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Future Spaceship Engine Designs

Batman

Not all those who wander are lost...
Joined
Oct 8, 2011
Location
40 lights off the Galactic Rim
Gender
Dan-kin
So, this thread is all about future spacecraft engine technologies (sub-light) likely to emerge in both the near and far future. While there are several other engine designs in the works, I’ve picked the ones (five in total) I think are the most interesting and most practical. Most of the topics/ideas/information presented here has been inspired by three books from theoretical physicist and technology futurologist, Michio Kaku. The books are “Visions: How Science Will Revolutionize the 21st Century”, “Physics of the Impossible: A Scientific Exploration into the World of Phasers, Force Fields, Teleportation, and Time Travel”, and “Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100”. The information below is largely a restatement of passages from the three books above.

The information below is very basic and is only meant to be a brief and simplistic look at the engine type.

Enjoy!

Ion and Plasma Engines:

The traditional chemical rockets NASA and other organizations have relied on to send us into space utilize powerful chemical reactions that produce sudden and dramatic blasts of superhot gases as their source of propulsion. However ion engines do not, and that is one of its virtues.

While the thrusts of chemical rockets are measured in thousands of pounds, the thrust of the ion engine is measured in ounces. In fact, on the surface of the earth, they would go absolutely nowhere. However, while they lack powerful thrust, they more than make up for it with surprising duration. They can operate for several years in vacuum of space (unlike modern rockets and shuttles which can only operate with fuel for a few minutes).

In ion engines, a filament is heated by an electric current, creating localized beams of charged atoms (ions) like xenon. These beams of ions are expelled out the end of a rocket, creating thrust that is certainly powerful enough to move even a large ship in the weightlessness of space. Instead of utilizing hot and explosive gasses, the ion engine rides on a thin but steady flow of ions.

In 1998, NASA tested its NSTAR ion thruster in space aboard the Deep Space 1 probe. The ion engine successfully fired for a total of 678 days (setting a record at that time). The Smart 1 probe, created by the European Space Agency was also successful, further strengthening trust in the abilities of this type of engine. While ion engines are quiet and unglamorous, they have proven themselves to be very useful for potential long-haul missions between the planets in our solar system. They could potentially become the work horses for future interplanetary transport. They may be slow, but they can operate in space for a very long time. It should also be noted that even though they have little thrust, it adds up over time and the ships powered by this type of engine would be going VERY fast after enough time.

Like the ion engine, but much more powerful, is the plasma engine. The plasma engine uses radio waves and magnetic fields to heat hydrogen gas to millions of degrees; creating hot plasma that is then forced out the end of a rocket. While this is very similar to the ion engine process, the plasma engine would yield much more thrust than the ion engine. While the plasma engine has never been tested in space, it has been tested in labs here on Earth, and seems to be a good candidate for future propulsion. In fact the plasma engine is one of the best candidates to power the ship that’ll take the first humans to Mars within the next 20 to 30 years. It would cut the travel time down dramatically, perhaps allowing future astronauts to reach Mars in only a few months.

Instead of using radio waves and magnetic fields, some other hydrogen-plasma designs utilize solar power to energize the plasma. Another possible way (but rather unsafe) is to create plasma via fission reactions. The potential for the plasma engine is great and is being vigorously tested around the world. There’s every reason to believe that the ion and plasma engines will have some role to play in future inter-solar system travel.

Neither the ion nor the plasma engine has enough power to take us out of the solar system however. I will talk about potential candidates for interstellar travel in addition to solar system travel next.

Ion thruster:

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Plasma thruster:

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If you would like more detailed and technical information on these engine designs, you can find them here:

Ion Engine

Plasma Engine

Solar (light) Sail:

So, just then I gave a brief summary of the ion and the plasma engine designs. While those engines could potentially change the way we travel in the solar system, they are not powerful enough to take us to the stars. While interstellar travel will not be realized for quite some time, I will begin to discuss some of the engine designs that could potentially take us to other solar systems in the Milky Way galaxy. First up: The Solar Sail.

The solar sail exploits the fact that sunlight (photons) exert small but steady pressure; enough to propel a large solar sail through space at modest speeds. Even though the photon has no mass, it does have momentum and so can exert steady (and quite powerful) pressure in the vacuum of space. In fact, sunlight is 8 times stronger in space than it is on Earth.

The sail would be made of a very thin, but durable plastic, and would orbit the sun for many years. After it gains enough momentum, it could slingshot away from our sun and move at about 0.1 % of the speed of light (making it to the nearest star in about 400 years).

While the physics behind this technology is rather simple, there have been many roadblocks in trying to create a prototype and send it into space. While a few attempts to launch solar sails into space have been successful, most have failed dramatically. Either the rockets taking them up failed, or the solar sails failed to deploy correctly once in space. As a result, there haven’t been many studies in space on how successful the sails actually are, although the ones that have been successful have given us promising results. They are however, being vigorously tested in labs here on earth. One example is the NASA Plum Brook Station in Ohio (the world’s largest vacuum chamber), where the solar sail and similar designs are being tested all the time.

The solar sail spacecraft of the future would consist of a capsule of some sort (for holding crew members), which would be tethered to a gigantic solar sail (like a parachute) that would extend from the front of the craft. The sun’s radiation would then push the craft through space, allowing it to travel far into deep space, while steadily picking up speed.

Another possible (and more practical) way to propel a solar sail, would be to build a battery of high intensity lasers (perhaps on the moon) and fire them at the solar sail, allowing it to coast easily to a nearby star and with much more speed (far greater than with the sun alone). However this type of solar sail is truly beyond our current technology. The sail itself would have to be many hundreds of miles across (meaning it’ll have to be built in space) and the lasers necessary to propel us quickly to another star would number in the thousands and would have to be so powerful that they would use up more energy than the current total power output of the entire Earth. While this seems (and is) beyond our current technological capabilities, it may very well be a viable method of quick interstellar space travel in the next 100 to 200 years.

If ever realized, the math says that these laser powered solar sails (or in this case; laser sails) would be able to reach a velocity of half the speed of light. This means that it would take a crew only 8 years to reach the nearest star (Alpha Centauri). By comparison, it would take today’s fastest rockets (assuming it could carry enough fuel) over 70,000 years to reach the nearest star! The sail would then have to come back by having a crew build (or place) another set of laser batteries on a distant moon to propel the ship back to earth. Or perhaps the ship could orbit around the distant star and gain enough momentum utilizing the slingshot effect and use this in tandem with the lasers. After that, the lasers on our moon would have to be fired again once the ship was near to slow it down. So, while the physics of building such a huge contraption are quite daunting, the speed at which it would travel and the practicality of this method would be incredible.

One of the great advantages of the solar sail (and other designs I’ll detail in the future) is that they would not require any new laws of physics to build. The solar sail uses pretty simple physics to work; but building it is the problem right now. The problems with this design are mainly technical and economic; problems that are likely to be unsolved for quite some time.

Another problem with this design is actually something ZD’s Matt brought to my attention. The solar sail would be in some serious trouble if it were to accidentally veer into an asteroid. The sail would actually have to be quite thin to work, thus making it pretty useless if it were to ever collide with interstellar or solar system debris.

The next engine I will discuss is the Ramjet Fusion Engine.

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If you would like more detailed and technical information on the solar sail, you can find it here:

Solar/Light Sail

Ramjet Fusion Engine:

The Ramjet Fusion Engine is my personal favorite because…well, it’s just really cool.

Everyone knows that the most abundant element in the universe is hydrogen. It is literally everywhere in space. The ramjet engine would contain a kind of “scoop” on the front of the spacecraft to literally scoop up hydrogen as it travels in deep space; giving it a virtually inexhaustible source of fuel. Once the hydrogen is collected, it would then be squeezed and heated by electric and magnetic fields to millions of degrees (using similar methods employed in creating plasmas) until it became hot enough to start the fusion process, creating helium. The energy released in fusing hydrogen is truly awesome. Fusion is what gives us the thermonuclear reaction of the hydrogen bomb. This enormous amount of energy would then be controlled into extremely powerful rocket thrust. According to the calculations, a ramjet fusion engine weighing 1,000 tons could maintain a steady thrust of 1 g of force (or 32 feet/sec squared). If the ramjet maintains a 1 g acceleration for one year (no reason to suspect it won’t) then a ship containing a ramjet engine would be traveling at 77% of the speed of light! This would make interstellar travel a real possibility. Calculations also show us that the scoop would have to be 160 km in diameter (meaning it’ll have to be built in space).

Theoretically, the ramjet should be able to propel itself forever. As long as the scoop effectively collects hydrogen, the engine will never stop firing. This means that human beings could potentially reach stars in the distant galaxy and beyond, in their lifetime. But how is that possible given that many destinations would take thousands of years to get to even going at the speed of light? I’ll explain:

According to Einstein’s theory of relativity, time slows down for things/people moving very fast (near the speed of light). Time is relative for the observer. But since time actually slows down for the ship moving really fast, the people/crew inside will actually not age that much for billions of years! On Earth it would seem like the ship took millions of years to reach, say, the Andromeda Galaxy and millions of years for the return voyage. But because of time dilation and the relationship between space and time at velocities near the speed of light, the guys in the ship will have only aged a few years. There would really be no need for suspended animation (cryonics, which I’ll do a blog about sometime in the future) when it comes to visiting distant stars in our own galaxy. After accelerating at 1 g for 11 years, relative to the crewmembers inside the ship, they would reach the Pleiades star cluster (which is 400 light years away!). In 23 years, they would reach the Andromeda Galaxy. In theory, such a spacecraft could reach the edge of the observable universe within a human being’s lifetime. While only decades have passed on the ship, billions of years would have passed on Earth. For more information on Relativity and the wacky-but-proven implications for space and time see the links below.

Needless to say, if we ever want to travel deep into our galaxy, we may need something like the ramjet engine.

There are a few problems with this design however. The key problem with this design is the fusion reaction itself. We understand how the fusion process works for the more complicated forms of hydrogen found here on Earth. We release its energy via the fusion proton-proton chain reaction in hydrogen bombs. But controlling this reaction specifically for a usable energy source in space (by utilizing the proton-proton fusion reaction of single electron-single proton hydrogen atoms found in space instead of the deuterium/tritium fusion process makes it very difficult to acheive the desired energy). We have only a basic understanding of how to burn pure hydrogen fuel to make it effective to power a spaceship. It’s unclear how to do this because it yields less energy than the deuterium/tritium fusion used here on earth in the H-bomb and future fusion plants. However it might be possible to introduce carbon into the mixture, as it could act like a catalyst, causing a sufficient fusion reaction to power a starship. While there are still many chemical mysteries regarding the ramjet engine, it’s being studied around the world by chemists and physicists as I write this.

Another puzzling conundrum is one of dragging. It’s unclear if the ramjet engine would be able to function at high speeds considering the stress of dragging as it approaches the speed of light. The friction created by the scoop coming in contact will unfathomable amounts of hydrogen atoms, could potentially slow the craft down; potentially keeping it from getting to the desired speeds.

The next engine I will discuss is the Nuclear Pulsed Rocket.

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If you would like more detailed and technical information on the Ramjet Fusion Engine, you can find it here:

Ramjet Fusion Engine

If you would like more information on nuclear fusion, see here.

If you would like more information on time dilation, see here.

Nuclear Pulsed Rocket:

The Nuclear Pulsed Rocket is an interesting one. I must admit that it sounds a little crazy, but it does have some potential. It’s based on using mini-nuclear bombs to propel a spacecraft trough space. A spaceship using this method would deploy a series of nuclear warheads (hydrogen bombs) in a sequence. The bombs would be detonated in sequence (by using electron beams) and the ship would ride on the shock waves created by these bombs; propelling the spacecraft to incredible speeds. Most estimates show that such a craft could effectively reach about 10% of the speed of light. At that speed it would take about 42 years to reach Alpha Centauri (the nearest star). However, a starship like this would require a multi-generational crew; meaning people would have to be born and raised on the ship.

The largest nuclear pulsed spacecraft ever envisioned was the Super Orion, which would weigh 8 million tons, and have a diameter of 400 meters. It would require a little over 1,000 hydrogen warheads to reach the desired speeds. While this design isn’t as practical as some of the others I’ve mentioned, it may have to be used if the ramjet engine design is never realized.

One major concern with this type of design, however, is the potential for nuclear fallout in the Earth’s atmosphere while transporting the warheads into space (if something went wrong during launch), as well as the effect of the fallout of detonations within the Earth’s magnetosphere. If something went wrong with the rockets carrying the bombs into space, it would mean certain trouble for the human population. While even the detonation in space (if close enough to earth), could cause some serious problems.

Yet another concern is that the EM pulses resulting from such detonations in space. The EMPs could potentially cause massive short circuits in the world’s power grid. The effects of the bombs on the ship’s hull are also quite questionable.

So, while the nuclear pulsed rocket looks great on paper, it is currently off the table as a method of star travel, and needs much more research before it will ever be realized. Perhaps it could be refined someday, with the bombs being detonated sufficiently far away from the Earth and the shielding on the spacecraft being strong enough to protect the integrity of the ship and health of the crew.

Some advantages of this design however, are that 1.) The technology required is already in our possession and 2.) It would be a great way to get rid of the world’s supply of atomic bombs.

The next (and final) engine I will discuss is the Antimatter Engine.

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If you would like more detailed and technical information on the Nuclear Pulsed Rocket, you can find it here:

Nuclear Pulsed Rocket

Antimatter Engine:

This is one of my favorite engine designs. Antimatter is fascinating stuff, and will very likely play a huge role in the future of space exploration. First of all, what is antimatter?

Antimatter is regular matter, but it contains the opposite charge. While electrons are negative and protons are positive, anti-electrons are positive and anti-protons are negative. The exact nature of antimatter is quite technical and I will not discuss it here. If you’d like to learn about the physics of antimatter, you can start here.

So antimatter is exactly like normal matter in every way except that the particles contain the opposite charge of their normal-matter counterparts. That doesn’t really seem that special until you learn what happens when antimatter comes in contact with normal matter. In short…things go boom. More specifically, when antimatter and normal matter come in contact, they annihilate each other and release truly enormous amounts of energy. In an ordinary atomic bomb (fission and fusion), only a tiny fraction (roughly 1%) of uranium and hydrogen are converted into energy. Only a small percentage of the nuclear materials in fusion and fission actually release detectable energy. Antimatter however would convert 100% of its mass into pure energy (via Einstein’s famous E=mc^2). While currently antimatter bombs do not exist (and never should), physics labs around the world can create this powerful stuff with relative ease (though only in small amounts).

To give you an idea of how powerful this stuff is, it would take only a teaspoon on antimatter to destroy the entire New York City metropolitan area. The energy in antimatter-matter annihilations is truly mind-boggling.

Assuming we will eventually be able to produce large amounts of antimatter in the future, it could potentially be used to power a spaceship. Putting antimatter into a normal container would be…well…stupid; because once the antimatter came in contact with the walls of the container (made of normal matter), it would cause a gigantic explosion that would dwarf even the most powerful fission bombs. The best way to contain this stuff would be to ionize the anti-atoms into anti-ions (which wouldn’t be hard), then confine them by using a magnetic field in a penning trap (which could store many trillions antiprotons. The penning trap would be fed the antimatter by a particle accelerator, which would create it). The antimatter would then be forced into a reaction chamber where it would be carefully introduced to normal matter, creating extremely powerful, but controlled explosions; causing propulsion. Because antimatter is 100% efficient, it is perhaps the most appealing engine-propulsion design for sub-light travel in the future. It would make the ramjet look like a remote control car.

It would take only 4 grams of positrons (anti-electrons) to power an antimatter rocket to Mars (which would only take a few weeks). It would take only a few hundred grams of antimatter to take us to the nearest stars. The energy packed into antimatter-matter collisions is almost 1 billion times more powerful than the energy released in a modern NASA rocket.

The engine design is actually very similar to the ion, plasma, and ramjet designs (minus the scoop). Such an engine would actually be pretty simple to build. The hard part is controlling the antimatter within a magnetic field and carefully forcing it to mix with regular matter. The technical challenges are pretty great, but there is no reason to believe antimatter engines could not be built someday. Currently, the main problem with antimatter is an economic one. The cost of producing even miniscule amounts of antimatter is prohibitive. However, as particle accelerator technologies improve, the price will drastically drop (to within realistic ranges) by the end of this century.

Now I will just take a minute to discuss all the engines I’ve mentioned in the context of “specific impulse”. In engineering, specific impulse refers to the ranking system of efficiency of various engine designs. Specific impulse is defined as the change in momentum per unit mass of propellant. Meaning the more efficient the engine design, the less fuel is necessary to power it. While NASA’s chemical rockets have enormous thrust, they only operate for a few minutes, thus they possess very low specific impulse. The ion engine can last for many years in deep space but it has very low thrust. But although the thrust is low, the ion engine contains very high specific impulse. The specific impulse scale is measured in seconds, and in theory, the maximum possible specific impulse would be an engine that could go the speed of light. Below I have a table listing the specific impulses for some current and future engines.


Type of Rocket Engine:--------------------Specific Impulse (seconds):
Chemical Rocket (most powerful) -----------> 542
Space Shuttle------------------------------------> 453
Solid fuel rocket---------------------------------> 250
Liquid fuel rocket--------------------------------> 450
Ion Engine ----------------------------------------> 3,000
Plasma Engine------------------------------------> 1,000- 30,000
Nuclear fission rocket----------------------------> 800-1,000
Nuclear fusion rocket-----------------------------> 2,500-200,000
Nuclear Pulsed rocket----------------------------> 10,000-1,000,000
Antimatter rocket----------------------------------> 1,000,000- 10,000,000


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If you would like more detailed and technical information on the Antimatter Engine, you can find it here:
Antimatter Engine
 

Batman

Not all those who wander are lost...
Joined
Oct 8, 2011
Location
40 lights off the Galactic Rim
Gender
Dan-kin
I forgot to mention this in the OP, but feel free to discuss these designs here. Which ones do you like or dislike? Which design(s) are the most interesting to you? What do you think about the future of space travel?
 

tysonrss

Keyblade Master
Joined
Jul 31, 2012
Location
OH, USA
Go ask Frieza what his designs of his spaceship were.

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You know $hit just got real, going to go meet God.
 

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