3 ms·

Why is the James Webb Space Telescope's data storage space so small?

24 points by soheilpro 5y ago

deleted 5y ago
[deleted]
rektide 5y ago
More noteable to me, it appears to top out writing at 6MBps!! I can't find any information on ram buffers- perhaps there are some deep ones about but I've searched & don't think so- & my first feeling is that this seems like an obvious & severe limitation on high-speed data-capture. Most astronomy seems like it happens at long time-scales but it still strikes me as shocking that such an incredible instrument is only able to use a very very small amount of it's aggregate sensing throughput at any given time. I'm not sure the use case & I admit it'd be minor compared to primary missions, but being able to take high-bandwidth clips- a multi-spectral version of a phone doing a slow-mo clip- seems like a nice to have. And for comparison, JWST uses Ka-band (~26GHz) to upload at over 3x the drive-write rate, 18.75MBps. Maybe we can just live-stream instead? :) I would also love to know more about this storage in general. What is the storage medium? Are there regular flash chips here, or something more exotic? What kind of expected life is there? What kind of unusual failure protections are built in? Really interesting set of questions raised here.
- pwg 5y ago
  > Are there regular flash chips here, or something more exotic? Something more exotic. It, at a minimum, has to be radiation hardened, which means it is not a regular consumer or enterprise SSD. Also, wikipedia says development began in 1996 (https://en.wikipedia.org/wiki/Jwst https://en.wikipedia.org/wiki/Jwst) so also keep in mind that the "storage unit" was probably chosen sometime circa 2000-2004, which probably goes a long way to explaining the (by today's standards) somewhat slow write speed. The radiation hardening also likely has a play in the write speed because whatever changes are needed for rad. hardening have to go in, even if they have a detrimental impact on performance.

24 points by soheilpro 5y ago

deleted 5y ago

[deleted]

More noteable to me, it appears to top out writing at 6MBps!! I can't find any information on ram buffers- perhaps there are some deep ones about but I've searched & don't think so- & my first feeling is that this seems like an obvious & severe limitation on high-speed data-capture. Most astronomy seems like it happens at long time-scales but it still strikes me as shocking that such an incredible instrument is only able to use a very very small amount of it's aggregate sensing throughput at any given time. I'm not sure the use case & I admit it'd be minor compared to primary missions, but being able to take high-bandwidth clips- a multi-spectral version of a phone doing a slow-mo clip- seems like a nice to have. And for comparison, JWST uses Ka-band (~26GHz) to upload at over 3x the drive-write rate, 18.75MBps. Maybe we can just live-stream instead? :) I would also love to know more about this storage in general. What is the storage medium? Are there regular flash chips here, or something more exotic? What kind of expected life is there? What kind of unusual failure protections are built in? Really interesting set of questions raised here.

pwg 5y ago
> Are there regular flash chips here, or something more exotic? Something more exotic. It, at a minimum, has to be radiation hardened, which means it is not a regular consumer or enterprise SSD. Also, wikipedia says development began in 1996 (https://en.wikipedia.org/wiki/Jwst https://en.wikipedia.org/wiki/Jwst) so also keep in mind that the "storage unit" was probably chosen sometime circa 2000-2004, which probably goes a long way to explaining the (by today's standards) somewhat slow write speed. The radiation hardening also likely has a play in the write speed because whatever changes are needed for rad. hardening have to go in, even if they have a detrimental impact on performance.