A billion years in the future, our sun is going to expand and that won’t bode well for Earth. Life will be extinguished, continents converted to deserts and the oceans will evaporate. Eventually, the sun’s expansion will swallow the entire Earth. That’s the granddaddy of disasters, the inevitable, inescapable fate of our planet, to be torched by the very body that once sustained us.

 Smaller disasters could befall us long before the sun goes homicidal. Imagine a global ice age or a meteor impact like the event that wiped out the dinosaurs millions of years ago. In his short story, The Great White Spot, science fiction author Thaddeus Howze envisions a frightful global storm ushering in humanity’s demise. A more robust revisiting of the biblical flood.

            As I sit here listing world-ending scenarios, I gloat at those poor souls of centuries past. They imagined all kinds of Extinction Level catastrophes, but were resigned to the reality that there was no escape for humanity. Living in an age of advanced technology, it is much easier for me to visualize humans migrating from a doomed Earth to populate a distant, habitable world.

            While the thought may trouble me a lot less than a medieval predecessor who had no conception of humans traversing the stars, I have to reign in my 21^st century arrogance. At present the human race is still doomed! I’m still doomed! As a science fiction writer, crafting tales of human activity beyond Earth’s skies is easy as tying my shoes. But in real life, there is no spaceship on standby to ferry me to safety should a life ending apocalypse strike Earth. I’m reasonably certain no such spaceship will be built in my lifetime. Alas, I’m no different in my position as a sitting duck than that medieval sod.

            Should a spaceship be built, with all the necessities required to comfortably accommodate its human passengers, how would it be powered? Scientists and engineers have studied different types of spacecraft propulsion. Some ideas have reached the experimental stage. Others remain on the drawing board.

            Ion propulsion is one idea. An ion engine is powered by ionized atoms called xenon. Heated by an electric current to its present state, xenon is ejected out of a rocket, providing thrust to a spacecraft. Ion propulsion does not deliver the explosive kick of a chemical engine, but its fuel is indefinite. A spacecraft with an ion engine can travel for years. NASA successfully tested an ion thruster in 1998.

            A plasma engine operates along the same lines as an ion engine, but its power is greater. Super heated hydrogen gas fuels a plasma engine. Unlike ion thrusters, plasma engines have not been tested in space.

            Solar sails operate on the principle that an enormous sail can be propelled through space by sunlight. Scientists have theorized that firing lasers at a solar sail could accelerate the craft to a speed approaching light. The Japanese and Russians have experimented with solar sails. The results haven’t been stellar, but the development of this new technology remains in progress.

            The ramjet fusion engine is by far the most fuel efficient of proposed engines. It uses space itself as a fuel source. Specifically, the engine scoops up hydrogen atoms floating in space and heats them to the point of fusion, a nuclear reaction. It is this highly energetic reaction that propels a spacecraft. The ramjet engine remains in the realm of theory. Right now, engineers are trying to determine how best to derive energy from hydrogen atoms in order to maximize their use.

            Compared to the cutting edge marvels of ion, plasma, ramjet engines and solar sails, an engine powered by nuclear energy seems clunky and anachronistic. Such an engine channels a nuclear explosion out the back end of a rocket, providing thrust. Early tests of nuclear engines in the late 1950s to the 60s were not wholly successful. The nuclear reaction often breached its containment. Extreme heat from burning hydrogen was also a problem, leading to debilitating corrosion. The possible dangers of nuclear rockets range from contaminating fallout to the release of an electromagnetic pulse that inflicts massive damage on electronics. Of course I don’t expect a little radiation leakage into the atmosphere to be of any concern to the lucky devils evacuating a dying Earth. An EM pulse could be a different matter if the spaceship’s onboard electronics are not properly fortified.

            Whatever means of propulsion our descendants choose for their deep space journey, other issues must be addressed to insure humanity’s survival. Space is bathed in radiation. We are protected from lethal radiation by the Earth’s ozone layer. A spaceship will have to be more than sufficiently shielded to protect its passengers and crew from deadly exposure. Micrometeorites pose another danger. A pebble is a nonthreat…as long as its not coming at you faster than a speeding bullet. Micrometeorites are many times faster than a bullet and they have the potential to punch a hole through a space vessel.

            A spaceship’s hull must be impervious to this danger if the vessel is to avoid looking like Swiss cheese upon reaching its destination.

Additionally, there is the effect on the human body of being away from Earth’s environment for a long period of time. Unless the spacecraft has a means of generating gravity, humans will be unable to function in sustained weightlessness. Bones and muscles will atrophy to the point where humans will barely have the strength to move. Cardiovascular functions will weaken, immunity levels significantly reduced.

 In the distant future, my descendants may likely be living in a world where the means to travel beyond the Solar System is readily available. Whatever type of engine a future spacecraft will use, my descendants can rest well knowing they can escape a meteor, flood or an expanding sun. I suppose they’ll have a legitimate reason to gloat at their perpetually Earth-bound 21^st century ancestor. But I get the last laugh, because while they may be able to get away from Earth before a natural disaster strikes, an alien invasion is a different matter. You can’t escape hostile aliens. They follow you. Ha! Take that descendants!