Gangale orbit
Developed by aerospace engineer and political scientist Thomas Gangale in 1998, Gangale orbits are designed to solve the problem of communicating with crews on Mars when the planet is in solar conjunction as seen from Earth, a planetary configuration that occurs near the midpoint of a conjunction class mission to Mars. A Gangale orbit minimizes the distance between Mars and the communications satellite, thus minimizing its size, weight, and power requirements, while providing a simultaneous line-of-sight to both Earth and Mars. Gangale orbits are solar orbits that have the same period as Mars, but are inclined a few degrees out of the plane of Mars' orbit and also differ in eccentricity from Mars' orbit. These differences cause a spacecraft in a Gangale orbit to rise north of Mars, then fall behind Mars, then drop south of Mars, and then pull ahead of Mars, by some desired distance in each case--typically about 20 million kilometers--in order to maintain an angular separation of a couple of degrees as seen from a point in Earth's orbit on the opposite side of the sun.
A satellite in a Gangale orbit would relay communications between Earth and Mars during the period of several weeks when direct communication is blocked by the sun. Gangale orbits are far superior for this purpose compared to stationing a satellite at one of the sun-Mars equilateral Lagrangian points, L4 or L5, for two reasons. First of all, L4 and L5 are 228 million kilometers from Mars, about 10 times the distance of a spacecraft in a Gangale orbit, and by virtue of the inverse-square law, all other things being equal, the signal strength received at L4 or L5 would be 1/100 the signal strength received by a spacecraft in a Gangale orbit. Thus a relay satellite stationed at L4 or L5 would have to be that much more powerful to receive data at the same rate, with concomitant increases in spacecraft size and weight. Secondly, a number of Martian Trojan asteroids have been discovered at the sun-Mars L4 and L5 points, and there are probably countless smaller objects that have collected in these regions that would pose a significant threat to any spacecraft located there.
External Links
MarsSat: Assured Communication With Mars, New Trends in Astrodynamics and Applications. Volume 1065 of the Annals of the New York Academy of Sciences. Ed. Edward Belbruno. New York, New York. New York Academy of Sciences.
