Question about the Trench Run

[Batman]

I'm not going to be able to prove that it would be time consuming with figures, but this is how I see it.

I see. Very convincing point you have there."I can't be arsed to do the numbers but that's my opinion, so there".

The DS is travelling very fast towards Yavin 4. The snubfighters are travelling very fast towards the DS. The fighters would have to basically "double back"...by actually reversing course in order to be "caught" by the DS and be travelling at its speed. These fighters can pull off massive G's, so it's definatly possible...but I would think it would take at least a few seconds to get oriented...

...whithout bothering to do the numbers so your estimate has no basis whatsoever. I like it how we're down to 'a few seconds' from your original 'time-consuming', though.

at which point they would be sitting ducks for TIE's and turbolasers.

Too bad neither came into play until the rebel forces were within spitting distance of the DS so that's a complete non-issue. The rebels had allthe time in the world to 'double back' BEFORE they got there.

Not very long, to be sure...but that would still be a bitch to have to do in the middle of a fire fight.

Too bad the firefight didn't start until AFTER they had lots of time to match velocities.

[LadyTevar]

Since the DeathStar was the size of a small moon, and had a magnetic field surrounding it (as per ANH), could the Death Star not have had a gravity well that would have allowed the Snubfighters to 'orbit' at a relative speed, and pull off the TrenchRun as if it was on a true planet?

Yes.

When you're moving in a circle with an 80 km radius at 1 km/s, the centripital force is 12.5 N/kg. That kind of acceleration is about the same as Earth's gravity(9.8 N/kg), the gravity of the Death Star's interior, the gravity of 1E21 kilograms of matter/antimatter(Death Star Fuel?) at 80km away(10.4 N/kg), and consistent with Saxton's derivation of the surface gravity of Coruscant(13.9 N/kg).

YAY!!! Someone knows the Math that makes my head spin just trying to think about!

So, in other words, the idea is that the DeathStar's own 'planetary' mass is going to keep the snubfighters in relative position to it, like I thought it wuold?

[LadyTevar]

Why would it take a few seconds, given they are accomplishing magintudes of order greater acceleration then the DS?

Why would it take a few seconds, when they can wrap around the DeathStar to lose that extra speed as they settle into orbit around it? Circling in for a landing, so to speak?

[Batman]

Since the DeathStar was the size of a small moon, and had a magnetic field surrounding it (as per ANH), could the Death Star not have had a gravity well that would have allowed the Snubfighters to 'orbit' at a relative speed, and pull off the TrenchRun as if it was on a true planet?

Yes.
When you're moving in a circle with an 80 km radius at 1 km/s, the centripital force is 12.5 N/kg. That kind of acceleration is about the same as Earth's gravity(9.8 N/kg), the gravity of the Death Star's interior, the gravity of 1E21 kilograms of matter/antimatter(Death Star Fuel?) at 80km away(10.4 N/kg), and consistent with Saxton's derivation of the surface gravity of Coruscant(13.9 N/kg).

YAY!!! Someone knows the Math that makes my head spin just trying to think about!

So, in other words, the idea is that the DeathStar's own 'planetary' mass is going to keep the snubfighters in relative position to it, like I thought it wuold?

I'm afraid not neccessarily(sp?). The above presupposes
1. That the X-Wings are moving at 1kps,
2. They're doing so to stay in 'orbit' ,and
3. that there's 1E21 kgr of mass present (whre does that number come from?).
None of which, IIRC, is backed up by canon.

[Hardy]

So, in other words, the idea is that the DeathStar's own 'planetary' mass is going to keep the snubfighters in relative position to it, like I thought it would?

Well, it does guarantee that the fighters don't have to do much to keep from flying off the surface of the Death Star. If the Death Star itself makes a sudden change in rotation rate or change in velocity, I believe that the Starfighters would have to artificially match that rate. Considering the monster accelerations they are capable of (17,000m/s² according to this site), that should be no problem.

EDIT: Come to think of it, if they were moving up a polar trench and the Death Star was rotationg, the fighters would have to deal with some Corolois forces and would have to add some lateral motion to compensate.

[Praxis]

You could also ask:
"How could airplanes hold a stable relative position to Earth?"
Earth moves with a speed, you would think of as high. But still anything reamains relative to Earth.

I think what he’s saying is that the fighters only seem to be traveling a few hundred miles/hour along the surface of the death star, but the death star itself would have been moving through space several orders of magnitude faster than that. It’s possible that the death star was moving at a constant velocity and the fighter ‘matched speed’ with it before beginning their attack run.

But even then, since the fighters were barely skimming along the DS’s surface any sudden acceleration on the part of the DS should have sent the fighters crashing into the surface or flying out into space. Since the death star apparently has fantastic acceleration abilities (100 Gs at least), it’s not clear why whoever was driving the death star didn’t just accelerate briefly and smash into the fighters. Or, during the trench run, they could presumably have decelerated suddenly and flung the fighters out of the trench and into space, where they could be easily picked off by defensive turbolasers. If the rebels were flying 100 meters from the surface and the DS accelerated suddenly the pilots would have had less than half a second to react before they crashed. Maybe their flight computers have some sort of 'terrain following' setting or something.

Since the earth doesn’t accelerate, air planes don’t have this problem.

Simple. Suddenly accelerating and decelerating would have ruined Tarkin's big show.

[Hardy]

1. That the X-Wings are moving at 1kps,

Look at Red Leader's targeting computer. It gives the range to the target in metres(that's the default assumption since SW uses metric units) and changes by about 1000 once a second.

2. They're doing so to stay in 'orbit'

That's the assumption I'm trying to prove.

3. that there's 1E21 kgr of mass present (whre does that number come from?).

1e38 J/c²=1.1E21kg

[Batman]

1. That the X-Wings are moving at 1kps,

Look at Red Leader's targeting computer. It gives the range to the target in metres(that's the default assumption since SW uses metric units) and changes by about 1000 once a second.

During the trench run. Invalidated by all other visuals of X-Wings moving across the DS, which show speeds wildly incompatible with that, leave alone NEVER show them 'orbiting'.

2. They're doing so to stay in 'orbit'

That's the assumption I'm trying to prove.

See above, and you can't use an assumption as evidence for a statement.

3. that there's 1E21 kgr of mass present (whre does that number come from?).

1e38 J/c²=1.1E21kg

Assuming the DS can shoot exactly once. Um-no?

[Alan Bolte]

The human element probably doesn't matter with respect to the possibility of the Death Star accelerating. When you have gravitic technology and EM thrust vectoring for a ship with accelerative capabilities an order of magnitude more than is required, together with tachyonic and other sensors, all controlled largely by an onboard computer system as well as the droid, the human is basically just there to say what to head for and what to aim at.

As for the Dagobah question, it would certainly help to go do some quote mining on the subject, but off the top of my head I think the best explanation is probably that Luke's a whiner and he'd have to clean out parts of it before flying off.

[Butterbean569]

Batman:

I don't have the numbers because I don't have time to crunch the numbers. Why? Because I have been studying for a final I have at 7 tonight. So yes, you're right...my statement was without technical evidence and was wrong. When I was first talking about "time-consuming", I referring to the "few seconds"...I didn't backpedal and go from minutes to seconds like you seem to think I did. Doesn't really matter, though, because I can't prove it so I'm wrong.


Go ahead and wank off to the fact that I conceeded to you


So the general consensus is that the flight computer is able to make the adjustments by itself? That seems pretty reasonable. I'm not trying to deny that any of this happened...because it obviously did happen...I'm just trying to figure out a way to explain it.

[Hardy]

During the trench run. Invalidated by all other visuals of X-Wings moving across the DS, which show speeds wildly incompatible with that,

If the Death Star had a surface gravity equal to Earth's, the the fighters would have to be moving at 890 m/s to avoid falling to the surface. Otherwise, they must have been applying a downward force to not fall to the surface. The latter is most likely during the dogfights, and I will concede that they were not orbiting during the dogfights outside the trench.

In the trench run, the Rebels were being chased by TIEs. There is no reason to assume that they were not going as fast as possible to try to outrun them. If the orbital velocity of the DS is 890 m/s, then the escape velocity is 1,250 m/s. The fighters had to have been staying below that or they'd leave the surface, which is why the TIEs didn't simply accelerate to catch up.
Speeds around 1km/s were observed on both Red Leader's and Luke's targeting scopes, which is between the estimated orbital and escape velocities.

leave alone NEVER show them 'orbiting'.

Define "orbit". I want to know if we're talking about the same thing.

See above, and you can't use an assumption as evidence for a statement.

I'm not.
1. I did not pull 1 km/s out of my ass; I used the the targeting computers of Red Leader and Red 5 as a reference.
2. I am trying to determine that they are in orbit using a=v²/r. I "know" v and r, and they should be in orbit if a is pretty close to the gravity of the interior of the DS.

I made sure that I did not resort to circular logic before I made the calculation.

3. that there's 1E21 kgr of mass present (whre does that number come from?).

1e38 J/c²=1.1E21kg

Assuming the DS can shoot exactly once. Um-no?[/quote]
True. That would make the DS more massive.
Nonetheless, we did observe Earthlike gravity in the interior of the station. Even without knowing the mass of the DS, we can infer that the fighters were subject to Earthlike gravity since they weren't too far from the surface.

[Batman]

During the trench run. Invalidated by all other visuals of X-Wings moving across the DS, which show speeds wildly incompatible with that,

If the Death Star had a surface gravity equal to Earth's,

Which is so far unproven.

the the fighters would have to be moving at 890 m/s to avoid falling to the surface. Otherwise, they must have been applying a downward force to not fall to the surface. The latter is most likely during the dogfights, and I will concede that they were not orbiting during the dogfights outside the trench.

Thank you.

In the trench run, the Rebels were being chased by TIEs. There is no reason to assume that they were not going as fast as possible to try to outrun them.

Yes there is, namely the fact that going as fast as they could would crash them into the Trench walls within fractions of a second. Those fighters are capable of thousands of g's of accelleration, remember?

If the orbital velocity of the DS is 890 m/s, then the escape velocity is 1,250 m/s. The fighters had to have been staying below that or they'd leave the surface, which is why the TIEs didn't simply accelerate to catch up.

Garbage. You're assuming they would behave like unpowered objects in orbit, which is patently untrue. As long as I have the engine power I can maintain any orbit at completely arbitrary velocities, and that's presupposing there's enough gravity to require them to do so in the first place.

Speeds around 1km/s were observed on both Red Leader's and Luke's targeting scopes, which is between the estimated orbital and escape velocities.

During the trench run. You already conceeded they propably DIDN'T elsewhere so that theory goes right out the window.

leave alone NEVER show them 'orbiting'.

Define "orbit". I want to know if we're talking about the same thing.

As I understand it (which, I will admit, might be 100% completely wrong as I positively suck at math) to maintain orbit requires a vehicle to maintain a given combination of altitude/velocity to stay in orbit. The X-Wings DON'T. They're flitting all over the place.

See above, and you can't use an assumption as evidence for a statement.

I'm not.
1. I did not pull 1 km/s out of my ass; I used the the targeting computers of Red Leader and Red 5 as a reference.

Both of which are during thwe Trench Run and contradicted by the other scenes.

2. I am trying to determine that they are in orbit using a=v²/r. I "know" v and r, and they should be in orbit if a is pretty close to the gravity of the interior of the DS.

Except there is no reason to assume the X-Wings need to maintain orbit, nor is there a reason to assume the (artificial, I might add) gravity INSIDE the DS extends so much as a millimetre beyond its surface.

1e38 J/c²=1.1E21kg

Assuming the DS can shoot exactly once. Um-no?

True. That would make the DS more massive.

Throwing your calculations off by a rather large margin, I'm afraid.

Nonetheless, we did observe Earthlike gravity in the interior of the station. Even without knowing the mass of the DS, we can infer that the fighters were subject to Earthlike gravity since they weren't too far from the surface.

Garbage. Artificial gravity is a known quantity in Wars. The gravity apparent within the station is completely irrelevant to deciding it's mass. By your reasoning, since the Millenium Falcon apparently had Earth-like gravity, it should therefore have the mass to go with it.

[Drooling Iguana]

Actually the problem gets even worse if the DS was still accelerating toward the planet rather than simply ‘coasting’ – and since the imperials were presumably trying to reach the planet as quickly as possible in order to blow it up, that might have been the case. Then matching velocities in the normal sense would have been impossible and the fighters would have had to constantly accelerate in the direction of the DS’s flight in addition to whatever other maneuvers they were performing. And since they were flying all over the curved surface of the DS while maneuvering erratically, that direction of acceleration would have been constantly changing from their point of view.

I don't have the movies with me right now to check, but I seem to recall some nameless crewman on the Death Star saying "We are preparing to orbit the planet" when it arrived at Yavin. If it was just in orbit, then the fighters could have kept up with it with their engines off.

[Hardy]

During the trench run. Invalidated by all other visuals of X-Wings moving across the DS, which show speeds wildly incompatible with that,

If the Death Star had a surface gravity equal to Earth's,

Which is so far unproven.

It is possible to get an estimation of the gravity by knowing the time it takes for objects like downed starfighters to hit the surface from an estimated altitude. It would be thrown off since they are travelling on a curved surface, though. But you could use the same type of calculations you use for ICBM trajectories.

Yes there is, namely the fact that going as fast as they could would crash them into the Trench walls within fractions of a second. Those fighters are capable of thousands of g's of accelleration, remember?

The trench is a virtually straight path. There'd be no risk of crashing into a wall unless you deviate. The fighters were travelling in a straight line relative to the trench.

Garbage. You're assuming they would behave like unpowered objects in orbit, which is patently untrue. As long as I have the engine power I can maintain any orbit at completely arbitraryvelocities , and that's presupposing there's enough gravity to require them to do so in the first place.

Yes. During the dogfights above the trench, this would be so since they are clearly moving at less than 900 m/s.

But why bother with your engines when you can go on a ballistic path down the trench?

During the trench run. You already conceeded they propably DIDN'T elsewhere so that theory goes right out the window.

I conceeded to the argument that outside the trench, they weren't always in orbit. I still do argue that they were orbiting inside the trench.

leave alone NEVER show them 'orbiting'.

Define "orbit". I want to know if we're talking about the same thing.

As I understand it (which, I will admit, might be 100% completely wrong as I positively suck at math) to maintain orbit requires a vehicle to maintain a given combination of altitude/velocity to stay in orbit. The X-Wings DON'T. They're flitting all over the place.

Well, you kinda-sorta have Kepler's second law down which effectively guarantees that the lower you go, the faster you need to go.

But orbits don't need to be completely straight paths. You can change inclination, velocity and altitude, mind you.

The X-wings in the trench are not "flitting all over the place", however.

Both of which are during the Trench Run and contradicted by the other scenes.

I am(and was initially) referring to the Trench Run itself, now. Not the other scenes. Note the title of the thread.

Except there is no reason to assume the X-Wings need to maintain orbit, nor is there a reason to assume the (artificial, I might add) gravity INSIDE the DS extends so much as a millimetre beyond its surface.

Downed fighters fell to the surface of the station despite originally moving away from its surface. Some force had to bring them down.
The simplest force that I can think of would be the gravity of the interior levels pulling them down.

Throwing your calculations off by a rather large margin, I'm afraid.

Not nescesarily. Remember that I used the 1E21 kg to compare my results with. It doesn't directly have any bearing on it.

On a side note, the Death Star didn't seem to have the gravity of a gas giant, so the gravity of the fuel must've been shielded against or it refuels after every shot.

Nonetheless, we did observe Earthlike gravity in the interior of the station. Even without knowing the mass of the DS, we can infer that the fighters were subject to Earthlike gravity since they weren't too far from the surface.

Garbage. Artificial gravity is a known quantity in Wars. The gravity apparent within the station is completely irrelevant to deciding it's mass. By your reasoning, since the Millenium Falcon apparently had Earth-like gravity, it should therefore have the mass to go with it.[/quote]
Didn't I just say "Even without knowing the masss of the DS..."?
If I know the surface gravity why do I need to know the mass just to know the surface gravity?


You may ignore the arguments if you may and prepare for a concession.

[Hardy]

Okay. I do realize that I am making too many assumptions about the gravity of the Death Star. Until I see the Battle of Yavin again, and have made throughrough observations, I will concede to your arguments, Batman.

EDIT: Now I have made some obsevations.
Two Rebel pilots are shot down at what looks to be 50 metres. It took two of them three seconds to hit the ground. This implies 11 m/s² accelerations.

Porkins hit the ground after one second and was cruising at about 10-20 meters, implying between 10m/s or 40m/s².

Red Leader hit the surface after about 5 seconds (I marked it when we last see him, not when Luke sees him hit the ground, which is about 7). At about 200-500 meters we have between 16 and 40 m/s². If there was no delay between when he hit the ground and when Luke saw him hit, then we have 8.2m/s² and 20m/s².

So it looks like the gravity of the Death Star is between 8m/s² and 40 m/s². Realistically, it seems that the DS' surface has a gravity close to Earth's
.
Though my height measurements were somewhat imprecise.

I also have Red Leader's approach down. He seems to be moving at about 1.2km/s according to his targeting display. But the speed may not be constant since his approach lasted longer than 40 seconds.
Also timing Luke's approach from 36km away, I derived an average speed of 233 m/s but it may be faster considering that there were so many interjections which may have made the scene appear longer.

So, again, I concede. An orbit is highly unlikely.

[Tychu]

Is it possible the Death Star wasnt moving at all, maby only slightly. Where does it ever say the Death Star was moving? When we see the snub fighter fleet passing Yavin the death star seems like its just sitting there and...
....waiting for Yavin and Yavin 4 to move about their orbits so the death star will relatively "clear the planet"

[Alan Bolte]

Tychu, there is no reason for the Death Star to come to a standstill relative to Yavin, as it would both require more energy and be slower than achieving an orbit opposite that of the moon base. Furthermore, large objects and great distances tend to distort normal perspectives of movement, so actual analysis of the movement would be far preferable to a face-value evaluation.

As to whether the DS actually is passively orbitting the planet, I suppose we'll have to determine the distance between the DS and Yavin and its speed, then compare that to the stated time to intercept. Hasn't someone already done that somewhere?

Also, whether it was passively orbitting for much of the duration is irrelevant to the topic at hand, because all you need is one quick burst of acceleration from the DS to swat the fighters on its surface if that is an effective tactic.

[Tychu]

Well the Empire did think that the Rebels stood no chance of destroying their beloved metal star isnt it possible that they planned on waiting?

I mean it did take some time for the Death Star to "clear the planet"

[The Original Nex]

Well the Empire did think that the Rebels stood no chance of destroying their beloved metal star isnt it possible that they planned on waiting?

I mean it did take some time for the Death Star to "clear the planet"

Did you miss the announcement of teh DS's Comm system: "We are orbiting the planet at maximium velocity" They weren't just sitting there.

And as to the point: "what's the rush," do you honestly think the Imperials wanted to take the chance that the Rebels would evacuate and the DS would arrive to Yavin IV only to find another abandoned base?? Of course not, that would be retarted. The DS wanted to get to the moon ask fast as possible to wipe out the Rebels once and for all, not make a leisurely trip around a pretty gas giant to see the sights.

[Connor MacLeod]

Look at Red Leader's targeting computer. It gives the range to the target in metres(that's the default assumption since SW uses metric units) and

That's a conservative guess. I estimated from frame by frame measurement it was probably closer to something between 2-2.5 km/s on average.. the more precise figure I typically used was like 2.34 or something.

There's also the small fact that according to the novelization that there were "distortion fields" that were of sufficient strength to disrupt starfighter mobility (something like .3 - 30% of normal? *shrug*)

There are also repuslors to consider - the fighters might very well be using repulsorlifts to prevent "falling" towards the Death Star during strafing runs or the Trench run.

[Hardy]

Look at Red Leader's targeting computer. It gives the range to the target in metres(that's the default assumption since SW uses metric units) and

That's a conservative guess. I estimated from frame by frame measurement it was probably closer to something between 2-2.5 km/s on average.. the more precise figure I typically used was like 2.34 or something.

That measurement is far more accurate. I had the DVD playing at 1/7 and was watching the counter.

There are also repuslors to consider - the fighters might very well be using repulsorlifts to prevent "falling" towards the Death Star during strafing runs or the Trench run.

If you're going at 2.3 km/s(definitely higher than what the DS' escape velocity is), you'd most defininitely have to apply a force to prevent flying off the Death Star. Falling would be the least of their concerns at such speeds. Then again, I did take gravity measurements that got 40 m/s², where the escape velocity would be 2500m/s.

[Hardy]

As to whether the DS actually is passively orbitting the planet, I suppose we'll have to determine the distance between the DS and Yavin and its speed, then compare that to the stated time to intercept. Hasn't someone already done that somewhere?

At fifteen minutes until the Death Star had a clear shot, the Rebel tactical display showed the DS pretty far away from the planet. At five minutes, the DS was much closer to the surface of the planet. When the Death Star finally got a clear shot it was pretty far away from the planet's surface.


The DS could be in a highly elliptical orbit like the other moons of Yavin or it could have been trying to take advantage of the planet's gravity by using a swingby.

Now you can probably tell if it's an orbit by judging if it adheres to Kepler's second law. I worked with this and the radius vector between the planet and the DS came pretty close to covering the same area in the same amount of time (Note that I did adjust for perspective at least twice when I did this). It would be better if someone else took a measurement of this.

In one measurement without any attempt to correct for perspective, I got one rate of 264 px²/minute for 15 to 5, then I got 457 px²/min for .
When I corrected perspective (made the gas giant appear as a circle perfect), I got 143.1 px²/minute and 901px²/min respectively. The latter measurment almost seems like it adheres to Kepler's second law.

Can anyone do better, since my area measurements sucked?[/list]

[Batman]

Word of caution: that display is obviously not to scale. While I can't come up with a reason of why it should arbitrarily show the DS closer to Yavin when it isn't really, so assuming that it was is reasonably safe, any distances and therefore velocities derived from this are highly suspect.
And that's assuming the DS was in a proper orbit in the first place.

[Hardy]

Word of caution: that display is obviously not to scale.

True, but it is worthless if it isn't positionally correct.

While I can't come up with a reason of why it should arbitrarily show the DS closer to Yavin when it isn't really,

How do you know that the DS maintained a constant altitude? Orbits don't require that. The rest of the planets around Yavin have highly elliptical orbits, themselves.

so assuming that it was is reasonably safe, any distances and therefore velocities derived from this are highly suspect.

I can agree with that.

And that's assuming the DS was in a proper orbit in the first place.

Did you even read the post? It was in response to whether or not the DS was in an orbit around Yavin.
Logic is as follows:
1. DS has a known trajectory.
2. If the trajectory is consistent with Kepler's second law, then we can say that the DS is orbiting the planet without assistance from the engines. Occam's Razor would not allow the DS' engines to be going about a trajectory that looks like an orbit.
3. If the trajectory is not consistent with Kepler's second law, then we can assume that the orbit was assisted by repulsors and engines.

I'm not assuming that it's a proper orbit; I'm checking to see if it has the properties of a proper orbit.

[Batman]

Word of caution: that display is obviously not to scale.

True, but it is worthless if it isn't positionally correct.

Um-it can't be positionally correct if it isn't to scale.

While I can't come up with a reason of why it should arbitrarily show the DS closer to Yavin when it isn't really,

How do you know that the DS maintained a constant altitude? Orbits don't require that. The rest of the planets around Yavin have highly elliptical orbits, themselves.

Um-that sort of was my point. No reason to show an altitude change that isn't there.

And that's assuming the DS was in a proper orbit in the first place.

Did you even read the post? It was in response to whether or not the DS was in an orbit around Yavin.

Oops.

Logic is as follows:
1. DS has a known trajectory.

Derived from where? Given that the rebel display shows us exactly three positions for the DS and is HIGHLY simplistic, that's a pretty shaky source. If you're treating it as a mere assumption, that's a whole different ballgame. (How does The Silence And I put it :'Here there be speculation' )

2. If the trajectory is consistent with Kepler's second law, then we can say that the DS is orbiting the planet without assistance from the engines.
Occam's Razor would not allow the DS' engines to be going about a trajectory that looks like an orbit.

Err-why not? If wouldn't require them and no sane person would assume they're on without further evidence but they're certainly not forbidden.

3. If the trajectory is not consistent with Kepler's second law, then we can assume that the orbit was assisted by repulsors and engines.

Okay.

I'm not assuming that it's a proper orbit; I'm checking to see if it has the properties of a proper orbit.

My mistake then.