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Big Hopes for Tiny Satellites
shelflife writes: "ST5, according to NASA, will usher in a new era of small, smart spacecraft. Why send a human into space when you can send a computer? And why send something almost as heavy as a UNIVAC if a laptop will do? Compact nanosatellites will have everything you'd want in a full-size, luxury satellite. They will have the attitudinal and navigational capabilities needed to maintain proper orbits, and they will be capable of complex, high-bandwidth communications functions."
This isn't entirely new. There were "microsats" flown in the 1980s, some sponsored by the Amateur Satellite Corp. (AMSAT), and some university sats like Webersat (from Utah).
With today's smaller and more powerful chips, of course, it's a lot easier to do more in a small package.
Solar radiation is an extremely serious problem for any computer in space. To be rad-hard, chips need to be made of silicon on sapphire, which means a $1 embedded processor suddenly costs twenty thousand dollars. This is not material cost, it's because the economies of scale in production of terrestrial processors are what drives the cost down. Nobody can afford sapphire RAM banks, and thus memories get a flipped bit per orbit, in general. The only way they keep working is that there is a "washing" process that scans memory and does ECC correction continuously. Shielding is simply too heavy to be practical (send up a lead-clad satellite, and your rocket becomes 10 times as large to boost the weight).
Because it's available in sapphire and is flight-proven, the microprocessor of choice for controlling satellites is the 1802. Remember the RCA Cosmac Elf? Most of you weren't born when that was a popular hobby computer
I was surprised to find that the Phase 3D satellite boots up with no ROM. Hardware loads RAM directly from a radio modem. They couldn't afford a ROM they could trust.
Heat is a problem, too. Heat sinks don't work so well without an atmosphere to carry away heat. You have to pipe heat around with heat-pipes filled with a phase-change gas, and then radiate the heat away.Bruce
Bruce Perens.
According to this page, ground based stations can track things down to 10 cm (about 4 inches). Admittedly they would be harder to see by an astronaut, but they typically aren't responsible for spotting the things visually. So long as people on the ground keep track of the satellites, it shouldn't be a problem.
Surrey's technologies are still pretty experimental and rely in some pretty difficult formation flying. Nanosats don't carry much in the way of tranceiving equipment and if you read the datasheets they carry uncooled CMOS cameras and basically are good for inspecing other spacecraft they're in formation with. Other formation flying ideas are lots of small birds with one or two tranceivers each that fly in formation and can output at least 10 watts PEP. You could have one sat with an uplink receiver that beams data to the rest of the birds in formation and they downlink different pieces of the signal on their tranceivers. Basically breaking a single comsat into a bunch of small pieces so if one component fails you could deorbit it hopefully and replace it by pushing another bird into the formation or having a backup fill its place. Nobody's really done this yet because formation flying in orbit is still a complex procedure and until recently birds weren't smart enough to navigate themselves. Also keep in mind that Surrey's sats are still all experimental and are using equipment that hasn't been recognized as spaceworthy quite yet. Trying to sell someone a satellite that has a 10% chance of working after a good sized solar storm won't be too effective. I think it is sort of interesting and cool they're powering their birds with StrongARMs.
I'm a loner Dottie, a Rebel.