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  18          \copyright  IEEE, 2015.  A doi and link to IEEE Xplore will go here after electronic publication.
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  29 \hyphenation{op-tical net-works semi-conduc-tor}
  31 \begin{document}
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  41 \title{Server Sky - Information Farming in Space}
  43 \author{Keith~Lofstrom, \IEEEmembership{Member,~IEEE,}
  44  	Ulises~Qui\~{n}\'{o}nez,
  45 	and~Gary~Barnhard
  46 \thanks{K. Lofstrom is with Server Sky, Beaverton, OR 97075 USA e-mail:}
  47 \thanks{Ulises Qui\~{n}\'{o}nez is with the Facultad de Ingenier\'{i}a, Universidad de San Carlos de Guatemala, Guatemala City, GT}%
  48 \thanks{Gary Barnhard is with ISP Inc., Cabin John, MD 20818 USA}}
  50 \maketitle
  51 \begin{abstract}
  52 Server sky is a proposal for vast constellations of tiny space satellites,
  53 computing and exchanging information directly with cell towers serving
  54 customers, students, researchers, and entrepreneurs in the developing world.
  55 Paper-thin 5 gram ``thinsats'' will power processors, memory, and 60/70 GHz
  56 radios with 4 watts of space solar power.  7842 thinsat arrays produce
  57 sub-kilometer ground spots.  Highly redundant, cryptographically secure,
  58 radiation-resistant thinsats will be recycled at end-of-life.
  59 \end{abstract}
  61 \begin{IEEEkeywords}
  62 Space Technology; Integrated Circuits; Solar Energy; Internet; Globalization
  63 \end{IEEEkeywords} 
  64 \IEEEpeerreviewmaketitle
  66 \section{Introduction}
  68 \begin{quote}
  69 \emph{``A telephone in every village ... I believe it is a realistic and
  70 desirable goal by the year 2000.  It can be achieved now that millions
  71 of kilometers of increasingly scarce copper wire can be replaced by a
  72 handful of satellites in stationary orbit.''}
  73 --- Sir Arthur C. Clarke, 1983 \cite{clarke}
  74 \end{quote}
  76 Billions of valuable minds are trapped in poverty and isolation in
  77 the developing world, performing manual labor in want and squalor,
  78 rather than participating in the design and deployment of an abundant
  79 and efficient global civilization.
  81 The developed world is enabled by the consumption of massive quantities
  82 of energy and minerals, much gathered in the developing world. 
  83 Fortunately, increased efficiency enabled by technological innovation
  84 has reduced resource consumption per unit of economic output;  for
  85 example, steel production in the United States consumed 67 MJ/kg of
  86 energy in 1950, reduced to 15 MJ/kg in 2005.  
  87 The annual power consumption of refrigerators made with that steel dropped
  88 from 1900 kWh to 500 kWh between 1972 and 2009.  
  89 Knowledge can reduce physical consumption \cite{naam}.
  91 The changing product mix reduces energy and resource consumption as well.
  92 Production and use of a 112 gram iPhone 5 creates 75 kg of CO$_2$ over a
  93 three year lifetime \cite{apple} and connects to the planet, while an
  94 875 kg, 4.9 liter/ 100 km Smart Car produces 75 kg of CO$_2$ traveling
  95 only 650 kilometers \cite{smart}.
  96 Telework, online shopping, and online social networking can save
  97 thousands of kilometers and hundreds of hours of driving per year in a
  98 society already centered on the automobile. 
 100 New information-centric societies optimized for personal electronics
 101 and global networking can develop faster, cheaper, and greener without
 102 replicating the developed world's consumption of materials, energy,
 103 and distance.  Innovation is inspired, or hindered, by everyday experience. 
 104 Information-centric cultures can invent new systems for living
 105 unimaginable in cultures chained to steel and carbon. 
 106 Info-cultures will have the key to the future, 
 107 which will open the door to the solar system.
 109 Information can be expensive.  Data centers consume more
 110 than 10 GW in the United States, almost 3\% of US electrical power
 111 \cite{epa}.  Most of this power is spent on voltage transformation 
 112 and cooling; less than 40\% of the incoming grid power reaches
 113 the computing load \cite{intelDC}.
 115 400 000 diesel-generator-powered cell towers provide rural India
 116 with basic telephone service, connected by microwave links \cite{indiasciam}.
 117 Basic communication bypasses middlemen and increases rural income,
 118 while bringing education, rule of law, and political power to
 119 remote and vulnerable communities \cite{roshan}. 
 120 Broadband internet offers more, but requires more power and bandwidth.
 122 Google manufactures information from energy, producing \$20 of revenue
 123 per kilowatt-hour of wholesale electricity.  Google's ``green" slogan
 124 is ``renewable energy is better than carbon" ( RE$>$C ) but they are
 125 enormously wealthy because information is better than energy ( I$>$E ). 
 126 Google sells their products worldwide, at the speed of light, because
 127 information is easier to move than energy. 
 128 Much of Google's workforce was born in the developing world \cite{diverse},
 129 and many more could work near their birthplaces with inexpensive
 130 and reliable high bandwidth infrastructure.
 132 While computation efficiency is increasing at Moore's Law rates, 
 133 computation demand is increasing faster.  The global power demand
 134 for computing and data distribution may someday exceed a terawatt. 
 135 Power consumption limits the continued exponential expansion of
 136 new information technologies,
 137 restricting the growth of the semiconductor industry
 139 \section{Power From Space}
 141 The earth intercepts 174 thousand terawatts from the sun.
 142 120 thousand terawatts passes through clouds to reach the surface,
 143 warming the earth to a black-body temperature $T_{bb} $ of 255 K,
 144 -18 {\textdegree}C.
 145 Most of that power lands on ocean, and the power reaching land is
 146 mostly gathered by plants drawing CO$_2$ out of the atmosphere. 
 147 Land covered with solar photovoltaics can displace carbon emission
 148 by power plants, but it also displaces natural carbon removal by
 149 soil microbes, trees, deep-rooted grasses, and other perennial plants. 
 150 Destruction of natural ecosystems by agriculture \cite{reick} \cite{plows}
 151 has already brought significant climatic change.  
 152 The pumped storage reservoirs needed to timeshift solar power,
 153 and the inefficiencies of storage and  power transmission that
 154 increase their extent, will disrupt nature further.
 156 The sun emits 380 trillion terawatts into empty space.
 157 600 million terawatts of 24x7 sunlight streams through the region of
 158 space closer than the Moon's orbit. 
 159 Diverting 100 terawatts of that power to the Earth's surface could
 160 power the entire world at US levels of energy consumption,
 161 while increasing the Earth's surface temperature by only
 162 \mbox{0.05 {\textdegree}C .} 
 163 100 TW can also convert up to 60 ppm of atmospheric CO$_2$ into
 164 elemental carbon and oxygen per year.  Space energy can provide
 165 massive benefits to earth.
 167 In 1968, Peter Glaser proposed capturing terawatts of space power
 168 in geosynchronous orbit, converting the power to 2.45 GHz microwaves
 169 with vast space solar power satellites (SSPS),
 170 and beaming it to equally vast rectifying antennas (``rectennas") on the earth,
 171 which would convert it to grid power \cite{Glaser}. 
 172 Transmitting and receiving antennas are scaled by diffraction
 173 limit over 39 000 kilometer distances - 12 centimeter waves
 174 result in antennas 5 kilometers across, assuming 25{\textdegree}
 175 above-horizon elevation and 9\% sidelobe loss. 
 177 %%  25° elevation:  57.13° radial angle, which can be an SSPS
 178 %%  deflected 5 degrees south by tidal perturbations,  talking to a
 179 %%  site at 46.2° north and 30° east or west (plus or minus 2 hours)
 180 %%  from SSPS meridian.
 181 %%  Geometry calculator and Fraunhofer integrator is file fra0.c
 183 2.45 GHz SSPS may interfere with terrestrial communications
 184 and radar.  Sidelobe power from a single 5 GW SSPS satellite is
 185 predicted to be 1mW/m{\tw} 300 km from the rectenna \cite{arndt},
 186 more than 70 dB higher than the Earth's thermal background.
 188 Alternatively, space power may be beamed as 183 GHz millimeter
 189 waves \cite{ssps183} to 20 km altitude aerostat \cite{stratosolar}
 190 rectenna platforms in the stratosphere,
 191 above the winds and shielded from the surface by tropospheric water vapor. 
 192 Transmit and receive antennas could be 75 times smaller than 2.45 GHz
 193 SSPS proposals, and run at higher power densities than sunlight. 
 194 Even scaled down, this is a huge first step, 
 195 and we do not currently have the technology to efficiently transmit
 196 and receive 183 GHz power.
 198 Instead of beaming low value energy at enormous power levels to
 199 vastly expensive rectennas on earth, with incredibly high initial
 200 costs,  what if we turn space power into high value, scalable,
 201 easy-to-transmit products - like information?
 203 \section{Global Data Transmission}
 205 Radio broadcasting works because vast amounts of information can
 206 be encoded in tiny amounts of energy.  Shannon teaches that
 207 information can be represented with an energy of $ln(2)kT$ per bit,
 208 2.9e-21 joules at 300K, or 26e-24 joules (26 yoctojoules) at the
 209 2.7K cosmic blackbody temperature.  Information transmission 
 210 requires enough power to overcome ambient thermal and artificial
 211 noise.  For example, across the 2.45$\pm$0.05 GHz ISM band,
 212 the earth emits 20 pW/m{\tw} and receives 20 fW/m{\tw} from the sun.
 213 This means that a small antenna on an IEEE 802.11g USB stick can
 214 receive 54 Mbps data from a 20 mW transmitter tens of meters away.
 215 Point-to-point information transmission can use much less power and
 216 tolerate far higher losses than bulk power transmission.
 218 %%  k=1.3806503e-23J,  kln2 = 9.57e-24    Tbb=2.735K  -> 2.617e-23
 219 %%  Skolnik p 2.29  effective noise temperature 100K at 0° elevation
 221 Cisco estimates that global IP traffic will exceed 1.1 zettabytes
 222 per year in 2016 \cite{cisco}, averaging 280 terabits per second.
 224 Even with 1\% power-to-microwave conversion efficiency, and 90 dB
 225 path loss, all global internet traffic can be received with 20 dB
 226 signal-to-noise ratio with only 200 MW of transmitter feed power,
 227 and 1 MW total broadcast power divided among millions of individual
 228 receivers on earth.  This is 40 dB less than a single space solar
 229 power satellite delivering 5 GW to the grid, and it will occur at
 230 frequencies much higher than existing services, creating no interference.
 232 Existing geosynchronous (GEO) satellite internet services are ``bent pipe"
 233 up-and-back paths relaying traffic to and from the wired internet. 
 234 A request-and-response transaction makes four 38 000 km journeys
 235 through space, adding 510 ms of delay to an internet transaction,
 236 as well as significant queueing time for the bitrate-limited link.
 237 Latency (round trip ping time) is at least 550 ms, typically 700 ms,
 238 and can exceed 1500 ms when the link is saturated \cite{vsat}.
 240 Can we do better?  What if servers orbit closer than GEO?
 242 \section{Space Power's Solid State Makeover}
 244 Satellites are essentially energy-processing surfaces, 
 245 converting sunlight into information broadcast to earth.
 246 Ivan Bekey teaches us to replace structures with information,
 247 build gossamer structures in distributed systems, and transport
 248 energy and information, not mass \cite{Bekey08}.  Middle Earth
 249 Orbit (MEO, $>$2000 km altitude) is subject to extremes of radiation
 250 and temperature, but is free of friction, contamination, and
 251 mechanical stress.  Satellites have line-of-sight access to vast
 252 areas of the earth.  Low drag orbits are precisely predictable.
 254 Mesh networks can connect thousands of small satellites in a
 255 three-dimensional obstruction-free environment \cite{techsat}. 
 256 Thin satellite array function-to-weight ratios can be orders of magnitude
 257 better than terrestrial infrastructure or aircraft-style satellites. 
 259 220 nm thick direct-bandgap indium phosphide photovoltaic cells
 260 collect sunlight with 15\% efficiency, 200 W/m{\tw}\cite{li03},
 261 weighing 1 g/m{\tw}.  More efficient multilayer cells are
 262 possible, but are far more expensive and vulnerable to radiation.
 264 Integrated circuit silicon is lightweight.  The lifetime power
 265 cost of a typical microprocessor is higher than the production cost. 
 266 Thinned to 20 {\textmu}m, a 10 mm{\tw} die weighs 500 {\textmu}g. 
 267 It is far cheaper to move silicon to a power source in space than
 268 to move space power to terrestrial silicon.
 270 Integrated circuit chips for RFID tags are as small as
 271 50 {\textmu}m x 50 {\textmu}m  x 5 {\textmu}m,
 272 draw milliwatts of power, weigh 30 ng, cost a fraction
 273 of a cent, yet contain thousands of 90 nm transistors \cite{50muA}
 274 \cite{50muB}.   Cost and size will plummet exponentially with time.
 276 \section{Server Sky}
 278 Server sky \cite{onlinecomm} \cite{sustech} proposes migrating
 279 gigawatts of data center computation into a ring of satellite
 280 arrays orbiting the earth, 
 281 directly servicing users between 40{\textdegree} north to south latitudes. 
 282 Individuals can communicate directly to arrays in the sky,
 283 through their own satellite antennas, or antennas on cell towers,
 284 without landline infrastructure. 
 285 Arrays will originate or proxy content and services without an
 286 additional round trip to earth.
 288 Server sky communication is point to point, using 70 GHz, 4.3 mm,
 289 phase-array-steered beams to paint sub-kilometer ground spots.  
 290 Cross-orbit and intra-array communications in vacuum can happen at 60 GHz.
 291 That frequency is strongly absorbed by atmospheric oxygen resonance and
 292 does not reach the ground.
 294 The primary task of server sky arrays will be data center computation;
 295 retrieving and formatting data from solid state memory, data analysis,
 296 simulation and modeling, video and sound, synthesis and recognition.
 298 Server sky \textbf{thinsats} will be rounded triangles 20 cm across,
 299 240 cm{\tw} in area, and weigh 5 g.
 300 Thinsat front sides will be covered with indium phosphide solar cells
 301 that directly power silicon chips millimeters away.
 303 \begin{figure}[!t]
 304 \centering
 305 \includegraphics[width=3.3in]{V5thinsat.png}
 306 \caption{Thinsat back side chip array, 20 cm wide, 70 {\textmu}m thick,
 307 5 g, not to scale, real thinsats will have 1400 2.1 mm slots and
 308 350 chips.  The black vertical bars represent slot antennas, the
 309 corners are electrochromic light pressure thrusters.  
 310 Antenna slots pass through the aluminum foil substrate to the front,
 311 covered with InP photovoltaic cells and corner thrusters}
 312 \label{thinsat}
 313 \end{figure}
 315 Thinsat back sides, illustrated in Fig. \ref{thinsat}, will be covered
 316 with 1400 2.1 mm slot antennas in a hexagonal grid at full-wave spacing,
 317 cut through a 70 {\textmu}m thick aluminum substrate \cite{fjelstad}.
 318 Groups of 4 slots are fed by one of 350 3.6 mm x 3.6 mm x 20 {\textmu}m thick
 319 customized integrated circuits, all with built-in RF power modulators
 320 fed by the nearest of 12 intermediate frequency synthesizers.  
 321 The rest of the chips are a mix of simple microprocessors, ROM, and RAM,
 322 and connected by a redundant mesh of low voltage high speed wiring. 
 323 Security will not be a software afterthought - encryption and decryption
 324 will be performed by dedicated hardware invisible to software.
 325 Advanced semiconductor chip design is complex and expensive; the high
 326 non-recurring engineering expenses will be spread over billions of production die.
 328 The larger-than-halfwave spacing will create grating lobes spaced 60 
 329 degrees from the main downlink lobe;  Fortunately, the earth occupies
 330 less than 60 degrees of the sky visible from the server sky orbit,
 331 so waste downlink power will disperse harmlessly into empty space. 
 332 The sidelobe waste power is defocused by thinsat curvature,
 333 frequency spread, and the nonuniform array. 
 334 There will not be enough concentrated power to interfere with other services, 
 335 though sidelobe waste from hundreds of millions of arrays may someday
 336 raise the noise floor.
 338 Thinsats will deploy into actively stabilized three
 339 dimensional geodesic arrays.  Array sizes can vary from hundreds
 340 to millions.  This paper considers arrays of 7842 thinsats,
 341 producing an average of 24 kW for computation and radio.
 343 Server sky orbits will not be geostationary.
 344 Thinsats will be launched in 40 kg solid-cylinder stacks into 6411
 345 km altitude equatorial orbits, about twice the radius of the earth.
 346 This is in the inner van Allen belt,
 347 a high radiation zone with few other active satellites.
 348 Compared to GEO, the MEO orbit reduces round trip ping time,
 349 path-length attenuation, and the size of the ground footprint
 350 for point-to-point communications.
 352 \begin{figure}[!t]
 353 \centering
 354 \includegraphics[width=2.6in]{Morbits20.png}
 355 \caption{Server sky M288 equatorial orbit radius, round-trip ping time,
 356 and northern visibility with 20 degrees elevation, compared to other orbits.
 357 Relay satellites such as O3B and traditional comsats do not originate data,
 358 so round trip pings will make two passes through these satellites,
 359 doubling ping time.}
 360 \label{orbit}
 361 \end{figure}
 363 Arrays will pass through the sky five times a day, every 288 minutes,
 364 so this orbit is called \textbf{M288}, as shown in Fig. \ref{orbit}.
 365 In the northern hemisphere,
 366 the M288 orbit appears close to the southern horizon, 
 367 below 20{\textdegree} elevation from latitudes above 42{\textdegree} N.
 369 \begin{figure}[!t]
 370 \centering
 371 \includegraphics[width=3.4in]{PopLatitude20.png}
 372 \caption{ Population and array visibility for 20{\textdegree} minimum
 373 antenna elevation.  The vertical axis is latitude south to north,
 374 and the horizontal axis represents M288 array midnight and daytime
 375 visibility vs latitude, and world population vs latitude.
 376 Array visibility is lower at midnight because arrays are eclipsed by the earth. }
 377 \label{population}
 378 \end{figure}
 380 Most of the developing world's population is below 42 degrees north
 381 as shown in fig. \ref{population} \cite{rankin}.  Farther north,
 382 and near midnight, server sky arrays can relay through existing
 383 constellations such as O3B, Iridium, and ViaSat to polar and
 384 insomniac customers.
 386 Arrays will eclipse 17\% of
 387 every orbit in spring and fall, 11\% in summer and winter. 
 388 Arrays will go into cold shutdown when eclipsed,
 389 while other visible arrays in full sunlight continue serving customers. 
 390 Extra arrays are cheaper than batteries.
 393 Server sky data centers do not need chip packaging, power conversion,
 394 air conditioning, land, structure, or fiber data links. 
 395 Thin film space systems assembled with photolithography and automation
 396 may cost less less than traditional earthbound systems,
 397 with more versatility and fewer environmental costs.
 399 A booster such as India's PSLV \cite{PSLV} can put 24 40kg arrays
 400 (with spares) into equatorial M288 orbits (5 overhead passes per day,
 401 288 minutes apart).  Any launch system capable of
 402 10 km/s delta V can dispense dozens to hundreds of server sky arrays.
 404 \section{Space Power Transformed}
 406 \begin{figure}[twopaths]
 407 \centering
 408 \includegraphics[width=3.4in]{twopaths6.png}
 409 \caption{(a) One minimum size 10 GW Space solar power satellite
 410 feeding terrestrial data centers.
 411 (b) Constellations of server sky arrays
 412 broadcasting directly to customer cell towers. 
 413 Server sky can start profitably with an 600 kW constellation of 25 arrays, and grow exponentially.}
 414 \label{twopaths}
 415 \end{figure}
 417 Fig. \ref{twopaths} shows two different ways space power can be
 418 used to power the internet.
 419 The first column represents a 10 GW SSPS satellite and one terrestrial
 420 rectenna feeding the electrical grid and powering data centers.
 421 The second column represents the power used directly in space to
 422 feed as few as 25 arrays of thinsats,
 423 scaling up to 80 000 arrays, 630 million thinsats,
 424 matching current global data center productivity.  
 425 Optimization reduces launched mass at these high production levels.
 427 Due to diffraction limits, everything about space power transmission
 428 must be large; 35 000 tonnes of material launched into orbit for a
 429 single SSPS satellite.  The complex path power takes from photovoltaic
 430 cells in space to a user such as a terrestrial data center has many
 431 energy conversion steps.  Radiating end-user waste heat into a 300K
 432 ambient environment requires more power to extract and dissipate it.
 433 PV-to-compute-load efficiencies may be lower than the 20\% shown.
 435 The second column represents Server Sky, moving electrical power directly
 436 from PV to the compute load centimeters away.  32 kW of full illumination
 437 computes and narrowcasts data over a microwave link that can tolerate high
 438 ( 90 dB! ) inefficiencies.  20 sunlit arrays out of 25 can provide complete
 439 24 hour coverage near the equator.
 440 There is room in the M288 orbit for millions of arrays.
 441 As the constellation grows exponentially, many more launch
 442 rockets will be mass produced, and the aerospace ``experience curve"
 443 will reduce launch costs significantly.  
 445 Server sky does not eliminate the need to make terawatts for other
 446 purposes - it merely increases the efficiency of a few of those
 447 terawatts, producing scalable revenue from a much smaller beginning.
 448 The greatest obstacle to space solar power is inadequate and expensive
 449 launch capacity. 
 450 Server sky, growing at Moore's law and internet rates,
 451 can pay for and rapidly develop that launch capacity.
 453 Server sky can be the kindling for a flame that has proven too
 454 difficult and expensive to ignite for half a century.
 456 \section{Light Pressure Maneuvering}
 458 Thinsats will have area-to-mass (``sail'') ratios of 5 m{\tw}/kg,
 459 maneuvering as light sails such as the
 460 Japanese Space Agency's IKAROS \cite{ikaros}.  
 461 Heavier than true solar sails,
 462 thinsats will have enough thrust to travel in formation,
 463 avoid colliders, and migrate from underutilized arrays to larger ones.
 465 1360 W/m{\tw} sunlight makes a tiny 4.54 {\textmu}Pa pressure if absorbed,
 466 and double that if reflected. 
 467 The three corners of a triangular thinsat 
 468 will be 5 cm diameter (19.6 cm{\tw}) electrochromic mirrors,
 469 which electrically switch from dark to reflective, changing
 470 acceleration by 3.5 {\textmu}m/s{\tw}, or turning in 15 minutes.
 472 Accelerations will be small, but accumulate to large displacements over
 473 hours and months.   A thinsat can move in nanometer increments, or
 474 move 40 000 km, halfway around the M288 orbit, in half a year.
 476 \section{Radiation}
 478 Radiation will be the number one problem for server sky thinsats.  
 479 Recent advances in solar cell materials and VLSI radiation hardness,
 480 a fortuitous result of transistor scaling,
 481 permit unshielded gram-scale satellites.
 483 The Intel hafnium oxide gate stack, designed to reduce gate
 484 leakage, produces transistor gates highly resistant to
 485 charging by ionizing radiation \cite{dixit08}. 
 486 Modern digital processes operate at supply voltages too low to sustain latch-up.
 487 New microprocessor designs that recover from noise errors \cite{razor08}
 488 can evolve into designs that recover from radiation-induced single event upsets.
 489 Thin indium phosphide solar cells can survive radiation doses of
 490 10$^{18}$ electrons/cm{\tw} (1 MeV) \cite{li03}. 
 492 \section{Geodesic Arrays, Radio, and Ground Patterns}
 494 The 1.1 million antenna slots on 7842 thinsat subarrays combine into a
 495 giant 100 meter aperture antenna.  The array of thinsats is shaped
 496 like a distorted geodesic sphere, which can beam packets
 497 to sub-kilometer-sized receiver footprints on the ground.
 498 Server sky internet cannot compete with optical fiber in a dense urban
 499 environment, but works well for suburban, rural, and mobile customers,
 500 in emergencies, and in war zones.
 502 An intriguing ground antenna design from Kymeta \cite{kymeta1} \cite{kymeta2}
 503 uses liquid crystals in a metamaterial configuration as a Ka band antenna.
 504 These antennas steer slowly (30{\textdegree}/s) and are not suitable
 505 for time-sharing many users to many server sky arrays at once.  
 506 Presumably, these antennas can evolve to faster LCD materials and shorter
 507 wavelengths, so they can timeshare between multiple arrays in orbit.
 509 Uplink from small antennas will be slower than downlink.  This
 510 matches typical asymmetrical internet usage.  There will be few customers
 511 in the mid-Pacific, so bulk content can be uploaded from large
 512 high-bandwidth surface antennas sited near trans-oceanic data cables.
 514 \section {Light Pressure, Ballast, and Space Resources}
 516 Light pressure distorts orbits, shifting apogee and perigee eastward
 517 (viewed sunwards).  The minimum eccentricity of a precessing orbit
 518 increases with sail ratio (area over mass) and orbit radius. 
 519 The elliptical orbit must not precess into the paths of other
 520 satellites, limiting the maximum sail ratio and the minimum mass.
 522 The minimum mass can be reduced by half if light pressure from the
 523 sun on the front is balanced by infrared emissions out the back.
 524 A frontside conductive grid with a mesh size of 2 micrometers can
 525 pass and focus optical photons on the photovoltaics, while
 526 reflecting (and not emitting) longer infrared wavelengths. 
 527 A high emissivity black coating on the thinsat backside will
 528 radiate the heat isotropically, and half of the infrared light
 529 pressure will be directed forwards,
 530 opposing the light pressure of incoming sunlight.
 532 Launch mass can be reduced further by attaching ballast mass in orbit. 
 533 Recycled obsolete thinsats will be one source of ballast,
 534 gram-weight pellets cut from captured space debris will be another. 
 535 This makes space debris into a valuable resource; hopefully we will
 536 capture and re-use all of it before plummeting rocket costs reduce
 537 the relative profitability of space debris recycling.
 539 \section{ Environmental Effects }
 541 If space computation power grew to a terawatt, 250 billion thinsats 
 542 facing the sun at M288 could reflect 25\% as much light into the night
 543 sky as the full moon, disrupting nature and optical astronomy.  So,
 544 thinsats will turn edge-on to the terminator in the night-side half of
 545 the orbit (see Fig. \ref{nightsky}) to eliminate night sky light pollution,
 546 reducing average power by 17\%.
 548 \begin{figure}[nightsky]
 549 \centering
 550 \includegraphics[width=3.4in]{ir-reflect3a.png}
 551 \caption{ Filtering infrared to emit away from the sun permits
 552 thinsat mass reductions.  Turning thinsats edge-on to the terminator
 553 (the day-night boundary) prevents sunside reflections from making
 554 light pollution in the night sky. 
 555 Turning the infrared emissive backside towards the earth keeps the
 556 thinsat warmer during eclipse, reducing thermal stress and increasing
 557 reliability.}
 558 \label{nightsky}
 559 \end{figure}
 561 Thinsats cool rapidly in eclipse,  Turning the high thermal emissivity
 562 backside coating towards the nearby warm earth (see Fig. \ref{nightsky})
 563  minimizes thermal shock.
 564 This protective measure encourages light pollution minimization turns.
 566 High latency computation tasks should deploy further out. 
 567 At lunar-distance Lagrange points, arrays are in continuous sunlight
 568 and have better access to lunar materials, while worst-case light
 569 pollution is reduced by a factor of 3000. 
 570 It is difficult to imagine how humanity will use more than 1 MW of
 571 computation per capita, but as recently as 1896, Arrhenius could not
 572 imagine reaching CO$_2$ levels of 400 ppm in less than a millennium. 
 574 When forecasting the consequences of our engineering designs, we should
 575 think about millenia and exponentials, not mere decades and S curves.
 576 Learn from nature, and choose designs that make environmental protection
 577 and material recycling the most profitable way to operate,
 578 without relying on good intentions.
 580 \section{Ownership and Security}
 582 Server sky thinsats will be owned and used by people with few
 583 security skills, and will sometimes run insecure, poorly-designed software. 
 584 The thinsats connect to an entire planet of spies, criminals, and cyber vandals. 
 585 Defending thinsats will be difficult but not impossible.
 587 Thinsats will contain large arrays of inexpensive one-time pad
 588 using ICID technologies \cite{icid}.  Bits may be extracted at
 589 at the wafer level during manufacturing, but are otherwise impossible
 590 to predict or intercept.  
 592 Thinsats will use custom chips designed for survival and reliable
 593 computation in a high radiation environment.  
 594 The same hardware that corrects radiation single-event upsets can
 595 be applied to security tasks.  Thinsats will have built-in
 596 cryptographic hardware primitives to perform kilobit integer
 597 arithmetic and other useful primitives found in most secure encryption 
 598 algorithms.  Large integer results can be tested
 599 with a verification modulus \cite{bos} ( a ``woop" \cite{ferguson} )
 600 computed with a small, randomly generated prime number.  
 602 Thinsats have many processors, and the user portions of each processor
 603 can be temporarily rented by others.  These ``proplets" \cite{proplets}
 604 will communicate to a restricted set of ground users, identified by
 605 affiliation, geography, and time.  Thinsats work at the speed of light.
 606 Physical attacks require slow satellite rendezvous, allowing hours for
 607 countermeasures or self-destruction.
 609 Thinsats can be transferred as property, or used as collateral for
 610 loans.  Hardware implementation of ``smart contracts" \cite{contracts}
 611 permits automatic transfers to lien-holders if payments are not made
 612 or terms are violated.  This lowers transaction costs and interest
 613 rates, permitting new borrowers without trustworthy credit histories
 614 to establish them.
 616 These capabilities are fragile if the owners and users are inept,
 617 gullible, and isolated.  Server sky will support protocols for users
 618 to team with friends, family, and trusted professionals to
 619 authenticate important transactions.  
 621 All security protocols fail over time; they may be compromised, or merely
 622 obsolete and inefficient compared to newer protocols.  Accumulating
 623 radiation damage, and new generations of higher performance thinsats
 624 competing for the same orbits, will eventually force the retirement
 625 and recycling of obsolete thinsats.
 627 \section{Serving Clients}
 629 The developed world needs help extracting itself from the material
 630 consumption trap.  Unleashing the creative power of billions of
 631 people can bring new ideas, new inventions, and economic growth
 632 rates undreamed of in national capitals and corporate boardrooms. 
 634 C. K. Prahalad teaches us that typical ``S" curve economic growth
 635 is compacted in time into an ``I" curve (double-digit percentage
 636 growth rates per month) for products that satisfy important needs
 637 in the developing world\cite{prahalad}.  Our goal is not merely to
 638 provide new clients for developed world corporations, but to connect
 639 the world to technical, entrepreneurial, educational and cultural
 640 products and services invented by billions of newly empowered people.
 642 We offer an alternative to the developing world:  replace material
 643 resources with information, just as a smart phone embeds vast
 644 intellectual resources and value in a few pennies of raw materials. 
 645 Information manufactured with space solar power can be expanded to
 646 vast scale, without extracting resources or dissipating heat in the
 647 biosphere.  This eliminates the tradeoff between economics and the
 648 environment that characterizes the resource consuming technologies
 649 of the developed world.
 651 A cruise ship arriving in port emits a flood of passengers flocking
 652 to the shops and sights on shore, followed by a flood of crewmembers
 653 seeking internet cafes to communicate with their families back home
 654 \cite{schwartz}.  High bandwidth server sky internet to cruise ships
 655 underway will not only provide sporting events and other realtime video
 656 to the passengers, but family connection for the crew during the voyage. 
 657 That increases the value of the cruise to everyone on board.  
 659 In 2015, almost 3\% of the world's population lives and works outside
 660 of their birth country, making the painful choice to leave loved ones
 661 and familiar landscapes behind.  Many of the passengers cruising on
 662 spaceship earth would find their lonely journey eased with video
 663 connections, news, and information gifts exchanged with those at home.
 665 Moving remittances (job wages sent home) between countries is difficult
 666 and costly with traditional services like Western Union and Moneygram,
 667 with fees taking as much as a 10\% bite of the transfer \cite{cryptocurrency}. 
 668 Some guest workers use Bitcoin to transfer
 669 money to ebanking services such as Kenya's M-Pesa, avoiding fees
 670 and risks.  The developing world, with its high percentage of
 671 ``un-banked" individuals, and high levels of corruption, may develop
 672 cashless economies long before complacent and wealthy countries do.
 674 All of this will cause massive cultural change.  We must not lose
 675 the values and wisdom of the past in our headlong rush to the future.
 676 In particular, young and educated people are ignoring their poor and
 677 illiterate elders, especially damaging to traditional elder-dominated
 678 societies \cite{crisis}.  An elder can verbally dictate her memories
 679 and values over voice uplink to server-sky storage,
 680 producing thousands of hours of transcriptions, available forever to
 681 her descendants, ethnologists, and historians.  When her callow children
 682 grow old and wise, they will treasure this storehouse of cultural
 683 knowledge, as will their distant descendants.  One poor village elder
 684 can leave a more permanent legacy than the kings of the ancient past.
 686 Some elders claim  ``I am too old to learn to read".  
 687 Many Guatemalans are enthusiastic f\'{u}tbol (soccer) fans, like many
 688 in India love cricket. 
 689 Adults watching sports on smart phones or tablets can choose
 690 ``education enhanced-sports",
 691 providing game information enhancements involving letters,
 692 then simple text, growing towards more complex text.
 693 An adult version of Sesame Street, with an important difference:
 694 each personal channel can individually adapt to the progress
 695 of the learning reader,
 696 and connect their lessons to those of their friends and neighbors,
 697 strengthening friendships and community while building literacy. 
 698 Machines are patient - if a new reader needs ten years to
 699 learn, they will be guided at a comfortable rate.
 701 Education designers can observe individual progress, and evolve
 702 better teaching software.  The 21st century will progress beyond
 703 universal literacy to continuous learning.  As new inventions
 704 emerge ever faster from a world full of new inventors,
 705 new teaching methods developed for adult literacy will help
 706 train everyone to master those new inventions and take control
 707 of their technological environment.
 709 \section{Creating Entreprenuers}
 711 Creative, newly educated server sky clients will become active
 712 providers of local and global content and services.  A farmer could
 713 tend her crops during the day, and sell her harvest on the Chicago
 714 Mercantile Exchange at night.  Her brother could drive a robot
 715 tractor for a farmer in Iowa.  Her sister could teach Kenyan
 716 schoolchildren.  And next year, they can run businesses employing
 717 hundreds of people around the world to do the same. 
 718 Work globally, live locally.
 720 It is an accident of history that computers are programmed with text;
 721 Inca quipu, Mayan and old world weaving, and Jacquard machine-woven
 722 brocades were designed and coded visually and tactually.  Programs
 723 may be created, compiled, and evaluated with other sensibilities;
 724 weaving a \emph{huipul} garment or hoeing a weed in a \emph{milpa}
 725 cornfield requires preception and skill, which may be transferrable
 726 to the creation of software and the visual presentation of information.  
 727 With the right interfaces, the corn farmers of the past may become the
 728 information farmers of the future.
 730 New income can be invested in thinsat hardware.  A thinsat might
 731 cost \$100 to build and launch, affordable by families or village
 732 cooperatives.  Thinsats can be collateral for loans.  When a strong,
 733 protected international market develops, this may be the first
 734 opportunity many people have to become investors and property owners. 
 736 Peruvian economist Hernando De Soto \cite{desoto} offers evidence
 737 that property rights in land and houses foster economic development,
 738 providing collateral for loans that purchase materials and tools
 739 to start new businesses.
 740 Individual server sky thinsats are depreciating capital goods, but
 741 are highly fungible and reusable during their functional lifetime. 
 742 When thinsat cost drops below \$100, even the poorest families can
 743 afford a ``piece of the action".  With proper community safeguards,
 744 and development environments usable by the uneducated but persistent,
 745 those families can develop their ``information farms" into valuable
 746 properties in the server sky information economy.
 748 Thinsat arrays can be international cooperatives.  Since different
 749 regions desire different content, ``regional" thinsats will source
 750 content to the rest of the array, which will synchronize the packets
 751 and send them to an owner's customers below as the array passes
 752 overhead.  If the rules and operation of a coop are not to an owner's
 753 liking, she can migrate her thinsat to a nearby array - or simply
 754 swap content and ownership with another owner in that other array.  
 756 \section{Three Billion New Researchers}
 758 Today, ecotourists travel the world searching for nature,
 759 while professional scientists travel to gather data. 
 760 Instead of travelers burning megatons of jet fuel and trampling
 761 wildlife underfoot,
 762 local people can place thousands of cameras and sensors in the
 763 wild places near their villages, observing nature without disturbing it. 
 764 Villagers selling data from an acre of forest can produce more annual
 765 revenue than one-time lumbering, or turning jungle into desert to get
 766 at the minerals underneath.
 768 But people can do more than maintain sensors.  We will need more minds
 769 than ever to interpret this flood of data, choosing what to gather next,
 770 finding and understanding patterns, and explaining those patterns
 771 to others.  Beyond literacy, we should develop a universal ethos of
 772 observational science, so that everyone learns what to look for, and why.  
 774 In the near term, we can use Server Sky to enhance the scientific
 775 and educational potential of existing tropical universities.   
 776 Remote education programs can be delivered nationwide and worldwide,
 777 with computer-assisted speech translation to regional and global
 778 languages.  We can connect resource-and-equipment-poor researchers
 779 in these universities to world-class labs elsewhere, stretching
 780 limited budgets and fostering international collaboration.
 782 Remote submersibles in the tropical ocean and satellites in space can be
 783 controlled via server sky arrays overhead.  One very exciting possibility
 784 is controlling small experiments directly on the International Space 
 785 Station (ISS), collecting vast amounts of experimental data for analysis
 786 in Server Sky arrays.  ISS is continuously visible from a large swath
 787 of the Server Sky constellation, far more visibility due to its altitude
 788 and the lack of atmospheric attenuation.  Someday, thousands of server
 789 sky arrays can provide petabit-per-second bandwidth to ISS and its 
 790 successors, using frequencies near 60 GHz, and precisely focused beams
 791 that do not penetrate the atmosphere. 
 792 This bandwidth, the automation it supports,
 793 and the torrent of data it can return,
 794 can enable many researchers to run millions
 795 of small experiments simultaneously, 24 hours a day.
 797 Developing world research institutions will have the resources to
 798 join their wealthy peers, releasing a flood of new space science
 799 accomplishments and discoveries.  Every country will become a space
 800 power, and the International Space Station will become truly
 801 international, the world's largest and most inclusive research center.
 803 \section{Serving the Future}
 805 Human prosperity will no longer be a zero sum game, played at the
 806 expense of nature.  Indeed, as good stewards and creative inventors,
 807 with doomsday pushed beyond the foreseeable future, we can help
 808 nature grow richer and more diverse than it has ever been during
 809 the long history of life.  Information is power,  and exawatts of
 810 off-Earth power can become information products that serve all of
 811 nature.  Humankind can become wealthy and smart enough to become
 812 nature's collaborators, not merely her cruel and ignorant destroyers.
 814 Server sky arrays will, like foraging ants serving their queen,
 815 serve and protect the human societies on Earth that gave birth to them.
 816 Myrmecologist (ant expert) Edward O. Wilson writes:
 817 \emph{``Laid before us are new options scarcely dreamed of in earlier ages.
 818 They empower us to address the greatest goal of all time,
 819 the unity of the human race.''} \cite{Wilson2}. 
 821 Server sky can be a first step towards opening the
 822 rest of the solar system, and beyond.
 823 Intelligence, mind and machine, can build gardens of life in space,
 824 and someday connect earth life to the stars.
 826 Wilson again: \emph{``Someday, perhaps in this century, we, or much
 827 more likely our robots, will visit these places in search of life.
 828 We must go and we will go, I believe, because the collective human
 829 mind shrivels without frontiers.  The longing for odysseys and far
 830 away adventure is in our genes.''}
 832 The authors of this paper are still discovering new opportunities
 833 for server sky, and for information resources provided from space,
 834 by developing world creators, for the world.  We hope
 835 GHTC2015 will connect us with innovators from around
 836 the world, who will suggest more improvements and opportunities. 
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1000 \end{thebibliography}
1002 \vspace{2mm}
1003 ghtc2015.tex / KHL / 2015 June 3 / 2340 PDT.  \emph{Note to reviewers:}
1004 During the draft review and editing of this paper, the pdf and the LaTeX
1005 file will be available and updated at
1007 \end{document}

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