>What if we just use fins on the first stage or two to get going and
>spin things up, and then just use the spin for all of the later stages?
>No control computer or servos at all!!!! If we can keep within 15 degrees
>of vertical we should be just fine, assuming the goal is just to get up.
No, not at all. You have to consider that an eastward launch gets
a big advantage from the earth's spin velocity, while a vertical
launch gets nothing and a westward launch gets a penalty. A 15
degree error is enough to make the difference between gaining
escape velocity and re-entering in a day.
>Getting into orbit would need active control and so ruin the scaling.
>You would need lots of servos and a computer. I don't think you need this
>just to "Aim For The Moon".
In that case, it is time to re-think the concept of servos.
Motors running gear trains are certainly too bulky and massy,
but what about piezoelectric plastic sandwiches pushing vanes
into the rocket exhaust (jetavators)? Can they be built?
(By amateurs? I am a double-E, not a mechanical engineer.)
Computers are light-weight, just order unpackaged semiconductor
dice or PLCC chips without the epoxy coating. A couple lithium
watch batteries will run a 5V CMOS microprocessor. I'm sure
that amateurs could assemble hardware from these (carefully).
The one element I see no simple way to shrink is the attitude
reference. Unless... Ha! This may be it!
Does everyone remember the magnet-hovering-over-superconductor
photos we all saw when the high-temp superconducting ceramics
hit the press? Okay, use tiny magnetic marbles as the gyros,
suspend them in nitrogen-chilled cups in a very small vacuum
chamber, and use coils to spin them up (with off-board power)
and read the signals from their spinning when they are off-axis.
Bingo. There is your gyro table. It will warm up and spin
down after a while, but after the boost phase is over you
don't care. Boost phase will last a couple of minutes.
It might be doable for a mass budget of a few grams. It will
need a lot of machining. (Definitely too much for a $5,000
budget, but maybe not too many times more than that.)
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