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A few minutes before SpaceIL's Beresheet spacecraft was launched into space, Israeli prime minister Netanyahu congratulated SpaceIL and all those involved and said: "We are already waiting for you to start working on a mission to Mars".

That got me wondering: would it be possible (i.e. in any way reasonable) to use the same fuel-saving method (ever-increasing elliptical orbits) to go to Mars? If the distance between the Earth and Mars is 225 million km (on average), while the Earth-Moon distance is ~384,000 km, how much time would it take to reach Mars this way? This website says that the spacecraft is going to travel 6.5 million km on its way to the moon, but it's supposed to take about two Earth months to get there.

So would it be possible to go to Mars this way? Will the reduction in fuel requirement offset the longer time it would take?

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The advantage of progressive orbit-raising is that it can be done with very short burns near perigee, maximizing the Oberth effect. You can look at it as either the Oberth effect saving fuel relative to doing one long burn, or as saving engine weight relative to doing one short burn.

The disadvantage is that it takes weeks instead of days to get to the moon.

For a Mars mission, the direct Hohmann transfer already takes months; doing progressive orbit raising would make the flight take several years.

For any crewed missions, the necessary consumable supplies would far outmass the fuel or engine mass savings, obviously.

For uncrewed missions, component lifetimes would be a big concern -- before you even reached the destination, every part of the science package will have been cold-soaking in space for years, increasing the risk of failure. It would almost always be a better risk-reward tradeoff to use a slightly more powerful launcher and a more direct trajectory to Mars.

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  • $\begingroup$ Also, since the direct Hohmann transfer takes months, your burn would have to similarly take months to miss out significantly on the benefit from the Oberth effect. Beresheet is in a much smaller orbit, and so a single ~30 minute burn would span a much larger range of distances from Earth. $\endgroup$
    – Christopher James Huff
    Feb 26, 2019 at 22:47
  • $\begingroup$ @ChristopherJamesHuff Ack, good point. $\endgroup$
    – Russell Borogove
    Feb 26, 2019 at 22:58

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