article_snippet.sent: Owing to the orbits of Earth and Mars, there are specific windows of opportunity when a mission can take place.
article_snippet.sent: For this reason spacecraft to Mars, such as the Curiosity rover, have to launch in certain windows when Our planets are aligned.
article_snippet.sent: The next window is open from January 2016 to April 2016, and will see the launch of two more missions to the red planet.
article_snippet.sent: For a future manned mission, they will need to launch out in one of the windows and return in another.