# How Long Does It Take To Get To Mars ( Complete Discussion )

If you wanted to pay a visit to the red planet, how long would it take? The answer depends on a number of things, ranging from the position of the planets to the technology that would propel you there. Let's examine a few of the most important points.

 In 2003, Mars made its closest approach to Earth in almost 60,000 years. The Hubble Space Telescope took the opportunity to observe the red planet while it was only 34,647,420 miles (55,757,930 km) from Earth. Credit: NASA, J. Bell (Cornell U.) and M. Wolff (SSI).

How far away is Mars?

To determine how long it will take to reach Mars, we must first know the distance between the two planets.

Mars is the fourth planet from the sun, and the second closest to Earth (Venus is the closest). But the distance between the two planets is constantly changing as they travel around the sun.

In theory, the closest that Earth and Mars would approach each other would be when Mars is at its closest point to the sun (perihelion) and Earth is at its farthest (aphelion). This would put the planets only 33.9 million miles (54.6 million kilometers) apart. However, this has never happened in recorded history. The closest recorded approach of the two planets occurred in 2003, when they were only 34.8 million miles (56 million km) apart.

The two planets are farthest apart when they are both at their farthest from the sun, on opposite sides of the star. At this point, they can be 250 million miles (401 million km) apart.

The average distance between the two planets is 140 million miles (225 million km).

The speed of light

Light travels at approximately 186,282 miles per second (299,792 km per second). Therefore, a light shining from the surface of Mars would take the following amount of time to reach Earth (or vice versa):
• Closest possible approach: 182 seconds, or 3.03 minutes
• Closest recorded approach: 187 seconds, or 3.11 minutes
• Farthest approach: 1,342 seconds, or 22.4 minutes
• On average: 751 seconds, or just over 12.5 minutes

Fastest spacecraft so far

The fastest spacecraft launched from Earth was NASA's New Horizons mission, which visited Pluto in 2015. In January 2006, the probe left Earth at 36,000 mph (58,000 kph). If such a probe traveled in a straight line to Mars, the time it would take to get to Mars would be:
• Closest possible approach: 942 hours (39 days)
• Closest recorded approach: 967 hours (41 days)
• Farthest approach: 6,944 hours (289 days)
• On average: 3,888 hours (162 days)
But then things get complicated …

Of course, the problem with the previous calculations is that they measure distance between the two planets as a straight line. Traveling through the farthest passing of Earth and Mars would involve a trip directly through the sun, while spacecraft must of necessity move in orbit around the solar system's star.

Although this isn't a problem for the closest approach, when the planets are on the same side of the sun, another problem exists. The numbers also assume that the two planets remain at a constant distance; that is, when a probe is launched from Earth while the two planets are at the closest approach, Mars would remain the same distance away over the course of the 39 days it took the probe to travel. [Countdown: The Boldest Mars Missions in History]

In reality, however, the planets are continuously moving in their orbits around the sun. Engineers must calculate the ideal orbits for sending a spacecraft from Earth to Mars. Their numbers factor in not only distance but also fuel efficiency. Like throwing a dart at a moving target, they must calculate where the planet will be when the spacecraft arrives, not where it is when it leaves Earth. Spaceships must also decelerate to enter orbit around a new planet to avoid overshooting it.

How long it takes to reach Mars depends on where in their orbits the two planets lie when a mission is launched. It also depends on the technological developments of propulsion systems.

According to NASA Goddard Space Flight Center's website, the ideal lineup for a launch to Mars would get you to the planet in roughly nine months. The website quotes physics professor Craig C. Patten, of the University of California, San Diego:

"It takes the Earth one year to orbit the sun and it takes Mars about 1.9 years (say 2 years for easy calculation) to orbit the sun. The elliptical orbit which carries you from Earth to Mars is longer than Earth's orbit, but shorter than Mars' orbit. Accordingly, we can estimate the time it would take to complete this orbit by averaging the lengths of Earth's orbit and Mars' orbit. Therefore, it would take about one and a half years to complete the elliptical orbit.

"In the nine months it takes to get to Mars, Mars moves a considerable distance around in its orbit, about three-eighths of the way around the sun. You have to plan ahead to make sure that by the time you reach the distance of Mar's orbit, that Mars is where you need it to be! Practically, this means that you can only begin your trip when Earth and Mars are properly lined up. This only happens every 26 months. That is, there is only one launch window every 26 months."

The trip could be shortened by burning more fuel — a process not ideal with today's technology, Patten said.

Evolving technology can help to shorten the flight. NASA's Space Launch System (SLS) will be the new workhorse for carrying upcoming missions, and potentially humans, to the red planet. SLS is currently being constructed and tested, with its first flight planned for 2019.

Robotic spacecraft could one day make the trip in only three days. Photon propulsion would rely on a powerful laser to accelerate spacecraft to velocities approaching the speed of light. Philip Lubin, a physics professor at the University of California, Santa Barbara, and his team are working on the Directed Energy Propulsion for Intersteller Exploration (DEEP-IN). The method could propel a 220-lb. (100 kilogram) robotic spacecraft to Mars in only three days, he said.

"There are recent advances which take this from science fiction to science reality," Lubin said at the 2015 NASA Innovative Advanced Concepts (NIAC) fall symposium. "There's no known reason why we cannot do this."

How long did it take?

Here is a list of how long it took several historical missions to reach the red planet. Their launch dates are included for perspective.
• Mariner 4, the first spacecraft to go to Mars (1964 flyby): 228 days
• Mariner 6 (1969 flyby): 155 days
• Mariner 7 (1969 flyby): 128 days
• Mariner 9, the first spacecraft to orbit Mars (1971): 168 days
• Viking 1, the first U.S. craft to land on Mars (1975): 304 days
• Viking 2 Orbiter/Lander (1975): 333 days
• Mars Global Surveyor (1996): 308 days
• Mars Pathfinder (1996): 212 days
• Mars Odyssey (2001): 200 days
• Mars Express Orbiter (2003): 201 days
• Mars Reconnaissance Orbiter (2005): 210 days
• Mars Science Laboratory (2011): 254 days

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How long does it take to travel to Mars?

The trip takes around seven months; a bit longer than astronauts currently stay on the International Space Station.

The precise duration of each journey depends on when it is taken. Because both Mars and Earth's orbits are not perfectly circular, the time it takes to travel between them varies from six to eight months.

How to determine the dates of departure and arrival

The exact dates and years in which Mars One plans to execute the various stages of the plan were chosen for the beneficial astronomical position of Earth and Mars. When determining the course to Mars, the maximum travel time for the astronauts is very important.

The most efficient route to take from Earth’s orbit to that of Mars is called the ‘Hohmann Transfer Orbit’ (see: illustration). The illustration shows a simplification of the process, as both Earth and Mars’ orbits are not perfect circles.

How long would a trip to Mars take?

Contrary to the 'point and shoot' idea, an actual trip to mars looks very round a bout as the figure above shows for a typical 'minimum cost' trajectory. This, by the way, is called a Hoeman Transfer Orbit, and is the main stay of interplanetary space travel. It depends on the details of the orbit you take between the Earth and Mars. The typical time during Mars's closest approach to the Earth every 1.6 years is about 260 days. Again, the details depend on the rocket velocity and the closeness of the planets, but 260 days is the number I hear most often give or take 10 days. Some high-speed transfer orbits could make the trip in as little as 130 days.

For a more detailed discussion, see the course notes for Physics 6 by Prof. Craig Patten at UC. San Diego. I will capture the relevant comments below:

How long does it take? It takes the Earth one year to orbit the Sun and it takes Mars about 1.9 years ( say 2 years for easy calculation ) to orbit the Sun. The elliptical orbit which carries you from Earth to Mars is longer than Earth's orbit, but shorter than Mars' orbit. Accordingly, we can estimate the time it would take to complete this orbit by averaging the lengths of Earth's orbit and Mars' orbit. Therefore, it would take about one and a half years to complete the elliptical orbit above ( solid and dashed parts! ). Since it would be nice to spend some time at Mars, we are only interested in the one way trip ( solid line ) which is half of the orbit, and would take half the time of the full orbit, or about nine months. So it takes nine months to get to Mars. It is possible to get to Mars in less time, but this would require you to burn your rocket engines longer, using more fuel. With current rocket technology, this isn't really feasible.

In the nine months it takes to get to Mars, Mars moves a considerable distance around in its orbit, about 3/8 of the way around the Sun. You have to plan ahead to make sure that by the time you reach the distance of Mar's orbit, that Mars is where you need it to be! Practically, this means that you can only begin your trip when Earth and Mars are properly lined up. This only happens every 26 months. That is there is only one launch window every 26 months.

After spending 9 months on the way to Mars, you will probably want to spend some time there. In fact, you MUST spend some time at Mars! If you were to continue on your orbit around the Sun, then when you got back to where you started, Earth would no longer be where you left it!

In order to get out of your elliptical orbit around the Sun, and into Mars orbit, you will again need to burn some fuel. If you want to explore the surface of Mars, you will also need fuel to get your lander off the surface of Mars. On the first trip to Mars, it is necessary to bring all of this fuel with you to Mars. ( Maybe someday we could manufacture rocket fuel on Mars ). In fact, you can only land a small part of the ship on Mars, because landing everything on the surface and lifting it off again would require enormous amounts of fuel. Therefore, you will probably leave part of the ship, including all the supplies for the trip home, orbiting Mars, while part of the crew goes to explore the surface.

Just like you have to wait for Earth and Mars to be in the proper postion before you head to Mars, you also have to make sure that they are in the proper position before you head home. That means you will have to spend 3-4 months at Mars before you can begin your return trip. All in all, your trip to Mars would take about 21 months: 9 months to get there, 3 months there, and 9 months to get back. With our current rocket technology, there is no way around this. The long duration of trip has several implications.

First, you have to bring enough food, water, clothes, and medical supplies for the crew in addition to all the scientific instruments you will want to take. You also have to bring all that fuel! In addition, if you are in space for nine months, you will need a lot of shielding to protect you from the radiation of the Sun. Water, and cement make good shielding but they are very heavy. All together, it is estimated that for a crew of six, you would need to 3 million pounds of supplies! The Shuttle can lift about 50,000 pounds into space, so it would take 60 shuttle launches to get all your supplies into space. In the history of the Shuttle, there have only been about 90 launches, and there are less than ten launches per year... So with the shuttle, it would take six years just to get the supplies into space. For this reason, you would probably need to develop a launch system that could lift more than 50,000 pounds into space. Even with a better launch vehicle, it is unlikely that you could launch the Mars mission all at once. You will have to launch it in several pieces and assemble them in orbit.

Second, you are going to be in space for an extended period of time, and there a physiological consequences of being weightless for long periods of time. For one, your muscles do not need to work as hard. In response to being used less, your muscles begin to shrink or atrophy. Remember, your heart is also a muscle, and pumping blood around your body is easier in the weightless environment of space, so your heart gets weaker as well. On an extended space voyage, your muscles might become so weak that it would be difficult for you to stand upright once you return to an environment where you are subject to gravity.

Just like your muscles have to do less work to move you around in space, your bones are not needed as much. The main function of your skeleton is to support the weight of your body. When you are weightless in space, your body realizes that the bones are not being used as much and they begin to lose calcium, and become more brittle. These are serious effects which may impair the ability of the astronauts to carry out experiments and tasks when they get to Mars, where they will be subjected to gravity again.

In order to study these physiological effects of long duration weightlessness, you need to do experiments on people who have been weightless for extended periods of time. Currently the Russian Mir space station is one place where astronauts can stay for extended periods of time, and research into these effect is ongoing. But since you will need to conduct many more experiments, and you will also need a place to assemble the mission, it will probably be necessary to construct a larger space station to be used as a staging ground for the mission to Mars.