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Hubble's Computers Upgraded
MRcow writes "A story at ABCnews.com says the Hubble Space Telescope that was recently repaired by the crew of space shuttle Discovery is having its computer system upgraded. The new system will be 'three linked computers that run on the Intel 486 microchip.' It says older processors are used because they have to be tested for radiation and such. That makes me wonder if the computers are going to be "linked" and if so, how? Maybe a Beowulf cluster on Hubble? Talk about 'geeks in space'." The processors on the Hubble are being upgraded from what I understand are 1980s versions. The new hard drive is going to be a whopping 10 gigs with three 486 processors. The processors and drive have to be specially shielded and made to handle heat/cold extremes.
The Sandia National Laboratory is currently preparing the Pentium for use in high radiation environments such as space, for more information check out the following sites
http://www.sandia.gov/media/rhp.htm
http://www.sandia.gov/LabN ews/LN12-18-98/intel_story.htm
There's (mainly) two issues as to the WHY:
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1. A time tested system (one that has proven itself over several years of "real world" as well as experimental development use) is a more acceptable one to them. Thy don't want to send a device into space and six months later have it fail because of a processor bug that know one knew about.
2. As the circuits on computer chips get smaller and smaller, there is a concern over the ability for solar radiation to trigger (or disable) the circuit's switches.
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Harris Semiconductor has spent a lot of time and effort making the iAPx86 processor line radiation hardened. And it works. But it doesn't work nearly as well for the newer generation as the older.
The tighter dies are more sensitive to charged particle events (Single Event Upsets, 'SEUs'), and the thinner nature of deposition makes the hardware more prone to heavy particle (permanent) events.
Older CMOS processors and memory were less prone to both types of error because of line thickness and spacing, depth of deposition and because of the voltage levels used.
The COSMAC 1802 is still a widely used space-borne processor!
Rad-hard planning is a non-trivial task, expecially when it's new to the designer. Trying to develop a design for a medium-altitude satellite was a challenge that a group I was once involved with was never able to satisfactorily overcome, and we lost the project because of it.
Having watched the evolution of the Shuttle system General Purpose Computers (GPCs) migrate from IBM proprietary processors to 80186s was a painful process. The software was clean-roomed, and 2 seperate groups of people developed code with identical functionality, while a 3rd group was responsible for testing. None of the groups was supposed to interact at all, and to the best of my knowledge, didn't even talk over beer... I suspect the Hubble ports are similar, although the rules for Manned Spaceflight code are more stringent.
Never ascribe to malice that which can adequately be explained by tenure.
The 80486 processor has a smaller instruction set than Pentium/MMX chipsets and their variants (AMD, CYRIX). The MMX sets are optimized more for multimedia functions than scientific calculations.
Another issue is the floating-point concern; though Intel has come a long way from the notorious Pentium 60.876564 MHz errors, there are still enough quirks in the more advanced calculations (especially in the IBM/Cyrix copycat processors) to make their use by an orbiiting telescope impractical.
As a 486 is exssentially a 386 chip with a built-in math coprocessor, its reliable calculation scale, along with the right operating command scheme would be as close to a RISC-based system as one could getwithout building a new chip out of whole cloth, or using larger clusters of older MAC - and of course, Motorola Dragonball - processors to achieve the same results.
In comment to a couple replies asking why such old technology is used... If I remember correctly it has to do with how radiation can effect the state of the processor and chipsets. Newer processors have increasingly smaller distances between the pathways on the surface of the chip. Since this distance is smaller, radiation can cause the electrical charge to "jump" across. There are ways to minimize these effects with shielding, but as far as I know this is an "add on" that is not done by the chip manufacturers themself. I guess this would create a lead time.. IE: A new P3 chip needs x months of work to have a good shielding design developed, x months to test that... Coupled with the fact that this hardware is designed years before launch and you can see how things can slip. Remember also that comparing your desktop to something in orbit that was designed 20 years ago for a specific task isn't as easy as it might appear...Until recently NASA custom designed it's hardware and software. So, the Hubble running at 25 Mhz using all custom hardware and software is going to be a lot more efficient than a 25 Mhz 486 running Windows since it's all task oriented. I'm no expert of course, but I haven't seen some of our resident Super-Technical Answer Dudes (tm) post anything yet. (Probably still working on the formulas for their posts hehe). Case