Speed of a Blaster Bolt

[Connor MacLeod]

Thats a good example: Wessels weapon fired a guided projectile, but it appeared the same as a regular blaster bolt.

Trade Federation repulsor tanks in TPM used projectile weaponry against the Gungan shields as well (visuals + novelization demonstrate this.)

There's also the AT-TE "Mass drivers" in AOTC/ROTS (movie + novelization, I IRC.), and the "Mass drivers" on the Separatists (and the Republic "laser cannons" that exhibit ballistic trajectories.)

Hell, the ANH novelization describes projectile-type weaponry being employed against the Rebel fighters by the Death Star too.

[Connor MacLeod]

This makes sense.. since blasters do appear to have recoil, it would make sense that the velocity of the bolt (regardless of its nature) would be related to the recoil impulse, yes?

Some guns do, some don't. In some cases IIRC the "recoil" seems fairly independent of the speed/momentum of the bolt. Presumably these might be "massless" beam guns or perhaps "particle beam" guns and the "recoil" is related to the generation process - the actual beam is low enough energy-wise to possess little to no noticable momentum despite a high velocity.

Alternately, the recoil effect might be due to the buildup/ejection of the waste gasses (coolant?) from the guns. (The Saxton ICSes seem to go with the "ejecting waste coolant gasses" idea for larger guns, so it might make sense for smaller guns as well.) Again, in that case noticable recoil could exist independent of the velocity of the beam/bolt.

The above might actually apply to the "projectile" style blasters as well, I suppose (with the same caveats.) - though Id o have a hard time figuring out what could generate the "recoil" for a projectile independent of its propulsion, even with chemical propellant.

[Dangermouse]

Here are some examples from ANH regarding blaster bolt speed:

1) Greedo / Han Scene

Assuming a shoe width of 10cm, the radius of the table is approximately 50cm. A reasonable estimate for the distance from the table edge to the wall that Han is leaning on is one table radius. Since Han and Greedo appear to be sitting directly opposite of each other, there is approximately 150cm between the wall and Greedo.



Greedo's shot: Greedo fires first and it takes two frames for the bolt to hit the wall. Note that in later frames, this same bolt is observed to deflect off the wall. Assuming 30fps, this implies a minimum bolt speed of 22.5 m/s.



Han's shot: Han actually fires twice in this scene. For both shots, Greedo's arm obstructs our view of the bolt three frames into the shot. A reasonable estimate for the distance between Han's gun and Greedo is 125cm. Assuming 30fps, this implies a minimum bolt speed ranging from 12.5m/s to 9.375 m/s.






2) Cell Corridor Scene



First we estimate the width of the cell block door and control panel. Assuming a 1.75m height for Luke, the shoulder to shoulder width of Luke is approximately 0.55m.



From this shot pair, we can get a reasonable estimate for the size of the door and control panel. I estimate approximately 70cm for the door based on Luke's measurements and approximately 25cm for the panel based on a hand width of 8cm. Thus, a reasonable estimate for the door and panel strip is 95cm.


From this view, we can time the stormtroopers bolt using the lines on the floor and noting that the line spacing is approximately equal to the width of door and control panel. I count thirteen lines from the camera plane to the end of the corridor implying a 12.5m distance.

In the scene, blaster bolts take three frames to exit the scene implying a minimum blaster bolt speed of 123m/s. Note that the true value is probably higher as the bolt exits the frame somewhere between frame 2 and 3.

3) Bridge Scene



In this scene, Luke and Leia cross the chasm using a grapple and line. From this shot, we can get an estimate for the distance by scaling the distance to Luke's shoe and assuming 26cm for the shoe length. In this case, I am measuring the distance to the platform as if a stormtrooper was standing there. For my pixel measurements of 434 and 17, I get a distance of 6.6m.



A reasonable estimate for the angle between Luke and the troopers is approximately 23 degrees. Thus, the absolute mimimum distance between Luke and the troopers is 7.17. The true distance is much longer as the troopers are not directly ahead but are at some unknown angle into the plane. Three-four frames are observed for shots in the crossing scene implying a mimimum bolt speed of 72m/s and 53 m/s. This value is a lower limit as I have ignored the off axis angle and thus underestimated the distance between the shooters.

[Dangermouse]

So in ANH, we see a variety of bolt speeds, with a large difference observed in bolt speed between the Greedo example and the two stormtrooper examples.

Suspending disbelief:
The small difference between the two stormtrooper examples is not surprising, especially since the chasm example is a gross simplification/underestimation of the problem. Using the right distance would probably bring the bolt speed more in line with the corridor example.

The difference between the stormtrooper example and the Greedo example is a little surprising at first. Han and Greedo are in extremely close range; perhaps both turned down the power on their blasters (to avoid killing themselves) which may affect the speed of propogation. The shorter bolt length may be also be a reflection of this. We also do see Han make a slight adjustment on his blaster in the scene as well.


Not suspending disbelief:

Feature films are typically shot at 24 fps. Depending on the angle of view for the shot, it can be extremely difficult to capture high speed events for a stationary camera in a close shot, especially when it is not panning or tracking the moving object. For example, consider the Greedo shot, which is a stationary close/medium shot. Assuming again a 1.5m distance, the maximum possible speed for a single shot in this scene would be (1.5m/1frame*30fps) or 45m/s.

It is very difficult to see a one frame effect in the movie. Rather, having a bolt visible for maybe two-four frames ensures that is still seen without sacrificing the illusion of speed too much; I think this is a much more cinematically and aesthetically desirable solution than to perhaps have more realistic and consistent special effects.

Unfortunately, the 24fps sampling limit will place a much tighter restriction on close shots than long shots for object speeds.

[Dangermouse]

It's sad that HDS no loneger has the site up, but the calcs have garnered from the low end a blaster goes about 150 m/s to 1500m/s within the movies.

The low marker I believe was the speed within ANH, the High is with AoTC.

Do you remember the examples showing the higher speeds?

ESB might have some good examples from Cloud City since the walls and floors are segmented making distance estimation much easier. I am not sure about ROTJ or the prequels.