Space Solar Power at Internet Speed
Keith Lofstrom / Server Sky PO Box 289 Beaverton Oregon 97075 / Email: email@example.com
Server sky is space solar power on solid state steroids. Using cutting-edge semiconductor technology for gram-weight satellite swarms, we can bring prosperity to the world's bottom billion, feed the internet's exponential appetite for electrical power, and grow a new space industry at Moore's Law rates. We don't need giant structures, government funding or new rocket designs, merely a new combination of existing technologies, generating trillions of dollars of wealth.
In 1969, Buzz Aldrin and Neil Armstrong landed on the moon. Gerard K. O'Neill and his Princeton students proposed settlements in space. Ted Hoff designed the architecture for Intel's 4004, the first integrated circuit microprocessor. Leonard Kleinrock installed the first Internet Message Processor at UCLA.
NASA cancelled Saturn V production in 1968, and the production lines shut down in 1970. O'Neill, a world renowned physicist, couldn't publish his ideas until 1975. Intel microprocessor sales doubled yearly, and global industry sells 300 billion dollars of semiconductors a year, 16 times NASA's shrinking budget. The internet drives 20% of global GDP.
We've pursued O'Neill's 1970's dream for four decades. Today, the U.S. cannot launch an astronaut, much less a solar power satellite or a space colony. It's time to change strategies.
"Space Solar Power is a great dream, achievement of which is a great necessity for the 21st century world." --- Dr. A.P.J. Abdulkalam
Data centers consume almost 3% of US electrical power, a fraction doubling every 5 years, growing faster than efficiency improvements. Developing rural regions in India, China, and Africa cannot afford capital-intensive, logistically sophisticated data centers and vast fiber optic networks requiring 24x7 electrical power and high-tech maintenance skills. How can we connect these people to the internet without massive regional infrastructure deployment?
The sun produces 384 trillion terawatts that nature cannot use, streaming past the planets into interstellar space. Space is expensive to get to, but zero-gee structures can be incredibly thin and ultra-light-weight, permitting solar photovoltaic systems that are cheaper to deploy in orbit than on the ground. A 5 hour orbit offers 20 hours a day of unattenuated, cloud-free 1367 W/m² sunshine in a stable, clean, zero-maintenance environment. Sunlight captured in space does not steal land and sunlight from agriculture and wilderness on the ground.
Some space enthusiasts imagine huge structures in geosynchronous orbit capturing gigawatts of solar power and beaming it as microwaves to receivers on earth, 40,000 kilometers away. Both transmitting and receiving antennas must be enormous because of beamforming diffraction limits.
Ivan Bekey teaches us to replace structures with information. What if we made arrays of tiny satellites instead, and moved petabits, not megajoules?
A Solid State Makeover
Satellites are currently built with aircraft technology: costly, slow to build and deploy, assembled and tested manually a few at a time. The electronic components are years to decades behind low cost consumer electronics.
Recent advances in solar cell materials and VLSI radiation hardness permit unshielded gram-scale satellites. Ultrathin graded junction indium phosphide solar cells can survive radiation doses of 1E18 electrons/cm² (1 MeV). HfO₂/SiO₂ gate stacks can survive ten megarads of ionizing radiation with millivolt threshold shifts. With occasional high temperature annealing, advanced electronics can survive in orbit for years, without heavy shielding.
Whole-system function-to-weight ratios can be 5 orders of magnitude better than terrestrial solar, and 3 orders better than aircraft-style satellites.
Server Sky converts space solar power into computation with arrays of tiny solid-state satellites. Server sky thinsats are 20 centimeters across and weigh 3 grams, with integrated circuits, wiring, indium phosphide solar cells and slot antennas built on a 50 micrometer thick glass substrate. Thinsats cool by black body radiation, and maneuver with light pressure,
Thinsats are deployed into actively stabilized three dimensional geodesic arrays of 30,000 thinsats. These arrays produce an average of 100 kilowatts of power for computation and radio. Phased array transmitters can simultaneously send hundreds of narrow beams to kilometer-sized receiver footprints.
Server sky orbits are not geostationary. Thinsats are launched in 100kg solid-cylinder stacks into 6411 kilometer altitude equatorial orbits. This is the middle of the van Allen belt, a very high radiation zone almost devoid of other satellites. The high radiation resistance of thinsats allows us to use this region of space without interfering with other services. The lower altitude greatly improves round trip ping time, reduces path-length attenuation, and reduces ground spot size for point-to-point communications. These arrays are not bent-pipe communication satellites; signals originate from computation in space.
Electrochromic materials can be electrically switched between transparent, opaque, or reflecting. 1367 W/m² sunlight makes a tiny 4.56 μPa pressure if it is absorbed, double that if reflected, none if passed through a transparent window. The three corners of a triangular thinsat are large switchable mirrors, producing adjustable thrust up to 20 nanonewtons. Accelerations are small and rotations are slow, but can accumulate to orbit-scale velocity changes and displacements, allowing thinsats to maneuver relative to the rest of the array. Thruster Isp is 10,000 seconds for 10 years in orbit, better than any rocket.
Between the thrusters, thinsats are comprised of many small cells in a surface-covering grid. Strips of solar cell alternate with slot antennas, radio chips, processors and memory. Distributed function makes thinsats highly redundant and resistant to micrometeoroid punctures.
Server Sky Applications
Server sky ground antennas can add new capabilities to existing cell towers, reducing the cost of new deployment in remote areas. New services may include local weather prediction and warnings, automated speech translation, emergency services, eGovernment, eBanking, eLogistics, and new job opportunities in a global market.
Small arrays will grow and numbers will multiply, eventually replacing ground data centers worldwide, relieving the global grid of their huge energy appetites. In time, we may revisit the old space-power-to-earth dreams, building gigantic arrays generating terawatts to feed the planetary electrical grid, eliminating the need for most terrestrial generation.
Note for reviewers: Since 2010, server sky has evolved. We've learned much about light pressure orbit stability, radio beamforming, geodesic array shapes, radhard InP solar cells, electrochromic materials, spring deployment, and other contributing technologies. New applications include rural internet in the developing world.
A companion presentation "Garbage into Gold" will describe using server sky arrays as radar illuminators and synthetic aperture receivers for precision location of space debris. Derelict rocket bodies may be captured and cut into gram-weight ballasts for future ultralight thinsat designs.