Hypothetically, do spaceships fly?

John221us

John221us

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Ok, so I am reading a sci fi novel and the author refers to the pilot "flying" the ship. So, this is deep space, not taking off from a planet. Is that flying, or would it be falling or traveling or something like that?
 
Flying in the sense of navigating a ship in three dimensions.
Not flying in that it is all inertia and delta-v management, not flying via interaction of a lifting body and a medium.

It's unlike flying, but more like flying than anything else humans do.
 
I say if the ship has thrusters, it can be flown. Failing that, it's a thrown rock.
 
"It's not flying, it's just...falling with style...."

Depends on how you define "flying". Most of the time, you're just in free-fall. Changing course is a computation-intensive problem, but extremely simple in execution unlike aeronavigation. Point it in the right direction, shoot the rocket for the right amount of time.

Ron Wanttaja
 
That is true if you are in free space, Ron. Orbital mechanics is a bit more involved. If you think pitch=airspeed, power=altitude is a fun concept in a plane, the "speed = altitude" of orbital mechanics is even more fun.
 
flyingron said:
That is true if you are in free space, Ron. Orbital mechanics is a bit more involved.
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No, it's the same. Just that your inertial velocity vector is constantly changing, hence "computationally intensive." Biggest problem aircraft drivers would have is a lack of visual reference to the velocity vector, because where you point isn't necessarily the direction you're traveling.

Ron Wanttaja
 
wanttaja said:
No, it's the same. Just that your inertial velocity vector is constantly changing, hence "computationally intensive." Biggest problem aircraft drivers would have is a lack of visual reference to the velocity vector, because where you point isn't necessarily the direction you're traveling.

Ron Wanttaja
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Relative movement. Although it may take a while time to notice visually.
 
flyingron said:
That is true if you are in free space, Ron. Orbital mechanics is a bit more involved. If you think pitch=airspeed, power=altitude is a fun concept in a plane, the "speed = altitude" of orbital mechanics is even more fun.
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Orbital mechanics is still free fall unless you're firing.
 
Again, if you can control it, you're flying it. Otherwise, you aren't.
 
While there are some concepts that have continual power for long periods, no existing spacecraft flies anything but purely ballistic trajectories almost all the time. That doesn't mean out of control. All spacecraft control attitude with inertial devices separate from propulsion, such as reaction wheels, or in some cases by spinning the spacecraft.

Orbital mechanics doesn't really change this. It's never possible to be "free of gravity" like sci fi books like to say. Every ballistic trajectory is curved. It's just "as straight as possible." You follow the trajectory that minimizes the "action" (kinetic - potential energy).

It's unlike flying because lines aren't really straight, and attitude is independent of velocity (not acceleration if it's nonzero). All the forces are zero in an Einstein Equivalence sense.

I'd say it's flying in the same sense that driving a car is. But there is no word separate for it. NASA uses terms like "flight hardware" and "flight physical" for space ops as well as airborne ops.
 
Well, if you want to get relativistic, then anytime the thrusters are not firing (I'll leave gyroscopic attitude maintenance for the moment), you are travelling in a straight line through 4 dimensional space-time.
 
JeffDG said:
Well, if you want to get relativistic, then anytime the thrusters are not firing (I'll leave gyroscopic attitude maintenance for the moment), you are travelling in a straight line through 4 dimensional space-time.
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Straight line orbit??
 
EdFred said:
Straight line orbit??
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It's a bit obfuscating....but yes.

It's straight in the same sense that a great circle is on the surface of the earth -- it's the shortest distance trajectory between two points. Spacetime is not flat in the presence of objects with signficant mass.

When dealing with trajectories on manifolds, you have to stay on the surface. It's cheating to tunnel through the earth to make a "true" straight line distance. And that tunneling trajectory is only straight if you consider the 2D surface in a 3D space. Mathematically, considering the intrinsic properties of curved surfaces is quite interesting and useful -- and you can indeed measure "flatness" and "straightness" without considering dimensions outside the surface.
 
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MAKG1 said:
It's a bit obfuscating....but yes.

It's straight in the same sense that a great circle is on the surface of the earth -- it's the shortest distance trajectory between two points. Spacetime is not flat in the presence of objects with signficant mass.

When dealing with trajectories on manifolds, you have to stay on the surface. It's cheating to tunnel through the earth to make a "true" straight line distance. And that tunneling trajectory is only straight if you consider the 2D surface in a 3D space. Mathematically, considering the intrinsic properties of curved surfaces is quite interesting and useful -- and you can indeed measure "flatness" and "straightness" without considering dimensions outside the surface.
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Except you can "burrow without cheating" between, say, L4 and L5. That's a straight line - ignoring the warping by the gravitational effects of the sun. Space time isn't warped enough by the sun that the orbit path of the earth is a straight line in the "fabric" of space-time. The mathematics of the two vectors do draw an arc - again ignoring the small effect of the warpage by the sun. I can't figure out a way you could get a true straight line orbit even if the mass of the orbited object was great enough to distort space time. It's always going to be an arc in relation to the Cartesian coordinates of that region of space, even if the coordinates are warped as viewed by an outside viewer.
 
You can "burrow" between Lagrange points by continuously spending fuel and applying an outside force. You will follow the straightest possible line in the curved spacetime without it -- that's the Relativistic equivalent of Newton's First Law. I said it was obfuscating....Relativistic orbital dynamics can't be explained well in this medium. If you're interested, I'll steer you to a book -- Taylor & Wheeler, "Spacetime Physics." It's meant for undergrads, so it has some math, but it's not overwhelming. J.A.Wheeler has a unique writing style for a physics author -- he's quite visual.

Tunnelling in this context is not just cutting corners. The "surface" is 4D, so making a tunnel would require taking advantage of some 5th dimension the spacetime is embedded within. You can do that conceptually and mathematically, but there is no evidence that such things actually exist. Sci fi writers love them, though -- that's a "wormhole."
 
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MAKG1 said:
You can "burrow" between Lagrange points by continuously spending fuel and applying an outside force. You will follow the straightest possible line in the curved spacetime without it -- that's the Relativistic equivalent of Newton's First Law. I said it was obfuscating....Relativistic orbital dynamics can't be explained well in this medium. If you're interested, I'll steer you to a book -- Taylor & Wheeler, "Spacetime Physics." It's meant for undergrads, so it has some math, but it's not overwhelming. J.A.Wheeler has a unique writing style for a physics author -- he's quite visual.
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Which is opposite of what Jeff said. He said when NOT firing thrusters, you are travelling in a straight line. When in reality the only way to travel in a straight line is to use thrusters. I already have a firm grasp on that, so the reading of the book is unnecessary. Now if we are talking a spherical coordinate system with say the sun being the center, then yes, I can buy the "straight line" argument, ignoring eccentricity of orbits, as r and either theta or phi depending which way you look at it, would remain constant. However in a cartesian system you aren't going to have that.
 
Calling him a pilot makes it easy for us to understand his job. You could just as easily say you pilot a car. In this, you have described the navigator, helmsman, and person responsible for the safety of movement. Not to be confused with captain, aircraft commander, or admiral. Their jobs may not include any of the jobs mentioned.
 
EdFred said:
Which is opposite of what Jeff said. He said when NOT firing thrusters, you are travelling in a straight line. When in reality the only way to travel in a straight line is to use thrusters. I already have a firm grasp on that, so the reading of the book is unnecessary. Now if we are talking a spherical coordinate system with say the sun being the center, then yes, I can buy the "straight line" argument, ignoring eccentricity of orbits, as r and either theta or phi depending which way you look at it, would remain constant. However in a cartesian system you aren't going to have that.
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The surface does not conform to a Cartesian system. That's the basic misunderstanding here. Cartesian systems describe inertial behavior in flat spacetime. It ain't flat. Much of general Relativity is making the coordinate system so you can describe orbital behaviors like you're trying to. Even for a black hole, you'll end up with something that looks a lot like polar coordinates. But the radial coordinate isn't linear in distance.

Read the Taylor & Wheeler book, or something comparable; it's an astonishingly good read if you're into exotic physics and geometry. If you understand polar coordinates, your math is good enough. I can't explain this properly in a few paragraphs with no diagrams. Relativity is describing the same physics, but in a vastly different mindset -- in GR, there is no gravity, only fictitious forces arising from curved spacetime. I don't think this is the best way to describe orbits far away from the event horizon of a black hole, but it's an interesting approach nevertheless.
 
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MAKG1 said:
While there are some concepts that have continual power for long periods, no existing spacecraft flies anything but purely ballistic trajectories almost all the time. That doesn't mean out of control. All spacecraft control attitude with inertial devices separate from propulsion, such as reaction wheels, or in some cases by spinning the spacecraft.

Orbital mechanics doesn't really change this. It's never possible to be "free of gravity" like sci fi books like to say. Every ballistic trajectory is curved. It's just "as straight as possible." You follow the trajectory that minimizes the "action" (kinetic - potential energy).

It's unlike flying because lines aren't really straight, and attitude is independent of velocity (not acceleration if it's nonzero). All the forces are zero in an Einstein Equivalence sense.

I'd say it's flying in the same sense that driving a car is. But there is no word separate for it. NASA uses terms like "flight hardware" and "flight physical" for space ops as well as airborne ops.
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I guess NCC-1701-D gets it wrong, as I've noticed the warp core working harder and continuously at higher warp factors; they need to continue outputting energy to maintain velocity.
 
MAKG1 said:
The surface does not conform to a Cartesian system. That's the basic misunderstanding here. Cartesian systems describe inertial behavior in flat spacetime. It ain't flat. Much of general Relativity is making the coordinate system so you can describe orbital behaviors like you're trying to. Even for a black hole, you'll end up with something that looks a lot like polar coordinates. But the radial coordinate isn't linear in distance.

Read the Taylor & Wheeler book, or something comparable; it's an astonishingly good read if you're into exotic physics and geometry. If you understand polar coordinates, your math is good enough. I can't explain this properly in a few paragraphs with no diagrams. Relativity is describing the same physics, but in a vastly different mindset -- in GR, there is no gravity, only fictitious forces arising from curved spacetime. I don't think this is the best way to describe orbits far away from the event horizon of a black hole, but it's an interesting approach nevertheless.
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I think we are talking past each other. I'm looking at it from completely outside the system. You're looking at it from inside the system. If I am an outside the universe observer and launch a projectile with an initial velocity of c, (I know, I know object with mass can't go c, blah blah blah) and I trace the path, I will see it curve towards every star, galaxy, supercluster, etc. Inside the system all measurements will show it going "straight". It's like walking on a train. How fast is the person walking? 5mph? Even though the train is traveling at 60? You're measuring the velocity relative to the train, because you're on it. I'm outside the train seeing the person moving at 60+/- whatever the vector sum is.
 
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Jaybird180 said:
I guess NCC-1701-D gets it wrong, as I've noticed the warp core working harder and continuously at higher warp factors; they need to continue outputting energy to maintain velocity.
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They built it already?
 
EdFred said:
I think we are talking past each other. I'm looking at it from completely outside the system. You're looking at it from inside the system. If I am an outside the universe observer and launch a projectile with an initial velocity of c, (I know, I know object with mass can't go c, blah blah blah) and I trace the path, I will see it curve towards every star, galaxy, supercluster, etc. Inside the system all measurements will show it going "straight". It's like walking on a train. How fast is the person walking? 5mph? Even though the train is traveling at 60? You're measuring the velocity relative to the train, because you're on it. I'm outside the train seeing the person moving at 60+/- whatever the vector sum is.
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Yes, you're getting it.

But general Relativity is explicitly built "inside the system." If you want to understand Relativity, you need to go there.

If you're "outside the system," you have to make some assumption about what goes outside -- and that something is completely unconstrained by reality.

One of the big discoveries of GR (well, really, differential geometry) is that it's possible to completely describe a system with a minimum of assumptions from inside. You don't have to embed a sphere in 3D to figure out how to move about on its surface.

When you start talking about the really big stuff -- like the shape of the universe -- you can't go outside to look, and no one has any idea what would be there if you could. This is a vast simplification; cosmology is impossible without it.
 
MAKG1 said:
When you start talking about the really big stuff -- like the shape of the universe -- you can't go outside to look, and no one has any idea what would be there if you could. This is a vast simplification; cosmology is impossible without it.
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I have my own theory about that.

Funny thing is I was reading Parallel Worlds and as I'm reading it I'm thinking "now wait a minute, if that's the case then this can't be right..." A little bit further into the book, Kaku goes on to point out what was wrong, and what we now believe was completely in line with what I was thinking.

He's one guy I would love to have lunch with. A really long lunch.
 
EdFred said:
I have my own theory about that.

Funny thing is I was reading Parallel Worlds and as I'm reading it I'm thinking "now wait a minute, if that's the case then this can't be right..." A little bit further into the book, Kaku goes on to point out what was wrong, and what we now believe was completely in line with what I was thinking.

He's one guy I would love to have lunch with. A really long lunch.
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That's not a theory. It's a guess.

If it's not testable, it's not a theory. Period. Regardless of what Kaku or Linde might say.

Superstring guys like to really go out on the metaphysical limb here. SUSY is a "pretty" model, but there is no evidence that reality conforms to it. I'll change my tune if one of the LSP searches ever succeeds, but I've been waiting 30 years for that. A neutralino observation would be a big deal. I'm not holding my breath.

I wrote my dissertation on several flavors of post-cold-dark-matter cosmology. No one knows what the dark matter really is, and it strongly affects the dynamics, particularly very early on (later, it's just conventional Newtonian gravity -- even at cosmological scales). Observing some would make it a much stronger theory. But as it is, there are an infinite number of free parameters to screw with -- self-interactions of the dark matter are completely undefined and can do just anything.
 
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MAKG1 said:
That's not a theory. It's a guess.

If it's not testable, it's not a theory. Period. Regardless of what Kaku or Linde might say.

Superstring guys like to really go out on the metaphysical limb here. SUSY is a "pretty" model, but there is no evidence that reality conforms to it. I'll change my tune if one of the LSP searches ever succeeds, but I've been waiting 30 years for that. A neutralino observation would be a big deal. I'm not holding my breath.
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Semantics.

1. a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena: Einstein's theory of relativity. Synonyms: principle, law, doctrine.
2. a proposed explanation whose status is still conjectural and subject to experimentation, in contrast to well-established propositions that are regarded as reporting matters of actual fact. Synonyms: idea, notion hypothesis, postulate. Antonyms: practice, verification, corroboration, substantiation.
3. Mathematics . a body of principles, theorems, or the like, belonging to one subject: number theory.
4. the branch of a science or art that deals with its principles or methods, as distinguished from its practice: music theory.
5. a particular conception or view of something to be done or of the method of doing it; a system of rules or principles: conflicting theories of how children best learn to read.
6. contemplation or speculation: the theory that there is life on other planets.
7. guess or conjecture: My theory is that he never stops to think words have consequences.
 
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Unless its powered flight, all spacecraft are all falling . . .
 
EdFred said:
Semantics.

1. a coherent group of tested general propositions, commonly regarded as correct, that can be used as principles of explanation and prediction for a class of phenomena: Einstein's theory of relativity. Synonyms: principle, law, doctrine.
2. a proposed explanation whose status is still conjectural and subject to experimentation, in contrast to well-established propositions that are regarded as reporting matters of actual fact. Synonyms: idea, notion hypothesis, postulate. Antonyms: practice, verification, corroboration, substantiation.
3. Mathematics . a body of principles, theorems, or the like, belonging to one subject: number theory.
4. the branch of a science or art that deals with its principles or methods, as distinguished from its practice: music theory.
5. a particular conception or view of something to be done or of the method of doing it; a system of rules or principles: conflicting theories of how children best learn to read.
6. contemplation or speculation: the theory that there is life on other planets.
7. guess or conjecture: My theory is that he never stops to think words have consequences.
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Are you a cosmological expert? What are your qualifications in this area? Maybe you should go back to talking about who can log PIC
:stirpot:

Just reminiscing...:D
 
PilotAlan said:
Whatever the strongest net gravity vector is.
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If it never enters orbit, I don't really consider it falling. Being influenced by the affecting body, sure, but falling, not until it is in orbit, or decaying orbit.
 
EdFred said:
If it never enters orbit, I don't really consider it falling. Being influenced by the affecting body, sure, but falling, not until it is in orbit, or decaying orbit.
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You don't get to define falling. It has a definition already. Free-fall reference frames appear precisely in this context in Einstein's papers as early as 1907, but the concept goes back at least to Galileo and perhaps much further.

If you exceed the escape velocity of the earth, you'll be in solar orbit. If you exceed the solar escape velocity, you'll orbit the galactic center. And so on. Your semantics aren't useful, hence the formal definition that differs from it.

And you seem to think all orbits are closed. I hope that's just poor language.

The restricted two body problem (where one mass is much larger than the other) always has the smaller body in an orbit. It may be a hyperbolic orbit, but it is still an orbit. Hyperbolic orbits exceed the escape velocity....
 
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EdFred said:
If it never enters orbit, I don't really consider it falling. Being influenced by the affecting body, sure, but falling, not until it is in orbit, or decaying orbit.
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MAKG1 said:
You don't get to define falling. ...
If you exceed the escape velocity of the earth, you'll be in solar orbit. If you exceed the solar escape velocity, you'll orbit the galactic center. And so on.
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Everything's orbiting something.

Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum.
 
MAKG1 said:
You don't get to define falling. It has a definition already. Free-fall reference frames appear precisely in this context in Einstein's papers as early as 1907, but the concept goes back at least to Galileo and perhaps much further.

If you exceed the escape velocity of the earth, you'll be in solar orbit. If you exceed the solar escape velocity, you'll orbit the galactic center. And so on. Your semantics aren't useful, hence the formal definition that differs from it.

And you seem to think all orbits are closed. I hope that's just poor language.

The restricted two body problem (where one mass is much larger than the other) always has the smaller body in an orbit. It may be a hyperbolic orbit, but it is still an orbit. Hyperbolic orbits exceed the escape velocity....
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And if it has an escape velocity higher than anything in the universe?
 
EdFred said:
And if it has an escape velocity higher than anything in the universe?
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Then, it's in a nonperiodic orbit. So what? Most comets are in nonperiodic (hyperbolic) orbits, but they are only approximately ballistic.

Orbits around extended objects like the Galaxy aren't closed even if they are bound, anyway.

You're making a distinction where none exists. It doesn't explain anything, simplify anything, or match what anyone in the field uses. Time to let it go.
 
MAKG1 said:
Then, it's in a nonperiodic orbit. So what? Most comets are in nonperiodic (hyperbolic) orbits, but they are only approximately ballistic.

Orbits around extended objects like the Galaxy aren't closed even if they are bound, anyway.

You're making a distinction where none exists. It doesn't explain anything, simplify anything, or match what anyone in the field uses. Time to let it go.
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So anything non closed or decaying is always in orbit arond .....well, everything?

Sounds like a cop out explanation. Or a way to make equations work that wouldn't otherwise. Every object inboud from the Oort cloud by that definition is in orbit around everything from Ceres to the sun. Something passing between the sun and Vega is in orbit around both?
 
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