Getting There and Back
Okay, we are going to dig into this topic, because getting around in space is so difficult that everything depends on how well that goes. To compare colonizing the Moon with colonizing Mars you have to understand all that is implied by the fact that every ounce of stuff you bring with you requires 150 or 200 ounces of other stuff in order to do the bringing. Yet you are going to a place where there is nothing of all the stuff you need to survive, not even water, not even air. The undertaking needed to establish a permanent base in either place is so humongous, you have to be reasonably confident not only of success, but that it will be worth the many, many billions of (insert monetary unit of choice) sunk into it. That money is entirely what has determined the course of space exploration over the decades. The argument for Mars boils down to the idea that there are ways you can really save on costs once you have the infrastructure in place. You can take advantage of the carbon dioxide air and the water permafrost in the soil to do this. Mars fans figure that will be all it takes, then people will line up to go live on a cold, isolated, alien world in great enough numbers that they at least don't go broke.
The Moon orbits the Earth and so it comes with the handy feature of being close by, always about the same distance from us, and a nice big target. Saying Mars is much further away just doesn't do the issue justice. Mars isn't just far. It is out there whipping around in a way even Isaac Newton said made his head hurt.
The planets are achingly, crushingly far from us and moving at high speed. The relationships between them are endlessly changing and really very complex. Each planet moves at its own speed, determined by its distance from the sun - about 30 km/s for Earth, 24 km/s for Mars. Their orbits are slightly oval so they slow down when they are farther from the sun and speed up when they are closer. Those ovals also rotate, tracing out a Spirograph shape over the course of many orbits. Each planet's orbit has its own little tilt from the plane of the solar system, too. All of these things need to be taken into account when you plot a trajectory between planets, and thus no two trips will ever be exactly the same. Now for the key point. Because of the gigantic distances and speeds we are talking about, you have to launch for Mars when it is in the right place. That only happens once every two years. If you go to Mars, unless you head back immediately there is no way you will be returning in less than two years. If you miss a launch window, it will be another two years until the next one comes along.
So this would be the time to ponder the fact that rockets are basically gigantic precision engineered cans of fuel with a few other bits on the ends. A rocket capable of landing on Mars will deliver about half of 1% of what it weighed at launch to the Martian surface. 90% of its weight on the launchpad is fuel. Then how do you get back from Mars, if 1/200th of what you started with is left and it took 180 times that much just in fuel to get you there? By building huge and junking almost everything along the way.
First, Mars ain't the Earth. It only has 2/5ths the gravity and 1% of the air. Now only about 80% of your ship needs to be fuel in order to get to orbit. Second, you will have been shedding parts of your rocket ever since first leaving the ground on Earth - after those parts shoved thousands of tons of fuel out their flaming butts creating smoke columns kilometers high. When the first stage separates after launch, it will have weighed empty as much as the ship that finally lands on Mars. Interplanetary rockets are basically a series of complete rockets all stacked on top of each other like vertical Russian dolls. In fact, when you leave Mars you will still be on a stack of three rockets - the two stages it takes to get to orbit, and one more to head to Earth. Together with the four stages it will have taken to get you to Mars, you started with 7 rockets all in a stack.
The mini-ship you have left will be just big enough for you, the stuff you need to live, and a few exotic rocks. Stuff like rovers, power plants, shelters, and tools all get left behind - maybe 10 tons of assorted gear and 10 tons of waste (including all your bodily excretions, which will undoubtedly be examined in detail one day by future Martian scientists seeking to understand the early days of their culture). Okay, so you have 0.5% of the mass of the original rocket left to get you back to Earth (minus the 20 tons that stays on Mars). 80% of that is fuel, about 3/4 of the rest is the ship itself and all its on-board systems, and 3/4 of what is left after that is food and water for you 4 crew members. Then there is you, and some rocks. Let's say that critical last bit weighs a ton - because seriously, for all that work you better bring back a decent haul of amazing rocks. Shall we work back through that tally to see how huge a rocket would need to launch from Earth to deliver all that stuff? Before listing the answer, let me say this is an extremely stripped down version of such a mission - it includes no spare parts, emergency rations, or fuel safety margins, and is a rather cramped set-up for four people a million miles from home for over two years. Launching it would take a rocket weighing 16,800 metric tons. It would be over 5 times the size of a Saturn V, the largest rocket ever built.
Yikes, right? There is of course a better way. You launch a bunch of rockets over time, and they stockpile stuff on Mars before you get there. Far better still, there is the clever idea first floated by the Mars Direct team in the 90s - manufacture the fuel you need to get home right on Mars. Start with some hydrogen brought from Earth, suck the carbon dioxide air into an automated mini chemical plant, and let it sit there churning out methane all through the mission. Awesome. NASA more recently proposed manufacturing liquid oxygen on Mars too, in a similar fashion. (In space you need to carry with you all the oxygen that's needed to burn your fuel.) Right there, you've saved like 3 Saturn V's worth of weight needed to launch from Earth. Now our example mission could be done with 3 Saturn V's, including safety margins and a bit more elbow room. Of course, there are no more Saturn V's. And you really need to have something that big.
So SpaceX is working away at creating a rocket that would 'make the Moon rockets look small'. (I vote they call them Krakens). Their engines will run on methane and liquid oxygen so they can use Martian home-brew. That makes the long term goal clear: once you have set up a supply of water you can electrolyse to get its hydrogen, you can stop bringing that from Earth. All your propellant would come from Mars. The hydrogen bit might be tough. But the rest is straightforward, relatively. If SpaceX booster stages attain reusabilty on Earth, such stages on Mars will be veritable work-horses in such flimsy air and low gravity. So assume there will essentially be shuttles on Mars capable of going back and forth to orbit possibly hundreds of times. Then add in automated fuel manufacturing plants on the surface just pumping away, waiting for ships to arrive with empty tanks. In that situation you could make ships with truly buxom tanks, just huge. And that changes everything. After all, the main ship (can we call it the mother ship?) would never need to land - it could be loaded by shuttles at either end of its trips. On the Mars end, shuttles could take as many trips as necessary to ferry up fuel from the surface, on the Earth end, Dragon capsules could deliver cargo and crew. The fuel for returning to Mars would already be on board. That would be one sweet set up. With that much fuel, you could extend the period when you can launch between the two planets somewhat, and shorten trip times a bit too. It makes the whole thing seem doable.
Of course you have to get to that point, of having all that infrastructure. That takes a lot of doing. Note that no payload weighing over a ton has ever been landed on Mars. Rough landings can ruin a lot of well-made plans. If the process of decelerating from a speed of 5 km/s to a soft landing goes slightly less than perfectly, your stuff is going to get dinged up more than simple hand tools operated from within a space suit can fix. Which will be your only repair option, assuming the beings needed to operate the hand tools survive. 5 km/s is a little hard to appreciate without experience. Imagine yourself on the sea looking at the horizon. Now imagine moving so fast you reach that horizon in a second. That is how fast we are talking about. Spacecraft come in at 8 km/s when they are returning to Earth from low orbit, but here, with good heat shields and a stubby shape, the air slows them down enough to land safely. You can't do that on Mars. There you have to do a powered landing, firing rocket engines into the screeching wind so exquisitely you pause in mid-air near the ground, and then plop the vessel down. To get something like colonial transport going, you would need to do that flawlessly maybe 10 or 12 times over probably 3 or 4 launch windows, mostly cargo ships without crews. Then you'd have your gas station on Mars and enough basic infrastructure to start flying a small bunch of semi-ordinary people out there. The undertaking is so daunting you have to work under the assumption you will have at least one complete disaster.
Major achievements tend to be like that. It certainly isn't a reason not to do it. The reason not to do it is the Moon is such a vastly superior place to put the first colony. That, and the fact you will be able to do the same thing even better if you wait until the Moon colony can back you up. In the long term there wouldn't even be any time lost, because when it comes to shipping vast quantities of building materials and machinery, the Moon is your best friend. You could arrive on Mars in style .
The big difference between going to Mars and going to the Moon is time. About 8 months to get to Mars, 3 days to get to the Moon. Wait, haven't i mentioned that yet? Yeah, 8 months in space. Each way. 6 months is the best you can hope for, if you have the fuel to go faster and Mars is in the right place. So bring all the personal electronics you can. They are the best remedy for cabin fever to come along since hard drugs. To step onto a ship to Mars would be to make a bigger commitment than stepping onto a ship from London to Australia in the 1700s. If you realized a few months after arriving that you'd made a terrible mistake and really wanted to leave, it would be over a year before you could. During that year you would grate on the nerves of the handful of hard-bitten pioneers around you, likely a lot. The chances of social deviance in a community like that are high. Once again the heart of the issue with Mars is human hearts, which just aren't made for isolation.
Meanwhile, at any time you wish to go, you can get to the moon in three days, or return to Earth in the same time. On the ship, your seat would probably be cramped but you'd be in zero gravity almost the whole time, which makes up for that. Also, if you have access to a window, the views would be awesome. Medical evacuations, emergency shipments, two-week tourist packages - all possible. Have you heard the phrase 'location, location, location'? It is hard to overemphasize how much it applies here. Investing 6 days in travel time and however long you want to stay is a totally different proposition than 12 to 16 months in space plus 2 years on Mars, mostly out of contact with home. So now it is time to talk about money.
SpaceX (and only SpaceX) may actually be capable of doing this Mars thing, and so it is their spritely band of visionary engineers who need to be convinced Mars is a bad idea before they actually do it. The world's various space agencies work away on their projects, of course, but none of them ponders colonization, and if they did, they'd probably target the Moon. Specifically, it is SpaceX CEO and founder Elon Musk who needs to be convinced the Moon is much niftier than he is giving it credit for. He has surely already had this conversation rather a lot without budging. Nothing about his past behaviour indicates he is disposed towards budging in general. The guy has a tendency to pick a direction and just go. But this could really be important. Musk has pitched the Mars colony as a way to 'back up the human race'. Then he carefully points out that he is an optimist, but still, you know, just in case. Just in case? Let's be clear here, he is defending investment in creating a Mars colony by saying that if something wipes out the entire human population on Earth, then having thousands of people on Mars would allow the species to carry on. Details beyond that are very fuzzy. Maybe we return on ships from Mars once the, um, radiation levels have dropped enough... or the biological warfare agents have expired... or the super-intelligent androids have learned to relax a little... Really, we are talking about potential threats a number of decades from now, and the world is changing mighty fast. There is no lack of people with prominent scientific credentials who fear this could be our last century. Spending vast funds to hedge against Apocalypse is certainly not the worst reason to spend money. (It would almost certainly be more honest to say he's doing it because Mars is really cool and he personally wants to go, but that's fine. He's not alone and after all, wouldn't the world be much better off if we were all a lot less concerned about making money?) The point is, it is a tacit admission that a Mars colony will never make money - so it is necessary to present the public with a reason to do it because it ought to be done.
A moon colony would make money. It would take a long time, but it would happen soon enough for the original investors to get their money back and even make some. Back that up with all the reasons to do it because it ought to be done and it is much more attractive. And there are a few. Hedging against Apocalypse? Sure. It might take longer for a moon colony to be truly self-sufficient, but not hugely, especially since it can look forward to a healthy income to help it along. Inspiring Earth so much it changes human culture, helping us blossom into the steward species we are so perfectly suited to be? Hell yeah, as argued earlier, and as we will delve into much further in later sections. Making space travel so, so much easier that any space project you can imagine becomes possible? Oh yes, your Moon base has you covered, they'll get you where you want to go. But that will come much later. First, broadcasting, film and tourism on the Moon works. The travel time and expenses are manageable once an efficient fleet of ships and their infrastructure are in place, and radio signals reach Earth in under 2 seconds. Globally the entertainment industry is approaching revenues of $2 trillion per year and tourism is at $1 trillion. Capture two thousandths of the market in each category and you have annual revenues of $6 billion. This seems quite achievable - if you do it right. Let's face it, NASA sucks at entertainment. Tell hot artists they can make productions ON THE MOON (if their project is chosen, they cede the rights to the Moon consortium, and accept only a small portion of profits). Then you'll see how amazingly entertaining the Moon is. Selling big-ticket Moon holidays? No sweat.
First, you need to send up the robots and the materials to make a roomy base. Most of this can be done in surprisingly low-tech ways, as space ventures go. We'll get to how under The Plan●. Main idea: it is amazing what you can do with enough feldspar and sunlight. Really, with those two things and the right equipment, you have glass, high-strength fabric and cable, and all your structural elements - beams, rods, bricks, panels and such. Plus you can extract oxygen as you make all those things, so you have air, and you can chill it to produce liquid oxygen, for use in rocket engines. The 10 or 12 flights discussed earlier, as being the minimum amount to start ferrying people to Mars with the intention that they then live there, would be enough to get that going. It's helpful that what you'd be shipping on those flights would be all robotic equipment. Nothing is coming back, and it doesn't need any food, water, air, or toiletries. It's going to need a lot of electricity and there will be challenges to running it from Earth with a 3 second round-trip transmission delay, that will slow things down. On the other hand, 12 flights to Mars takes 7 years just to get everything there, if you manage to send three ships per launch window. And you can't run equipment round the clock remotely from a comfy control center on Earth (hopefully also through the long lunar night with a power storage setup). The Mars version of this project would have only maybe 20 astronauts to do all the work, and a lot less equipment and supplies to do it with.
So if you are using hydrogen - oxygen rockets, which are a common choice for upper stages of rockets that fly only in vacuum, 4/5 of the mass of your fuel would then be Moon-made - the oxygen, which is the heavy part. Not as good as the all-homebrew Mars option, but not bad. At that point, you can set up a system of mother ships and shuttles, same as you can for Mars, though clunkier and more finicky because of the 1/5 hydrogen part that has to be shipped from Earth. Shipping hydrogen is difficult, and so is storing it, your system could take a big hit because of that. It won't set you back for long though. Give it another few years, and the ongoing expansion of the base will allow you to set up ore refining that makes it possible to start fuelling rockets with propellant based on aluminum and oxygen, or magnesium and oxygen. The ability to start mining the deposits in the deep shadows of the pole's craters could provide you with hydrogen from the moon itself, that is another possibility. Give it a few more years, and the possibilities multiply. Build a mass driver and start flinging things into space magnetically. Build big lasers and start powering your rockets from the ground by focussing the lasers on specially designed fuel tanks or ablative coatings. Fall in with an asteroid mining company and start bringing in ice and ore from the asteroid belt, because conducting such a venture from the Moon has many advantages. Use that to manufacture fuel. Any one of these things would vastly expand how much can be launched from and landed on the Moon, and because it is so close to Earth, the Moon would become the transport hub for everything buzzing around in space. Then you can colonize Mars with ease. And Venus. And build giant space stations. And gigantic motherships/factories that loop through the asteroid belt or out to Jupiter or Saturn between swings by Earth.
For all these reasons, to leave home, step out to the place closest to it, don't try to leap to a place far away. That place needs to come a couple of steps later.next - Being There