There are fundamentally two options for an H2M (Humans to Mars) mission:
- Conjunction class or “short stay” mission.
- Opposition class or “long stay” mission.
The option utilised by Blue Dragon is the long stay, using the same rationale as Mars Direct and DRA5. While the long stay option means a longer and more expensive mission, it greatly increases the period spent on Mars, decreases the period spent in space (where health effects are more serious), simplifies trajectories and reduces fuel requirements.
Opposition-class or “short stay” mission
A short-stay mission involves a trip out to Mars (around 5-7 months), then spend, say, 14-30 days on the surface doing science and exploration, then launch and come home. However, after a few weeks Mars and Earth will have moved to new positions in their orbits, and will no longer be optimally aligned. Since we are constrained by fuel requirements, the return trip must necessarily be longer; in fact, more than 1 year.
Numbers will vary depending on the timing of the launch, propulsion technology and available fuel, and these are yet to be calculated precisely for the Blue Dragon architecture. However, this diagram will give you an indication of how time is apportioned during a short stay mission:
|In transit Earth to Mars||217 days|
|Mars surface||30 days|
|In transit Mars to Earth||403 days|
|% time on Mars||5%|
|% time in space||95%|
A short stay mission may, at first glance, seem very safe and conservative and sensible. It makes sense to start with shorter mission, then advance to longer ones as we gain experience, right? The problem, though, is that the crew will spend almost all that time in space, and only a very small fraction of the overall mission duration on Mars. But going to Mars is the whole point. Furthermore, the space environment is more dangerous to the crew’s health in terms of exposure to micro-gravity and radiation than the Martian environment, so we want to minimise the time they spend in space.
Conjunction-class or “long stay” mission
A long stay mission involves flying out to Mars when Earth and Mars are in conjunction, minimising the trip duration to approximately 5-7 months. The crew remain on the surface while the two planets orbit the Sun on their respective paths until they are again at conjunction approximately 18 months later. They then launch and return to Earth, again on a minimum duration trajectory of about 5-7 months.
This diagram showing an example mission profile for a 2039 launch may help to illustrate:
|In transit Earth to Mars||210 days|
|Mars surface||496 days|
|In transit Mars to Earth||210 days|
|% time on Mars||54%|
|% time in space||46%|
As you can see, although the long stay option increases mission duration by 266 days or about 40%, the amount of time spent on Mars increases by a factor of almost 14 (over a year longer), and accounts for more than half the mission duration. Most mission planners agree that this option delivers improved safety, and a much greater ROI.
It may seem that a 2.5 year mission is a big risk. But then, so is an 1.8 year mission. If we think we can do a short stay mission, then we should be able to stretch that little bit further and do a long stay one, in return for a much greater pay-off.
The outbound and inbound trips will occur when Mars and Earth are at conjunction, which means on the same side of the Sun. This occurs about every 26 months.
However, we can minimise the trip time even further by traveling in the right years. Due to Mars’ elliptical orbit, every 15-16 years the distance between Mars and Earth reaches a minimum.
The next time Mars and Earth are at their closest approach will be in 2018, which is therefore a popular choice for a trip to Mars, especially since this also coincides with the solar minimum (a point in the 11-year solar cycle when solar activity is at a minimum, and therefore risk to the crew of being fried by a CME is correspondingly minimised). Denis Tito’s Inspiration Mars mission proposes a Mars flyby in 2018.
To minimise the amount of time spent in space and/or the amount of fuel required to get from Earth to Mars or vice-versa, we could fly the crew out in 2018 and bring them back in 2020. It doesn’t matter how long it takes the uncrewed components such as the hab to travel out there, so we could start launching those items in 2014 or 2016.
However, this is unrealistically soon, so instead Blue Dragon flights are scheduled for 2033 and 2035. That’s 20 years away at the time of writing, which is much more time than we need. It’s possible we could go sooner, but if we want to conduct this mission within an international framework and prepare everything as well as possible, perhaps this is realistic. Of course, we don’t have to select these launch windows – they are just the best ones. So, let’s work off that timeline for now.
2031 We send out the MSH, MAV and cargo capsules.
2033 If everything’s working tip-top, we send out the crew.
2035 We bring the crew back.
This schedule gives us 18 years from the time of writing (2013) to develop and build the necessary hardware components, as well as the international collaboration framework. That may seem like a lot, but there’s a lot to do.