Comment Space AI? A less-bad way ... (Score 1) 114
ALL server farms radiate into space - they just use everybody else's atmosphere (or perhaps a river and then the atmosphere) to convect the heat to the less-infrared-opaque upper stratosphere.
Absorbing the energy Out There, processing the energy into computation, and radiating it Out There, can be expensive and inefficient Especially if it is done with big hermetic boxes and circulating coolant. We do boxes and coolant on Earth because chips are sensitive to contaminated air and dirty fingers. We crowd everything into small packages because of propagation delay, and because we learned to design software on uniprocessors, and use those same habits on parallel tasks.
A less-bad space processor is an array of gossamer-thin, widely spaced compute surfaces. The simplest "thinsat" ( see http://server-sky.com/ThinsatV... ) is a thin surface with solar cells on the sunward side, and a grid of small "naked"chips on the back, radiating heat into 2.7 Kelvin deep space. A shape like a "T" is better; the top bar of the T is the solar cell, and the larger area perpendicular downstroke of the T is the surface with the compute fabric. The naked chips will be bathed in radiation - but the newest silicon production processes bathe chips in 100eV (13.5 nm) extreme UV photons during manufacturing. In higher energy space radiation, there will be bit flips and an occasional fried transistor - but 10 nanometer transistors are a very small target for space radiation.
So, design with error detection, correction, and redundancy. Design code for loosely coupled autonomous processes. Spread the grid of small chips over a area much larger than the solar cell, so that it can radiate heat at lower temperatures. Rule of thumb, chip "wearout" lifetime doubles for a 10C drop in temperature, so why not aim for a very large area and 250C operating temperature?
If the sun-facing solar cell array reflects infrared and UV without absorption, and is 50% efficient with the 40%-of-1366W/m midband light that it does collect, the solar cell array waste heat is 275 W/m, and a 90% infrared-emissive solar cell back side would be 270K. The angular size of the Sun near Earth's orbit is 32 minutes of arc, about 0.01 radians, so the triangular dark shadow umbra behind the solar cell is 50 times longer than the solar cell is wide.
In theory, a two-sided triangular chip-covered "pennant" in back could have a Stephan-Boltzmann law radiating area (both sides) 50 times larger than the solar cell, hence 40% of the temperature in Kelvins of that solar cell - perhaps 110K - but it would be cheaper to make the heatsink blade thinner, hotter near the chips and colder between, with a truncated blade. A properly designed solar-powered computer segment needs no plumbing or coolant if the computer chips are small, numerous, and distributed.
Also, naked and replaceable. Chip technology advances, compute markets change, upgradability extends system lifetime. The mass of the chips will be small compared to the mass of the solar cells, substrates, and interchip connections. Extend lifetime by replacing old naked chips with new ones.
Another emerging technology is fiber-optic chip interconnect. Optical fiber fed by wavelength division multiplexing/demultiplexing etalon chiplets can move Tbps data over a 125nm fiber optic core, with practically zero path loss over sub-kilometer distances. My 300/300 Mbps fiber internet link is all optical from my house to the switching center 20 km away; nothing to de-power or burn out. A 10-meter-scale compute surface could have tens of thousands of short optical fibers embedded in a heat-sink "sandwich" - a few grams per square meter.
Chip size? Perhaps 1000x1000x20 micrometers, 50 micrograms. More than a decade ago, I licensed circuit technology to Hitachi ULSI for their "smart dust" RFID chips, 300x300x60 micrometers. Using the "fluidic self assembly" techniques developed by Alien Technologies (cool name!) of California, we could have made RFID product tags cost less than a paper price sticker, and saved storefront retail. Then came the Sendai earthquake; Hitachi shifted corporate focus to recovery, and Amazon soon engulfed retail.
Orbital location? 1400 km altitude (7778 km equatorial radius) Low Earth Orbit is SILLY; the orbit is in shadow 30% of the time, 2000 seconds every 1.9 hours. Besides the downtime, thousands of huge thermal stress cycles per year could cripple a low-mass satellite.
A better place for thinsat arrays is in front of Earth-Sun L1, 1.5 million km sunwards; 10 second round trip signalling time. Four space probes are there now (SOHO, Wind, ACE, and Aditya-L1) in "Lissajous orbits" around the L1 gravity cusp. Continuous sunlight, no thermal shock, very small station-keeping thrust - which can be created by "solar sailing". There is room in that region to collect almost 100 Earth's of sunlight without reducing Earth's illumination more that 1%.
The 10 second delay is actually a bonus. I prefer that humans to have a wee bit of terrestrial reaction-time advantage compared to exawatt AI.