The Space Reviewin association with SpaceNews

Could a spherical spacecraft be more effective and less expensive in turning solar power into power beamed down to the Earth? (credit: © Mafic Studios)

SSP: a spherical architecture

Space solar power (SSP) is gradually beginning to take flight. Enterprising SSP ventures, such as Solaren Corp. and Space Energy, Inc., are in the midst of developing initial projects to supply energy from space. Solaren Corp. of California has recently reached an agreement with Pacific Gas and Electric, a California utility, to supply 200 megawatts of energy beginning in 2016, while Space Energy, Inc., a Swiss based company, is producing a prototype demonstration satellite that will help it close purchase power agreements with entities it is currently in discussions with. But while these pioneering companies in the vanguard of a nascent industry are surmounting many technical and economic obstacles, significant barriers remain before the dissemination of energy from space can become truly widespread.

The greatest challenge for producing meaningful amounts of energy for competition in terrestrial energy markets continues to be the ability to establish extremely large photovoltaic surface areas in space.

As SSP advocates are painfully aware, the high expense of launching numerous payloads into space for the assembly of satellites large enough to transmit meaningful amounts of energy to Earth is cost prohibitive. While very large structures in space are theoretically within the realm of the technically possible for legitimate SSP interests, the launch costs associated with the construction of a satellite a few kilometers in length, as would be necessary for large scale energy transmission, are exorbitant. Additionally, the expense of space systems and operations—robotic technologies and the supporting space and Earth-based infrastructure—are extremely high and must be dramatically reduced. While proponents hope that large-scale space infrastructure projects will achieve certain economies of scale that will bring down the cost of each individual launch, component, and support system, the prevailing price tag for the whole of such a project would doubtless be enormous, making it very difficult to compete in the broader energy marketplace.

Accordingly, SSP has been criticized for requiring large numbers of breakthroughs to become feasible. It has long been held that before a critical mass of interest from the private sector can be forthcoming there must be drastic improvements in space transportation, on-orbit construction techniques, and power transmission capabilities. The common wisdom has traditionally been that these developments must be attained before SSP can become commercially viable and competitively brought to energy markets en masse.

Significant improvements in the performance of photovoltaic cells have often been heralded as bringing SSP closer to fruition. But whatever improvements in photovoltaic (PV) efficiency occur—even if photovoltaic cells were of absolute quality—the greatest challenge for producing meaningful amounts of energy for competition in terrestrial energy markets continues to be the ability to establish extremely large photovoltaic surface areas in space.

As such is the case, a critically sought after breakthrough may not be in space construction techniques or in PV performance, but rather in the nature of the physical composition of photovoltaic cells. If photovoltaic cells were produced with elastic properties affording them the capability of expanding, then a significant opportunity would arise for a novel new architecture for SSP: an inflatable sphere.

Scientists at the Technion - Israel Institute of Technology have already made certain strides in spherical photovoltaic technology with the development of photovoltaic balloons. While the Israeli development is of terrestrial photovoltaic balloon technology, the basic premise of crafting an inflatable sphere with elastic photovoltaic cells capable of expanding in reaction to the pressure of gases is a novel approach that could be a game-changing solution for cost-to-orbit factors and issues of on-orbit assembly that are necessary to resolve before establishing SSP architectures in space.

Indeed, the concept of an inflatable photovoltaic sphere is a simple idea that could possibly overcome many of the obstacles that SSP faces. As basic math bears out, such a design would enable extremely large satellites to be lofted into space with substantially increased surface areas. For example, whereas a satellite 5 kilometers in length and 2 kilometers in width would provide a surface area of only 10 square kilometers and would have to maneuver so that its photovoltaic cells could remain in the Sun, a sphere inflated to a diameter of 5 kilometers would provide an illuminated surface area of over 39 square kilometers with no orbital maneuvers necessary. Such architecture would be a far more ideal for damming the nearly 1.4 gigawatts of solar energy continuously pouring through every square kilometer of space in Earth orbit.

The key to the concept’s feasibility is the ability to inflate the sphere rather than painstakingly assemble it in orbit. The sphere could of course be condensed into a very small package for transport into space and would then expand once it achieved orbit. The use of gases would be critical in this regard—large amounts would be compressed very tightly, would weigh virtually nothing, would cost very little, and crucially, would do the “heavy lifting” once the platform reached its orbit. Such a system would still face major technical challenges, including maintaining integrity in a space environment filled with micrometeorites and space debris.

The concept of an inflatable photovoltaic sphere is a simple idea that could possibly overcome many of the obstacles that SSP faces.

According to the 2007 National Security Space Office (NSSO) study on SSP the United States has limited capabilities to build large structures in space and cannot at present move large amounts of mass into orbit. The United States correspondingly has extremely limited capabilities for in-space manufacturing and construction or in situ space resource utilization. By crafting a balloon-like satellite the amount of on orbit construction for SSP infrastructure would at once be drastically reduced in tandem with the amount of launches necessary for establishing this architecture in space. In wholesale fashion the inflatable sphere would eliminate the many structural components that conventional SSP spacecraft possess, mooting many questions of modularity maximization in the process.

The spherical concept would enable cost-to-orbit factors to be lowered considerably as the platform would weigh much less than conventional models and would require far fewer launches to be brought online. Whereas other SSP plans call for slashing the cost per pound to orbit with substantial increases in launches, the inflatable sphere would slash the overall launch costs by lessening the amount of launches required while still producing a massive surface area for the production of solar energy.

While it would be highly desirable to possess the capabilities discussed in the 2007 NSSO study, an inflatable sphere would be a design that could by-pass the necessity of their development in the short term, making SSP technically and financially practical in the immediate future. Perhaps the resources engendered from the success of spherical SSP could then in turn be utilized to advance the aforementioned capabilities for other commercial, scientific, or military endeavors in the medium of space.

However, for large systems, pieces of the sphere would have to be sewn together in orbit before it can be inflated. If this were the case, larger spheres would doubtless face similar technical obstacles as the smaller conventional SSP platforms in that a significant amount of launches and on orbit assembly would be required for both. It would therefore be necessary to develop the capabilities previously mentioned in the 2007 NSSO SSP study before the project could be undertaken.

Nonetheless, the spherical design would nevertheless continue to afford a satellite with a far larger surface area producing far more solar energy for the amount of resources that were invested. Once an extremely large sphere—100 kilometers in diameter—had been crafted in space, it could be inflated to its full size and would then have the potential of producing tens or hundreds of terawatts of energy from an illuminated area in excess of 15,700 square kilometers. By comparison, the alternative designs, which would also require numerous launches and on orbit assembly, would only produce gigawatts. With the ability to produce such vast amounts of energy, large-scale spheres would surely overcome the manifold economic barriers that have thus far thwarted SSP endeavors, justifying the incursion of the full spectrum of costs—launch, in space assembly, supporting space systems, and supporting terrestrial infrastructure.

Indeed, inflatable space-based spheres with elastic photovoltaic cells could be the energy technology breakthrough that much of the world has been waiting for. Should a spacefaring nation with the requisite resources proceed to ring the Earth in GEO with relatively small photovoltaic spheres, or if it should fashion giant photovoltaic spheres, or if it should proceed to do both, the energy resources that the nation in question will have availed itself would be more than considerable. A nation such as the United States would have developed enough clean and renewable solar energy to become one of the world’s foremost energy exporters.

The spherical concept would enable cost-to-orbit factors to be lowered considerably as the platform would weigh much less than conventional models and would require far fewer launches to be brought online.

If solar power satellites such as these did come into being, they would very likely necessitate the overhaul of the entire global economy to achieve broad compatibility with the new energy technology. The resultant economic transformation would be incredible, creating many new high technology jobs in industries across the world, but especially in the nation that was at the epicenter of the SSP breakthrough. In fact, of greatest economic impact may not be the new energy technology itself, but rather the wave of innovation arising in complement to the new energy technology.

And yet the tremendous symbolic power that these satellites could possess may have a profound impact far beyond the realm of economics and the environment. Due to their photovoltaic properties, large enough spheres could have a crystalline appearance in space visible from the Earth with the naked eye, giving them the appearance of diamonds in the sky. If this were the case, these satellites would not only drastically reduce carbon emissions and provide a plentiful source of renewable energy, but there physical beauty across the backdrop of both day and night skies could be surreal for onlookers, causing many around the world to become enamored with the entrepreneurial verve of a nation that developed them as well as with the culture that created them. A nation that owned and operated what appeared to be diamonds in the sky producing abundant clean energy would surely be at the forefront of global leadership, attracting the sentiments of much of the world’s population into its socio-political camp.

Of even greater socio-cultural impact could be their effect on the technological aptitude of a nation, as the case may very well be that crystalline discs shining like diamonds in the sky could inspire an entire generation of young Americans to excel in math and science like never before. With the tangible, ever present symbol of mathematical excellence glimmering in the sky by day and by night, kids could very likely develop a whole new appreciation for the “coolness” of science.