptical orbit at a tangent to that of Earth at launch, at a tangent to that of Mars at arrival, and timed so that the space mission and Mars reach the same point at the same time. Is this hard? To get a feeling for just how hard it is, create an analogy in terms of throwing a dart at a dime. How far away must the dime be to present an equally small bull's eye?