So used to the idea of safety on Earth we are, we seldom think about its vulnerabilities. Doomsday prophecies from time immemorial, the recent Mayan scare, predicted asteroid hits…we haven’t seen the last of them and the threats and predictions will continue. At any random moment, an asteroid, comet or some other unwelcome extra-terrestrial material can barge into our home, safe home, Earth and wipe out all that is there, and will be, in one debilitating stroke. The worst case scenario is a neutron star* spinning its way to us. It’s the worst case scenario because “you cannot blow it apart, you cannot steer it off-course, you get out of its way or you can suffer the consequences of being in its path”. So, in this most extreme of scenarios, where we have no choice but to escape for our survival, can we really evacuate the Earth with the technology we have now? This is the answer we seek in the 7 part series, The Ultimate Escape.
The first question that would arise is—where do we go when we evacuate Earth. The nearest Earth like planet, where the scientists place there safest bets is the star system around a star called the Bernard’s star. The problem—it’s a little less than 6 light years away. Imagine taking a little more than 7 round trips around the earth along the equator in a second. Travelling at that speed will take us 6 years to reach the planet. It’s going to be 40 trillion miles away. We obviously cannot use the present space shuttles considering the fastest man-made object in space is the voyager craft which travels at 0.006% of speed of light. We need to find a method of propulsion that would take the craft to a considerable percentage of speed of light.
The very basis of “propelling” something is Newton’s third law: every action has an equal and opposite reaction. Conventionally, when a rocket is launched, the exhaust from the chemical combustion of fuel is shot out of the rocket and the reaction force propels the rocket. Thus, the faster you can shoot out the material, the faster you travel. But for our new spacecraft, we cannot use this way of chemical propulsion. To achieve really high speeds, you need to shoot out materials faster which would mean more fuel. But if you use more fuel, you would need to shoot out materials even faster to propel the space craft with the extra weight. This is essentially a “cat chasing its tail scenario”—the more fuel we use, the heavier it becomes, the more fuel we need to move the space craft!
An entirely different idea for propulsion is the solar sail. Just as the wind drives a sail boat on the seas, a solar sail can drive the space craft in space. The only difference is, in a sail boat, it is the reaction force of the sail on the air molecules as they strike the sail in the form of wind that impels it forwards. In case of the solar sail, it is the radiation pressure—the reaction force of the photons in form of solar energy—that drives it to very, very high speed. The problem however is that as the craft moves farther from the sun, the solar intensity decreases, and hence the increase in speed goes on decreasing so that by the time the space craft reaches the orbit of Neptune, it does not acquire sufficient speed to cover the rest of the distance to the destined planet in a feasible time.
A solution that might appear to be straight out of science fiction is the use of anti matter—mirror image of matter. When anti matter and matter come into contact with each other, they annihilate, releasing energy equal to 10, 000 times the energy obtained by chemical combustion. However, this energy is extremely difficult to control and can be contained only by strong magnetic fields in a vacuum chamber.
The most feasible answer is, surprisingly, not new. The idea is to propel the space vehicle by nuclear bombs. If big plates of shock absorbers are fitted to the back of a large space craft and nuclear bombs are exploded at some distance behind the shock absorbers, the pressure would accelerate the space vehicle to high velocities. The space craft can achieve speed equal to 7% that of light with continuous such explosions every 3 seconds for 10 days. This idea called project Orion is 60 years old. A working model was made and it was a success. However, nuclear ban treaty was introduced and the research was suspended. We can just pick up the research from then and design our new propulsion system.
Now that we have found a way to reach our destination, the next important thing to consider is the conditions inside the craft itself—at the speed achieved with the help of our new propulsion system, it will take us 80-100 years to reach the new planet Earth2. Gravity, light, air, water and food are what we need.
(The article is based on a National Geographic series: Evacuate Earth.)
*When a star much more massive than our sun (more than 10 times the mass of the sun) runs out of its fuel of hydrogen, its outer core collapses causing a supernovae explosion, hurtling colossal amount of matter at enormous speeds. The core that is left behind is extremely dense and made of neutrons. Barely 10 kilometer in diameter, even one spoonful of this matter would weigh as much as Earth. Its immense gravity tears apart and pulls in everything that comes into its way.Share this post