4 ms·

A 6 month integration time is going to generate massive amounts of data. How do they intend to receive all this back from 500 AU away?

tomtom1337 2y ago
Well, one single long exposure would literally generate a regular sized image. Though I do guess they’ll be doing multiple exposures if only to avoid saturating their dynamic range. Does anyone know what a typical number of acquired frames is for a space telescope?
andy_ppp 2y ago
The computer onboard likely merges everything into a final image in space?
- Cthulhu_ 2y ago
  Sure, it would discard a lot of data / noise, and would send a preview over first, but like with the Pluto probe, they do want to get as much data as possible, as an image is only a representation thereof.
- defrost 2y ago
  Orbiting instruments typically transmit raw instruments data blocked into lines or segments that are are each surrounded by checksums. It might be compressed for transmission, but raw data (warts and all) is king .. once it's "processed" and raw data is discarded .. there's no recovering the raw. Years later raw data can be reprocessed with new algorithms, faster processes and combined with other sources to create "better" processed images. Onboard hardware errors (eg: the historic Hubble Telescope erros) can be "corrected" later on the ground with an elaborate backpropagated trandfer function that optimally "fixes" the error, etc. Data errors (spikes in cell values, glitches from cosmic rays, etc) can be combed out of the raw in post .. if smart people have access to the raw. Baking processing into on board instrument processing prior to transmission isn't a good procedure.
  - tlb 2y ago
    You could store all the data on the satellite, upload new code to process it differently, and download the resulting image. Then, the communications link just has to handle code (several MB up) and images (several MB down) instead of petabytes of data. The launch mass of a petabyte of SSD is under 10 kg. I don't know if it would survive 17 years of space radiation though.
    - defrost 2y ago
      Well, you could. I don't think I'd do that. Ignoring the failure modes of a petabyte of SSD spending decades in deep space, what kinds of things are difficult and|or impossible if you were to > store all the data on the satellite, upload new code to process it differently, and download the resulting image ?
    - modderation 2y ago
      Just as a thought experiment, would it be viable to send up an array of traditional hard drives? Arrange them all for use as reaction wheels, then spin them up to persist/de-stage data while changing/maintaining targets. Probably worse than sending up well-shielded flash, but I don't think the Seagate/WD warranty expressly forbids this usage.
  - bkfunk 2y ago
    But this wouldn’t be in orbit; it would be in what NASA calls “deep space”, which relies on the Deep Space Network [1]. The DSN is severely bandwidth constrained, due primarily to a lack of ground antennas. Indeed, for instruments that are located outside Earth’s orbit (e.g. SOHO, which is at Sun-Earth L1 [2]), bandwidth is often a limiting constraint in the design. My understanding is that some newer instruments do both compress and select data to be downloaded (i.e. prioritizing signal over noise), and that there is more and more consideration of on-board processing for future missions, as well as possibly introducing the capability within DSN itself to prioritize which instruments get bandwidth based on scientific value of their data. Source: A presentation from people at NASA Heliophysics last week, where this very topic came up. [1]: < https://www.nasa.gov/communicating-with-missions/dsn/ https://www.nasa.gov/communicating-with-missions/dsn/> [2]: < https://science.nasa.gov/mission/soho/ https://science.nasa.gov/mission/soho/>

tomtom1337 2y ago

Well, one single long exposure would literally generate a regular sized image. Though I do guess they’ll be doing multiple exposures if only to avoid saturating their dynamic range. Does anyone know what a typical number of acquired frames is for a space telescope?

andy_ppp 2y ago

The computer onboard likely merges everything into a final image in space?

Cthulhu_ 2y ago
Sure, it would discard a lot of data / noise, and would send a preview over first, but like with the Pluto probe, they do want to get as much data as possible, as an image is only a representation thereof.
defrost 2y ago
Orbiting instruments typically transmit raw instruments data blocked into lines or segments that are are each surrounded by checksums. It might be compressed for transmission, but raw data (warts and all) is king .. once it's "processed" and raw data is discarded .. there's no recovering the raw. Years later raw data can be reprocessed with new algorithms, faster processes and combined with other sources to create "better" processed images. Onboard hardware errors (eg: the historic Hubble Telescope erros) can be "corrected" later on the ground with an elaborate backpropagated trandfer function that optimally "fixes" the error, etc. Data errors (spikes in cell values, glitches from cosmic rays, etc) can be combed out of the raw in post .. if smart people have access to the raw. Baking processing into on board instrument processing prior to transmission isn't a good procedure.
- tlb 2y ago
  You could store all the data on the satellite, upload new code to process it differently, and download the resulting image. Then, the communications link just has to handle code (several MB up) and images (several MB down) instead of petabytes of data. The launch mass of a petabyte of SSD is under 10 kg. I don't know if it would survive 17 years of space radiation though.
  - defrost 2y ago
    Well, you could. I don't think I'd do that. Ignoring the failure modes of a petabyte of SSD spending decades in deep space, what kinds of things are difficult and|or impossible if you were to > store all the data on the satellite, upload new code to process it differently, and download the resulting image ?
  - modderation 2y ago
    Just as a thought experiment, would it be viable to send up an array of traditional hard drives? Arrange them all for use as reaction wheels, then spin them up to persist/de-stage data while changing/maintaining targets. Probably worse than sending up well-shielded flash, but I don't think the Seagate/WD warranty expressly forbids this usage.
- bkfunk 2y ago
  But this wouldn’t be in orbit; it would be in what NASA calls “deep space”, which relies on the Deep Space Network [1]. The DSN is severely bandwidth constrained, due primarily to a lack of ground antennas. Indeed, for instruments that are located outside Earth’s orbit (e.g. SOHO, which is at Sun-Earth L1 [2]), bandwidth is often a limiting constraint in the design. My understanding is that some newer instruments do both compress and select data to be downloaded (i.e. prioritizing signal over noise), and that there is more and more consideration of on-board processing for future missions, as well as possibly introducing the capability within DSN itself to prioritize which instruments get bandwidth based on scientific value of their data. Source: A presentation from people at NASA Heliophysics last week, where this very topic came up. [1]: < https://www.nasa.gov/communicating-with-missions/dsn/ https://www.nasa.gov/communicating-with-missions/dsn/> [2]: < https://science.nasa.gov/mission/soho/ https://science.nasa.gov/mission/soho/>