Value chain · CLM-1441
In plain terms
Documents give the size of the CASSIOPeiA satellite design as anything from 1 to 2 km across. For a full-size version delivering 2 gigawatts from geostationary orbit, the best supported figure is about 1.7 km, from a 2021 study for the UK government. A 2020 report gives 1.6 km and credits the designer's 2019 paper, but that paper gives 1.6 km only as a general minimum for any such antenna at one radio frequency, not as this design's size. None of these is a measured size: the satellite has not been built.
The claim as recorded
Held documents give different sizes for CASSIOPeiA, and they are not all the same quantity. Frazer-Nash's 2021 summary gives "1,700m diameter" for a 2,000-tonne satellite in "Geosynchronous Orbit - 35,786km", drawn on a scale bar as a "Concept for Solar Power Satellite to input 2GW power into the grid". Frazer-Nash's 2020 report gives, "For a 2GW system", "an antenna of 1.6km diameter (Cash, 2019)". Cash's 2019 paper does not give that size for CASSIOPeiA. Its 1.6 km is a general minimum for any transmitter in geosynchronous orbit whose ground spot matches its own size, "at-least 1.6 km in diameter (@ 10 GHz), independent of the actual transmitted power", and its 2 GW-class variant (2050 MW AC, 2010 t) is given by power and mass only. The 2018 patent gives "1km to 1.5km across" for a typical array "From GSO (36,000km)", with no power stated. Two later secondary documents give 2 km (CLM-0942). One of them, a 2026 paper on a test array, says "The ultimate goal of the CASSIOPeiA array is to transmit 2 GW of power from a geostationary orbit to Earth" with an aperture "approximately 2 km x 2 km", and for both it cites the UK government's 2021 publication of the Frazer-Nash study, whose summary gives 1,700m. For a 2 GW CASSIOPeiA in geostationary orbit, about 1.7 km is the best supported figure: it is the only figure that a held document gives first-hand for that power and orbit.
Evidence behind this: T4 by the weakest-source convention, from the two Frazer-Nash documents; the figure judged best supported is an infographic in the summary of a study commissioned by the UK government (BEIS), with no derivation on the page. The inventor's paper is T2 and his patent T3.
Scope and limits
All are design figures for an unbuilt satellite. The 1.7 km is an infographic figure with no derivation, in the summary of a commissioned study, and the drawing is marked approximate. The patent's "X,Y,Z dimension" is a three-axis extent and may not be the same quantity as an aperture diameter (CLM-0942). The two Frazer-Nash documents describe the 2 GW system differently: the 2020 report gives a "5km wide rectenna", the 2021 summary a 6.7 km by 13 km ellipse (CLM-0003). Cash's 1.6 km is stated for 10 GHz; the 2021 summary gives 2.45 GHz as an example frequency, and at a lower frequency diffraction needs a larger antenna for the same spot (the relation is in CLM-0889). Cash's 2 GW-class variant is for a geosynchronous Laplace-plane orbit, which the paper puts at an inclination of 7.7 to 8.7 degrees, not the equatorial geostationary orbit. The 1.7 km rests on one document, so conf is not HIGH.
What it assumes
That SRC-023's "1,700m diameter" is the width of the helical transmitter across its axis. The page 16 diagram draws "1700m" as an arrow across the helix, and the page 15 scale drawing, with the axis horizontal, puts the top of the satellite at the 1700m line. Neither page gives a length along the axis.
Where it comes from
PDF p.15, zoom 5 crop: "2,000 tonnes", "1,700m diameter", "Geosynchronous Orbit - 35,786km", "CASSIOPeiA Solar Power Satellite concept (International Electric)"; zoom 4 crop of the scale bar: "Scale (approx)", a dotted line marked "1700m" at the top of the CASSIOPeiA drawing, label "CASSIOPeiA Concept for Solar Power Satellite to input 2GW power into the grid". SRC-023 PDF p.16, zoom 5 crop: a diagram with the satellite's axis vertical and the reflectors above and below, and a double arrow marked "1700m" across the helix beside the label "2. Solar panels and transmitters". SRC-024 PDF p.16, section 3.2 on CASSIOPeiA: "For a 2GW system, the estimated mass is 2,000 tonnes with an antenna of 1.6km diameter (Cash, 2019) beaming to a 5km wide rectenna." SRC-026 PDF p.2 / printed 171, zoom 4 crop, in paraphrase: to focus a beam from geosynchronous orbit down to a spot the size of the transmitting antenna needs a transmitter at least 1.6 km in diameter at 10 GHz, whatever power is sent. PDF p.3 / printed 172, in paraphrase: a 2 GW (AC) variant should have a mass of only 2,000 tonnes. PDF p.8 / printed 177, Table 2 "GLP orbital variants", zoom 5 crop: columns System Insolation, Reflector Type, Power (MW AC), Mass (T); 4-sun, SSSC, 2050, 2010; no dimension column (as CLM-0507). A search of all nine pages of SRC-026 for "km", "kilometre", "diameter", "metres", "D =" and "H =" finds no diameter or height for any full-size variant. SRC-001 PDF p.2: "The ultimate goal of the CASSIOPeiA array is to transmit 2 GW of power from a geostationary orbit to Earth [3]. To ensure high efficiency, the antenna aperture is designed to be approximately 2 km x 2 km" (the page prints a multiplication sign); PDF p.10, reference [3]: UK Government, "Space-Based Solar Power - De-risking the Pathway to Net Zero", with a gov.uk publications address. SRC-088 PDF p.19: "From GSO (36,000km), typically the array may have an X,Y,Z dimension of 1km to 1.5km across - taking account of the fundamental diffraction limit and setting an ideal/safe 230W/m^2 ground peak intensity." (the text layer prints Greek capitals for X, Y, Z and "mA2" for m^2, as CLM-0942 records).
Basis: metres across the transmitting structure; 2 GW delivered to the grid from geostationary orbit
Cite this
energyaperture.com/c/clm-1441
CLM-1441, Energy Aperture, as of 2021-09.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-001
- CLM-0511The first real, built, and measured version of CASSIOPeiA's beam-steering hardware converts electricity to radio power at 42%, against...CLM-0512The small prototype achieved a beam strength close to what a real system would use, but only over an area the size of a small table, using...CLM-0516Public money funded a real piece of hardware that was built and tested, not just another report -- a rare outcome in this field -- even...CLM-0903The shared clock tells every sensor to take its reading at the same moment. How precise that clock must be depends on how fast the thing...CLM-0916The built prototype gives every single antenna its own steering circuit rather than sharing one between a group. The steering signal...CLM-0942Three documents held here give three different sizes for the same satellite's transmitting antenna. The patent says 1 to 1.5 km across and...
- Also from SRC-023
- CLM-0002The summary report says the beam is strongest at the middle of the receiving site, at about 240 watts per square metre, and argues that...CLM-0003The report gives the receiving site as an ellipse roughly 7 km by 13 km, and states a beam strength of 245 watts per square metre.CLM-0005A second figure of 29 watts per square metre appears in the same report, but it measures electricity produced per unit of land, not beam...CLM-0006None of the five main studies mentions the international radio-frequency exposure limits, or any safety standard, or a restricted area...CLM-1436A UK study says that one space solar power system would typically deliver about 2 gigawatts to the grid, and it compares this with the...CLM-1442A 2021 study for the UK government shows one design, CASSIOPeiA, as about 1.7 km across and 2,000 tonnes, sending 2 gigawatts to the grid...CLM-1443The 2021 study for the UK government says the leading designs need no new materials, but that building them at a sensible cost needs two...CLM-1444The 2021 study for the UK government concluded that space-based solar power is technically feasible, affordable at a competitive cost per...More on the source page.
- Also from SRC-024
- CLM-0001The UK government's own feasibility study describes a system beaming microwaves at about 230 watts per square metre onto the ground.CLM-0006None of the five main studies mentions the international radio-frequency exposure limits, or any safety standard, or a restricted area...CLM-0007The UK study's own experts expect the beam to interfere with electronics in its path, and think it unlikely to have much effect outside the...CLM-0235A 2020 UK study rated the UK behind other countries in many technologies for a solar power satellite. For three key ones, large mirrors...CLM-0714The 2021 UK study by Frazer-Nash Consultancy proposed that the satellite fly itself to its final orbit, using its own solar panels to run...CLM-1436A UK study says that one space solar power system would typically deliver about 2 gigawatts to the grid, and it compares this with the...CLM-1452By our rough arithmetic, the beam of the UK's full-size reference design would carry about a million times more power than the...CLM-1472The designer of the UK's CASSIOPeiA satellite says it has no moving parts and is built from many small identical pieces, so when pieces...More on the source page.
- Also from SRC-026
- CLM-0004The author of the 2019 CASSIOPeiA paper states the beam's strongest point is about 230 watts per square metre, and says that figure was...CLM-0006None of the five main studies mentions the international radio-frequency exposure limits, or any safety standard, or a restricted area...CLM-0013The paper that modern UK studies rely on for the beam figure calls anything below 1 kilowatt per square metre safe, with 230 watts per...CLM-0336Different design studies over four decades have each simply assumed a different working lifetime for a solar power satellite, from about 15...CLM-0339A 2019 paper said solar power satellites are often assumed to need visits in orbit for repairs and refuelling, but that no system yet...CLM-0441A normal geostationary satellite needs a small, regular fuel-based nudge every year to stay in place. One 2019 design proposes cutting most...CLM-0504None of the main CASSIOPeiA-related documents in the register mentions any named safety or exposure standard, or describes any restricted...CLM-0660The 2019 CASSIOPeiA paper does not discuss electric propulsion for getting the satellite to its orbit. It only prices delivery using...More on the source page.
- Also from SRC-088
- CLM-0896The patent describes measuring the incoming steering signal at scattered sensors, not at every antenna, and working out the values in...CLM-0897The satellite aims its beam by listening for a low-power signal sent up from the receiving station, measuring the shape of that arriving...CLM-0899The patent never says the steering signal is protected in any way. There is a difference between scrambling that signal so nobody can read...CLM-0900The satellite can point its beam far further than there is Earth to point at, so moving power from one receiving station to another is not...CLM-0903The shared clock tells every sensor to take its reading at the same moment. How precise that clock must be depends on how fast the thing...CLM-0905Sharing a clock is not the same as being told what to do. The clock and the carrier tell the antennas nothing about where to send the power...CLM-0913When the satellite corrects its own bending by listening to the ground signal, what is left over is not how far the antennas moved. It is...CLM-0942Three documents held here give three different sizes for the same satellite's transmitting antenna. The patent says 1 to 1.5 km across and...More on the source page.