Slashdot Mirror
Computers in Space Examined
Wil Harris writes "There's an article about the computers used in space missions over at bit-tech this morning. It covers the processor types and speeds, why space stations are less powerful than the laptops that astronauts take up with them and why tape storage is still de rigeur. An interesting and concise couple o' pages."
also, older components tend to use larger signaling thresholds, which makes a big difference considering the mag-flux caused by radiation in space is much higher than on earth. id guess those tapes are also done with a high bias, as platters could be wiped with a decent flare, and fine-process cmos chips could be knocked out completely with a suprisingly small charge. even a small spike in power from a line surging or regulator going bad could take down some hard-disks, while all you have to do is rewind the tape and it's good.
you only need enough cpu power to handle some basic tasks and send the rest down to earth. considering most of the software is in c or assembler a 486 is an awful lot of power for most tasks.
The first rule of USENET is you do not talk about USENET.
Because of the density of memory now-day, bit-flipping is becomming a real problem for home PCs and workstations running with an uptime of over a week. Bit-flipping happens all the time and even on your PC. It just may be happening in a region of the wafer that does not currenly have anything important addressed to it...hence not an issue. But someplace, somewhere, a slashdot reader is getting a bitflip causing data-rott once it's commited to the harddrive. By the way, these bit-flips are causes cosmic rays.
If you serious about data integrity and stability, you would be foolish not to use ECC. You may take a 5% performace hit, but it's best to get used to it. If you need that extra 5%, then upgrade your processor to make up for it.
Life is not for the lazy.
Unfortunately, radiation hardening a processor involves altering the fabrication process (some processes - e.g. SOI - are more resistant to bit flips than others), inserting guard rings, adding self-checking logic, and a bunch of other changes. Doing all of this stuff takes time (and money) so space-ready processors typically lag COTS processors by a generation or two. Example: the current "hot new" rad-hard processor is the RAD750, which is a rad-hard version of the venerable PowerPC 750.
Having said all of that, some small, risk-tolerant missions do use standard COTS processors (PowerPCs and StrongARMs are popular, as are industrial embedded processors like the Hitachi SuperH line). But you won't tend to find them in most NASA projects.
Some 9 years ago I worked on some chip design for Hughes and ESA.
Back then, we used 1.2um on 4" (or 6" in the new fab) wafers - and everything was built on a sapphire substrate instead of a silicon substrate to make them radiation hard (when they went through the van allen belt).
It was dull, as every single chip had about 12 inches of paperwork from QA. Every *instance* of every chip had its own paperwork, I mean. It was also dull because they wanted tried and tested tech, not any of this new fangled sub-micron stuff.
That was then. Can anyone let me know how much things have changed?
Your concern about the blade is misplaced as well -- the "business end" of the device (both the hammer spike and blade) is kept safe in a capsule you need to unscrew to get them out. The blade is also protected by a guard rather like the one on a letter opener.
If I'm in a serious enough accident where I need to worry about my rearview coming off the windshield, the case braking open and me getting stabbed by this piece of emergency gear then... I think getting stabbed by this piece of emergency gear will be the least of my worries.
I want a new world. I think this one is broken.
Unmentioned in the article is why the unlock code was hidden from him.
The Soviets were afraid of a defection, which would be possible if he could run the navigation system himself.
While I could easily imagine designing a disk that could work in space, you can not pull the old ST41201J out of your box and launch it into space. The flying head effect requires an atmosphere between the surface of the disk and the head. Stock disks have a vent (wiht a filter similar to that of a filter-tip cigarette), such that exposed to vacuum, the heads would crash.
Even manned aircraft might experience low atmospheric pressure (or even total vacuum) from time to time -- I guess they could pack a pressurized "space suit" enclosure for the computer .... quick -- get to work and make a mint.
How does the Slashdot Effect happen given that no slashdotters ever RTFA?
Better idea. Go read the Honor Harrington series. (Go to baen.com, click on Free Library, and select "On Basilisk Station".) While they have hyperdrives and gravity propulsion, space battles are heavily dependent on orbital vectors, base velocities, missile loadouts, and missile counter-defenses. The author (David Weber) does a really good job of showing how a space battle might play out. Oh, and it is quite exciting. :-)
Javascript + Nintendo DSi = DSiCade
You must not have seen the Car and Driver article where they tested about five or six of those things.
Absolutely, utterly, 100 percent useless. They couldn't break a window if you shot them out of a railgun. Seriously.
p
In Korea, long hair is for old people!
You beat me to it; good thing I decided to re-check before I hit submit (that's what happens when you take half an hour to compose your reply). Anyway, Weber is definitely an interesting source for the possible future history of space warfare. Pretty much everything he writes is based on historical precedent, but he does (in my estimation) a great job of bringing it into the future and into the three-dimensional (or maybe a few more) world of space.
Drives need atmosphere to work. I think it has something to do with the heads
The head floats on a molecule thick cushion of air. While it needs that air to prevent the head from smashing into the drive platter, I think that modern drives are completely sealed. Thus they have their own atmosphere and don't need to be exposed to nasty particles and bacteria that could cause drive crashes. (Or vacuum for that matter.)
Also, they could not be cooled, but I don't think that is the main issue.
Cooling is provided by the surface area of the drive. Heat is transmitted through the metal case and radiated away. In space this is slightly more problematic as there are no cool particles to help radiate the heat away. That means that the heat will have to be lost through inefficient infrared coversion.
I'm sure that others can provide a few more details.
Javascript + Nintendo DSi = DSiCade
Hmmm ... should I believe the AC, or Wikipedia? http://en.wikipedia.org/wiki/Yuri_Gagarin
Allow me:
David Weber - On Basilisk Station
Read Online
HTML Zip
MS Reader Zip
Palm / Win CE / Psion Zip (Mobipocket)
Rocket / REB1100 Zip
Rich Text Format Zip
Javascript + Nintendo DSi = DSiCade
Yes I love that proc. I don't recall the top speed, but it would run reliably all the way down to DC. I always thought that was cool.
I had great fun learning to program assembly on an 1802 based ELF computer...
I've had experience with some of the computers in older government satellites.
Simple processors are preferred because that makes it much easier to figure out the time bounds on a subroutine. You don't want one routine to use up so much time that it keeps something else from being done. Timing information is rigoriously analyzed to make sure that the system won't miss something if lots of things happens at once. Fancy modern archetectures like cache, pipeline stalls, out-of-order operations, etc. make timing analysis very difficult.
Generally interrupts are not used - instead conditions are polled at a regular time slice. One reason for this is that polled data is also down-linked in a telemetry stream for status monitoring and trouble shooting. Also interrupts greatly complicate timing analysis.
It is hard to dissipate heat in space. Even if the few atoms that hit your cpu are of very low temperatures, there aren't enough of them to keep it cool enough to run.
Frylock: "We should have cloned twenties, Jackson wouldn't have given a fuck."
Per experience working for a NASA subcontractor making (non-critical) instrumentation...
The pressure the craft is operated at is less than standard sea level air pressure. (I don't know how much less.) It was, though, so much less that the hard drives sent up (on the project I worked on) were failing due to the lack of air for the Bernoulli effect (the pnenomena that holds the heads up when the drive spins), along with not enough air for cooling. We moved to Flash memory, which had just come out at that time.
The heat from hard drives is another significant factor (from TFA).
The whores get mad when the sluts give it away for free.
As I pointed out in another comment in this thread, it's not that NASA wants old processors. They want processors that are hardended to radiation, and the reengineering required for hardening causes rad-hard processors to lag commercial processors by a generation or two. Both EDDI and CFCSS work fairly well (~97% error recovery rate IIRC), but not as well as having a rad-hardened processor (> 99% error recovery rate). In addition, SIHFT can't do much to protect you from ionization-induced degradation, which causes cumulative damage to a processor that eventually causes it to stop functioning: rad-hard processors are far less susceptible to damage caused by ionizing dose.
The FPGAs on Spirit and Opportunity seem to be overlooked. NASA's new Reconfigurable Scalable Computer (RSC) Project for space applications is exploring using FPGAs (instead of CPUs) which offer increased performance and radiation tolerance at a fraction of the power consumption.
What's past is NOT ALWAYS prologue for the future!
See Rover FPGAs and RSC.
Future NASA space computers may not look like what most expect.
What's past is NOT ALWAYS prologue for the future!
I work for NASA on the manned programs and my experience is that hard drives are a headache on long term space missions.
u z_iss_010427.html
The laptops onboard Space Station are primarily IBM laptops (many of which will soon be running Linux - yeah!). While the drives are easy to replace, they fail fairly often (compared to other space hardware) and new ones need to be launched. The software on the drives also becomes corrupted frequently (maybe once every few weeks), requiring the crew to waste time recopying the software from CD. While these COTS laptops and hard drives were cheap up front (almost zero development cost, custom stuff would have been tens of millions of dollars) we are paying for it now because we waste a lot of operational time fixing them.
The Honeywell Command and Control computers (the primary flight computers onboard, which are triple redundant and manages core systems in the US segment) used to have a 300 megabyte hard drive to store flight software.
In 2001 during a shuttle mission, hard drive problems caused ALL THREE of those computers to crash simultaneously in a massive cascading failure. While it never got a lot of press, recovering from that took several days and an effort reminiscent of Apollo 13. You can read a contemporary article on it here: http://www.space.com/missionlaunches/launches/soy
When we got the things back and did a post-mortem, it turned out that the hard drive had a design flaw where the arm was dragging across the disk during power down and scratching it, which eventually led to failure.
They were replaced with solid state units shortly thereafter (which were already in the development pipeline). No moving parts, and much less problematic.
Worst...sig...ever!
See Computers in Spaceflight: The NASA Experience by James E. Tomayko.
Mea navis aericumbens anguillis abundat
Remember that space is a vacuum. Much like a thermos bottle. Unless there's energy being transmitted to an object (like from sunlight), the hot stays hot and the cold stays cold.
Unfortunately there's almost always sunlight to add some heat into your system.
So the many faults of this platform are well understood, which is what really counts. Interesting article on this here
(Loving my T40... er... in the abstract sense only)