[ExI] Obama Transition Team Examining Space Solar Power

Tue Dec 23 10:08:50 UTC 2008

On Mon, Dec 22, 2008 at 9:33 AM, Kevin H <kevin.l.holmes at gmail.com> wrote:

> On Sun, Dec 21, 2008 at 5:53 PM, Keith Henson <hkeithhenson at gmail.com>wrote:
>>
>> it largely depends on the cost to lift power sat parts to GEO.
>
>
> http://www.spacex.com/falcon9_heavy.php#pricing_and_performance
>
> It's probably the most realistic near-term method, unless we're looking to
> NASA, ESA, etc.  Looking at the numbers, if we can somehow do this from a
> lower orbit it would be much cheaper.  I know a low earth orbit would have
> some of the same disadvantages as on earth: only twelve hours of sunshine a
> day.
>

I'd think it'd be much much worse than on earth, you would need several
rectennas per satellite, driving up the costs greatly.  I'd expect that
atmospheric absorption of the microwaves would start to play a much bigger
role when you're forced to use extreme angles as well, which would negate a
lot of what energy savings you're getting from the height alone.  Unless I'm
missing something, a low earth orbit would be the worst of both worlds,
intermittent power generation at a relatively low efficiency combined with
extremely high costs.

> Someone mentioned a sun-synchronized orbit, but I don't see how that is
> possible.  The satellite would have to orbit the earth once every year,
> which would be way to slow and, to my knowledge, much higher than GEO.  But
> it seems that full GEO isn't necessary, we could tolerate a couple hours of
> night every day, and the costs savings would probably add up when you're
> doing this on a large scale.
>

Remember, GEO isn't just about distance, it's about actually being able to
synch with the ground...  A couple hours may not seem like a huge deal, but
if an object is orbitting 15 times a day like the ISS, and you only get
efficient power generation at, say, an angle less than 30 degrees, then a
given rectenna only is capable of receiving about 4 hours of power a day.
These are spaced out relatively evenly throughout the day

Lower orbits degrade much more quickly anyway,

>
>
>>  The
>> advantages are not just in the power multiple, but in the fact that
>> the energy is steady, no clouds, no wind stopping, i.e. no storage.
>> The other advantage is that you don't have to build massive and very
>> expensive lines from the southwest to the mid west and east.  You just
>> plunk a rectenna down close to the load.
>
>
> I guess I just don't have a rubric to compare costs here.  But yeah,
> storage is a big problem here on earth.  The other issue, I think, is how
> *light* they can make the SPS's.  Some of the proposals I've seen (sorry, I
> can't find the links right now) don't use solar powers at all, but mirrors
> to some device that directly turns visible light radiation into microwaves.
>
> But the solar constant is on average 1366 W/square meter.  There's just no
> more energy out there from the sun than that at the distance of the Earth (1
> AU).  That's our upper bound of what we could expect.  That's 732 square m
> of panels/reflectors to transmit 1GW.
>
>
>>
>>
>> If you can haul the parts up on a space elevator, there is no question
>> that power sats are the less expensive approach.  If you have to haul
>> the parts up on rockets, it's marginal.
>
>
> I think that's the show-shopper here.  Rocket technology is here and now.
>  I think even if we could build a space elevator, even a partial one, it
> would take too long to build the technology.  Honestly, to save us from the
> energy crisis, I think at least part of the system needs to be up and
> transmitting power within twenty years, and even that might be stretching
> it.  Some experts believe that we've already reached peak oil.
>
>
>>  The hybrid methods of using
>> rockets to suborbital and lasers to kick the payload into GEO meets
>> the penny a kWh requirement.
>
>
> Except, you know NASA, it would take twenty years to research laser
> propulsion before they can approve writing a report on it.
>
>
>>  Of course the old method of developing
>> extraterrestrial materials works best of all, but there is not enough
>> time to develop space industry.
>
>
> Has anyone considered pumping hydrocarbons, methane and ethane, from Titan?
>  We know the lakes are there, the trouble is it would take a long time for
> us to get anything back from it.  The advantages are that Titan has a
> smaller gravity well than the Moon, and the interplanetary transport network
> could cause it to cost nearly nothing to transport fuel ships there and
> back.  Of course, we haven't solved the problem of cost to orbit....
>
>
>>  It's not entirely obvious that any
>> long term energy solution is needed.  If I were confident the
>> singularly would get here before famines and resource wars I wouldn't
>> worry about it.  But I can't put a firm date on either.  The
>> consequences of running out of energy are really dire.  Some models
>> show the population dropping a hundred million a year, bottoming out
>> at 1-2 billion.
>>
>> Keith
>
>
> I know.  This is stuff we should have been working on since the 70's, but
> instead forward their problems into the future.  BTW, I'm not confident that
> a singularity will ever happen.
>
> Kevin
>
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