(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 (Note: The 7 gram estimate given in the paper is slightly out of date—the wiki describes 3 grams as the current target.)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.
“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 research, not industry, so the costs there might be way higher.
This page was the only thing I could find on the economics (he mentions elsewhere he wants to keep the business plan private).
Another thing to think about: have we sent up stacked things to space like this before, and managed to disengage them from each other? I believe a number of solar sails have failed to unfold correctly, and so there might be a similar problem here. Thankfully, they don’t need to be attached to each other, like solar sails do, but now it’s a problem if they do get attached to each other, and I don’t know which of those is a more difficult engineering problem. (The only description I saw of that on the wiki was ‘peeling’ them apart.)
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.)
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.
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 research, not industry, so the costs there might be way higher.
This page was the only thing I could find on the economics (he mentions elsewhere he wants to keep the business plan private).
Another thing to think about: have we sent up stacked things to space like this before, and managed to disengage them from each other? I believe a number of solar sails have failed to unfold correctly, and so there might be a similar problem here. Thankfully, they don’t need to be attached to each other, like solar sails do, but now it’s a problem if they do get attached to each other, and I don’t know which of those is a more difficult engineering problem. (The only description I saw of that on the wiki was ‘peeling’ them apart.)