QUESTION:
How did you go about calculating the days or months it 
will take to get to Mars?

ANSWER from Pieter Kallemeyn on February 17, 1997:
Ah, you've asked one of the more complex questions about spacecraft 
navigation. Since the spacecraft doesn't travel at a constant velocity, 
you need to do a little more than just divide "distance" by "velocity" 
to get "time".  We use high-speed computers to do the actual numerical 
modeling of the spacecraft's trajectory as part of routine navigation 
duties, and that always tells us very accurately how far we have to go.  

There is a more simple method to calculating the time it takes.  It's 
called "Kepler's Equation", after the first person who figures out how 
planets actually move about the Sun, Johannes Kepler. 

The Sun-centered orbit of Mars Pathfinder is actually 155 degrees of an
elliptical orbit that encircles the Sun.  For all you math buffs, Kepler's
Equation is given as:

       Time = SQRT ( A**3 / M ) * ( E - Ecc * sin ( E ) )               (1)

       Where:  Cos (E) = ( Ecc + cos (N) ) / ( 1 + Ecc * cos (N) )      (2)
               N = 155 degrees
               Ecc = The eccentricity of the orbit (0.236386 for Pathfinder)
                       (eccentricity is a measure of the orbit's shape)
               A = the semimajor axis of the orbit (193,216,491 km)
                       (semimajor axis is a measure of the orbit's size)
               M = A measure of the gravitational influence of the sun.
                       (the value to use is 132,712,440,017.987 )

When you plug all these numbers into the above equation, you'll get E = 148.5
degrees (or 2.5917 radians), and the time it takes to get to Mars is 18,195,149
seconds, or 210.5 days.