Worst Ideas for Space Travel. Ever.

This idea is good compared to some on this list...

     As a race, humanity has used brilliant and unconventional ideas to take our spacecraft to the Moon, Mars, and most recently Pluto. Since the 1920's, scientists and aerospace engineers have been designing and tweaking rocket propulsion to more efficiently reach for our nearest celestial neighbors.

     So far, we haven’t done a bad job, conjuring a wide range of propulsion methods varying from conventional chemical rockets, to electrical and nuclear rockets of the near future.

     However, the pressure induced upon the space travel industry during the Cold War lead to a lot of improbable, impractical, and downright awful ideas for propelling payloads into orbit and beyond that make Han Solo’s ‘bucket of bolts’ look like a space travel masterpiece (no disrespect to Star Wars or the Millennium Falcon). So with no further ado, I give you the top 5 worst ideas for space propulsion!

5) The Space Tether

Space tether (cord shortened for detailed craft)

     Take a small spacecraft in orbit. Now take a 4 kilometer long rope and tie it to another spacecraft. Now have them both fire up their engines and whip around each other like a ladder ball, until the centrifugal force on both objects is barely enough for the rope to withstand. Finally, cut the cord. This is the space tether.

     In theory, the idea of a space tether is sound. If you have the two crafts attached to each other in orbit, then they are both already traveling at orbital velocity. If you get them both to swing around each other at significant speeds, then you could send one of the crafts whizzing into space at pretty astonishing speeds.

     But what about the other craft? Well, the added velocity to the first craft is identical to the subtracted velocity of the second craft (if they are the same mass). Either we use more fuel to speed the second craft back into orbit, or we just let it fall back down to Earth. So even though the first spacecraft gets off using very little fuel, the second will end up using all of the necessary fuel that the first craft didn’t use just to return to its initial orbit. Either that, or fall back to Earth, and with NASA charging $10,000 to put up a pound of material in space, I don’t think anyone would want to launch up another space tether to try this experiment again.

     All things aside, the space tether would actually work, which is more than some of the other items on this list will be able to prove.

4) Star Tram Magnetic Launch System

Star Tram proposed magnetic launch system

     This whole idea was a disaster waiting to be constructed and then happen. Fortunately, it never got to phase 1.

     The Star Tram launch system was proposed as a way to completely eliminate the use of rocket fuel at all. It was to be a 5 kilometer long magnetic track propped up against a mountain to force a payload to astonishing velocities in order to blast them into orbit. If you have ever taken a physics introductory course, you can already see every problem with this idea.

     First of all, the amount of power necessary to launch even a small payload to high enough velocities to blow through the atmosphere and into orbit is unbelievable; upwards of 3000 Gigajoules. That’s enough energy to power 100 households for a year.

     Secondly, the shear material and construction prowess required to build such a track is immense. And to build it up against a mountain no less.

     Another major issue with such a launch mechanism is the acceleration undergone for the payload. Astronauts reach low Earth orbit in about 8 minutes, accelerating the entire way up into space. The Star Tram system intends to launch the payload to orbital velocity in 30 seconds within a few kilometers of the ground where it still has the entire atmosphere to traverse. Atmospheric conditions are chaotic, and often difficult to predict.

     Finally, the payload would still need some form of propulsion on board to guide it into a stable orbit, at which point a scientist on Earth should probably ask himself if it was worth the $40 billion to build what is essentially a giant space gun.

3) Project Orion

Artist's rendition of Project Orion

     It takes a lot of expelled scientific knowledge and prowess to remember that at one point, Project Orion was a real idea. In fact, the idea was so prominent that in the early 1960's, the math for such a craft had already been worked out and was actually small scale tested! Project Orion was proposed as a means for interplanetary travel in the near future.

     Devised by Ted Taylor in 1958, Project Orion was the study of using nuclear bombs to propel a spacecraft at extreme velocities (upwards of 3% the speed of light) so it could cover large distances relatively quickly. Yup. This was a thing.

     The craft was to be designed as such: The payload (or crew) would be positioned at the front of the craft. Stowed away just below them would be hundreds upon hundreds of nuclear warheads. During flight, the craft was to launch a nuke out the back of the craft, and detonate shortly after exit. The resulting explosion would push on a shock absorber and consequently force the craft forward. What could possibly go wrong?

     Temperatures within a nuclear explosion exceed 67,000 K. Even if you could find a material that remains solid in such heat, repeated subjection to a nuclear blast isn’t ideal for structural integrity. This temperature would also correspond to a ton of high energy radiation, dousing any crew or equipment in a deadly shower ultraviolet photons.

     On top of this (or on the bottom of this), the shock absorber would be a feat to engineer. Subjected to such rapid fluctuations in heat and pressure, the absorber would most definitely be the first piece of equipment to fail on the ship.

     Even if you could design a safe absorber and crew compartment to shield from radiation, this craft would be dangerous to launch on, or anywhere relatively near to Earth. Even in space, radioactive particles could still get caught in Earth’s magnetosphere and directed back to the Earth’s surface.

     And even if one could engineer a safe, practical, and reasonable design for a Project Orion spacecraft, it would still be illegal due to the nuclear testing ban treaty of 1963! That’s right, this idea was so bad, they banned it. Under world law.

2) A Space Cannon

A 1940's space cannon proposition

     The other ideas on this countdown wouldn’t be half bad if they could overcome a few key issues. This idea for spacecraft propulsion, however, is the issue.

     The theory is as simple as it sounds; to use an extreme explosion to thrust a projectile into space. As one can already predict, this one is going to have a pile of problems.

     Like the Star Tram, we face the issues traveling through the atmosphere for the majority of the trip and the fact that we would need some form of propulsion to guide the craft into a stable, circular orbit once at altitude. The cannon, however, has even larger issues.

     To launch a projectile from the base of a cannon to orbital speeds (about 7 kilometers per second) would require an impossibly immense explosion. So much so, that you probably wouldn’t have a cannon anymore after launch. But now that you’ve got your payload up to speed, it’s all smooth sailing, right? Nah.

     Unlike Star Tram, where you have at least cleared the bulk of the atmosphere by launching from a mountain, a cannon would face the difficulty of actually burning up its projectile within a couple kilometers of the ground. Meteorites, which are composed of mainly iron, burn up in just a few kilometers traveling just 5 or so kilometers per second. Name a material that can sustain that heat for 60 kilometers of atmosphere traveling 40% faster and you’ve got a lot in the aerospace industry!

     What could be worse that a space cannon?

1) Current Conventional Rockets

The Saturn V, a conventional rocket

     Shots fired? Maybe, but let’s take a step back and analyse our current methods of spacecraft propulsion.

     Since the dawn of the space age, we have utilized the same basic formula for rocket propulsion:

Liquid hydrogen (LH)+ liquid oxygen (LOX) + fire = thrust.

     Granted, the reaction between LH and LOX has the highest specific impulse of any potential chemical rocket (with some minor exceptions, but these are mostly dangerous and volatile reactions). Hydrogen and oxygen are also two of the most abundant elements in the universe, making them cheap and ease to get a hold of. Both gasses are easy to store and transport as well, and not difficult to synthesize into their liquid counterparts.

     Okay, here comes the kicker. We have been using this method for 60 years. If we were still using the same computers from 60 years ago, we would all be using Touring Machines. Most of our parents don't even know what those are!

     You may say to yourself, “so what? why fix something that isn’t broken?” Well brace yourself. Here comes more.

     Conventional rockets are extremely dangerous. When you launch a LOX-LH rocket into space, you are basically putting a pile of astronauts on the top of a massive chemical bomb. About 500 people have been to space. 18 have died, 14 of whom were killed in fuel related explosions. This equates to roughly 3%, which is a huge fatality fraction. If NFL football had this magnitude of fatality ratings, 300 players would have been killed on the field since the dawn of the sport, compared to the actual value of 1.

     Chemical rockets are also insanely inefficient. The space shuttle has a mass of 75,000 kg. The culmination of LOX and LH fuel weighes in at 754,000 kg, meaning that only 10% of the space shuttle’s mass at launch is the mass of the shuttle itself.

     Traditional propulsion is also highly expensive. As I have already discussed, it costs $10,000 to send every extra pound of material into space due to the shear cost of fuel for a space flight.

     Finally, though exhaust velocities for conventional rockets are suitable for orbital flight, they are incredibly slow for reaching out to farther destinations. Using our best chemical engines today, it takes days to reach the moon, years to reach Mars, and hundreds of millennia to get close to any neighboring stars. If we ever want to leave our doorstep, we are going to need more powerful propulsion systems.

Conclusion

     Are chemical rockets really a worse method than a cannon for achieving space travel? No, obviously not. But we have been squeezing every last ounce of efficiency out of these engines since the 1960's, and it’s about time that someone made a change. Whether it be some form of fusion powered rockets, or a higher impulse ion drive, we need to replace traditional propulsion in the near future if we ever expect to get off the ground and begin to study and colonize other planets and star systems. Earth is a great place, but there is so much more offered out there than we can ever achieve by staying here.

     The universe is a big place. And some forms of propulsion just won’t cut it.

Where Should we start Looking for Habitable Planets?

Artist's Depiction of extrasolar Earth-like planet.

     It's impossible to look up at the stars and not wonder about the ever growing possibility of life elsewhere in the universe. As I discussed in my previous blog regarding the Drake Equation, life may be as abundant as dirt in our galaxy alone. Many scientists disagree on whether or not meeting intelligent extraterrestrials will result in the wetting of our feet in the vast ocean of interstellar travelers, or the end of humanity as we know it. One thing, however, is certain; humanity is upward bound. Regardless of whether or not we have any desire to make first contact with the Vulcans from Star Trek, it is necessary that we, as a human race, find another planet hospitable for life. We are an ever growing species. Our energy, food, and resource needs will soon outpace the population (if it already hasn't) and we will be left in the devistating wake of our own needs. Furthermore, consider this. An asteroid just nine kilometers across wiped out the dinosaurs. There are at least 100,000 asteroids this big or larger in our asteroid belt alone. We all live on this one planet. Care to gamble humanity?

     Besides extraterrestrial influence and safety of the human species, finding an extrasolar planet hospitable to life would be an immense impact on the scientific realm. Just think of the astrophysical and geologic knowledge we could gain from the data obtained from an entirely different star system hosting a planet similar to our own. We would gain insight on what kinds of stars are suitable for life, how planet mass, density, and temperature influence that life, and finally, how that life affects us. We may have only explored 1% of earth's oceans, but we have observed just a minuscule fraction of a percent of all the stars, clusters, and galaxies in the universe. So, where do we start?

Hertzprung-Russel diagram of stars.

     The first step in finding a planet that is hospitable to life surely begins with finding the right star. Many wrongly assume that size and temperature of a star do not matter in finding such a planet, citing that, 'if the star is hotter, the planet just has to be farther away'. This is not entirely true. We must first look at stellar mechanics. The first thing to know about main sequence stars (normal stars, see diagram above) is that everything about them can be determined by their mass and composition. A star that is more massive has more gravity, which crunches its contents inward towards the core. This makes the pressure very high. As the internal pressure of a star increases, so does its temperature, and in turn, its luminosity. Luminosity, or brightness of a star, can also be thought of as energy consumption. This means the brighter the star, the faster it burns up its fuel. The lifetime of a star, then, is dependent upon two things: its mass (how much fuel it has), and its luminosity (how much fuel it is burning away). Knowing that our own sun has a lifetime of 10 billion years (10^10 years. There is a formula for computing this too, but it's much longer and not necessary for this blog), the formula for the lifetime of a star is:

T = (10^10)(M/Ms)(Ls/L)

Where:

T = stellar lifetime
M = mass of star
Ms = mass of sun
L = luminosity of star
Ls = luminosity of sun

     Now, I know what you're asking, "what does stellar lifetime have to do with finding a planet suitable for life?" It turns out that planets need time to form. With that formation, a planet needs time to settle and mature before it would ever be suitable for life. On Earth, it took about 2.5 billion years for our planet to develop conditions that could satisfy life. If a star burns up faster than that time frame, a suitable planet can never form around it and can thus be discluded in our search for life-harboring planets. So, stellar lifetime (T) must be greater than or equal to 2.5 billion. This leaves us with two unknowns: M and L for the star in question. Fortunately, main sequence stars have predictable luminosity for known masses. Plugging in the numbers with Ms = 1 and Ls = 1:

2.5*10^9 = (10^10)(M/L)

M/L = 0.25

     For main sequence stars with M/L = 0.25, M = 1.59 Ms (solar masses) and L = 6.39 Ls (solar luminosities). This mass corresponds to a mid-sized F class star, a little larger than our G class sun. This may seem like we're really narrowing our search, however, stars much more massive than our sun are incredibly rare. It turns out that only 1% of stars exceed 1.59 solar masses, so we really haven't cut much off of our search. It would seem like the planetary hunt can begin, but (as always), there's another hurdle in the way of finding a star acceptable for planetary life. Obviously a star can't be too large, but what if a star is too small?

An 'A' class star, about 2-3x the mass of our sun. Burns up too fast to form habitable worlds.

     In many ways, small stars (or red dwarfs) seem even more hospitable to life than our own sun. They burn for trillions of years, allowing plenty of time for life to evolve, and they are incredibly abundant, making up about 75% of all stars in the galaxy. However, there are some unforeseen dilemmas with life sustaining planets forming around small stars. The first problem is their magnetic activity. Smaller stars tend to experience increased solar activity, such as solar storms, much more frequently and violently than our own sun. This makes the survival of life around such a star quite difficult. In more massive stars, the interior stabilizes and consequently mellows any violent solar activity that might occur.

Artist's depiction of a magnetically active red dwarf star.

     Another major difficulty with life in a red dwarf system is a process called tidal locking. Tidal locking is the phenomenon where one side of a planet or moon always faces its host. This occurs when that object (like our moon) orbits too closely to the host and the tidal "bulges" of the host actually tug on the object gravitationally and slow its revolution. Over millions or billions of years, the object becomes tidally locked. In our solar system, this isn't a problem because our planet orbits so far away from our sun. However, the habitable zone distance for a red dwarf is much closer to the star, leading to accelerated tidal locking. One can see where this would be a problem with a life-stable planet around a red dwarf star. If one side of the planet always faced the star, that side would always be a baked crisp while the other would be a frigid tundra, both sides devoid of life. Fortunately for us, there is a formula for how long it would take for a star to tidally lock a host planet as well! The equation is:

T = (w*(a^6)*I*Q)/(3*G*(Ms^2)*k*(R^5))

Where:

T = Time to tidal locking
w = initial radial velocity of planet
a = distance from star
I = moment of inertia of planet
Q = dissipation factor
G = gravitational constant
M = star mass
k = Love's number (no, not 'love' the phenomenon)
R = radius of planet

A tidally locked planet, half desert, half tundra.

     Some of these variables are difficult to explain, but basically, tidal locking depends on the distance, radius, revolution and orientation of the planet at its formation, and the mass of the star at hand. Remember, we want the planet to be stable for at least 2.5 billion years, so we will set 'T' equal to that. 'a' is the distance from the star, which is really just the habitable zone distance of a red dwarf star. You may have noticed that we can't calculate 'a' if we don't know the mass of the star, which we are trying to solve for. To overcome this, we must write out 'a' as a function of luminosity which, in itself, is a function of mass for main sequence stars. Also, the variables 'Q','G', and 'k' are all just constants for any system. These numbers can easily be found or equated from information online. Finally, for the variables 'w', 'I', and 'R', I used the equivalent Earth values (because we are solving for an Earth-like planet). The formula is rough, but it comes out with a reasonable answer:

M = 0.568*Ms

     This number indicates that any star with a mass of less than 0.568 solar masses will consequently lock any earth-like planet in a death stare for the remainder of its existence, quenching all and any chances of finding life there. This is the mass of a small K type star. This number is also a devastating blow to the percentage of habitable stars systems out there. 80% of stars in our galaxy have masses of 0.568*Ms or less, meaning that there is little chance of finding a life supporting planet around this vast majority of stars. Adding this to the 1% of stars that are too big for habitable planets, this leaves us with just 19% of stars in our galaxy that can construct life harboring planets.

A 'G' class, sun-like host star.

     And the onslaught doesn't end there. Even if a star is the right size for a planet doesn't necessarily mean it will be in the right system to form planets. I am talking, of course, about multi-stellar systems. Though it is possible for binary, trinary, and even quadrinary systems to form planets (as has been proven with the kepler space telescope), it is unlikely that any of them would ever remain in a stable habitable zone because their distance from the host star is constantly changing. This would cause dramatic seasonal changes. On top of this, multiple host star systems are notorious for causing wild planetary orbits, shooting planets way out into the cold only to drag them back through the inferno of two suns. It is estimated that 1/3 of all star systems in the Milky Way, are in multiple star systems. This means that 1/3 of our 19% of "Goldilocks" stars are in multiple star systems as well. Oh, I also forgot to mention that only 90% of stars in the galaxy are main sequence stars... Sorry about that. Simple multiplication will lead us to the inevitable conclusion that about 5.7% of stars are really "Goldilocks" stars.

A quadrinary system, a very unstable environment for habitable planets.

     In the large scale of the galaxy, 5.7% isn't a small number at all. This is equivalent to roughly one stable, single star for every 18 stars around it. In our galaxy alone, this is still 17 billion stars. The math seems to hold true for our plot in the galaxy as well. Within 20 light years of our own sun burns 150 stellar objects. of these 150 stars, 9 of them are single, main sequence stars between 0.568 and 1.59 solar masses (including the sun), or 6% of them. These stars may be the hosts of planets with strange and complex extrasolar life, or these planets may serve as a second home for humanity in the distant future. Whatever the future holds the most important thing is that we, as a race, remain curious as to what might be out there. Who knows, life might surprise us after all.

THE LIST: These are the 9 single stars between 0.568 Ms and 1.59 Ms within 20 light years of Earth. Enjoy!

1) Sun
   -distance: 0 ly
   -mass: 1.00 Ms
2) Epsilon Eridani
   -distance: 10.52 ly
   -mass: 0.82 Ms
3) Tau Ceti
   -distance: 11.89 ly
   -mass: 0.78 Ms
4) Lacaille 8760
   -distance: 12.87 ly
   -mass: 0.60 Ms
5) Groombridge 1618
   -distance: 15.85 ly
   -mass: 0.67 Ms
6) Wolf 1453
   -distance: 18.53 ly
   -mass: 0.57 Ms
7) Sigma Draconis
   -distance: 18.77 ly
   -mass: 0.88 Ms
8) 82 Eridani
   -distance: 19.71 ly
   -mass: 0.97 Ms
9) Delta Pavonis
   -distance: 19.92 ly
   -mass: 1.05 Ms

Straight out of Star Trek: Antimatter Propulsion

An actual proposed antimatter rocket

     As a child, I grew up watching Star Trek. I grew up watching a lot of science fiction TV series, but Star Trek was different. Whereas Star Wars was a spectacular story aliens and spaceships of a different galaxy far, far away, Star Trek was closer to home. It depicted a future version of humanity, where we had all given up wars and savagery for a greater good; the exploration and discovery of the cosmos. With the recent death of renowned Star Trek actor Leonard Nimoy, many of us are wondering if the Star Trek legacy will continue to remain true to its standards. I cannot speak for Paramount on that issue, but I can say that the ideas and technology that Star Trek set the standards for are becoming closer to reality every single day. Communicators, computer pads, and even the universal translators first conceived by Star Trek are becoming analogous to the technology that we see around us every day. It is only a matter of time before our top scientists sit down and discuss the reality of a mission to another star. And the technology behind that mission was also predicted by, you guessed it, Star Trek.

Star Trek inspired many of today's technologies

     Antimatter propulsion has been on the scope as a potential form of space propulsion for decades. The idea is actually really simple. E = mc^2. Whereas other forms of space propulsion require muddy formulas that may give us the energy output of the engine estimating on a feasible efficiency, the formula for an antimatter rocket depends solely upon how much antimatter you are supplied. Okay, let's do a little experiment. Let's say that CERN has decided to use their atom smasher to collect antimatter for the use of energy yield. Slaving away for thousands of years (our current technology is not very suitable for collecting antimatter), they have amassed a grand total of one gram of antimatter. Plug that into our formula for energy yield:

E = mc^2
E = (.001)(3*10^8)^2 = 9,000,000,000,000 J = 90,000,000 MJ

     One measly gram of antimatter provides us enough energy to power a 100 watt light bulb for an astonishing 2854 years, providing that the light bulb doesn't burn out. Okay, but what about traversing the cosmos? If you can recall my post about nuclear fusion propulsion (you might want read that one first if you haven't yet), one gram of tritium-deuterium fuel gets you 3.6*10^11 joules of useful energy in one gram, after you multiply by efficiency. Simple math will tell you that antimatter is a whopping 250 times more efficient than nuclear fusion. Recall also that a mission to Mars required roughly 460 grams of total fuel. That's right, a trip to Mars using an antimatter propelled rocket would be able to make a round trip to the red planet and back with just 1.8 grams of total fuel, or just 0.92 grams of antimatter!

A matter-antimatter collision results in energy and gamma rays.

     Slap me twice and call me stupid, but that number is shockingly low. If the human race were to ever harness that kind of technology, traversing within our solar system would become a snap! Any spacecraft would only need a few grams of fuel to reach their destination, and return home with fuel to spare. But the real question remains; is it enough to get us to the stars? Mars is (on average) 225 million kilometers away. Our nearest neighbor, Proxima Centauri, is 4.22 light years. This equates to 4,000,000,000,000, or four-trillion kilometers. I could simply divide Mars's distance by Proxima Centauri's distance and multiply by 0.92 grams to find how much fuel it would take to perform a round trip, but let's be real. There are a lot of limitations and specifications that need to be addressed before we begin calculating our fuel consumption.

     First of all, traveling across the cosmos does not happen instantaneously. We are restricted by the speed of light. This means that any manned mission to another star would need enough volume for not only the crew, but also the food, the water, the engine, and all other electronics and systems on board. Secondly, a trip to another star is very different from a trip to a planet. We would most likely be dealing with relativistic speeds which require more complex math (which I will get to) to accommodate for the acceleration of the craft. Finally, due to the duration of such a mission, it is unlikely that our first manned mission to another star will involve a return trip. The crew of whatever craft leaves the Earth, is most likely destined to remain upon whatever planet they decide to go to.

What a habitable exoplanet might look like around Epsilon Eridani

     Now the year is 2150 and we are finally ready to send a manned mission to another star. Top scientists have identified a habitable planet in the Epsilon Eridani system, using gravitational microlensing, approximately 10 light years away. They have constructed a massive craft in high Earth orbit weighing in at over 840 million kilograms (roughly 420 times the mass of the space shuttle) that is suitable to support 1000 human passengers for a multi-year mission to this strange new world. The ship is designed so that it will accelerate at one Earth gravity until it reaches its maximum speed at 70% of the speed of light, where it will coast until it nears Epsilon Eridani. From there, it will spin around and reverse accelerate at 1*g, taking in hydrogen using a Bussard collector from interstellar space to use as matter for her matter-antimatter engines, until it comes into orbit around the young, orange star. The ship will maintain artificial gravity while coasting by having the crew live on a giant rotating hub, which spins just fast enough to simulate the gravitational forces of Earth. Now here's the kicker; how much fuel do they need? Imagine that one on your next physics exam!

     Let's start off small. How long will it take the crew to accelerate to 70% the speed of light (0.7*c) at 1 Earth gravity. The formula for that is decently simple:

v = a*t

     Where "v" is desired velocity, "a" is the acceleration, and "t" is time. 0.7*c is equivalent to 2.1*10^8 m/s accelerating at 9.81 m/s^2. Plugging in the numbers, we get that:

t = 21.4 million seconds = 0.68 years

     End of story? Not exactly. Because the ship will ultimately be traveling at relativistic speeds (which really just means speeds close to the speed of light), we will need to use a formula that compensates for the relativistic effects. This "relativistic acceleration" formula, is as follows:

v = (a*t)/(1+(a*t)/(c))^0.5

     Wait a minute, so why don't we see this formula when calculating the acceleration of a ball as it falls towards the Earth? Because the ball is not traveling near the speed of light. This formula is only useful for objects that accelerate to velocities close to "c". Once again solving for "t", we get:

t = 3.0*10^7 seconds = 0.95 years

     Assuming a constant acceleration of 9.81 m/s^2 (Earth gravity), this gives us that the total distance traveled is about 0.45 light years. Since it took the craft 0.45 light years to accelerate to 0.7*c, it will take that same distance to slow down. this means that the craft only needs to burn fuel for 0.9 light years of its 10 light year trip! 9.1 light years will be spent coasting at 0.7*c. Due to the fact that we are accelerating to relativistic speeds, our fuel percentages will shift as well. For any engine that is 100% efficient at converting mass to energy, the projected weight of the fuel for a 0.9 light year voyage is approximately 2.1 kg for every kg of spaceship. Recall that our spacecraft is 8.4*10^8 kg, meaning that our fuel mass is 1.8*10^9 kg! Yikes, this number seems pretty high. but let's break that down, quite literally. What I mean is, let's take that amount and split it into six spherical fuel tanks, each of which is equipped with powerful magnetic fields to ensure that the antimatter does not touch the walls of the tanks.

An antimatter rocket in the interstellar mod of Kerbal Space Program

     For the purpose of this calculation, I will assume that the vessel uses anti-hydrogen, which should have all of the same properties as regular hydrogen except its charge, which is reversed. The density, then, of compressed, liquid anti-hydrogen is the same as that of liquid hydrogen: 70.85 kg/m^3. Take our mass and divide by the density to find the volume of fuel we need:

(1.8*10^9)/(70.85) = 2.54*10^7 cubic meters

     Now we take that volume, and divide it into six identical spherical fuel tanks:

(2.54*10^7)/(6) = 4.23*10^6 cubic meters per fuel tank

     Finally, we set that volume equal to the formula for the volume of a sphere to find the radius of each tank:

4.23*10^6 = (4/3)*pi*r^3

r = 100 meters

     So that's the answer. Our proposed interstellar craft would need six spherical fuel tanks containing compressed anti-hydrogen each having a radius of about 100 meters. Is this realistic? Definitely not with today's technology. But who's to say that in a hundred years or so scientists won't come up with a way to produce antimatter in bulk? Criticisms aside, how long would this voyage really take? Assuming acceleration is constant at the beginning and end of the trip, and that speed is a constant 0.7*c for the 9.1 light year trip, calculation of duration becomes quite simple:

t = 2*((d_1/(0.5*a)))^.5 + (d_2)/(v)

d_1: distance traveled in ly during acceleration  phase(0.45)
d_2: distance traveled in ly during coasting phase (9.1)
a: acceleration (9.81)
v: velocity of coasting in "c" (0.7)

t = (((0.45)/((0.5)(9.81)))^.5)/(9.46*10^15) + (9.1)/(0.7) =  14.87 years

     That is, 14.87 Earth years. Due to the fact that the craft is traveling at relativistic speeds, strange things start to happen to the crew of this ship. Time actually passes slower for the crew of the ship than it does for a bystander on Earth. The factor of this time dilation, as it is called, can be derived as such:

y = 1/((1-(v^2)/(c^2))^.5)

y: time dilation factor
v: velocity
c: speed of light

     Plugging in 0.7*c for "v", we find that our time dilation factor, "y", is 1.40. This equates to time being 1.4 times slower for the crew of the ship at 70% of the speed of light. While central command at Earth would record the vessel as taking nearly 15 years to reach Epsilon Eridani, the crew of the spacecraft would have only aged less than 11 years. 15 (or 11) years is a very realistic time span for an interstellar crew. It is not so long that it would require a generational ship, but that is still 11 years of supplies that need to be carried along with the ship on its epic voyage to Epsilon Eridani. Alas, there are other problems with antimatter propulsion that need to be addressed.

Artist's rendition of the known Epsilon Eridani system

     Besides the fact that you need to amass a crew of 1000 who are willing to depart on a decade long mission to a planet light years away from which they will never return, there are many hurdles that need to be overcame before we make a trip to another star. As I have already mentioned, antimatter has proven difficult to produce. So far, we have only been able to produce a few atoms of anti-hydrogen, far short of the two billion kilograms needed for an interstellar mission. There is also the problem that matter-antimatter annihilation results in the formation of a lot of heat and dangerous gamma radiation that would be harmful to a crew that was near such an engine. Internal problems, however, are the least of the crew's worries when they realize that we need to come up with a material or energy field capable of protecting them from the dangerous blue-shifted mass of cosmic radiation that is capable of penetrating even the densest materials known to man.

     However, we have 100 or more years to devise ways to overcome these problems. If there is anything that the human race has taught me so far, it is that we don't stop when we believe that something is impossible, we try even harder. Though antimatter engines may not be able to take us to Vulcan, or fly us at Warp speeds, they are the first step in reaching humanity's ultimate goal of achieving a higher existence. It is only a shame that Leonard Nimoy will not be around to see the wonders that our brilliant race will create in the centuries to come. But I hope now that he can rest in peace knowing that his character has sparked the intuition multiple generations to reach for the stars, quite literally. Star Trek has already correctly predicted the invention of the cell phone, the iPad, and Google translate. Next stop: Epsilon Eridani.

In memory of Leonard Nimoy
-"Live long, and prosper..."

Ion Propulsion: A story of the Conservation of Momentum

     Behind every theory for future forms of spacecraft propulsion lies a terrible truth. They are all either too costly, to difficult, too dangerous, or too inefficient for practical use today for reaching towards the planets. But what if there were a form of propulsion for which the fuel would cost 33 times less than traditional fuel? What if there were a fuel that was non-toxic, non-volatile, and unlikely to cause an explosion or other catastrophic failure? What if there were an engine that had an average efficiency rating of 70%? And what if it were available and ready to launch today? Ladies and gentlemen, this is the truth behind the xenon ion propulsion drive.

     The ion thruster is a feasible solution for space travel in the not-so-distant future. The truth is, it has already been done. In 1998, NASA launched Deep Space 1, a probe designed to do a close flyby of an asteroid. What was supposed to be a fairly short, straightforward mission turned much more complicated when they realized that Deep Space 1 also had the opportunity to study the attributes of passing comet Borrelly first hand. Though the encounter with the asteroid was only considered a partial success, the information gathered from Deep Space One's flyby of comet Borrelly turned out to be a huge success. And it was all thanks to the highly efficient and decently cheap ion propulsion system mounted on board.

     The theory behind an ion drive is actually quite simple. Xenon atoms are initially stored in a containment unit. Since xenon has a full valence shell of electrons, it is non-volatile and non-toxic. This also means that xenon is very easy to ionize. Ionization is a process where a stream of electrons are shot at regular atoms in such a way that electrons get knocked loose from the atom, creating a net positive charge on the atom. Since positive charges are attracted to negative charges, these ions are then subjected to two powerful charged plates, the one behind the ions being positive, and the one in front of them being negative. As the positive plate forces the ions away from the craft, the negative plate pulls the ions out into space. The potential difference accelerates these positive ions out of the exhaust tube at speeds upwards of 40 kilometers per second! Since leaving a trail of positive ions behind the spacecraft can induce a charge upon the spacecraft, which can be dangerous, a stream of electrons is shot into outgoing ions to neutralize them so they have no net charge.

Theory Behind an Ion Drive

     However, at this point you may have noticed the problem. Though the exhaust velocity is 40 kilometers per second, we can only accelerate a few atoms of xenon at a time. This makes acceleration a very difficult and tedious process. It would be like instead of pressing the gas pedal to accelerate your car to work, you threw grains of sand at extreme velocities to slowly accelerate your car to its top speed. Granted, you would save gas money, and your car would actually achieve a higher speed (neglecting friction), but it would take you hours or days to even get your car to go a modest speed. An ion powered spacecraft would either need to be constructed in space, or blasted into orbit via chemical rockets. This is the only major downfall of ion propulsion.

     The ion propelled thruster works on a very simple level. The law of conservation of momentum states that the mass multiplied by the velocity of one object which exerts its energy upon a second object is equal to the other mass multiplied by the other velocity. In simpler terms:

m1v1 = m2v2

     Where m1 and v1 are the mass and velocity of the xenon atoms, and m2 and v2 are the mass and velocity of the spacecraft. We know that the mass of one xenon atom is 2.18*10^-25 kg, and that they are being expelled from the spacecraft at 40 km/s, or 40,000 m/s. Let's say that we wanted to launch a 500 kg probe to Mars. How much xenon would we need. Well:

m1 = 2.18E-25

v1 = 40,000

m2 = 500

v2 = ?

(2.18E-25)*(40,000) = (500)*(v2)

v2 = 1.74E-23 m/s

     Let's say we want our top velocity to reach 20,000 m/s, about 5 times the speed of a conventional rocket:

(20,000)/(1.74E-23) = 1.15E27 xenon atoms = 250.7 grams.

     This mass of xenon will get the craft to 20,000 m/s. The craft will then coast at that speed until it is time for it to begin to slow down to arrive at its destination. This does mean, however, that it will need another 250.7 grams of xenon to slow back down to starting velocity, bringing the total amount of fuel to about 502 grams. But how fast can we get up to this speed? Let's say that our engine has a diameter of half a meter. This will give it an output of about .044 Newtons of thrust. For our 500 kg craft, this is equal to an acceleration of  8.8*10^-5 m/s^2. This means that, starting from 0 m/s, it would take upwards of 6 hours to reach our desired speed of 20,000 m/s. So time is the only sacrifice of the ion engine.

     But what about the benefits? The cost of 501 grams of xenon fuel for a 500 kilogram spacecraft would cost just proud of $600. Compare that to the $20,000 of liquid fuel that it would take to get a space vessel from low Earth orbit to Mars's orbit. And even with all that expensive fuel, it would still only be able to achieve a peak net velocity of around 4000 m/s, though it may only take a few minutes to get there. This is only a fraction of the top speeds achievable by the ion drive. Plus, with no explosive or volatile chemicals on board, the journey would be much less prone to accidents. The far future may hold the keys of space exploration in nuclear and antimatter drives, but getting us to our celestial neighbors today may be much more feasible by means of the xenon ion drive.

A Trip to Mars: A New Form of Propulsion

     On November 6th, 2011, NASA launched the Atlas V space vehicle en route to the red planet, nearly a nine month trip ahead of it. On board the Atlas V, a small rover, about the size of a car, was curled up within the nose. That rover would later land on the surface of Mars to discover that the seemingly cold, dry dust of Mars once long ago had the ability to support life as we know it. The Curiosity project is regarded as one of the most informative and successful missions to Mars to date; but it didn't happen overnight. The unsatisfying truth of the Curiosity rover's trip to Mars is that it took 253 days from liftoff at Cape Canaveral, to touchdown at Gale Crater on Mars's dusty surface. Whats more is that this rocket requires 284,000 kg of fuel just to escape the strong pull of Earth's gravity and maintain a stable orbit. Since time is one of humanity's most valued possessions, and the cost of rocket fuel is not expected to drop in the near future, its time to start searching for new sources of fuel and propulsion to get us to the surfaces of our nearest celestial neighbors.

Atlas V Rocket

     At its closest approach, Mars is 55 million kilometers away. Since the Atlas V accelerates the Curiosity probe to about 20,000 kilometers per hour, one would think that you could just the distance and divide by the speed to get the length of time required for a trip to Mars. This, however, is not the case. Since everything that travels around the Sun goes in elliptical orbits, the rocket will not be an exception. It's path too will be curved by the gravitational pulls of the Earth, the sun, and Mars. At 20,000 kilometers per hour, a spacecraft launched from Earth when Earth and Mars are in sequence (in line with the Sun), the craft will have arrived at Mars after Mars has done one half orbit in its path around the Sun. So, the actual distance traveled by the craft itself is the average of the lengths of Earth's and Mars's orbits divided by 2. This gives us a total distance of about 593 million kilometers. 

     However, this is (clearly) not the most efficient way to launch a craft to Mars using conventional methods, seeing that it would take the craft more than three years to reach Mars. If the craft is launched at a higher velocity, the curved orbit from Earth to Mars will have flattened out. The only down side to launching spacecraft at these trajectories is that once at the red planet, the vessel will have to begin to slow down to enter her orbital velocity.

     In this image, the distance traveled between Earth and Mars is closer to 300 million kilometers, slicing the trip time down to only about 18 months. The truth is, there's no limit to how fast you can fly a ship from Earth to Mars (except the speed of light), thus the path between Earth and Mars will grow continually shorter with velocity. If you could accelerate a craft to the near the speed of light, the shortest possible distance would only be about 55 million kilometers. Take that divided by the speed of light and you get a trip time of about 3 minutes. So, if there is no limit, the only question is how fast can we go?

     There has been a lot of talk in recent years about the possibility of using nuclear fusion power to propel a rocket to Mars. The theory behind nuclear fusion is actually quite simple. Take, for example, the fusion of deuterium, an isotopes of hydrogen. Deuterium is simply a hydrogen atom with two neutrons. In the image below, blue spheres represent neutrons while red spheres represent protons. When heated to extreme temperatures, these hydrogen atoms will begin to gain velocity. Once a certain velocity is achieved, these atoms will slam into each other with enough force to combine into a single helium atom and release a tremendous amount of energy.

     Let's compare this to the energy released by liquid hydrogen, currently the most efficient and powerful rocket fuel in use today. The specific energy of a substance tells us exactly how many megajoules of energy are released per kilogram of whatever it is you are using as fuel. The specific energy of liquid hydrogen is about 141.86 megajoules per kilogram. That is a lot of energy. And that is in just 1 kilogram of liquid hydrogen. putting that into perspective, 1 kilogram of liquid hydrogen could power an average American household for 31 hours.

     So how about nuclear fusion? The net reaction of one deuterium-tritium fusion (tritium being another isotope of hydrogen, actually more efficient than a deuterium-deuterium reaction) creates about 12.5 megaelectron volts, or about 2*10^-12 joules. This may seem like a tiny amount of energy, but this is only in one reaction of just one deuterium and one tritium atom! Since one mole of hydrogen is equal to one gram, we just multiply that by Avagadro's number (the number of atoms in one mole of hydrogen) to obtain how much energy is released in one gram. This turns out to be 1.2*10^12 joules in one gram, or in a kilogram, 1.2*10^15 joules. Using nuclear chemistry, we find that one gram of reacted dueterium-tritium fuel generates 1.2 billion megajoules of raw energy! Modern experiments show that at best, a fusion engine could only utilize about 30% of the total energy created. This means that the energy density of the nuclear fusion of deuterium and tritium fuel at 30% efficiency is 361 million megajoules per kilogram. This is 2.5 million times more efficient than liquid hydrogen fuel. Recall from before that the Atlas V takes 284,000 kg of traditional fuel to launch off, leave Earth's orbit, slow to Mars's orbit, and land on the surface of the planet. Using a vessel of the same mass and a fusion powered rocket, we find that a voyage to Mars would only require about 113.6 grams of fuel! If it were a manned mission, we must assume that it would be nice for the crew of the craft to return home, bringing the grand total to about 227.2 grams of both deuterium and tritium fuel, or 454.4 grams of total fuel (about 1 pound for all you Imperial system goers).

Proposed NASA Nuclear Fusion Rocket

     Using the ideal gas law, we can determine the volume of two spherical fuel tanks to hold the deuterium and tritium as well. For a system at reasonable temperatures and pressures, PV = nRT, where:

P = Pressure
V = Volume
n = moles
R = .08206 (constant)
T = Temperature

     We want a pressure of 1 earth atmosphere, and since one gram equals one mole for hydrogen, n will equal 227.2. Room temperature in Kelvins is 294. Thus:

(1)*V = (227.2)*(.08206)*(294)

V = 5481.3 liters, or 5.48 cubic meters

For a sphere:

V = (4/3)*pi*r^3

Thus:

r = 1.09 meters

     So we would need two spherical fuel tanks just over 1 meter in radius to bring a manned crew to Mars and back in a vessel about the mass of the Atlas V. This is an incredibly small amount of fuel compared to the thousands of kilograms needed to launch the Atlas V towards Mars. Nuclear fusion is definitely a cheaper source of spaceflight, but what about faster? According to NASA, the exhaust velocity of a nuclear fusion powered rocket is likely to be upwards of 30 kilometers per second. Compared to that of the Atlas V rocket, whose exhaust velocity is approximately 4 kilometers per second, this would cut the trip time from here to Mars by more than 7 times, leaving the ETA at about 36 days. Not to mention that the only byproduct of nuclear fusion is helium and neutrons. So there you have it; cleaner, faster, and cheaper. So, why are we not using it?

     The sad fact of the matter is that fusion isn't easily achieved. For deuterium and tritium atoms to smash together with enough force to fuse and release energy, we must first heat them to 700 million degrees Kelvin, a temperature hotter than the core of the sun. Not only do we not have the means with current technology to heat anything to such a temperature, but no known material could contain such heat without deformation. Furthermore, though hydrogen is very abundant, deuterium and tritium only compose a fraction of a percent of the total amount of hydrogen in the universe.

Temperatures for Achieving Fusion (Blue line is Deuterium-Tritium)

     So fusion may not be practical as a source of rocket propulsion today. It is only a matter of time, however, until we are able to find a way to heat hydrogen to such temperatures, possibly by way of microwaves, and keep it contained maybe in an extremely rigid futuristic material or with a powerful electromagnetic field. In the near future, we may even be able to synthesize deuterium and tritium fuel by somehow combining excess neutrons with hydrogen atoms, using the strong nuclear force as a glue for the new isotopes. Though fusion may seem difficult today, we will, as a human race, find way to overcome these setbacks in order to further mankind. Mars is our nearest celestial neighbor besides our own moon, and we know so little about it under its mysterious, dusty red crust. With the nuclear fusion rocket, a trip to the red planet may be only a few pounds of fuel and 36 days away. So what are we waiting for?

Life in our Galaxy: How Many Other Intelligent Species Are There?

     It seems pretty unlikely that there is other life in the galaxy from our perspective right now. As a human race, we have been communicating radio waves for 78 years giving extra-terrestrials a chance to respond to our inadvertent hails. We have projects like SETI that have been actively searching for and attempting to communicate with potential visitors of the Milky Way. We even have powerful telescopes that have accurately mapped thousands of nearby stars and extrasolar planets with no traces of life, intelligent or otherwise. But what if I told you right now that there is almost certainly at least 126 advanced, technological civilizations that have the willingness and ability to communicate with Earth right now in our own stellar neighborhood, the Milky Way? It would probably sound a lot like science fiction. Maybe so, but it is a real possibility. Let me present you to the famed Drake Equation:

     This equation is literally the key to telling us exactly how many alien civilizations are out there right now, alive and well, and able to communicate. So, what's the problem? why haven't we found extra-terrestrial life in our galaxy if we know where to look? The truth is, we don't. This is because four of these variables, f_l, f_i, f_c, and L, we simply don't know the values to. If the Drake equation is broken down into its variables, we find that:

N = The Number of communicating civilizations in our galaxy right now.
R = The Rate at which stars are formed each year.
f_p = The Fraction of those stars which have Planets.
n_e = The Number of Earth like planets that can potentially support life.
f_l = The Fraction of these planets which actually forms Life.
f_i = The Fraction of these planets with life that develops Intelligent life.
f_c = The Fraction of these civilizations that develop a means to Communicate effectively.
L = The Length of time that these intelligent species communicate for.

     Many of these variables are very clear, and have been accurately measured and tested. R, for example, has been calculated and known for many years. NASA has clocked the average star birth rate to be approximately 7 stars per year based on patches of radioactive aluminum throughout our galaxy. so, for our equation, R = 7. Now, with the launch of the Kepler space telescope, f_p has also been determined relatively accurately over the past decade or so. Of the 153,000 stars that were accurately measured for planets using multiple means, they discovered that approximately 34% of stars have some form of planets around them. However, this does not even account for the number of planets that were missed or not observed long enough to discover a planet. Recent studies have now estimated f_p = .80, meaning about 80% of stars form planets. But of these planets, how many are in the "Goldilocks" zone for the potential formation of life or habitability? Studies show that approximately 22% of stars have Earth-sized planets within the habitable zone. Out of the 34% that had planets, this means that about 65% of the planets are habitable. This percentage seems to be quite accurate closer to home. Even in our own solar system, there are 2 or 3 roughly Earth-sized planets within our habitable zone (depending of whether or not you count Venus or Mars), and only one of them supports life. So, averaging the 65% with the low estimate of 33% in our solar system, then multiplying by the 22% of stars with planets in the habitable zone, we can equate n_e = .11 or about 11%.

Goldilocks Zones of Sun-Like and Other Stars

     Alright, about half way done. Now here's the real problem. The last four variables in the Drake equation are impossible to determine precisely with our current knowledge of the galaxy. Since we have never discovered another example of life in our own Milky Way, the estimation range of these last four numbers is quite vast. So now we must start using ranges. Of the Earth-sized planets in habitable zones of their sun, how many of these will develop life? According to some, the answer to this is 100%, meaning if a planet has the potential to support life, it will develop life. This is not an unreasonable suggestion. Geological records of the Earth show that once our home planet developed conditions stable enough for life, it developed rather quickly. However, we do not know if our creation was a chance accident or a common occurrence. This number could literally be anywhere between 0% and 100%. Averaging these two will assign a probability of approximately f_l = .5, or 50% of planets will develop life at some point after they become habitable. Once life is created, what are the chances that this life becomes intelligent? So, lets step back a moment and take a look at what humanity had to overcome to become an intelligent community. Our journey from a puddle of primordial goo to walking, talking, bipedal beings had a few speed bumps along the way. We endured billions of years of evolution, a total of 5 mass extinctions, and factors that we can't even begin to imagine! However, if humanity is indeed "average", then over our 3 billion years of evolution on planet Earth, there were 5 chances that could have extinct life on this planet. This puts the value of f_i = .2, at around 20%. This is assuming, of course, that if life exists on a favorable planet, that it will "strive" to become intelligent on its own. This is, however, still reasonable due to the effects of evolution that can be seen across the globe.

Some Extrasolar Planets Discovered by Kepler Project that may Host Life

     So now we have an intelligent species that has overcome all odds on an Earth-sized planet around a star in its Goldilocks zone. Will they develop a means to communicate. If they are truly intelligent, then yes, of course they will. Think about it. There were civilizations on opposite ends of the globe, like the Mayans and the Egyptians, that both developed independent, effective languages without having any prior knowledge of each other. An intelligent species strives to share their intelligence with others. Assuming that in the 10,000 years from intelligence to when they develop some means of interplanetary communicative means, like radio waves, they don't kill themselves or are wiped out by a natural disaster (the latter of which is unlikely due to the fact that an average mass extinction only occurs once every 700 million years), the civilization will communicate. This puts the value of f_c = .9, allowing for a 10% chance that they will either never develop communications or they will be wiped out somehow. Good. So the final variable remains; how long will the civilization communicate for before they either are wiped out by natural disaster, destroy themselves, or move on to a more advanced form of communication that we cannot detect? Once the civilization has become intelligent, they will almost immediately become space-faring and colonize and terraform many other worlds. This makes destruction by means of natural disaster unlikely. What is more likely is that they will destroy themselves.

     Since we have developed radio communication in 1936 (and yes, it was a radio broadcast by Hitler), we have sustained 2 world wars, a cold war, and multiple terrorist groups that threaten to rid of all others who don't agree with their beliefs. The first world war was mostly waged in Europe and had little chance of wiping out the entire human population, but with the invention of the atom bomb in the 1940's, this threat is all too real. There have been two circumstances in the last 70 years where the world almost destroyed itself with nuclear warfare, the first of these being World War II in 1945, and the second being the Cold War nuclear scare of 1983. Both of these events could have ended humanity, making our radio transmissions cut short at a mere 9 or 37 years. however, it has been 31 years since the nuclear scare in 1983 and no such event has occurred since then this means that tensions of humanity (though far from gone) are generally decreasing as time moves onward. I will give a civilization a 60% chance of surviving their own destruction, leaving us with just one final element; how long will this civilization communicate for with simple radio waves? History has shown that technology advances exponentially. However, we are still using radio waves after 78 years. I would estimate that we will sacrifice this open source of communication to a more specific, private form of communication like lasers or some form of telepathic enhancement within the next 500 years. averaging that with the civilizations that kill themselves within 20 years, we can calculate 20*(.4)+500*(.6) 300 to give us an approximate value of 300 for L. So, lets put it together:

R = 7 stars per year.
f_p = .8 ratio of stars with planets.
n_e = .11 ratio of these planets which are habitable.
f_l = .5 ratio of these habitable planets which develops life.
f_i = .2 ratio of these life forms that become intelligent.
f_c = .9 ratio of these intelligent life forms that will develop effective communication.
L = 300 years of active, effective communication.

N = (7)*(.8)*(.11)*(.5)*(.2)*(.9)*(300) = 16.63

     So what exactly does this mean? There are currently about 17 civilizations in our Milky Way galaxy right now that are intelligent and willing and able to communicate. This, however, does not mean that there are only 17 intelligent civilizations within the milky way. This is only the number of them that we are likely to find and communicate with in the next 200 years or so. If we assume that species are more friendly at communicating, the value of L may shoot up to however long that civilization has been alive for, which, in a 13 billion year old galaxy, may be close to 10 billion years. The chances that an alien civilization that advanced would ever have the motive to talk to us would be astronomically small, however, as they have probably already discovered millions of other civilizations just like us in galaxies all across the universe. So the true question for "L" is how long will a civilization be interested in contacting other life. Some studies report that it is humanity's drive to discover other life in the galaxy. But if there really is 30,000 civilizations in the galaxy right now, that would get pretty boring after a while. life would no longer be unique. so how many civilizations would it take for an intelligent species to consider life "common"? Lets say a civilization discovers the nearest 15 civilizations before either becoming bored with communicating with lesser beings or conjures laws against tampering with the development of these civilizations.Well, the galaxy has approximately 5,500,000,000,000 (5.5 trillion) cubic light years of area and about 200,000,000,000 (200 billion) stars. This means that there is an average of 27.5 cubic light years per star, or, if you prefer, a stars nearest average neighbor is about 1.87 light years away. This means our civilization will have communicated with every other civilization within 65450 cubic light years, or about 25 light years in all directions. Taking into account that it takes them about 50 years to go from a communication era to a space era, then another 100 years from space era to interplanetary era, then another 150 years from an interplanetary to an interstellar era, then another 200 years to explore all of their nearby star systems before becoming bored (with the speed of light as a barrier), the value of L can now be expanded to L = 500, then:

N = (7)*(.8)*(.11)*(.5)*(.2)*(.9)*(500) = 27.72

     This is almost 28 potential intelligent life forms, willing to communicate just within our galaxy alone right now! But this still doesn't answer the question as to how many intelligent species have lived in our galaxy ever. To find this, we simply eliminate the first and last factors of the Drake equation to find out what percentage of stars in the milky way have had an intelligent species living on a habitable planet at one point in time.

N% =  (.8)*(.11)*(.5)*(.2)*(.9) = .0079 or 0.79%

Multiplied by the number of stars in our galaxy:

N = (.0079)*(200,000,000,000) = 1,580,000,000 life forms

     1.58 billion intelligent life forms have existed in the galaxy at one point or another. Since that number is approximately the length of time in years that life could have been erupting in our galaxy, we can assume that these civilizations would have spawned proportionally with time. This means that every six years, a new intelligent species is born in our galaxy on average! This leaves us with about 80 alien civilizations within just 500 years of our own technology that may be willing to communicate with us! Now, since the galaxy is so vast, the closest of these civilizations would be on average 1800 light years away (as can be seen from the graph above), but still, there is a chance! So, in conclusion there is approximately:

• 17 intelligent civilizations in our galaxy that are not too much more advanced and are within the technological realm of communicating with us.
• 28 intelligent civilizations in our galaxy that may or may not be more advanced than us, but still are willing to communicate with us.
• 1.58 billion intelligent species that have ever existed in the Milky Way.
• A new intelligent species is born every 10 years on average.
• About 80 intelligent civilizations in our galaxy right now that are within 500 years of our technology.
• The nearest intelligent civilization that is willing to communicate with us is most likely over 1800 light years away from us.

     And what about humanity? Where do we fit into the Drake equation? Well, if we consider ourselves an intelligent life form, we just entered into the vast network of communicating aliens just 78 years ago, and we are still alive. This means we know for a fact that there is no willing or able species within 39 light years that will communicate with us (given that they have to respond to our radio waves). Given time and technology advances in the coming years, there is a high chance that we will discover extra-terrestrial life within the next 1000 years. It is only a matter of time.