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Monster European Environmental Satellite
andygood writes: "Spaceflight Now has this article about the 'Mother of All Earth Observation Satellites' which will be launched by Europe in early 2002. This thing is the size of a juggernaut and 'every hour will gather as much data as can be stored on a dozen PC hard disks'. 'ENVISAT' (ENVIronmental SATellite) has been in the works for almost fourteen years with a price tag of 2.3 billion (Euro)."
how much data the European Space Agency thinks can be stored on a "PC Hard Disk" nowadays... 1 GB, 10 GB, 100 GB? They're a little short on meaningful statistics. But it's a press release - the only time the press does math is when one of them gets stuck with the bar tab and figures out a tip.
It would also be interesting to hear what storage technology they're using. Surely they're not flying a Terabyte RAID5 array (what with launch vibration, etc.). More likely dense and hardened DRAM (and lots of it), I'd guess. It almost makes me want to go read the article to find this out.
I assume this data rate is decoded, not the raw telemetry, which is quite useless. Lets see.
The 'housekeeping data' of a satellite contains thousands of satellite parameters, e.g. orbital position, currents, voltages, radiation level, temperatures, what is on/off, status of each instrument. On many scientific satellites, all this affects the performance of all instruments. Often the HK data is recorded once per a few seconds.
This is because when voltage across some critical part is raising, you have to shut the satellite down. Then, from the last set of HK data, you have to fig out what is wrong, and correct or shut down the dangerous part, and still have a 90% functional satellite.
Lets assume you have of the order 10000 parameters to monitor, and the values are recorded 15 times/minute. Assume each values takes five bytes when decoded (including a STRING for parameter name. The raw telemetry will of course be more compact). This gives 10000x15x60x24x5 bytes/day, or about 1 GB/day, just to know the satellite is OK.
Now, add the HK, calibration and science data for each instrument. I have analyzed some data from satellite X-ray instruments, so I use it as a crude estimate. (This is very crude, other instruments may be completely different) A modern X-ray instrument produces about 1GB/hour in decoded data (instrumental HK, calibration, science). Thus,we have about 20 GB/day/instrument. I haven't bothered to read the article, but I assume the satellite contains about half a dozen instruments.
This would produce about 100 GB/day. Problem solved.
I can not understand why so many people continue to be taken in by the global warming/cooling scam. My only supposition is that, faced with the realization that man has essentially no impact on the universe at large, it become vitally important for them to believe that at least they are having a major impact on the earth. The fact that we are still minor players in the biosphere (there are, for example, well over a metric ton of termites per human, and termites are minor players among the insects. The insects, in turn, are dwarfed by the plant kingdom,...) is evidently so scary to them that they simply can't accept it.
-- MarkusQ