Dyson Dots: Changing the solar constant to a variable with photovoltaic lightsails

Abstract

No study of coping with climate change is complete without considering geoengineering. Leveraging Tsiolkovsky's and Tsander's 1920s idea to use mirrors for space propulsion, Fuller's 1940s Dymaxion Grid, Glaser's 1970s study of solar power satellites, and Forward's 1970–90s concepts of “statites” and “Starwisps”, we propose placing one or more large (Σarea=700 K km²) lightsail(s) in a radiation-levitated non-Keplerian orbit(s) just sunward of the Sun–Earth Lagrange-1 point. The purpose of this syncretic concept is twofold: (I) As a parasol, it would reduce insolation on Earth by at least one-quarter of a percent, same as that which caused 1.8 °C drop during the “Little Ice Age” (∼1550–1850), and same as the IPCC Third Report's mid-range value for global warming by 2050. Lowering temperature will reduce the atmosphere's water vapor content, which should reverse the increasing frequency and severity of storms, likewise reducing the damage accompanying climate change. It transforms the “solar constant” to a controlled solar variable. The sail would utilize the very photons it diverts from us to maintain its position without expensive fuel. (II) As a ∼100+ K km² photovoltaic power station, the parasol could displace over 300 EJ/a (∼100 trillion kWh/yr) of fossil-fired electricity for its creators, roughly the entire global demand forecast by 2050, in turn displacing most carbon burners from the terrestrial grid, providing US$trillions in revenue from clean energy sales to amortize the scheme. This approach to geoengineering is not precluded by international treaty, but it is not a panacea either because it does not fix the other consequences of exponentially growing combustion of fossil fuels. However, it would buy time because it is self-funding (“pay-as-you-go”); furthermore it is linear, scalable, minimally intrusive, and above all, reversible. If Tellurian spacefaring civilization bootstraps its exponential growth with lightsails, there might eventually be enough of them to have a detectable effect on Sol's apparent luminosity as seen from far away, similar to the eponymous Dyson Sphere. So we tagged our concept with the moniker “Dyson Dot”.

Introduction

Water means life, and we live on a water world. Ultimately, climate change is about water also: too much water where it is not supposed to be or when; not enough water where or when it is supposed to be; plus drying soils, changing habitats and ocean currents, and rising sea levels over the next century. Warm air holds much more water than cool air, and when it is released, weather events tend to be much more violent and concentrated toward the extreme ends of the probability distribution. Agricultural practices and our few staple crops (not to mention the wider ecosystem) are adapted to long term averages with predictable error bars. But as the old saying goes, climate is the weather one expects, while weather is the precipitation one gets, therefore climate change means getting the unexpected. Since the IPCC's Fourth Report in 2007, it has become clear that a certain amount of global warming is already “dialed in” [1]. Therefore, coping with climate change means managing the unavoidable, while avoiding the unmanageable [2].

There are three elements to global warming: The first, which most people think of, is greenhouse gases (GHG) in the atmosphere, e.g., water vapor (H₂O), carbon dioxide (CO₂), methane (CH₄), plus other minor ones. The second element is heat and light continuously coming in from the Sun, also known as “the radiative forcing function”. The third is how much incoming energy is immediately reflected, or albedo. Dark surfaces (e.g., water) absorb energy; light ones (e.g., ice) reflect it. Sunlight directly warms our planet because our atmosphere is transparent to the predominant wavelengths of solar radiation: visible light. But GHGs in our air partly block the IR re-radiating from the warmed surface, trapping some heat. This greenhouse effect keeps the overall planet warm (even at night) making it possible for life to exist. Without a blanket of GHGs, plus lots of that truly amazing substance, liquid water, to moderate temperature extremes, Earth would be a cold, inhospitable place.

Humanity's efforts are currently focused (unsuccessfully) on reducing the GHGs (principally CO₂) being emitted to the atmosphere, mainly via (ineffective) top-down attempts to limit the consumption of carbonaceous fossil fuels. Conservation, recycling, more efficiency, altered lifestyles, and new low-carbon sources of energy are all needed to reduce our GHG emissions. But so far, all that these tactics have achieved is reducing the rate of emission growth, and not even that in most places. Absolute consumption of fuel, and concomitant emissions and concentration [CO₂] in the atmosphere, continues to rise dramatically. To avoid the worst effects of climate change, humanity needs to do more than merely reduce growth; we must bring down the absolute amount of these gases in the atmosphere to levels below those of the last century. However, with more people (numbers, N) entering the global middle class (affluence, A) with commensurate use of more energy per capita yet nearly flat energy intensity (I) in the developing world, it does not seem we will be able to reduce the footprint of the gross energy product, E=N×A×I, and stop global warming. We certainly will not be able to conserve our way to pre-20th-century GHG concentrations—not without falling back to pre-20th-century living standards at any rate. Who would willingly accept that? Who would enforce it?

Traditional risk analysis fails in such situations because Black Swans [3] are more common than people living comfortable lives in the developed world realize, while traditional economic analysis fails because typical discount rates diminish the present value of a benefit beyond a generation in the future to virtually nothing, and because survival considerations trump the ordinary calculus of decision-making. (Hence the aphorism, “National security has no price.”) If we cannot eliminate the causes of climate change, then is there anything we can do to mitigate it? What if existing and expected cash flows were harnessed to meet this challenge? What if the answer to the problem directly and organically paid for itself in near-real time? What if we could reduce the overall amount of sunlight hitting Earth so that global atmospheric temperatures and weather patterns can return to what we consider normal? What if we were to build a large sunshade in space allowing Earth to cool off, thus buying time to do the really hard thing: changing our behavior and attitudes?