Table of Contents

The Outbound Trip

[ The Inbound Trip ]

In planning a realistic mission to Mars one must consider the amount of fuel, the size of the rocket and the length of time required for the entire journey, as well as the physical needs of the crew.

These factors, and the current technology available to accomplish this mission, dictate that only a free flight (ballistic) trajectory to Mars is possible. This requires a very precise alignment of Mars and the Earth at launch time (called the "launch window") so that as the spacecraft "coasts" through space it converges on the planet Mars.

A practical mission is outlined in the diagrams below.

• On all diagrams of the solar system all the planets orbit the Sun in a counter-clockwise direction (as seen looking down on the Earth's North Pole);

• The images are not drawn to scale;

• The relative positions, travel times, and trajectories of the Earth, Mars, and the imagined spacecraft, are approximately correct for a real Mars mission;

• Multiple images on each diagram indicate the apparent motion of Mars and the Earth during the mission;

• Red arrows indicate the flight path of the spacecraft.

Day 0

Blast off!

A rocket trip to Mars is rather like throwing a baseball. The spacecraft is given a huge push as it leaves the Earth and then it "coasts" all the way to Mars.

Once the spacecraft leaves the Earth no further thrust is applied, except for minor course corrections.

Because the spacecraft is on a "coasting flight path" (called a ballistic trajectory) to Mars, mission planners have to anticipate the position of the planet Mars so that it will coincide with the position of the spacecraft when it reaches Mars' orbit.

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Day 45

After a few weeks the motion of the Earth and Mars are apparent as they move along their orbital paths. The spacecraft, moving slightly faster than the Earth, begins to move ahead of the Earth and outwards towards the orbit of Mars.

The spacecraft is launched in the direction of the Earth's orbital motion. By doing this the spacecraft gets a "boost" from the Earth's orbital speed (about 30 km/s).

To move outward (away) from the Sun, one must increase one's speed.

If the rocket were launched in the other direction the spacecraft would "fall" inwards towards the Sun and not move outwards towards the orbit of Mars.

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Day 90

Halfway to Mars!

The spacecraft is still moving outwards towards the orbit of Mars. It is also gaining on Mars as it continues to coast toward the planet.

Like a baseball thrown upwards, the spacecraft (in its "upward" climb away from the relentless gravitational pull of the Sun) is gradually slowing down.

As the distance to Mars shrinks, the Earth falls further behind.

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Day 135

Almost there!

As the spacecraft gets closer to the orbit of Mars a strange thing is observed by the crew. Their speed has slowed so much that the Earth begins to gain on them.

For the remainder of the trip they will be getting closer to both the Earth and Mars.

During the next few weeks the crew undertake careful navigational observations and make any necessary course corrections to ensure their arrival at Mars.

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Day 180

Arrival.

The spacecraft's flight path has allowed it to coast the entire distance from the Earth's orbit, uphill against the Sun's gravity, to the orbit of Mars.

By carefully selecting the launch time from Earth, the paths of Mars and the spacecraft have converged at exactly the right moment.

In order to land on Mars the crew must first slow down their spacecraft. This can be accomplished by using small rockets or aerobraking in Mars' thin atmosphere.

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550 Days on Mars

Working and Living in a Closed Environment.

• The green (curved) arrow shows the motion of the Earth around the Sun during the crew's stay on Mars;

• The orange (curved) arrow shows the motion of Mars around the Sun during the crew's stay on Mars.

Once safely on Mars' surface, the explorers will need to wait 550 days in order for the orbital positions on the Earth and Mars to allow a return trip home.

During their stay on Mars, the crew will live entirely within a small pressurized habitat, depending entirely upon their resourcefulness and preparedness for survival.

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