The Race to Mars in 2020

Mars is our next door neighbor, yet we almost never visit. But in July of 2020 humans are launching four separate missions to Mars. The missions are all launching in July 2020 because it is the ideal time to get a spacecraft to Mars while using the least amount of rocket fuel. But not because the two planets are at their closest, instead it has to do with something called a Hohmann transfer orbit—the most efficient way to send a spacecraft to Mars. This orbit is elliptical, and uses the sun as one focal point. The spacecraft’s launch is at the closest point to the sun, or perihelion, and it crosses Mars’ path at its farthest point from the sun, or aphelion. It is very important that Mars is actually there when the spacecraft arrives, but for that to happen the spacecraft has to be launched at just the right time. The time it takes a spacecraft to travel from perihelion to its aphelion in Mars’ orbit is approximately 259 days. During that time Mars will move about 136 degrees, since Mars is farther from the sun than Earth and takes longer to move the same angular distance. So in order to sync up the 180 degrees the spacecraft will travel while Mars moves 136 degrees, the spacecraft needs to launch when Mars has a 44 degree head start. This happens for a few weeks once every 26 months, and the next time it will happen is mid-July of 2020. And so, this time around a lot of space agencies are geared up for launch.