...IT'S ALIVE....PENTAGON to Study Space Solar Power Program.

In article ,
Fred J. McCall wrote:
:That's why microwave thermal propulsion is at least slightly
:interesting...

Can you really get a big enough receiving antenna onto such a
satellite to get any reasonable benefit from beamed microwave power?

Depends on wavelength. The proposals for beamed-microwave propulsion
mostly use much shorter wavelengths than powersat concepts, so with a
substantial transmitter array you can indeed get useful amounts of power
into a modest receiver at modest distances. (*This* sort of beaming
wouldn't be done from GSO.)

Whether it is a good way to do rocketry is a more complicated question --
not least, because most any externally-heated thermal rocket really wants
to use LH2, with all the bulk and complexity penalties that incurs.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Henry,

Depends on wavelength. The proposals for beamed-microwave propulsion
mostly use much shorter wavelengths than powersat concepts, so with a
substantial transmitter array you can indeed get useful amounts of power
into a modest receiver at modest distances. (*This* sort of beaming
wouldn't be done from GSO.)

Exactly. The point is to build a small subscale pilot plant, probably
in some
higher LEO orbit to test out the basics. And then to find a small
market that
can use that subscale pilot plant so you can get some early revenue.
If that
market also happens to reduce the cost of transportation for building
the
bigger systems (including the cost of transportation to wherever you
get the
materials for bigger systems), its all the better.

Whether it is a good way to do rocketry is a more complicated question --
not least, because most any externally-heated thermal rocket really wants
to use LH2, with all the bulk and complexity penalties that incurs.

There are drawbacks to LH2 indeed, but there's also a large and
growing
experience base with the stuff. With the advent of large, thin-gauge
FSW
tanks like what the ULA guys have been proposing for their "Wide Body
Centaur", I think you might actually be able to get away with a
reasonable
propellant fraction.

Now, whether it will actually make technical sense compared to normal
LOX/LH2 or LOX/HC upper stages remains to be seen. I'm actually a bit
skeptical, but at least it's politically feasible (unlike say NTRs or
Gas Core
NTRs). The other thing in its favor is that it is one possible
customer for a
subscale SPS demonstrator. And that alone might make it worth
further
pursuit for someone who wants to pursue Space Solar Power.

~Jon

On May 5, 9:43 am, Monte Davis wrote:
(Henry Spencer) wrote:
The central difficulty with powersats is not that they are obviously
uneconomical, but that they do not scale down well..

One potentially interesting baby step would be a powersat supplying
other satellites. Are there reasonable assumptions under which that
could that be a win over satellites having their own photovoltaics?
(GeoffLandis, you out there?)

Yes, given that space is currently the place where electricity sells
for the highest price per watt, it makes sense to sell electricity to
space markets as a first market.

There are definitely markets where it might be valuable, but I haven't
found one where it's valuable enough to overcome the risk-aversion of
the satellite engineering community. Power for orbital transfer
vehicles might be one, if you had a reusable orbit-raising tug running
on electric propulsion, but unless the market expands radically, I'm
not sure that you can make it profitable enough to pay off the
required up-front investment. (which supports what Henry Spencer
posted, I think; a big problem with these concepts is high up-front
investments required.)
--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis

On May 5, 8:45 pm, Geoffrey wrote:
On May 5, 9:43 am, Monte Davis wrote:

(Henry Spencer) wrote:
The central difficulty with powersats is not that they are obviously
uneconomical, but that they do not scale down well..

One potentially interesting baby step would be a powersat supplying
other satellites. Are there reasonable assumptions under which that
could that be a win over satellites having their own photovoltaics?
(GeoffLandis, you out there?)

Yes, given that space is currently the place where electricity sells
for the highest price per watt, it makes sense to sell electricity to
space markets as a first market.

There are definitely markets where it might be valuable, but I haven't
found one where it's valuable enough to overcome the risk-aversion of
the satellite engineering community. Power for orbital transfer
vehicles might be one, if you had a reusable orbit-raising tug running
on electric propulsion, but unless the market expands radically, I'm
not sure that you can make it profitable enough to pay off the
required up-front investment. (which supports what Henry Spencer
posted, I think; a big problem with these concepts is high up-front
investments required.)
--
Geoffrey A. Landishttp://www.sff.net/people/geoffrey.landis

Maybe for beamed microwave power, you have to start off beaming it in
the "wrong" direction. Does it save you anything, anywhere, to beam
power to GEO satellites from Earth? One such power station might
serve several satellites.

If that works, maybe you have a spin-off application: use power beamed
from Earth for electric propulsion to circularize the orbits of
satellites destined for GEO, rather than using kickstages. With that
proven, maybe you have a case for powering orbital tugs from Earth-
based beam stations -- re-use the propulsion units you use to get
satellites into the right orbits. And with that proven, maybe you get
a case for an *orbital* power station for all of the above purposes,
perhaps assuming less-than-breakthrough reductions in Earth-to-orbit
launch costs (such as those SpaceX claims), plus those same orbital
tugs that have proved their worth already.

Admittedly, these seem like marginal propositions at best. Even if
you could make a case right now, they face competition from
improvements in self-contained space-based photovoltaic power for
probes, satellites and manned craft, and I've seen recent evidence
that this isn't yet a mature technology arena. Those space-based
photovoltaic improvements arguably improve the case for SPS (for
terrestrial power markets) in the long run, but could cannibalize
potential niches for smaller-scale SPS applications in the near term
(if it's OK to say "cannibalize" when there's nothing to eat yet ;-).

As long as I'm thinking "wrong-way charlie" about this (i.e., that
getting power beam networks going through space at all, even if
collection has to be done on Earth initially, is conducive in the long
run to making space the main source of that power) ... how efficient
would microwave power relaying be? How much less material on orbit do
you you need? There are vast areas on Earth -- the Sahara, the
Arabian peninsula's Empty Quarter, the interior of Australia, others
-- now receiving a wealth of near-constant, high quality sunlight. If
you can collect a fraction of the potential PV power from it
economically, can it be beamed up to relays and back down to major
electrical power markets, at a small fraction of the investment
required to put equivalent collectors in space? And if so, is that
likely to be more cannibalistic of eventual space-based collection,
rather than an incentive to space-based ISRU approaches?

SPS as rationalized by O'Neill et al. was somewhat eschatological. If
it all went off half-cocked, it may have been simply because, in the
70s, with all its talk of "an Era of Limits", the Club of Rome report,
Paul Ehrlich's theories of an impending global Malthusian crisis and
so on, the environmental eschaton seemed a whole lot closer. (And of
course, with disastrously optimistic estimates of what the Shuttle
would be able to do, the Space Colonies solution seemed much nearer at
hand.) Earth may not, in fact, be the place for an expanding
industrial civilization, but the models indicating this were fed with
somewhat arbitrary constants where they should have variables.
Something like those times may be creeping back upon us, though.
Anthropogenic global warming is very nearly proven, and the costs of
addressing it seem lower than feared, but still much higher than SPS-
scale investment.

-michael turner
http://www.transcendentalbloviation.blogspot.com

Michael Turner wrote:

:
:Maybe for beamed microwave power, you have to start off beaming it in
:the "wrong" direction. Does it save you anything, anywhere, to beam
ower to GEO satellites from Earth? One such power station might
:serve several satellites.
:

Since, as Henry pointed out, a different frequency would be used for
this than would be used for an SPS feeding power to Earth, does this
really get you much closer to where you want to go?


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

(Henry Spencer) wrote:

:In article ,
:Fred J. McCall wrote:
:The problem is that SPS energy is *NOT* particularly cheap. If it was
:space would already be full of SPS generating and transmitting
:stations.
:
:Not exactly: the problem is that the *first* powersat is not particularly
:cheap. The 50th could be the cheapest energy source around, depending on
:what assumptions you make -- analyses claiming that powersat energy is
:excessively expensive tend to make stupid assumptions like launching all
:materials from Earth.
:

The problem is that folks who try to make a case that using space
materials in a big way generally hand wave away the development of the
technologies and space industrial base that makes that really
possible. If you bill all that to the SPS effort rather than assuming
is springs full grown like Athena from the head of Zeus, is space
development really cheaper?

:
:The central difficulty with powersats is not that they are obviously
:uneconomical, but that they do not scale down well, which means that (at
:least with current technology) a very large up-front investment is needed
:to test their viability.
:

And that leads to both an immense barrier to entry, as it makes sure
prices for a working system stays preposterously high until the point
where you have a large working system, at which point what economies
of scale may exist don't help you all that much (because the system is
already built).


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

"Geoffrey" wrote in message
oups.com...
On May 5, 9:43 am, Monte Davis wrote:
(Henry Spencer) wrote:
The central difficulty with powersats is not that they are obviously
uneconomical, but that they do not scale down well..

One potentially interesting baby step would be a powersat supplying
other satellites. Are there reasonable assumptions under which that
could that be a win over satellites having their own photovoltaics?
(GeoffLandis, you out there?)

Yes, given that space is currently the place where electricity sells
for the highest price per watt, it makes sense to sell electricity to
space markets as a first market.

There are definitely markets where it might be valuable, but I haven't
found one where it's valuable enough to overcome the risk-aversion of
the satellite engineering community. Power for orbital transfer
vehicles might be one, if you had a reusable orbit-raising tug running
on electric propulsion, but unless the market expands radically, I'm
not sure that you can make it profitable enough to pay off the
required up-front investment. (which supports what Henry Spencer
posted, I think; a big problem with these concepts is high up-front
investments required.)
--


If SSP is only considered as a business investment
that's correct I'm sure.

That's why it needs to be wrapped up in the Global
Warming and Energy issues that are rapidly gaining
steam. SSP could be 'sold' as a matter of global
and/or national survival. As a matter of global or
national prosperity. Of ending wars over resources
and bringing hope to an impoverished third world.

Changing the cost to benefit analysis by political
and emotional leaps and bounds.

But maybe all of you are correct. If Kennedy had demanded
that all the technological hurdles for going to the moon
be solved in advance, I doubt he would've ever given
.....'that speech'.

But he knew that if he set a goal that was high enough, one
that could change the world and inspire people to act.
That the breakthroughs would find a way to happen.

To initiate a self organizing system, one that settles on
the best possible solution just as any complex adaptive
system does, the most important thing is the 'push'
from equilibrium. The goal.

The goal must simultaneously maximize two primary
variables, then connect them together dynamically, with
a sense of urgency.

The static attractor of maximum tangible returns to society
And the chaotic attractor of dreams of a better future.


SSP, has the potential to maximize and connect
both of those inspiring ambitions at once.
By being seen as a single solution to climate
change and the dependence on dwinding fossil fuels.
And within an urgent time frame defined by the rate
of climate change.

Just as Kennedy connected a single solution to
winning the omminous cold war /while/ ushering
in an age of technology and discovery.
With the single and lofty goal of landing a man
on the moon by a date certain.

If the goal is designed properly, designed to self organize.
It cannot fail to find the best possible solutions.
We simply have to have faith, faith in science, that
once set in motion towards a worthy goal we
will succeed.


The goal is the thing, design that first, not SSP.


Jonathan




Some Complexity links

CALResCo Complexity Writings
http://www.calresco.org/themes.htm

Self-Organizing Systems (SOS) FAQ
http://www.calresco.org/sos/sosfaq.htm

DYNAMICS OF COMPLEX SYSTEMS
http://necsi.org/publications/dcs/index.html

London School of Economic Complexity Programme
http://www.psych.lse.ac.uk/complexity/


Paul J. Steinhardt
Department of Physics
Princeton University
http://www.physics.princeton.edu/~steinh/

Complexity Digest
http://www.comdig.org/index.php


Complexity Science: A Worldview Shift
by ERIC B. DENT
George Washington University
http://polaris.umuc.edu/~edent/emergence/emerge2-r.htm




s



Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis

In article .com,
Michael Turner wrote:
Maybe for beamed microwave power, you have to start off beaming it in
the "wrong" direction. Does it save you anything, anywhere, to beam
power to GEO satellites from Earth? One such power station might
serve several satellites.

There is considerable value in laser beaming to GSO satellites from Earth
(as Geoff and others have pointed out), because of GSO's eclipse seasons.

Earth's axial tilt means that GSO is in continuous sunlight for much of
the year, with Earth's shadow passing "above" or "below" the orbit. But
for a few weeks around the spring and fall equinoxes, a GSO bird passes
through Earth's shadow once a day, experiencing about an hour of darkness
max. Maintaining operation during those eclipses calls for considerable
battery mass, even though the total eclipse time is only a day or two per
year. (Some TV-broadcasting satellites simply shut down their broadcast
transmitters during eclipses, and hence need only small batteries to run
internal "housekeeping" functions, but most comsats have to keep working.)

This is a particularly interesting application for power beaming, because
the satellites already have suitable receivers -- their solar arrays are
already there and are even pointed in pretty much the right direction --
and ground laser stations do not need huge lasers or enormous optics to
put adequate light on the satellite. (It's less than you would think,
because solar cells are quite a bit more efficient for monochromatic light
at the right wavelength than for sunlight.) You *would* need several
widely-separated beaming stations to try to make sure that they aren't all
clouded over simultaneously.

The problem is that the GSO comsat market is *intensely* conservative, and
the benefits mostly don't show up until they launch new satellites. They
won't shrink their batteries on speculation. (Indeed, they will want
quite strong assurances that the beaming service will still be there 10-20
years later.) So such a service would take a long time to start paying off
its startup costs.

The other wart is that while such a service could help legitimize power
beaming, it doesn't really get a foot in the door for powersats otherwise.
Despite the weather hassles, for this application you clearly want to put
the beaming stations on the ground, and you clearly want laser rather than
microwave beaming.

... how efficient
would microwave power relaying be? How much less material on orbit do
you you need? There are vast areas on Earth -- the Sahara, the
Arabian peninsula's Empty Quarter, the interior of Australia, others
-- now receiving a wealth of near-constant, high quality sunlight. If
you can collect a fraction of the potential PV power from it
economically, can it be beamed up to relays and back down...?

It's been suggested. The actual energy-conversion processes should be
80-90% efficient without great difficulty -- better than long-haul
transmission by high-voltage power line! -- provided the antennas are big
enough to get almost all of the transmitted beam into the receiver. You
save *something* on orbited mass due to no solar collectors, but you still
need kilometer-scale orbiting structures to make it work.

likely to be more cannibalistic of eventual space-based collection,
rather than an incentive to space-based ISRU approaches?

*Probably* not. If for no other reason, because there is considerable
long-term advantage in moving the one inefficient step -- initial
conversion of sunlight -- outside the biosphere. And even at a desert
site, averaged over a long period, a ground solar array collects only
about 1/5th of the energy of a similar array in orbit, due to night,
weather, and atmospheric losses.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Jonathan Goff wrote:

Exactly. The point is to build a small subscale pilot plant, probably
in some
higher LEO orbit to test out the basics. And then to find a small
market that
can use that subscale pilot plant so you can get some early revenue.


Speaking of pilot plants: http://news.bbc.co.uk/1/hi/sci/tech/6616651.stm

Pat

On Mon, 7 May 2007 04:13:03 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:


... how efficient
would microwave power relaying be? How much less material on orbit do
you you need? There are vast areas on Earth -- the Sahara, the
Arabian peninsula's Empty Quarter, the interior of Australia, others
-- now receiving a wealth of near-constant, high quality sunlight. If
you can collect a fraction of the potential PV power from it
economically, can it be beamed up to relays and back down...?

It's been suggested. The actual energy-conversion processes should be
80-90% efficient without great difficulty -- better than long-haul
transmission by high-voltage power line! -- provided the antennas are big
enough to get almost all of the transmitted beam into the receiver. You
save *something* on orbited mass due to no solar collectors, but you still
need kilometer-scale orbiting structures to make it work.

Yes, Peter Glaser used to call this one of the "terraces" on the way
to full SPS.