The ITU has identified 5.8 GHz for space-based solar power. Every word of that
sentence traces to a real document, and the claim is false.
The document is ITU-R Report SM.2392, "Applications of wireless power transmission via
radio frequency beam". A new edition appeared in June 2026, superseding the 2021 text.
Its Section 5 addresses spectrum for RF-beam wireless power transfer and names 915 MHz,
2.45 GHz, 5.8 GHz and 24 GHz as the bands the field uses. Section 2.9 is titled "Space
based solar power via satellite". If you work on power beaming, this is a genuinely
useful document, and until it existed much of the frequency discussion in this field
cited nothing at all.
None of that makes it permission.
Reports describe. Recommendations bind.
The ITU-R publishes several kinds of text, and two of them are easy to confuse.
A Recommendation is a technical standard. Other instruments incorporate it by
reference. When a national regulator writes a licence condition that points at ITU-R
P.618, the propagation model in P.618 acquires legal force in that jurisdiction through
the pointer. Recommendations are what the phrase "the ITU says" usually means when
somebody says it and is right.
A Report is a description of a state of affairs. It surveys, it summarises, it
records what practitioners do. It recommends nothing and it binds nothing. SM.2392
behaves like one throughout. It observes that 2.45 GHz is more desirable than the higher
bands because propagation impairments are smaller, which is a statement about physics
rather than about spectrum.
One of these you can cite in a licence application. The other you can cite in a
literature review.
Why 5.8 GHz is the one that will catch people
Take the tempting inference at face value and follow it. The ITU has named 5.8 GHz among
the bands used for RF power transfer. Space-based solar power appears in the same
document. Therefore 5.8 GHz is a candidate for space-to-Earth power beaming.
The first two steps are accurate. The third does not follow, and the reason is in a
different document entirely.
5.8 GHz sits in an ISM band: industrial, scientific and medical, shared, unlicensed for
many uses, and busy. What matters for a satellite is not the ISM status
but the Radio Regulations, and specifically Article 21, which sets power flux-density
limits on what a space station may deliver to the Earth's surface in a given band. The
Radio Regulations carry no Article 21 space-to-Earth power flux-density row for 5.8 GHz.
There is no limit written for it because the Regulations do not contemplate a space
station transmitting at these power levels into that band at all.
So the honest statement is that **5.8 GHz is not regulatorily available for
space-to-Earth power beaming today.** The band is not restricted or subject to
coordination; there is no framework in which to ask the question at all. A Report naming
it as the band the field uses on the ground describes engineering practice. It is not an
allocation and not a change to Article 21, and a regulatory assumption built on it rests
on nothing.
That sentence is uncomfortable if you are raising money on a 5.8 GHz architecture. It is
considerably more uncomfortable to discover it at the point where a regulator asks.
The ISM problem cuts the other way too
There is a second reason to be careful with 5.8 GHz, and it is not regulatory at all.
The Radio Regulations designate certain bands for industrial, scientific and medical
applications, and the arrangement comes with a condition attached: radiocommunication
services operating in an ISM band must accept harmful interference from ISM equipment.
The band is shared on the understanding that nobody in it is protected.
For a microwave oven that is a reasonable bargain. For a power link it is a strange one.
A receiving site is being asked to accept interference from every other user of the band
while delivering a service somebody is paying for, and the whole commercial case for
beamed power rests on the delivery being predictable enough to contract against. Choosing
a band precisely because it is lightly regulated means choosing a band in which you have
no standing to complain.
That is not an argument against 5.8 GHz on physics. Propagation at 5.8 GHz is workable
and the hardware is mature, which is exactly why the field converged on it for ground
demonstrations. It is an argument that the band's convenience on a test range and its
suitability for a contracted service are different questions, and the second one has
barely been asked.
What we did with it
We file the documents we cite in a public registry, with a column recording how far we
actually go with each one. The categories are deliberately unflattering to ourselves:
whether a method is computed in our code, whether we parse data in that format, whether
we merely use the vocabulary accurately without executing anything.
SM.2392 went in as vocabulary. We cite it for its terms, which are the ITU's own
description of the application, and we execute nothing from it, because there is nothing
in it to execute. Our Article 21 caveat stayed exactly where it was, because nothing in
the new edition touched it.
That is the whole of what a Report can do to a system like ours. It improved the
citation behind a definition. It did not move a limit, enable a band, or alter a
constraint.
The narrower trap, for anyone flying low
There is a second inference in this document worth ruling out, and it is subtler than
the spectrum one.
Section 2.9 describes a geostationary system. Most published work on beamed power at
scale is geostationary, for the good reason that a satellite parked over one spot solves
the intermittency problem that a low orbit creates. Ground-footprint figures in that
literature follow from aperture and range, and at geostationary range the numbers are
large.
If you fly in low Earth orbit, your range is two orders of magnitude shorter. Should one
of the areas stated in a geostationary study happen to sit near a number in your own
model, that agreement is a coincidence of scale across a fundamentally different link.
It is not the ITU validating your case. Citing it as though it were is the kind of error
that survives internal review precisely because the citation is real and the number
matches.
Take a citation for what it covers, and no further.
What would change my mind
A Recommendation. If ITU-R published one governing RF power transfer from a space
station to the ground, or if a World Radiocommunication Conference agenda item opened
work on a space-to-Earth allocation for power beaming, the regulatory position in this
piece would change materially and I would say so here.
A power flux-density row in Article 21 covering these bands for this use would do it
too, and would be the single clearest signal available that the question has moved from
description to permission.
Short of that, a national regulator granting an experimental licence for a space-to-Earth
power beaming demonstration would not change the international position, but it would be
the first real evidence of how a regulator intends to reason about one — and that is
worth more than another survey.
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