Science Fiction is about speculation. As such, we are often asked to suspend our disbelief and imagine what could be in the future. I'm not sure how gravitons behave exactly or why they don't bend the Enterprise in half, but I'm O.K. with them so long as Jordie can use them to outwit those pesky Ferengi. Having said that, many authors and screenwriters take this liberty to mean that they can ignore what we do already know about the universe. Some of these can be subtle. Why, among other questions, didn't Ripley's eardrums burst when she opened the airlock to outer space in Aliens. Or they can be absurd such as the sonar "pinging" that went on in "Wing Commander." Here are a few important notes that will help your space ships jive with the real world.
First, and this is a pet peeve of mine, no one in the movies ever bothers to slow down. In order to escape Earth orbit, a ship needs to accelerate to about 25,000 MPH. If this ship heads directly to another planet (not really possible) at 25,000 MPH, the receiving planet has to be more massive than the Earth or its gravity won't catch the ship. There are conditions, of course. If the planet is moving away from the spaceship, the relative velocity is lower and a smaller planet will make the grab. If the ship and planet are moving toward each other, the catch is even harder. This impacts science fiction in near future stories such as "Armageddon" where a very shuttle like craft accelerates the crew toward an object the size of Texas, where they land. What? At 25,000 miles an hour Texas couldn't catch that ship, plus the ship and the asteroid are headed straight for each other increasing the relative velocity. In the real world Bruce Willis would have had a line something like. "Here comes the aster...there went the asteroid. Does anybody know how to turn this thing around?"
There are several solutions to this problem. The first is to turn your ship around and burn your engines until you slow down enough to be caught. This is very expensive in terms of fuel, if that's important on your spaceship. NASAs favorite approach is to let its craft swing around in orbit until they're moving in more or less the same direction as the object they want to study. In order to put the NEAR Shoemaker spacecraft into orbit around the asteroid Eros, NASA needed a very slow approach. Eros is only about the size of Manhattan and would only capture a slow moving object. Rather than launch tons of expensive fuels to slow NEAR, they sent it on a looping course around the inner solar system so that it fell into pace with Eros and could be put into orbit with a relatively small engine burn. The final tactic is to approach the target at full speed but allow yourself to hit the atmosphere so that friction will slow you enough for the planet to capture you. This is hazardous and frightening. The movie 2010 offered an accurate and visually stunning example of this.
The second concern has to do with pressure bottles. The habitable portion of any spacecraft is a pressure bottle just like the tank on your gas grill only more so. In deep space, density is measured in terms of atoms per square meter. At sea level, where humans are comfortable, density is measured in kilograms per square meter. It takes a serious container to hold the soupy atmosphere in. While many science fiction venues have toyed (more or less unrealistically) with the idea of opening a hatch and letting the air out, there is another major concern that doesn't seem to bother folks. Anything that changes the air pressure inside a space ship risks rupturing the hull. Fires, for example, are not uncommon in space stories but are a deadly peril. In addition to using up all the oxygen and cooking crew members, fires heat and expand the atmosphere and release a tremendous amount of many gasses. A ship with an size fire on it is in danger of a rupture if it doesn't quash the fire or start out-gassing soon. Also, in addition to the inherent peril of putting a bullet through the hull, firearms are dangerous on ships because the gunpowder expands as it burns increasing pressure. In a small ship this could be very hard on the eardrums or pressure sensitive equipment.
Finally, there's an important lesson about space ships in the tag line to the space classic Alien, "In space no on can hear you scream." Good point, because a vacuum won't carry vibrations away from the ship. In fact, no vibration can get off a ship, not the vibration from the cooling fan, not the stomp of Storm Troopers feet, nothing. A rod of iron, struck with a hammer and left drifting in space could well ring for years. In practical terms, space ships have dampeners and flexible joints to absorb routine rattles, but a ship subjected to unusual trauma, hit by and asteroid or space torpedo for example, may well continue to damage itself as energy waves roll back and forth. The only place I've ever seen this issue dealt with in any fashion was the movie "Apollo 13." For some time after the explosion, the cabin is filled with groaning squeaking and rattling noises, much as Fred Haise, who was actually on Apollo 13 described the scene.
Well, that's it for this month. Till next time, see you in the stars.
Now get out there an write.
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