SRC-019

Space Based Solar Power as a Contributor to Net Zero - Phase 2: Economic Feasibility - Annex B: Input Data Sources

Published claims resting on this source

• CLM-0172 The study uses a high assumed rate of return (20%) to work out the headline cost-per-unit-of-electricity figure, but uses a much lower official government rate (3.5%) when working out whether the whole programme is worth public money - these are not the same number and should not be confused.
• CLM-0176 The launch-cost range that drives most of this study's cost uncertainty is not based on any launch that has actually happened - for Starship, a rocket not yet in service, it assumes a launch costs about the same as a Falcon Heavy launch did in 2021 (100 million US dollars), and it also uses a British spaceplane concept (SABRE) that has never flown.
• CLM-0177 The cost model assumes the satellite gets cheaper to build the more of them are made, using a range that runs from the faster cost-learning of a 2010s space-industry estimate (Mankins) down to the slower cost-learning the study estimates for SpaceX's Starlink constellation; separately, it assumes the system generates power 100% of the time with zero downtime, which the study's own authors call optimistic.
• CLM-0531 Neither the UK nor the US figure for what it costs to get a kilogram of hardware into the power station's real orbit is based on an actual, completed transaction. Both are assumptions about future launches, and NASA says it makes no claim that its assumed launch price is reliable. For the same rocket and the same starting price per launch, the two figures differ mainly in how hardware is assumed to get from low orbit to its final orbit, and that is what changes the number of launches needed.
• CLM-0539 A UK consultancy, working for the European Space Agency and using the same design as its reference point, actually published a full weight breakdown -- something the original 2019 paper never did. It comes out lower than the headline claim, at about 0.70 kilowatts per kilogram rather than 1, even though it leaves out several categories of weight altogether. It also rates one of the satellite's power-conversion stages as barely more than an idea on paper, and its input notes say the lightest case for the radio equipment is an expert's judgement, not something anyone has measured or built.
• CLM-0522 The UK study used a 20% return requirement, based on what institutional investors are expected to want. The US study used 3%, on a one-line assumption of government funding, and did not test what a different rate would do.
• CLM-0714 The 2021 UK study by Frazer-Nash Consultancy proposed that the satellite fly itself to its final orbit, using its own solar panels to run its own electric thrusters. Chemical tugs would take the parts only partway, to about 5,900 km, just above the inner radiation belt, where the satellite would be built. The study said the plan needed further work and gave no figures for the self-powered trip.
• CLM-0715 The 2021 UK study assumed one extra fuel launch for every payload launch; NASA's 2024 study assumed twelve. The reason, which neither study states, is not that they disagree about the price of a rocket: the UK plan used chemical rockets only part of the way up, to about 5,900 km, and then switched to electric, while NASA's used chemical rockets all the way to the top. The two studies also assumed different amounts of cargo reach the top per launch.
• CLM-1430 Put in 2024 money, a reliable British grid built on wind, sun and stored hydrogen would cost about 61 to 107 pounds per megawatt-hour in 2050. Set against the top of that range, the UK government's space solar study comes in at about half, and NASA's study, rebuilt in 2024 money, at nearly nine times. The two sides are costed differently, so this is a rough guide, not a like-for-like price comparison.
• CLM-1450 (low confidence) SpaceX's price sheet lists a Falcon 9 launch at 74 million dollars, and 22,000 kilograms as the most it can carry to low orbit if the rocket is not recovered. Using those listed figures with the US study's own way of counting the extra launches needed to reach the power station's orbit gives a cost per kilogram about four times what the US study's own assumptions give, and the UK study's lowest input would need launches about ninety times cheaper than that listed figure. Both studies turn to electric propulsion for part of the climb, NASA only in the case where it finds a competitive cost, and this has not been shown at power-station scale.
• CLM-1453 A 2021 UK study estimated what it would cost to carry satellites to high orbit on two reusable launchers: 3,260 dollars a kilogram for SpaceX Starship and 1,340 pounds a kilogram for the British SABRE spaceplane. The study does not set the two side by side in one currency, but converted at any of the exchange rates it lists, the Starship figure is the higher. The cost range its model actually uses runs from 358 to 2,410 pounds a kilogram.
• CLM-1468 The basic idea, a solar power satellite climbing to its final orbit on electric engines run by solar panels it carries, with no separate fuel tanker, is real: it has flown on communications satellites, though not at the scale of a power station. A 2013 design does it with a separate, smaller set of panels. The stronger version, where the satellite's own main panels run the engines, has been proposed, for example by a 1977 US study, which found the panels used for the trip would be badly damaged on the way, and by a 2021 UK study for the last part of the climb only, after chemical stages carry the parts past the inner radiation belt. None of these designs has flown.
• CLM-1477 The UK government's 2021 cost study for a power satellite assumes that parts fail and wear over the satellite's life, costing it between nothing and a quarter of a per cent of its output each year.

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