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So I've always assumed Mars never had enough available CO2 on-site for terraforming, something that new research seems to have confirmed.

But my ideas have always relied on getting CO2 from alternate sources, e.g controlled impacts or in this case borrowing gas from Venus. The atmosphere of Venus is about 90 bars of pressure, and we'd only need around one (or more?) to bring Mars to a livable pressure. Transporting that gas however is a bit of a pickle.

One idea I've had is using a fleet of Venus-Earth-Mars cyclers to transport pressurized Venusian gas (perhaps mostly unfiltered as Mars can make use of the nitrogen and trace elements too) to Mars. As an added bonus, the canisters can be created from on-site carbon and burn up on Martian entry. I'll opt for the cargo capacity of the average oceanic cargo ship of 25,000 tons, or a little under 23 million kilograms. In terms of mass, I'm not sure how much gas is required to bring Mars to 1 bar of atmospheric pressure. I assume it would be slightly more than Earth however due to the lower gravity. Earth's atmosphere has a mass of about 5.15 * 10^18 kg. To make things simpler, I'll go with that. It would take one of our cyclers 2.239 × 10^11 trips to complete its objective, but a fleet of 100,000 would bring that to a more modest number...at 2.239 million trips.

This is where my already poor math starts to fail: I can't calculate gravity assists and I don't know how long it would take a Venus-Earth-Mars cycler to complete a round trip. So I'll REALLY fudge it from here and just put in the time of an Aldrin Earth-Mars cycler, 779.27 days, and add an additional 200 days for the ~100 days it takes for the average spacecraft to reach Venus. ~2.683 years * 2.239 million trips means Mars would have 1 bar of atmosphere in...6,007,200 years. Even with an accurate round-trip time for the cycler, that's still a 'yikes' from me. By the way, it would take only 300 years for 2 billion 25,000 ton ships to transfer the gas...I'm sure there is a much better use of interplanetary resources, probably.

Another idea I've recently had is a mass driver (or a 'space hose'?) that would constantly fire Venusian gas towards Mars. It would be an orbital (either conventional or as an orbital-ring space elevator) or very high altitude platform (possible with helium aerostats and solar powered turbofans) that would fire gas either in the form of the pressurized containers mentioned earlier (good for in-atmosphere installations) or straight up unprotected gas straight from the nozzle, a high-velocity narrow jet being fired straight into space.

From there I have no idea where to start...I don't even have my ideas for the 'space hose' solidified just yet. Still, I wonder how long it would take an array of mass drivers to terraform Mars, and importantly would the naked gas in Venus-Mars transit have issues with drifting away from solar influence?

If anyone would like to offer math of their own, or their own ideas on how to transport the gas, feel free!

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    $\begingroup$ Please pick one between science based and hard science. Per their description they are mutually exclusive. $\endgroup$ – L.Dutch - Reinstate Monica Dec 15 '18 at 14:46
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    $\begingroup$ If you search on this stack for "Mars magnetosphere" you will find more entries than I can link dealing with the issue of Mars losing atmosphere to the solar wind and ways to prevent that. $\endgroup$ – Willk Dec 15 '18 at 16:14
  • $\begingroup$ And then you will need to convert most of that carbon to biomass and oxygen or atmosphere will be toxic for humans and animals.. $\endgroup$ – Artemijs Danilovs Dec 15 '18 at 16:27
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    $\begingroup$ Rather than pressurizing the gas into containers, I’d recommend just freezing it into blocks of dry ice and throwing it at Mars that way. That lets you skip the hand-waved carbon containers $\endgroup$ – Dubukay Dec 15 '18 at 20:20
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    $\begingroup$ Remember gas dissipates. A space hose spraying a jet of gas will lose it to the vacuum of space. The solar wind won't help either. Hardly any will reach Mars. Even mass drivers will require containerized gas. You're back to big numbers of vessels transporting the gas. The numbers will be the same as your cycler containers. $\endgroup$ – a4android Dec 16 '18 at 7:17
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There is no such question "How long" in the situation, as you noticed that for yourself, starting with estimating values for one ship and moving to 100'000 and then considering an option for 2 billion of those.

The answer depends on - what do you have to complete the task?

And it also makes sense to get an understanding of the scale of the problem. You estimated the mass of a gas moved quite right, to create 1 bar of pressure it means it needs about 10t of gas per 1m^2 of the surface in earth case and mars case it needs about 3 times more(as gravity is about 1/3), and the total surface of mars is about 1/4 of earth.

So as you noticed that doing that with a teaspoon is quite a long process. so it rather how long it should take to make sense and from that, you deduce what you may need for that.

Launch window, and massdrivers won't free you from the necessity of following that, is about once a year(plus minus), for maybe abut few weeks of a month.

So if we think about transporting let's say 6e18 kg per 100 years, we have 100 cycles to do that and need to launch 6e16kg per each cycle in a period of a few weeks.

Hohmann Transfer maneuvers from venus orbit to mars orbit are 6.5km/s+5.3km/s

so energy spend on launching material in one cycle is (proportional to first manuver 6.5km/s) : 6e16 * 21.125e6

to do that in a week it needs about a square of solar panels or whatever about 39'000km x 39'000km. Generally, it is possible to accumulate that energy over a year, you have gravity based accumulator (the planet) and with 100% efficiency in all the process discussed, you may need a square with edge 5500km. Another one (and a little bit bigger one) you need to gain the energy you need to lift the 6e16kg from the gravity well of the veny, which is as deep as the earth's one.

So a number of ships and resources spent on their construction, is not only expenses to worry, and 2 billion ships maybe isn't that much, as let's say they are 10% of the mass they carry which can be easy, as it 0g environment most of the time for them, rockets which start from earth have better ratios. And it can be about the right number of them in the case, and it is something like 6e15kg of construction. World steel production per year is about 1.7e12kg, but we do not have a goal of lifting a mass equivalent of our entire atmosphere, to lift that in space.

moving atmosphere is a big task and you can't make it smaller by closing eyes on how big it is. You need to create an infrastructure of proper size on venus, around venus, and between mars and venus. For to provide the necessary energy for the task - lifting, processing, packing, launching etc.

The energy source you may need is a scale of K1, and on its own is about 1e15 in case you accumulate energy, and more if you do not.

Using carbon as for the construction of vessels which will contain the CO2 is a good idea, then you have a material you need to transport and the same material can be a source for construction material in the case, and it is possible to use carbon for the purpose.

Also then you can worry less about returning of ships, so as about second delta-v maneuver in Hohmann Transfer, which is quite big actually and makes sense to save it.

By making CO2 ice and make some reflective foil-like shell it possible to but the stuff in a collision with mars, what you need some msall correction engins attached to the thing.

Generally, the task is big, and it needs big enough means to make it so.

Transporting ice is viable and it saves a lot of efforts in thems of construction. Just streams are no go because of the launch window. You need a lot of energy and a lot of infrastructures hear venus. Making the stuff in 100 years is realistic if a right approach is chosen. Carbon as structural material so as carbon ice as structural material is a good thing in the situation. Massdrivers is probably the only viable option in the case.

Hohmann Transfer, Sun orbits

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