• Question: How long would it take to get to mars in a rocket????

    Asked by Toby and Dan to Alice, Bose, Christian, Emma, Steve on 13 Mar 2016.
    • Photo: Steve Marsden

      Steve Marsden answered on 13 Mar 2016:


      That very much depends on how much money you’re willing to throw at the problem. The way that uses the least fuel would get you there in 9 months. The more fuel you take with you, the quicker you could make the journey. I believe NASA plans on about a 3 month journey.

      If you’re not interested in the most efficient method, you should probably skip this paragraph. If you are, it uses what’s called a Hohmann transfer. Both the Earth and Mars have roughly circular orbits around the sun. In the Hohmann transfer, you would burn your engines only twice. The first time, would change your orbit from Earth’s circle, into an ellipse. The part of the ellipse closest to the sun (perihelion) touches Earth’s orbit, and the furthest point from the sun in the orbit (aphelion) touches Mars’s orbit. When you reach the aphelion, you’ve arrived at Mars, and need to burn your engines a second time to slow down and not to hit it at an insane speed.

      That method takes the least amount of fuel, but it takes a whole 9 months! In the high radiation environment of interplanetary space, you really don’t want to stick around for that long. It is possible to use more fuel to go much quicker. But remember, you have to take more fuel with you in order to slow down when you reach Mars. That fuel isn’t light, and taking it means that your ship is a lot heavier. That in turn means you need even more fuel to get it up to those higher speeds. The cost of making these quicker spaceships becomes impossibly high very quickly.

      If I recall correctly, NASA’s most recent plans for a Mars mission are to send the heavy supplies there using an efficient 9 month mission. The astronauts would then take much quicker, more expensive transfer, taking about 3 months (I’m not sure on this value, and plans always change, so it’s worth googling).

      There are alternative forms of propulsion being developed. One of these is ion engines. These would produce extremely small thrust, only accelerating a spaceship at about 1 mm/s^2, however they are extremely fuel efficient, so you could leave the engine burning for very long periods of time. Even with such a low acceleration, over a long time you could build up a huge speed. NASA believe that this technology could allow for a 40 day transit.

      In the news recently was a laser powered propulsion. In this situation a laser would be based on Earth, firing a powerful beam at the spaceship. The laser beam bouncing off of the ship would be able to accelerate the ship. Using this method, the transit could be as low as 3 days! However, I very much doubt this will be a practicality for a very long time.

      By the way, if you’re interested in this kind of thing, I would definitely recommend playing Kerbal Space Program. 🙂

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