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So You Want To / Write a Hard Science-Fiction Story with Space Travel
Heartbreak HotelSadly, the rules of writing about realistic future space travel — like the rules of writing about anything realistic — are primarily a set of rules about what you can't do. The more ideas you have about what you'd like to have your characters do, the more ways reality will step in and say "No." First off, here is a list of tropes that are frowned upon in a realistic universe: There are sound reasons why all of the above tropes will probably not work in Real Life. It's not impossible to have them work in a way that doesn't violate the laws of science or good sense, but it will requite extra painstaking labor from the author to make that happen.
Doing the ResearchThis should go without saying, but: If you're going to set your story someplace we already know something about — like Mars or Alpha Centauri — for goodness' sake, read up on what we know about the place before you start writing! We've sent space probes to every planet in the solar system, we've accrued reams of data on just about every star that has a name, we've even mapped out the interstellar medium in our neck of the galaxy. The data are out there, and thanks to the Internet they're not even hard to acquire any more. You wouldn't set a story in the Sahara Desert and have your hero go swimming in one of the "numerous lakes" there. You wouldn't set a car chase in downtown Florence, Italy and then make up the street names and city layout. Similarly, don't set your story on Mars and have your hero swelter in the unbearable heatnote I'm looking at you, Babylon 5 novel #1 "Voices" by John Vornholt!, or put an Earthlike planet in orbit around Alpha Centauri without at least mentioning the bright "B" star that should be visible from time to time in the sky. Making up details about places we don't have strong data about is one thing, but making up details about places where our existing data would make those details flat-out impossible is quite another.
Doing the mathIf doing an arithmetic problem like "A train leaves Chicago at 8 AM going 60 miles per hour" taxes the limits of your skills, putting realistic space travel into your story is probably not for you. Space travel is all about doing the math, and the math can get hairy — especially when dealing with speeds above 5-10% of the speed of light, where special relativity starts to rear its ugly head. But if you're up for the challenge, it's definitely worth doing. Even if you don't show your work to your readers, getting the numbers right (or nearly right) will go a long way toward your story's sense of realism. Let's take as our example a rocket trip from Earth to Saturn. How long will it take to make the flight? You could go the easy route, and look up how long it took for the Voyager 1 space probe to fly from Earth to Saturn, and just assume that you space ship flies about as fast as the Voyager probes did. But when you do look it up, you balk — it took nearly three years for Voyager 1 to make this trip! You can't have your intrepid space cadets waiting around for three years just to get to Saturn, they've got important space adventures to have, space wars to fight, and space women to woo. You want them to get to Saturn a lot quicker. So, you give them a space ship that never runs out of fuel — or uses fuel that's so efficient that it won't run out even if it runs its engines continuously between Earth and Saturn. So, with the ability to accelerate indefinitely, now how long will it take to get to Saturn? Let's say you decide to limit your space ship to a cruising acceleration of 1g, so that the crew will experience thrust equal to Earth's surface gravity. After all, this is a hard science fiction story, right? You can't just go slinging Inertial Dampening around. Any acceleration your ship undergoes will be experienced by your crew as G forces. So, if they're going to be cruising under engine power for anything longer than a few minutes, you'll probably want to keep your acceleration down to 1g. 1g works out to an acceleration of 9.8 meters per second per second — at the end of one second, you'll be going 9.8 m/s, at the end of two seconds, you'll be going 19.6 m/s, and so forth. At speeds much less than the speed of light, which is the speed we're dealing with in the Earth-to-Saturn example, the formulas relating speed, acceleration, time, and distance travelled while undergoing constant acceleration are pretty straightforward. Ignoring the sun's gravity (which can indeed be neglected for a ship that accelerates at one g) we have:
- v = a * t + v0
- d = 0.5 * a * t2 + v0 * t
- 2 * a * d = v2 - v02
- d = 0.5 * a * t2 + v0 * t1,280,000,000,000 m = 0.5 * 9.8 m/sec2 * t2 + 0 * t1,280,000,000,000 m = 4.9 m/sec2 * t2
- 1,280,000,000,000 m / 4.9 m/sec2 = t2260,000,000,000 sec2 = t2Taking the square root of both sides:
- v = 9.8 m/sec2 * 510,000 sec + 0
- 640,000,000,000 m = 0.5 * 9.8 m/sec2 * t2640,000,000,000 m = 4.9 m/sec2 * t2640,000,000,000 m / 4.9 m/sec2 = t2130,000,000,000 sec2 = t2Taking the square root of both sides:
- v = 9.8 m/sec2 * 360,000 sec
- 0 = -9.8 m/sec2 * t + 3,500,000 m/secSubtracting 3,500,000 m/sec from both sides:-3,500,000 m/sec = -9.8 m/sec2 * tDividing both sides by -9.8 m/sec2:-3,500,000 m/sec / -9.8 m/sec2 = t
Special RelativityNow ... what if our heroes can go faster than this? Let's say we've decided we need shorter flight times, so screw it, we're introducing Inertial Dampening technology into our story, like in the Honor Harrington or Star Trek universe. Now our space ships can accelerate at 1,000 g, or 9,800 m/sec2, and we should be able to get to Saturn much faster. In fact, using the first equation above, it looks like we should be able to accelerate to 30,000,000 m/sec in less than an hour — that's a tenth of the speed of light. And there's where we run into problems. Because above about a tenth of the speed of light, acceleration doesn't affect velocity in a straightforward manner any more. Your clock runs a little slower to a fixed observer than it does to you. Your momentum is slightly higher to a fixed observer than your acceleration history says it should be. The universe shrinks slightly in the direction you're moving. In short, you run smack-dab into special relativity, and now the math gets a lot more complicated. For one, the change in your velocity per second, given a constant acceleration from your space ship's reference frame, now depends on your current velocity — which turns the relationship between the two into a first-order differential equation. The basic relativistic equation for determining your "gamma factor" — the amount by which your mass goes up, time slows down, or distances in the direction of motion shrink — is as follows:
- γ = 1 / sqrt (1 - v2/c2)
|At rest||γ = 1|
|At 10% of c||γ = 1.005|
|At 50% of c||γ = 1.15|
|At 86.6% of c||γ = 2|
|At 90% of c||γ = 2.29|
|At 99% of c||γ = 7.09|
|At 99.9% of c||γ = 22.37|
|At 100% of c||γ = ∞|
- T = (c/a) * ArcCosh[a*d/(c2) + 1]
- t = sqrt[(d/c)2 + (2*d/a)]
- v = c * Tanh[a*T/c]
- v = (a*t) / sqrt[1 + (a*t/c)2]
- γ = Cosh[a*T/c]
- γ = a*d/(c2) + 1
- t = sqrt[(d/c)2 + (2*d/a)]t = sqrt[(640,000,000,000 m / 300,000,000 m/sec)2 + (2 * 640,000,000,000 m / 9800 m/sec2)]t = sqrt[4,550,000 sec2 + 130,600,000 sec2]
- T = (c/a) * ArcCosh[a*d/(c2) + 1]T = (300,000,000 m/sec / 9800 m/sec2) * ArcCosh[9800 m/sec2 * 640,000,000,000 m / ((300,000,000 m/sec)2) + 1]T = (30,600 sec) * ArcCosh[0.06969 + 1]
- v = 300,000,000 m/sec * Tanh[9800 m/sec2 * 11,360 sec / 300,000,000 m/sec]v = 300,000,000 m/sec * 0.3549
OrbitsIf your space ship is close to a large gravity source like a planet or a star, and is moving at a low enough speed, it isn't going to travel in a straight line. The gravity of the big object will cause your spacecraft to follow an orbital trajectory. The equations for an orbit are more complicated than the equations for straight-line movement, because your acceleration is always changing; it depends on how far you are from the big object at that particular instant. Whole volumes have been written on how to calculate an orbit precisely, but there are some simple straightforward cases that are at least somewhat easier to calculate. All orbits are shaped like conic sections. If your space ship is moving slower than the "escape velocity" — or more precisely, if its total kinetic energy and gravitational potential energy is less than the gravitational potential energy it would have at an infinite altitude — its orbit will be shaped like an ellipse. If it's moving precisely at the escape velocity, its orbit will be shaped like a parabola. If it's moving faster than the escape velocity, its orbit will be shaped like a hyperbola. This is assuming, however, that your space ship spends all its time from this moment forward in free-fall, without firing its engines. Parabolic and hyperbolic orbits are basically escape trajectories. The spacecraft leaves the big object in question and never comes back. An elliptical orbit, on the other hand, is stable, and allows your space ship to go around and around the big object over and over again. It's what most people think of when they hear the word "orbit." An ellipse looks an oval-ish shape, with two points inside it called the "foci" (plural of focus). In an elliptical orbit, the center of the big object you're orbiting is going to be at one focus, while the other focus won't contain anything at all. The formula for how long it takes to make one complete orbit was first deduced by Johannes Kepler when studying the motions of the planets around the sun. Sir Isaac Newton expanded on this formula so that it applied when orbiting any object. The formula is: .. where P is the period of the orbit in years, M is the total mass of all objects involved in the orbit in solar masses, and A is the semi-major axis of the orbit's ellipse in Astronomical Units. The simplest kind of elliptical orbit is one with no eccentricity at all. We call this a circle. In a perfecly circular orbit, both foci are at the same point in space, which is at the center of the circle. The semi-major axis A of a circle is just its radius (half its diameter). Suppose you want your space ship to orbit the Earth in a perfect circle 200 kilometers above the surface, like the Space Shuttle does. What will the period (P) of that orbit be? If we want to use the equation above — P2M = A3 — we'll first have to find the combined mass of the Earth and your space ship in solar masses. The Sun's mass is about 2 x 1030 kg, while the Earth's mass is about 6 x 1024 kg. Let's say your space ship weighs in at 1000 tonnes, i.e. a million kg. Here's the mass of the Earth in solar masses:
- 3.003740720000000000 x 10-6
- 3.003740720000000001 x 10-6
- P2 * (3 x 10-6) = (4.39 x 10-5)3P2 * (3 x 10-6) = 8.47 x 10-14P2 = (8.47 x 10-14) / (3 x 10-6)
- Mass of Mars = 6.4 x 1023 kg = 3.2 x 10-7 solar massesRadius of orbit = 100 km (orbital altitude) + 3397 km (radius of Mars) = 3497 km = 2.3 x 10-5 A.U.P2 * (3.2 x 10-7) = (2.3 x 10-5 A.U.)3P2 = (2.3 x 10-5 A.U.)3 / (3.2 x 10-7) = 4 x 10-8P = 2 x 10-4 years = 105 minutes.
Why rockets are so bigYou've doubtlessly seen the footage of the Apollo moon mission launches. An enormous Saturn V rocket, hundreds of feet tall, lumbered off the launch pad on an enormous column of flame. Yet the actual Apollo spacecraft was just a tiny cylinder perched atop it, with an even smaller cone on top of that where the crew actually lived. Why was the rocket so big, and the actual usable space so small? Cars can pull themselves along the ground by spinning rubber tires. Boats can push water through their propellers. Airplanes can push air through their propellers or turbines. Rockets, on the other hand, have none of these options. Every ounce of thrust their engines produce has to come through the expenditure of onboard propellant — in other words, they accelerate forward by throwing material backward. (Boats and airplanes also accelerate forward by throwing material backward, but they get this material from the environment around them. Rockets have to carry all this "reaction mass" on board.) This severely limits the efficiency of a rocket engine when compared with a fluid-breathing or surface-friction engine, even moreso than the need to carry their own oxygen to combust with their fuel. Even worse, it means that at the start of your flight, you have to produce that much more thrust just to push all your unburned fuel along with you, so each kilogram of fuel you add provides progressively less and less total acceleration. This cascade effect can add up very quickly. The equation for how much total acceleration your rocket can undergo before it runs out of fuel — the total "delta-v budget" of your rocket — was derived by Tsielkovsky over a century ago:
- Total delta-v = ve * ln(M/Me)
- 7,000,000 m/s = 4500 m/s * ln(M/Me)Dividing both sides by the exhaust velocity:(7,000,000 m/s) / (4500 m/s) = ln(M/Me)To get rid of the natural log, we need to take the natural exponential of both sides:
- Nuclear fission (NERVA) engines
- Ion engines, such as those on the Dawn and Deep Space One spacecraft
- The Orion Drive
- Controlled nuclear fusion engines
- Ground-based laser pushers
- 7,000,000 m/s = 6,000,000 m/s * ln(M/Me)Dividing both sides by the exhaust velocity:(7,000,000 m/s) / (6,000,000 m/s) = ln(M/Me)To get rid of the natural log, we need to take the natural exponential of both sides:
Realistic World BuildingWe humans evolved on, and (so far) all grew up on, Earth. We instinctively expect the air to be breatheable, the temperature to be liveable, the gravity to be 9.8 m/s2, the days to last 24 hours, trees and grass, animals and plants and fungi, et cetera, et cetera. The sad fact is, though, that no other planet we've detected thus far is even remotely habitable by human standards. The bigger ones are Jupiter-like balls of gas, while the smaller ones are almost universally airless. The few worlds we've found that do have both an atmosphere and a solid surface have been blanketed in gases that no human can breathe, at pressures anywhere from near-vacuum to 90 times Earth's sea level. While it's theoretically possible that a planet out there might harbor life as we know it, it would have to fit a long, narrow list of parameters, and even then, the kind of life that might have actually evolved there will most likely be very different from the multicellular-eukaryote-rich biome inhabiting Mother Terra. In order for a planet to be able to support life as we know it on its surface at all, it will have to lie in a very narrow range of distances from its parent star. Too close, and any water would evaporate. Too far, and any water would freeze. Liquid water — and life as we know it requires liquid water — can only exist if the planet lies within that narrow zone where it's receiving just the right amount of energy from its star for the surface temperature to allow it. This is called the star's "comfort zone," or "Goldilocks Zone" (as in: not too close, not too far, but juuuuuuuust right). The exact width of a star's Golilocks zone is a matter of some debate, due to the fact that some atmospheres can trap heat (*cough* Venus *cough*) and some can't, and a number of other factors that astrogeologists can make whole careers out of. All we can say for sure is that, for a star as bright and hot as the sun, Venus is too close, Earth is clearly within the Goldilocks zone, and Mars is probably close to the tail end of it. How far away from the star the Goldilocks zone is depends on the star's energy output. A very dim red dwarf star, like Wolf 359, would require a planet to be only about 1.5 million kilometers away from it to receive as much energy as Earth does from our sun — that's only 0.01 A.U., 1% of the Earth-sun distance. A bright and powerful star like Sirius A, on the other hand, would require a planet to be 5 A.U. away from it to receive as much energy as the Earth does from the sun. Interestingly, both of those distances have potentially disastrous consequences. If a planet is only 0.01 A.U. away from its star, the star's tidal influence is going to be enormous. The strength of tidal forces varies directly with the larger object's (i.e. the star's) mass, but inversely with distance cubed. The tidal forces on a planet only 0.01 A.U. from a star 1/10 the mass of the sun are, therefore, going to be 0.1 / 0.013 = 100,000 times as strong as the tidal forces the Earth experiences from the sun. This all but guarantees that the planet will be locked in synchronous rotation with its star — that is, its rotational period must match its orbital period, so the same side is always facing the star. One side of such a planet would be in perpetual daylight, while the other would be in perpetual night. The climate on such a world would be much different than the climate on Earth. Dim stars also have the disadvantage that their Goldilocks Zones are going to be narrower. There is disagreement as to exactly how wide
Traveling - The First Thing on Your To-Do List
There is nothing quite like traveling, like seeing a new place for the first time or returning to a favorite place. People of all ages, from all countries, travel to foreign places for many different reasons – namely work, family and leisure. Whether by plane, train, ship or automobile, travel is generally a pleasurable experience, at least for the people who can financially afford comfortable and safe methods of travel. But it has more benefits than satisfying one’s need to make money, as well as to see loved ones and enjoy one’s self on vacation. There are other benefits of traveling that many people often overlook.
HOW DIETING AND EXERCISING CAN CHANGE YOUR LIFE?
One of the traveling benefits is finding and keeping humility. Too often, people get wrapped up in their lives, their daily routine of working, sleeping, eating and living. They become self-absorbed to the point it affects their health, their happiness, and their perspective.
It’s a great, big world out there with billions and billions of people, who each day live their life and have their own unique experiences.
Travel reminds those paying attention that they are not the only ship in the sea, that this is a huge world and that they are only a small, insignificant pea in it. This is quite a humbling experience – to go to another country and see large numbers of peoples living differently, and coming to understand how large the crazy world actually is. When people who learn return home, they keep with them this perspective for the rest of their life and they benefit from this is knowledge and perspective.
Another benefit to traveling is coming to see one’s native country in a different light, in a different way. This is done through being able to compare and contrast home from a foreign location, done most always through traveling. A new perspective may be formed.
Away from home, one comes to understand what “home” actually is and what it means.
Perhaps their native country is not as free as they had been told or originally thought it to be, for example. One does not understand what it means to be a citizen of their native country until they have seen it from a distance, from another, completely different country. When traveling elsewhere and having to live according to a foreign place’s laws and social norms, one immediately thinks of how things are done in their own country and culture and begins to favor one way or another. This changes how one feels about their native country, whether in a better or worse light. This notion can be applied to various characteristics, such women’s rights, human rights, customs and traditions, beliefs, a trust of government, etc. Traveling is always beneficial for the individual experiencing it.
Another great benefit to traveling is the life experience. Many people in the world do not have the luxury of going to another country for pleasure, or even to another city in their native country for that matter.
Traveling gets a person out of their comfort zone, away from all their normal pleasures and comforts and way of doing things.
This forces them to be adventurous, to live life to the fullest, to take the most of this precious gift of life and use the time they have to discover new things, meet new people and experience a completely different life – much like people experience when reading fictional stories: They get to become whoever they are reading about, just like in travel they get to become the citizens of the country they are visiting, even if for just a short time. They live outside themselves.
To conclude, traveling is good for a person of any age. It not only helps people to form a better understanding of themselves, their beliefs and their lives, it also provides people with a better understanding of the world in which they live, even if it's beyond their immediate environment. And it may even help a person to feel connected to the many people living in the world, even if their lives never meet, even if their lives are so completely different that they may as well be from different planets.
There are no hesitations. Go. Privatewriting.com will take care of your academic success. Just place an order and get ready for the trip.