> The claim has been made by Gregg Maryniak on Economist.com that it would be cheaper ("The moon is the best near-term source of the materials that we need to do useful things in space"), because the moon's escape energy is 1/22nd that of a hypothetical non-rotating Earth, to source raw materials for orbital habitats from the moon than from the earth. My response is that it might not be cheaper, when we factor in the negative aspects of doing business on the moon.
> You're attempting to counter a known, hard-and-fast quantity (the kinetic energy difference resulting from the different delta-V) with a hypothetical (that lunar industries will be crippled by the lower gravity).

Nope.

> nothing will ever reverse the energy difference.

Is energy expensive? Nope. Today, we pump Saudi oil for $2/bbl and buy U3O8 fission fuel for the equivalent of $0.01/bbl of oil energy.
http://www.uxc.com/review/uxc_g_2yr-price.html

Therefore, energy differences are not directly relevant. Only 3% of the Saturn 5 launch costs covered fuel (ref.: LEO on the Cheap). Launch costs have virtually nothing to do with energy costs.

First stage dry weight:288,000 pounds (131,000 kg) and fully fueled at launch had a total weight of 5.0 million pounds (2.3 million kg)
Second stage:80,000 pounds (36,000 kg) and fully fueled, weighed 1.06 million pounds (480,000 kg)
Rgird stae:25,000 pounds (11,000 kg) and fully fueled, weighed about 262,000 pounds (119,000 kg)

Total fuel weight to rocket weight ration of nearly 20:1
which ampints to about 5,956,000 lbs of fuel.

At current costs of production, 50 kw of electricity/kg H2 at 8 cents/kw $4/kg and of liquid O2 at about 4 cents/kg the total costs of fuel would be roughly $2,080,000. to get that large payload to orbit. Which is fine as far as you go however,,,the over riding cost consideration is in expensive hardware, while on Luna, the hardware,(mass driver) once constructed, plays little furthur role in expense(well, ok, it has to be amortized but that's amortization for a single launch structure) .The launch costs then become a comparison between the cost of electricity/kg to orbit vs chemical fuel costs PLUS hardware costs for launch from earth to orbit. Granted, the Space Elevator would also be a one time construct, but you're still looking at a 20 to one cost for the electricity to get to orbit(but the materials for a space elevator don't yet exist, while the tech for a mass driver does). Luna comes out cheaper no matter what you're comparing.
As Mike has already pointed out, reduction in the hardware costs may provide numerous options we do not currently have.

You remind me of my ex-wife, who was very good at finding problems but totally inept at providing solutions to those problems,,,which is one reason she's my EX.

GAry 7

Oh Yeah, and that silliness about fork lifts being prone to tipping over,,,
A fork lift is exactly as likely to tip over on earth while lifting a 1000 kg mass as that same forklift on the moon lifting the same mass(1000 Kg). You'll note I use MASS rather than WEIGHT???

GAry 7

> Therefore, energy differences are not directly relevant. Only 3%
> of the Saturn 5 launch costs covered fuel (ref.: LEO on the Cheap).
> Launch costs have virtually nothing to do with energy costs.

Yes, granted, fuel costs are not the primary costs for spaceflight (at least in the current era). But we're not primarily talking about fuel costs. All other things being equal, higher delta-V destinations are more challenging than lower delta-V ones. Higher delta-V's require larger systems which are more expensive to build and operate. If we had been able to wave a magic wand and reduce the delta-V to land 2 astronauts on the moon to 1/20 its value, the Saturn 5 could have been a much smaller rocket and Apollo missions would have been less expensive.

The 1/20 delta-V advantage of the lunar surface over the Earth's surface is a significant advantage, and one which will easily outweigh any operational difficulties relating to the moon's lower gravity. If engaged in a program to build 30 or more SPS, the costs savings associated with this energy difference will pay for development of the lunar mine and mass driver, the mass catcher, and the orbital ore refineries and manufacturing facilities.

Regards,

Mike Combs

I partly agree with Mike and partly disagree.

>
>> Therefore, energy differences are not directly relevant. Only 3%
>> of the Saturn 5 launch costs covered fuel (ref.: LEO on the Cheap).
>> Launch costs have virtually nothing to do with energy costs.
>
> Yes, granted, fuel costs are not the primary costs for spaceflight (at least in the current era). But we're not primarily talking about fuel costs. All other things being equal, higher delta-V destinations are more challenging than lower delta-V ones. Higher delta-V's require larger systems which are more expensive to build and operate. If we had been able to wave a magic wand and reduce the delta-V to land 2 astronauts on the moon to 1/20 its value, the Saturn 5 could have been a much smaller rocket and Apollo missions would have been less expensive.

Put another way, the fuel isn't a major cost, but the rocket structure
wrapped around the fuel is.

> The 1/20 delta-V advantage of the lunar surface over the Earth's surface is a significant advantage, and one which will easily outweigh any operational difficulties relating to the moon's lower gravity. If engaged in a program to build 30 or more SPS, the costs savings associated with this energy difference will pay for development of the lunar mine and mass driver, the mass catcher, and the orbital ore refineries and manufacturing facilities.

I have not gone over his figures, but in conversation with Dr. Peter
Schubert he mentioned that the crossover between building up lunar
industry to supply parts for power satellites was around $450/kg.
I.e., below that figure it was less expensive to build them with parts
from the earth. He also mentioned that the capital investment for
lunar industry was around $1.2 trillion and that the time frame was
around two decades to build up the capacity to produce ~300 GW per
year of power satellites. (Not certain I remember the time
correctly.)

By splitting the delta V to GEO between a low mass ratio chemical
stage that provides 4 km/sec and a low mass ratio laser stage that
provides 10 km/sec, I make a case for reducing the cost to GEO to well
under $100/kg. (see http://www.theoildrum.com/node/5485 for more
detail.)

Does that drop the moon out of consideration? Maybe not. One quarter
to one third of the mass of a high efficiency thermal power satellite
is radiator heat transfer fluid (2 km^2/GW of waste heat). Back in
the late 70s Eric Drexler and I wrote a paper for the Princeton Space
Manufacturing Conference on using finely ground lunar rock and a
little gas as a pseudo fluid for this purpose. (Heterodensity heat
transfer apparatus and method U.S. Patent Office: #4,759,404)

The velocity from lunar surface to EML1 is 2.5 km/sec, to GEO from
earth surface is 14.3 km/sec. The energy required to lift is
(2.5)^2/(14.3)^2 * 14.75 kWh/kg or ~0.45 kWh/kg. 100 t/hr from earth
surface to GEO takes 1.5 GW. 100 t/hr from LEO surface to L1 would
need 45 MW, 33 t/hr would require ~15 MW.

In the context of 500 MW/day power satellite construction this is a
nit. The question is efficient application. Space elevators in the
earth to GEO context are not possible at present because we lack
strong enough cable. An elevator from the moon to L1 is well within
existing materials, it need not even be tapered. As an endless loop,
driven from the L1 end it could even provide a few MW of mechanically
transmitted power to a moon base.

If the elevator delivered 2% per day of its mass (1650 tons) and
giving some margin for materials handling on the lunar surface, it
would take the the transport system up from earth less than a day to
lift it. Moving lunar rock from L1 to GEO is only 400 m/second. This
would be about 1.3% of the laser capacity being used to move 100 t/hr
to GEO.

I don't know if it would be less trouble to screen out fine materials
on the lunar surface or to send up unsorted regolith and grind it to
dust in a vibratory ball mill in space.

Best wishes,

Keith

PS, for station keeping reasons, you want a power satellite to be as
efficient as possible (to reduce the area). And the more mass the
better. Lots of mass averages the light pressure acceleration over a
year. Really light power sats require many tons every year of station
keeping reaction mass to prevent light pressure from blowing them away
like dandelion fluff.

Just so everyone knows, Leik Myrabos Lightcraft Flight Handbook is now available. I just received my copy. Managed to buy it off Allibris. I've just begun reading it and so far it looks good. I note that SSI was one one of the principle movers on microwave powered lightcraft, back in 1991, with a call from Lee Valentine to Leik.

Gary 7

> PS, for station keeping reasons, you want a power satellite to be as
> efficient as possible (to reduce the area). And the more mass the
> better. Lots of mass averages the light pressure acceleration over a
> year. Really light power sats require many tons every year of station
> keeping reaction mass to prevent light pressure from blowing them away
> like dandelion fluff.
You could use a power satellite like a solar sail spacecraft.
In fact, a solar power satellite IS a spacecraft producing at least half
the thrust which a solar sail spacecraft produces also.
Why not using this thrust to steer the craft and sort of tack it to keep
station?

If the collector unit with it's large solar cell arrays is able to steer and
point like a spacecraft using "Roller Reefing" for fuelless steering and
attitude
control, it wouldn't need fuel for it.

For Roller Reefing take a look at
http://solar-thruster-sailor.info/figs/fig18.html

Best wishes

Frank

>> PS, for station keeping reasons, you want a power satellite to be as
>> efficient as possible (to reduce the area). And the more mass the
>> better. Lots of mass averages the light pressure acceleration over a
>> year. Really light power sats require many tons every year of station
>> keeping reaction mass to prevent light pressure from blowing them away
>> like dandelion fluff.
> You could use a power satellite like a solar sail spacecraft.
> In fact, a solar power satellite IS a spacecraft producing at least half
> the thrust which a solar sail spacecraft produces also.
> Why not using this thrust to steer the craft and sort of tack it to keep
> station?

If you can show me how to do this, I would be much obliged. The way I
see it is like trying to tack upwind without a keel.

Keith

>
> > You could use a power satellite like a solar sail spacecraft.
> > In fact, a solar power satellite IS a spacecraft producing at least half
> > the thrust which a solar sail spacecraft produces also.
> > Why not using this thrust to steer the craft and sort of tack it to keep
> > station?
>
> If you can show me how to do this, I would be much obliged. The way I
> see it is like trying to tack upwind without a keel.
>

> .
> Take a look here:
http://www.ugcs.caltech.edu/~diedrich/solarsails/intro/tacking.html or
http://wiki.solarsails.info/index.php?title=Tacking_Solar_Sails

The solar sail spacecraft can point the thrust into the direction of
orbit motion or
against it and with this slowing it's orbit speed down or accelerate it.
When slowing the orbit speed down, the spacecraft moves towards Sun.

Best wishes

Frank

I understand the vectors, in fact, I once proposed hanging a bunch of
gravitationally coupled solar sails ahead of the earth to move the
earth back from the sun (over geological time).

The problem with a power satellite is it is in orbit around the
*earth.* And the force on the satellite is radially out from the sun
in all places on its orbit around the earth. 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.

The force egg shapes the power sat orbit, which is not good for it
staying in the same place over its rectenna.

There is computer code to analyze this dating back decades, but I have
not located a working copy yet.

Keith

> I understand the vectors, in fact, I once proposed hanging a bunch of
> gravitationally coupled solar sails ahead of the earth to move the
> earth back from the sun (over geological time).
>
> The problem with a power satellite is it is in orbit around the
> *earth.* And the force on the satellite is radially out from the sun
> in all places on its orbit around the earth.
If the power sat looks like this at http://www.nss.org/settlement/ssp/
I would agree.

Two large primary mirror arrays pointing toward Sun and trying to keep
the symmetry
while concentrating the energy onto secondary mirrors, which concentrate
the energy
onto the real solar cell array with transmission antenna which points
towards the rectenna.
Looks like tilting and changing pointing would be very difficult if
possible at all.

Why all this mirror-stuff? 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.
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.

In contrast to a solar sail spacecraft, which tries to get out of the
Earth orbit
and is orientated to the Sun for one half of the orbit, while orientated
edgewise
to the Sun on the other half of the orbit, the Solar Power Station could
be orientated
always toward Sun. On the first half of the (Earth) orbit it would be
accelerated on the
second half it would be slowed down using it's pointing capability to
fine tune the process.
> The force egg shapes the power sat orbit, which is not good for it
> staying in the same place over its rectenna.
>
The Power Station would not be exactly above the same place but it could
make good about
that through pointing with the antenna onto the same place.
It could also point onto other rectenna places too.

Best wishes

Frank

>> I understand the vectors, in fact, I once proposed hanging a bunch of
>> gravitationally coupled solar sails ahead of the earth to move the
>> earth back from the sun (over geological time).
>>
>> The problem with a power satellite is it is in orbit around the
>> *earth.* And the force on the satellite is radially out from the sun
>> in all places on its orbit around the earth.
> If the power sat looks like this at http://www.nss.org/settlement/ssp/
> I would agree.
>
> Two large primary mirror arrays pointing toward Sun and trying to keep
> the symmetry
> while concentrating the energy onto secondary mirrors, which concentrate
> the energy
> onto the real solar cell array with transmission antenna which points
> towards the rectenna.
> Looks like tilting and changing pointing would be very difficult if
> possible at all.
>
> Why all this mirror-stuff?

It is an attempt to get the light concentrated and to keep the power
connections between solar cells and transmission antenna short. I.e.,
it is for low mass

>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.

> 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.

> In contrast to a solar sail spacecraft, which tries to get out of the
> Earth orbit
> and is orientated to the Sun for one half of the orbit, while orientated
> edgewise
> to the Sun on the other half of the orbit,

I always thought that a sail just kept a constant tilt to the sun
either slowing it down or speeding it up.

> the Solar Power Station could
> be orientated
> always toward Sun. On the first half of the (Earth) orbit it would be
> accelerated on the
> second half it would be slowed down using it's pointing capability to
> fine tune the process.

I don't understand this.

>> The force egg shapes the power sat orbit, which is not good for it
>> staying in the same place over its rectenna.
>>
> The Power Station would not be exactly above the same place but it could
> make good about
> that through pointing with the antenna onto the same place.
> It could also point onto other rectenna places too.

Hmm. If one is forced into a non 24 hr orbit, then it is really going
to be hard to use it.

Best wishes,

Keith

> 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.

One would think that it might be possible to extend a boom with a weight at the end of it toward and/or away from Earth, where it would oscillate like a pendulum in Earth's tidal forces, swinging the station back and forth in time with it, consuming no reaction mass in the process.

Michael McNeil

>> I understand the vectors, in fact, I once proposed hanging a bunch of
>> gravitationally coupled solar sails ahead of the earth to move the
>> earth back from the sun (over geological time).
>>
>> The problem with a power satellite is it is in orbit around the
>> *earth.* And the force on the satellite is radially out from the sun
>> in all places on its orbit around the earth.
> If the power sat looks like this at http://www.nss.org/settlement/ssp/
> I would agree.
>
> Two large primary mirror arrays pointing toward Sun and trying to keep
> the symmetry
> while concentrating the energy onto secondary mirrors, which concentrate
> the energy
> onto the real solar cell array with transmission antenna which points
> towards the rectenna.
> Looks like tilting and changing pointing would be very difficult if
> possible at all.
>
> Why all this mirror-stuff?

It is an attempt to get the light concentrated and to keep the power
connections between solar cells and transmission antenna short. I.e.,
it is for low mass

>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.

> 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.

> In contrast to a solar sail spacecraft, which tries to get out of the
> Earth orbit
> and is orientated to the Sun for one half of the orbit, while orientated
> edgewise
> to the Sun on the other half of the orbit,

I always thought that a sail just kept a constant tilt to the sun
either slowing it down or speeding it up.

> the Solar Power Station could
> be orientated
> always toward Sun. On the first half of the (Earth) orbit it would be
> accelerated on the
> second half it would be slowed down using it's pointing capability to
> fine tune the process.

I don't understand this.

>> The force egg shapes the power sat orbit, which is not good for it
>> staying in the same place over its rectenna.
>>
> The Power Station would not be exactly above the same place but it could
> make good about
> that through pointing with the antenna onto the same place.
> It could also point onto other rectenna places too.

Hmm. If one is forced into a non 24 hr orbit, then it is really going
to be hard to use it.

Best wishes,

Keith

>
>> 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?

In fact, if I were to design a solar power satellite, I would try to use
roll able thin film solar cell arrays like that
http://www.energyenv.co.uk/PowerfilmHome.asp
along with my Roller Reefing System to steer and operate the solar
power satellite.

This should save construction costs also, since the solar cell arrays
come up
on rolls to the operation or construction orbit and are just clipped in
into their
retaining frames on the Outer Ring of the structure.

You could use the same arrangements to produce energy and to point and
operate the solar power satellite.

To try, if Roller Reefing works to operate an SPBS, you could just stuff my
System Sail of the Solar Sail Launch System
http://solar-thruster-sailor.info/figs/fig19-21d.html
(patented in UK and Germany, US-application pending)
with thin films on it's sail rolls
http://solar-thruster-sailor.info/figs/fig14-15.html.

The System Sail carries a central docking station for daughter units
where a
a microwave transmitting unit and also a laser unit could be docked in
already
at launch.
This would be a low cost precursor to test if the technology works.

Direct Launch to GEO but also to LEO would be possible.
As the System carries also SEP-thrusters it would be able, to reach GEO
from LEO
by using them instead of the solar sails, which are unfurled of their
rolls not before
GEO is reached. There they would be used to produce energy and for station
keeping and attitude control.

>
>> In contrast to a solar sail spacecraft, which tries to get out of the
>> Earth orbit
>> and is orientated to the Sun for one half of the orbit, while orientated
>> edgewise
>> to the Sun on the other half of the orbit,
>>
> I always thought that a sail just kept a constant tilt to the sun
> either slowing it down or speeding it up.
>
There are different strategies one of them for planet centered
Non-Keplerian orbits
is that I described above for a solar sail spacecraft, which tries to
get out of Earth
orbit for instance. It is a suboptimal trajectory and called On-Off
switching.

I am not an expert in the area of Non-Keplerian orbits, but Prof. Colin
Mc Innes
http://www.mecheng.strath.ac.uk/staffprofile.asp?id
has written a book where the one strategy mentioned above is described
in detail.
The title is "Solar Sailing, Technology, Dynamics and Mission Applications".

I really think, when operating a SBPS you'll need some solar sail
orbit/control experts
also to do that.
>
>> the Solar Power Station could
>> be orientated
>> always toward Sun. On the first half of the (Earth) orbit it would be
>> accelerated on the
>> second half it would be slowed down using it's pointing capability to
>> fine tune the process.
>>
> I don't understand this.
>
As you wrote, the solar sail can be tilted to slow it down, or to speed
it up.

One half of the orbit the solar power station, which is a solar sail
spacecraft
is tilted to slow it down, the other half of the orbit it is tilted to
speed it up.
In the end after 24 hours it will be at the same orbit location as 24
hours before.

>
>>> The force egg shapes the power sat orbit, which is not good for it
>>> staying in the same place over its rectenna.
>>>
>>>
>> The Power Station would not be exactly above the same place but it could
>> make good about
>> that through pointing with the antenna onto the same place.
>> It could also point onto other rectenna places too.
>>
> Hmm. If one is forced into a non 24 hr orbit, then it is really going
> to be hard to use it.
>

See above, it can be operated, that the power station is on the same
location after 24 hours, so in my eyes this would be a 24 hours orbit.

But during those 24 hours the location above Earth would change,
perhaps only slightly, how much I don't know and should be found
out by solar sail orbit and trajectorie experts.
Besides, a change of orbit-location might be welcome to deliver energy
to different locations on Earth.

Best wishes

Frank

>
>> On Fri, Aug 21, 2009 at 2:45 PM, Frankrd@...
>>
>>> 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.
>>
> One would think that it might be possible to extend a boom with a weight at
> the end of it toward and/or away from Earth, where it would oscillate like a
> pendulum in Earth's tidal forces, swinging the station back and forth in
> time with it, consuming no reaction mass in the process.
>
> Michael McNeil
>
Moving mass is surely a way to swing the station. A boom might be
a way, - perhaps a bit hard to implement.

Roller Reefing combines moving the center of mass with moving the
center of radiation force - into opposite directions, which enhances
the impact of the steering moves.
Due to the number of steering foils, fine tuning the steering process
might be a bit better.

Best wishes

Frank

>>
>>> 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?

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.

Keith

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

Just ignore the power collecting function. Can you station keep in
GEO with a solar sail?

Normal solar sail use has the light source and the orbital center in
the same place, the sun. By angling the sail you can get velocity
change either speeding up or slowing down. If the sail slows down,
gravity will pull it into a lower orbit.

In GEO the earth is the object being orbited around and the light
pressure is not radial from the earth.

Consider a very light sail in GEO. If it is anything but edge on to
the sun, it would be blown out of GEO and away from the earth like
dandelion fluff.

Heavy objects are accelerated one way and then 6 months later the
other way. Light power sats pick up nearly 1000 m/sec velocity over 3
months compared to orbital velocity of 1500 m/sec.

Perhaps there is a way, but I just don't see how to couple the force
vectors you can get out of a light sail into keeping a sail in GEO.

If you can, please explain how to do it.

Keith

Why not both mass drivers and elevators? A high velocity mass driver can move a large amount of lunar material in a short amount of time in the required direction for collection in space, presumably L-2. In another application, a mass driver can slow and tow a NEO to where it's needed, using the NEO itself as reaction mass. The low acceleration required for human trafficking (couldn't resist) and tools, electronics, and parts can be handled by an elevator, if it's proven that it can "rise above" fiction.

Sugg

Keith Henson schrieb:
> Just ignore the power collecting function. Can you station keep in
> GEO with a solar sail?
>
I am pretty sure that the orbit solar sail specialists could do
something that comes near station keeping through slowing the craft
down and speeding it up once a day, so that the craft is on the same
position relative to Earth after 24 hours.

If you want to verify that, just ask one of them.
Or even better, help to get the funding to prove it in space.
> Normal solar sail use has the light source and the orbital center in
> the same place, the sun. By angling the sail you can get velocity
> change either speeding up or slowing down. If the sail slows down,
> gravity will pull it into a lower orbit.
>

That is correct.
> In GEO the earth is the object being orbited around and the light
> pressure is not radial from the earth.
>
Even a sailboat on the water cannot bank on the wind coming from
the same direction, the sailor has to steer the boat accordingly and the
wind
angle is not radial either.

> Consider a very light sail in GEO. If it is anything but edge on to
> the sun, it would be blown out of GEO and away from the earth like
> dandelion fluff.
>

A solar power satellite is no dandelion fluff, - you are speaking of
several tons
of mass.

Even a solar sail design with our best todays technology (that is mainly
a sail
thickness of about 2 microns) is far away of the
lightness number of one, which is the point were the solar power pressure
and the gravity of Sun would cancel each other out when the sail is
fully facing
Sun's surface, so that the solar sail could hover on a point over the
Sun without
having to orbit it.

To blow the craft outwards, a lightness number under 1 would be necessary.

The point were the solar cell arrays including the holding structure
reach a
lightness number of 1 seems very, very far away for me :-) .

> Heavy objects are accelerated one way and then 6 months later the
> other way.
I think this is because you have hight thrust propulsion and you want
to save fuel in this case.

Solar sailing is low thrust propulsion and changing the orbital speed does
not need fuel at all, no matter how often you do that.
So I would prefer 24 hours as a cycle.
The benefit is that the craft could be above the same place on Earth every
24 hours.

> Light power sats pick up nearly 1000 m/sec velocity over 3
> months compared to orbital velocity of 1500 m/sec.
>

> Perhaps there is a way, but I just don't see how to couple the force
> vectors you can get out of a light sail into keeping a sail in GEO.
>
> If you can, please explain how to do it.
>

I don't see your problem. You already can imagine, that slowing the
craft down or speeding it up by turning the force vector is possible.
The rest does the gravity of Earth.

Best wishes

Frank

> Keith Henson schrieb:
>> Just ignore the power collecting function. Can you station keep in
>> GEO with a solar sail?
>>
> I am pretty sure that the orbit solar sail specialists could do
> something that comes near station keeping through slowing the craft
> down and speeding it up once a day, so that the craft is on the same
> position relative to Earth after 24 hours.
>
> If you want to verify that, just ask one of them.

The only solar sail specialist I know is Eric Drexler. He has not
worked in this area for decades and is too busy with nanotech designs.

Any suggest as to who should be brought into this discussion?

> Or even better, help to get the funding to prove it in space.

No possibility of getting funding before it is well understood.

Keith

>
>> Keith Henson schrieb:
>>
>>> Just ignore the power collecting function. Can you station keep in
>>> GEO with a solar sail?
>>>
>>>
>> I am pretty sure that the orbit solar sail specialists could do
>> something that comes near station keeping through slowing the craft
>> down and speeding it up once a day, so that the craft is on the same
>> position relative to Earth after 24 hours.
>>
>> If you want to verify that, just ask one of them.
>>
> The only solar sail specialist I know is Eric Drexler. He has not
> worked in this area for decades and is too busy with nanotech designs.
>
> Any suggest as to who should be brought into this discussion?
>
I don't think we should ask someone to take part in this discussion.
But I think, a private email to those mentioned here might help also.

Prof. Bong Wie, http://www.aere.iastate.edu/index.php?id=4360
The author of Solar Sailing, Prof. Colin Mc Innes,
http://www.mecheng.strath.ac.uk/staffprofile.asp?id
Prof. Bernd Dachwald, http://www.spacesailing.net/

Best wishes

Frank