On July 31, 2008, the Phoenix Lander confirmed the presence of actual water ice on Mars. Not that we didn’t already know it was there, but the fact that the water is there, at only a few inches depth, means finally we can actually go there and USE it. This is a huge discovery because water is one of the most valuable resources in space. Not only can you drink it, or grow food with it, you can also separate oxygen from it and breath it, or separate hydrogen from it and BURN it as rocket fuel. You can also, with relative ease, combine the hydrogen with CO2 and make Methane. This can be done with an Sabatier reactor, which is essentially a semi permeable gas membrane. It can also be used as radiation shielding.

Liquid Gold

So, water is darn useful stuff, the beginning of a nearly self sufficient outpost on mars. Just add water! The confirmed presence of abundant reserves of water ice on Mars could factor significantly into a manned mission to Mars. For one thing, you can count on not needing to bring fuel for a return trip, it can be extracted easily from Mars resoucres.

The Bottom of a Deep, Dark Well

But, of course, the only reason it is so hard to bring the water with us from earth, where we have water in abundance, is the enormous cost of launching ANYTHING into space from earth. And the reason for THAT is the fact that we are the unfortunate inhabitants of one of the deepest gravity wells in the solar system. Well, to be fair, that’s nothing compared with those giants Saturn and Jupiter, but our main problem in reaching space is that anything we send there first needs to be accelerated to 9.7 km/s. and that’s just to reach low earth orbit (LEO). Escape velocity from the surface of the earth is 11.2 km/s.

Why Rockets are Exponentially Expensive 

Now, why is it that that is so darn hard? The answer comes from basic physics. Rockets accelerate a payload by burning some kind of propellant which is directed through a nozzle to produce thrust. The amount of thrust is simply related to the mass and velocity of propellant expelled, according to Newton’s third law: Any force is met by an equal and opposite force. So, expel propellant out the back of a rocket, and the rocket is accelerated by an equal and opposite force, simple physics. It’s a simple matter to compute now how much total acceleration you can get out of any rocket, based on the velocity and mass of the exhaust. This is known as the Tsiolkovsky rocket equation, which is the change in velocity is equal to the exhaust velocity times the natural logarithm of the initial mass of the rocket plus propellant divided by the final mass rocket, after the propellant has been expended (sometimes called the mass ratio).

DeltaV = Ve ln (m0 / m1).

Exhaust velocity is more commonly stated in terms of specific impulse, and the specific impulse of any rocket is directly related to the temperature of the rocket motor. The most powerful rocket motor ever designed, the shuttle main engine, generates about 450 seconds of specific impulse. This engine runs so hot it nearly melts the engine as it runs. Thi8s is the main problem. More energetic fuels could be used, and the engine operated at higher temperatures, but at those temperatures, any material known to man would simply melt. So 450 seconds of specific impulse is more or less it. Unless you can change the laws of physics, or find some material that is as strong as steel but doesn’t melt, you can’t do significantly better than that.

Now, plugging 450 seconds of impulse into the Tsiolkovsky equation gives us an exhaust velocity around 4.5 km/s. Which, working backwards, means that the mass ratio to reach LEO is 8.63. That means that, to launch a rocket to LEO, 88% of the initial launch mass must be propellant. That leaves only 12% for rocket plus payload. The actual rocket itself (tanks, motors, and structural support) general makes up 10% of the total mass, leaving just 2% of the mass as payload. And that’s assuming 450 seconds of specific impulse, which is actually quite high. No rocket motor has ever been developed which can deliver the total thrust to weight ratio of the SME at better specific impulse.

Fountains of Paradise

This is why sending anything into space is so ridiculously expensive. For every kg of material sent to space, you need 49 kgs of rocket and propellant to put it there. And rockets are expensive. That’s where the space elevator comes in. Nova science did a spot on space elevators this week, if anyone saw it. The idea of a space elevator is to anchor a cable in geosynchronous earth orbit (GEO), then simply lift cargo into orbit just like an elevator. If you release the payload at the geosynchronous point, it will naturally fall into a geosynchronous orbit itself. Payloads can also be relapsed just below geosynchronous, and they’d fall into an elliptical orbit with whatever perigee you want, even dipping as low as LEO if you choose. In practice the cable would actually extend BEYOND GEO, and if you could also release payloads there they go into elliptical orbits out beyond GEO, up to a lunar transfer orbit and even earth escape orbits. You could even place a payload on a clean trajectory to Mars by releasing at just the right point. Sounds great, but the problem is building a cable at least 35,786 km long (that’s the distance to GEO) or longer, if you want to extend beyond GEO for balance, which in practice you have to do. Just imagine a simple steel cable 35,000 km long. It would in fact snap under its own weight. The cable needs to be tapered so it is thickest at GEO, where the load is the greatest, and thinnest near the earth’s surface, but even still steel simply isn’t strong enough to build a single cable to lift anything 35,000 km +. The problem is tensile strength. Steel has a tensile strength of 2-5 GPa. But to build a space elevator on earth, we would need a lightweight material with a tensile strength between 65 and 120 GPa. Turns out carbon nanotubes, if they could be made into a cable 35,000 km long, might actually be strong enough to actually do this. And, some progress actually has been made in turning a carbon nanotube into a long cable like this.

So, the problem is earth just isn’t a very good starting place for space travel, and gravity is the problem. 9.7 km/s just to reach LEO, which means even the most advanced materials and technology give can deliver a payload of just 2% of a rocket’s launch mass into orbit. And, space elevators look great on paper, but imagine lifting a cable 35,000 km long into orbit, even if we could actually make a cable strong enough not to break under it's own weight.

The Economic Advantages of Mars

What about Mars? In addition to having water, Mars is also small compared to the earth. It is physically smaller in diameter, and has a surface gravity just 38% of earth’s. The Delta V from Mars' surface to low mars orbit (LMO) is just 4.1 km/s. So, the same rocket that can deliver just 2% of it’s total launch mass to LEO on earth, could deliver 30% of it’s mass to LMO. And, running the rocket motors at 450 Isp means they are very very hot. They have to be to achieve that kind of efficiency. What if we cooled them down and ran at just 350 Isp. With less wear and tear on the rocket motor, maybe we could use them (and the spacecraft) more than once. In other words, we could build a reusable, single stage to orbit (SSTO) vehicle, the holy grail of space flight, on Mars! At 350 Isp, the mass ratio to reach LMO is just 3.23. Put another way, 69% of the launch mass is propellant. Assuming 15% of the spacecraft weight is the spacecraft itself, that still leaves 16% for payload, still 8 times more than a SINGLE usage rocket on earth. The SSTO Mars spacecraft could use aero braking, parachutes, and a rocket assisted controlled landing, similar to how Phoenix itself landed.  And it could do it again and again.

What about a space elevator on Mars? Mars synchronous orbit (MSO) is much lower than GEO, just 17,000 km, plus the gravity is lower to begin, so the tensile strength of a Mars space elevator cable would need to be much less than on Earth. In fact, on Mars a space elevator could be built out of “normal” high tensile strength materials like Kevlar or carbon fiber, maybe even ordinary steel.

The Boundless Bounty of our Solar System

So, we can see that space travel on Mars is a lot easier than it is on Earth. The same is true of a lot of smaller bodies in the solar system, many of which have some interesting physical properties. The moon, being closest to the earth, has long been seen as a potential stepping stone to space. Lunar regolith often includes oxides of useful metals like Aluminum and Titanium. So, in addition to being able to extract the oxygen itself, you could also get the metals. Ceres is another interesting body. Its conveniently located in the asteroid belt, and is quite likely an icy body, with significant resources of water and perhaps other volatiles. Jupiter has many icy moons, rich in water ice, the “blue gold” of space travel. And then there is Saturn, with moons like Titan. Titan is an interesting body itself, the moon with a thick atmosphere, plus organics (methane and ethane) and Nitrogen. But Mars is the real winner. Relatively close to the earth, and near enough to the sun that solar power is still practical. Plus the moons deimos and phobos likely have large reserves or water ice, which our own moon most likely lacks. But down on Mars, there is iron ore in abundance, its what gives the planet its red color, plus CO2 and of course water ice. CO2 is another key element, which can be used as a source of carbon to synthesize methane (by combining with hydrogen). Methane itself can be then reacted to form base polymers which lead to various synthetic plastics. And, gravity itself may be a boon. The 38% gravity on the surface of Mars is probably enough to stave off the worst effects of weightlessness on the body. After all, the human body cannot withstand weightlessness indefinitely. Bones and muscles deteriorate without gravity.

So Mars seems to have it all. A low escape velocity, yet enough gravity to prevent bone and muscle atrophy. Water, iron, a thin atmosphere of CO2. Enough sunlight to be an effective power source. Even dirt has its many uses. And, although it takes 6 months or more to get there on a reasonably efficient transfer trajectory (9 months for a Hohman transfer, the most efficient possible), it takes surprisingly little energy. Once you are in LEO, getting to Mars requires only an additional 3.8 km/s, using aerobraking to achieve a capture orbit (and even landing). That’s less than ½ the energy to get to LEO in the first place. And, from the LMO all the way to LEO takes again only 2.1 km/s, again using the atmosphere at earth to slow down and capture into LEO. So, including the 4.1 km/s to get from Mars surface to LMO, that’s just 6.2 km/s all the way to LEO from the surface of Mars.

Location, Location, Location

In fact, Mars is ideally situated to become the prime real estate in the solar system. Once we can overcome the pull of our own voracious gravity well, like Sisyphus with his rock, we will find the solar system will open up to us. Building first a small outpost, eking out a meager existence with solar and nuclear power brought from earth, but using water, dirt, and maybe iron collected locally, over time our presence on Mars would grow. Soon we would be able to build glass, iron, and steel from local resources. Harvesting CO2 from the atmosphere, we would then synthesize Methane. As the outpost grew into a small colony, more of what we need on Mars could be made from local resources. Methane would form the basis of plastics. Sand, rich in silicon, can be used to make glass.  With plastic, glass, and steel, you can make just about anything.

The Human Conquest of Space 

The colony on Mars would soon reach a critical mass and begin to grow exponentially. Slowly at first, maybe only 10% per year. But even at only 10% per year, an outpost of only a dozen humans on Mars would grow to a city of more than 100,000 in less than a century, with parallel growth in industrial capacity. We would build factories on Mars. If the same growth rate applied for another century, there would be 19 billion people on Mars, but they would not be bound to one planet like we are on Earth. They could move easily between Mars’ surface and the rest of the solar system.

Ceres would become a major industrial center as well, in the middle of the mineral wealth of the asteroid belt. M type asteroids, made of nearly pure nickel and iron, with trace impurities like silver, gold, platinum, and any other metals you can think of, would be there for the taking. Jupiter and even Saturn would be within easy reach, with the vast wealth of water and volatiles on their icy moons. Other places would be visited too. Mercury, so close to the sun that only 2 spacecraft have ever visited there, would be a natural hub for solar energy. Energy, perhaps stored as liquid hydrogen and oxygen, and shipped out to the colonies on Ceres and Mars. Or, maybe even factories orbiting the sun directly, between Venus and Mercury, choosing the optimal orbits based on their power needs, blocking the sun with solar arrays that act as great sunshades, providing power for whatever industries the future may dream of.

Just two centuries after establishing a self sufficient outpost of a dozen people on Mars, we would have conquered the entire solar system. Then, we would be on the very doorstep of the universe, poised on the first rung of Jacob’s ladder.