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Comment by defrost | Hacker News Reader

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.

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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.

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

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.

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/> [2]: < https://science.nasa.gov/mission/soho/>

From the interview linked, it sounds like the current plan doesn't involve the DSN at all: they're effectively out of transmission range past a certain point, and the transmission back is optical, using a big earth or space-based telescope. Which is one of the scary things he mentioned: they're going to be entirely autonomous when collecting the data.

"Which is one of the scary things he mentioned: they're going to be entirely autonomous when collecting the data."

With no way to send commands to the decices?

Sounds like we need to drop little relay nodes along the way to build the first SpaceNet

*Kerbnet

Engrave it on a hair and coilgun it towards a receiver?

The DSN is a radio network. In its present form, this is going to be ineffective for receiving a meaningful amount of imagery data from signals emitted by a lightweight space probe at 500AU. At ~150AU the current 25-70m dishes are getting less than 40 bits per second from Voyager 1.

Instead, we would use lasers with a far superior gain to what radio communication is capable of. The divergence on even a decent pocket laser pointer diode is less than 0.1 degree. This is a gain of 10*log10(41,253/(0.1*0.1)) = 66 degrees. Launch telescopes of modest size can increase this further. Then receiver telescopes fitted with narrowband filters can hone in on that laser signal.

> "First, transmitted beams from optical telescopes are far more slender than their radio counterparts owing to the high gain of optical telescopes (150 dB for the Keck Telescope versus 70 dB for Arecibo)." - https://www.princeton.edu/~willman/observatory/oseti/bioast9...

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