Saving energy is silly; the bottom line is money (was Forklifts tip

Keith Henson schrieb:
>
>>>
>>>> You only need power generating solar cell
>>>> arrays and
>>>> the transmission antenna.
>>>>
>>>> I would try to get rid of those mirrors, using a solar cell array and a
>>>> transmission antenna
>>>> only. Both would be independent spacecraft but connected through power
>>>> lines.
>>>>
>>>>
>>> I could not find any dimensions on the drawings so I don't know how
>>> much power you are thinking about. However, the minimum is about a
>>> GW. It is worth considering the size and stiffness of a GW power
>>> connector.
>>>
>>>
>> It was just a design using a Ring Segment System
>> http://solar-thruster-sailor.info/rss/rss.htm
>> thought for very large space structures in the square km region,
>> like solar sail spacecraft or Solar Power Satellites.
>>
>> Since it comes up into space in segments,
>> the size of the construction and the dimensions are up to you.
>> If you want a gigawatt SBPS, choose the size which fits to your
>> solar cell arrays you'll need for 1 GW.
>>
>> How to get those segments into space look here:
>> http://solar-thruster-sailor.info/lth/lth.htm
>>
>>>> While the larger collector-unit with it's solar cell arrays points
>>>> toward Sun,
>>>> the transmission antenna unit points toward Earth. They both move and
>>>> point independently.
>>>>
>>>> The torus-like Solar Power Station would look about like this :
>>>> http://solar-thruster-sailor.info/figs/fig11.html
>>>>
>>>>
>>>>
>>>>
>>>>> If you tilt the power
>>>>> sat, the non radial force against orbital motion on the near side of
>>>>> the earth toward the sun is opposed when it is on the far side of the
>>>>> earth from the sun. And changing the tilt of something that big over
>>>>> a short time is going to take an awful lot of reaction mass or some
>>>>> heavy other method.
>>>>>
>>>>>
>>>>>
>>>> I think you would change the tilt of the craft gradually during 24 hours,
>>>> not twice a day in a few minutes.
>>>>
>>>>
>>> Fast or slow makes no difference in the amount of reaction mass it takes.
>>>
>>>
>> No, but if you can steer and point the craft without reaction mass at all,
>> that would be a difference!
>> The Roller Reefing System I link to at,
>> http://solar-thruster-sailor.info/figs/fig18.html
>> delivers that
>> - Fuel less attitude control, Steering and Station-keeping for solar sails.
>>
>> In my eyes a solar power satellite is a solar sail spacecraft.
>> You have to operate it like a spacecraft - constantly, since you constantly
>> get thrust, at least 4.5 N per square km of solar cell arrays.
>> Why not using this thrust for station keeping, steering and pointing
>> instead of reaction mass?
>>
> The force is in the wrong direction?
>
It is not the direction of the force which is wrong, it is their design
which is
wrong.

They designed it as a satellite which is always in a stable direction
towards
Sun due to those mirrors. To get this pointing stability the mirrors
are placed
in a way, that the resulting light pressure force of them is pushing
outwards.
But through this they lost the ability to change the pointing direction.

Put those mirrors away and use larger solar cell arrays (as large as the
mirrors)
instead and you will have the same or even better energy production
capacity.

If they would design the SBPS like a solar sail spacecraft first, which
has to change the
pointing direction often, they could use Roller Reefing as a fuel-less
way to change
the pointing direction to slow the orbital speed down and gravity pulls
the craft
inwards while when the pointing direction is changed again to speed the
orbital speed
up, it heads outwards again.

You will need a constant flight crew which is operating the collector
spacecraft
and the transmission sender daughter unit spacecraft by remote control,
but save the replacement reaction mass.

> Seriously, this is a huge problem with some of the designs companies
> are currently considering putting up. They are talking extremely
> large amounts of money to service the power sats with replacement
> reaction mass for station keeping, mainly against solar light
> pressure.
>

> If you or any of the solar sail people know how to solve it this
> problem, it would be of huge interest.
>
I think I wrote above how to solve this design-problem.

Regarding orbital control of the solar-sail/-solar-power-spacecraft
there are some solar sail and low thrust orbit- and trajectory
specialists available which already have put up the theoretical base
to do the job.

The SBPS designers should just contact them if they
choose to design a solar-sail like SBPS.

Best wishes

Frank