Value chain · CLM-1454
In plain terms
The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which one theory says the beam might start to focus itself in the upper atmosphere (42 times uses a 2008 estimate, 19 times uses measured conditions), and 23 times lower than the 230 that a 2019 CASSIOPeiA paper gives as a typical peak. Those atmospheric figures are estimates, not hard limits. 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 over the beam's footprint; it gives no figure for the beam's strength at that edge, and a diagram in it shows the receiving site taking 245 watts per square metre.
The claim as recorded
ICNIRP's 2020 general-public whole-body reference level of 10 W/m2 (identical to IEEE C95.1-2019 above 30 MHz, as ITU-T K.52 reports) is, by our arithmetic, 18.9 times below 189 W/m2, the median 5.8 GHz thermal self-focusing threshold when one Perkins-and-Goldman-derived relation is evaluated over measured mid-latitude ionospheric conditions, 42.5 times below 425 W/m2, the value the same relation gives at a single nominal condition (Usui 2008), and 23 times below the 230 W/m2 "typical" peak beam intensity stated in the 2019 CASSIOPeiA paper; neither threshold value is a hard limit. Report ITU-R SM.2392-2 (06/2026), in a section that takes CASSIOPeiA as its reference architecture, states that the maximum power density can be limited by design so that the intensity at the edge of the receiver is less than the regulation limit for public exposure, that a nationally managed physical safety and security zone would be required at the receiving rectenna, and that the rectenna's area, the beam footprint, coincides with the safety exclusion zone; it gives no intensity figure for the edge and no compliance calculation, and its Figure 40, a Frazer-Nash graphic of the CASSIOPeiA reference system, shows the rectenna receiving 245 W/m2.
Evidence behind this: T3, the weakest of its sources: the ICNIRP guidelines, the ITU recommendation and the ITU report are T1 (SRC-137, SRC-138, SRC-672; the report's SBSP section reports contributors' material and is not a regulatory decision); the CASSIOPeiA paper is T2 (SRC-026); the 1978 NASA contractor study in the limits is T3 (SRC-108). The two thresholds come from a modelled relation (CLM-0500, T2), and the ratios are our arithmetic.
Scope and limits
The 189 and 425 W/m2 figures are one relation evaluated at two input sets, a median over measured conditions and a point value, so they are not a range of independent estimates; and the 1978 NASA study states "It is not possible to determine a threshold power in the usual sense for thermal self-focusing because the threshold power depends on the striation width" (SRC-108 PDF p23, printed 3-10). The ITU report's statement is a design approach carried from contributors' material: it is not a regulatory decision and not a compliance demonstration, and the paragraph itself does not name CASSIOPeiA; it describes features common to the architectures the 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 IEEE equivalence is reported by ITU-T K.52; the IEEE standard itself has not been obtained.
What it assumes
The reference level, not the more permissive underlying basic restriction (0.08 W/kg SAR), is the comparator used here; ICNIRP allows basic-restriction compliance as an alternative route: reference levels "provide a means of demonstrating compliance" and "in most exposure scenarios the reference levels will be more conservative than the corresponding basic restrictions" (SRC-137 PDF p13, printed p494); the 0.08 W/kg restriction is at PDF p11 (printed p492).
Where it comes from
PDF p14 (printed p495), Table 5, "Reference levels for exposure, averaged over 30 min and the whole body", gives an incident power density of 10 W/m2 for the general public in the row for above 2 to 300 GHz, which covers 2.45 and 5.8 GHz. SRC-138 PDF p30 (printed p24): "[b-ICNIRP] and [b-IEEE C95.1] limits are largely harmonized, and the power-density limits for whole-body exposure to continuous fields are identical above 30 MHz", where [b-IEEE C95.1] is the 2019 edition (PDF p43). SRC-026 PDF p7 gives a safe peak beam intensity below 1 kW/m2, with 230 W/m2 typical. SRC-672 PDF p35 (printed 33), under the heading 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 "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" and says it highlights commonalities between the architectures shown. SRC-672 PDF p34 (printed 32), Figure 40, an image with no text layer, read at the render: the CASSIOPeiA ground station is a rectenna about 5 km across receiving 245 W/m2 of high frequency radio wave power and generating 2 GW into the grid; the graphic is credited to Frazer-Nash Consultancy. PDF p32 to 37 give no intensity figure for the edge of the receiver. The 189 and 425 W/m2 figures are taken from CLM-0500.
Basis: W/m2, general-public whole-body reference level vs self-focusing threshold range and a stated peak beam intensity
Related records
- Answers question
- QST-001 not published in this release
- Supersedes
- CLM-0502 not published in this release
Cite this
energyaperture.com/c/clm-1454
CLM-1454, Energy Aperture, as of 2026-06 (SRC-672); 2020-05 (SRC-137).
Connected records
Other published records linked to this one. A list, not a judgement.
- 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-108
- CLM-0043The study the 1978 reference system cites put the level where the beam may start to disturb the ionosphere at about 20 milliwatts per...CLM-0045The apparent conflict between 12 and 23 was not an error. The underlying study gave a range, and the figure adopted sits near the top of it.CLM-0066The figure adopted in 1978 was higher than each of the lower figures in the studies it cited, though those figures were themselves...CLM-0072The 1978 study gives 12 milliwatts per square centimetre for runaway, give or take a factor of two, and says no threshold can be set in the...CLM-0082The formula is the right one for the conditions space solar power would create. It was written for this case, not borrowed from a different...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-0085The 1978 formula does not give a threshold. It relates threshold power to the width of the plasma structures produced, so getting a single...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-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-1467 (low confidence)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...
- 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-1467 (low confidence)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...
- 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-1467 (low confidence)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...