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> Data gathered from its scientific instruments, once collected, is stored within the spacecraft’s 68-GB solid-state drive (3 percent is reserved for engineerin
by qazpot 4y ago
> Data gathered from its scientific instruments, once collected, is stored within the spacecraft’s 68-GB solid-state drive (3 percent is reserved for engineering and telemetry data)
Hope the SSD does not fail after 32768 or 40000 hours of operation.
- aqme28 4y agoIIRC 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.
- re-actor 4y agoNo currently available spacecraft can make the trip and service JWST, it's also not really intended to be serviced.
- hoseja 4y agoSpaceship might (Elon time) fly this August.
- danpalmer 4y agoIt'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.
- hoseja 4y agoOh yea. Much less memorable than BFS.
- queuebert 4y agoSpitballing here ... could we de-orbit it back to Earth with what propellant remains? Then fix whatever and refill the propellant?
- brokenmachine 4y agoThe sunshield had a complicated unfurling sequence, I very much doubt they could fold it back up while still in orbit.
- patmorgan23 4y agoJWST is not serviceable. If the ssd dies, then it's dead. There's no replacing it.
- zimpenfish 4y ago> 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?
- Sporktacular 4y agoDepends if the sensor readout is slower than 28 Mb/s.
- zimpenfish 4y agoIf 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)."
- Sporktacular 4y agoThat 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.
- Sporktacular 4y agoEdit: 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-solid-state-recorder https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-s...).
- 4y ago
- 317070 4y agoThe 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.
- Aperocky 4y agoIt'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.
- martinskou 4y agoDidn’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.
- beached_whale 4y agoI 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.
- sp332 4y agoMaybe we could send up a data buffer with a high-bandwidth, short-range radio.
- dotnet00 4y agoEven 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.
- Victerius 4y ago1365 to 1666 days, or 4-5 years of operations. Maybe they should have chosen a HDD drive? Cosmic particles can flip bits on an SDD, can't they?
- curling_grad 4y agoI guess hard drives would be dead because of enormous acceleration on launch day.
- Schroedingersat 4y agoIf they're not on, hdds can handle surprising amounts of acceleration, like 100s of gs
- ahartmetz 4y agoYeah. Fluid dynamic bearings and parked heads don't seem very vulnerable to shock and vibration.
- xeromal 4y agoYou could almost invert your logic too. Perhaps the spinning on the HD throws off the telescope enough to be troublesome. I'm not sure how stable the lagrange point orbiting is, but it can't be super stable.
- dr_orpheus 4y agoAny moving mechanism is potentially a source for disturbance to the telescope. Not something that affects the stability of the orbit. But the small vibrations can translate to small vibrations in the instruments and secondary mirror which then cause distortion over the integration time of the image. I don't know that that is the primary reason HDD's have been avoided. But any moving part is another source of failure so my guess is the HDD's life is not as long. As far as I'm aware I don't know of any spacecraft that has flown a HDD (but there certainly could be). However, some early spacecraft did use tape drives. Hubble originally used tape drives and was replaced with solid state memory during one of the servicing missions.
- iamgopal 4y ago68 GB ? Just ? Shouldn’t that be some 10-15 1-2 TB SSD in parallel ?
- danpalmer 4y agoTechnology for space lags behind consumer technology by 10-20 years. There are a few reasons for this: - Long lead time to test and certify hardware. - Higher reliability requirements (e.g. must work non-stop for 10 years) - Must be able to operate in a higher radiation environment with little to no cooling. In a vacuum, and in zero gravity, cooling works very differently to how it does on Earth. - These missions often take a decade or more to come together, and changing requirements throughout that process is hard, costly, and risky, so often they stay the same from the beginning. Notably, SpaceX are bucking this trend a bit with their avionics which just runs on standard Linux machines rather than specialist machines or with a realtime OS, but they have mission lengths measured in minutes to hours, not decades.
- deleted 4y ago[deleted]
- urthor 4y agoThey also simply do not store data locally. The onboard storage is basically a buffer, they beam everything back to earth.
- ceejayoz 4y agoYep. That means bandwidth is the limiting point, and that maxes out at 28 megabit in ideal conditions. A multi-terabyte array would be a waste.
- zackmorris 4y agoSometimes the smartest people in the world still stink at their short game
- urthor 4y agoAll jokes aside, tbere's an article floating around about NASA's software development practices. They are big TLA+/formal specification fans (the article predates TLA+'s rise) with well resourced and antagonistic Q/A engineers. That hard drive will have been ordered, custom, and the controller verified by hand I imagine.
- _fat_santa 4y agoAlso likely that they are already super experienced with that particular SSD. I read an article a long time ago that talked about a spacecraft with some camera on it. They said the camera was 10 years old when it was installed and although their were better cameras out there, they picked this one specifically because of reliability. I’m sure the same happened here.
- ceejayoz 4y agoChances are they or the manufacturer have a room full of those cameras clicking away on a schedule for the last ten years, too, as an early warning system.
- boilerupnc 4y agoCould it perhaps be this? Interesting read about the level of effort and process invested in the Space Shuttle's software (~1996) [0] For a TLDR, this answer [1] is great. My favorite excerpt: The Shuttle software consists of ca. 420,000 lines. The total bug count hovers around 1. At one point around 1996, they built 11 versions of the code with a total of 17 bugs. [0] https://www.fastcompany.com/28121/they-write-right-stuff https://www.fastcompany.com/28121/they-write-right-stuff [1] https://space.stackexchange.com/questions/9260/how-often-if-ever-was-software-updated-in-the-shuttle-orbiter https://space.stackexchange.com/questions/9260/how-often-if-...
- urthor 4y agohttps://www.fastcompany.com/28121/they-write-right-stuff https://www.fastcompany.com/28121/they-write-right-stuff Edit: oh you found it
- onetwentythree 4y agoI know this is a joke but... JWST does not use a typical flash-based SSD. The mass storage is all SDRAM. There are layers of error correction and scrubbing to handle bit flips.
- boredemployee 4y agothat means no sandisk or the like
- deleted 4y ago[deleted]