Engines: most science fiction depicts spacecraft with their engines running the entire time they are shown on-screen; Prometheus, The Martian, Star Wars, Star Trek, and on and on. This is probably because the graphic designers were in love with the deep blue glow they created in the engine exhaust.
Why this is a problem: aside from conserving fuel, the obvious problem with engines that run all the time in space is that it creates constant acceleration. Any time you move a vehicle, that movement requires Delta-v (), defined as change in velocity. If you had unlimited fuel, you certainly could continue to accelerate, but that’s not how it’s done. In space flight, Delta-v is applied, accelerating the craft to the required speed, followed by coasting in space until another change is required. Think about the Apollo Program. Once the vehicles were in Earth orbit, another force was required to push the vehicle toward the moon, Delta-v exerted by the S-IVB (the third stage), increasing the eccentricity of the orbit (not, as is sometimes asserted, to “leave Earth orbit”). This maneuver is called the trans-lunar injection (TLI), and lasts about 300 seconds. By then, enough Delta-v has been applied, the S-IVB is left behind, and the remaining vehicles coast into the moon’s gravity.
All the time in science fiction we see spacecraft depicted as arriving at their destinations with their engines, in the back of the vehicle, producing thrust, when, in fact, the goal is to slow down, which would require a different vector than blasting forward.
Important exceptions: Apollo 13, Solaris, 2001 A Space Odyssey
Gravity: this one is only a factor if you need actors to walk around as they do on earth. Various fictions are used to simulate normal Earth-like gravity inside spacecraft. Sometimes freefall (not “zero gravity” as is sometimes asserted) is simulated in practical affects (Apollo 13), or with computer graphics (The Martian). The most popular sci-fi explanation for artificial gravity is to have the crew on the inside of a spinning mass, like a hamster wheel, though Star Trek only addresses this a couple of times with some bullshift like having gravity plates, and it’s only a problem in one of the movies for about two minutes. Also for fans, one of the often re-used background voices in the original series is “gravity is down to point-8.”
As bad as The Midnight Sky was, props at least for the scene of the injured crew member’s blood floating inside her helmet.
Also, The Martian, Ad Astra: gravity on the moon is only 1/6 Earth’s, and Mars’ is only about 2/3 Earth’s, yet actors pounce around like they were in their back yards.
The difference between CO and CO2: this one is so aggravating to me because it’s so easy to understand. Carbon monoxide (CO) is deadly even in small doses, while carbon dioxide (CO2) is present in the atmosphere and in ever breath we exhale. I saw this error recently in Prometheus, in which a character compares the atmosphere to an “exhaust pipe,” at almost three percent CO2. Screen writers: figure this out!
Ignoring distances and the speed of light: Solaris really bugs me on this one, but Star Trek loves to change the rules based on the plot (“out here we won’t get a reply for weeks,” vs livestreaming via subspace). Solaris is set on a distant world in a distant solar system (unless my map of our solar system is missing a planet or small star), yet it seems to take George Clooney maybe six months (?) to reach it (and in the mean time, surely stuff must have changed on the space station in six months), yet if we acknowledge speed of light is the speed limit of the universe, the next closest star to our sun is Proxima Centauri, which is 4.2465 light years aways. Thus, even if you could accelerate Clooney to just ten percent of the speed of light, it would take him more than 42 years to get there, and Proxima Centauri certainly isn’t anything like Solaris, so that’s not where he is going.
Related: distance, warp drive, and hyperspace. This one gets flattened into nothingness all the time by lazy screen writing. “We’re the only starship within range,” or, “at warp seven we can be there in ten minutes.” Star Wars goes one lazier in The Last Jedi by having the ships lope along at sub-light speeds on the way to Crait, but didn’t we just discuss the speed of light and how far apart stars are? Even in the tightly-packed star cluster, even travel at nearly the speed of light equals months. Don’t believe me? Light, which of course is at the speed of light, takes 13 minutes to travel from Earth to Mars. How far is Crait supposed to be?
Related: time, speed, distance. Pilots know all about time, speed and distance. In the Star Trek episode Tomorrow is Yesterday, the Enterprise flies toward the sun at multi-warp-speed to “break away” at the last second to re-create the time warp that got them to 1967 in the first place. Uh, Captain? The sun is just eight light-minutes away. Then, as we are flashing across the solar system at Warp Zillion, we see stars zipping by like fireflies. At one point, and Sulu says they are traveling at Warp 8. Spock says, “Since we have passed Mercury, the sun’s pull on us has increased greatly. From here, we’ll move even faster.” Mercury is just 3.2 light minutes away from the sun, and Warp 8 is 512 times the speed of light, so, there’s the … oops, splat.
And of course, the time paradox. You knew this was coming. If you go back in time and change anything, everything changes in the “present.” Sure, it was super-cool to let Joan Collins get run over by a car, but you still changed about a hundred things around you, like stealing those clothes? Huh? Maybe naked Audie Murphy decided not to join the army. What then?
Battles in space. Okay, I know, it’s only science fiction, but if energy weapons like phasers, blasters, and photon torpedoes move at the speed of light, and your ship can go faster than that, why don’t you just scurry away from the danger?
Also related: gravity in open space. This is one of the most glaring problems with The Last Jedi, when the rebellion sends in “bombers” to drop bombs on a star destroyer. Drop bombs in space? Drop bombs in space?
Text makes sound: spy movies also do this, but science fiction is the worst about it. When text appears on the screen, little blipping sounds accompany it. Why did anyone ever think this was a thing? Think I’m wrong? Create a text document right now and listen for the blips. No? Text is silent?
Propellers that stop: this isn’t directly connected to science fiction, but it’s an aviation fact: when an airplane engine stops producing power for whatever reason, the propeller almost always continues to turn, a process called windmilling. It’s actually hard to get a prop to stop on an airplane in flight – I’ve tried it a time or two, by choking the mixture to fail the motor, then pulling to nose up to an imminent stall, when airflow over the prop no longer forces it to spin. Some of the time, lowering the nose and letting the aircraft accelerate toward the ground will make the prop start to windmill again; in fact, this is the relight procedure on many aircraft after an engine failure.
Okay, yeah, the reason directors show this in movies is to tell the audience that the engine quit.
Growing potatoes on Mars: as I rewatch The Martian, and simultaneously look up how to grow potatoes, I realize the missing piece: there isn’t enough sunlight on Mars, especially indoors, to grow potatoes. It’s that pesky inverse square law: since Mars is twice the distance from the sun as the Earth is, meaning the amount of sunlight on Mars is eight times less than on Earth.
In conclusion, I need some really realistic science fiction to read. Ideas?