Duke University Out of This World

Out of This World

Producing Energy in Outer Space

Matthew Feng

Math 89S – Mathematics of the Universe

Prof. Hubert Bray

28 Mar 16

Introduction

Gone are the days of long lines at the gas station for scarce supply; instead, the oil market now faces the opposite problem: a supply surplus. But while consumers do not feel a pinch at the pump anymore, the reality is that oil is a non-renewable resource, so while supply may be high now, eventually “easily accessible oil” will reach its peak quantity at which point future production will continually decline (Allmendinger 2007). Thus, the pursuit of sustainable energy becomes more important by the day, and the more efficient and practical the proposed alternative energy, the more likely the suggestion is to garner public, private, and political support. One such potential alternative is space-based solar power, which entails stationing satellites in outer space to collect then transfer energy back to the Earth’s surface either via a surface-to-space wire or wirelessly by means of microwaves. Space-based solar power is particularly attractive in theory because exposure to the Sun is constant and not affected by the night-day cycle on Earth that is a result of the planet’s rotation or by inclement weather. While seemingly fictional at first glance, the requisite technology may finally be developed for this futuristic fantasy to become a reality. This paper will first further on the necessities for an alternative to the world’s petroleum-based economy and then explain how space-based solar power can alleviate those concerns especially when compared to similarly undertaken projects. Lastly, inhibiting factors that could render such an undertaking physically impossible will be discussed with some given serious consideration while others dispelled.

The importance of energy to the global economy is highlighted on both a macro and micro level. On the macro level, ample energy supply is critical for economic growth across almost every major sector or industry, and on the micro level, energy enables consumers to warm their homes, move from point A to point B, and, of increasing importance, access vital means of communication and information online.

However, dwindling supply is particularly problematic because as a resource becomes scarcer, its price also increases due to constant demand for decreasing supply. Higher prices for resources that are geographically unequal in distribution poses a risk for stability, as thus the control and extraction is significantly profitable because of their centrality to virtually every facet of economic function, and consequently, “global trade in these high-value commodities creates conditions that increase the likelihood of conflict” (Messer 2004). Another key result of higher prices is a direct relationship with higher food prices as the world observed in 2008, which hit hundreds of millions of people around the world who are already struggling to live on less than a dollar a day and plunged a further 115 million into poverty (Rubin 2012, Livingstone 2012).

Of equally grave consequence and arguably of greater urgency is the environmental damage that oil consumption causes. More specifically, carbon-based fuels and their subsequent emissions contribute to the mounting problem of climate change, which would threaten the way of life for everyone on the planet, rich or poor (Klein 2014). Thus, the necessity for a clean and alternative source of energy arises not just from a shrinking supply but also from what havoc the remaining quantity of oil can wreak on our planet.

Space-based solar power satellites are an unorthodox proposal for the problem of limited carbon-based fuels, but it is nonetheless as competitive as, if not more, its mainstream alternatives. Its biggest comparative advantage over land-based solar or wind power is the exposure to the energy source, in this case the Sun. While land-based solar power is highly dependent on it being daytime with clear skies and wind power is innumerably variable and rather weather-fickle, space-based solar power has near-constant exposure to the Sun, and the only exception to that is during “twice-yearly equinox periods, with eclipses less than 70 minutes per day” (Space Enterprise Council 2008). The reasons such eclipses are necessary lies in an inherent aspect of the satellite – in order for transmission of energy back to the Earth to be consistent, wired or wireless, the satellites must have a geosynchronous orbit, which means that such an object would appear stationary to ground observers, i.e. the satellite would rotate above a single point on and around the Earth. For a wired system, a geosynchronous orbit is necessary so that any cables do not wrap around the earth due to either a slower- or faster-than-Earth orbit. For a wireless proposal, such an orbit is still important because otherwise there is an inconsistent ability to connect and transmit waves from point A to point B, as point B, the position on the ground underneath the satellite (point A) is constantly shifting depending on where the satellite is.

Another corollary benefit of space-based solar power is that the physical infrastructure is out of the way of communities and ecosystems. Instead of looming turbines or fields of solar panels, satellites pose no risk of interference with humans, plants, or animals. While largely insignificant, this problem is brought up by some who oppose alternative energy, so accounting for it could build a larger base of support because of its fewer side harms.

A different space-based proposal is the Dyson sphere, which involves surrounding a star and directly collecting its energy – for example, a Dyson sphere could be “a star enclosed in a shroud of solar-cell calculator chips” (Carrigan 2009). Because such an idea is currently being discussed a means to search for and identify the presence of extraterrestrial intelligence, it is an technological accomplishment beyond what humans are currently capable of and thus should not be considered a viable status quo consideration for alternative energy despite its magnitude of benefits.

The crux of space-based solar power is the transmission of energy from the satellite itself back to Earth – the other aspects of the process, including collection and storage, involve already-developed and known technology. Transmission could potentially be accomplished in two ways – wired or wireless. With each, there are some practical limitations; however, space-based solar power could draw a lot of inspiration from a couple of other sci-fi ideas – the space elevator and the intergrid. These correspond respectively with the wired and wireless proposals for how to implement space-based solar power.

Inhibiting Factors - Wired

To explore reasons why a wired approach potentially would not work, it would be best to first understand why it could potentially work. While infeasible at first glance because of gravity, a wire used to transmit energy downward can be compared to a cable required for what is known as a ‘space elevator,’ which could imaginatively look like an enormous beanstalk. Instead of collapsing, “the cable … [would be] long enough that the spinning of the Earth would sling it outward” in a manner that would be similar to centripetal/”centrifugal” force (Edwards 2000).

While it is physically therefore possible to keep such a cable taut, there are a number of other requirements in order for it to remain taut. The main issue pertains to the material of the cable, which has to have enough tensile strength in order to support its own weight, i.e. it must be very strong for its density. Unfortunately as Keith Henson, co-founder of the National Space Society explains, “No current material exists with sufficiently high tensile strength and sufficiently low density … not even carbon nanotubes” (Dvorsky 2013). Thus, pending further technological advancements, such a requisite material has yet to exist for a stable and successful wire to extend from outer space down to the Earth.

A second issue for any space elevator-esque structure is one of stability. No matter the strength of the material, the cable itself is incredibly fragile because it is inherently very thin and long – any thicker than necessary and it is merely extraneous weight. However, “lunisolar perturbations and other minor forces may affect the stability in the initial phase and will cause oscillations in the operational phase” (Perek 2008). In essence, unpredictable and relatively violent movements caused by gravitational pulls or pressure could move the satellite into relative danger, risking collision with debris or other satellites.

Wireless transmission of energy seems equally implausible at first, but technological leaps and bounds have been made in recent years that render it feasible and possible in the (relatively) near future. For example, in 2008 physicist John Mankins, formerly of NASA, was able to beam energy from a mountain in Maui to the main island of Hawaii 92 miles away. While the actual amount of energy transmitted was meager and most lost in transit, “the system was limited by the budget not the physics” and “could do much better– possibly up to 64% efficiency” (Whitesides 2008). Indeed, as Jeremy Rifkin describes in his book, The Third Industrial Revolution, the capacity for the world to establish an ‘intergrid’ whereby individuals produce their own energy and can transfer surpluses to one another is largely based on existing telecommunications infrastructure spawned by the advent of the Internet (2011). Indeed, the concept of energy transmissions has become increasingly realistic and possible.

Similarly for wired transmission, wireless energy transfer faces its own hurdles. The first of which regards the frequency of the waves being beamed back. This is simply a political barrier and not one that is physically insurmountable, as frequency regulation is an important facet of space-based solar power that would need to go through the International Telecommunication Union Radiocommunication Sector (ITU-R) (Matsumoto 2009). Similarly, Matsumoto details that international cooperation is vital, regardless of transmission means, because space-based energy inevitably will be commercialized.

A second concern for wireless transmission is one of radiation. Of all the problems listed for the two respective means of distribution, this one should receive the least attention, as the maximum intensity outside of its center is less than 1 mW/cm², whereas the standard exposure thirty years ago in the United States was 10 mW/cm² (Hanley 1980). Simply put, concerns for health are a non-issue, particularly considering that the technology used to transmit energy is by-and-large the same technology we use on a day-to-day basis for telecommunications.

Overall, the problems facing space-based power are ones of technological advancement, not of physical incapability, which means that this is a field worth studying and investing in as society progresses. However, a major concern with space-based objects is the degradation of the physical infrastructure. Specifically, “energetic particles from the sun and cosmic rays from elsewhere in space, produce physical damage to silicon-based solar cells – the most common and lowest-cost technology used for satellite power generation” (Odenwald 2000). Quantitatively, satellites have a lifespan of 10-15 years which can vary based on random-chance solar flares and proton storms (Odenwald). Similarly, space debris can not only affect a cable, as discussed earlier, and steer it toward collision but can also be the collision itself, damaging expensive solar panels or satellite technology. This is a problem not with the transmission but with the collection process, but again, this is a problem that can be addressed as the technology comes around and is not grounds for discouragement or surrender.

Another issue with satellite construction is that the requisite materials, many of which are rare-earth metals, would require damaging extraction during the construction phase. Even so, such an argument does not seem compelling enough to warrant looking in another direction for alternative energies, as land-based solar and wind power generators, panels and turbines respectively, also use rare-earth metals. Additionally, maintenance and upkeep of satellites would require costly expeditions into outer space and onto the satellite itself for repairs. All in all, while there may be limited environmental and economic damage to construct the satellites and maintain them, the cost-savings from establishing an infinite source of energy is far more valuable.

Conclusion

The desire for a clean alternative to modern-day carbon-based fuels like oil and natural gas is only as strong as these alternatives are cheap. While present-day prospects for space-based solar power seem unlikely, there are no permanently insurmountable barriers to the principle idea; instead, with technological advancements, what once seemed like a science-fiction figment of the imagination can one day become a reality. Not only would a project generate enough energy for the world multiple times over but such a project would also help sustain the planet’s health for centuries to come.

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Ellen Messer, “Breaking the Links Between Conflict and Hunger in Africa,” International Food Policy Research Institute, 2004, Web. http://www.ifpri.org/publication/breaking-links-between-conflict-and-hunger-africa

George Dvorsky, “Why we’ll probably never build a space elevator,” io9, 2013, Web. http://io9.gizmodo.com/5984371/why-well-probably-never-build-a-space-elevator

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Jeff Rubin, “The Big Flatline,” 2012, Print.

Jeremy Rifkin, “The Third Industrial Revolution,” 2011, Print.

Loretta Hidalgo Whitesides, “Researchers Beam ‘Space’ Solar Power in Hawaii,” Wired, 2008, Web. http://www.wired.com/2008/09/visionary-beams/

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