Slashdot Mirror

← Back to Stories (view on slashdot.org)

What's Inside the Mars Rovers

Posted by michael on from the remote-root dept.

Captain Zion writes "Space.com has a story about the hardware and software of Mars Rovers Spirit and Opportunity. Basically, they're radiation-shielded, 20MHz PowerPC machines wirh 128Mb RAM and 256Mb of flash memory, running VxWorks. I wonder if I could make a nice firewall with one of these for my home network..."

20 of 458 comments (clear)

  1. Radiation hardness by swordboy · · Score: 5, Interesting

    Does anyone know what the deal was with the flash memory that caused the outage? I heard something about a "solar event" that caused a problem with the flash memory that led to the outage. It was subsequently resolved by disabling the flash. If so, BAE Aerospace has a possible solution with their upcoming line of rad-hard memory.

    --

    Life is the leading cause of death in America.
    1. Re:Radiation hardness by TwistedGreen · · Score: 5, Interesting
      It appears to be a software error, and not hardware-related. It actually looks like it ran out of swap space and the OS crashed. This article explains what they think happened, and this article has more information on their recovery plans.

      A quote:
      It is now believed that the rover's flash memory had become so full of files that the craft couldn't manage all of the information stored aboard. Spirit bogged down because it didn't have enough random access memory, or RAM, to handle the current amount of files in the flash -- including data recorded during its cruise from Earth to Mars and the 18 days of operations on the red planet's surface.
      Raises some interesting questions about software reliability, I think. Did nobody think about running out of disk space?
  2. What's inside the rover? by Chilltowner · · Score: 5, Funny

    Darn. Interesting articles, but I was hoping that inside it was filled with creamy nougat center. Oh, wait. I'm thinking Mars bar. Nevermind.

  3. Wait a second... by deitel99 · · Score: 5, Insightful

    The machines aren't as slow as the top post says... they don't run at 20MHz, they are "capable of carrying out about 20 million instructions per second". Depending on the complexity of the instructions, the processor actually runs several times faster than 20MHz.

    1. Re:Wait a second... by Rootbear · · Score: 5, Informative

      Actually they are running at 20MHz. I've seen several write ups which clearly state that. The RAD6000 can apparently run at up to 33MHz, with a claimed 35MIPS. The rovers are "underclocked", probably due to power budget concerns.

      Go to
      http://www.iews.na.baesystems.com/space/rad600 0/ra d6000.html
      and click on the rover picture to get a PDF brochure, which gives the 33MHz/35MIPS figure.

      Rootbear

  4. Self-warming by Faust7 · · Score: 5, Funny

    To survive the frigid Martian night, MER computers are housed in warm electronics boxed heated by a combination of electric heaters, eight radioisotope heater units as well as the natural warmth from the electronics themselves.

    Just leave off the heatsinks and fans, and everything should be fine.

    --
    The coolest voice ever.
    1. Re:Self-warming by Cyclopedian · · Score: 5, Interesting
      To survive the frigid Martian night, MER computers are housed in warm electronics boxed heated by a combination of electric heaters, eight radioisotope heater units as well as the natural warmth from the electronics themselves.[Emphasis added by me]

      If obsessed environmentalists don't like NASA sending up probes with any radioactive material ('it might blow up, ohh..'), then how did this little tidbit get by them? Do they consider it non-radioactive? If they're only concerned by radioactive propulsion systems, then I think they're a bunch of hypocrites. Radioactivitiy is radioactivity whether it's propulsion or heating.

      If they don't mind it, then let's send up those dune buggies with RTG and 18-inch wheels and cover a lot more of Mars.

      -Cyc

      --
      /.'s 10 Millionth
    2. Re:Self-warming by Zog+The+Undeniable · · Score: 5, Funny

      If only they'd used an Athlon, the planet would have been habitable in Bermuda shorts by the end of the week.

      --
      When I am king, you will be first against the wall.
  5. Re:What's the bus speed on that thing? by gerf · · Score: 5, Insightful

    Does a 20mhz processor really need 128mb of ram? I mean, with a bus speed that low, you can probably put the data to flash ROM just as fast. What are the chances of you using all 128mb of ram?

    I imagine they can use all the storage they can, since there's no hard drive. So, the RAM acts as a cache for everything that is transmitted (which is a lot, actually). The Flash is used for more permanant software, like OS, commands, other files, ect. I'm amazed they can do it all with as little as they have.

  6. Re:What's the bus speed on that thing? by GoofyBoy · · Score: 5, Funny

    >What are the chances of you using all 128mb of ram?

    Ask Bill Gates.

    --
    The surprise isn't how often we make bad choices; the surprise is how seldom they defeat us.
  7. A nice Firewall? by blorg · · Score: 5, Funny

    "I wonder if I could make a nice firewall with one of these for my home network..."

    You could, but the latency would be a bitch.

  8. Re:Radiation Shielding by pi+eater · · Score: 5, Funny

    A modded alienware case perhaps?

    geeky stuff.. offensive stuff!

  9. Re:Radiation Shielding by the+real+darkskye · · Score: 5, Informative

    The CPU is fabricated to withstand the radiation, a brief summary can be found here or by googling

    --
    Music is everybody's possession.
    It's only publishers who think that people own it.
    Fuck Beta
    ~John Lenno
  10. Flying VxWorks to Mars by Hiroto.+S · · Score: 5, Informative
    I googled across following presentation with a little more details.

    Flying VxWorks to Mars

  11. Re:I hope the flash memory was not commodity hardw by Rootbear · · Score: 5, Interesting

    There is very little on the Rovers that is "commodity" in any sense. The CCD image sensors, the computers, everything, is all custom made. Everything has to be made to withstand the rigors of flight and the harsh environments of space and Mars. The CPU does not have a backup, which is a bit unusual for NASA (I'm a contractor at NASA/Goddard, but not involved in any flight missions). However, the particular computer used on the rovers (the RAD6000) has a very good record. There are something like 150 in use on various spacecraft and they've all worked very well.

    And the flash memory has probably not failed. It seems to have been a software problem, not hardware.

    Rootbear

  12. Re:Redundency Check? by vofka · · Score: 5, Informative

    If I recall correctly, the Shuttle has 5 GPC's (General Purpose Computers), three of which are "online" at any one time.

    The online GPC's each carry out the same set of calculations (potentially each uses code designed to do the same thing, but written by different programmers), and they compare each others results. If any single GPC is considered to be too far wrong, the offline GPC's submit their answers. The three GPC's that are in closest agreement then become the new online GPC's, and the remaining two go offline. The GPC's can reboot themselves if they are too far out of whack, if they fail in one of the "results elections", and of course when they are told to do so by the crew.

    Also, whenever a GPC is sent offline by one of the others, a specific caution indicator (and potentially the master caution indicator and klaxon) is activated, and the relevant error codes are shown on one of the forward CRT's. The error codes, along with other information such as the currently running program and the current mission phase, determine the crew's actions. Actions can be as simple as disabling the master caution klaxon for the current alert, all the way to hand-checking certain results and manual GPC restarts.

    This is all from memory (from about 5 years back), so some of this may have changed recently, particularly on Atlantis with the "glass cockpit" upgrade that happened 18 months or so ago, but the general gist should be about right (and I'm sure I'll soon know if it isn't!!)

    --
    Disclaimer: I meant what I thought, not what I wrote! What? You can't read my Mind? Oh dear!
  13. space shuttle uses 1969-vintage ibm 360 computers by peter303 · · Score: 5, Interesting

    The space shuttles run on five AP-101 computers, originally designed in 1969. The started with 32 kilowords of magnetic core memory for radiation protection, since upgraded to semiconductor memory. These computers were chosen due to their success in the Apollo, Skylab, and B52. For science and personal work the astronaut specialists usually bring personal laptops which are thousnds of times more performant.

  14. Processor is *not* a PowerPC by GileadGreene · · Score: 5, Informative
    radiation-shielded, 20MHz PowerPC machines

    No, they're not.

    The processors in MER are RAD6000's, which are radiation-hardened versions of the RS/6000, the predecessor to the PowerPC (see this for details). The RAD6000's younger brother, the RAD750, is indeed a rad-hardened PowerPC.

    As an aside, there is a big difference between a radiation-shielded processor and a radiation-hardened processor. Shielding implies just sticking some kind of rad-absorbent material between the processor and the environment. A rad-hardened processor is actually manufactured in a different way - different gate layout, different design rules, often different materials (Silicon-on-Insulator is popular). These things are done to minimize or prevent the effects of single-event upsets (when a bit is flipped by high-energy particles) and single-event latchups (which basically turn a couple of gates into a glorified short-to-ground). The materials changes may also improve the overall total dose tolerance of the processor. The work required for redesign is one of the reasons that space-qualified rad-hard processors lag the commercial market. The NASA Office of Logic Design has some good papers on space processors available online if you're interested in learning more.

  15. Re:What's the bus speed on that thing? by 3waygeek · · Score: 5, Funny

    In other words, the Spirit is willing, but the flash is weak.

  16. RAD6K by Anonymous Coward · · Score: 5, Informative
    I am an engineer that works with the RAD6K processor boards. A couple of observations here.

    1. The RAD6K really does run at 20 Mhz. They're creakingly slow. They're spec'd to run up to 33 Mhz, but the customer can get them to clock at lower speeds (I've seen them run at 12.5 Mhz). The only drawback is the PCI bus is also clocked as the same speed as the CPU. This is a mixed bag - but a slower PCI bus helps improves signal integrity and decreases power consumption.
    2. The board is PCI, but NOT compact PCI. There is a proprietary PCI connector and a proprietary PCI backplane. You cannot plug commercial PCI products unless you have an adapter to interface to the proprietary PCI connectors.
    3. For those who are not aware, there are three types of memory being used on the rovers. There is the SRAM (the RAD6K boards use SRAMs, not DRAMs), the EEPROM, and apparently, FLASH RAM. The EEPROM and the SRAM are on the processor board itself - there is probably more EEPROM memory in the system on another board. The EEPROM usually holds the flight code, and there are usually two copies. An original version that was launched with the spacecraft, and one patched version made possible via uplinks.
    4. I am amazed at the presence of FLASH RAM's. I am not aware of any rad-hardened FLASH RAM devices for spaceflight use. In addition to radiation hardness, the device must be made reliable with an approved QML-Q or V manufacturing flow. Radiation hardness is just icing on the cake, but the key is that the device must be reliable to withstand temperature extremes, shock and vibration. So, I have yet to see a FLASH RAM device that can be used. I am aware of the Chalcogenide based RAM's which are essientially uses the same substrates on CD-ROMs as memory cells. These products are hard to come by right now and are a high risk because we don't have sufficient data and flight heritage. A catch-22 in flight design is if it hasn't flown before, we don't want to fly it. But at some point, someone has to fly the first generation (someone who is willing to take a huge risk). Anyway, the FLASH RAM's on the rovers are in all likelihood upscreened commercial products. In other words, a mass buy of an entire lot of dies of commercial FLASH RAM's may have been bought, packaged in-house or through a vendor, and then screened for reliablity at extended specifications. This is not the same as the manufacturer who can guarantee the specs by design by designing it from the outset with increased reliability in mind.
    5. Radiation shielding? Minimal at best! The RAD6K shields its SRAMs by placing it on the underside of the processor board and orienting it such that the particles hit the processor side of the board instead of the RAM side of the board. There is some degree of radiation shielding for particles of sufficiently low energy. The truly high speed particles are going to get through and the only thing that will truly stop them is shielding whose thickness is measured in feet. That amount of shielding is too heavy for launch. The best we can do is mitigate the effects of radiation by guaranteeing devices can withstand a certain amount of radation dosage (measured in kRads) and design for latchup protection (latchup is a parasitic condition in which an ionizing particle impacts a transistor structure in a way that causes a SCR to be formed and a runaway current condition is initated leading to the device being burned out by high currents). Radiation effects in the form of SEE's (single event effects) such as bit flips can be mitigated by redundancy and voting circuits, memory scrubbing, and error checking using checksums/CRC's.