Value chain · CLM-1467
Low confidence
The evidence behind this statement is thin, indirect or second-hand. Read it as a lead to check, not as a settled finding.
In plain terms
Keeping people out of the area where the beam is strong is a plausible way for a strong beam to meet the 2020 international limit for public exposure, and international exposure guidance accepts limiting access as a way to comply. Other designs have worked this out: a 2013 Japanese review plans a no-entry area 3.5 kilometres across, and a 2007 international study sizes a 4-kilometre receiver this way. A 1977 US study set aside 204 square kilometres for one receiving site, without saying in its cost table what fixed that size, and costed buying and preparing that land. A 2026 international radio report that takes CASSIOPeiA as its example says the beam can be designed to fall below the public limit at the edge of the receiving site, with a safety zone matching the beam's footprint, about 3.5 to 6.5 by 7 to 13 kilometres in the UK. A diagram in it shows the receiving site taking 245 watts per square metre, but the report gives no figure for the beam's strength at the edge and no cost for the zone. A 2021 UK cost model for a CASSIOPeiA design includes the land for the receiving site but names no safety zone.
The claim as recorded
A beam-centre intensity in the 230-425 W/m2 range could in principle be reconciled with the 10 W/m2 general-public reference level of the 2020 ICNIRP guidelines via a controlled-access exclusion zone sized so that public exposure at the boundary falls below the reference level, following the general compliance route that ITU exposure guidance describes, in which exposure limits apply to locations accessible to people and compliance can be achieved by limiting access to areas where the limits are exceeded. The design is stated and sized for comparable concepts: a 2013 Japanese review plans a restricted area coincident with a 3.5 km-diameter beam for a 1 GW-class SPS with the outside kept well below 10 W/m2; the 2007 URSI White Paper derives a 4 km rectenna diameter from a 300 W/m2 centre and a 10 W/m2 edge. Boeing's 1977 system definition study for NASA gives a total controlled area of 204 km2 for one rectenna and costs its land acquisition and preparation as a line of the rectenna cost estimate, though the table does not say what sets the controlled area's boundary. Report ITU-R SM.2392-2 (06/2026), in a section that takes CASSIOPeiA as its reference architecture, states in general terms that the maximum power density can be limited by design so that the intensity at the edge of the receiver is below the regulation limit for public exposure, that a nationally managed physical safety and security zone would be required at the receiving rectenna, and that at UK latitudes the receiver is 3.5 to 6.5 km east-west by 7 to 13 km north-south, which is the beam footprint and coincides with the safety exclusion zone; its Figure 40, a Frazer-Nash graphic of the CASSIOPeiA reference system, shows the rectenna receiving 245 W/m2, and the report gives no intensity figure for the edge, no compliance calculation and no cost for the zone. The 2021 Frazer-Nash cost model for a CASSIOPeiA design costs the land for the rectenna site and names no controlled area.
Evidence behind this: T4, the weakest of its sources: the ITU and ICNIRP texts are T1 (SRC-138, SRC-137, SRC-672; the ITU report's SBSP section reports contributors' material and is not a regulatory decision); the URSI White Paper, the CASSIOPeiA paper and the 2013 review are T2 (SRC-100, SRC-026, SRC-127), as is the modelled 425 W/m2 (CLM-0500); the 1977 Boeing study for NASA is T3 (SRC-480); the 2021 Frazer-Nash study and its cost-model annex are T4 (SRC-021, SRC-018).
Scope and limits
This is a reasoned synthesis made here, not a finding replicated in any external source; it identifies a plausible path, not evidence that the path has been validated for CASSIOPeiA. The 425 W/m2 upper end is a modelled ionospheric self-focusing threshold (CLM-0500), not a stated design intensity. The ITU report's statement is a design approach carried from contributors' material: it is not a regulatory decision or a compliance demonstration, and the paragraph does not name CASSIOPeiA; it describes features common to the architectures its section covers. The 245 W/m2 in Figure 40 is in a graphic credited to Frazer-Nash Consultancy, which does not say where on the rectenna it applies. The 1977 controlled area belongs to a different and larger design, and its cost line is not carried forward here as a price. Neither the Frazer-Nash cost model nor the ITU report says that the land costed for the rectenna site is the safety exclusion zone.
What it assumes
A Gaussian or similarly peaked beam profile, as the URSI White Paper assumes for its sizing; CASSIOPeiA's own paper calls 230 W/m2 "typical" in one place and its "optimum peak" in another, so it does not establish the profile for CASSIOPeiA.
Where it comes from
Compliance route: SRC-138 PDF p13 (printed 7), "exposure limits are not emission limits; they apply to locations accessible to workers or members of the general public. Thus, it is possible to achieve compliance by limiting access to areas where the field limits are exceeded", and PDF p21 (printed 15), "An effective way to control exposure where other installations characteristics cannot be changed, is to restrict access to areas where the limits are exceeded." Reference level: SRC-137 PDF p14 (printed p495), Table 5, gives 10 W/m2 for the general public from above 2 to 300 GHz. Beam profile: SRC-100 PDF p31 (printed p11), the URSI White Paper's sizing, assumes "a Gaussian distribution of the power at the ground" with 300 W/m2 at the centre and 10 W/m2 at the edge, and its Table 2 gives a 4 km rectenna diameter. SRC-026 PDF p7: CASSIOPeiA's paper gives a "safe peak beam intensity" below 1 kW/m2 with 230 W/m2 "typical", but at PDF p8 it calls 230 W/m2 its "optimum peak beam intensity", so it does not itself establish a profile; the 425 W/m2 is taken from CLM-0500. SRC-127 PDF p5 (printed p1442), in paraphrase: for a typical 1 GW-class commercial SPS, 1 kW/m2 is expected at the centre of a beam 3.5 km across; the plan is to control the inside of the beam as a restricted area that people may not enter, and to keep the density outside it well below the regulatory value of 10 W/m2. SRC-480 PDF p179 (printed 169), Table 3.2.6-3, Rectenna Nominal Cost Estimate, in paraphrase: the total controlled area (land acquisition) is 204 km2, or 50,400 acres, and Land is a line of the estimate, priced per acre for acquisition and preparation. SRC-672 PDF p35 (printed 33), under Ground Energy Receiver: "The maximum power density can be limited by design, so that at the edge of the receiver the microwave intensity is less than the regulation limit for public exposure at this frequency." and "A nationally managed physical safety and security zone would be required at the location of the receiving rectenna."; at UK latitudes the receiver is 3.5 to 6.5 km E-W and 7 to 13 km N-S, and "This is the beam footprint which coincides with the safety exclusion zone." The section opening, SRC-672 PDF p33 (printed 31), describes the subsystems "with reference to the CASSIOPeiA architecture". SRC-672 PDF p34 (printed 32), Figure 40, an image read at a crop, in paraphrase: the CASSIOPeiA ground station is a rectenna about 5 km across receiving 245 W/m2 and generating 2 GW into the grid; the graphic is credited to Frazer-Nash Consultancy. SRC-672 PDF p32 to p37 give no intensity figure for the edge and no cost for the zone. SRC-021 PDF p3, in paraphrase: the study uses the CASSIOPeiA concept as its reference design and builds a cost model for a CASSIOPeiA design. SRC-018 PDF p16, section A.6.2, in paraphrase: the ground facility cost is the rectenna, the land for the site, the control facilities and the electrical balance of plant, and the land cost is a cost per unit area times the rectenna's elliptical area. Modal verbs preserved as each source sets them.
Basis: engineering-path synthesis, not a modelled or measured figure
Related records
- Answers question
- QST-001 not published in this release
- Supersedes
- CLM-0506 not published in this release
Cite this
energyaperture.com/c/clm-1467
CLM-1467, Energy Aperture, as of 2026-10.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-021
- CLM-0170A UK government-commissioned study estimates the cost of electricity from a mature (fifth-built) space solar power satellite at roughly 3.5...CLM-0171The same model shows the cost of electricity is noticeably higher for the first unit built than for the fifth, and when this study compares...CLM-0172The 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...CLM-0173Developing a working space solar power system for the UK is estimated to cost somewhere between about 7.5 and 16 billion pounds (in 2021...CLM-0174On the study's own numbers, a first space solar power system would not, by itself, earn investors the return they would expect (20%) - it...CLM-0175For every pound of public money put into the whole programme, the study estimates the UK economy gets back between GBP 1.30 and GBP 1.80...CLM-0522The 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...CLM-0538The US and UK studies are not just using different toughness levels for the same test -- they are answering different questions. The US...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-100
- CLM-0032In 2007 the international radio science union published a white paper saying that nobody had measured this heating effect from the ground...CLM-0047Heating falls with the square of frequency. In 2007 no ground-based measurement of it was available at gigahertz frequencies, and...CLM-0048An international scientific body reviewed the proposed figures, found them ranging from 230 to 1,000 watts per square metre, and chose 300...CLM-0049The stated design intent in a 2007 URSI white paper is that the beam would be shaped to fall to 10 watts per square metre by the edge of...CLM-0067According to a 2007 international report, Japanese designs of the time chose their beam strength on cost and land grounds; the report does...CLM-0079The 1978 paper modelled both a ground facility and a satellite case, and its 500 watts per square metre figure is a power flux for a given...CLM-0083The formula is the right type but nobody has said how far it can be pushed, and at space solar power frequencies the wave is about 200...CLM-0101The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3...More on the source page.
- Also from SRC-127
- CLM-0111An authoritative 2013 review says the 230 watt per square metre figure was chosen early in the design as a cautious maximum. It does not...CLM-0112The same review says modern work finds about 1 kilowatt per square metre acceptable at 5.8 gigahertz, more than four times the older...CLM-0113As of 2013 the experiment needed to check these predictions had still not been done.CLM-0128A 2013 review gives three references for the 1 kilowatt per square metre figure: two Japanese papers from 1995 and 1996, and a 1981 paper...CLM-0133A 2013 review paper says calculations suggest a stronger microwave beam than the usual safety limit would still be fine at a higher...
- Also from SRC-137
- CLM-1169Under the 2020 international guidelines, which keep the 1998 values, for a microwave beam at either SBSP frequency the public may be...CLM-1170In the 2020 international guidelines, besides the half-hour whole-body limit there is a six-minute limit on the hottest spot on the body...CLM-1171In the 2020 international guidelines, the lower public limit exists because the public includes children, the sick and the unaware, and...CLM-1454The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which...
- Also from SRC-138
- CLM-0120There is still no international radio allocation for beaming power from space, and the studies are not due until 2031.CLM-1454The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which...
- Also from SRC-672
- CLM-0054None of the seven ITU documents on wireless power transmission that were searched mentions what a power beam does to the ionosphere.CLM-1320The radio regulator's 2026 report on beamed power now has a section on power satellites, built around a UK design, and repeats that UK and...CLM-1454The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which...