Universe Today article by Fraser Cain asks, "How Long Does it Take to Get to Mars?" It may not be a practical question a long trip by any measure at five months, but still interesting and educational. Space seems reinvigorated, possibly, due to all the private ventures? Or, is it the human race searching elsewhere for salvation since our chances at home seem diminished? Whatever the case, space travel is perceived exciting and Mars closer than ever! Cain puts in perspective Mars proximity:
"The planet Mars is one of the brightest objects in the night sky, easily
visible with the unaided eye as a bright red star. Every two years or
so, Mars and Earth reach their closest point, called “opposition”, when
Mars can be as close as 55,000,000 km from Earth. And every two years,
space agencies take advantage of this orbital alignment to send
spacecraft to the Red Planet."
"When you consider the fact that Mars is only 55 million km away, and the spacecraft are travelling in excess of 20,000 km/hour, you would expect the spacecraft to make the journey in about 115 days, but it takes much longer. This is because both Earth and Mars are orbiting around the Sun. You can’t point directly at Mars and start firing your rockets, because by the time you got there, Mars would have already moved. Instead, spacecraft launched from Earth need to be pointed at where Mars is going to be."
The Hohmann Transfer Orbit is predominate method used to reach Mars, a nice link to video illustrates path. German scientist Walter Hohmann first described transfer orbit in his 1925 work, "The Attainability of Heavenly Bodies." Hohmann was influenced, in an interesting note, as was the German Rocket Society by science fiction novel, "Two Planets," written in 1897 by Kurd Lasswitz. Cain supplies data Mariner 7 reached Mars in 1971 in 131 days. Huntsville researchers are working to shorten that time to eight weeks as covered in a recent post.