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The trouble with solar sails is they become less effective as they go further from the Sun. Why not use a solar sail to build up lots of energy relatively close to the Sun (i.e., at L1 near Earth)?
Pivot a radial array of long spokes about a heavy mass. At one end of each spoke attach a tackable solar
sail. The sail is adjustable so that the pushing effect of incident solar radiation can be modulated. Each sail is opened/turned when the push goes the right direction and closed when coming round again. At the end of one of the spokes, attach your spaceship.
Now wait a while for the array to spin up to the desired angular speed, and then detach your spaceship at the appropriate time and watch it go hurtling off into deep space.
The spokes should be as long as possible to reduce centripetal forces. And [MechE]'s idea of having a hub where cargo and very brave humans could be lowered in. The hub means you never have to stop the rotation and the thing might just keep accelerating, giving us an ever increasing range into space (until it tears itself apart).
Ultracentrifugal satellite launcher
Similar, but not solar wind powered. [the porpoise, Nov 12 2015]
Launch from angular momentum
Nanotube_20fuel
conceptually related [Voice, Nov 12 2015]
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//At one end of the rod attach a one-way solar sail,
which is like a one-way mirror,// |
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There is no such thing. A one way mirror reflects an equal
amount of light on each side, it's just that there's much
less light on the "transparent" side. |
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That being said, you can you a solar sail to "tack". |
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The correct structure is the rod with solar sails on both
ends, and they fold or spread or angle as needed to get
the desired thrust. The ship is launched from one end,
and the sails are balanced to return the rod to the
correct orbit. |
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Issue two: //solar wind is nice and strong// The "solar
wind" has nothing to do with the operation of a solar sail.
The solar wind is charged particles, a solar sail works on
the basis of photons. Of course, the photon flux is also
higher closer to the sun, but that brings us to... |
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Issue three: a //close solar orbit // is a much, much
lower energy orbit than earth's. Assuming a terrestrial
starting point, the energy spent to decelerate to a low
solar orbit is going to be more than any physically
possible structure could impart to your ship. (IE your
structure falls apart before your ship has enough energy
to return to earth orbit. You're far better off building
this structure in earth orbit and accepting the longer run
up time necessitated by the lower thrust. Especially
since you're only going to be launching cargo with this,
which doesn't care about time delays. And you'll only be
launching cargo because... |
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Issue 4: Centripetal acceleration. To get any
appreciable velocity out of this device, the centripetal
acceleration at the ship end is going to be much, much
greater than humans can withstand. I'll admit, I can
think of a way to fix this (the ship with 99.9% of the mass
is spun up, the humans are lowered from the hub in a
transfer capsule at a constant 1-3 g, and the two parts
mate and launch in the same motion, so the capsule
never experiences high g, and the loss in angular
momentum due to the capsule transfer is relatively low.)
but, any solution is much more complex than the
basic launching system, and still doesn't have humans
sitting in the ship waiting for it to spin up. |
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All of that being said, the basic concept is not impossible. |
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All good points [MechE]. Thanks. I will update the idea. |
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This is less efficient than just saving up the electricity. And
since you're adding mass to the system to be accelerated
the device will be pushed closer to the sun at each launch
with a force proportional to launch force. It will have to
push itself back out again. |
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//This is less efficient than just saving up the
electricity.// |
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How do you use pure electricity to launch? Unless you are
proposing a catapult type launcher, which is much harder
to build. |
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It's also even more subject to the issues with it's orbit
shifting after use since it has no way to correct it's orbit,
whereas this idea can
just adjust it's sails. |
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You couldn't build a big solar sail and woven carbon nanotube line to put a craft up into space. |
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//The trouble with solar sails is they become less effective as they go further from the Sun.// |
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The solution is obvious: just build a large parabolic reflector around the sun to send all its light in the direction of your spacecraft. |
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I really like this idea. This could maybe also be used to
launch things perpendicularly to the ecliptic, which is
traditionally difficult. |
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// And since you're adding mass to the system to be
accelerated the device will be pushed closer to the sun at
each launch with a force proportional to launch force. It
will have to push itself back out again. // |
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Which will happen naturally as a side effect of the solar
sails that spin it up. |
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