26th November 2013 Sol 466

Two years after launch from Cape Canaveral we have been slowed up temporarily by a minor short circuit, but are now getting back to analyses and driving.

Every 26 months Mars and Earth are relatively close e.g. 55 million km (!), and  so a Hohman transfer orbit can take  place.  Thus it is no coincidence that MAVEN has just been launched. 

A Hohman transfer orbit is the most fuel efficient way of getting between the 2 planets.  The Hohman transfer orbit is part of an ellipse with the Sun at one focus within the ellipse, and the 2 planet’s orbits just touching the ellipse.  This is based on Keplers’ Laws, for orbiting bodies in the Solar System.  Kepler was a 17th Century astronomer.  He worked out that:

•All planets move in elliptical orbits with the Sun at one focus within it (his first law)

 •A line joining a planet to the Sun sweeps out equal areas in equal times (his second law)

•The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit (his 3rd law).