Fin Controlled Active Rocket Stabilization System

[electronx]

This is a  project blog .I will continue to make additions as I find time and the system develops. I have been unemployed for about a month and I am starting to get bored (Nepotism

[Andy Chee]

There's a good reason why the control surfaces of a rocket are at the back near the motor.

[electronx]

There's a good reason why the control surfaces of a rocket are at the back near the motor.

Thanks ! yes there are hundreds of articles about this. but there is no statement like one solution is better than the other. there are advantages and disadvantages from application to application.

[moffy]

There's a good reason why the control surfaces of a rocket are at the back near the motor.

Thanks ! yes there are hundreds of articles about this. but there is no statement like one solution is better than the other. there are advantages and disadvantages from application to application.

The further back the fins are they become easier to use, a more stable system, the further forward they become more dynamic or unstable. It is similar to going from stabilizing a pendulum to an inverted pendulum, one is inherently stable the other is inherently unstable.

[electronx]

Absolutely right, in fluid mechanics, parametric mechanical sweep can be done and stability can be easily seen and the point of the fins can be determined. However, if you want to get a more responsive-dynamic rocket, you should bring the fins closer to the front. What we call flow separations will definitely limit the angles of the fins. It is possible to see ridiculous oscillations at the slightest imbalance.Obviously some things were experimental (extended Kalman filter implementation and such), which is why I wanted to develop a modular system. After the basic structure, playing with the mechanics will become much simpler.

[moffy]

It is not so much a rocket but a missile.

[Andy Chee]

After the basic structure, playing with the mechanics will become much simpler.

On the contrary, the mechanics will be the most difficult part! 

Specifically, you need instantaneous response between your computer and your control surface, so any signal delay, servo gear backlash, or balance misalignment in your assembly will not accumulate as errors in the computer calculations, and cause your already unstable fin configuration to be impossibly uncontrollable.

And the biggest signal delay won't necessarily be from your control surface mechanics.  The biggest signal delay will be from your electronic gimbal/accelerometer sensor.

[DaJMasta]

Why would you want a dynamic, responsive rocket?  To keep attitude you want tiny adjustments to keep the thing going mostly straight, not do somersaults and whatnot.  With control surfaces that large, even tiny motions (including flexing and the aforementioned backlash) will end up causing huge errors even if you can find and react to them fast enough.  Think of driving a car, when you're moving at high speed, you would only want to make tiny adjustments to the trajectory or you'll lose control quickly.  With rocket fins, you have next to no control when moving slowly, since they're only changing aerodynamics, but when you're at speed, if you move a degree, you could easily send yourself end over end in a fraction of a second.

And I think moffy nailed it as to why there isn't tons of information out there.  Missile guidance is sort of inherently a military technology, so publishing specifics of the control loops is not something most governments/development contracts are fond of.

[jbb]

Uh, yeah, there are laws about like ITAR which could be A Problem. And could perhaps bite you even if you’re not a US citizen and located outside the USA (paranoid fever dream: you use GitHub to store files, which counts as an import to the USA. Then someone from the US makes a code suggestion, which you implement. You are now considered to have exported military technology from the USA…)

https://en.wikipedia.org/wiki/International_Traffic_in_Arms_Regulations

[electronx]

Uh, yeah, there are laws about like ITAR which could be A Problem. And could perhaps bite you even if you’re not a US citizen and located outside the USA (paranoid fever dream: you use GitHub to store files, which counts as an import to the USA. Then someone from the US makes a code suggestion, which you implement. You are now considered to have exported military technology from the USA…)

https://en.wikipedia.org/wiki/International_Traffic_in_Arms_Regulations

Does just sharing photos and graphics fall under these regulations?

[DaJMasta]

At least in some cases, yes.  SpaceX covers portions of their recovered rockets because people take pictures of them and some of their space technology is considered ITAR protected.  That's not to say you probably couldn't scrape it off of somewhere, but at least clear, intentional pictures may be.

Honestly, the rules are complex enough and it comes down to "will they care enough" that I aim not to risk it.

[Jeroen3]

It may even implicate Dave in this. However, I suspect most trouble will come your way when you start going into the guidance systems.

Plus, we don't want to give the ruskies any new tech now do we?

[electronx]

This is not a new technology.The technology is probably older than my grandfather. As for the system, I have a few prototype hardware pcbs (mcu based), I will convert it to a cpu based structure, and for this I coded an extended Kalman filter from scratch. The Kalman filter works quite well, but no launch tests have been performed.there is still a long way to go.