(I expect it will take more energy to put into orbit than the solar panels will accumulate over their lifetime.)
This is answered in the wiki: it takes roughly 2 months for a 3 gram thinsat to pay for the launch energy if it gets 4 watts, assuming 32% fuel manufacturing efficiency. The blackbody cooling is a significant reason as well. (Note: The 7 gram estimate given in the paper is slightly out of date -- the wiki describes 3 grams as the current target.)
What about memory? Bits being flipped by cosmic radiation is an issue on Earth; I imagine it must be more significant in space, and annealing won't fix that.
This is discussed as well, albeit briefly:
"The most radiation sensitive components are likely to be the flash memory. These incorporate error correction, but software error correction and frequent rewrites may be necessary to correct for radiation-induced charges. Some errors may need to be restored from caches on other thinsats partway around the orbit."
So it looks like he is thinking of a combination of redundancy and memory-repair algorithms.
As well, periodic annealing eventually results in your circuit no longer being a circuit, as the wires and capacitors have diffused until there's a short. You might be able to build these with a large enough heat budget that you can get a reasonable number of reheats out of it, but the lifespan is going to be fairly short.
This is also somewhat mentioned in the manufacturing section, where the concern is that differentials in material thermal properties could cause damage.
"The vast bulk of the material, and the largest pieces of of the thinsat, will be laminated engineering glass and metal. Since the thinsat undergoes wide temperature changes when it passes in and out of shadow, or undegoes thermal annealing, it will be more survivable if the glass can match silicon's 2.6E-6/Kelvin coefficient of thermal expansion (CTE). Metals have very high CTEs, while SiO2 has a very low CTE, so slotted metal wires with SiO2 in the gaps is one way to make a "material" that is both conductive and has the same CTE as silicon."
Also there is the fact the wires and capacitors are going to be all two dimensional in nature. My guess is that not all of the same assumptions necessarily apply in this situation as do for three dimensional wires and capacitors.
Thanks for the more direct links. I'm starting to update in favor of this working, but I'm still bothered by the amount of speculative tech involved. (If we're going to use new RAM coming out in a few years that'll be cheaper/faster/less error prone, our comparison needs to not be to current tech / costs, but to tech / costs after that new RAM has been integrated.)
I suspect it'll be easier to replace silicon than to get the rest of the thinsat to match the thermal expansion of silicon, but that suspicion is rooted in professor friends who do semiconductor ...
The following is intended as 1) request for specific criticisms regarding the value of time investment on this project, and 2) pending favorable answer to this, a request for further involvement from qualified individuals. It is not intended as a random piece of interesting pop-sci, despite the subject matter, but as a volunteer opportunity.
Server Sky is a an engineering proposal to place thousands (eventually millions) of micron-thin satellites into medium orbit around the earth in the near term. It is being put forth by Keith Lofstrom, the inventor of the Launch Loop.
Abstract from the 2009 paper:
Links:
Papers and Presentations
Slide Show
Wiki Main Page
Help Wanted
Mailing List
Some mildly negative evidence to start with: I have already had a satellite scientist tell me that this seems unlikely to work. Avoiding space debris and Kessler Syndrome, radio communications difficulties (especially uplink), and the need for precise synchronization are the obstacles he stressed as significant. He did not seem to have studied the proposal closely, but this at least tells us to be careful where to set our priors.
On the other hand, it appears Keith has given these problems a lot of thought already, and solutions can probably be worked out. The thinsats would have optical thrusters (small solar sails) and would thus be able to move themselves and each other around; defective ones could be collected for disposal without mounting an expensive retrieval mission, and the thrusters would also help avoid things in the first place. Furthermore the zone chosen (the m288 orbit) is relatively unused, so collisions with other satellites are unlikely. Also the satellites have powerful radar capabilities, which should lead to more easily detecting and eliminating space junk.
For the communications problem, the idea is to use three dimensional phased arrays of thinsats -- basically a bunch of satellites in a large block working in unison to generate a specific signal, behaving as if they were a much larger antenna. This is tricky and requires precision timing and exact distance information. The array's physical configuration will need to be randomized (or perhaps arranged according to an optimized pattern) in order to prevent grating lobes, a problem with interference patterns that is common with phased arrays. They would link with GPS and each other by radio on multiple bands to achieve "micron-precision thinsat location and orientation within the array".
According to the wiki, the most likely technical show-stopper (which makes sense given the fact that m288 is outside of the inner Van Allen belt) is radiation damage. Proposed fixes include periodic annealing (heating the circuit with a heating element) to repair the damage, and the use of radiation-resistant materials for circuitry.
Has anyone else here researched this idea, or have relevant knowledge? It seems like a great potential source of computing power for AI research, mind uploads, and so forth, but also for all those mundane, highly lucrative near term demands like web hosting and distributed business infrastructures.
From an altruistic standpoint, this kind of system could reduce poverty and increase equitable distribution of computing resources. It could also make solving hard scientific problems like aging and cryopreservation easier, and pave the road to solar power satellites. As it scales, it should also create demand (as well as available funding and processing power) for Launch Loop construction, or some other similarly low-cost form of space travel.
Value of information as to whether it can work or not therefore appears to be extremely high, something I think is crucial for a rationalist project. If it can work, the value of taking productive action (leadership, getting it funded, working out the problems, etc.) should be correspondingly high as well.
Update: Keith Lofstrom has responded on the wiki to the questions raised by the satellite scientist.
Note: Not all aspects of the project have complete descriptions yet, but there are answers to a lot of questions in the wiki.
Here is a summary list of questions raised and answers so far:
In his reply to the comments on Brin's post, Keith Lofstrom mentions using obsolete sats as ballast for much thinner sats that would be added to the arrays as the manufacturing process improves. Obsolete sats would not stay in use for long.
Ping times are going to be limited (70ms or so), and worse than you can theoretically get with a fat pipe (42ms), but it is still much better than you get with GEO (250+ ms). This is bad for high frequency trading, but fine for (parallelizable) number crunching and most other practical purposes.
It takes roughly 2 months for a 3 gram thinsat to pay for the launch energy if it gets 4 watts, assuming 32% fuel manufacturing efficiency. Blackbody cooling is another benefit.
Flash memory is acknowledged to be the most radiation sensitive component of the satellite. The solution would involve extensive error correction software and caching on multiple satellites.
Circuits will be manufactured as two dimensional planes, which don't short as easily. Another significant engineering challenge: Thermal properties in the glass will need to be matched with the silicon and wires (for example, slotted wiring with silicon dioxide between the gaps) to prevent circuit damage. Per Vanvier, it may be less expensive to replace silicon with other materials for this purpose.
Efficient power/cooling, increased communications, overall scalability, relative lack of environmental impact.
Yet to be answered:
Insightful comments: