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Comment by aqme28 | Hacker News Reader

IIRC the hard part with this thing is the lenses. I wonder how hard it would be for astronauts to swap an SSD if it came to that.

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The JWST is about three times further than the furthest a human has ever been from earth, which was on the moon.

So, it would be __really__ hard for astronauts to swap an SSD.

It's much easier to get there and fix JWST than it is to land on the moon though.

Because the landing part was the hardest and take more delta V than actually getting to JWST. Not to mention going back from moon surface.

Didn’t JWST use some kind of grivitational breaking to stop at the LGPoint? A manned mission would require much more fuel to shorten the time of the trip and fuel for returning.

I think the engineering that would go into a mission to do maintenance/repair would be quite valuable and help with many other missions. It’s far enough to be far, but not so far that other factors like communication is extremely delayed. Getting that far out of LEO has a huge set of new challenges, I assume, we should be able to learn about.

Even if a crewed spacecraft could be sent to it (honestly not that crazy given JWST's predicted lifespan of 20 years. Starship should be crew rated in 10 years at most and if not, Orion could be sent with some sort of expanded service module for the trip) the issue would be that docking to or even approaching the telescope is extremely risky.

You don't want to fire any thrusters in its direction to avoid damaging the sunshield or the mirrors, but of course to slow down at it you would need to do that at some point.

If the SSD failed and a constant connection to Earth cannot be maintained, the more realistic solution would probably be to launch a satellite to a high orbit to maintain permanent connectivity with JWST which can act as a store-and-forward relay, effectively replacing the SSD without having to actually go to the telescope.

JWST is not serviceable. If the ssd dies, then it's dead. There's no replacing it.

It isn't meant to need servicing, but it does have a docking port if it ever does need it and we have the desire to do so.

Yes, but a servicing mission for replacing the memory would still be an unlikely operation to be able to do. The most likely use for the docking port is if the electronics onboard exceed their design life, but JWST is running out fuel (to maintain its position at the Lagrange point) so they basically strap a "jet pack" on to the satellite to keep in operation. This has been the business case of some companies trying to do this for GEO satellites:

https://astroscale.com/astroscale-u-s-enters-the-geo-satelli...

> If the ssd dies, then it's dead.

Presumably they could operate in a reduced mode where it does live transmission of the data when it's in contact with Earth?

Depends if the sensor readout is slower than 28 Mb/s.

If it generates, at most, 57GB per day[1], assuming 22h operation (2h for transmission), the sensors are generating 2.6GB/h or about 750kB/sec which is just about 6Mb/s (unless my math is wonky.)

[1] "JWST can produce up to 57 GB each day (although that amount is dependent on what observations are scheduled)."

That is the average rate over a day. If storage is not available to buffer it, then a sensor's peak readout rate could easily exceed the transmission rate.

Edit: Which apparently it does, which is why the SSD can ingest up to 48 Mb/s to be read out more slowly later (https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-s...).

But also "The actual data rate depends on the number of detectors simultaneously in use, their exposure parameters, and the precise timing of when their exposure readouts arrive in the ICDH for processing" - in a reduced operation mode, they can turn down the number of sensors, etc., to keep the data rate below the live transmission rate.

No currently available spacecraft can make the trip and service JWST, it's also not really intended to be serviced.

Spitballing here ... could we de-orbit it back to Earth with what propellant remains? Then fix whatever and refill the propellant?

The sunshield had a complicated unfurling sequence, I very much doubt they could fold it back up while still in orbit.

Spaceship might (Elon time) fly this August.

It's "Starship", and it's unlikely to be able to get to where the JWST is in the next few years due to needing to be refuelled in orbit. Plus they have no payload bay design. Then there's the robotics necessary for doing a repair, or human-rating Starship, either of which is years worth of time.

Oh yea. Much less memorable than BFS.

Maybe we could send up a data buffer with a high-bandwidth, short-range radio.

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