With the James Webb Space Telescope (JWST) now powered up and snapping some spectacular images, you may wonder exactly how it's storing them. Surprisingly enough, it carries a relatively tiny 68GB SSD, according to IEEE Spectrum — enough to handle a day's worth of JWST images, but not a lot more.
While that might sound ludicrously small for a $10 billion satellite, there are multiple reasons NASA chose the system. To start with, the JWST is a million miles from Earth where it gets bombarded by radiation and operates at a temperature of less than 50 degrees above absolute zero (-370 degrees F). So the SSD, like all other parts, must be radiation hardened and survive a grueling certification process.
While not nearly as fast as consumer SSDs, it can still be nearly filled in as little as 120 minutes via the telescope's 48 Mbps command and data handling subsystem (ICDH). At the same time, the JWST can transmit data back to Earth at 28 Mbps via a 25.9 Ghz Ka-band connection to the Deep Space Network.
That means that while it collects far more data than Hubble ever did (57GB compared to 1-2GB per day), it can transfer all that data back to Earth in about 4.5 hours. It does so during two 4-hour contact windows each day, with each allowing the transmission of 28.6GB of science data. In other words, it only needs enough storage to collect a day's worth of images — there's no need to keep them on the telescope itself.
There is one puzzler, though. NASA estimates that only 60GB of storage will be available at the end of the JWST's 10-year lifespan due to wear and radiation — and 3 percent of the drive is used for engineering and telemetry data storage. That will leave the JWST very little margin, making us wonder if it will have anywhere near the longevity of Hubble — still going strong after 32 years.
from Engadget is a web magazine with obsessive daily coverage of everything new in gadgets and consumer electronics https://ift.tt/sQ6zvG1
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