Answers and comments on What is the data storage capabilities onboard the James Webb Telescope? which reference the James Webb Space Telescope User Documentation item JWST Solid State Recorder mention that JWST's total onboard storage capability is almost 59 GB, and that

The rate at which science data can be written to the SSR is regulated by the ISIM Command and Data Handling subsystem (ICDH). The maximum ICDH sustained data rate is about 48 Mbits per second, including data packetization overheads. This corresponds to about six 2048 × 2048 full frame image files every 10.7 s...

48 Mbits/sec is 6 MB/sec and that would fill 59 GB in about 160 minutes if it ran flat out which it wouldn't always do.

Question: Some deep space telescopes have onboard data processing capabilities to reduce the burden on the downlink, for example GAIA has a SCS750 PowerPC Board with triple redundancy and TESS has an Athena-3 Single Board Computer (SBC) (and) a Re-Configurable Computer (RCC) with three Virtex-5 FPGAs. What are the general properties and specs for JWST's onboard data and image processing capabilities? Is there a rack full of processors or GPUs? A total gigaflop specification?

As an aside, TESS has 192 GB of mass data storage or three times what JWST will have!

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    $\begingroup$ The JWST source I used to answer the linked question only said that the storage was "at least 59GB" and since that was a 2017 document, they may have upgraded. On the other hand the download bandwidth limit is likely to be much more rigid, so either avoiding taking images at maximum speed, or doing some on board data compression or cropping or whatever will clearly still be essential. $\endgroup$ Apr 29, 2020 at 7:57
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    $\begingroup$ TESS is a survey instrument with lots of CCDs designed for a wide field view and short exposures for time series and exoplanet detection. JWST has a tiny field of view and is designed for deep stares and long spectroscopic exposures so it's data storage needs are totally different. $\endgroup$ Apr 29, 2020 at 14:43
  • $\begingroup$ Just conjecturing here, but one of the biggest design goals of the JWST seems to be keeping the instruments cool. So a big, hot processing array might be a bit counterproductive. Also keep in mind that much of astronomy is long term exposure, on the scale of minutes, if not hours per image. If your observation produces its image after a few seconds, then what you are looking at will likely be so bright that it can be seen from earth anyway. $\endgroup$
    – mlk
    Apr 29, 2020 at 14:43
  • $\begingroup$ @astrosnapper ya I think this is why I wanted to ask about the processing capabilities; presumably the "deep stares" are many exposures (or digitizations or readouts or whatever it's called) rather than one long one, so I'm wondering if all raw data is sent (the quoted "maximum ICDH sustained data rate is about 48 Mbits per second") or if there is some substantial local processing capability. $\endgroup$
    – uhoh
    Apr 29, 2020 at 15:15
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    $\begingroup$ Normally onboard processing is avoided unless you are forced into it by data rate downlink considerations (bandwidth to ground station). It also much easier to do for single purpose observing as TESS and Gaia do than for general science observatories like JWST - how do guarantee you won't destroy or prevent someone's science with the processing if they do something it doesn't expect ? More info on the processing and data/rate limits in the JWST proposal preparation docs, $\endgroup$ Apr 29, 2020 at 16:25


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