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On Fri, 3 Jun 2005 19:21:58 -0700, Eunometic wrote
(in article .com): I think its not to hard to derive. If gravity is so high that escape velocity (eg for a missile) excedes the speed of light you get it. The fitgerald-lorentz contraction equations. http://en.wikipedia.org/wiki/FitzGer...tz_Contraction It isn't the black hole solution that gives the error. The radius of the event horizon (the place where the speed of light equals escape velocity) is the same when calculated classically or with Einstein's gravitation. The problem comes with the singularity, or what happens after that. You get the equivalent to a division by zero in the center, like with anything where you divide by a radius and you try to see what happens at the center. Radius is zero -- oops, condition red -- global causality error! The universe does not allow division by zero. Perhaps it falls in the realm of the absolute elsewhere, or perhaps not. Nobody knows. -- Charlie Springer |
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Charlie Springer wrote: On Thu, 2 Jun 2005 22:39:21 -0700, Eunometic wrote (in article . com): I'm not sure I understand what you mean. There were 'rossete scans' that ended up in latter versions of sidewinder thse use a sort of rotating and oscialting mirror. These also ended up in early German infrared seekers intended for terminal homing on the Wasserfall missile but actually derived from infrared imaging systems such as "Spanner". There is a tracker form with a reticule that is half transparent and half opaque and spun by a synchronous motor, so there is a reference for the position of the reticle over time. The amount of time and the angle over which the target is obscured generates the error signal. When perfectly centered the signal is constant (half is always blocked). If I could center it well enough, I could half mask the secondary of a Cassigrain and spin it. I just find the analog solution more satisfying than a digital image tracker. I think I know how to do it. You need to understand "phase sensitive demodulators". There are like rectifiers whose polarity of rectification is dependent on a reference phase. In their most basic form they consist of vibrating relays, biased diodes or amplifier valves or transisters whose gates/grids/bases are switched by a phase reference such that the signals polarity is demodulated according to its phase. So, consider, as the disk rotates you want to resolve into rectangular x-y co-ordinates to opperate your star tracking device or missile fins. To generate the x co-ordinate for instance you have a square wave reference of period equal to the rotation of the disk and in phase with it (generated by a light source and photocell on the priphery for example or a commutating switch, or your stepper reference etc). This is the reference phase for the demodulator. The demodulator could be as simple as a fast relay or it could be electronic. The demodulator will generate negative or postive value depending on whether the 'target' is in the positive (right) or negative (left). For the y (vertical axis) co-ordinate you need to have a second square wave 90 degree delayed created by a second light/photocell or some such internal reference. It's crude as you only get +/-x and +/-y signals. You don't really need a square wave, sinusoid is uselff. Sin-Cos potentiometers also resolve polar to rectangular co-ordinates. I thought the turbine wheels in the fins of the Sidewinder were stabilizers and generators, so it didn't need any batteries. I may be thinking of something else. I'm pretty sure they acted as gyros mechanically on the fins to roll stablise it. -- Charlie Springer |
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