I think a better solution is nuclear propulsion since traveling to the outer system moons- even out to Neptune- simply cannot be done without it. Wasting time on chemical propulsion is just that; wasting time.

To Mars — .5
To Vesta — .86
To Ceres —  .4
To Jupiter — 2.6

Plus, Zubrin makes the point that modern astronauts would be much less isolated from home than has been successfully endured in many situations such as multi- year shipping expeditions. I think that the key is having large, even unshielded volumes to go to periodically.

Amen Brother!

Cyclers to Mars, our closest “habitable” neighbor planet take a couple years- these least energy merry go rounds are not practical simply because of the psychological limits of human beings. 14 feet of water for any large crew compartment, plus a tether system to generate artificial gravity works out to Battlestar Galactica size craft.

The faster you get there and back means a smaller crew compartment- means a faster ship. These least energy flight plans will not work going to the outer solar system destinations. Which is why chemical, nuclear thermal, and low thrust forms of propulsion are all worthless.
It is all about the bombs.
Thanks for the reply John. Please check out my new essay.
Regards, Gary

According to LCROSS results, lunar ice has about as much carbon monoxide as water (5.7% vs 5.6% respectively) and there is also ammonia in the ice. So in the process of processing the ice, you are getting the carbon and nitrogen useful for growing food. Tunnel deep into a lunar hill and you’ve got shielding. So shielding, oxygen, water, and food…that’s a fair ways to long-duration stays. Magnetically extract iron from the regolith, melt it with concentrated solar ice and now you can make the bulky structures. All of this stuff has use in cis-lunar space. So we’re making good progress to where we (e.g. Lifeboat Foundation) need to get in terms of a small, off-Earth self-sustaining colony.

BUT, I am with you Gary, that, after we are able to produce the shielding necessary for long-duration interplanetary travel, then we need to do exactly that. Once we establish a small self-supporting colony in one place, then we’ll have the skills needed to do it in many other places ever further out into the solar system which is something we need to do. Those would be the ultimate guarantee of the survival of humanity.

> “The cycler is.…too slow and only goes to Mars”.

There are a number of cycler orbits with different periods. I don’t know, but it might be possible to establish regular cycler orbits to various asteroids as well. As for “too slow”, instead of the pattern necessarily being frequent launches of single ships, instead it could be launches of numerous crew and supplies only, regularly every two years. It would be akin to occasional transatlantic voyages of large ships carrying large numbers of people. But also, trips could be more frequent if you use different cycler orbits. The beauty of the cycler orbits is that you launch the shielding only once and don’t have to come up with the fuel again and again, forever.

> Liquid Hydrogen…It is really bizarre stuff.

Yes, I understand that it just loves to leak. But given the that there is a lot of carbon monoxide in the icy lunar regolith, we could get around that problem by producing methane which is much easier to handle. Boiling points:
— LH = 20.4 K
— LOX = 90 K
— Methane = 112 K

The delta-v from Lunar orbit to C3 is about 2.3 km/sec. The isps for hydrogen versus methane fuel are:
— LH = 453 sec
— Methane = 368 sec
So the mass fractions of LLO to C3 are about:
— LH = 40%
— Methane = 47%
Although I’m no aerospace engineer, it seems to me as though transporting that much more to LLO when you already have the system in place to transport water for shielding wouldn’t be that difficult.

The cycler is.….too slow and only goes to Mars- which I do not think is a good destination.
Thanks for correcting me on the Moon and Ceres.

“The most efficient shielding material is provided by liquid
hydrogen. It shows the greatest attenuation of high LET
components with minimal addition of troublesome
secondary radiations.” — http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080013522_2008013354.pdf

Anticipating the obvious response, keeping hydrogen liquid could be accomplished using sun shades and/or solar powered condensors.

@ Gary “The only way to propel this much mass around the solar system is with nuclear energy”.

14 feet of water comes to just over 500 tonnes. The mass fraction for ion propulsion from LEO to C3 is about 15% = 75 tonnes. So, if we were to have the 130 mT SLS, then it would take about five launches to assemble enough mass and accelerate it on an interplanetary mission. Could this be an intermediate step?

Why don’t you find the Aldrin Cycler orbit as practical? What are your reasons?

Finally, I wasn’t aware that you wanted to start by shooting past the Moon, past Mars, and go for Ceres. Then, if you overcome the hypogravity with sleeper trains my question is, “Is this the earliest, lowest-cost approach to achieving the earliest self-sustaining, minimalist colony”?

I am not a believer in chemical propulsion except to get from the Earth to the Moon with an HLV. Once a base is set up near water the last thing we should waste our time on is making rocket fuel; chemical propulsion is useless for interplanetary travel.
The Aldrin Cycler is not practical IMO. First, Mars is a deep gravity well and for this reason it is actually NOT the place to go to set up a colony. Second, there is little or no protection from radiation. Icy moons in the outer system have low gravity and allow for antarctic type under ice habitats. They are the place to go and set up colonies using small nuclear reactors- and we will not get there with chemical rocket fuel. I would suggest Ceres as the first colony. Hypogravity debilitation can be remedied using “sleeper trains” in circular tunnels to allow small apartment living in 1G for half the day and the other half outside.
Thanks for the comment John.

Second, what about lunar-sourced water shielding and lunar ice-derived propellant to place the shielding into an Aldrin Cycler orbit?

Thanks.