Quote from: pagheca on 02/08/2015 07:31 amMost of those sats will be idling while flying over inhabited areas, while a few will be struggling for a few minutes with zillions of high-demanding users. I can't see a sat internet network siding ground based competitors. I would rather see sats network backing up fibers and radio ones in semi-deserted areas. That would make price very high.Those sats over pacific/atlantic are not idling, but serve as the backbone/transocean bridge for the "over land" sats. And if you think about how many paths via different sets of sats you can have over pacific (assuming the direct links can be established between sats orbiting not adjacent to each other), you realize Elon's desire to compete with transatlantic fiber...
Most of those sats will be idling while flying over inhabited areas, while a few will be struggling for a few minutes with zillions of high-demanding users. I can't see a sat internet network siding ground based competitors. I would rather see sats network backing up fibers and radio ones in semi-deserted areas. That would make price very high.
It seems like a few relatively simple steps can improve tolerance quite a bit. For example choosing a SOI process for the chip (which many fabs use anyway) seems to help. The avionics would want to do more than the communications payload.[...]4000 satellites with multiple chips is getting to the sort of scale where an ASIC makes sense, this is plausible. You can build multiple cores onto a single chip and have them do their votes on the chip. Still need multiple chips but I suspect the part count can be reduced compared to the current Dragon system.
The chips are tiny and very cheap. This is exactly the kind of thing where SpaceX can leverage its cheap launch costs -- just use cheap off-the-shelf chips and pay for the extra mass it takes to have lots of redundant chips, shielding, or both.
Quote from: ArbitraryConstant on 02/09/2015 02:33 amIt seems like a few relatively simple steps can improve tolerance quite a bit. For example choosing a SOI process for the chip (which many fabs use anyway) seems to help. The avionics would want to do more than the communications payload.[...]4000 satellites with multiple chips is getting to the sort of scale where an ASIC makes sense, this is plausible. You can build multiple cores onto a single chip and have them do their votes on the chip. Still need multiple chips but I suspect the part count can be reduced compared to the current Dragon system.I think you are greatly underestimating the cost of doing an ASIC comparable to off-the shelf multi-processor DSP chips. An enormous amount of engineering goes into optimizing a chip like that. 4000 is a tiny, tiny volume for an ASIC. And it's not just the cost (maybe $100 million to design an ASIC like that), it's the time it takes. If they have to build a chip design team from scratch, don't expect the first production chips for 3 years. There's also the risk -- they might not find out until 2 years in that their chip won't have the performance they projected. Meanwhile, TI comes out with a new, improved multi-chip DSP that beats the ASIC.The chips are tiny and very cheap. This is exactly the kind of thing where SpaceX can leverage its cheap launch costs -- just use cheap off-the-shelf chips and pay for the extra mass it takes to have lots of redundant chips, shielding, or both.
I think you are greatly underestimating the cost of doing an ASIC comparable to off-the shelf multi-processor DSP chips.
So the cost does depend on how much reuse you can have, and therefore how much new work is required, and how much of it there is to do. But $100M is much too high, probably double.
I would think they would need make in excess of a million to make the decision to go with an ASIC, prior to that any recent FPGA would do (assuming they are robust enough).
But the volume will be much higher than 4000. They'll have at a very minimum 3 times that due to their redundancy/reliability strategy, and if you add in multiple chips to handle the workload, you easily could be talking over a dozen chips per satellite. Dragon uses dozens of chips, for instance.
Quote from: JamesH on 02/11/2015 03:03 pmI would think they would need make in excess of a million to make the decision to go with an ASIC, prior to that any recent FPGA would do (assuming they are robust enough).Considering there probably isn't a chip scale phased array solution that meets their needs, that seems like a fairly easy number for them to hit (not that the development effort will be easy!). They're going to need billions of phased array elements, total, for the constellation and billions more for the ground terminals.
Quote from: Robotbeat on 02/11/2015 11:02 pmQuote from: JamesH on 02/11/2015 03:03 pmI would think they would need make in excess of a million to make the decision to go with an ASIC, prior to that any recent FPGA would do (assuming they are robust enough).Considering there probably isn't a chip scale phased array solution that meets their needs, that seems like a fairly easy number for them to hit (not that the development effort will be easy!). They're going to need billions of phased array elements, total, for the constellation and billions more for the ground terminals.Slightly different from the FPGA/ASIC stuff though - this is the transmission side rather than the processing side.
There is one thing I am positively certain about. They won't be using commercially available space grade arrays unless the producers find a way to sell them a huge lot cheaper than they do now.
Quote from: guckyfan on 02/06/2015 12:23 pmThere is one thing I am positively certain about. They won't be using commercially available space grade arrays unless the producers find a way to sell them a huge lot cheaper than they do now.What is the price?
Going into the future a bit does anyone expect non solar power to be used on the sats around Mars? It seems a perfect time to use an ASRG rather than Solar.
Quote from: BobHk on 02/14/2015 02:05 pmGoing into the future a bit does anyone expect non solar power to be used on the sats around Mars? It seems a perfect time to use an ASRG rather than Solar.Europa Clipper is being baselined with solar power... Jupiter is at 5.2AU. Mars is at 1.5AU.Inverse square law... Mars solar = 12x Jupiter solar.
18 square meter solar panels are a bit hard to repair on something around Mars if you want them to work for years eh?
Which was a cost decision....
Quote from: BobHk on 02/14/2015 02:32 pmWhich was a cost decision....If this is meant to suggest SpaceX won't make cost decisions for Mars satellites I think you're wrong.Quote from: BobHk on 02/14/2015 02:32 pm18 square meter solar panels are a bit hard to repair on something around Mars if you want them to work for years eh?No harder than Juno's 24 m2 panels around Jupiter, or any of the current Mars orbiters.