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As far as i understand we are going on a route shown in the picture. When we can actually let Mars do the travelling for us and just take the short route and wait for Mars to arrive... Won't that be faster? I have added a picture with some arrows to show what i mean. alternative route to Mars

The original picture can be found here -> http://www.extremetech.com/wp-content/uploads/2013/03/Inspiration_Mars_trajectory.svg_.png

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    $\begingroup$ The way we're going about it takes change in velocity of about 5.5 km/s (from LEO). The way you propose would require reducing orbital velocity of the Earth from roughly 30 km/s to 0, then climbing up the Earth's and Solar system's gravity well to Mars' orbital altitude, and waiting there for Mars to hit us at its orbital speed of about 24 km/s! In other words, the way it's done is the shortest way to Mars. The way you do it is the shortest way of connecting two static points on a piece of paper. It doesn't work like that even for radio communications that travel at the speed of light. $\endgroup$
    – TildalWave
    Oct 29, 2015 at 19:13
  • $\begingroup$ okey guys, now i feel stupid again :-) Thanks for the fast reply! It seems with current technology this is not an option. $\endgroup$
    – Steven Lebègue
    Oct 29, 2015 at 19:24
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    $\begingroup$ Short of someone inventing an anti-gravity drive, if that's even possible as it assumes gravitons are real and that their antiparticles (antigravitons) can be produced, we'll never travel to Mars in such a direct line, and even then it would be energy inefficient. Say, beamed propulsion of extreme power and efficiency would prescribe an inverted S shape (two brachistochrone curves with a turn in the middle) trajectory. Even if we uploaded to Mars, we'd have to target its position anywhere from 3 to 22 minutes in the future. $\endgroup$
    – TildalWave
    Oct 29, 2015 at 19:43
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    $\begingroup$ OP: As an aside, if this kind of thing interests you, and you want to really get an intuitive feeling for this kind of thing, try Kerbal Space Program. My experience was such that a lot of this stuff went from "somewhat mysterious" to "obvious". $\endgroup$
    – Beska
    Oct 29, 2015 at 20:40
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    $\begingroup$ @CGCampbell Just three are sufficient for the question at hand (see e.g. this trajectory, click on the single result an hit play). Inclination change is minute (from 1.5° to 0, depending when you launch) and can be achieved directly from launch site by targeting a specific time of the day launch window when Earth's axial tilt aligns with target inclination. $\endgroup$
    – TildalWave
    Oct 30, 2015 at 17:51

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When a spacecraft is launched from Earth, it's moving counterclockwise across your diagram at a speed of 30 km/s (the same speed as Earth itself), plus a speed of 10-15 km/s in the direction of the launch.
The trajectory you propose is only possible if you reduce the spacecraft's counterclockwise speed to zero. The fastest launch ever (New Horizons) reached about 16 km/s, so at the moment we can't fly the trajectory you've drawn.

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  • $\begingroup$ I wouldn't say we can't - we can certainly send up big enough rockets to get a few multiples of our record without much trouble. It's just... who would pay for it? $\endgroup$
    – corsiKa
    Oct 29, 2015 at 22:24
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    $\begingroup$ @corsiKa Can't is the operative term. The rocket equation is extremely brutal. Even disregarding the energy needed to climb from Earth to Mars the path given has a 54 km/sec delta-v requirement. The size of the rocket grows exponentially with with delta-v. The best exhaust velocity that can be gotten from LH2/LOX engines is 4.4km/sec. Thus every additional 4.4km/sec of velocity requires a rocket e times bigger. (And reality is even worse as you need fuel tanks etc.) At least (and probably much more) a quarter million pounds of rocket to deliver one pound to Mars. $\endgroup$
    – Loren Pechtel
    Oct 30, 2015 at 1:23
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    $\begingroup$ The question also asks "and wait for Mars to arrive" you would need to stop moving out, when you got to Mars orbit (more energy) and speed up (counter clockwise) just before Mars arrived (more energy) so you did not get hit by a planet moving at 24 km/s while you are parked in orbit waiting for it. $\endgroup$
    – James Jenkins
    Apr 4, 2017 at 14:12
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Fuel mass and time of flight are the two main variables to be traded off for deep-space spacecraft. In this case, they decided to design their spacecraft and orbit around a minimum-fuel operation (and also a unique opportunity to do a human flyby of Venus, "Plan B")

If you had a lot (A LOT) of fuel mass to spare, you could use thrusters during the entire flight (accelerating for halfway, decelerating for the rest), you could drastically decrease the time of flight, but the amount of usable mass you'd have at the end of the flight would be negligible (or the takeoff mass would be insane)

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