8 ms·

1365 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 ago
I guess hard drives would be dead because of enormous acceleration on launch day.
- Schroedingersat 4y ago
  If they're not on, hdds can handle surprising amounts of acceleration, like 100s of gs
  - ahartmetz 4y ago
    Yeah. Fluid dynamic bearings and parked heads don't seem very vulnerable to shock and vibration.
- xeromal 4y ago
  You 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 ago
    Any 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.
wongarsu 4y ago
Since cosmic rays are charged particles I'd expect even more bit flips on the magnetic platter of a HDD.
- bitexploder 4y ago
  I am completely guessing here: it is shielded as are most of the computing components. It probably also has error correction of some sort built in.
  - harshreality 4y ago
    Shielding adds significant weight, which isn't good for space-bound components. I would guess they just use RAID, do round-trip data verification before writes succeed, and then reinitialize and scrub any storage module behaving improperly. For bits stored on SSDs which already rely on error correction, if they were willing to make custom hardware rather than use something off-the-shelf, they could add more chips and scale up the error correcting code to deal with more errors.
willis936 4y ago
Data at-rest in SSDs isn't really at rest. The controller is constantly scrubbing and correcting errors. The real hazard with SSDs is leaving them unpowered. I know of a story of several systems purchased a decade before they were needed and by the time they were used the boot drives were corrupted.
- sillysaurusx 4y ago
  Huh. Interesting. That explains why my SSD died at boot time. I thought it was just coincidence, and that it had died the night before or something, but that obviously doesn’t make sense.
tambourine_man 4y ago
This thing uses gyroscopes to orient itself. My guess is the less moving parts, the better
- jimsmart 4y ago
  Here's an interesting article about the gyroscopes / related tech used on the JWST. TL;DL — it uses reaction/momentum wheels to change orientation, and it uses non-mechanical gyroscopes to detect changes in orientation. https://www.universetoday.com/143152/spacecraft-gyroscopes-and-reaction-wheels-you-can-never-have-enough/ https://www.universetoday.com/143152/spacecraft-gyroscopes-a...
  - ddingus 4y ago
    I just went down a small, but very interesting rabbit hole: I was not aware of non mechanical gyros! Apparently, light travelling along a fiber optic cable will travel a slightly different distance when the device has angular momentum. That is COOL. https://en.wikipedia.org/wiki/Sagnac_effect https://en.wikipedia.org/wiki/Sagnac_effect
    - jimsmart 4y ago
      I believe that the tech you mention is the same tech as used by the flat-earthers in Behind The Curve in the $20k gyroscope they bought, to try and prove that the Earth did not rotate (except they found it picked up a 15-degree-per-hour drift, debunking themselves, so then doubted the technology, heh) [1]. But, aside from the laser/fibre-optic tech, there are also MEMS [2] gyroscopes also — which is almost nanotech IMO — which are used as sensors in modern phones/tablets, and also on drones (to assist with navigation), plus various other robotics uses, and more. MEMS gyros — often with an accelerometer (aka IMU / inertial measurement unit) and maybe a magnetometer (compass) — can be bought from folk such as Adafruit [3], SparkFun, etc. (I've got a few different ones myself), and hooked up to e.g. an Arduino or similar MCU (or indeed anything else that speaks can speak the appropriate protocol, e.g. I2C/SPI/etc depending on the board in question). Hmm, just looked for a good image of how a MEMS gyro works, and didn't come up with what I was looking for / recall seeing before (I'm a bit pushed for time), but there's a diagram on this WP page [4]. Edit: ah, here's a better diagram [5] [1] https://www.triplem.com.au/story/flat-earthers-spend-20-000-trying-to-prove-earth-is-flat-accidentally-prove-it-s-round-129953 https://www.triplem.com.au/story/flat-earthers-spend-20-000-... [2] https://en.wikipedia.org/wiki/Microelectromechanical_systems https://en.wikipedia.org/wiki/Microelectromechanical_systems [3] https://www.adafruit.com/category/521 https://www.adafruit.com/category/521 [4] https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#MEMS_gyroscopes https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#... [5] https://www.researchgate.net/figure/Block-diagram-of-the-MEMS-gyroscope_fig1_266022526 https://www.researchgate.net/figure/Block-diagram-of-the-MEM...

curling_grad 4y ago

I guess hard drives would be dead because of enormous acceleration on launch day.

Schroedingersat 4y ago
If they're not on, hdds can handle surprising amounts of acceleration, like 100s of gs
- ahartmetz 4y ago
  Yeah. Fluid dynamic bearings and parked heads don't seem very vulnerable to shock and vibration.
xeromal 4y ago
You 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 ago
  Any 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.

wongarsu 4y ago

Since cosmic rays are charged particles I'd expect even more bit flips on the magnetic platter of a HDD.

bitexploder 4y ago
I am completely guessing here: it is shielded as are most of the computing components. It probably also has error correction of some sort built in.
- harshreality 4y ago
  Shielding adds significant weight, which isn't good for space-bound components. I would guess they just use RAID, do round-trip data verification before writes succeed, and then reinitialize and scrub any storage module behaving improperly. For bits stored on SSDs which already rely on error correction, if they were willing to make custom hardware rather than use something off-the-shelf, they could add more chips and scale up the error correcting code to deal with more errors.

willis936 4y ago

Data at-rest in SSDs isn't really at rest. The controller is constantly scrubbing and correcting errors. The real hazard with SSDs is leaving them unpowered. I know of a story of several systems purchased a decade before they were needed and by the time they were used the boot drives were corrupted.

sillysaurusx 4y ago
Huh. Interesting. That explains why my SSD died at boot time. I thought it was just coincidence, and that it had died the night before or something, but that obviously doesn’t make sense.

tambourine_man 4y ago

This thing uses gyroscopes to orient itself. My guess is the less moving parts, the better

jimsmart 4y ago
Here's an interesting article about the gyroscopes / related tech used on the JWST. TL;DL — it uses reaction/momentum wheels to change orientation, and it uses non-mechanical gyroscopes to detect changes in orientation. https://www.universetoday.com/143152/spacecraft-gyroscopes-and-reaction-wheels-you-can-never-have-enough/ https://www.universetoday.com/143152/spacecraft-gyroscopes-a...
- ddingus 4y ago
  I just went down a small, but very interesting rabbit hole: I was not aware of non mechanical gyros! Apparently, light travelling along a fiber optic cable will travel a slightly different distance when the device has angular momentum. That is COOL. https://en.wikipedia.org/wiki/Sagnac_effect https://en.wikipedia.org/wiki/Sagnac_effect
  - jimsmart 4y ago
    I believe that the tech you mention is the same tech as used by the flat-earthers in Behind The Curve in the $20k gyroscope they bought, to try and prove that the Earth did not rotate (except they found it picked up a 15-degree-per-hour drift, debunking themselves, so then doubted the technology, heh) [1]. But, aside from the laser/fibre-optic tech, there are also MEMS [2] gyroscopes also — which is almost nanotech IMO — which are used as sensors in modern phones/tablets, and also on drones (to assist with navigation), plus various other robotics uses, and more. MEMS gyros — often with an accelerometer (aka IMU / inertial measurement unit) and maybe a magnetometer (compass) — can be bought from folk such as Adafruit [3], SparkFun, etc. (I've got a few different ones myself), and hooked up to e.g. an Arduino or similar MCU (or indeed anything else that speaks can speak the appropriate protocol, e.g. I2C/SPI/etc depending on the board in question). Hmm, just looked for a good image of how a MEMS gyro works, and didn't come up with what I was looking for / recall seeing before (I'm a bit pushed for time), but there's a diagram on this WP page [4]. Edit: ah, here's a better diagram [5] [1] https://www.triplem.com.au/story/flat-earthers-spend-20-000-trying-to-prove-earth-is-flat-accidentally-prove-it-s-round-129953 https://www.triplem.com.au/story/flat-earthers-spend-20-000-... [2] https://en.wikipedia.org/wiki/Microelectromechanical_systems https://en.wikipedia.org/wiki/Microelectromechanical_systems [3] https://www.adafruit.com/category/521 https://www.adafruit.com/category/521 [4] https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#MEMS_gyroscopes https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#... [5] https://www.researchgate.net/figure/Block-diagram-of-the-MEMS-gyroscope_fig1_266022526 https://www.researchgate.net/figure/Block-diagram-of-the-MEM...