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Report: Japan to Issue Solicitiation for Development of Microwave-Based Space Solar Power System

The Nikkei reports that the Japanese government will soon issue a public solicitation for firms to participate in a project to develop technologies for a space solar power system that would beam electricity generated by orbital solar panels and converted into microwaves in space down to the earth.

The hope is to commercialize orbital solar power by 2030. Such a system would have such advantages as generating electricity regardless of the weather on the ground.

The project will develop technologies to transmit power down to the earth. The idea is to convert solar electricity into microwaves, which would then be converted back into electricity at the surface. The team will first attempt to transmit microwaves for a distance of around 10m; the hope is to extend this to 100m within three to five years.

The Japan Aerospace Exploration Agency (JAXA) has been conducting studies on both microwave- and laser-based Space Solar Power Systems (SSPS) for years, organizing a special committee and working groups. In case of microwave based SSPS (M-SSPS), the solar energy must be converted to electricity and then converted to a microwave beam. The on-ground rectifying antenna would collect the microwave beam and convert it to electricity to connect to commercial power grids.

In the laser-based SSPS (L-SSPS), a solar condenser equipped with lenses or mirrors and laser-generator would be put into orbit. A laser beam would be sent to Earth-based hydrogen generating device.

JAXA has proposed a four-step roadmap ending with commercial SSPS around 2030:

  1. Tens of kW-class space technology demonstration satellite to demonstrate microwave or laser power transmission. This satellite will be launched in a low earth orbit by the H-IIA class rocket.
  2. Demonstrate robotic assembly of 10-MW class large scale flexible structure in space on ISS co-orbit.
  3. Build a prototype SSPS in GEO.
  4. Build commercial GW class SSPS in GEO.



And in a low earth orbit or ISS co-orbit, a multi-MW system could be used to provide N. Korea with some much needed electric power if they were ready for it and had ground receivers prepared - and the aim was good.

I all depends on the aim.


I actually like the concept from the movie Real Genius; use a space based laser to vaporize Kim Jong IL and other military targets.

richard schumacher

Why lasers? Laser efficiency is hardly more than 10%, versus 90% for microwaves, and the concept invites Joe Twelvepack to think of weaponry.


At first, I wondered why anyone would even consider solar PV from space, it would cost SO much. Then it occurred to me that they could get power 24/7 so then on it made a bit more sense.


In order to minimize infrastructure costs for power transmission lines, and transmission losses it would be desirable to build receiver stations near big consumers, ie near large cities.

Think of these scenarios:
a) For whatever reason high power concentrated beam moves off desired target, and gets pointed to a small location in city centre, or worse to a packed sports stadium or a concert. Thousands could get microwaved. A loss of control over satellite or a collision with a piece of space debris could cause it. These type of satellite needs to have very large "solar wings" to collect as much as possible energy. It means large surface and increased likelyhood of a collision.

b) As a result of a collision the satellite and its beam starts oscillating (like a pendulum) so that the deadly beam now covers perhaps a line of over 10 km on Earth, possibly including some very busy highways, city streets etc.

? Is there any way to prevent the scenarios above (without shooting down a satellite - may be too late for many)?


Only the geosynchronous equatorial orbit will provide power 24/7.
GEO is up at 22,000 mi, while an ISS orbit is at 220 mi and low earth orbit is even lower.
An SSPS in GEO (Steps 3 or 4) is not likely to occur in the near future.

I think there would be adequate levels of protection to make inadvertent termination of an entire city highly unlikely.

On the other hand “highly unlikely” is nowhere near good enough.

The microwave SSPS is no less a possible weapon than the laser type.


I don't think the security risk is that great:
Put a device on the ground that sends "Ok" all the time, IF the beam is directed at the right place. If the ground station stops recieving the beam (meaning it is going elsewhere), it stops sending "Ok" and the satellite is switched off. And that is only the first failsafe to put.
On the other hand, I hope they get their air traffic control right, an airliner under this wouldn't be too good.


There are a number of misconceptions in the comments here.
Proposals for microwave power are all to have a fairly dispersed beam, so that birds could fly through it unharmed and if it wandered off-course no-one would get fried.
In any case, ensuring that it does not wander off course is trivially easy.
All you need in the field is a transmitter which if any part of the field looses power due to the beam wandering off-course would cease signalling back to the satellite.
The satellite could easily be set up so that without the positive signal, it does not transmit any power.

You would also not necessarily need to have satellites in geosynchronous orbit to have pretty constant power, though that would help.
As long as you have a number of receiving arrays, and a number of satellites, then they can switch transmission to different fields.

The real difficulty with these schemes is purely in lift costs.
All the rest is fairly straightforward.

richard schumacher

As Davemart writes the necessary basic technologies for safe delivery of microwave power from orbit are already known. If photovoltaic cells are too expensive an alternative is Solar thermal using reflective concentrators and Stirling engine generators.

Launch costs are the sticking point for affordable civilian power. It's a shame that NASA has been screwing around for nearly 40 years not developing lower-cost highly reliable reusable launchers. Now we must scramble.

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