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Friday Space Power Technology Session

Here's where I'll be picking up from yesterday, and blogging today's session, as I get time.

The first speaker this morning is Jay Penn of Aerospace (again) talking about laser power beaming demonstrators. He's describing the same apps as yesterday for the military, but also talking about space-to-space beaming for other spacecraft. Reviewing yesterday's talk with concept that can put 2.5 MW into the grid per satellite. Two solar panels, two laser transmitter panels on a deployable backbone. Providing more of a description of the "halo" orbits than yesterday, but I still don't understand it from an orbital mechanics standpoint. I'll have to read the paper or talk to Jay later.

He's showing several charts that demonstrate how inserting technology into the laser system can dramatically increase the power available per EELV flight (not sure how relevant this is, other than as a benchmark, because it's very unlikely that an economically viable system is going to go up on EELVs). Also shows that you don't save much money by scaling down the system to smaller power levels--R&D dominates the costs. His bottom line is that we could do a 125kW demonstrator on an EELV, that could scale up to 200kW with technology insertion. Laser appears to be the only practical means to provide acceptable small spot beams from GEO. Laswers have 10,000 times smaller spot for the same range and aperture compared to microwaves. In response to a question, he notes that the individual lasers are not phased, and they don't need to be. There is a question about maintenance/repair. They hadn't looked in detail but a quick look suggested that degradation wasn't a major issue. he makes one other point--the system was self-lifting from LEO to GEO using ion propulsion, to save mass.

Now another talk by Jordin Kare, on laser diode power beaming. Talking about the NASA beamed power Centennial Challenge. While it's about elevator climbers, it is essentially a contest to build a beamed-power system. Prize has almost been won, but not quite, and is now at $500K. None of the teams are using lasers. Laser-Motive (his company) was formed to develop laser power beaming technology, but the current focus is on winning the prize. Their concept uses a fixed set of laser diodes and optics, with a steering mirror below the climber. Operating on a shoestring. They are estimating 10% efficiency, but actually getting more like 13%. They have eight kW of laser power to deliver a kilowatt to the climber. Got good price on "seconds" for the lasers (a little less than $10/watt so about $80K) Didn't care about beam profile, as long as they got the power on target. Didn't do custom optics--used float-glass and amateur telescope mirrors, with old HP stepper motors to drive them. Lasers share (more expensive) parabolic mirrors. Bought some 50% efficiency cells that can operate at ten suns, with help from Boeing. Unfortunately they had some final integration issues (smoking a power supply) that prevented them from winning, but no on else won either.

The 2008 contest is a kilometer climb up a rope hung from a helicopter (the faster the climb, the more the money)--lasers are the only option. DILAS is offering to build a custom system ($35,000 for 2.5kW), and will set a new radiance standard. Can go to much more range with bigger optics and more power. deliver tens of kilowatts at tens of kilometers with this technology.

Laser-Motive is ready to build these kinds of systems tomorrow. Could be used for ground to aircraft or ground vehicles of mirrors on aerostats, or air to ground to simulate space-to-ground. ISS to ground is also a possibility. Next steps: higher radiance, coherent systems (e.g., fiber lasers), lightweight low-cost optics, and then operational systems.


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Jay Manifold wrote:

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

Rand Simberg wrote:

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."

David wrote:

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!)

Rand Simberg wrote:

There are no pilots on the climbers.

Jay Manifold wrote:

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.

Carl Pham wrote:

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.

David wrote:

No Rand - the helicopter pilot!

kert wrote:

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.

the truth wrote:

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

kert wrote:

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

The Truth wrote:


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

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"... :)

Stan Wright wrote:

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.

Tom Nugent wrote:

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.)

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This page contains a single entry by Rand Simberg published on October 3, 2008 5:17 AM.

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