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Post by colinr on Nov 18, 2005 9:39:17 GMT -4
Don't hate me for having it easy..... ;D Even maged to run a car on my grant
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Post by linuxboatr on Nov 22, 2005 20:00:05 GMT -4
For those who are interested in the technical aspects of the Apollo flight computers, here are a couple links of interest: starfish.osfn.org/AGCreplica/www.ibiblio.org/apollo/index.htmlThe first link details how to build a working replica of the AGC including running the original flight rated software! For computer history buffs (which I am), this is very fascinating stuff. The second link is for a virtual (emulated) AGC, again running the flight software. For those who don't want to build their own replica in their basement! For those interested in the evolution of computer technology in the early NASA era, see www.hq.nasa.gov/office/pao/History/computers/Compspace.html. This provides coverage of computer usage and evolution in manned and unmanned spaceflight. I would love to see this updated to include details on the Mars rovers/orbiters and Cassini hardware/software design. Matt
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Post by Kiwi on Nov 23, 2005 6:03:57 GMT -4
From what I've read, it seems like it's almost impossible to compare the Apollo CSM and LM computers with modern ones, because they are so different.
But something that would be a big help in conveying their capabilities to a hoax-believer, would be list of what would do the job today.
For instance, physical restraints aside, would something like my first computer, a 1983 Kaypro 4 with CP/M operating system, 64 Kb memory, green screen (no graphics, no mouse, no hard drive), 2x 360 Kb floppy disk drives, and a copy of BASIC, do their job adequately, and could the programs be stored on the floppies?
(I have fond memories of how blindingly fast a memory-resident word-processor worked in that machine.)
This would probably need to be expressed in today's terms, but again, would 64 Kb of memory, MS-DOS, BASIC, and floppy disks be enough?
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Post by Tanalia on Nov 23, 2005 8:36:39 GMT -4
From what I've read, it seems like it's almost impossible to compare the Apollo CSM and LM computers with modern ones, because they are so different. But something that would be a big help in conveying their capabilities to a hoax-believer, would be list of what would do the job today. For instance, physical restraints aside, would something like my first computer, a 1983 Kaypro 4 with CP/M operating system, 64 Kb memory, green screen (no graphics, no mouse, no hard drive), 2x 360 Kb floppy disk drives, and a copy of BASIC, do their job adequately, and could the programs be stored on the floppies? (I have fond memories of how blindingly fast a memory-resident word-processor worked in that machine.) This would probably need to be expressed in today's terms, but again, would 64 Kb of memory, MS-DOS, BASIC, and floppy disks be enough? From NASA Office of Logic Design, specifically following Apollo Guidance Computer (AGC) to Design Principles for a General Control Computer (4MB PDF), we can find that the AGC has the equivalent of 12K ROM and under 1K RAM The low-end system you describe has more than enough storage and raw computing power. However, the AGC needed to be able to interface with numerous sensors and controls, and this capability was directly built in. The newer system would need an extra microprocessor of some sort, either an internal card interface, or an external one connected through something like a serial or parallel port, to translate between electrical signals and some sort of control/value designations.
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Post by linuxboatr on Nov 23, 2005 12:14:12 GMT -4
Many modern microcontrollers have multiple interfaces to support sensor hookups including built-in DACs and ADCs. Depends on the controller and the capabilities needed. I've played with PIC controllers that had built-in ADCs (used to built a crude autopilot for an R/C sailplane to maintain an optimum glide angle with an external AoA vane; I helped the builder debug the software). It all boils down to requirements. Apollo was one of the forces that lead to miniaturization of electronics and spurred IC development. ICs were expensive then but cost was secondary to weight and reliability (both of which the ICs had in their favour compared to discrete systems of the time).
Many aviation applications (specifically 70-80s era fighter and attack aircraft) used relatively weak amounts of computing power as compared to what was available to the civilian populace. Again, a specialized need. A Tornado strike fighter only had 64K of RAM and computing power roughly equal to a Commodore 64 during its early career. That ran it all. Radar, navigation, displays. It didn't need more. Same applied to the F/A-18 Hornet and most other aircraft.
Even the computers on newer generations of spacecraft are still "weak" by consumer standards but incredibly powerful by spaceflight standards. But reliability is the #1 need in spaceflight and it takes a lot of time and effort to certify a specific system as good for space. And engineers are a conservative lot. Once they have something that works, they'll stick with it and improve it incrementally. In fact, modern computers are actually worse for spaceflight because they very thing that makes them so powerful works against them in a high radiation environment: component density! The odds are higher in more sophisticated, denser designs for cosmic radiation to introduce errors in the circuit by the creation of spurious voltages in the chip. The tighter you pack it, the greater the odds of error. Radiation hardening becomes a really big deal with the use of modern hardware in spaceflight. Otherwise, many modern computer chips fry in deep space.
Matt
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