Nuclear Propulsion

In my last blog post, I wrote about a type of propulsion that would provide extremely high fuel efficiency with the trade off of using extremely large amounts of electrical power. What I will be writing about in this blog is a crazy sounding method of providing thrust that is practically the polar opposite of the ion thruster.

This method uses hybrid fission/fusion nuclear bombs as fuel. The idea is that the bombs would be ejected out the back of an extremely large space ship with a bell shaped protrusion attached to a giant “spring” on the back. When the bombs reached the edge of the bell, they would be detonated, and the half of the matter/energy cloud that has “forward” momentum would hit the bell, compressing the spring so that the energy is not pushing the spacecraft all at once (which would be the equivalent to nuking it.

The reason that it cannot just be any bomb, but has to be a nuclear bomb, specifically a fusion bomb, is that the energy produced per weight of a nuclear fusion bomb has no man-made comparison. It is not just a fraction more efficient, it is millions of times as efficient. Plutonium, being 1.75 times as dense as lead, is quite dense, but the hydrogen used in the fusion part of the bomb is the lightest element in existence, and produces multitudes of the power as even Plutonium.

One obvious problem would be the manufacturing of the nuclear materials. This would be quite simple with minor modifications to any of the reactors from my previous blogs, or even current nuclear reactors. I am not going to say anything else related to the manufacture of nuclear bombs, because, well...

Another problem would be the bell structure. It would have to be light, otherwise you ended up where you started. It would have to be able to withstand massive temperature variance from the near absolute zero temperature of space to the extreme heat of the nuclear flash. It would also have to block the radiation from the nuclear blasts from the ship without damaging itself. And, of course, the shock waves from the nuclear blasts that would be its primary purpose. This is unfeasible with our current material technology, but perhaps in a later blog, I will discuss some materials that could be used to accomplish this, but for now, I am going to stay on the topic of space.

Ion Thrusters

In my last blog post, I wrote about an idea for a more efficient method for getting things into space. I also mentioned more efficient engine design with lower throughput. That is what I will be writing about in this blog post. The type of propulsion that I will be writing about will be an ion thruster. This type of thruster is only viable in space, it does not produce much thrust, but it uses only absolutely tiny amounts of fuel. It works by ionizing xenon and repelling the ions electromagnetically at extremely high velocities.

There is one main positive quality to this type of propulsion (high-five to whoever got that joke). This is the fuel efficiency. It is more fuel efficient because of the higher speed at which the working mass is ejected. This is due to Newton's Second law which is commonly shortened to F=ma, or Force equals Mass times Acceleration. This means that in order to decrease the amount of mass required (fuel), you would need to give it more acceleration. This is achieved by the electromagnetic acceleration. While the space shuttle's main engine had a exhaust velocity of about 4.5km/s, the ion thruster would have an exhaust velocity of about 20-50km/s, making it much more efficient. An example of an achieved efficiency with this type of thruster is the Deep Space 1 spacecraft, which accelerated by 4300 m/s with only about 74 kg of xenon.

There are also two major negative qualities to this type of propulsion (same joke). One of these is the fact that it cannot be used in atmosphere. The electrical fields and electrodes require a near vacuum to function. The second is the low thrust. The thrust of current ion thrusters range from 20 to 250 milinewtons, which is tiny compared to the Space Shuttle Main Engine's 2,279 kilonewtons of force. The Space Shuttle Main Engine has about 9,116,000 to 113,950,000 times as much thrust.

Overall, in my opinion, the idea of low thrust, high efficiency engines should be explored more. In my opinion, the lower thrust is counted for in the less fuel it has to push and in the increased fuel economy. In my opinion, these types of engines could be how we power long distance ships for the future.

Rotating Skyhook

For my last blog post, I wrote about a problem with space travel. This problem was fuel. For this blog, I will be writing my opinion about an idea proposed by scientists in 1976 and 1994 for getting an object into space, which is the main reason for the need for so much fuel and for such powerful engines. This idea is the rotating skyhook.

The idea behind a rotating skyhook is a massive space station in orbit that has a tether, or hook, attached to it that rotates in the direction opposite of the orbit of the station. The orbiting station will allow the hook to stay suspended “from the sky”, hence the name. The opposing orbital spin and tether spin will have the effect of making the hook travel in an epicycloidal pattern around the planet. This means that the hook would be momentarily stationary relatively low in the atmosphere, allowing it to travel deeper into the atmosphere without drag, and allowing the object to be attached to the hook at very low speeds. It also will have the interesting visual effect from the ground of a hook on a tether suddenly descending vertically from the sky, slowing, stopping, and reversing to leave. The hook would lift the object away from the planet and accelerate it so that when it is the farthest distance from the planet, it would be moving very fast, allowing it to enter orbit or leave the planet very efficiently.

There are some problems however. The force of lifting the object into orbit would have an equal and opposite effect on the station. This means that every time an object was lifted, the station would move to a lower orbit. This is not as bad as it sounds, the station could have a small amount of thrust over a large amount of time, balancing to the force to lift the object. This can be achieved by more efficient but less throughput propulsion methods that I will be writing about in some upcoming blog posts. The other problem is that the station would have to be many multiples of the mass of the object being lifted. The tether would also have to be very light and strong, but nothing past what we are capable of. These two problems would lead to an extremely large cost to build.

Overall, in my opinion, this is one of the less outrageous methods of getting to space more efficiently. I feel as though the costs would be massive to build and require cooperation of nations, but that the benefits outweigh the costs.