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X37 space plane seems to work very well

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  • #16
    Originally posted by RB211 View Post
    Not bad for a balsa airplane
    ..?, it's a what
    Mark

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    • #17
      Originally posted by Dan_the_Chemist View Post
      Interesting problem... Spinning up a lathe will impart rotational forces to the floor mounts, thus causing the ship to rotate. This will require expenditure of mass through the Reaction Control System thrusters... Not a good thing since that mass has to be boosted from the surface.

      I can imagine a lathe with a counter-rotating balance wheel. Thus one would not only have to center the part (or indicate it in), one would have to counterbalance the part with an equal mass in the counter rotating chuck... As you machine the part it's mass will change, which means the forces from the counter rotating chuck will have to change to keep it balanced. Changing the mass is feasible, but perhaps a better answer is to change it's rotational velocity to keep the angular momentum equal and opposite.

      Next we have the question of the sudden change of forces when we start cutting... igg, not enough coffee yet. Somebody else take over.
      A lathe in orbit would be better off being gimbal mounted rather than fixed to the structure of the spacecraft for the sake of orbital navigation. If fixed to the spacecraft, gyroscopic precession would either alter the course of the spacecraft, or at least change its attitude in relationship to the planet it orbited, even if just a little.
      I was assigned to repair airborne inertial navigation systems while in the NAVY. One of the factors that had to be included in the terrestial inertial navigation equation was ERC - Earth Rotation Compensation, an "error" introduced into the gyro-stabilized platform to maintain local level where the motion sensing accelerometers resided. A perfect gyroscope, fully gimbaled, running for 24 hours, would rotate or tumble 360 degrees as the Earth turned.

      Another method used to minimize gyroscopic precession errors was to employ 2 sets of gyros that alternately reversed direction of rotation - much as Dan hinted at in his post.

      I suppose a science fiction story could be written about a spacecraft that had lost the use of its maneuvering thrusters and only had its main propulsion engine. The ship's machinist saves the day by spinning up the lathe with a large hunk of tungsten in the chuck. Why the ship would have such a heavy material in stores.....?

      I wonder if there was any gyroscopic compensation considered for all the ventilation fans onboard the Space shuttle or the ISS?
      Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
      ~Practitioner of the Electromechanical Arts~

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      • #18
        Originally posted by Weston Bye View Post
        A lathe in orbit would be better off being gimbal mounted rather than fixed to the structure of the spacecraft for the sake of orbital navigation. If fixed to the spacecraft, gyroscopic precession would either alter the course of the spacecraft, or at least change its attitude in relationship to the planet it orbited, even if just a little.
        Yer exactly right... I didn't think about the idea of a gimbal... To quote from Wikipedia about Reaction Control Systems:

        Because spacecraft only contain a finite amount of fuel and there is little chance to refill them, some alternative reaction control systems have been developed so that fuel can be conserved. For stationkeeping, some spacecraft (particularly those in geosynchronous orbit) use high-specific-impulse engines such as arcjets, ion thrusters, or Hall effect thrusters. To control orientation, a few spacecraft, including the ISS, use momentum wheels which spin to control rotational rates on the vehicle.

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


        Originally posted by Weston Bye View Post
        I suppose a science fiction story could be written about a spacecraft that had lost the use of its maneuvering thrusters and only had its main propulsion engine. The ship's machinist saves the day by spinning up the lathe with a large hunk of tungsten in the chuck. Why the ship would have such a heavy material in stores.....?
        The "Rod from God"...

        The system most often described is "an orbiting tungsten telephone pole with small fins and a computer in the back for guidance". The system described in the 2003 United States Air Force report was that of 20-foot-long (6.1 m), 1-foot-diameter (0.30 m) tungsten rods, that are satellite controlled, and have global strike capability, with impact speeds of Mach 10. The idea is that the weapon would naturally contain a large kinetic energy, because it moves at orbital velocities, at least 8 kilometers per second. As the rod would approach Earth it would necessarily lose most of the velocity, but the remaining energy would cause considerable damage. Some systems are quoted as having the yield of a small tactical nuclear bomb. These designs are envisioned as a bunker buster.

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

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        • #19
          When you first fire up the lathe, there will be a finite amount of 'twist' imparted to the spacecraft. When you are machining, the lathe itself will balance the cutting forces. As the rpm drops with loading, there will be some 'counter-twist' induced. When you shut the lathe off, the counter-twist will reverse what the start-up caused, and you're back to normal. There will be gyroscopic effects all the while the lathe is running of course. There will also be effects caused by the relative orbital position of the spacecraft while the lathe is running. Balancing out the effects could get a little complicated, and expensive of fuel as someone else mentioned.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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