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I was rewatching some good old Babylon 5 episodes at the weekend and realised something I never thought about before.

It looks like the Starfuries shoot out radially from Cobra Bays at launch, like driven by centrifugal force. I found this website which even explicitly states that Starfury fighters are launched using centrifugal force (you need to scroll down a bit to Cobra Bays.) How can that work?

The point is, centrifugal force is an inertial or pseudo force. You feel it because your velocity vector is constantly forced to change direction. Your body wants to maintain in uniform motion while the ground ( = rotating station) on which you stand comes closer and presses against your feet causing a centripetal force pointing to the rotation axis (which is a real force). From your point of view it feels like you are pressed to the ground.

Anyways, if you are released through a hole in the hull, like Starfuries at launch, both centripetal and centrifugal force will disappear and you would just follow the tangential velocity vector you have in that moment. Like in hammer throwing, where the hamner moves away tangentially when released, not radially. I drew a picture explaining that better. The red trajectory is the one a Starfury would take in my opinion.

enter image description here

On the other hand, they did a lot of work to make the show realistic, so I wonder if I have a misconception because this is an obvious issue.

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    The Star Fury comes out under its own power, with thrusters firing. Any inertial effects that they want to negate can be done so once the ship has left the bay.
    – Valorum
    Commented Dec 18, 2023 at 21:18
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    The camera PoV is tracking the rotation of the station (the bays remain stationary in frame) as the Starfuries are dropped, so even if their inertial motion is tangent to the curve of the station from a point stationary relative to the starfield, from the PoV of the camera they will appear to move directly away from the station.
    – DavidW
    Commented Dec 18, 2023 at 21:30
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    Further, their initial velocity is relatively low - a few tens of metres/second - compared to their flight speed, so it will take a matter of seconds to cancel it once they turn on their engines.
    – DavidW
    Commented Dec 18, 2023 at 21:34
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    @DavidW - The engines are glowing as soon as they exit the station. m.youtube.com/watch?v=sVhUcFgev-Q
    – Valorum
    Commented Dec 18, 2023 at 21:56
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    Relevant XKCD.
    – Cadence
    Commented Dec 18, 2023 at 22:16

1 Answer 1

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After receiving some good comments and rethinking and doing some calculations I got it!

What we see in the show is that the Starfury hangs in some device having arms. Maybe rails, maybe even a small catapult (if you have references, feel free), for me it looks like simple metal arms. Moments before launch, these arms are tilting the Starfury down, pointing outwards.

My missing link: As long as the Starfury rotates around Babylon 5's rotation axis, there will be centrifugal force, and these metal arms force so the Starfury to rotate even if pointing outwards, meaning that it will indeed slip from these metal arms.

However, there is still inconsistency, because as soon as the Starfury is free, it will move along a tangential trajectory, like the one I have drawn in the question. This would look strange like flying sideways, and it's not what we see in the show where Starfuries head straight forwards. However, we see that engines are glowing immediately after launch, so the Starfury is apparently correcting and/or accelerating by its own thrusters immediately after launch.

How large is the speed to correct? Babylon 5 creates an acceleration of a = 1 g = 9.81 m/s^2 and has a radius of r = 420 m. From ma = mv^2/r an orbital (tangential) speed of v = 64 m/s = 230 km/h is obtained. And Cobra Bays look like being closer to the station's rotation axis than the maximum radius, so v is likely even smaller. 230 km/h is really not a lot in space, so it's absolutely plausible that the Starfury is firing thrusters correcting this after launch and creating forward speed.

In summary, physics are fine but nevertheless I find Cobra Bays not as cool as before thinking about it. Always assumed that the Starfury is fired out using the station's rotation, but that will last only for as long as the Starfury leaves the device it's hanging in. Assuming this device is s = 2 m and the acceleration is a = 9.81 m/s^2, it takes t = 0.6 s for the Starfury to slip from the device (s = 1/2 * a * t^2). Which is close to what we see in the show. The speed gained, and this is really the speed in radial direction, is v_r = a*t = 5.9 m/s = 21.2 km/h. Not very much... However, guess you will still save some time compared to starting from a normal hangar like in Omega class destroyers, but for the price that pilots have to correct after launch and it's presumably some effort to get Starfuries back to the Cobra Bays. But it still looks cool...

P.S. If anyone knows how to activate math mode... I failed, but it's all possible with school physics!

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