Various speeds, accels and decels in SW (no big ship)

[Mr. Oragahn]

First, don't get any Trek stuff into that thread, thanks.
An ongoing discussion at SBC had me want to try to tackle as many more or less linear acceleration/deceleration cases as possible, as well as speeds.

This would, for the moment, strictly be limited to atmospheric vessels and small ships (fighters, bombers, small cargos), and also missiles and torpedoes.
For each case, it would be most necessary to provide an explanation as to the usefulness and context of each observation.

First, we could list the observable and exploitable instances:



TPM

Time needed for the N-1 to reach the Trade Federation Droid Control ship.
Anakin leaving the Trade Federation ship before it explodes.
Speed of torpedoes.

AOTC

Acceleration of the yellow speeder used by Anakin.
Accelerations of Zam's speeder.
Acceleration and speed of the missile fired by Jango, against Obi-Wan's fighter.
Acceleration of Dooku's ship as he leaves Geonosis.
Speed of various missiles fired by the droids or republic transports on the plains of Geonosis.

ROTS

Speed of the missiles fired at Obi-Wan by the droid fighters.


ANH

The rebel fighters reaching the Death Star.
Time necessary for the Millenium Falcon to reach the Death Star despite a late take off.
The Millenium Falcon and surviving rebel fighters being far away from the Death Star before it explodes.
Speed of torpedoes.

TESB



ROTJ

Acceleration of the Millenium Falcon to escape the menacing wall of flames catching up inside the straight tube.
Acceleration of Luke's shuttle, used to flee the Death Star II.
Speed of missiles, fired from the A-wings, and from Wedge and Lando inside the DSII.
Acceleration of imperial motospeeders.

[Roondar]

Keep in mind that most (if not nearly all) space-based speeds you're likely to find are going to be relative speeds and that this might not be indicative of the real performance of the ships in question*.

It's probably going to be really hard to determine some of those speeds anyway - we can't really assume that what we see is how long it takes. As an example why this is relevant: most Sci-Fi I've seen on TV or in movie format tends to 'shorten the trip'.

We don't actually see starships fly for hours on end if they need those hours to reach their destination, they appear to only take minutes or even seconds to reach their destination.

*) Case in point: when the rebels flew at the DS in ANH, the DS was also nearing them. Now, the DS was obviously not as fast as the fighters, but this does lower the speed and acceleration needed by the fighters to reach the DS.

[Mike DiCenso]

You know, that's an excellent point, Roondar. I don't think in any of the calculations I've ever seen done by anyone on either side of the debate takes the Death Star's velocity and speed into account. Do we even have any other good landmarks in the Yavin system, besides the Death Star to measure against the starfighter's speeds?
-Mike

[Mr. Oragahn]

As far as ANH is concerned, it's precisely this point I also wanted to raise. The Death Star was moving towards Yavin IV, and if we assume the Imperials wanted to take the shortest route (they were on max velocity, so that's likely), that is, intercept the moon instead of trying to catch by going the other way round, then Yavin IV was also moving towards the Death Star.

Based on what I remember from the script and the film, it could have took the fighters between five and less than fifteen minutes to reach the battle station, I think.

We could substitute the Death Star with a light rockball of the same size, to obtain a high end. We'd be looking at the move of the Death Star - now an inert satellite - and the rotation of Yavin IV around Yavin.

Still, speeds and accelerations for torpedoes can be obtained relative to the Death Star, by using the super structure as a yard stick.

[Roondar]

If you truelly want to factor everything in then it will get horribly complicated:

* The fighters and the DS did not approach in a straight line but both followed an orbit around Yavin IV (this may or may not make sense to do depending on a number of issues).

* Depending on which engine is used, the DS and the fighters may or may not have had to compensate for the gravity of the gasgiant.

* The DS may or may not have had an entry-velocity that was non-zero compared to Yavin IV when it exited hyperspace.

* The fighters likely had a desired 'end velocity' relative to the DS that was near-zero (otherwise they'd never be able to do their 'stunts') but not quite zero. This is complicated by the fact that the DS itself may have still been accelerating, depending on what they meant by maximum velocity (this could both mean "we're at maximum velocity now" or "we'll aim to get our highest possible velocity as soon as we can").

* Ironically, the DS may have aimed for an end-velocity of zero, relative to Yavin IV, so as to get a clear shot. This would seem likely because they where obviously at or near to zero relative speed when they shot Alderaan. The irony here is that they'd probably would need to decelerate near the end of the trip to make that possible.

---

Ah, the fun of determining velocity in space. Reminds me of the rather old game Elite II: Frontier. That game, by the way, shows off exactly what is wrong with the dogfights we see in Starwars and all the rest of Sci-Fi. From a real-world physics point of view those scenes make zero sense.

[Jedi Master Spock]

You know, that's an excellent point, Roondar. I don't think in any of the calculations I've ever seen done by anyone on either side of the debate takes the Death Star's velocity and speed into account. Do we even have any other good landmarks in the Yavin system, besides the Death Star to measure against the starfighter's speeds?
-Mike

Actually, my calculations here do take into account the Death Star's incoming velocity, and make the "worst case" distance assumption of a circular orbit.

The inward acceleration due to the curvature of the orbit happens to be in the same direction as the acceleration due to Yavin's pull, which in turn is likely to be able to account for a significant fraction of the difference; that difference, however, is negligible on the whole (although not for the Death Star.)

The initial velocity of the Death Star is also a parameter I considered carefully. The calculations I made concluding that the Death Star has an acceleration of around 5-10 g "at most" assume the Death Star has an initial velocity of zero and an initial position just barely out of sight of the moon on the far side of Yavin - i.e., that the Imperials picked one of the least efficient methods of approaching the moon.

The most important parameter is probably the diameter of Yavin, which for the sake of calculation I assumed to be 50,000 +/- 25,000 km, as my website is calculated without consultation of the more unreliable fringes of the EU.

However, the EU does give us explicit size and "surface" gravity for Yavin IV - 198,500 km and 4g - which for the purpose of making calculations on SB.com, should be acceptable figures.

This gives a distance of 353,000 km for the arc of orbit at 1.5 radii from which Yavin IV cannot be seen.

The least generous neutral-assumptions model under these assumptions is that the Death Star performed a uniform speed orbit from the reverse side of Yavin, with an inward acceleration of 48.5 m/s^2, of which Yavin provided 22 m/s^2 thanks to its own gravitational pull, i.e., the Death Star tractored itself towards Yavin at 2.7 g.

The most generous "neutral" assumption model by Roondar's comment above is that the DS comes out of orbit on the opposite side of Yavin, with no initial velocity, and proceeded to make a zero-zero intercept along a path of length 177,000 km (not the most efficient path, mind you) then we end up with an average velocity of 98 km/s, which must be reached after 450 seconds - i.e., 218 m/s^2, or 22 g.

If we do not work with a zero-zero intercept, which I frankly think is ridiculous given the cues that we have, this figure is halved, or 11 g; using an actual optimal flight path, which I don't feel like computing on a napkin, will probably shave a couple g off this.

I've said many times that 10 g is the generous limit to Death Star acceleration with some good reason.

Using the radius of 198,500 km also affects the fighters. This means the fighters traveled 298,000 km in 7-13 minutes. This gives us 170 g if the magnetic field does the braking, 340 g if they make a zero-velocity intercept with a zero-zero intercept traveling Death Star, and the absolute outer ballpark is 400 g for matching its incoming velocity (twice the distance I used originally and twice the incoming velocity I used originally means twice my original acceleration estimate).

Curve the path and extend it to have the fighters intercepting the Death Star substantially before it actually arrives, and you can maybe justify 500 g if you're in a particularly generous mood.

Regarding the Falcon... it's worth noting that while the Falcon may have left a little later, it also arrived later than the fighters - quite literally, right as the Death Star was getting ready to fire. I don't think we'll find it to be faster.

[Roondar]

There is one thing that puzzles me though.

I'm pretty sure we've had a discussion on the fighters approaching the DS back on the old forums I frequented (this being before starfleetjedi.net).

The SW proponents at the time presented some figures that would suggest an acceleration for the X-wing fighters in the tens or even hundreds of thousands of G's. They did this basing themselves on the distance of the DS from the rebel base.

Can assuming the DS is standing still really make that much difference?

(I'll admit I didn't calculate it myself but ~three orders of magnitude difference seems to be rather a lot for two calculations describing the same event. Especially since their description was a whole lot simpler)

[Jedi Master Spock]

Even the SDN website only estimates "1700+g" by stretching the distance to 400,000 km and compressing the time to "less than five minutes" (when, in fact, it seems somewhere between 7 and 13, which is best neutrally estimated as ten minutes' transit.)

I can't recall a single time I've seen someone seriously estimate 10,000g for the Yavin run. Estimates based on assumptions that we could call neutral will pretty much all fall in the 50-500g range.

And while I don't think we can nail the Falcon's transit down any more precisely than the fighters', the fact that the Falcon made it in similar time suggests it has similar acceleration. Meanwhile, in the same movie, the Falcon flees Tatooine at a top speed somewhere in the low end of that range.

[Mr. Oragahn]

Well, consider how fast Luke and Lando left the DSII despite the imminent destruction of the station, you've got very low, low ends there.

My point about the DSI is that the torpedo had to travel down to the reactor. During that time, the rebels would fly away.
If the design is more or less similar to the DSII, the explosion of the torpedo wouldn't immediately trigger the destruction of the DSI.
Now, since the DSI was complete and sealed, there would be less flames seen through the skeletic framework, like it happened on the DSII.

Still, how long do you think it took for the torpedo to reach the reactor, once it got into the shaft?

[Kazeite]

Well I think we could, in theory, determine the speed of X-wings in the trench based on how fast trench' walls were moving past them when viewed from cockpit (or, when we saw X-wings and Y-wings being blown up), which, again in theory, could help us determine the speed of photon torpedoes when they were fired by Luke.

At the very least, we could eyeball their speed during "entering the exhaust port" shot :)