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## Journalmcgrew's Journal: Ask Slashdot: Orbital Mechanics4

I'm having a math and physics problem: math and physics is getting in the way of the plot in Mars, Ho!

I originally thought it would be a six month trip, but math got in the way since they were getting gravity from propulsion. So I shortened it to a two month trip, and to do that I had to have Earth and Mars on opposite sides of the sun -- but orbital mechanics makes waiting shorten the time.

The best bad way around it I can see is a little hand-waving, with the captain wondering why the company didn't wait a week to launch. But I'm not satisfied with this. Does anybody have any ideas?

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• #### Indirect Route? (Score:2)

Either they used a couple orbits around the Earth to get a slingshot, or to save the most fuel or used Lagrange Points as way points. That is supposed to be the most efficient in the way of fuel.

• #### Re: (Score:2)

Yeah, with enough hand waving, anything is plausible. You could have something in between a low energy transfer on the http://en.wikipedia.org/wiki/I... [wikipedia.org] and waiting lots of time, or some kind of slingshot, or just burn fuel to do simple transfers between orbits. But I guess since your propulsion is on all the time for artificial gravity, you're kinda doing a propellant-assisted slingshot. The slingshot does require the planets and the sun have to be lined up just right, so it does make sense that the c

• #### Two ways to tackle it (Score:2)

Either with new plot elements or with physics, probably some combo of both though.

I don't know orbital mechanics well enough to say (particularly under constant propulsion), but could you argue that they needed to move to a larger orbit to avoid solar flare radiation/aliens/asteroids?

The other question would be if you've specified how much propulsion is provided. If we're talking .01 g, that's a much different scenario than 1 g, in which case you would do better to write in artificial gravity or cent
• #### Unscientific fix for a scientific problem (Score:2)

The shipping company would weigh the cost of transport against the risk of losing the cargo and choose a route that wasn't so direct that pirates would expect you to take it, but not so long that the extra fuel and time costs would make it unprofitable.

It would make the pirate encounter all the more surprising, too.

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