Flying carpets in space to harness the sun’s energy
Yes, that’s right! A multi-million-dollar research project is underway to develop giant carpets of nanostructured material to capture illuminating sunlight in space.
Picture this: a gigantic magical flying carpet floating endlessly above Earth made up of a myriad of glittering tiles, forever facing a Sun that never sets. What manner of fairytale do we speak?
Is this the mythical carpet belonging to Prince Husain, eldest son of the Sultan of the Indies in ‘One Thousand and One Nights’ (‘Arabian Nights’ to you and me), that bears him aloft from place to magical place? Or is it Soloman’s carpet made of purest green silk with a golden weft, made an impressive 60 miles long and 60 miles wide, flying by the wind at his very command? Perhaps it’s Ivan the Fool’s carpet, gifted to him by the Baba Yaga of old Russian folk tales, helping him find his way ‘beyond thrice-nine lands, in the thrice-ten kingdom’?
Then again, perhaps it’s the magic wishing carpets of Mark Twain’s Captain Stormfield, travelling ceaselessly through the heavens, that bear the closest resemblance to the flying carpet that concerns us here; combined with the speed at which Prince Husain is ‘in the twinkling of an eye borne thither’, plus the scale of Soloman’s green carpet. However, where Soloman’s carpet was shielded from the Sun by a canopy of birds, this flying carpet is destined to continually face it, to capture, endlessly, the energy of its illuminating sunlight.
Where the literary traditions of many cultures feature magical carpets, literally flying and transporting their passengers from place to place, a project called the Space Solar Power Initiative (SSPI) is developing flying carpets of a very different kind.
A team from the California Institute of Technology (Caltech) has joined forces with global aerospace and defence technology company Northrup Grumman in a three-year, $17.5m project to develop solar-catching carpets of nanostructured material to be deployed in space. There they will capture and convert the Sun’s energy before beaming it back down to specific destinations on Earth as microwaves to be transformed into electricity.
Now, you’d be forgiven for thinking that this all sounds a little far-fetched, but you’d be wrong! Prince Husain’s magic carpet is set to enter a brave new world, and it cannot come too soon.
According to the global development network the United Nations Development Programme, some 1.4 billion people across the world have no access to electricity and a billion more only have access to unreliable electricity networks. In addition, about three billion people rely on solid fuels such as traditional biomass and coal to meet their basic needs. Access to modern energy services for cooking and heating, lighting and communications, and mechanical power for productive uses is consequently a vast area of unmet need and the challenge of energy access is particularly acute in the least developed countries of South Asia and sub-Saharan Africa.
The SSPI is developing the scientific and technological innovations necessary to enable a space-based solar power system comprising a network of billions of greeting-card sized ultralight, high-efficiency photovoltaics, plus a phased-array system to produce and distribute power dynamically, and ultralight deployable space structures, capable of generating electric power and all this at a cost comparable to that from fossil-fuel power plants.
The project was conceived and is being led jointly by three professors in Caltech’s Division of Engineering and Applied Science (EAS): Harry A Atwater, Howard Hughes professor of Applied Physics and Materials Science and director of the Resnick Sustainability Institute; Ali Hajimiri, Thomas G Myers professor of Electrical Engineering; and Sergio Pellegrino, Joyce and Kent Kresa professor of Aeronautics, professor of civil engineering, and a senior research scientist at Caltech’s Jet Propulsion Laboratory.
SSPI will develop technologies in three areas: high-efficiency ultralight photovoltaics, ultralight deployable space structures, and phased array and power transmission. Atwater’s group is designing the ultralight, high-efficiency photovoltaics, optimised for space conditions and compatible with an integrated, modular power conversion/transmission system. Hajimiri’s team is developing the integrated circuits and the antenna design for the system’s large-scale phased array, timing control, and the conversion of direct current to radio frequency power.
Describing their aims, Hajimiri said: “Through a modular approach, power will be generated, converted, and radiated locally at the same place in space using a distributed power conversion and transmission solution created with modern integrated electronics that eliminates inter- and intra-module power wiring in the system. This significantly reduces the system mass, and thereby its cost.”
He added: “This space-based, highly adaptive power generator will enable versatile on-demand power anywhere on the planet and will be able to almost instantly distribute the power to different locations. This is enabled through an agile phased-array system that can dynamically direct the power to the desired locations on Earth and simultaneously provide power to multiple destinations on demand. This can substantially reduce the need and the cost associated with the power distribution network across the globe.”
The converted power from the orbiting solar panels will be beamed to these receiver ground stations using mechanisms similar to those used in phased array radars. Areas without power plants or a lack of major transmission capabilities would be ideal candidates to host these ground stations to capture the microwave radiation, which would then be transmitted to local communities.
Any such system must first be able to collect the solar energy and then convert and distribute it and one of the key barriers to the realisation of cost-competitive space-based solar power systems is the deployment in space of large surface area structures (flying carpets) to collect solar power, at low cost.
Pellegrino’s research group is designing and prototyping the key components for the architecture of the self-folding, origami-like, flexible, ultralight structures that can adaptively change shape and orientation in real time. As Pellegrino explains: “The cost and complexity of launching and deploying conventional deployable structures would be unacceptable for many applications.”
To circumvent this barrier, his team is developing novel architectures for multifunctional deployable space structures with an overall areal density on the order of 100g per square meter, equivalent to one or two sheets of paper. “The concepts that we are investigating build on over ten years of research on deployable thin-shell structures, which most recently had resulted in the development of low-cost fibre-composite booms and reflectors in which elastic hinges are created simply by making small cuts in the wall of a shell structure,” he added.
To achieve the project’s goals, Atwater, Hajimiri and Pellegrino have assembled a team of students, postdoctoral scholars and senior researchers. In addition, the EAS division is in the process of building specialised laboratory facilities to support the team. Meanwhile, Northrop Grumman engineers and scientists are collaborating with the Caltech researchers to develop solutions, build prototypes and obtain experimental and numerical validation of concepts that will allow for the eventual implementation of the system.
Harvesting energy in space isn’t a new idea. Isaac Asimov’s 1941 science-fiction short story ‘Reason’, published as part of his Robot series, explored the concept of a manned space station that supplies energy via microwaves beamed to other planets, with robots controlling the energy beams. No mention of carpets though.
Like Asimov’s idea, SSPI is striking and impressive in its concept and its challenges: to send millions of clean kilowatts back to an energy-hungry Earth, in the grip of climate change.
However, despite its breathtakingly ambitious nature, the SSPI project is tantalisingly feasible. With no night-time, coupled with the ideal conditions that space offers in order to harvest the immense amounts of raw solar energy on offer, perhaps magic flying, solar-catching carpets do indeed provide the answer to Earth’s search for sustainable clean energy.
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