I thought I might contribute a word or two about your article on space-based power, as my day-job has been in the electricity industry since 1980, and my early years were spent, in part, keeping tabs on the development of solar power generation. I remember giving an internal talk on it, including the subject of space-based power genration around 1982-3, I guess. I obtained a sizeable NASA report from the early 1980s dealing with space-based power generation, using silicon photovoltaic cells with microwave re-transmission to Earth. As you mentioned in your article, the microwave reception array is a sizeable thing, of the order of a square kilometer at the least. I don't think there has been any change in the technology envisaged for space-based electrical power generation over the previous 30 years. At least, silicon solar cells are somewhat improved in efficiency now, though the fundamental limit on efficiency is, as I remember, somewhere around 25-30%. The genration losses in a magnetron microwave oscillator are not so great, but a lot of waste heat will have to be radiated into space by the satellite, somehow.
You might think that, being an electricity generation industry person, I might be in favour of this technology, but I'm not. Apart from the mind-boggling cost of hoisting enough hardware into space (to geostationary orbit too!) to make a difference, i.e. 2000 MW of power sent out on the ground, I am certain that a microwave beam of that intensity, which would have to be at least 2 kW/m2, would be a whopping safety risk. Stand in it and you would die quickly, so how can Col. Smith imagine that a 200 MW microwave beam might not be a weapon? Perhaps he and his Pentagon friends are being a bit disingenous here. Such a power satellite could lay waste to a city in short order, not quite as quickly and efficiently as a Starship's phasers might manage, but it would be "good" enough. Bumping the beam power up only a factor of ten would help.
[...] There are signs that wealthy oil producers (such as Abu Dhabi) are seeing the writing on the wall and are now contemplating a massive expansion of solar photovoltaic (see recent newspaper articles) as well they might, given the amount of money, open desert and sunshine they have. Who needs power satellites?
Incidentally, I do realise that the only way re-usable space planes are going to be even built as prototypes any time soon is if someone like Richard Branson decides that he wants to just do it, and creates an orbital version of Spaceship One/Two/etc. For the rest of us enthusiasts, I don't believe that any business plan will ever be good enough to convince an investor who isn't already an enthusiast (thus not motivated by profit), whether governmental, institutional or a private individual. I do not believe that a business plan consisting of a proposal to build solar power satellites is ever going to convince anyone, unless the intention is to build a microwave beam power weapon (same thing) to hold entire nations to ransom, but then, nuclear weapons are cheaper.
With best wishes,
Dr. Raymond D. Wright
1 June 2008
The NSSO report gives an equation for the peak intensity of the microwave beam on the ground (on p.30 of the Acrobat document, numbered p.27 on the page -- and NB there is apparently a typo in that the last expression on the right must be squared in order to make the units balance).
A little experimenting with this equation shows that you can make the peak ground intensity of the beam as low as you like, so long as you make the ground rectenna as large as necessary. So for example you might have:
wavelength = 0.052 m (microwaves at 5.8 GHz)
transmission distance = 35,800 km (GEO to Earth's surface)
transmitter diameter = 1 km
transmitter power = 2 GW
Then the peak intensity on the ground, in the centre of the beam, works out as 227 W/m2 (a tenth of the 2 kW/m2 you suggested). The rectenna would need to be somewhat over 10 km2, say about 4 km diameter. This probably represents a reasonable compromise between ground intensity and size of rectenna.
"Bumping the beam power up only a factor of ten", which you suggest as a means of turning it into a weapon, could not be done quickly or secretly, as it would require multiplying by a factor of ten either the light-gathering area of a power satellite or its transmitter area.
As for launch costs, the LEO to geostationary part would be done by solar electric power using the power satellites' own power-gathering capabilities. As for the surface to LEO part of the journey, I believe you may be able to help lower costs here?
Please let me know if you notice any errors in my arithmetic above!
4 June 2008
I agree with you that expanding the ground antenna means that the beam density can be less. I am sure that few people would be happy about a beam of even ~200 W/m2 going walkabout in the event of a system failure or mischief. That still amounts to intensities comparable to the interior of a microwave oven, albeit set on "defrost".
I also agree with you about the effort needed for greater power in the beam, but then, given the US's aggressive stance on space utilisation and general demeanour, I would imagine that the Pentagon is more interested in the technology we have been discussing, as a weapon.
Come to think of it, there could well be adverse consequences for microwave communications. The radio spectrum is pretty well parcelled up and sold off right up to 30 GHz and more. The 6cm wavelength has a number of services in it, including wireless broadband and satellite comms. There would be plenty of scatter of the power beam for large distances around the receiving antennae.
I really don't like the power satellite idea at all, as you may have gathered. However, it would be nice to see a breakthrough in space access, but the only way I see that happening is if some billionnaire, or maybe a club of billionnaires, decides to finish what NASA started with the X-33, for absolutely no business justification at all -- just because he, she or they want to do it. The communications and remote sensing satellite industry will never deliver this, because the costs of the throwaway launches are just too small an item when compared with the revenue streams from the services provided by the satellites, and the launch rates are too low.
Dr. R. D. Wright
5 June 2008
Dwayne Day, "Knights in shining armor", says: the renewed interest in space solar power following the National Security Space Office's recent review is largely misplaced, given the lack of clout possessed by this office as well as the significant technical challenges that space solar power still faces.
Stephen Ashworth, "In defense of the knights", says: space-based solar power does face technological and political challenges, but they may not be as insurmountable as some critics argue. In particular, Dwayne Day has misread the NSSO report as being pessimistic about the prospects for this energy source, whereas the report is in fact highly optimistic, and urges immediate action to build a 10 MW prototype demonstration system for $10 bn in 10 years.
Read the full articles on The Space Review website.
Dave Wright has launched a new space newsletter focused on the UK. He writes:
Welcome to the inaugural Space.co.uk newsletter. Since Space.co.uk was launched several months ago we have seen our vision for a UK Space Community website grow from an idea, to taking the first steps toward becoming a reality. We are fortunate to have met many individuals who are not only enthusiastic and excited about the UK's historical and future involvement in space, but who are also passionate about reaching out to a wider community of current and "to be" enthusiasts. It is thanks to these individuals that fantastic events like the UK Space Conference are born and they are a constant source of inspiration as we continue our efforts to develop Space.co.uk.
More on the Space.co.uk website.
Whereas Astronautical Evolution is intended mainly for debate and comment, and particularly for critical analysis of the conventional wisdom, the first issue of Space.co.uk is devoted to news and announcements, particularly about events on space in the UK. No doubt these two electronic publications will act to support each other.
In addition, the HME-HS team at ESA's Strategy and Architecture Office prepares a very useful fortnightly e-mail digest of space news stories, giving a few words of description and a link to major stories from the BBC, Spaceflightnow.com, Spaceref.com, Spacedaily.com, The Space Review, and many other online sources. Enquiries to Jacqueline Myrrhe (Jacqueline.Myrrhe -- at -- esa.int).
More than twenty astronauts, scientists and cultural leaders have joined forces to announce the formation of the Overview Institute.
Its object is to raise public awareness of the Overview Effect, a term used to describe the experience astronauts have when seeing Earth firsthand from outer space, and the resulting sense of unification that is brought on by this unique perspective. This is described in Frank White's book of that title, together with many interviews with astronauts (Frank White, The Overview Effect: Space Exploration and Human Evolution, Haughton Mifflin, 1987).
News announcement here.
Jacqueline Myrrhe writes: "The news about the foundation of the so called "Overview Institute" was included into my last exploration news sent last Friday. Over the weekend I had time to read the declaration and I did sign it with pleasure. I wished someone in Europe would take such an initiative. Feel free to sign as well and forward the web site!"
According to Matt McGrath of BBC news, the French government under new President Nicolas Sarkozy is setting its sights on ambitious European missions to the Moon and especially Mars (as reported here).
Apparently, la révolution française is being driven by the political quest for prestige in the face of competition from India, China and Japan. There is talk of "shaking up" the ancien régime at the European Space Agency to make it more like NASA. Documents seen by the BBC say that a politically led space enterprise is necessary for Europe to be taken seriously in the international arena, and that Europe must play an "indispensable" part in the manned exploration of Mars.
But this would be a strategic mistake.
In the current climate of anthropogenic global warming panic and rocketing energy prices, the last thing on the European public's mind is exploring Mars.
A politically driven Moon-Mars programme designed around prestige, science and spinoff may produce one or two brilliant successes, but would eventually face the guillotine.
The only space strategy which makes sense for Europe (or anybody else) is to focus on the fundamental facts that space contains the resources for the next great expansion of human civilisation, and that the resource of most immediate application to life on Earth is sustainable, low-pollution (or are microwaves worse than coaldust? -- see Ray Wright's letters in item (1) above) solar power from space.
The logic of the situation demands that first the space agencies focus on supporting commercial space tourism (for large-scale, low unit cost access to orbit) and on asteroid exploration (for access to rocket propellants in space), at the same time building and operating a 10 MW space solar power (or astropower) demonstrator, as advocated by the National Security Space Office report.
In ten or fifteen years we have practical experience with large-scale harvesting of astropower and beaming it to Earth on microwaves, we have regular spaceplane access to orbit carrying hundreds of fare-paying passengers a year, and we have the beginning of deliveries of asteroidal water to Earth orbit. We are then in a position to begin a massive expansion of astropower, with the potential to supply a large fraction of the baseload of terrestrial power supply by say 2050 -- by which time that baseload could well be double its current level of around 15 TW.
In other words, we attack the problem of building solar power satellites to solve Earth's energy problems on three fronts at once:
We can then massively expand deliveries from interplanetary space to Earth orbit of firstly asteroidal water, then asteroidal metals and other construction materials, to create a space construction and refuelling industry which supports an expanding space economy based primarily on energy, orbital tourism and conferencing, and lunar tourism a little later on.
Starting from such a space economy, access to Mars for passenger-carrying ships can quickly become affordable, sustainable, growth-capable, and ultimately as routine as a transatlantic voyage or flight.
But without it, the only option is an expensive, heroic dash to Mars -- a recent (2004) ESA study suggested that each single launch to Mars with a crew of 6 astronauts would use up more Saturn-V-class superbooster launches than did the entire Apollo and Skylab programmes.
Such a project would see declining public and political support for exploration which is seen as irrelevant to terrestrial problems as Apollo seemed in 1970.
Let us above all focus on the concrete material relevance of space to our problems on Earth!
Astronautical Evolution is an e-mail forum devoted to debate and comment from an astronautical evolutionist perspective. To subscribe / unsubscribe / contribute / comment, please e-mail Stephen Ashworth, sa--at--astronist.demon.co.uk.
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