Friday Space Power Technology Session

Possibly stupid question - are these halo orbits around Lagrangian points?

No, they're around geostationary satellits. The seem to circle them out of plane, in a plane perpendicular to the vertical. As I said, I need to talk to Jay to understand how they're "orbiting."

Perhaps this:

1. Start in GEO
2. fire thrusters to push you directly towards Earth
3. alter your now eccentric orbit so that it still has a period of one day.

This could be described as an "orbit" around GEO - as in, you spend half your orbit above GEO, half below, so it averages to a GEO orbit.

(And am I the only one scared about the prospects of climbing a cable attached to a helicopter using beamed laser power? I hope the pilot uses really dark sunglasses!)

There are no pilots on the climbers.

Thinking about it and expanding on David's suggestion, a 24-hour orbit of both eccentricity and inclination != 0 would indeed appear, both from the viewpoint of a regular geosynchronous satellite and the ground, to describe a closed path around a point in GEO once per day. But I'm still very much guessing and will be interested to hear the actual description.

What is this 13% efficiency figure? It seems hard to believe that's the efficiency with which the laser turns electricity into light energy. My impression is that that efficiency is usually down around 5-7%, even for diode lasers, which of course spread like crazy. For good collimated laser beams, my impression is that the efficiency with which electric power is turned into light is maybe 2 to 3%.

Which is why, I dunno, I'm having a very hard time seeing why one would put solar panels on satellites for transmission of power to the ground with lasers. Losing 90% of your energy in the electricity-light conversion (and maybe 40% more on your light-electricity conversion on the ground) completely obviates any advantage you have in higher solar flux in orbit.

Why not just take the same solar panels and set them out in the desert outside of Phoenix?

For the same reason, why not outfit your tether climbers with a tiny fuel cell? I'm missing something here, unless this is just a Can It Be Done? sort of basic research thing.

No Rand - the helicopter pilot!

I dont know about the laser efficiency figure but i recall from some papers published by Kyoto university power beaming research department that they have achieved around 70% efficiencies with microwaves over short distances.
By the way, higher solar flux in orbit is not the only benefit of putting your cells up there. For geostationary concepts, continuous illumination is another, which is kinda hard to achieve in desert outside of Phoenix.

it's UNBELIEVABLE that there are engineers and scientists' conferences on the THOUSANDS TRILLION$$$ "Space Solar Power" project!

one hundred billion dollars, to be precise, and they are going to hold the world for ransom for it. with fricken laser beams

@kert

cover the full U.S. electric energy needs, may cost up to $4.5 trillion with Earth-built power plants:

http://news.cnet.com/8301-11128_3-10056099-54.html?tag=newsLeadStoriesArea.0

just multiply it by 300 to 1000 to know the "price" to launch in space the same solar power plants...

laser beams, space elevators, nuclear rockets?

just sci-fi devices now... like a "Warp Engine"... :)

I have been watching Space Solar Power since studying it during my Engineering studies 15 years ago. This new look at SPS from DOD seems to possibly be looking at "gold plating" their energy suppy chain far in excess of the already inefficient supply chain. The initial focus on solar power beamed from space is understandable, given the awareness of the concept, as well as the operational, tactical, & strategic concerns for the supply chain of deployed troops. However more efficient means propbably exist to meet the requirements for 5 MW delivered to forces on the ground. For starters, how about a fleet of massive airships "hovering" high in the stratosphere. Each airship could contain a single PWR generating at least 9 MW ( thermal ) Weight is the obvious problem, however I would think the barriers are less than for a space based system. NASA did significant work on low mass nuclear power with the cancelled JIMO project. Every other technical risk is at least an order of magnitude smaller than putting the generating capacity near GEO. Beaming the power from distances on the order of 20 miles to 100 miles vs. GEO is much more achievable. Dumping excess thermal load can be both radiative and convective within the stratosphere. Propulsion while on station can be fully electric, drawing from the power generation. The high altitude would be impervious to most ground based anti-aircraft weapons, and deployment can be within the envelope of established air superiority.

Carl Pham,
Diode lasers have become relatively efficient - the ones we used last year were around 45% efficient (from electrical power in to photons out). And bandgap-tuned photovoltaic cells (i.e., PV cells tuned to match the incident monochromatic wavelength) can be very efficient - over 50%. Add in some minor losses from not capturing a small fraction of the light, motor inefficiencies, etc. and the efficiency drops a bit more, but is still respectable.

As far as fuel cells, the problem with that or batteries or similar technologies is that they generally can't store enough energy to lift themselves to orbit (or at least not much more mass than themselves.)