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The article isn't as interesting as I thought it would be. > JWST can produce up to 57 GB each day (although that amount is dependent on what observations are

The article isn't as interesting as I thought it would be. > JWST can produce up to 57 GB each day (although that amount is dependent on what observations are scheduled). Just use a lot of hard drives? And delete junk data when it's no longer needed.

rsfern 4y ago
The problem is how to get the data back to earth, no?
- Victerius 4y ago
  > JWST is transmitting data back to Earth on a 25.9-gigahertz channel at up to 28 megabits per secon 0.028*3600 = 100 Gbit/hour No problem here.
  - mikepurvis 4y ago
    The article mentions that there are blackout windows, I guess when the US is facing away from JWST. Only the low bandwidth DSN has coverage all the time.
  - rsfern 4y ago
    Cool, that does seem like plenty of overhead even if JWST spends the bulk of its time imaging. Reading the article further, I was sort of surprised there’s only 68 GB of solid state storage on board. Does anyone know if that’s considered very large for space-grade systems?
  - exitheone 4y ago
    That's 100Gigabit/hour or 12.6Gigabyte/hour or 11.7Gibibyte/hour
  - SECProto 4y ago
    Note that's a peak rate, and that should be 100Gb (12.5 GB). Without knowing the variability it's impossible to say if that's a problem or not.
  - deleted 4y ago
    [deleted]
  - joshvm 4y ago
    This is discussed in the article, as the sibling (Mike) comments, JWST uses the Deep Space Network (DSN) for comms. The issue isn't so much blackout (the segments are 120 degrees separated^), but that contact time is expensive and you don't get 100% of the uptime to yourself. The DSN is basically the only infrastructure we have for this sort of long range communication. There are only three stations and JWST is sharing time with a bunch of other missions including everything that's currently on Mars. Scheduling takes place far in advance. The problem also isn't absolute storage space onboard, even if capacity degrades at a gig a year, it's whether you can drain it faster than you fill it. That said, there is likely to be some limit on hard drive space depending on what the current rad hardened solutions are. JWST is built on very robust and well-known hardware that has good provenance in space. For a LEO mission you might be willing to risk less tolerant components to get terabytes of capacity, but out there you want extremely resilient components and 68 GB is probably the balance. Sentinel 2 (an ESA Earth observation satellite) has 2.4Tb/300GB onboard for example. Ultimately the missions planners budget for how much data they're allowed to stream back and they've figured out an amount that is acceptable. But in general, yes. If you can write to a disk and ship it, that's a good solution. IceCube (South Pole) generates TBs of data. We send back 0.5 TB of critical data every month over a fast satellite link, crucial alerts and telemetry are sent over Iridium (24/7 avail) and the rest gets sent back to Madison (WI) on a plane each summer. ^ In theory this means that you can service three missions at a time though, if they're not all in the same direction.
    - LegitShady 4y ago
      it seems weird to spend $10billion on a telescope that lasts for 4-5 years and then not spend the money on a communication system that isn't limited by traffic and is 'expensive', or a spare drive to double its lifespan.
      - count 4y ago
        Ground comms is a construction project, which, as a federal govt thing, means it'd take even longer and be another billions of dollars.
  - rideva 4y ago
    > 0.028 * 3600 = 100 GB/hour You forgot the units. 0.028 Mb/s *3600s = 100 Gb/hour = 12.6 GB/h
    - Sporktacular 4y ago
      0.028 Gb/s * ...
  - onetwentythree 4y ago
    There are only 8 hours of downlink time per day. DSN resources are limited and shared among many missions. Everything was sized based on the expected volume of data that the telescope would be able to take. The instruments only generatedata at a certain rate, and there are inefficiencies involved with slewing between targets. Having a larger recorder or faster downlink would not mean that JWST could take more science data.

rsfern 4y ago

The problem is how to get the data back to earth, no?

Victerius 4y ago
> JWST is transmitting data back to Earth on a 25.9-gigahertz channel at up to 28 megabits per secon 0.028*3600 = 100 Gbit/hour No problem here.
- mikepurvis 4y ago
  The article mentions that there are blackout windows, I guess when the US is facing away from JWST. Only the low bandwidth DSN has coverage all the time.
- rsfern 4y ago
  Cool, that does seem like plenty of overhead even if JWST spends the bulk of its time imaging. Reading the article further, I was sort of surprised there’s only 68 GB of solid state storage on board. Does anyone know if that’s considered very large for space-grade systems?
- exitheone 4y ago
  That's 100Gigabit/hour or 12.6Gigabyte/hour or 11.7Gibibyte/hour
- SECProto 4y ago
  Note that's a peak rate, and that should be 100Gb (12.5 GB). Without knowing the variability it's impossible to say if that's a problem or not.
- deleted 4y ago
  [deleted]
- joshvm 4y ago
  This is discussed in the article, as the sibling (Mike) comments, JWST uses the Deep Space Network (DSN) for comms. The issue isn't so much blackout (the segments are 120 degrees separated^), but that contact time is expensive and you don't get 100% of the uptime to yourself. The DSN is basically the only infrastructure we have for this sort of long range communication. There are only three stations and JWST is sharing time with a bunch of other missions including everything that's currently on Mars. Scheduling takes place far in advance. The problem also isn't absolute storage space onboard, even if capacity degrades at a gig a year, it's whether you can drain it faster than you fill it. That said, there is likely to be some limit on hard drive space depending on what the current rad hardened solutions are. JWST is built on very robust and well-known hardware that has good provenance in space. For a LEO mission you might be willing to risk less tolerant components to get terabytes of capacity, but out there you want extremely resilient components and 68 GB is probably the balance. Sentinel 2 (an ESA Earth observation satellite) has 2.4Tb/300GB onboard for example. Ultimately the missions planners budget for how much data they're allowed to stream back and they've figured out an amount that is acceptable. But in general, yes. If you can write to a disk and ship it, that's a good solution. IceCube (South Pole) generates TBs of data. We send back 0.5 TB of critical data every month over a fast satellite link, crucial alerts and telemetry are sent over Iridium (24/7 avail) and the rest gets sent back to Madison (WI) on a plane each summer. ^ In theory this means that you can service three missions at a time though, if they're not all in the same direction.
  - LegitShady 4y ago
    it seems weird to spend $10billion on a telescope that lasts for 4-5 years and then not spend the money on a communication system that isn't limited by traffic and is 'expensive', or a spare drive to double its lifespan.
    - count 4y ago
      Ground comms is a construction project, which, as a federal govt thing, means it'd take even longer and be another billions of dollars.
- rideva 4y ago
  > 0.028 * 3600 = 100 GB/hour You forgot the units. 0.028 Mb/s *3600s = 100 Gb/hour = 12.6 GB/h
  - Sporktacular 4y ago
    0.028 Gb/s * ...
- onetwentythree 4y ago
  There are only 8 hours of downlink time per day. DSN resources are limited and shared among many missions. Everything was sized based on the expected volume of data that the telescope would be able to take. The instruments only generatedata at a certain rate, and there are inefficiencies involved with slewing between targets. Having a larger recorder or faster downlink would not mean that JWST could take more science data.