Designing SPS to accommodate tidal forces (was Nuke vs. SPS)

--- In spacesettlers@yahoogroups.com, Frank wrote:
> Am 23.06.2013 02:33, schrieb hitssquad:
> > --- In spacesettlers@yahoogroups.com "brooksn" wrote:
> > > --- In spacesettlers@yahoogroups.com "hitssquad" wrote:
> hitssquad, Why do you need an SPS in one huge piece.

Frank, I'm not the party making these proposals. If you don't like the proposals, talk to the people making them.

> Wouldn't two huge pieces combined with a separate transmitter unit do the trick?

Why not a thousand, or a million, separate pieces? One reason for having larger pieces, if they are to be larger all the way around, is to have more collector area along the North-South axis, since GEO has a limited amount of length along the East-West axis (265,000 km).

If the two pieces you are proposing were both in GEO (as opposed to one being below GEO and other above it, as the two halves of the single large SPS were) then one would block the other from receiving sunlight at 6 PM, and vice versa at 6 AM.

> the ISS arrays [...] are rather stiff and heavy

That keeps them from being thrust out of GEO by light pressure. See:

"This light-pressure problem was mentioned by Keith Henson almost three years ago, by the way. See his posts on light pressure, here:"

+++---+++
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.
+++---+++

...and here:

+++---+++
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.
+++---+++

...and here:

+++---+++
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.
+++---+++

...and here (the original light-pressure message from Keith Henson):

+++---+++
Countering light pressure on powe satellites.

Unfortunately these tricks do not eliminate the cost of fuel to offset
light pressure.

This is a serious problem on very lightweight power sats (0.4kg/kW or
less) where light causes accelerations in the 1/10,000 m/sec^2 range.
Unless opposed, this acceleration builds up ~8 m/sec/day, ~1km/sec
over 120 days. Orbital velocity at GEO is ~3km/sec. It is easy to
see uncorrected light pressure would cause a serious orbital
disturbance. A satellite in the 4kg/kW range only builds up ~100m/sec
over the same time and can to some extent average out the light
pressure over a year (galactic east half the year, galactic west the
other half).

While modeling this situation it occurred to me that an active gravity
gradient control might be able to offset light pressure.

At 1 AU the radiation pressure is around 4.6 micro newtons per square
meter, 9.2 micro newtons per square meter reflected.

That's 4.6 to 9.2 newtons per square km. (See attached spreadsheet)
+++---+++

> combined with the absence of the ISS-staff

Who's going to build and maintain and repair the SPS, then?

> would allow a much lighter and therefor cheaper SSPS per area unit compared to the ISS?

The cost of SPS isn't driven by mass. The burden of proof lies upon those claiming it is.