For just change in direction, you have a good point. But if it’s accelerating – say, speeding off away from the mother ship – then I think banking would make sense, for the comfort of the pilot and other passengers. Isn’t consistently feeling being pushed down into your seat (along with back into it) more comfortable than inconsistently being shifted to one side?
Talking about SciFi nonsense: What about the times in Star Trek, the ship is told to make a full stop. Full stop compared to what? The local center of the solar system? The nearest planetary object? The center of the galaxy? In space, all motion is relative. As long as you’re not accelerating, you can think of yourself as stopped and the rest of the universe moving.
Or, you have all these ships that travel umteen faster than the faster than light. However, as an enemy ship approaches the Enterprise, you’ll have Sulu saying “Captain: That ship is three thousands meters and closing (two seconds of dramatic pause) Two thousand meters! (another two seconds of dramatic pause) One thousand meters!..”
Do the writers realize how big a meter actually is? At 3000 meters and futuristic technology, the enemy ship should be able to knock the toupee off William Shatner’s head with a spitball. My son calculated once that the enemy ship was heading towards the Enterprise at less than 20 miles per hour.
You are correct, airplane flight controls (i.e. flaps, ailerons, spoilers, and elevators) work on the atmosphere by displacing it, pushing against the air. Ergo, they would be useless on a pure space vehicle.
You have a misunderstanding with respect to Newton’s 3rd Law. When Newton talks about an action and a reaction, what that means is that in order for me to push on an object, that object also pushes back on me. If you push on a door to open it, the door also pushes back on your hand. That is what creates the force that you must overcome. Forces push both directions - on the pusher and the pushee.
Now as for rockets, you are under the misunderstanding that the exhaust is pushing on the air, and that is why the air is pushing the exhaust. This is incorrect.
The exhaust does not need to push on anything, all it needs to do is move away from the rocket. By pushing the exhaust out the back of the rocket, the exhaust has to push forward on the rocket.
Once pushed out the back, the exhaust gases are free to travel under the momentum they were given during the rocket’s push. They then interact with any ambient environment. But those interactions are irrelevant to the push that the rocket gets. The rocket’s motion comes from the push it gives the exhaust gases.
To look at it differently, the burning of the fuel in the chamber produces a rapid expansion of gas (think explosion). However, the chamber constrains the pressure in all directions except one - out the nozzle.
This is the same way an internal combustion engine sprays gasoline into the cylinder, then ignites the gasoline. The burning gas expands, pushing the piston. It pushes equally on all sides of the cylinder, but the rest of the cylinder is rigid and doesn’t give, but the piston is free to move. Ergo, the piston moves, which pushes the shaft that transfers that motion on down the line.
It is the expansion of the gas in the rocket chamber that provides the push on the rocket engine. The expanding gases push in all directions, but can only move out the back. All the pushing in the sideways directions is canceled out (the left push equals the right push, etc). What is left is the push forward on the rocket and the gas motion backwards out the exhaust opening. Gases moving backwards are not pushing on the rocket, so the rocket has an imbalance in forces - a push forward, gases moving out the back.
That expanding exhaust goes through the nozzle, which constricts the flow to make it faster. Faster means more momentum and energy transferred to the exhaust gases. That pressure that squeezes the gases to push them out the back faster is the flipside of the gas pushing on the nozzle to push the rocket faster.
Even if it’s not accelerating in the direction of motion, banking is useful from an inertial standpoint. Consider the simple roller coaster, for instance: banked turns greatly reduce the lateral g-forces on riders by turning them into vertical g-forces (which riders can more easily withstand).
Granted, such sci-fi ships usually have gravity generators and inertial dampeners and such, but it’s not unreasonable to think that they might prefer to lessen the wear on such systems by banking into a turn.
Not very useful if you want the rest of the universe to stop, too. Presumably the galaxy-spanning governments in sci-fi establish reference points against which ships can compare their motion.
Such cases usually involve a chase, meaning the differential between the two ships’ speeds is small, or fine maneuvering, in which case minimal speed is apropos.
Powers &8^]
Ah, of course. Why didn’t I think of that? Of course, most of those space shows have them employing artificial gravity technology and inertial dampers, so you would think that would supersede the g-forces.
My favorite Star Trek blunder was when 2 crew members were out of phase with the universe, allowing them to move through solid objects like walls and doors, yet the floor still held them up.
Well, you might have some arbitrary frame of reference. The nearest twenty stars, taken as an average, would do reasonably well in most “smooth” parts of space.
In James Blish’s old Star Trek novel, “Spock Must Die,” the ship was on a mission to deploy benchmark buoys, which could be used to define an artificial coordinate grid, just as we, on earth, use the observatory at Greenwich, England, as our artificial zero longitude.
Yeah but it would be a bit weird to be heading towards a star that relative to the benchmark buoys is moving, so when the captain says “full stop” you have to crank up the engines and accelerate away from the target star…
But anyway, “full stop” seems interchangeable with “turn off all the engines”, which I think is fair enough in practice. The speed at which the Enterprise can drift is necessarily less than c and negligable compared to its warp speed.
And we can further handwave / postulate that within a star system “full stop” means relative to the nearest astronomical body.
And what did they set those benchmark buoys against? Stars constantly move around in relationship with each other. There was an article I read about searching for the sun’s siblings. These are stars that were born in the same gas stelar nursery as the sun. Now, these stars are scattered throughout half of the galaxy. Even if those buoys somehow managed to stay in a constant framework with each other, the various stars are moving around that framework. It’d be like having the longitude and latitude of New York changing week by week.
Star Trek made space travel like a station wagon trip to Cleveland. You never see a situation where people’s clock’s were out of sync. It’s a universe where it’s always two o’clock in the afternoon, no matter which side of the planet you’re on. You never see two spaceships in different axises with each other. A Klingon ship was never upside down compared to the Enterprise.
I understand why this was done. They didn’t want a show where Captain Kirk had to be wired up on five or six cups of coffee because it’s 4:00am on the Enterprise, but 2:00pm on the capital city of Planet Whatsis. That would interfere with their overall hopeful theme of the show that made it so popular – the Universe is filled with hot aliens that just want to make out with geeky trekkers.
Not sure I agree. Nobody knows what would happen momentum-wise when the warp engines are turned off - obviously it wouldn’t continue at warp speed, but other than that, since warp drive was a fictional construct at the time, I don’t think there’s any way to know. But surely the impluse drive would cause the Enterprise to accelerate in one direction, and that motion wouldn’t instantly cease once the impulse was discontinued. There would have to be an impulse in the opposite direction to make it stop. Considering how close they got to alien ships when they were communicating with them, if “full stop” just meant “turn off the thrust”, they would have crashed into a lot of other ships.
Obviously, “full stop” was a stupid thing to say. It would have made more sense to say, “Maintain current distance from alien ship and match rotation”, or something like that. But I’m sure they didn’t want to get that detailed.
TNG did hint at this. There was an episode where they accessed something that I believed was called a “Federation time beacon”, and they had a few episodes where the captain had to be rousted out of bed to deal with some important situation. And some of the movies explored 3-dimensional space a bit.
It’s strange that you quoted one line of my post, ignoring the very next line that addresses exactly this.
Agreed. Just like I was saying with being in a star system. “Stop” would have to mean maintain distance from the nearest astronomical body.
I don’t believe I did that. This was the rest of your post:
That does not at all address the issue of having to apply opposite thrust. It might be what you meant, but it wasn’t what you wrote. I quoted the part of your post which I was addressing. In my opinion, it gets confusing fast when people quote an entire post when they are only addressing one particular sentence, so I tend not to do that. Sorry if that offends you.
A simple example that should be clear.
You are in a space module. No engine. There is a bomb beside your space module. It explodes. Expanding explosion in every direction. Your space module gets blown outward from the explosion.
Now. Consider your space module has a tank of hydrogen and a tank of oxygen. Tubes lead out beside each other. They mix together and you add a spark. Boom. Explosion of oxygen and hydrogen pushes your module away.
Keep doing that. You have a rocket motor. The explosion expands outwards. Against your space module. Pushing you. It expands in every direction. But there is nothing but your space module to push. The explosion expands in all directions from the ignition spark. Energy. Shape the explosion chamber well, to take advantage of as much of the explosion as possible.
Of course it is easier for the explosion to expand into empty space. But some of it will still push you.
Well in that case you’ve mis-parsed what I was saying, or I was not clear.
I was saying that in interstellar space, it doesn’t matter if the ship drifts, not that it won’t drift. So “stop” can mean just switch off the engines.
But then I also said, yeah it would have to have a different meaning if you’re in the vicinity of a ship or planet where the “stop” would have to be relative to the nearest body. And I am aware that would require an acceleration but didn’t think it necessary to mention that (especially considering what I’d said about the benchmark buoys).