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Physics/Travel to and from mars


I understand its a short window for a round trip to be successful due to distances and orbits. My question is, instead of. Waiting the two years you would need to on mars if you missed your windo, could you instead launch in the opposite direction of normal orbit and cut the travel time to around six months and meet the planet on its way around? If not why?

First of all, my apologies for my delay. It's been such a busy time over the last few days that maybe I should have just listed myself as unavailable to answer.

Anyway, there's a simple reason why space ships from our Earth to Mars need to travel in the same direction as the orbits of these planets. It's the minimize the difference in speed when the ship reaches Mars. If the ship, when it reaches Mars, is moving too fast relative to the motion of that planet, orbit or landing on Mars becomes impossible. Thus starting the ship in the direction opposite to the direction of planetary orbits, and a lot of fuel will need to be expended to slow down the ship when it gets there. Using gravity to speed up and slow down a ship is cheap; fuel is VERY expensive.

Here's a good overview of the requirements to get humans between the two planets.


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I can help with understanding physics that does not involve eggs. I will NOT help with academic or professional questions, which are NOT limited only to homework. Please do not waste your time by asking a question that comes out of ANY kind of academic, professional, or business matters.


Have been fascinated by physical laws ever since I learned, at age seven, that magnets work under water. My study continued through college and has not ceased even after I retired.

B.A. in Physics (with honors) from University of California at Berkeley.M.A. in Physics (with honors) from University of Texas Austin.

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