NASA Report Sparks Debate over Cost Effectiveness of Space-Based Solar Power

NASA has released a report on space-based solar power that acknowledges its viability, but questions its cost-effectiveness. 

While NASA grants that the technology could be used as a renewable source of energy by 2050, they raised concerns as to its potential cost vis-a-vis terrestrial generation, which sparked responses focused on whether NASA’s cost assumptions were accurate or overly pessimistic.

Space Based Solar Power

SBSP is a technology that, as the name implies, generates solar power in space. In short, large satellites consisting of immense arrays of solar panels are manufactured (or assembled) in geosynchronous orbit, generating solar power in much the same fashion as terrestrial solar generation. The power is then converted into low-power microwaves, which are beamed to ground-based “rectennas,” a kind of antenna that turns electromagnetic energy into DC power, which is then AC power and transmitted to wherever it’s needed. 

In theory, this could be a tremendously efficient form of energy generation. While some power may be lost through the microwave transmission, the fact that space-based arrays don’t have to deal with weather, climate, or time-of-day considerations means that they could generate potentially enormous amounts of renewable power compared to many forms of terrestrial power generation, and produce it much more consistently than most terrestrial renewables. And since it’s low-power microwave energy, the threat to both humans and wildlife would be minimal. 

While theories and speculation on SBSP have existed for decades, the prohibitive cost of sending these gigantic arrays into orbit left most observers believing it simply wasn’t feasible. As the cost of launch has dropped rapidly in the last decade, however, SBSP is being revived as a potentially serious plan for power generation. The European Space Agency (ESA) has SOLARIS, for example, an initiative which will “prepare the ground” for a decision in 2025 on whether to pursue a full SBSP development program, and Caltech conducted successful research last year on wireless power transmission in space. 

With that in mind, NASA undertook to study the issue, and released their report on SBSP in January of this year. 

NASA’s perspective on SBSP cost drivers

NASA took a look at the issue by examining two leading proposals for SBSP: the Innovative Heliostat Swarm and a Mature Planar Array. The Innovative Heliostat Swarm is based on John C. Mankins’ SPS-ALPHA proposal, which describes  “a large number of modules will be assembled to form a single enormous satellite” that turns solar energy into microwaves. Meanwhile, the Mature Planar Array is a more traditional design, using flat panels that, NASA’s report said, has “flat panels, with solar cells facing away from the Earth and radiofrequency (RF) emitters facing toward the Earth.” 

NASA called the Heliostat swarm Representative Design One (RD1) and the Planar Array Representative Design Two (RD2).

They found that both approaches were plausible, assuming anticipated technological development over the coming decades. RD2 generates power 60% of the year, owing to “its limited ability to reposition itself,” while RD1’s swarmed design means that it can generate power 99% of the year. Owing to these factors, as well as the general design, NASA found that the RD1 could generate five times the power as the RD2 design. Nevertheless, both were seen as viable approaches, and RD2 was more achievable using current technology. 

The issue is mass. NASA noted that RD1 would involve 5.9 million kilograms of mass per satellite swarm, while the RD2 approach would require 10 million kilograms of mass to create the same amount of generating power. That is a daunting amount of mass to lift to orbit, but especially when considering that it needs to be taken all the way out to geosynchronous orbit. Even when it’s in orbit, a SBSP satellite will still need development, assembly, operation, maintenance and eventual decommissioning, which will all take resources, but NASA made it clear that the cost of hauling all that mass into GEO is the main factor. 

Notably, fuel is a major concern for cost estimates of geosynchronous SBSP. NASA estimated that, assuming reusable SpaceX Starship vehicles are used, 12 out of every 13 launches will be carrying nothing but fuel for other vehicles to bring the satellites from LEO to GEO. That would mean that 2,321 launches will be needed in total for RD1 and 3,960 for RD2. There is anticipated to be a Starship variant that can go straight to GEO, but as those vehicles won’t be reusable, it will create a heavy manufacturing burden on SpaceX and, in turn, a potentially higher price. 

12 to 80 times more expensive”

With all this in mind, NASA’s price assessment for SBSP is that—assuming the satellites generated power in GEO from 2050-2080—the overall cost for RD1 would be $0.61 per kilowatt/hour, and the cost for RD2 would be $1.59 per kilowatt/hour. 

This is exorbitantly expensive compared to terrestrial generation, even renewable generation; “12 to 80 times more expensive than if you were going to have renewable energy on the ground” said Erica Rodgers, science and technology partnership forum lead in NASA’s Office of the Chief Technologist, in a presentation at the AIAA SciTech Forum conference. While terrestrial renewables may not generate as much power, nor generate it as consistently, they generate it far more cheaply, at around $0.02 to $0.05 per kilowatt/hour. They also arguably generate far less of a carbon footprint than thousands of Starship launches would, which is a factor that NASA took into consideration.

That said, NASA did identify some factors that could affect this seemingly-enormous price difference. As the fuel requirements for lifting the satellites to GEO would be so onerous, NASA said that electric propulsion (like ion engines) could be used instead to bring the cost and carbon emissions down to 0.20 $/KWh for RD1 and 0.50 $/KWh for RD2. A great improvement, but not enough alone to make SBSP competitive.  

NASA said that a combination of various factors would need to change: not just electric propulsion in orbit, but cheaper terrestrial launch, less expensive manufacturing costs, solar cell efficiency, and hardware longevity among others. If every possible cost input were improved, however, NASA did estimate that a “favorable combination” could reduce the cost and carbon footprint enough to make it potentially competitive, at 0.03 $/KWh for RD1 and 0.08 $/KWh for RD2, with carbon emission intensity lower than nuclear and some types of wind. 

The report refrained from recommending that SBSP should be a technological focus for the agency. Instead, their conclusion was that NASA “could maintain its focus on core Agency missions and technologies, while documenting their relevance to SBSP,” while keeping an eye on global SBSP developments to see if that more cost-effective model was becoming more likely. It also suggested that NASA could focus on pursuing partnerships that both align with their existing missions and goals and with the ultimate goal of making SBSP more viable. 

Responses from SBSP advocates question NASA assumptions

NASA’s perspective provoked several responses from SBSP advocates, with several questioning their assumptions. 

One opinion piece in SpaceNews, by former NASA deputy chief technologist David Steitz, argued that the important part of the report wasn’t the estimations of the cost-effectiveness of SBSP. Instead, Steitz said that the most important finding was that “there appear to be no clear technical showstoppers for an in-space solar power demonstration mission.” The piece grants that development of SBSP “will require a lot of work to get from today’s concepts to tomorrow’s demonstration mission,” the spin-offs from the technological development could lead to “remendous returns for domestic industrial advancement, space sector expansion and abundant clean energy.” 

The piece also noted that governments around the world are pursuing SBSP; not just in Europe, but in Japan and China as well. Steitz said “make no mistake: whichever nation develops this technology first will hold the high ground in future energy supply systems.” 

The creator of the Innovative Heliostat Swarm, John Mankins, said in an interview with SpaceNews that the report “seems to be driven by a wide variety of assumptions that are [a combination of]…the worst possible cases from years ago.”  He said that their assumption that launch costs would be $1,000 per kilogram, plus a 15% block buy discount, was “pessimistic” considering the work being done by SpaceX and other launch companies to reduce launch costs. He thought this was especially pessimistic considering NASA was assuming that the launches would be happening in the 2040s.

Mankins said “if it were really true that everybody believed that there was never going to be any improvement in launch beyond the Falcon 9 reusable, I don’t think Blue Origin would be wasting their time working on New Glenn.” He expressed concerns that the report’s tone might discourage other countries from pursuing SBSP, even if its assumptions turn out to be overly negative, and brought up the growing viability of electric propulsion for orbital transfers from LEO to GEO.

The National Space Society, associated with Mankins, also criticized the report, saying that it “leaves critical gaps in technology and economic assessments.” The Society said that the report “offers an incomplete assessment of the viability of space-based solar power as a solution to the world’s rapidly expanding energy needs.” In particular, it pointed to Starship, noting that if Starship reaches “even a fraction of its projected capability,” it will dramatically reduce launch costs to GEO. 

The Society also criticized the report for assuming a ten-year lifespan for the orbital power satellites, when Mankins’ own analysis suggested a much longer 30-year lifespan.