June 07, 2012

A new paradigm for space-based solar power

Although the concept of space-based solar power has existed since the 1970s, several intractable technical problems have impeded its development. In particular, thousands of tons of equipment would need to be sent into orbit to create a single large power satellite. A space-based solar power advocate, John Mankins , has created a concept that could substantially ameliorate the concept. Mankins has come up with a concept that employs vast numbers of identical, modular components, which can be sent up in repeated rocket launches. Although the initial cost for electricity from a modest sized power satellite would be high, the cost would drop as a robotic space-based infrastructure is built up, standards emerge, solar cell efficiencies increase, and the industry benefits from economies of scale. In an interview with Sander Olson for Next Big Future, Mankins discusses how the first prototype power satellite could be up and running within a decade, and how space-based solar power could eventually supply a significant fraction of the entire earth's energy requirements.

John Mankins

Question: How long have you been examining the idea of space-based solar power?

I have been researching the concept since 1995. My background is in physics, and I have worked for Caltech and at NASA. About seven years ago I left Government service and founded Artemis innovation Management Solutions with my wife. Artemis Innovation has a number of projects, but concentrates on space-based solar power.

Question: When and how did the concept of space-based solar power emerge?

In the late 1960s, a pioneer named Dr. Peter Glaser examined the range of emerging technologies and first invented the idea of using a “Solar Power Satellite” to supply Earth with power from space. In the mid to late 1970s, the first comprehensive studies of space solar power were funded. These studies examined the concept of constructing huge, monolithic structures in space, which would have necessitated initially building a massive in-space infrastructure and new, very large launch systems before the first Solar Power Satellite (SPS). Assessments by the Congressional Office of Technology Assessment, and the National Research Council concluded that for these reasons, space solar power would be prohibitively costly, and further research by the US government was abandoned.

Question: What emerged in 1995 to change the equation?

By 1995 the technology needed for space solar power had progressed sufficiently to warrant a reexamination of the subject. The most promising concept that emerged was the use of modular systems approaches, which involves sending smaller mass-produced sections up individually and then assembling these in space. After further analysis it became clear that the modular approach was the optimal method for achieving space-based solar power in a reasonable timeframe and budget.

Question: How exactly has the technology evolved since the 1970s?

There have been a number of improvements. The efficiency of solar photovoltaics has improved from less than 10% efficiency to more than 30% efficiency now. I'm confident that within the next decade, solar photovoltaics could achieve efficiencies of up to 50%. There have also been substantial improvements in key electronic components, such as solid-state power amplifiers. The efficiencies have gone from 15% in the 1970s to 70% now. With focused investments, we should be able to get devices with efficiencies approaching 80% by 2020. This will further increase the viability of space-based solar power. A wide range of other technologies have also improved dramatically, including light-weight and high-strength materials, robotics, in-space propulsion and others.

Question: You are the chief architect behind the SPS-ALPHA design. What are the central aspects of this new paradigm?

The SPS-ALPHA concept facilitates the design and development of a very large solar power satellite out of a large number of very small pieces. Each piece weighs perhaps 25-100 kilograms, but there are tens of thousands of pieces in the final product. The beauty of this system is that all of the parts of the design can be manufactured readily in a standard factory – resulting in very low costs for the system hardware.

Question: So the power satellite would be composed of vast numbers of identical modules?

Yes, the modules would be stackable – like pizza boxes – for ease of transportation to space, and then unstacked and assembled once they reach the operational orbit for the satellite. There might be about 6 or 8 different types of modular elements, and each type would be mass produced with from hundreds to tens of thousands of copies. They would initially be launched into a low Earth orbit, and from there transferred to a higher orbit for integration into the SPS platform. We are looking at using robotic systems to assemble the panels.

Question: So your plan employs robots for most of the construction?

Yes. The SPS-ALPHA architecture would only employ people on the ground to supervise the robots operating in space. The goal would be to assume the intervention of astronauts only in the event of a problem that could not be resolved using robots. As a rule of thumb, we expect that it may cost from 100-times to 1000-times more to have a suited astronaut perform a task in a high Earth orbit than to have a remotely-supervised robot do it. This field of technology has advanced rapidly in the past decade, and so we plan to employ robots extensively.

Question: How long would it take to get a prototype system up and running?

With sufficient funding, we could have a ground based, rudimentary prototype up and running by 2014. An early prototype in orbit could be built by 2017-2018. And in about a decade, a larger pilot plant could be in geosynchronous Earth orbit, generating 10 megawatts. The total cost for this roadmap could be several billion dollars, with most of the cost coming in the last few years. As a point of comparison, the pilot plant would be approximately the same size as the International Space Station, which cost $100 billion to manufacture, launch into space and assemble. The cost savings would result from using standard, mass-produced pieces, standard launch systems and robotic assembly in space.

Question: What would the cost per kilowatt hour for the first plant?

We believe that the cost of power from the first pilot plant would be $3-5 dollars per kilowatt hour. We would be producing relatively few units per year, so the per-unit cost would be high. But as we ramp up production, multiple factories would be producing solar power satellite modules, and per-unit costs would plummet.

Question: How much would it cost to get all of the material into orbit?

Initially we plan on using standard chemical expendable rockets, but we would aim to employ reusable launch systems as soon as they become available. For example, there is the Startram concept, invented by Jim Powell in the 1990s. Such a system might eventually reduce launch costs to $100 per pound. But in the near term, $500 per pound launch costs are adequate to make this scheme viable, and that should be feasible by employing reusable rockets.

Question: What is the optimum size for a solar power satellite?

Although larger satellites are more cost-effective, it costs more to get larger platforms operational. So we should initially see 200-500 megawatt power stations. As the technology matures, we should see still larger platforms capable of generating several gigawatts. But the original dream from the 1970s of having 10 gigawatts delivered from a single satellite will probably never be cost-effective.

Question: Would power be beamed to the ground using microwaves?

That is my preferred approach. The end-to-end efficiency could be as high as roughly 64%. By comparison, the best laser power transmission systems have an end-to-end efficiency of only about 15%-25%. Another problem for laser power transmission is that they don't work well when there is cloud cover. By contrast, microwaves at the right wavelength will pass through clouds easily. There are proponents of millimeter microwave power transmission, but these approaches are extremely inefficient, and won't pass through clouds either.

Question: Is the ultimate goal to have thousands of the space-solar power systems in orbit?

Perhaps, but it really depends on market demand. And the vision is to combine ground-based solar power and other green energy options with space-based solar power. Wind and solar are intermittent power sources, so space-based platforms could provide supplemental power for overcast days, as well as nighttime power.

Question: How low can costs eventually drop?

In order to compete, we need to get costs down to approximately 10 cents per kilowatt hour. At or near that price point, space solar power should be competitive for many global markets. All of the enabling technologies, such as computing, solid-state, robotics, and materials are all being driven by other applications.

Question: What proportion of the earth's energy could space-based solar eventually provide?

By the end of the 21st century, space-based solar power could be providing 15%-25% of Earth's energy needs. By the 2030s, space-solar could be expanding exponentially, hitting the knee of the s-curve. The situation would be similar to that of electrification in the US in the 1890s.

Question: What is next after the current SPS-ALPHA project for NASA?

After the current Phase 1 NASA-funded SPS-ALPHA study, the next stage would take a couple of years and cost a couple of a million dollars. That would get us to the point of having prototype engineering models of all of the key system elements. Then, about 20 million dollars over the next five years or so. That would get all of the necessary pieces for the platform developed, and an initial, but very small scale prototype operating in low Earth orbit. Once that is accomplished, the next step would be getting the factories up and running for the large pilot plant.

Question: But getting factories up and running could be a multi-billion dollar endeavor.

Yes, but the cost would be a fraction of the cost of other major infrastructure projects – such as the construction of the Big Dig in Boston, or the cost of the Channel Tunnel in Europe, or any of a number of other large engineering projects. A visionary multi-billionaire could single-handedly fund the project.

Question: Have you contacted Elon Musk about funding, or perhaps using SpaceX rockets to build the space solar power platforms?

Certainly SpaceX launch vehicles would be excellent candidates for launching future Solar Power Satellites. As for funding, it is my understanding that Mr. Musk decided some years ago that space-based solar power wasn't viable, at least for the foreseeable future. His personal vision is sending people to Mars. We need to find a wealthy individual to fund this concept, but haven't yet found that person.

Question: Given sufficient funding, when is the earliest that you could have an orbital power platform in operation?

We could have an initial pilot plant in space within a decade, by 2022. This prototype plant would continuously deliver megawatts of power to the ground at a couple of dollars per kilowatt-hour. If we can harvest and deliver a tiny fraction of the solar energy that passes by earth constantly, Space Solar Power would be able to provide a significant share of humanity’s energy requirements, and to do so essentially forever. The concept of Space Solar Power could become a critically important piece in solving the world's energy challenges.

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