[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

starship-design: Re: Laser or maser?

Kevin Wrote:

>Platforms need not be in direct line of sight, they must merely have an
>electrical connection to each other.  this is especially true of Maser arrays
>(more on this later)

I know, but it would probably easier to have the energy supply
(Solar-receivers) and masers at the same place.

>> No, that polar region is not small, it is rather big.
>> If a star deviates 45 degrees from the rotation axis of the moon/planet, it
>> can be seen downto the 45th longitude. (There is a small band in wich the
>> Sun and other planets will move along (on Earth that is between +23 and -23
>> degrees).)
>As I recall, Tau Ceti is in the southern hemisphere.  Anyone know what 
>the angle is?  (I think the proper term is ascention)

Its ascention is 16 degrees (74 degrees deviation from the axis), so we
hardly could have made a worse choice. So maybe we should rethink...

>> >>I wonder are semiconductor lasers more efficient and cheaper than ordinary
>> >>lasers. What will be the costs compared to masers which cannot be made in
>> >>semiconductors?
>> >
>> >Can't remember.  I thought free electron lasers had the highest efficency?
>> >
>> >>Also on the receiving side, what are the pros and cons?
>> >>On the receiver-end we not only need a mirror, but also an absorber. Are
>> >>photocells better than skottky diodes?
>No, Schottky diodes are more efficient and cheaper (eff ~ 90%) Photocells
>are only about 15% efficient, and that is for super high end cells.  While
>this is not a problem in the collection of solar energy, (we can always 
>make the solar array bigger without increasing the energy costs) such 
>a low efficiency would be disastrous for the ship.

I think the efficiency of photocells is a bit decreased by the fact that
photons with low energy (Infrared ?) don't contribute to the electrical current.
However I have no idea if this is really true and how much the efficiency is
influenced by that.

>> >Why an absorber?
>> During the deceleration phase, energy is used to accelerate repulsion mass.
>> (I know, you proposed some ingenious reflecting system, so that the
>> EM-radiation directly accelerates the repulsion mass, but somehow that seems
>> to ingenious.)
>I have to agree with tim on this one kelly, a direct conversion to 
>electricity to run the lineac seems the simplest.  perhaps a plasma
>mirror will have to be considered if the wavelength is going to 
>be so short (because the conversion eff will be so lousy) but until
>we rule out microwaves totally,  I'd like to keep the conversion to

Hey, we should use microwaves of 2.45 MHz, that way we could directly power
a steam engine ;)

>>>What are the disadvantages of a reflective sheet compared to a wire 
>>>mesh? Is it only the weight?
>>Increased drag and more limits in materials I think?
>Along with drag, there is erosion.  A wire mesh would allow interstellar
>particles to slip by, while a reflective sheet would be under constant 
>bombardment by hydrogen atoms blowing by at nearly the speed of light

Of course a sheet has a bigger surface as a mesh, however if the mesh needs
to be bigger...
(To be fair, I don't think the one covers the other.)

>> We (also others than me and Kelly) should try to find some more pros and
>> cons about laser and maser.

Thanks for the list.
If solar-pumped lasers can work, they may even be cheaper.
I don't think the redshift effects will be dramatic, most mirrors for
visible light also work for parts of infra-red.
I do not understand why "laser-photons having more energy" is an advantage...

<Pros and cons removed>