On Sep 25, 8:08*am, Tom Francis - SWSports
wrote:
On Thu, 24 Sep 2009 22:19:31 -0700, "nom=de=plume"



wrote:
"Frogwatch" wrote in message
....
We officially have "water on the moon" so let's have some lunar
boating ideas. *Only problem, it is basically some ice crystals mixed
with dust, not even good for ice boating. *However, I still think that
lunar lava tubes might have lots of ice and other volatile materials.
Lava contains lots of dissolved water vapor. *When it cools, the water
may come out of solution and freeze in the lava tube where there would
be no air movement to cause it to heat up. *So, maybe kayaking with
runners on the bottom in lunar lava tubes. *Could combine my three
interests, caves, boating and space.

I don't know about sailing on the moon, but how about just space sailing....
using solar sails from the engery of protons bouncing off. Nasa's been doing
some studies, but didn't this concept start with the Planet of the Apes book
published in 1963 (I actually read the book)?

Earlier than that - as early as 1913 ("light sail") and was based on a
"invention" by Leonardo DaVinci - he used a candle and reflected light
to move a paper mobile.

"Star Trek: Deep Space 9" did an episode in Season Three called
"Explorer", call it an homage to Thor Hyderdahl, where Commander Sisko
and his son Jake built a replica Bajoran vessel to prove that the
Bajorans had discovered interstellar travel before the Cadassians
which was powered by light pressure sails.

It's a sci-fi staple - I think every major sci-fi author has written
at least one light sail story. *In the late '50s, "Astounding"
magazine devoted an entire issue to it including a novella by Issac
Asimov - I have a copy, but it's in storage so I can't point you to
the issue number.

The actual concept is called radiation pressure. I've done an
experiment with a wide aperature laser to move a piece of paper about
four feet back in the day. :)

Orders of magnitude in sail size. *Larry Niven, a mathematician and
sci-fi author, developed a design for a light powered vessel in the
mid-70's. He estimated that a single sail, six miles across, could
boost an object the size of our moon out of orbit and complete one
grav of acceleration in ten years. Sails larger than that, the process
becomes quicker. *Doing some simple math, one could accelerate an
object the size of a semi-tractor to light speed in less than a year
with a six mile wide light sail.

It's a fascinating subject that's for sure.

Tom:

Being somewhat familiar with lightsails but being too lazy to
calculate right now, something about the" 6 mile wide sail boosting
the moon out of orbit" thing didn't sound right. Here is the flaw.
The moon is already a light sail a couple thousand miles wide and it
does not get boosted out of orbit.

This says nothing about boosting smaller objects with large sails.
However, the thrust/sq km of sail is very low necessitating very small
payloads, really small, in order to get to any substantial fraction of
c (speed of light).

Another similar idea is called Mini-Magnetospheric Plasma Propulsion
or M2P2. It is a magnetic sail that interacts with the "solar wind"
of charged particles emanating from the sun. It uses a plasma
contained in a magnetic field to interact with solar protons. The
plasma gets "inflated" by injecting it into a mag field so it is miles
wide. Also low thrust.
One can increase the thrust of a lightsail by using high power lasers
pointing at it but even the best laser will diverge enough to have low
power density at astronomical distances. I have proposed to use
plasma lenses based on the M2P2 idea to re-focus said lasers on the
sail. These lenses would be miles in diameter and have extreme focal
lengths.

In my opinion, the 2nd best drive system for a prototype interstellar
probe would be something called Mini-Mag Orion that uses tiny fusion
explosions produced by laser driven inertial confinement. The plasma
from said explosions interacts with a mag field on spacecraft driving
it forward. Spacecraft would encounter fuel packets sent from solar
orbit that match its velocity so the spacecraft does not have to carry
the fuel. The fuel gets its speed from an accelerator in solar
orbit. It is called Orion after Freeman Dysons nuclear bomb driven
spaceship. I say it is second best because we currently cannot get
laser driven fusion done well.

Best near term drive system for an interstellar probe would be
something called a Nuclear Salt water Rocket where salts of uranium
dissolved in water are fed by nozzles to an area behind the rocket
where they reach critical mass forming a continuous nuke explosion
driving the rocket. Again, it gets its fuel from an accelerator in
solar orbit. I think this is more near term than the Mini Mag Orion
because it uses fission and does not rely on unknown technology. At
least this one uses water so is tangentially related to boats.