So You Want To/Write a Hard Science Fiction Story With Space Travel: Difference between revisions

{{quote|''"Did you ever notice when you're jacking off, that it's more of a turn-on to fantasize about the girl next door than it is to fantasize about a supermodel? Because with the girl next door, you're thinking, hey, ''this could really happen!''"''|'''[[George Carlin]]'''}}

 

Since space travel is involved, it's important to remember that human beings have traveled in space for over five decades now. We ''know'' what is involved in getting from the Earth's surface to low Earth orbit. We know what's involved in landing on a rocky world 400,000 kilometers away. We know what effect micro-gravity has on human bones and muscles. A realistic story involving space travel must take all this accumulated human knowledge into account. The cartoonish world of 1950s B-movie astronauts having a "navigational error" that sends them to an "uncharted planet" with an Earthlike ecosystem inhabited by alien women who speak English is, and should be, a [[Discredited Trope]] -- but so should portraying space travel like anything other than space travel just because it [[Rule of Cool|looks neater that way]] in your head. In many ways, you'll just have to dispense with the story making artistic sense so the story can make logical, scientific, engineering and micro-economic sense as something that could actually happen in the future, so be ready for a lot of artistic disappointments.

 

 

== Outline of Artistic Disappointments and Non-recommended Tropes ==

* [[Faster-Than-Light Travel]] / [[Time Travel]]. Example: The [[Xeelee Sequence]] by Stephen Baxter implements this with [[Sufficiently Advanced Technology]].

* [[Techno Babble]]. Example: Orion's Arm implements this with such phrases as "hyperdenebola collapse" to refer to the de-assimilation that tends to happen when a colony's communications with [[The Assimilator| the Amalgamation]] are cut off. According to Wikipedia, Denebola is Beta Leonis, a star in constellation Leo about 43 light-years from Earth. What this star has to do with "hyper", "collapse", and the Amalgamation is not actually obvious.

* [[Did_Not_Do_the_Research| Inaccuracies]] that aren't, strictly speaking, about math, natural sciences, microeconomics or futurology, liberties that are not painstakingly [[Deconstructed]] or [[Reconstructed]] or [[Rule of Index| are revealed to be just too implausible by their deconstruction or reconstruction]], and [[Acceptable Breaks From Reality| breaks from reality without regard to how acceptable they are in other genres]]. Inaccuracies that are not about these topics are liable to be confused with inaccuracies that are about these topics, and hard SF is all about [[Consistency]] and [[Shown Their Work| accuracy]], so even if inaccuracies are not confused topic-wise, inaccuracies are still kind of wrong for hard SF.

 

Let's take as our example a rocket trip from Earth to Saturn. How long will it take to make the flight?

 

 

So, with the ability to accelerate indefinitely, ''now'' how long will it take to get to Saturn?

... where sqrt means square root, and c is the speed of light in a vacuum (about 300,000,000 m/sec). As you can see, it varies according to how fast you're going (that pesky v² term in the denominator).

 

 

# T = (c/a) * ArcCosh[a*d/(c²) + 1]

... where v_e is the exhaust velocity of your engines, ln means "natural log" (there's a button for this on all scientific calculators), M is the mass of the rocket ''with'' fuel, and M_e is the mass of the rocket ''without'' fuel (the empty weight). M/M_e is sometimes called the "mass ratio" of the rocket.

 

 

With such a stultifying mass ratio ''just'' to get into Earth orbit, you can see why flying to other planets in a matter of days -- or worse, flying to another star within a human lifetime -- just isn't practical for modern chemically-propelled rockets. Most hard SF authors will solve this problem by using more exotic forms of rocket propulsion which have much much higher exhaust velocities, or which can derive their propellant from someplace other than the rocket's fuel tanks. These include:

* Nuclear fission (NERVA) engines

* Ion engines, such as those on the ''Dawn'' and ''Deep Space One'' spacecraft

* Controlled nuclear fusion engines

* [[Ramscoop|Ramscoops]]

With the exception of ion engines, all of these are mere drawing-board designs at present, and all of them have practical problems. NERVA engines require shielding to protect the crew (and the ship's more delicate electronics) from their radioactivity, but saving weight is so important that there is only enough shielding to protect a cone in front of the reactor. Ion engines have extremely low thrust levels (the engines on the ''Dawn'' spacecraft can, at max throttle, produce about 1/3 of an ounce of thrust). Orion drive requires an enormous pusher plate that dramatically increases the dead weight the spacecraft has to carry. Controlled nuclear fusion has never been accomplished, at least not in a way that produces more energy than it consumes. Ramscoops rely not only on the controlled nuclear fusion of light hydrogen (which is even trickier than the controlled nuclear fusion of heavy hydrogen), but also on the ability to collect the extremely rarefied interstellar gas without inducing significant drag, which might not even be possible.

 

 

== [[World Building]] ==

Third, if any 1000 tonne space ship can easily accelerate to a tenth of light speed, then every two-bit spaceship owner has in his possession a weapon of mass destruction. Those 100,000 megatons of TNT-equivalent kinetic energy will act like 100,000 megatons of ''actual'' TNT if they strike a planet. Want a future populated by plucky tramp space-freighters and sneaky space pirates? It ain't gonna happen if every ship is a Hiroshima-on-steroids waiting to happen. Every spacecraft captain will be on too short a leash. Any spacecraft that even ''looks'' suspicious will be killed before it can become a threat. (And, yes, ''all'' fast-moving spacecraft, and even stationary spacecraft, will eventually be detected -- there ain't no [[Stealth in Space]].) Any civilization that didn't take these precautions wouldn't ''be'' a civilization for very long. This might work as a setting for your future totalitarian dystopia, but is hardly the right world for romantic swashbuckling adventures.

 

 

So what do you do when you ''need'' your characters to be able to move between the stars faster-than-light, or [[Transporters and Teleporters|teleport]], or have a [[Tractor Beam]], or do any of the other myriad things that our current best guesses at the law of nature say are impossible? You set the technology up in such a way as to '''limit the damage''' to your story and your setting. Maybe your [[Deflector Shields]] are magnetic, and can only affect charged particles and ferromagnetic metals -- and your spaceship needs to open up holes in its shields to shoot iron slugs or particle beams at an enemy. Maybe the high speeds needed to traverse interplanetary distances in days or hours are imparted not by your space freighter's own engines, but by planet-side pushers that will only push it onto a predictable course, thereby eliminating the threat of rogue spaceship commanders turning their vehicles into WMDs. Maybe your transporters only let you beam between one transporter pad and another (unlike the transporters in a certain [[Star Trek|softer SF franchise]]). Maybe the violations of the Laws of Thermodynamics needed to make [[Stealth in Space]] work are curtailed in some way that prevents you from getting useful energy out of any warm object (which, like some types of [[Reactionless Drive]], would have driven your Space Oil companies out of business).

Maybe faster-than-light travel only works between certain [[Portal Network|rare points in space]], and your ships must maneuver in normal space to get to and from them. Maybe FTL movement is impossible within some large distance from a gravity source, requiring your space ships to leave the solar system -- or at least leave Earth orbit -- before they can go FTL. Maybe your space pirates ''can'' jump to hyperspace at the first sign of trouble, but so can your space cops, and they have FTL weapons they can shoot at each other while in hyperspace.

 

 

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