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| Silicon circuits, solar cells, interconnect, are essentially two-dimensional systems. The horizontal dimensions of an integrated circuit die may be measured in millimeters, but all the important action occurs within a few microns of the top surface. Indeed, modern IC die are thinned to increase thermal conductivity and reduce package height. The target thickness for this version 0.3 design is 50 microns, but much thinner silicon wafers are used in current production, often loosely bonded to a thicker "handle" wafer for ease of processing. The thinsat will likely be built and tested with a thick handle wafer attached, but the handle wafer will be removed when the thinsat is attached to the deployment stack. | Silicon circuits, solar cells, interconnect, are essentially two-dimensional systems. The horizontal dimensions of an integrated circuit die may be measured in millimeters, but all the important action occurs within a few microns of the top surface. Indeed, modern IC die are thinned to increase thermal conductivity and reduce package height. The target thickness for this version 0.4 design is 75μm, mostly aluminum, thicker than previous versions to insure orbit stability against [[LightOrbit|light pressure perturbations.]] |
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| ||[[attachment:serversatV3a.png|{{attachment:serversatV3a_488.png }}]]||Thinsats are thinned glass sheet covered with very thin Indium Phosphide solar cells and combined with thinned integrated circuit chips, radios with antennas, and three disks of electrochromic material that act as electrically switched mirrors/windows. The glass disk is thinned to reduce weight, and the chips are thinned to match. Reduced weight reduces launch cost and results in a more effective solar sail. The current thickness target is 50 microns, though production glass is often thinned to as little as 30 microns for some applications. 50 micron thick glass is very flexible, and can be rolled to diameters less than a centimeter without breaking. It is not unreasonable to assume that future thinsats can be as thin as 1 to 5 microns, weighing less than a gram.<<BR>><<BR>>Everything is coplanar - the chips are in cavities in the glass, and power is fed horizontally from the solar cell. If a portion of the cell shorts out or is otherwise damaged, the remaining circuitry should still work<<BR>><<BR>>''This is a front view - from the side, a thinsat is thinner than a piece of paper. '' [[ attachment:serversatV3a.png | full size drawing | target="_blank" ]]|| | ||{{attachment:ThinsatV4_488.png }}||Back side of a thinsat, facing the dark, not the sun.<<BR>><<BR>>The 5 gram '''thinsat''' substrate is two 35μm thick layers of aluminum foil (main power and ground), embossed with die cavities, antenna slots, and die bonding cavities. The foil is selectively oxidized perhaps a micron deep; the front surface foil is patterned in the center area with a molybdenum, indium phosphide, and AZO coatings to form solar cells. The circular corners get a WO₃/Alumina/Ni(OH)₂/AZO stack for the electrochromic thrusters.<<BR>><<BR>>'''This is a drawing of the back side of the thinsat.''' The back side foil gets radios(red chips), processors (tan chips), frequency setting resonators(blue), more solar cells (light blue), and wiring (gray), and an overcoat of black carbon. Like the front side, the back side corners get electrochromic thrusters [[brown chips]], exposed if a collision puts the thinsat into a pitch or yaw spin.[[ attachment:Thinsat_V4.png | full size drawing | target="_blank" ]]|| |
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| If the solar cell at end-of-life is 15% efficient, then the solar cell will produce 3.5 watts peak, less during maneuvering, and nothing during eclipse. | If the 180cm^2^ of solar cell at end-of-life is 16% efficient, then the solar cell will produce 3.9 watts peak. This will vary with night side maneuvering (for light pollution control) and eclipse, producing 2.6 watts average at EOL. |
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| || || mass || 3e-3 || kg || || || || thickness || 5e-5 || m || || || || density || 2.5e+3 || kg/m^3^ || average for aluminum || |
|| || mass || 5e-3 || kg || || || || thickness || 75e-6 || m || || || || density || 2.7e+3 || kg/m^3^ || average for aluminum || |
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| || || moment || 8.8e-6 || kg-m^2^ || pitch/yaw inertia crude WAG || | || || moment || 1.4e-6 || kg-m^2^ || pitch/yaw inertia crude WAG || |
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| || || acceleration || 4.19e-5 || m/s^2^ || average, half thrust || | || || acceleration || 2.51e-5 || m/s^2^ || average, half thrust || |
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| ||$ \dot v $ || delta accel. ||'''2.95e-6'''|| m/s^2^ || relative acceleration with 3 thrusters || | ||$ \dot v $ || delta accel. ||'''1.06e-6'''|| m/s^2^ || relative acceleration with 3 thrusters || |
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| ||$\large\ddot\theta$|| angular accel. || 6e-5 || rad/s^2^ || not sure about moment of inertia || | ||$\large\ddot\theta$|| angular accel. || 3.8e-5 || rad/s^2^ || not sure about moment of inertia || |
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| ||$\large\ddot\theta/\omega^2$|| norm. accel. || 1.1E4 || - || normalized to m288 (tilt stability) || | ||$\large\ddot\theta/\omega^2$|| norm. accel. || 7E3 || - || normalized to m288 (tilt stability) || |
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| ||<:-5> rotational moment 9.6e-6 for triangle, 5.8e-6 for hexagon, assume 8.8e-6, needs accurate calculation || |
||<:-5>rotational moment 1.6e-5 for triangle, 9.5e-6 for hexagon, estimate 1.4e-5, needs accurate calculation|| |
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| '''Electronics:''' A thinsat used for database and web service may need as much as a terabit or more of flash memory (note - databases will be distributed over many thinsats). That will be about 4 by 4 centimeters of silicon area. Computational thinsats will probably need less. While some high-performance processors and chipsets use hundreds of watts, Giga-instruction-per-second level machines can get by with far less. [[ http://wiki.keithl.com/index.cgi?SL5Alix | Here ]] is a complete 4 watt system (including IO and power conversion losses) with 990 bogomips performance. Optimized thinsats should be able to do far better. | '''Electronics:''' A thinsat used for database and web service may need as much as a terabit or more of flash memory (note - databases will be distributed over many thinsats). That will be about 4 by 4 centimeters of silicon area, distributed in hundreds of pieces. Computational thinsats will probably need less. While some high-performance processors and chipsets use hundreds of watts, Giga-instruction-per-second level machines can get by with far less. [[ http://wiki.keithl.com/index.cgi?SL5Alix | Here ]] is a complete 4 watt system (including IO and power conversion losses) with 990 bogomips performance. Optimized thinsats should be able to do far better. |
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| Because the sthinsat is extremely thin, some common electronic components cannot be used: foil-wound electrolytic capacitors, cored inductors, etc. Bypass capacitors can be made thin, but it is better to keep peak impulse currents low. Some components such as crystal frequency standards may be replaced by surface acoustic wave (SAW) devices. However, other devices such as radios can be operated at low voltages and low impedances, and if some devices need higher voltages at trickles of current they can be powered with capacitive charge pumps. At microwave frequencies, resonators can also be made with striplines and other components. The potential of solid state integrated phased array lasers needs to be investigated for communications, small debris location and control, power transmission and active optical propulsion. | Because the thinsat is extremely thin, some common electronic components cannot be used: foil-wound electrolytic capacitors, cored inductors, etc. Bypass capacitors can be made thin, but it is better to keep peak impulse currents low. Some components such as crystal frequency standards may be replaced by surface acoustic wave (SAW) devices. However, other devices such as radios can be operated at low voltages and low impedances, and if some devices need higher voltages at trickles of current they can be powered with capacitive charge pumps. At microwave frequencies, resonators can also be made with striplines and other components. The potential of solid state integrated phased array lasers needs to be investigated for communications, small debris location and control, power transmission and active optical propulsion. |
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| The thinsat will use a small array of slot antenna radios (many more than the 14 shown) to communicate with neighbors in the array, with other arrays, and with the ground. Besides communication, thinsats will measure radio propagation time to neighbors to accurately compute spacing and orientation, with additional location information provided by other arrays, ground stations, and possibly GPS. Multiple bands will be used, with frequencies that can penetrate atmosphere and clouds used for the downlinks, and other atmosphere-opaque bands used for thinsat to thinsat communication. The thinsats will ''not'' have dishes, but will act together as a phased array antenna. Given the wide array spacing, there will be many spurious lobes, but it will still be possible to compute solutions allowing separate beams to many ground stations, far more than a traditional dish-and-transponder comsat. While each thinsat may only dedicate one or two watts to the ground transmitters, the sum of thousands of transmitters will allow quite a lot of power for each beam. With the thinsat in a 4 hour orbit, it will be 7 times closer than a geosynchronous comsat, so there will be a 50x advantage in beam power and ground spot area. Round trip ping time will be 70 milliseconds, less than U.S. transcontinental ping time through optical fiber. | The thinsat is patterned with slot antennas and transmitters to communicate with neighbors in the array, with other arrays, and with the ground. Besides communication, thinsats will measure radio propagation time to neighbors to accurately compute spacing and orientation, with additional location information provided by other arrays, ground stations, and possibly GPS. Multiple bands will be used, with frequencies that can penetrate atmosphere and clouds used for the downlinks, and other atmosphere-opaque bands used for thinsat to thinsat communication. The thinsats will ''not'' have dishes, but will act together as a phased array antenna. Thinsats are widely spaced in a rotating geodesic array, although the vast majority of the radio energy is scattered over a 100km ground spot, only the main lobe is high power. |
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| ||'''Optical thrusters''' are a sandwich of patterned, transparent indium tin oxide conductors around a solid state electrochromic material. The conductors are separately controlled strips to permit partial functionality in spite of top to bottom shorts. For more about electrochromic thrusters, see [[http://en.wikipedia.org/wiki/Electrochromism|electrochromic materials]] ||{{attachment:thruster1.png|}}|| | By superposition, the array can send different high bandwidth signals to many closely or widely spaced ground stations simultaneously, far more than a traditional dish-and-transponder comsat. While each thinsat may only dedicate a few milliwatts to the ground transmitters, the sum of hundreds of thousands of transmitters will produce high power, high bandwidth beams. With the thinsat in a 4 hour orbit (repeating overhead 5 times a day), it will be 7 times closer than a geosynchronous comsat, so there will be a 50x advantage in beam power and ground spot area. Round trip ping time will be 70 milliseconds, less than U.S. transcontinental ping time through optical fiber. |
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| Three optical thrusters are shown, which perform pitch and yaw control for the thinsat. Normally, the thinsat is pointed straight at the sun, and the thrusters are electrically stimulated into transparency. If one or two of the disks are unstimulated, they turn reflective, and produce about half a nanoNewton of thrust. This is enough to slowly rotate the disk. If all the thrusters are stimulated, this increases centerline thrust. Again, the thrust difference is not much, but it is enough to keep an array of thinsats on station relative to each other. | Three optical thrusters perform pitch and yaw control for the thinsat. Normally, the thinsat is pointed straight at the sun, and the thrusters are electrically stimulated between black and reflective. The difference between the states is about half a nanoNewton of thrust. This is enough to slowly pitch or roll the disk. If all the thrusters are stimulated, this increases centerline thrust. Again, the thrust difference is small, but it is enough to maintain relative spacing of thinsats in an array to sub-micrometer accuracy. |
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| In orbit, the stresses are very small; the disk is relatively rigid by comparison. Maneuvers such as rotation and acceleration will take hours to days; microgee forces are involved. The main stresses on the disk will be from thermal contraction. When exposed to sunlight, the disk will be at 300K; as it passes into earth shadow, it will quickly cool to 150K or less, heated only by the infrared radiation from the night side of the earth. The system is mostly silicon, with some glass and metal. Interconnect metal layers should be designed with strain relief, and the whole metal and insulator stack should have about the same average thermal coefficient as the silicon. | In orbit, the stresses are very small; the disk is relatively rigid by comparison. Maneuvers such as rotation and acceleration will take hours to days; microgee accelerations are involved. The main stresses on the disk will be from thermal contraction. When exposed to sunlight, the disk will be at 300K; as it passes into earth shadow, it will quickly cool to 150K or less, heated only by the infrared radiation from the night side of the earth. The thinsat is mostly aluminum. Interconnect metal layers should be designed with strain relief, and the whole metal and insulator stack should be designed for the same average thermal coefficient. |
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| Thinsats are designed to have uniform thickness, so they can be stacked in cylinders for launch. Some kind of very thin separator will be needed, or the thinsats may stick together with vacuum welding or vander Waals forces. If a thinsat plus separators is 60 microns thick, then a stack of 20,000 3 gram thinsats will be 1.1 meters (43 inches) tall and weigh 60 kilograms (130 pounds). | Thinsats aare stacked in cylinders for launch. Some kind of very thin separator may be needed, or the thinsats may stick together with vacuum welding or vander Waals forces. If a thinsat plus separators is 100 microns thick, then a stack of 10,000 5 gram thinsats will be 1 meter (39 inches) tall and weigh 50 kilograms (110 pounds). |
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| kilograms (10,800 pounds) and has a 14kW array, launched by an Ariane 5 ECA, which can put 10,500 kg of satellite and apogee kick motor into a geosynchronous transfer orbit. The planned m288 thinsat orbit is lower; a larger payload is possible. 4200 kilograms is 1,400,000 thinsats and 5.6 megawatts of electricity. Thus, a thinsat array can produce more than 400 times the power (and communication capacity) of typical comsats. Note: This is version 0.3 of the serversat. Earlier versions were thicker and wider, and made from silicon rather than silicon-matched glass. |
kilograms (10,800 pounds) and has a 14kW array, launched by an Ariane 5 ECA, which can put 10,500 kg of satellite and apogee kick motor into a geosynchronous transfer orbit. The planned m288 thinsat orbit is lower; a larger payload is possible. 10,000 kilograms is 2 million thinsats, producing an average of 5 megawatts of electricity. Thus, a thinsat array can produce more than 300 times the power (and communication capacity) of typical comsats. |
Thinsat Details
Silicon circuits, solar cells, interconnect, are essentially two-dimensional systems. The horizontal dimensions of an integrated circuit die may be measured in millimeters, but all the important action occurs within a few microns of the top surface. Indeed, modern IC die are thinned to increase thermal conductivity and reduce package height. The target thickness for this version 0.4 design is 75μm, mostly aluminum, thicker than previous versions to insure orbit stability against light pressure perturbations.
|
Back side of a thinsat, facing the dark, not the sun. |
If the 180cm2 of solar cell at end-of-life is 16% efficient, then the solar cell will produce 3.9 watts peak. This will vary with night side maneuvering (for light pollution control) and eclipse, producing 2.6 watts average at EOL.
Characteristics
Server Sky satellite parameters |
notes |
|||
|
mass |
5e-3 |
kg |
|
|
thickness |
75e-6 |
m |
|
|
density |
2.7e+3 |
kg/m3 |
average for aluminum |
|
volume |
1.2e-6 |
m3 |
|
|
area |
2.40e-2 |
m2 |
|
|
length |
0.184 |
m |
rounded thruster top to flat bottom |
|
center of mass |
6.98e-2 |
m |
above flat bottom |
|
moment |
1.4e-6 |
kg-m2 |
pitch/yaw inertia crude WAG |
|
black light pr |
5e-6 |
Pa |
albedo 0.10, 1361W/m2 |
|
50% light pr |
6.5e-6 |
Pa |
half black, half reflecting |
|
refl light pr |
8e-6 |
Pa |
albedo 0.76, 1361W/m2 |
|
thruster diam. |
0.05 |
m |
|
|
thruster area |
5.89e-3 |
m2 |
3 thrusters |
|
core area |
1.81e-2 |
m2 |
total area minus thrusters |
|
core minus slots |
1.75e-2 |
m2 |
transparent for slot antennas, WAG |
|
min thruster F |
2.95e-8 |
N |
3 thrusters albedo 0.10 0% thrust |
|
avg thruster F |
3.83e-8 |
N |
3 thrusters half thrust |
|
min thruster F |
4.71e-8 |
N |
3 thrusters albedo 0.76 100% thrust |
|
core thrust |
8.75e-8 |
N |
average albedo 0.10 |
|
average thrust |
1.26e-7 |
N |
average, half thrust |
|
acceleration |
2.51e-5 |
m/s2 |
average, half thrust |
|
thruster deltaF |
8.83e-9 |
N |
half to min or half to max thrust |
\dot v |
delta accel. |
1.06e-6 |
m/s2 |
relative acceleration with 3 thrusters |
|
thruster arm |
8.95e-2 |
m |
thruster center - center of mass |
|
thruster moment |
5.27e-10 |
N-m |
one thruster at 100%, two at 25% |
\large\ddot\theta |
angular accel. |
3.8e-5 |
rad/s2 |
not sure about moment of inertia |
\large\omega |
m288 orbit |
7.2722e-5 |
rad/s |
m288 orbit angular frequency |
\large\ddot\theta/\omega^2 |
norm. accel. |
7E3 |
- |
normalized to m288 (tilt stability) |
tilt stability is a ratio of angular acceleration to tidal forces. It probably should be > 10 |
||||
all forces and accelerations for perpendicular sunlight, multiply by cosine if tilted |
||||
rotational moment 1.6e-5 for triangle, 9.5e-6 for hexagon, estimate 1.4e-5, needs accurate calculation |
||||
Electronics
Electronics: A thinsat used for database and web service may need as much as a terabit or more of flash memory (note - databases will be distributed over many thinsats). That will be about 4 by 4 centimeters of silicon area, distributed in hundreds of pieces. Computational thinsats will probably need less. While some high-performance processors and chipsets use hundreds of watts, Giga-instruction-per-second level machines can get by with far less. Here is a complete 4 watt system (including IO and power conversion losses) with 990 bogomips performance. Optimized thinsats should be able to do far better.
Because the thinsat is extremely thin, some common electronic components cannot be used: foil-wound electrolytic capacitors, cored inductors, etc. Bypass capacitors can be made thin, but it is better to keep peak impulse currents low. Some components such as crystal frequency standards may be replaced by surface acoustic wave (SAW) devices. However, other devices such as radios can be operated at low voltages and low impedances, and if some devices need higher voltages at trickles of current they can be powered with capacitive charge pumps. At microwave frequencies, resonators can also be made with striplines and other components. The potential of solid state integrated phased array lasers needs to be investigated for communications, small debris location and control, power transmission and active optical propulsion.
The thinsat is patterned with slot antennas and transmitters to communicate with neighbors in the array, with other arrays, and with the ground. Besides communication, thinsats will measure radio propagation time to neighbors to accurately compute spacing and orientation, with additional location information provided by other arrays, ground stations, and possibly GPS. Multiple bands will be used, with frequencies that can penetrate atmosphere and clouds used for the downlinks, and other atmosphere-opaque bands used for thinsat to thinsat communication. The thinsats will not have dishes, but will act together as a phased array antenna. Thinsats are widely spaced in a rotating geodesic array, although the vast majority of the radio energy is scattered over a 100km ground spot, only the main lobe is high power.
By superposition, the array can send different high bandwidth signals to many closely or widely spaced ground stations simultaneously, far more than a traditional dish-and-transponder comsat. While each thinsat may only dedicate a few milliwatts to the ground transmitters, the sum of hundreds of thousands of transmitters will produce high power, high bandwidth beams. With the thinsat in a 4 hour orbit (repeating overhead 5 times a day), it will be 7 times closer than a geosynchronous comsat, so there will be a 50x advantage in beam power and ground spot area. Round trip ping time will be 70 milliseconds, less than U.S. transcontinental ping time through optical fiber.
Three optical thrusters perform pitch and yaw control for the thinsat. Normally, the thinsat is pointed straight at the sun, and the thrusters are electrically stimulated between black and reflective. The difference between the states is about half a nanoNewton of thrust. This is enough to slowly pitch or roll the disk. If all the thrusters are stimulated, this increases centerline thrust. Again, the thrust difference is small, but it is enough to maintain relative spacing of thinsats in an array to sub-micrometer accuracy.
There is no direct way to control roll. However, the thinsat can be rolled by combinations of pitch and yaw.
In orbit, the stresses are very small; the disk is relatively rigid by comparison. Maneuvers such as rotation and acceleration will take hours to days; microgee accelerations are involved. The main stresses on the disk will be from thermal contraction. When exposed to sunlight, the disk will be at 300K; as it passes into earth shadow, it will quickly cool to 150K or less, heated only by the infrared radiation from the night side of the earth. The thinsat is mostly aluminum. Interconnect metal layers should be designed with strain relief, and the whole metal and insulator stack should be designed for the same average thermal coefficient.
Thinsats aare stacked in cylinders for launch. Some kind of very thin separator may be needed, or the thinsats may stick together with vacuum welding or vander Waals forces. If a thinsat plus separators is 100 microns thick, then a stack of 10,000 5 gram thinsats will be 1 meter (39 inches) tall and weigh 50 kilograms (110 pounds).
A typical modern geosynchronous communication satellite such as HotBird 9 weighs 4880 kilograms (10,800 pounds) and has a 14kW array, launched by an Ariane 5 ECA, which can put 10,500 kg of satellite and apogee kick motor into a geosynchronous transfer orbit. The planned m288 thinsat orbit is lower; a larger payload is possible. 10,000 kilograms is 2 million thinsats, producing an average of 5 megawatts of electricity. Thus, a thinsat array can produce more than 300 times the power (and communication capacity) of typical comsats.
Thinsat geometry.
L |
15.504 |
cm |
|
Center to center distance of thrusters |
R |
2.500 |
cm |
|
thruster radius |
H |
18.427 |
cm |
2 R + \sqrt{ 3 } L / 2 |
shortest dimension, "vertical" |
W |
20.504 |
cm |
2 R + L |
longest dimension, "horizontal" |
A_{t1} |
19.635 |
cm2 |
\pi R^2 |
area of one thinsat |
A |
240.000 |
cm2 |
A_{t1}+3LR+\sqrt{3} L^2 /4 |
whole thinsat area |
A_{t3} |
58.905 |
cm2 |
3 \pi R^2 |
area of three thinsat |
A_{core} |
181.095 |
cm2 |
A - A_{t3} |
core area of thinsat, minus thrusters |