"We take Sabatier reactors with hydrogen as feedstock to run a basic exothermic chemical reaction process to produce methane (CO2 -> 4H2 -> (CH4 +H2O). This provides us with water and fuel. We then use electrolysis to produce oxygen and recapture some hydrogen from the water to cycle back into the system. We now have methane and oxygen."

They did this in Ben Bova's book on Mars and "As It Is on Mars". I don't understand how it works. You still have to bring the H2 and some energy source capable of producing electricity for electrolysis. The only thing Mars provides is the the CO2. I guess it doesn't take that much H2, and you could have some small nuclear reactor doing the electrolysis.

It's a good point that they could send this to Mars, get telemetry on how well it worked and only launch humans to Mars if the return vehicle is ready. I suppose that's obvious to anyone in the space program.

So why don't they do it? Is it that probes are cheaper and some people believe sending humans would just be an emotional gesture that would not actually get more science done than sending multiple probes?

Wow! another comprehensive link from Wikipedia. Not the most rigorous scientific source, but interesting.

Yes, lower gravity on Mars helps departure. Re the other point, unfortunately it does not work like that, unless you are stationary, as once on Mars they have the orbital velocity of Mars so requiring the same energy whether they want to depart inwards or outwards relative to the sun.

You are certainly overgeneralizing here. A "backup" is not Malthusian but rather a disaster preparedness scenario. Malthusian is running out of resources by growing to more demand than exists, not said resources (for example) getting destroyed.

There is a difference between how you seem to be using the phrase "rational argument" and how you may be using it. If you ask me why I climb a mountain and I say because it was there and I wanted to, that is a rational argument. It was in my self interested because I'd rather do fun things than not, am happier when I do so, and so I did. Whether you accept the reasons as "good enough" is a personal choice for you, but that choice does not invalidate the argument itself. You can think climbing a mountain is fun, but that simply reflects your conclusion not the argument itself.

Now, to answer the question I think you are actually asking: *why* go?

Part of scientific exploration and discovery is the collection of data and performing experiments. A key portion of analyzing data is obtaining a broad enough sample size. Our current planetary sample size is one. Essentially, on a larger scale our geological knowledge is an anecdote. Now, it is entirely possible you do not consider advancing scientific knowledge and understanding a goal worthy of effort, but that does not mean it is irrational.

Another reason is expansion of markets and human capability. While I am nowhere near agreeing with any Malthusian argument, it is not realistic to think or assume that while we *can* continue to populate at higher and higher densities that we all *want* to live in high density cities. Thus I find it rational for those who do not want to live under increasingly dense cities and resulting side-effects on nearby areas to be able to choose to go elsewhere. This is reflected in historical and modern history by those who choose to not live in cities today.

Put me in a high density setting with no escape options and I am not a happy camper, nor do I play well with the usual results of such a setting. It is my interest, as well as yours, that we are not in that setting together.

If we want to establish any serious level of spacefaring, Mars is the best bet from a purely rational view. When looking at transportation technologies outside of those currently the realm of fantasy, you have to consider the mass budget. A standard way of doing this is to compare "delta-V" and "mass-ration". The former is how much change in velocity is needed (i.e. how hard you have to hit the thrusters", while the latter is how much mass the vessel has fully fueled compared to it's dry weight. With that explanation in mind, I'll show you why Earth based operations are a last-choice option.


From Martian surface to low orbit: 4.0dV with a mass ratio of 2.9.
For Earth: 9 and 11.4

Big deal, right?

Now let us look at other destinations in our solar system. How about to the surface of Earth's moon.
From Mars' surface: 9.4 / 12.5
From Earth's surface: 15 / 57.6

Yes, it is takes less energy to put a man on Earth's moon from Mars than it does from Earth. And it isn't chump change either.

How about mining ye olde asteroid belt? Let us consider Ceres as many, if not most, proposals about doing so call out Ceres or similar ones.

From Mars' surface: 8.9 / 11.1
From Earth's surface: 18.6 / 152.5

Again, Mars is the clear winner here. But what about the return trip? After all that is the path of the cargo, yes?

To Mars' Surface: 2.7 / 2.1
To Earth's Surface: 4.8 / 3.7

Any transportation scheme we come up with which is mass sensitive favors Mars. Even if you consider nuclear-electric proulsion, Mars still enjoys a 7X advantage over earth. Based on the physics of space travel as we currently know of them, Mars will be the economic hub of a spacefaring human race. Why? Because doing things more efficiently, cheaper, or with more opulence at the same price level is how we accomplish things and advance the state of man.

This also applies to manufacturing of space vessels, such as is referenced in another post on "building the Enterprise". We won't be building that in Earth orbit. The answer to why is simple: it is far cheaper. If you want to build a vessel massing 150 megatons, you aren't finding that mass laying around in orbit, you are importing it from somewhere.

Said somewhere will be planet-side or from the Belt. Now think back to the figures above. Where will it be cheapest to push that mass from? Mars, once again.

Once we've built the tether relay to handle the delta-V of interplanetary travel, the costs will drop even further. But again, that material will not be coming from Earth.

You don't have to be a Malthusian to want to use less resources to accomplish a goal - that is simple efficiency. You don't have to accept the Malthusian argument of overrunning resources to understand that the existence of resources on Earth doesn't mean those who control them are willing to part with them. If some entity controls a crucial resource and will not do business with you, you must find new sources - unless you're a looter. It may be presumptuous but I don't assume we are looters here.

In many ways Mars is richer than Earth in terms of resources. Why not go to where more sources of materials are? That seems to be more of a Looter style argument - "don't develop more resources" - which if acted on would create an artificial Malthusian scenario.

I would also assert there is a case to be made that humanity needs frontiers. Yes, America's free society compared to the rest of the world in the era between the Civil War and the first World War was a significant factor in our technological and industrial advancement. However, it was the frontier nature of the country which provided the fertile ground and even a need for the innovation to be born.

We are rapidly outpacing our terrestrial frontiers - by simple progress and by legislative fiat declaring sections of continents, and even an entire continent, off limits. Even the ocean is becoming more and more off-limits. As we lose our frontiers our innovation will shrink. There is a breed of man which must have the frontier. By nature of not being one, you may not understand it. That does not, however, mean your lack of vision or understanding constitutes these reasons as being irrational.

Your argument about government is a strawman. We are not currently heading to Mars on taxpayer dime as the government isn't currently going to Mars. Robot toys aren't considered us going as we aren't *going* anywhere. The notion of us "doing science" with robotic rovers is a fallacy. It is woefully inefficient. Single manned mission to mars of even as little as four people would accomplish far more than all RoV missions to date.

To explore a planet you need planetary mobility. Yes, that seems obvious. Yet proponents of excluding human exploration for their vastly inferior methods seem oblivious or willfully ignorant of that basic fact. If you devise a ratio of cost-per-explored-area (feel free to use square meters, miles, acres, etc.) you'll find that done is a simple and direct method (i.e. not the enterprise, moon base, or other options - in other words the same way robots are done), you'll find the cost favors human exploration over robotic.


Whilst I am against the government running the show for space exploration, I must disagree with your assertion of "freedom can't be bought that way". It absolutely can, and has been. It was governments which paved the way for the Americas to be explored and settled. Just to be clear I am not arguing government should do it today, simply that history counters your claims.

Freedom of association by building your own settlement is freedom. However, you will not be building your own ships or you the initial colony infrastructure. You will be purchasing that from someone. Buy your transport from Elon Musk, and your settlement starter kit from me, then do whatever trade with other people and settlements you want. ;)

The magnetic field isn't a problem given the short duration of exposure. Thus it isn't worth it to build a ship that size. The radiation increase is far too minor for anything of this scale.


The method I speak of isn't a quick and dirty mission, but part of a larger strategy to build a perhaps less sexy but orders of magnitude more achievable system.

We didn't start with cruise liners and 747s for many a good reason. We didn't begin westward expansion by beginning with railroads, but rather later - one the economy and demand was there. I think the cost estimate for what you describe is very low given the lack of supporting technology, experience, and expeditious implementation.

Before you could even get, to borrow a phrase, the keel laid for this ship we'd have a fully running colony and likely be mining an asteroid or two and possibly building a tether relay. :)

Someday we will build the enterprise, and it will be a glorious event. But it will be built at Mars (as it should be ;) ) instead of for the purpose to get there. :)

See the resources I listed, particular the Zubrin books as they are the most detailed yet accessible. Something most don't realize is the existing space industry is far, far larger than is generally discussed.