Thanksgiving update, recent ideas
We're back from Connecticut, after a seven hour car ride featuring stop-and-go traffic and vomiting. Avoid the Nathan's hotdog place at the Molly Pitcher rest stop on the New Jersey Turnpike. Although I'm not entirely sure they're to blame, I wouldn't take the risk.
Otherwise the trip was ok. Kalina had a great time playing with her grandma and her cousins. We all had a fun Thanksgiving dinner, and I got to see Naomi's new baby cousin Kayla(not sure on spelling). I opted out of some of the shopping and side trips to see relatives, and got some thinking done. I've decided that radiometers/thermal transpiration thrusters are probably not a good way to get to orbit. The maximum pressure difference that can be produced by such a thruster is, at best, double the ambient pressure around the craft. Which means that at 100 km altitude, where atmospheric pressure is less than 1/1,000,000 the pressure at sea level, even a lightweight (100g/sq. meter)* radiometer sail won't have enough force to lift, even assuming you have enough incoming light, perfect material and pore geometry, etc.
*Minimum weight per unit area for a radiometer is much higher than for a solar sail, since the radiometer must maintain a temperature difference between the hot side and the cold side, which means a thicker film.
I looked at pantographs, which seem a good way to get precise geometry at reduced size for rapid prototyping, even when your starting machinery is coarse.
I reached back to an old line of thought on trebuchet orbital launchers, and considered combining the power source (large falling weight)of a trebuchet with the compactness of a centrifugal launcher. Basically you send a large weather balloon up to 30 km, carrying a 1-ton weight tied to a cable wound on a spool. Once you reach altitude, you drop the weight 10 km. The falling weight pulls on the cable, which spins the spool (still mounted on the balloon basket). The rim of the spool reaches exceedingly high rotational velocity. If there's a small (10 kg) payload attached to the rim, you can release it at orbital speeds. Difficulties include the added rotational inertia of the spool, and the difficulty of designing a spool, quick-release clamp and robot payload rocket that will withstand thousands of g's of centrifugal force. This is not a good passenger vehicle.
Otherwise the trip was ok. Kalina had a great time playing with her grandma and her cousins. We all had a fun Thanksgiving dinner, and I got to see Naomi's new baby cousin Kayla(not sure on spelling). I opted out of some of the shopping and side trips to see relatives, and got some thinking done. I've decided that radiometers/thermal transpiration thrusters are probably not a good way to get to orbit. The maximum pressure difference that can be produced by such a thruster is, at best, double the ambient pressure around the craft. Which means that at 100 km altitude, where atmospheric pressure is less than 1/1,000,000 the pressure at sea level, even a lightweight (100g/sq. meter)* radiometer sail won't have enough force to lift, even assuming you have enough incoming light, perfect material and pore geometry, etc.
*Minimum weight per unit area for a radiometer is much higher than for a solar sail, since the radiometer must maintain a temperature difference between the hot side and the cold side, which means a thicker film.
I looked at pantographs, which seem a good way to get precise geometry at reduced size for rapid prototyping, even when your starting machinery is coarse.
I reached back to an old line of thought on trebuchet orbital launchers, and considered combining the power source (large falling weight)of a trebuchet with the compactness of a centrifugal launcher. Basically you send a large weather balloon up to 30 km, carrying a 1-ton weight tied to a cable wound on a spool. Once you reach altitude, you drop the weight 10 km. The falling weight pulls on the cable, which spins the spool (still mounted on the balloon basket). The rim of the spool reaches exceedingly high rotational velocity. If there's a small (10 kg) payload attached to the rim, you can release it at orbital speeds. Difficulties include the added rotational inertia of the spool, and the difficulty of designing a spool, quick-release clamp and robot payload rocket that will withstand thousands of g's of centrifugal force. This is not a good passenger vehicle.