Space solar has yet to be fully demonstrated at scale in
space but successful experiments have been conducted on Earth and wireless power
transfer from space to Earth has very recently been demonstrated. Space solar
has long been seen as technically feasible but economically unfeasible and
uncompetitive. With advances in solar technology, robotics, and “large, low
cost, reusable launch vehicles such as SpaceX’s Starship”, deploying the
tech can get cheaper. Like many technologies, with modularity in construction
and economies of scale the tech could get cheap enough in the future to be
competitive.
Space solar systems
require three main components: solar collectors in space, a way to transmit the
energy to Earth (microwaves), and a receiver deployed on Earth to receive the
microwaves. Solar panels work very well in space without clouds and other atmospheric
interference, without seasonal variations, and without night, which means 24-hour
availability. Solar panels power space missions to other planets, moons, and asteroids.
They also power the International Space Station. “Sandwich” modules with solar
collectors facing the sun, electronic in the center, and microwave transmitters
facing the earth are the emerging model. Individual cells the size of pizza
boxes is the most promising configuration.
There are several downsides to space solar that need to be mitigated. Some are: the cost per kg of transporting stuff to space, the technical difficulties of folding out large arrays that are folded in transport, the difficulties of maintenance and replacement of components, and efficiency limitations of amplifiers and photovoltaic cells. Another issue is the time required for demonstrating and deploying the technology. Realistically, it could be generations, or at least several decades before space solar begins deployment at scales that could make an impact.
Spaced
Based Solar Power System (SBPS). Raja Vignesh. C.R. August 2017.
(PDF)
SPACE BASED SOLAR POWER SYSTEM (SBSP) (researchgate.net)
History of Space Solar
From Wikipedia –
“In 1941, science fiction writer Isaac Asimov
published the science fiction short story "Reason", in which a space
station transmits energy collected from the Sun to various planets using
microwave beams. The SBSP concept, originally known as satellite solar-power
system (SSPS), was first described in November 1968. In 1973 Peter Glaser was
granted U.S. patent number 3,781,647 for his method of transmitting power over
long distances (e.g. from an SPS to Earth's surface) using microwaves from a
very large antenna (up to one square kilometer) on the satellite to a much
larger one, now known as a rectenna, on the ground.”
Glaser later
worked with NASA but high costs of deployment and lack of experience in space
construction were the big hurdles. Further research was found to be merited. Between
1978 and 1986 the U.S. Congress authorized the Department of Energy to work on
the idea. As a result, the Satellite Power System Concept Development and
Evaluation Program was formed with $50 million in spending total. Some
engineering feasibility studies were done but the idea was scrapped in 1980 by
the new Reagan administration, citing the high risk and many unknowns. NASA did
a “fresh-look” at the technology in 1997, pointing out that what was needed to
make the tech potentially competitive was a large lowering of costs of earth-to-orbit
transportation. In 2012 China and India expressed an interest in collaborating
on space-based solar. In 1999, NASA initiated the Space Solar Power Exploratory
Research and Technology program (SERT) to explore feasibility and design
concepts. The goal was to one day develop a system bringing 1 Gigawatt of power
to Earth. NASA concluded that “Launch costs in the range of $100–$200 per
kilogram of payload from low Earth orbit to Geosynchronous orbit are needed if
SPS is to be economically viable.”
NASA’s Solar Power Satellite by means of
Arbitrarily Large Phased Array (SPS-ALPHA)
In 2011-2012 NASA
announced their space solar research idea, the Solar Power Satellite by means
of Arbitrarily Large Phased Array (SPS-ALPHA). This represented a different
approach, utilizing biologically inspired architecture. It also envisioned
mirrors, or reflectors, to concentrate solar power and a thermal management
system. This satellite system could also be used to beam power to other
spacecraft or space stations. Former NASA researcher John C. Mankins of Artemis
Innovation Management Solutions, who worked on the project, described it in a
2013 article: “SPS-ALPHA involves three major functional elements: (1) a
large primary array that is nadir pointing; (2) a very large
sunlight-intercepting reflector system involving a large number of reflectors
that act as individually pointing “heliostats,” mounted on a non-moving
structure (the “bowl” of the goblet in the figure); and (3) a truss structure
that connects those two. As conceived, SPS-ALPHA is not a traditional
three-axis stabilized satellite with one or more solar arrays; rather,
SPS-ALPHA entails bodymounted (non-moving) solar power generation on a
gravity-gradient stabilized satellite, with an axi-symmetric physical
configuration.” SPS ALPHA was a preliminary Phase 1 study and represented a
unique hyper-modular approach to space solar.
Clean Technica reported in 2022 that the US Air Force Research Lab is involved in power beaming experiments for the purpose of powering remote military operations. A test mission is expected by 2024.
Japan’s JAXA Moving Forward
The Japan Aerospace
Exploration Agency (JAXA) began researching space solar in the 2000’s. Wiki
notes: “JAXA announced on 12 March 2015 that they wirelessly beamed 1.8
kilowatts 50 meters to a small receiver by converting electricity to microwaves
and then back to electricity. This is the standard plan for this type of power.
On 12 March 2015 Mitsubishi Heavy Industries demonstrated transmission of 10
kilowatts (kW) of power to a receiver unit located at a distance of 500 meters
(m) away.” JAXA had a goal of 1GW of space solar by 2031. JAXA first
announced in 2022, then reiterated in May 2023 that they will attempt to beam
power from space to Earth in 2025. It is not known how much power they plan to
transfer with their first deployment. It was noted that deploying an array
capable of producing 1 Gigawatt of power, comparable to a nuclear reactor or
other large thermal power plant, would cost about $7 billion at present.
Cal Tech’s Endowment, Their Space Solar Power
Project, and Recent Success of Their Microwave Array for Power-transfer
Low-orbit Experiment (MAPLE)
The California
Institute of Technology (Cal Tech) got a huge boost in Space Solar R&D in
2011 as philanthropist Donald Bren, a wealthy businessman and member of Cal
Tech’s Board of Trustees, agreed to donate through time $100 million toward the
development of space solar. Northrop Grumman Corporation also donated $12.5
million to the project. Cal Tech launched the Space Solar Power Project (SSPP) in
January 2023 on a Momentus Vigoride spacecraft aboard a SpaceX rocket on the
Transporter-6 mission. The 50kg SSPP includes three experiments. The first, the
Microwave Array for Power-transfer Low-orbit Experiment (MAPLE) is the one that
is collecting solar electricity, converting it to microwaves, and sending it to
receiving antennas on Earth. The second experiment is the Deployable on-Orbit
ultraLight Composite Experiment (DOLCE), a six feet by six feet structure
demonstrating the “architecture, packaging scheme, and deployment mechanisms
of the modular spacecraft.” The third experiment is called ALBA and
involves testing 32 different kinds of photovoltaic cells to assess their durability
and functionability in the harsh environment of space. As of June 1, 2023, the MAPLE
has successfully demonstrated wireless power transfer from space to Earth, DOLCE
has yet to deploy, and ALBA is ongoing. Cal Tech notes: “Individual SSPP
units will fold up into packages about 1 cubic meter in volume and then unfurl
into flat squares about 50 meters per side, with solar cells on one side facing
toward the sun and wireless power transmitters on the other side facing toward
Earth.” A video of Cal Tech’s space solar power demo can be found here. The unfolding of
the DOLCE components is expected to be a delicate maneuver, not unlike the
unfolding of the James Webb Space Telescope, which was successfully deployed in
January 2022. According to a January 2023 article in Interesting Engineering
the DOLCE experiment was planned to be the first to deploy, within days of
launch, so it is not known why Cal Tech has not deployed it yet. In a 2021
article in IEEE Spectrum, Cal Tech researchers noted that launch costs had
dropped from 1kg per square meter to about 100-200 kg/square meter with a roadmap
to 10-20kg/m2. Components like lightweight gallium-arsenide PV cells
and design features like modularity are the means to lower the mass which also
lowers the cost to transport it.
China’s Orb-Shape Membrane Energy Gathering Array
(OMEGA) at Xidian University: Demonstrated Wireless Power Transfer Through
Microwaves 180 ft in 2022
China’s Orb-Shaped Membrane Energy Gathering Array was first proposed by Chinese engineer, Duan Bayoan, at Xidian University in 2014. The idea was based on NASA’s Solar Power Satellite via Arbitrarily Large Phased Array (SPS-ALPHA) proposed a few years before that. On June 5, 2022, it was announced that researchers successfully tested the “world’s first full-link and full-system solar power plant” consisting of a 246-ft (75 meter) tall steel structure with five different subsystems involved in the development of space solar power production. It has also been reported that China plans to launch a space solar satellite by 2028.
The European Space Agency and Aerospace Firm Airbus:
The Munich Demo Wirelessly Transmits 2KW 36 Meters in 2022
In 2022 the
European Space Agency (ESA) and Aerospace Firm Airbus successfully demonstrated wireless
transfer of 2kW of power across 36 meters. Although the efficiency was just a
mere 5% overall, they noted that if it can be increased to 20% efficiency it
can compete with existing solar power systems. That should be achievable in
time. The U.S. Air Force’s Naval Research Laboratory (NRL) experimental space
plane has reached 8% efficiency in converting solar power to microwaves but
does not transmit them to Earth. Researchers at the NRL noted: “current
transmitters and receivers lose half their input power. For space solar, power
beaming needs 75% efficiency, “ideally 90%.” Most researchers around the
world think that if these engineering problems can be solved, then space solar
can eventually compete with other forms of energy production.
The ESA also noted on their website: “By coming “close to the theoretical transmission efficiencies via electromagnetic waves (50–60%) … we could produce around 400 W of electricity per square meter on Earth receivers, which is about two to three times the amount we could receive from the same area of terrestrial PV panels.”
Wireless Power Transfer Basics
Basically, the
two most currently feasible ways by which energy may be transmitted wirelessly
are microwaves and lasers, both far-field techniques. Overall, microwave transmission is cheaper and
better than lasers. Wireless energy transmission has the downside of energy losses
during transmission, and this is another of the main economic hurdles to space
solar. Other methods of Wireless Power Transfer (WPT) utilize solar cells and electromagnetic
wave resonance. Electromagnetic fields have different characteristics depending
on relative positions of power sources and receiving antennae. These different “regions”
are divided into the near-field or non-radiative region (within one wavelength
of the antenna) and the far-field or radiative region (beyond one wavelength of
the antenna). Near-field techniques include inductive coupling, resonant
inductive coupling, capacitive coupling, resonant capacitive coupling, and
magnetodynamic coupling. The main far-field techniques are microwaves and
lasers. Shorter EM wavelengths make microwaves the long-distance power
transmission technique with the best conversion efficiency, up to 95%. The
microwaves are converted back to electricity by rectifying antennae, or rectennae.
Experiments are also ongoing to beam power by this method to spacecraft leaving
orbit. The technique has also been demonstrated to power helicopters,
airplanes, rovers, balloons, and cars. Rectennae were invented in 1964 as the
first experiment confirmed the power conversion. In 1975 the U.S. Jet
Propulsion Laboratory beamed 30kW of power from a 26m diameter parabolic dish
to a rectenna 1.54 km away with 85% efficiency. Lasers have several huge drawbacks
including the ability to blind and kill humans and animals, the need for a
direct line of sight, atmospheric absorption and clouds can cause up to 100%
losses, and the conversion efficiency between light (laser is in the light
spectrum) and electricity is only 40-50%.
As noted, Japan’s
JAXA successfully demonstrated wireless energy transfer in 2015– 10kW to a
receiver 500ft away and they demonstrated conversion of electricity to
microwaves then back to electricity. On June 1, 2023, Cal Tech announced that
they successfully transmitted power from their space solar demo satellite launched
in January 2023 to Earth.
The ability to
transfer power at a distance relies on the concept of energy interference.
Constructive interference, where waves amplify one another (rather than cancel
one another out as in destructive interference) is utilized to concentrate and
direct the energy to receiving points. Cal Tech has a video about it here.
Basic Space Solar Concept
The Earth’s geosynchronous
orbit is located in space 22,236 miles up where a satellite can keep a single spot
on Earth in steady view all day, every day. That is where the best solar energy
can be collected without clouds, winter, or twilight, with 24-hour availability
except for about 44 hours per year near the eclipses. The downsides of space
solar are cost, the difficulty and unknowns of maintenance, launch costs, and
conversion losses. Launch costs are dropping with the advent of private satellite
launch providers like SpaceX. Advances in robotics may lead to the biggest drop
in costs as designs can be built out and unfolded in space. Use of lightweight
composite materials can help lower payloads. Space solar satellites will also
require an electric propulsion system with thrusters. These electric thrusters
rely on a propellant, typically Xenon. The rectennas deployed on Earth will
need to be very large, likely over 1 km to a few kilometers in diameter, to receive
microwaves from a space solar deployment at scale. This will require real
estate. However, the land use required will be much less than for equivalent earth-based
solar energy production.
Source: A Review of Space Based Solar Power. Shubham S. Gosavi, Hrishikesh G. Mane, Asiya S. Pendhari, Aditya P. Magdum, Sangram Deshpande, Aditya Baraskar, Mandar Jadhav, Avesahemad Husainy. Journal of Thermal Energy System. Volume-6, Issue-1 (January-April, 2021). AReviewonSpaceBasedSolarPower.pdf
References:
Japan will
try to beam solar power from space by 2025. Igor Bonifacic. Engadget. May 28,
2023. Japan
will try to beam solar power from space by 2025 | Engadget
Japan
to demonstrate space solar power by 2025. Steven Gislam. January 2022. Industry
Europe. Japan
to demonstrate space solar power by 2025 - Industry Europe
Space-Based
Solar Power. Wikipedia. Space-based
solar power - Wikipedia
Space-based
solar power: How it works, and why it's being considered now. ABC Science. James
Purtill. December 19, 2022. Space-based
solar power: How it works, and why it's being considered now - ABC News
A Review
of Space Based Solar Power. Shubham S. Gosavi, Hrishikesh G. Mane, Asiya S.
Pendhari, Aditya P. Magdum, Sangram Deshpande, Aditya Baraskar, Mandar Jadhav,
Avesahemad Husainy. Journal of Thermal Energy System. Volume-6, Issue-1 (January-April,
2021). AReviewonSpaceBasedSolarPower.pdf
Spaced
Based Solar Power System (SBPS). Raja Vignesh. C.R. August 2017.
(PDF)
SPACE BASED SOLAR POWER SYSTEM (SBSP) (researchgate.net)
Solar
Power from Space? Caltech’s $100 Million Gambit. Ned Potter. August 11, 2021.
IEEE Spectrum. Solar
Power from Space? Caltech’s $100 Million Gambit - IEEE Spectrum
Space-based
solar power is getting serious – can it solve Earth’s energy woes? Daniel
Clery. October 19, 2022. Science, Vol 378, Issue 6617. Space-based
solar power is getting serious—can it solve Earth’s energy woes? | Science |
AAAS
Scientists
Successfully Transmit Space-Based Solar Power to Earth for the First Time.
Kevin Hurler. Gizmodo. June 2, 2023. Scientists
Beam Space-Based Solar Power to Earth for First Time (gizmodo.com)
In a
First, Caltech's Space Solar Power Demonstrator Wirelessly Transmits Power in
Space. June 1, 2023. California Institute of Technology. In
a First, Caltech's Space Solar Power Demonstrator Wirelessly Transmits Power in
Space | www.caltech.edu
We're
about to get our first demonstration of space-based solar power. John Loeffler.
Interesting Engineering. January 2, 2023. Space-based
solar power gets its first real test this month (interestingengineering.com)
New
Tower in China Brings Us a Step Closer to Space-Based Solar Power. Kevin
Hurler. June 14, 2022. Gizmodo. New
Tower in China Brings Us a Step Closer to Space-Based Solar Power (gizmodo.com)
SPS-ALPHA:
A Novel Approach to Space Solar Power. John C. Mankins. Ad Astra, Volume 25
Number 1, Spring 2013. SPS-ALPHA:
A Novel Approach to Space Solar Power - National Space Society (nss.org)
We're
about to get our first demonstration of space-based solar power. John Loeffler.
Interesting Engineering. January 2, 2023. Space-based
solar power gets its first real test this month (interestingengineering.com)
Space-Based
Solar Power Is Back On The Table. Steve Hanley. Clean Technica. June 8, 2022.
Space-Based
Solar Power Is Back On The Table - CleanTechnica
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