• Mars Date/Time:  Year 1, Sur One, Sol 13 (1.1.13)  11:19 PM NST
• Earth Date/Time:  16 January 2016  2:00 PM PST

Any journey begins with a beginning point and an ending point. Our journey to Mars is no different; however, in this case the beginning point and the ending point are in motion and the distance between them varies depending on where each planet is in their orbit.

Mars and Earth will be at their closest point on 30 May 2016. To take advantage of this the ESS Queen Elizabeth II and the ESS Carl Sagan will depart for Mars in late February and arrive in June. We call this a “up” orbital transfer because the ships are coming up from behind the planet to meet it in its orbit.

However, we will also be using a “head” orbital transfer in future missions. This is when the departure planet is ahead of the destination planet. It requires more fuel in most cases; however, it gives us more opportunities to send ships between the two planets. The next three missions to Mars will be using the head orbital transfer.

Because Earth moves faster than Mars, an up orbital transfer to Earth is impractical once it is ahead of Mars in orbit. For this reason the first return mission to Earth will be a ‘head’ orbital transfer in April 2017, and that mission won’t arrive at Earth until November 2017.