Going Interstellar (collection)

Forward, in his Air Force report, expresses the opinion that antimatter engineers will store frozen anti-hydrogen rather than antiprotons or an antiproton-positron plasma. A ball of anti-hydrogen with an electric charge could be levitated using electric fields. Care must be taken, though, to adjust the field to compensate for the starship’s acceleration. And some mechanism must be developed to cleanly remove anti-hydrogen atoms from the ice ball and transfer them to the reaction chamber without prematurely and disastrously annihilating them.

The levitated ice ball concept might be workable in the frigid wastes of interstellar space. But frozen anti-hydrogen might be very hard to store in the much hotter environment of a near-Sun antimatter factory.

We are a long way away from being able to produce and store the amounts of antimatter needed for an interstellar voyage.

Antimatter Rockets

Antimatter technology is in its infancy. But as it matures, its application to space flight is a natural outcome. Figure 1 presents major features of an antimatter rocket. The payload rides ahead of the fuel tanks. The fuel consists of normal matter (probably hydrogen) and antimatter. Antimatter is fed into an “annihilation chamber” where it reacts with normal matter. An electromagnetic nozzle is used to expel the charged particles as exhaust.

Figure 1. Artist concept of an antimatter rocket. (Image courtesy of NASA.)

Let’s say we desire an interstellar cruise velocity of 0.09c after all the fuel is expelled, which allows a ship to reach Alpha Centauri in about fifty years (not counting the time required for acceleration and deceleration).

If our starship has a mass of about one million kilograms, then it would require twelve thousand eight hundred kilograms of antimatter. The hypothetical Mercury-based antimatter factory discussed in a previous section could produce this mass of antiprotons in about twenty-five years.

Instead of a crewed starship, let’s say we wish to launch a robotic probe with an unfueled mass of one thousand kilograms. In this case, only 12.8 kilograms of antimatter will be required! And if further miniaturization is possible, the antimatter mass required for an interstellar probe can be reduced still further.

We next consider the acceleration process. If the ship requires about 10 years to accelerate an average of about 10⁷ kilograms of matter will be converted into energy each second. The probe generates matter/antimatter annihilation energy at an approximate average rate of 10¹⁰ watts, roughly equivalent to that of a large city. The ship’s generated power level will be about one thousand times greater, approximating that of our entire global civilization! Antimatter propulsion is clearly not for the faint hearted!

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Further Reading