Page 29 - PEN eBook October 2025

AEROSPACE

Delivering 5 GW to the grid would require a vast with advances likely to spill over into mainstream
orbital array. A representative concept might use a terrestrial photovoltaics.
solar collector spanning ~50–60 km , a transmitter
2
~1 km in diameter, and a ground rectenna about NASA’s vision for space-based
10 km wide. Billions of high-efficiency photovoltaic power beaming
cells would feed microwave generation units—such Unlike the ESA, NASA focuses on experimental
as solid-state power amplifiers, traveling-wave tubes, demonstrations, modular prototypes, and cutting-edge
or klystrons—with individual conversion efficiencies component development, involving energy transmission
exceeding 70%. between spacecraft.

At 5.8 GHz (λ ≈ 52 mm), achieving safe power After testing low-power transmission modules
density and low loss requires limiting beam designed to explore beam steering, transmission
divergence to ~100 µrad and maintaining pointing efficiency, and receiver optimization, including small
accuracy near 10 µrad. Such precision is beyond arrays of klystron-type microwave oscillators and
the routine capability of current spaceborne high-efficiency photovoltaic converters for laser
communications hardware. reception, NASA’s long-term aim is to make SBSP
scalable, flexible, and resilient—not only for civilian use
Among obstacles are high launch costs, but also for enhancing future missions where energy
large-scale robotic assembly in orbit, and addressing resupply is difficult. While it doesn’t yet have a timeline
environmental concerns, such as optical pollution for deploying gigawatt-level systems like the ESA’s
for astronomy, radio-frequency interference, and program, NASA’s work underpins much of the theoretical
potential biological effects of low-level microwave and technological foundation.
exposure. While SBSP remains technologically
demanding and capital-intensive, pilot-scale Caltech’s pioneering space solar power test
systems could appear in the 2030s, with large-scale In early 2023, Caltech deployed its Space Solar Power
commercial deployment possible in the 2040s. Demonstrator aboard a SpaceX Falcon 9 to evaluate
key technologies for orbital solar energy systems.
SPACE SOLAR POWER INITIATIVES The mission validated three subsystems: lightweight
Several nations (Japan, China, Korea, U.S., U.K.) are deployable structures, high-efficiency photovoltaic
actively researching SBSP systems, but three projects arrays, and MAPLE—an experimental microwave array
look well placed to advance technology in the next for WPT. MAPLE achieved two benchmarks: transmitting
years, run by the European Space Agency (ESA), energy from orbit to Earth and intra-spacecraft
NASA, and Caltech. transmission between rectennas. The ultimate goal
is the commercial deployment of a constellation of
ESA’s Solaris project modular spacecraft that can beam solar energy to Earth.
The ESA’s Solaris initiative is exploring the feasibility
of SBSP systems, targeting commercial deployment WHAT TO EXPECT NEXT
by around 2040. Concept studies envision WPT has evolved from theoretical concept to tested
kilometer-scale satellites in GEO, up to 2 km across technology, promising solutions for untapped energy
and weighing about 11,000 metric tons. These access. In orbital solar platforms, the physics of
massive platforms would be assembled from roughly electromagnetism converges with precision engineering
100 heavy-lift launches and designed to deliver to open new frontiers.
gigawatt-scale power, on par with nuclear plants.
As global demand for clean energy surges and space
A near-term milestone planned for the early 2030s infrastructure becomes increasingly accessible, WPT
is a ~1-MW orbital demonstrator that could scale up could emerge as a cornerstone technology of the
through automated modular expansion to gigawatt 21st century. Building and deploying a 1-MW orbital
capacity. plant—and eventually scaling to hundreds of
megawatts or more—will likely require an international
A key enabling technology is III–V multijunction consortium, comparable to Europe’s CERN in
photovoltaics (e.g., InGaP/GaAs/Ge or InGaAs-based). fundamental physics or ITER in nuclear fusion
By stacking layers with different bandgaps, each research. This time, however, the goal is not to discover
sub-cell captures a distinct part of the solar ephemeral particles but to fully harness the privilege
spectrum, boosting total conversion efficiency. of having a star at just the right distance from an
Efficiency is expected to rise from 30% today to inhabited planet.
40% within a decade when commercially deployed,

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