Hacker News Reader

Comment by Victerius | Hacker News Reader

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?

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.

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.

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

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-a...

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

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-...

[2] https://en.wikipedia.org/wiki/Microelectromechanical_systems

[3] https://www.adafruit.com/category/521

[4] https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#...

[5] https://www.researchgate.net/figure/Block-diagram-of-the-MEM...

The FE link is awesome!

The others are interesting and informative. I am gonna buy me a few parts to play with.

Thanks!

No problem, have fun! — and if you enjoyed that FE article, you will likely enjoy the 'Behind The Curve' movie too, it's really quite amusing :)

I've used the MPU6050 to build a two-wheel self balancing robot (roughly this: https://www.instructables.com/Arduino-Self-Balancing-Robot-1...). Basically, apply PID to the motor angle to keep the robot level with the gravity vector.

I still think MEMS sensors are very cool and extremely convenient/cheap for what you get.

Nice!

I've done some projects myself with MPU6050 and some with its 9-axis "bigger brother" the MPU9250 (same as 6050, but with added 3-axis magnetometer/compass). I've also used the LSM9DS1 — another 9-axis IMU, just a different chip.

— Yeah, definitely amazing tech for the price. Cheap as chips! /me gets coat.

Ingenuity, the Mars helicopter/drone, apparently includes a bunch of off-the-shelf kit like this — IIRC I think a bunch of the parts are made by SparkFun. I don't recall any specifics though.

Yep, ring laser gyro :)

They are pretty awesome. Once got some data that seemed to be bad out of one and realized that the entire error was exactly accounted for by the Coriolis effect from the rotation of the earth.

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

If they're not on, hdds can handle surprising amounts of acceleration, like 100s of gs

Yeah. Fluid dynamic bearings and parked heads don't seem very vulnerable to shock and vibration.

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.

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.

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

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.

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.

Reply on news.ycombinator.com