"Slow" sublight speeds for advanced starships?

[Jean Paul]

I timed the Devastator's overpass in the ANH opening scene.

11 seconds stem to stern.

An ISD is a mile (1.6) km long. This makes it 327 mph. (526 km/h)

This is about the same speed as the fastest Top Fuel dragsters.

Why does the Empire's premier warship, when chasing another vessel, move at a speed that a primitive internal combustion ground vehicle can match? Surely this should be snail's pace for such a vessel.

Not bashing it or trying to say it can't go faster than that, I'm sure there's an logical explanation but I thought I'd thow the question out and see what you all think.

[Rogue 9]

Simple: The camera's not stationary. It's in orbit, and thus is moving along at an orbital velocity, which the Devastator and Tantive IV are exceeding.

[StarshipTitanic]

Simple: The camera's not stationary. It's in orbit, and thus is moving along at an orbital velocity, which the Devastator and Tantive IV are exceeding.

That would make sense, as the Tantive IV was about to pick up Obi-wan and probably parked in orbit.

[McC]

Naive question of the day: then how come the planet doesn't appear to be moving? Because the camera's orbit is geostationary?

[Rogue 9]

Naive question of the day: then how come the planet doesn't appear to be moving? Because the camera's orbit is geostationary?

Because it's uniformly desert?

I'm tempted to say geostationary orbit, but that can't be right, as the planet would be much farther away. However, it could be that the camera is artificially maintaining station over a point on the planet through means other than simple orbital mechanics, which would make it be moving even faster than I'd originally thought in order to keep up with the planet's rotation.

[Praxis]

Naive question of the day: then how come the planet doesn't appear to be moving? Because the camera's orbit is geostationary?

Do you have any idea how big a planet is? They'd have to be moving VERY fast for us to see the planet move visibly in the few seconds we saw.

[McC]

Because it's uniformly desert?

I'm at my girlfriend's presently, so I don't have direct access to my DVDs, but IIRC there are clouds and such visible that are unchanging. Besides, it's uniformly desert but not uniformly terrained (if that makes any sense), and noticable variations of surface coloration and texture exist.

I'm tempted to say geostationary orbit, but that can't be right, as the planet would be much farther away. However, it could be that the camera is artificially maintaining station over a point on the planet through means other than simple orbital mechanics, which would make it be moving even faster than I'd originally thought in order to keep up with the planet's rotation.

That's usually what I think whenever I see a space scene that depicts such slow velocities: the camera has to be moving damn fast too.

Do you have any idea how big a planet is?

A little bigger than a tennis ball?

They'd have to be moving VERY fast for us to see the planet move visibly in the few seconds we saw.

The planet is rotating at 0.0042º per second, to be precise (assuming 24 hour day). Assuming Earth diameter, for total circumference 40,074 km, that's about 0.47 km/sec past a "stationary" point.

Dunno if that's remotely relevant or anything, but there it is anyway.

[Armored Goldbar]

Or because the ISD's shot pattern combined with the damage sustained by the Tantive IV are doing a whole lot to slow the Rebel ship down. She's already one solid hit from disabled and I really doubt she's moving anywhere near top sublight speed.

Furthermore the Devastator might even be slowing down as they are ridiculously close to the corvette and have most likely made up lots of ground on her already. If anything, the situation shows that the Devastator is extremely fast for its size since it managed to chase down a damn blockade runner.

[The Silence and I]

Ok, using McC's figures:

A planet ~85,300 pixels wide should exhibit one pixel of movement per second past a point.

[.47km/sec, 40,074 km; therefore to achieve one pixel/sec, divide 40,074 by .47.]

Now in this image (600x240 pixels) Tatooine is very large, the line traced around the horizon is part of a circle I drew 6800x6800 pixels. [Obviously working with this scale there is some inaccuracy, but the difference is significantly less than an order of magnitude.] Therefore this planet should be observed moving at a rate of ~0.08 pixels/sec. Now I'm aware this is not the exact scene in question, but the planet's size relative to the camera doesn't change that much IIRC (I had to use google, I have yet to get the new DVD's, hence the wrong scene). So every 12 or so seconds we should see one pixel of rotation...

So if someone wants to take a look, go for it. But I think it will be hard to see such small rotation (assuming the camera shows Tatooine that long).

And Armored Goldbar, I'm not sure that is a terribly valid point; supposedly things in space do not slow down when the engines stop firing (I say supposedly because SW makes me question that from time to time). The Tantive IV would have needed engine power to slow down at all, and a shot pattern from behind cannot slow them down, only inspire them to go faster, and guide them in some direction.

[Armored Goldbar]

Ok, using McC's figures:
And Armored Goldbar, I'm not sure that is a terribly valid point; supposedly things in space do not slow down when the engines stop firing (I say supposedly because SW makes me question that from time to time). The Tantive IV would have needed engine power to slow down at all, and a shot pattern from behind cannot slow them down, only inspire them to go faster, and guide them in some direction.

Hmm....good point. *shakes fist at physics*

And when I cited the shot pattern, I didn't meant to imply that it would cause the ship to slow in and of itself, but rather that it would keep her captain from exercising very many options (including, but not limited to, escaping Tattooine's gravity well and jumping to hyperspace), thus allowing the ISD to run her down.

[Mange]

I timed the Devastator's overpass in the ANH opening scene.

11 seconds stem to stern.

An ISD is a mile (1.6) km long. This makes it 327 mph. (526 km/h)

This is about the same speed as the fastest Top Fuel dragsters.

Why does the Empire's premier warship, when chasing another vessel, move at a speed that a primitive internal combustion ground vehicle can match? Surely this should be snail's pace for such a vessel.

Not bashing it or trying to say it can't go faster than that, I'm sure there's an logical explanation but I thought I'd thow the question out and see what you all think.

Jean-Paul, this is the second time you've started a new thread when there is plenty of material on Mike's site (in articles and in response to hate mail) that deals with this.

[McC]

Jean-Paul, this is the second time you've started a new thread when there is plenty of material on Mike's site (in articles and in response to hate mail) that deals with this.

Mange, sometimes it's nice to pull old topics out and just give them some fresh air, y'know? I really don't see why talking about a topic that has "already been addressed" is such a negative thing around here.

[Ghost Rider]

Jean-Paul, this is the second time you've started a new thread when there is plenty of material on Mike's site (in articles and in response to hate mail) that deals with this.

Mange, sometimes it's nice to pull old topics out and just give them some fresh air, y'know? I really don't see why talking about a topic that has "already been addressed" is such a negative thing around here.

If he provided something fresh it would be different.

Covering ground already trod upon is stupid unless one has something new to actually give meaning to it.

[Chardok]

How about this one: we know the ISD was tractoring the Tantive, right? (Or was it?) Well, if the tantive was trying her damnedest to get the hell out of dodge, and the ISD had that tractor locked onto it, would it not make sense to slow down? perhaps the SD was "Wrangling" the Tantive, so to speak? then, when the Main reactor was shut down, the engines finally went offline (From the strain of trying to power away?) and the SD simply pulled it into the boarding area.

(Yeah, I'm ignoring the shot which hits the satellite thingy on top)

[Jean Paul]

I timed the Devastator's overpass in the ANH opening scene.

11 seconds stem to stern.

An ISD is a mile (1.6) km long. This makes it 327 mph. (526 km/h)

This is about the same speed as the fastest Top Fuel dragsters.

Why does the Empire's premier warship, when chasing another vessel, move at a speed that a primitive internal combustion ground vehicle can match? Surely this should be snail's pace for such a vessel.

Not bashing it or trying to say it can't go faster than that, I'm sure there's an logical explanation but I thought I'd thow the question out and see what you all think.

Jean-Paul, this is the second time you've started a new thread when there is plenty of material on Mike's site (in articles and in response to hate mail) that deals with this.

Well I didn't know this.

I've looked through some of the site but not the whole thing. It is fairly extensive as sites go.

[Mange]

I was a bit grouchy there, Jean Paul. I'm sorry.

[Gil Hamilton]

Well, remember what they were at Tantooine to do. They weren't just passing through, they were there to get Obi-Wan or at least get a message to him. They'd have to slow significantly to get into orbit and the ISD chasing them changes the situation very little. It would be impossible for them to get into contact with Obi-Wan with the Death Star blueprints if they attempted to outrun the StarDestroyer at high sublight speeds, since that would make it impossible to softland anything on Tatoonine. As it was more important to get the DS plans to Obi-Wan with instructions to take them to Alderaan than it was to evade capture, they had to slow to what is nearly full stop in space. Likewise, the StarDestroyer can't exactly dock with them to look to see what happened to the DS plans and to capture who was responsible from a radically different relative velocity, all they could do would be to blow up the Blockade Runner. So, they had to match velocities with a ship that was breaking into orbit.

The only thing that is queer about the scene to me is that neither the Blockade Runner or the StarDestroyer were pointed "backwards", since in space, in order to break, you need to turn over to use your engines to slow. However, that's a very minor cavaet, since they never do that in movies.

[Connor MacLeod]

high acceleration via Ion Drives are usually a big no no close to a planet (considering its a stream of charged particles shot out of the ship's ass at near-c) they obviously wouldn't try moving all that fast (There are repulsors of course, but they're probably using those to keep afloat above the planet ATM.)

Furthermore, they have to divert power to the tractor beams and other systems (weapons, shields, etc.) while trying to capture the Tantive IV - the Tractors and guns at this point are going to be the most power-intensive system, which means that there isn't goign to be as much power to devote to engines or others.

And lastly, there is a consideration that blasting all out at top acceeleration is going to more rapidly drain the ship's fuel supply than a much lower acceleration - so why would they need to? THey can easily slow the ships with tractors, so there's no need to chase after it.

[Jean Paul]

The only thing that is queer about the scene to me is that neither the Blockade Runner or the StarDestroyer were pointed "backwards", since in space, in order to break, you need to turn over to use your engines to slow. However, that's a very minor cavaet, since they never do that in movies.

No you don't. Never heard of reverse thrust? If you've ever had a window seat aft of the wing of a commercial jet you could hardly have missed the large thrust reversing assembly deploying.. it comes out on landing, moving behind the engine nozzels and redirecting the exhaust forward, creating backwards thrust. They use it for braking the plane. (The cut it once they get down to taxiing speed... otherwise the plane would stop, then start reversing up the runway)

No such assembly is visible on either the blockade runner or the star destroyer, however, it is entirely possible that they may use precisely manipulated forcefields to channel and direct the thrust and achieve the same effect.

[Connor MacLeod]

The only thing that is queer about the scene to me is that neither the Blockade Runner or the StarDestroyer were pointed "backwards", since in space, in order to break, you need to turn over to use your engines to slow. However, that's a very minor cavaet, since they never do that in movies.

No you don't. Never heard of reverse thrust? If you've ever had a window seat aft of the wing of a commercial jet you could hardly have missed the large thrust reversing assembly deploying.. it comes out on landing, moving behind the engine nozzels and redirecting the exhaust forward, creating backwards thrust. They use it for braking the plane. (The cut it once they get down to taxiing speed... otherwise the plane would stop, then start reversing up the runway)

No such assembly is visible on either the blockade runner or the star destroyer, however, it is entirely possible that they may use precisely manipulated forcefields to channel and direct the thrust and achieve the same effect.

He's referring to the fact that ISDs appear to have no visible reverse thrusters - at least none large or presumably powerful enough as the rear engines. (Which is actually a valid observation.)

[Batman]

He's referring to the fact that ISDs appear to have no visible reverse thrusters - at least none large or presumably powerful enough as the rear engines. (Which is actually a valid observation.)

Modern jet aircraft don't have reverse thrusters, either. What Jean Paul quite correctly described are thrust reversers on the main engines, and I fail to see what's wrong with his idea that Wars uses particle shielding instead of material-based reversal mechanisms.
The geometry of those reversers is certainly going to be interesting, because the rear profile the thrust needs to be directed around is a lot more massive than the engines of a jet airplane, but I see no flaw in the theory.

[Praxis]

The only thing that is queer about the scene to me is that neither the Blockade Runner or the StarDestroyer were pointed "backwards", since in space, in order to break, you need to turn over to use your engines to slow. However, that's a very minor cavaet, since they never do that in movies.

No you don't. Never heard of reverse thrust? If you've ever had a window seat aft of the wing of a commercial jet you could hardly have missed the large thrust reversing assembly deploying.. it comes out on landing, moving behind the engine nozzels and redirecting the exhaust forward, creating backwards thrust. They use it for braking the plane. (The cut it once they get down to taxiing speed... otherwise the plane would stop, then start reversing up the runway)

No such assembly is visible on either the blockade runner or the star destroyer, however, it is entirely possible that they may use precisely manipulated forcefields to channel and direct the thrust and achieve the same effect.

He's referring to the fact that ISDs appear to have no visible reverse thrusters - at least none large or presumably powerful enough as the rear engines. (Which is actually a valid observation.)

We don't know enough of how SW engines work. It's possible there are numerous small braking thrusters on the hull that don't eject as much visible glowies, OR it's even possible that they can just flip a switch from "forward" to "reverse". Hey, who knows?

[Gil Hamilton]

No you don't. Never heard of reverse thrust? If you've ever had a window seat aft of the wing of a commercial jet you could hardly have missed the large thrust reversing assembly deploying.. it comes out on landing, moving behind the engine nozzels and redirecting the exhaust forward, creating backwards thrust. They use it for braking the plane. (The cut it once they get down to taxiing speed... otherwise the plane would stop, then start reversing up the runway)

No such assembly is visible on either the blockade runner or the star destroyer, however, it is entirely possible that they may use precisely manipulated forcefields to channel and direct the thrust and achieve the same effect.

It's not a matter of that. ISDs are big fucking ships and you don't build mammoth engines on something unless you really need them to move your ship (otherwise, why bother?). When you are dealing with something that is easily the mass of a small moon, you aren't going bother with tiny little engines for breaking, because they can't possibly be as effective as flipping your ship 180 and using your main engines to break. Especially when you consider that if breaking thrusters exist on a ISD or the Blockade Runner, they are so small as to be invisible.

And using an elaborate system of forcefields is so convoluted in terms of engineering that it begs the question "Why bother?" when you can flip the ship and break without elaborate power consuming systems being in place to do the same thing less efficently.

[Praxis]

No you don't. Never heard of reverse thrust? If you've ever had a window seat aft of the wing of a commercial jet you could hardly have missed the large thrust reversing assembly deploying.. it comes out on landing, moving behind the engine nozzels and redirecting the exhaust forward, creating backwards thrust. They use it for braking the plane. (The cut it once they get down to taxiing speed... otherwise the plane would stop, then start reversing up the runway)

No such assembly is visible on either the blockade runner or the star destroyer, however, it is entirely possible that they may use precisely manipulated forcefields to channel and direct the thrust and achieve the same effect.

It's not a matter of that. ISDs are big fucking ships and you don't build mammoth engines on something unless you really need them to move your ship (otherwise, why bother?). When you are dealing with something that is easily the mass of a small moon, you aren't going bother with tiny little engines for breaking, because they can't possibly be as effective as flipping your ship 180 and using your main engines to break. Especially when you consider that if breaking thrusters exist on a ISD or the Blockade Runner, they are so small as to be invisible.

And using an elaborate system of forcefields is so convoluted in terms of engineering that it begs the question "Why bother?" when you can flip the ship and break without elaborate power consuming systems being in place to do the same thing less efficently.

And yet when they approached the Death Star, the Rebel fleet didn't flip around and brake to stop their momentum (though they did flip around to avoid smacking in to the Death Star, their momentum didn't keep carrying them toward the Death Star until they fired the engines or anything). And when the Imperial fleet shot around the moon and cut off the Rebel fleet, they stopped and just sat there, no spinning around to stop or anything.

[The Silence and I]

snip

It's not a matter of that. ISDs are big fucking ships and you don't build mammoth engines on something unless you really need them to move your ship (otherwise, why bother?). When you are dealing with something that is easily the mass of a small moon, you aren't going bother with tiny little engines for breaking, because they can't possibly be as effective as flipping your ship 180 and using your main engines to break. Especially when you consider that if breaking thrusters exist on a ISD or the Blockade Runner, they are so small as to be invisible.

And using an elaborate system of forcefields is so convoluted in terms of engineering that it begs the question "Why bother?" when you can flip the ship and break without elaborate power consuming systems being in place to do the same thing less efficently.

That is of course logical, but requires newtonian maneuvering--I am hardly the first to point out no one in Star Wars uses that. I do not suggest that newtonian motion is a flawed model for Star Wars, but it is clear standard engine drives--including those on an ISD--operate on some different principle.