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ArmchairPhysicist

Strange physics bug needs discussion.

Question

To begin with, I have no clue where to put this thread, it's not really a bug report that needs fixing, and it's not a call for help. So mods help me out. 

Im posting this because I made a discovery with regards to KSP physics. If I launch an object at ridiculous velocities within the atmosphere, the object will travel a certain distance before it reverses its trajectory and flies back to its starting point, almost as if it bounced off on the air.

Related mods, BDARMORY, NK dynamics.

As I normally do when I get bored in KSP, I revert to my go to physics game exercise, launch things at ridiculous velocities and or nuke something. Today I tried both. 

Enter the Thermonuclear space gun.

My inspiration for this insane idea came fun accidentally detonations of warheads in orbit. One space plane of mine collided with its bomb mid orbit with indestructiblity cheats enabled, only for the ship to be catapulted into space like a bat out of hell. 

So I got to work. I put together a quick shell (really a single crew pod), mounted it on top of a nuclear testing tower, and dropped the bomb. 

As expected the pod flew upwards at a few thousand m/s, only to slingshot back into the launcher a second later. 

I'm not sure exactly why the atmosphere becomes a rubber band, but I suspect it's a side effect of an atmospheric drag calculation in the code where the drag becomes high enough to push the pod back to its origin. 

Im going to test later to see if I can bounce pods off of the atmosphere from orbit at high speeds.

If I can get around the rubber-air bug, the applications of atomic space guns are very fun, but slamming into the runway to 3k m/s isn't good for a kerbals health.

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9 minutes ago, ArmchairPhysicist said:

If I can get around the rubber-air bug, the applications of atomic space guns are very fun, but slamming into the runway to 3k m/s isn't good for a kerbals health.

Or, there could be applications if you could harness it rather than get around it :wink: 

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Sadly no, the oscillation is exactly that, it oscillates. If it gets high enough it will bounce a second time, this time in the correct direction, and then again and again and again until it decelerates enough to stop triggering the bug. 

And as I'm writing this I realized that it could be possible to perform an oscillation aero breaking maneuver. Theoretically you could hit the atmosphere at insane velocities to bounce back and forth in the atmosphere to kill that 10 km/s return velocity. The thermal shielding would be a problem. How to you protect a pod going that fast?

Time to cheat, going to slingshot a pod around the mun and burn on the way back, going to set myself on a tower buzzing trajectory at 20 kms 

Need to see if it's possible to trigger the bug like that. 

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5 hours ago, ArmchairPhysicist said:

with indestructiblity cheats enabled,...

So I got to work. I put together a quick shell (really a single crew pod), mounted it on top of a nuclear testing tower, and dropped the bomb. 

As expected the pod flew upwards at a few thousand m/s, only to slingshot back into the launcher a second later. 

Assuming you did not detach the pod from the rest of the launcher before firing and you had unbreakable joints turned on, I suspect what you're looking at is the rubber-banding of the joint between the parts as the force of the explosion is great enough to propel the pod away from the base while the joint remains intact to pull the pod back into position. Joints can do funny things when they're set to unbreakable.

That would be my suspicion based on what you've mentioned.

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Ah. So logical. So frustratingly logical :(

Now the magic is gone.

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I was voted "Most Likely to Kill a Buzz" by my class many years ago.

 

The magic isn't gone! It was inside those unbreakable joints all along... all we had to do was believe.

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Soo... what would happen if you turned off unbreakable joints partway through?

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Try separating the munition before launching, but keep indestructibility on. That would confirm the joints theory. Also use a single part for the munition so there's no inter-play there.

1 hour ago, GluttonyReaper said:

Soo... what would happen if you turned off unbreakable joints partway through?

h0: The forces involved would probably break the joint, but it's hard to say what the end effect would be. The munition might carry on its course or something else crazy might occur.

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On 8/10/2017 at 10:27 AM, ArmchairPhysicist said:

If I launch an object at ridiculous velocities within the atmosphere, the object will travel a certain distance before it reverses its trajectory and flies back to its starting point, almost as if it bounced off on the air.

The planet is flat and you ricochet off the firmament.

(that's a joke people, lighten up)

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As I have never heard of this happening in the stock game, the thread has been provisionally moved to modded support. 

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