perfidy

The first two parts of this series are here and here.

In the first post, I discussed how we could quickly and relatively cheaply develop the means to launch people and large cargos into orbit. That is the necessary precursor to any significant endeavor in space. While the methods I outlined would reduce costs to orbit, they would not make them exactly cheap. But they would give us a ladder while others could work on building an escalator. The second post discusses, in broad outline, one idea for developing the life support technology that the Mars mission would require.

Once we have the first step under control, we can begin thinking about the precursors for a Mars mission: the ability to live, unsupported, in space for long periods; a ship that can get us to Mars; and the technology to live and explore on the Martian surface.

How do we get around?

There is much more research to be done on propulsion systems for a future Mars mission. Right now, the two best possibilities are Bob Zubrin's Mars Direct concept and nuclear fission rockets. Zubrin suggests that we send, in advance of the human crewed flight, unmanned gas stations to Mars. These automated facilities would land in a likely spot, and then use solar or nuclear-thermal energy to suck in Martian air and refine it into oxygen and rocket fuel. Only when the gas station signals that its tanks are full will the crewed mission depart. This is a very clever idea, because it does not require that we take every last ounce of food, fuel, water and air needed for the return journey all the way around. There is every indication that Zubrin's idea is feasible, but it would require some solid engineering effort to bring it into being.

The second idea is to use nuclear rockets. In this concept, instead of using the traditional chemical rockets we're all familiar with, hydrogen fuel is passed through an extremely hot, Uranium reactor core. The as the hydrogen passes through the reactor, it is heated and the expansion of the hydrogen gas provides the thrust. This type of rocket is more effective than typical chemical rockets for two reasons: 1, the reactor can operate at a higher temperature, yielding greater thrust; and 2, since only very light hydrogen is used, we need far less mass to get the same thrust compared to burning hydrogen and much heavier oxygen. The first experimental nuclear rocket, called the Kiwi, achieved a specific impulse of over 850 seconds. (Specific impulse is a measure of a rocket's efficiency.) The Shuttle Main Engine is among the most sophisticated and efficient chemical rockets ever built, and has a specific impulse of around 450. With a little effort, there is no question that we could develop nuclear rockets with twice the efficiency of the best chemical rockets.

Either way, the effect is to cut the fuel requirements for a trip to Mars, which makes the whole thing significantly easier to manage. While we research both methods, we can begin planning our first mission beyond the moon. To prepare for the Mars mission, we should have some experience with long duration flights. We can do a dress rehearsal of the Mars mission by mounting an expedition to one of the Near Earth Asteroids. These asteroids are small bodies of rock or metal that have orbits that cross Earth's. Some of these asteroids are very close to Earth, at least in terms of how much fuel we need to burn to get to them. Rather than a three-year mission to Mars, we can plan a one-year mission to an asteroid.

There are several advantages to an NEA mission. First, we get to test much of the hardware for a Mars mission on a shorter mission. Second, we can test the propulsion, guidance, system integration, and construction of our space ship without being held up by delays in either the life sciences or surface exploration programs. A shorter mission means that if need be, we could do the whole thing on canned air and food in toothpaste tubes if necessary - though obviously we would want to test whatever life support technologies have emerged from the lab described in the previous post. Also, we won't need to worry about complicated tasks like refueling on Mars' surface, aero-braking, etc., that a full Mars mission would require. Third, it will provide good science - asteroids are remnants from the formation of the solar system, and will tell us much about that history. Further, geological assays will tell us how easy it might be to mine or otherwise develop asteroids for commercial uses. All in all, it would be a good work up to prepare us for our ultimate goal of reaching Mars.

Whichever method - chemical or nuclear - the NEA mission will be both a useful test of Mars mission technology and skills and valuable in its own right for prestige and scientific gain.