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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."
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.
Well, the microsats sent out from my home state were fairly well one-purpose, one-use machines (amateur radio for webersat, rotation/attitude manipulation with tracking for the JAWSAT)- see here for an optimistic description. See here for other previous microsats. NASA's microsats, according to their page, "carry a wide range of spacecraft services including guidance, navigation and control, attitude control, propulsion, high bandwidth and complex communication functions," some of which are diagrammed on that page and its successor. With the previous story and the other ways in which NASA has exceeded expectations on almost all of their craft in mind, I think this is an idea whose time has come.