News James Webb Space Telescope's Images Are Safely Stored on a 68GB SSD

[Admin]

The James Webb Space Telescope is one of the modern miracles of engineering. Why then did its $10 billion cost only cover 68GB of SSD space?

James Webb Space Telescope's Images Are Safely Stored on a 68GB SSD : Read more

 

[chaz_music]

The James Webb Space Telescope is one of the modern miracles of engineering. Why then did its $10 billion cost only cover 68GB of SSD space?

James Webb Space Telescope's Images Are Safely Stored on a 68GB SSD : Read more

As someone who has worked on space vehicles and other craft, I would suggest that you consider how difficult and expensive radiation hardened storage actually is. An off the shelf SSD wouldn't last very long at all, and the tricks used to create large amounts of flash storage for terrestrial use would die very fast in space. There are single event failures (gamma ray events and others), ELDRS, and other fun stuff that happened to electronics. The most obvious one is that the CMOS threshold voltage will slowly drift down until one day, one of the CMOS devices does not turn off any more. The enhancement MOSFET devices found in CPUs, DRAM, and SSD will slowly turn into depletion mode devices. So zero volts no longer makes a logic zero. It requires a more negative voltage, say like -5V to guarantee a logic low.

So the storage in the JWST is not anything at all like the Samsung SSD that you can buy and would be completely custom made, including the IC lithography.

 

[paul.nicolezim]

Great comment thanks for posting this.

 

[alceryes]

Wouldn't much of the environmental hardening be done on the design side? (housing, power delivery, controller, etc?)

I'm thinking it was more a real estate issue than anything else. Every mm of area on the JWST is extremely valuable. When the craft was designed, they already knew exactly how much physical space that storage would take. They couldn't add SSD/SSRs (storage space) without increasing the storage footprint onboard.

Also, they can't just swap out tested/approved hardware for newer, smaller versions without testing the Hell out of it and knowing how it will fare in space. Basically, the design and components were locked in (barring catastrophic issue) many years ago.

 

[uwe239]

"... Lagrange Point 2, one of the spots where gravity interactions between different celestial bodies cancel each other out, enabling as stable pictures as can be had in the tapestry of the cosmos."

Nope, not the reason. See here:
"To have the sunshield be effective protection (it gives the telescope the equivalent of SPF one million sunscreen) against the light and heat of the Sun/Earth/Moon, these bodies all have to be located in the same direction." https://webb.nasa.gov/content/about/orbit.html

 

[chaz_music]

Hey, Chaz!

Thank you so much for adding your expertise to this thread. Very interesting technical details.

You'll notice that there are several moments throughout the piece where I refer to the need to achieve radiation hardening, and how that is a very specific requirement for this type of storage. I also clarify that it's not to be considered an SSD, but an SSR device, and jokingly remind users that their own SSDs wouldn't survive being thrown through the atmosphere, much less deep space. Finally, also in the article, I do refer how it's likely that the contract for the JWST being finalized back in 2003 likely had something to do with the size of the storage.

Great article Francisco, and I was trying to be respectful and point out the things that I have had to consider. You created some good journalism here.

They did have issues early on with changes that they had not considered. Often, these are things that get left out of the concept specification or consequences of design decisions that are not thought out or not know until they are built.