Reply to post: Re: Launch-smaunch

LOHAN ideas..

Poor Coco
Boffin

Re: Launch-smaunch

Despite her backronym (which has been recognized as inaccurate from the time it was suggested) nobody says that LOHAN will be anywhere near the Kaman line or anything like in orbit. However, at the altitudes we expect her to launch the atmosphere is exceedingly tenuous — 3–5% of sea level pressure, tops. That’s thicker than the Martian atmosphere at ground level, but not by a whole lot.

In order to achieve aerostabilization in this tenuous air, the craft will require airspeed and lots of it. Since the craft will necessarily be unstable until this high speed is reached, unless it is otherwise stabilized it will tumble and wil simply never get to a speed where it IS stable.

So how do we stabilize the craft initially? I can see four possible approaches:

• Launcher: stabilize the craft mechanically while it accelerates, like ground level rocket launchers.

• Gyroscopes: an internal gyro maintains the craft’s heading as it accelerates; shortly after aerostabilization occurs the gyro is halted so as not to impede control.

• Thrust vectoring, which in my view is only attainable with vanes impinging on the rocket exhaust.

• Reaction control thrusters — this is almost certainly impractical.

Disadvantages of these approaches:

• Mechanical stability during launch must be done without an anchored launcher; this means it must use inertia, which means it must be heavy, which limits the balloon’s maximum altitude. It also implies a large launcher, since it will take some distance for the aircraft to reach speed. This can be mitigated ONLY by using a piston launcher. (I feel like I am talking to a wall here; is anyone reading these? I am the only person to utter the words “piston launcher” or to suggest capturing and utilizing otherwise-lost initial thrust energy.)

• Gyroscopes are necessarily massive and/or bulky (in order to get a large moment of inertia) and they require a strong, rigid mounting to the airframe; this could be tricky. On the other hand, when the aircraft reaches aerostable speed, it’s simple to stop a gyroscope using an H-bridge — just short the terminals of the motor. (It will coast freely while an open circuit is maintained.)

• Thrust vectoring will require making some pretty serious components; I imagine a ring with vanes being steered by servos. Problem is, it will place a heavy component at the extreme aft of the craft, which is the worst possible location for a massive component as far as aerodynamic stability goes.

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