The first human mission to Mars will have as its primary mission objectives

• to learn more about the history and current conditions on Mars.

• to answer pending scientific questions about water, life, global geology, the atmosphere, etc.

• to demonstrate the feasibility of future longer term missions and the colonization of Mars.

The risks involved in such a mission include high-risk conditions such as launch, orbital maneuvers, and atmospheric entry. Each of these is inherently dangerous and has caused problems for spacecraft in the past.

Medium-risk factors include issues faced by the crew in transit to Mars and upon return to Earth, such as radiation and zero-g exposure. Low-risk concerns involve time spent on the surface of Mars. There is gravity (about 1/3 that of Earth) on Mars, and there is less exposure to solar radiation due to the day/night cycle and to some protection by the Martian atmosphere. The exposure to galactic cosmic rays is also less on the surface of Mars compared to in space (where these rays come from every direction). System and equipment redundancy (backup systems) can reduce some of the risks, and intensive training of crews and rigorous testing of equipment can help to reduce the probability of accidents. The testing of systems on the Moon and on the International Space Station before we undertake the trip to Mars can also counter some of the low- and medium-risk situations.

Since the in-space environment during transit is most dangerous to the crew, it is important to minimize transit time. Time spent on the surface of Mars conducting scientific experiments and exploring the planet will provide the most important returns, so it is important to try to maximize surface operation time.

In order to plan a mission to Mars, engineers need to understand orbital mechanics (the movement of the planets) and trajectory planning (how to get to another moving target from the Earth). For a tutorial on planning trajectories to Mars, click here. For a tutorial on orbital mechanics, click here.

Three current mission strategies for a mission to Mars are the

• Short Stay Mission
• Long Stay Minimum Energy Mission
• Long Stay Fast Transit Mission

This allows little time for the astronauts to get exposed to 1/3g on the surface. About 90% of the mission time is spent in transit. Adding a Venus swing-by can increase the trip by up to 360 days.

(Click image for larger view)

The long stay minimum energy mission scenario provides stays on the surface of up to 500 days with a round-trip time of about 900 days. The energy required for this mission is the lowest of the three mission scenarios, but, in exchange, it has a long transit time. This trajectory provides the opportunity to send a more massive spacecraft (more cargo).  The disadvantage is the crew’s long exposure to the space environment.

This trajectory scenario is best for cargo transport and could perhaps be used to send unmanned cargo vehicles at a minimum energy cost.

The last scenario is the long stay fast transit mission. This mission scenario minimizes time spent in space and the crew’s exposure to harmful radiation and the zero-g environment, while it maximizes surface stay time. This allows crews to re-adapt to gravity and to complete the most in terms of exploration, science, and development of infrastructure. The fast transit energy requirements are higher, but the physical and mental benefits to the crew may be worth the investment.

(Click images for larger view)

Current thinking encourages the idea of a split mission strategy, which would employ the minimum energy long transit method for sending unmanned cargo ships with surface equipment and the return vehicle ahead of time; and the fast transit method for sending the crewed ships.

(Click image for larger view)

For more details on the three mission profiles, click here.

Questions to think about:

• If you could only choose one mission for sending a human crew, which of the three mission scenarios would you choose? Why?

• What are the primary benefits of the split mission strategy?

The Spacecraft