This is a follow up question my earlier question about sending supplies to Mars.

It's 2250 AD (or some such future date). Say you have a young man with a dream that inherits a 500 billion widget fortune. He decides to plow his windfall into a space freighter business. For his inaugural loads, he plans to send as many 10,000 kg blocks of ice to Mars at the end of the next 24 month cycle, where he'll fetch a decent price from the Martian colonists.

What's the cheapest practical flight plan to send 10,000 kg of water ice to Mars from LEO?

Let's assume no breakthrough physics, just perhaps incremental increases in current technology. Let's also say he already can get his payload into orbit at a low-enough cost, and the Martians can retrieve it by whatever means from low Mars orbit (LMO). He wants to ship from LEO to LMO at the lowest cost per kilogram.

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    $\begingroup$ Two swallows tied together. (African or European though?) $\endgroup$
    – geoffc
    Aug 12, 2015 at 1:32
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    $\begingroup$ Give each colonist a glass of water to drink on departure, ask them to pass it back on arrival? $\endgroup$
    – TildalWave
    Aug 12, 2015 at 1:50
  • $\begingroup$ With current monetary policy $10 bn won't even buy you a bus ticket in 2250 AD. Just look 250 years back and compare prices. $\endgroup$
    – LocalFluff
    Aug 12, 2015 at 4:41
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    $\begingroup$ The cheapest way would be to not send it from Earth at all. It would be to send it from the asteroid belt. Earth's gravity well is way too deep. Also it would be cheaper to not have to put it in Mars orbit. It would be much cheaper to send it directly in. In fact, you could just send it in as giant blocks of ice. For big enough blocks, most of it would make it to the surface, where it could be mined before it sublimates. So you a) picked the most expensive source (LEO), and b) the most expensive destination (LMO), but then c) asked how to get it between those the most inexpensively. $\endgroup$
    – Mark Adler
    Aug 12, 2015 at 5:11

2 Answers 2


Cheapest: Orion.

Getting your hands on the bombs and getting permission to launch are quite another matter....

Also, perhaps he can find an icy comet and use those bombs to send it to Mars. If it's not too big it might be possible to hard land it in an unoccupied part of Mars--although the result would more go into the Martian atmosphere than be readily collected.


This answer will almost certainly prove to be wrong (but you'll have to wait until 2250 to know)!

If we operate under the assumption that we don't do anything new from the point of view of physics, then we can just look at the limits of some current technologies.

Conventional momentum exchange rockets: by this I mean solid, liquid, electric etc. anything that carries it's fuel with it. These aren't going to win out in the long run simply because the rocket equation can not be worked around. You need to carry the fuel with you, and that makes launch and transfers expensive.

Space elevator: I'm going to assume we manage this at some point in the next few hundred years. A space elevator would significantly reduce the energy cost of launch - we don't need to carry the fuel for launch with us! I'm not suggesting our entrepreneur builds his own elevator, but use of one would be the equivalent of an extrememly high energy bill!

Solar sails: if you can build a big enough surface the solar sails are a great way to get where your going without carrying any fuel. The mass of the sail is typically reasonably small but the support mass can often be significant. However in a world where we have a space elevator we can probably build a very large sail for low mass.

Now when you get to Mars 10,000 kg of anything is going to reenter with a lot of momentum, but who's to say we don't have a Martian space elevator as well. In fact a Martian space elevator is much more achieveable since Mars has a lower gravity.

  • $\begingroup$ I'm going to edit the question to narrow the scope to from LEO to LMO. $\endgroup$ Aug 12, 2015 at 2:38
  • $\begingroup$ I have no clue how the numbers work out, but beam-powered propulsion looks like a very good possibility. ​ ​ $\endgroup$
    – user2822
    Aug 12, 2015 at 2:55
  • $\begingroup$ The problem with beam powered propulsion is the mass of propellant is still required $\endgroup$
    – ThePlanMan
    Aug 12, 2015 at 2:58
  • $\begingroup$ @ThePlanMan: Ah, no. The point of beam-powered propulsion is that the power source is not accelerated: it uses photons as a force transmission over the distance from launch to destination. No rocket equation involved. $\endgroup$ Aug 12, 2015 at 18:31
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    $\begingroup$ @NathanTuggy Well it depends on the type of beam powered propulsion. Yes in a light sail you are just using the photons directly however the conversion efficiency is very low as photons don't have much momentum. It takes a massive laser and a massive sail to move a small cargo. There are other proposed beam propulsions where the beam provides the energy for a themal or electro propulsion system. There can still be significant mass savings because you reduce potentially by up to 50% the total propulsion weight (engine, powerplant, and fuel). $\endgroup$ Sep 15, 2015 at 13:31

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