[ExI] Power satellites are being developed now

[John Clark]

On Fri, Dec 19, 2025 at 6:47 PM Adrian Tymes via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

* >> Over long distances it's much easier to transmit data than power, so
>> if space-based power transmission to earth is economically viable (is it?)
>> then it would make even more sense to have power satellites use their
>> energy to run data centers that are also in space. After all, these days
>> running data centers is the economic sector where energy usage is growing
>> the fastest, so why not build them where energy is the cheapest?*
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> * > Among other reasons: AI hardware calls for refresh (which requires
> getting there or launching replacements) far more frequently (1 GW is still
> 1 GW 5 years from now, but 2020's AI hardware doesn't compete nearly as
> much with today's) much more frequency, and latency (1 GW delivered in 1
> second, every second, is a constant 1 GW stream; an AI's answer from 1
> second ago may be too late).*
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*To be economically viable a data satellite would need one of two things: *

*1) A system, probably automated, that would provide maintenance and allow
for hardware upgrades to be made.*
*Or*
*2) The satellite is able to recoup the costs of construction and of
launch in just two or three years.   *

*As for latency, I don't think that would be a major problem because it
doesn't matter much if it takes 3 seconds for an AI to answer your question
instead of 2 seconds, although you wouldn't want to use it to operate a car
or a robot that's on the Earth. The lower the orbit orbit the cheaper the
launch costs, and the less latency you have, but you can't go too low for
various reasons, so I asked Claude the following question: *

*ME: What would the lowest orbit you could place a satellite if you wanted
to avoid space junk and also the intense radiation in the earth's two Van
Allen belts?*

*===*
CLAUDE: The sweet spot for avoiding both space debris and Van Allen belt
radiation would be an orbit around* 600-800 km altitude*.

Here's why:

Van Allen Belt Boundaries:

   - The inner Van Allen belt typically extends from about 1,000-6,000 km
   altitude  though it can dip as low as 200 km in certain areas like the
   South Atlantic Anomaly
   - The outer belt covers approximately 25,000-45,000 km altitude
   - There's a "slot region" of reduced radiation between the two belts

Space Debris Distribution:

   - Maximum debris concentrations occur at altitudes of 800-1,000 km and
   near 1,400 km
   - Over 70% of debris is distributed between 500 km and 1,000 km
   - Below 600 km, debris normally falls back to Earth within several years
    due to atmospheric drag, while at 800 km altitude, orbital decay takes
   centuries

The Optimal Zone: The 600-800 km range offers a compromise: you're high
enough to avoid the very low altitude debris that decays quickly, but low
enough to stay below the inner Van Allen belt's main concentration. You'd
also be just below the 800-1,000 km zone where both debris density and
radiation exposure increase significantly.

That said, there's no perfect answer—you're trading off between different
hazards at any altitude. Below 600 km gives you less radiation exposure but
higher atmospheric drag, while above 800 km increases both radiation and
debris risks.

*===*

*But then I realized I had forgotten to mention avoiding significant
atmospheric drag in my first question, so I needed to ask another question:*
*ME: At 800 km would atmospheric drag be a problem for something as large
as a power satellite?*
*===*

CLAUDE: Yes, atmospheric drag would be a *significant problem* for a power
satellite at 800 km, and here's why the scale matters:

*The Size Challenge:*

Power satellites are truly massive. Proposed designs have solar reflectors
spanning up to 3 km and weighing over 80,000 metric tons  One reference
design has a solar panel area of 11.5 km² and mass of 5.9 million kg . A
1.4 GW satellite design weighs 2,000 tonnes and measures 1.4 km in diameter.

*Why Size Makes Drag Worse:*

Atmospheric drag force is directly proportional to the cross-sectional
area. A power satellite with square kilometers of solar panels presents an
enormous surface area to atmospheric friction—thousands of times larger
than typical satellites. The drag equation shows that a larger area (A)
means proportionally more drag force for the same atmospheric density.

*The Numbers at 800 km:*

Research on small satellites at 800 km shows orbital decay rates ranging
from 13-23 meters per day during quiet solar conditions, increasing to
65-120 meters per day during solar storms. But those are for small
satellites with ballistic coefficients measured in the range of 2-3×10⁻³
m²/kg.

A power satellite would have a vastly worse ballistic coefficient due to
its enormous area-to-mass ratio (all those lightweight solar panels). This
means:

   - Much faster orbital decay
   - Continuous fuel expenditure for station-keeping
   - Accelerated decay during solar maximum when the atmosphere expands and
   density increases at orbital altitudes

*The Practical Solution:*

This is precisely why most power satellite designs target *geosynchronous
orbit (GEO) at ~36,000 km*, where atmospheric drag becomes negligible . At
GEO, you're well above both Van Allen belts and essentially all atmospheric
effects. The trade-off is the enormous distance for power transmission and
the colossal size needed for the microwave transmitter.
At 800 km, you'd be fighting a losing battle against atmospheric drag with
something that large.
===
*ME: Being in synchronous orbit is not as important in a data satellite as
it is in a power satellite, so could you go a bit lower than 36,000 km and
still avoid significant atmospheric drag and the van Allen radiation belts?*

CLAUDE: Yes, absolutely! For a data satellite where you don't need the
geosynchronous orbital period, you have some excellent options in *Medium
Earth Orbit (MEO)* that avoid both atmospheric drag and the worst of the
Van Allen radiation.

*The Sweet Spot: 8,000-20,000 km altitude*

This MEO range is often called the "safe zone" or "safe slot"  because it
sits in the gap between the two main Van Allen belts:

   - The inner belt extends from about 600-10,000 km
   - The outer belt spans approximately 10,000-40,000 km
   - Between them is a "slot region" where electron flux decreases
   substantially

*Real-World Examples:*

This MEO zone is already heavily used for exactly this reason:

   - *GPS satellites*: orbit at approximately 20,200 km with a 12-hour
   period
   - *O3b communications constellation*: operates at 8,000 km altitude  for
   low-latency data services
   - Other navigation systems like GLONASS (19,100 km), Galileo (23,222
   km), and BeiDou (21,528 km) all use similar MEO altitudes

*Why This Works:*

At these altitudes, atmospheric drag becomes negligible , and you only need
about six satellites for near-global coverage compared to thousands
required in LEO. The radiation environment is dramatically better than
either Van Allen belt, and satellites require radiation-hardened components
but face much less intense radiation than in the belts themselves .

So for your data satellite, something around 10,000-20,000 km would be
ideal—well above any atmospheric concerns and right in that safer slot
between the radiation belts.


*  John K Clark *
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