Light Powered Spacecraft

Wayne Throop wrote:
: "Alex Terrell"
: Once the laser beam becomes too diffuse, you have a repeater station,
: on the route of the interstellar probe sent out a few decades before.
: This has a larger mirror, and therefore captures all the beam, which it
: turns into a new high powered beam.
:
: Of course, all depends on the capture and transmit efficiency.
:
: The repeater station could find an Oort cloud object, and use this as
: anchor mass / thrust mass to stay in position.

Ah. Sort of like the bombtrack proposal, but with persistent,
much more intelligent, bombs in the track. Of course... why make
them relays? If they are going to anchor to an oort object, couldn't they
just use it for fuel to produce beams? Or are the quantities unfeasible?

I'm sorry, I don't have a good understanding of the economics of fusion
versus solar power in the 23rd Century. This is especially the case for
levels of 100 TWe.

If fusion on this scale is possible, then a light highway could be
built to the stars.

I suspect the nearest stars could be reached by small craft in a decade
or two.

In article .com,
Alex Terrell wrote:
Or you can put holes in the aluminium, as long as these holes have a
diameter somewhat less than the wavelength. I assume one could thereby
reduce weight by up to Pi/4, at which point strength becomes zero.

You can do better than that -- the holes don't have to be round. The
microstructure of the sail surface can get complex. Robert Forward's
design for this was a square mesh, with occasional spikes perpendicular to
the surface on the back side. (The spikes are antennas [!] for thermal
IR, to improve the efficiency with which the sail can radiate heat.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Starwisp looks like one of the most likely near-term ideas for an
interstellar probe that has a reasonable travel time. The size of it
enable you to use the junctions as multiple "fly's eye" imaging sensor
points, able to do interferometric measurements.

If you have the SPS in orbit beaming microwaves at it for 1-2 weeks to
get it to about .5 of "C", that's a good deal.

meiza wrote:
Robert L. Forward proposed a sparse lattice sail propelled by microwaves.
That way, density could be really low.
In a light, fast, one-way robotic probe, it would also act as a sensor at
the destination and be an antenna to send back information.

I can't find the sources on the net right now.

The concept name was "Starwisp"
http://en.wikipedia.org/wiki/Starwisp

wrote:
Mercury will NEVER be used as an anchor. The laser will be a large
number of small lasers (possibly no more than a kilowart). They will be
built by a Von Neumann machine from lunar/asteroid material. As the
machine will be self replicating their TOTAL mass my be asssumed to be
(very roughly - order of magnitude) equal to that of the Moon.

The lasers will be phase linked and the total effective diamer of the
aperture could be the orbit of Mercury or even the orbit of Earth. The
main momentum transfer will be the sunlight it uses to power it.

Have you noticed just how often you claim that something or other will
be built by von Neuman machines lately?