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Reverse engineering the 59-pound printer onboard the Space Shuttle
- kens 2y agoAuthor here if anyone has questions...
- hobo_in_library 2y agoThis is really cool. How did you discover all this information?
- kens 2y agoI had to go to the Library of Congress to get some of the information...
- urda 2y agoWhere else did you get info from that might be, unconventional, to readers here?
- kens 2y agoMost of the rest of the information is from various web sources (see the references in the footnotes). One source that might be interesting to others is the National Archives Catalog https://catalog.archives.gov/ https://catalog.archives.gov/ which has a zillion photos. I had to go through hundreds and hundreds of photos, though, to find the ones that I used in the article, photos that showed just the right things. So I hope you all appreciate the photos :-)
- breakingcups 2y agoI really appreciate all the effort you and your compatriots put into all of this.
- ASalazarMX 2y agoWas this printer radiation-hardened? As others have pointed out, a commercial dot-matrix printer would have saved many valuable kilos of weight. There must have been other priorities besides weight.
- kens 2y agoNo radiation hardening. Their main priority was building a system in 7 months that meet their toxicity and flammability standards. The original military teleprinter weighed 100 pounds. They cut it down to 59 pounds, so that's a win, I guess.
- crazygringo 2y agoWere commercially available dot-matrix or daisy-wheel printers toxic or flammable? My initial thought was also that this was for radiation hardening. But if not, I still don't understand at all why they didn't buy something lighter and cheaper off the shelf. Do you know specifically what component(s) didn't meet the toxicity and flammability requirements? And why any specific components like that couldn't just be swapped out, rather than redesigning the entire thing?
- colechristensen 2y agoVibration is a big deal in space. Launches aren’t gentle. Think “repeatedly thrown down a flight of stairs” toughness is required. And it’s a closed atmosphere so any amount of outgassing is paid close attention.
- deleted 2y ago[deleted]
- jcrawfordor 2y agoMost plastics of the era would not meet requirements for aviation fire safety, they produce toxic smoke when burning (still a significant problem today). There's an obvious tension between "reduced weight" and "not using plastics," but that was kind of the deal in aviation technology at the time. Aviation equipment is still pretty chunky today, because of the materials needed for low/no smoke evolution and vibration tolerance. Considering it probably also had to meet a MIL-STD environmental spec, stripping a commercial printer and putting it in some kind of aftermarket metal chassis seems like a much more expensive/higher risk route than using something that was already made to those standards. Environmental specs, in this context, usually mean min and max operating temperatures and acceptance of vibration and shock, within certain G-force and frequency measurements, with "without malfunction" and "without damage" thresholds. Aviation and military equipment have to go to environmental testing laboratories to be certified to these requirements, which can be a considerable expense on its own, and another reason it's smart to use an existing design. Besides, the military already made use of teleprinters in aircraft and so there was operating experience to build confidence. The space shuttle model is based on the family made by MITE, which included airborne variants used on bombers for example.
- magnat 2y agoIs the drum rotating smoothly at constant RPM, or is it stopping briefly (using gears [1] similar to those found in analog movie projector) when hammers hit the paper to prevent them from tearing it? [1] https://en.wikipedia.org/wiki/Geneva_drive https://en.wikipedia.org/wiki/Geneva_drive
- jmole 2y agoit's stopping, like all printers of the era, e.g. https://youtu.be/A_vXA058EDY?&t=41 https://youtu.be/A_vXA058EDY?&t=41 edit: I see now you were asking about the drum, rather than the paper
- tim333 2y agoIt looks like a regular line printer where the drum keeps spinning. See wikipedia: >Because the drum carrying the letterforms (characters) remains in constant motion, the strike-and-retreat action of the hammers has to be very fast. https://en.wikipedia.org/wiki/Line_printer https://en.wikipedia.org/wiki/Line_printer
- nyrikki 2y agoThe platen and paper feed stops line for line. the drum or similarly the chains used on the hammer printers were in constant motion. I am just old enough that I had to repair both types at the beginning of my career. Although typically rebranded Data Products and other OEMs, which I am probably wrong but vaguely remember being a supplier for the DEC L20?(maybe). But different than this printer. To these hammer action printer, the ribbon and the paper weren't even a consideration. If you have a Newton's cradle, put a piece of paper between the inner balls and it will still mostly work if you release a single ball. The high speed drum printers they typically had to rotate twice for each line (at minimum) so a 600lpm printer would have the drum rotating at about 1200rpm. If you look at the video posted in another comment, you can see the ragged vertical alignment of the chars. IIRC that is why IBM preferred chains in their hammer printers, because the human eye was more forgiving of vertical misalignment compared to the vertical misalignment that was a natural result of the mechanical differences. Edited to add link to video from page: https://www.youtube.com/watch?v=EDeL15amsus https://www.youtube.com/watch?v=EDeL15amsus
- zelphirkalt 2y agoWhy do you make it impossible to highlight text on the website? EDIT: Apparently not the whole text cannot be highlighted, but only the initial lines of text.
- slater 2y agoWorks for me? macOS, Firefox
- zelphirkalt 2y agoThe div with class cap-top is defined with a height of 400px and seems to overlap with the text. That seems to be the issue. I don't know what that div is actually for or why it needs to be 400px high, or why its position must be absolute or why it is 100% wide.
- eichin 2y agoHow much does the paper move when the hammer hits it? even with the padding of the ribbon (and having seen the video clips of it in action - ps. would love to see high-speed closeups if you get a chance) I'm not sure why the paper doesn't tear when the hammer hits it - or if it's a very short distance, does it instead smudge?
- cbhl 2y agoI think the paper gets sandwiched between the hammer on one side and the drum on the other side. This would be not too dissimilar to how a typewriter would have worked, I think?
- userbinator 2y agoLess than 100 thou, I think. It's also a very rapid process, so the drum would have barely moved meanwhile.
- kens 2y agoYou'd think that hammering the paper against the spinning drum would result in a blurry mess at best, but the hammers are fast enough that it works. It's the same principle as a chain printer such as the vintage IBM 1403, where the chain is zipping along at 90.3 inches per second when it gets hammered.
- dTal 2y ago>often printing thousands of lines per flight >with a Shuttle flight costing $27,000 per pound, putting the 59-pound teleprinter in space cost over $1.5 million per flight. That budget calculation is just the weight of the printer itself. I am curious how much blank paper was flown to feed it, and how this was decided? From the font size shown in photo we can assume it was at least several more pounds of paper for "thousands of lines" to be true.
- kens 2y agoThe printer took a big roll of paper, maybe 5 inches in diameter (although I don't have it here to check). I was a bit surprised that they didn't trim the roll down to the minimum size necessary, but just used a full roll. I guess they didn't want to waste paper :-) Also, I'm surprised that they used cheap-looking yellow paper rather than white paper, but maybe there's a reason teletypes used yellow paper. (The paper hasn't yellowed due to age; it's yellow in contemporary photos.)
- Stratoscope 2y agoMost or all Teletype paper was yellow in the 1970s when I learned to program on Teletypes. Apparently white paper is more common today. (It looks like you used white in one of your photos.)
- kens 2y agoThe photo with white paper is the Thermal Impulse Printer System, a different printer from the Interim Teleprinter. As far as I can tell, the teleprinter always used yellow paper. (This helps to figure out which printer is being used on the Shuttle in a photo, since the captions are usually wrong.)
- SoftTalker 2y agoI remember the yellowish teletype paper rolls from when I was a kid. I always assumed it was just inexpensive paper that was not bleached to pure white. I have never heard of a reason it was that particular color. Some quick searching indicates that yellow is easier on the eyes than pure white (that is given as the reason legal pads are yellow). Or that different wire services would use different color paper. E.g. news wires used white paper, weather services used yellow. So news editors would know the source by the color of the paper.
- metadat 2y agoHow does a hammer strike cause only one character to be printed? For example, striking the leftmost hammer not also causing the neighboring character to also be printed.
- jdlshore 2y agoThere’s 80 hammers, one for each character. They’re small.
- metadat 2y agoBut only 1 drum, which is a cylinder with a flat printing profile. Imagine if you want to hammer a single nail, but with a steel beam in between: Hammer strikes here v ============= Steel beam | | | | | | | ~~~~~~~~~~~~~~ wood How does the second nail not get pushed in a little, too?
- naikrovek 2y agoIt does, but you have to squeeze the ribbon enough to get ink out of it. The print ribbon is simply drier than you are imagining.
- metadat 2y agoGot it, thanks!
- wildzzz 2y agoThe hammer strikes the backside of the paper and presses it against the drum with the ribbon in between the drum and paper. The drum only rotates, it doesn't move otherwise. The ribbon and drum won't imprint a character unless something is pressing on the back of it.
- kens 2y agoAlmost, the hammer strikes the ribbon and the front side of the paper. The drum is behind the paper.
- skissane 2y ago> and a ROM that holds its program code Did you manage to dump the ROMs? (I understand from your article that article there are 3, a 4KB ROM on the CPU card, and two 8KB ROMs on the word processor card)
- kens 2y agoI'd like to dump the ROMs, but they are soldered in and covered with conformal coating, so it would be moderately destructive to remove them and dump the contents.
- skissane 2y agoI understand. One thought occurs: I assume these are mask ROMs, and so likely unchanged from the AN/UGC-74 original. So, if someone somehow managed to get their hands on an AN/UGC-74, you'd feel less bad about engaging in this kind of "sacrificial" action, given it would lack the unique historical association with Space Shuttle. Another thought: maybe there is some way to monitor the signals on the ROM pins non-destructively, by picking up the electromagnetic radiation? I'm guessing the answer is "no", at least not in practice. P.S. You have a typo on the page, at one point you have "AN/UCG-74" instead of the correct "AN/UGC-74". The other three times you mention it, you have it written correctly.
- chiph 2y agoGreetings Ken. Thanks to you and Marc for another great dive into obscure NASA hardware. They must have considered that the spinning drum had a gyroscopic effect on the shuttle. One of the reasons why the shuttle computers used tape drives and not hard drives was because they would have affected it's attitude in microgravity. Perhaps there wasn't enough mass there to be a problem, and also that it wasn't spinning 100% of the time like hard drives would have been? I'm also surprised they didn't consider the Teletype Model 40. It was lighter, didn't have a spinning drum, came in a receive-only configuration (no need to hack off the keyboard), was ASCII-based, and was already flight qualified on military aircraft. Maybe my timing is off - I first saw one in 1984 and it was considered "new" then, so it might not have been available in 1981. The Model 40 used a rotating belt with individual character pallets in it. It also used 80 hammers that would fire at the correct time to produce a printed character. You can see the pulleys for the belt spinning (one is behind the red plastic part on the left) in the video. It would also power down after a period of inactivity. One of the jokes you could play was to swap pallets around. They weren't tracked individually, but the belt had a flag that would indicate the start of the pallet sequence. So any monkey-business afterwards would result in M's for N's etc. being printed. https://www.youtube.com/watch?v=whKVGefscro https://www.youtube.com/watch?v=whKVGefscro
- ars 2y agoThe gyroscopic effect of a hard drive is easily removed by having two identical ones attached together back-to-back. You would anyway want two for redundancy.
- Pinus 2y agoNow I want to see a print sample! =)
- johnklos 2y agoThere's a short video of the printer printing towards the bottom of the article. You can see the printing in that. On the other hand, a Snoopy calendar printed on that would be cool :)
- ASalazarMX 2y agoWonder if it's as incredibly noisy as a regular dot-matrix printer. In the video it sounds almost pleasant.
- kens 2y agoIt's loud enough that NASA put acoustic down in the locker for the printer. But it's not screeching like dot matrix.
- SoftTalker 2y agoYeah they are loud. The printers used in data centers had soundproof (well, sound-reducing) enclosures. If you raised the lid while one was printing, it was very loud.
- beardyw 2y agoI worked with line printers for many years and they were as noisy as hell. Pretty fast though.
- SoftTalker 2y agoI'm pretty sure we had commercial/consumer dot-matrix printers in 1981. Something like that would have been much lighter and lower-power than a drum line printer.
- treyd 2y agoBut would it have worked after the intense vibrations and acceleration of launch and in zero gravity?
- cyberax 2y agoWhy wouldn't it? Matrix printers are extremely robust.
- michaelcampbell 2y agoAre they printing during launch? Not sure what part of a dot-matrix required gravity to work; the tractor feeds for the paper (if they used that sort), and nothing in the print mechanism requires a "down" other than possibly paper "exhaust" collection?
- lysace 2y agoWeren't they primarily Japan-made at the time? (I imagine that could present a political problem.)
- darreninthenet 2y agoCentronics (American...) built the first "true" dot matrix in 1970 although IBM built a line printer that was similar in the late 50s
- lysace 2y agoAh. That's where the name of that giant connector came from.
- 2y ago
- cyberax 2y agoI wonder why they didn't use a matrix printer. Or even a thermal printer. Fax machines were ubiquitous at that time.
- annoyingnoob 2y agoMechanical parts likely still work, does not need an ink subscription.
- cesarb 2y ago> Mechanical parts likely still work Towards the end of this article, Ken says that the mechanical parts did not work: "The printer had many mechanical problems, mainly because the rubber rollers had turned to liquid and gummed up the mechanism."
- annoyingnoob 2y agoNow imagine a printer made of mostly plastic and a bunch of elastomers. Your subscription based Inkjet is not going to last even half as long.
- deleted 2y ago[deleted]
- rkagerer 2y agoThe drum for the Shuttle teleprinter replaces 10 ASCII special characters with symbols that are more useful to the Shuttle, such as Greek letters for angles. Specifically, the characters ;@[\]^!"#$ are replaced by θ~αβΔ. Sigh... This ancient printer could render them, but apparently the Chrome browser on my modern Android cannot.
- tialaramex 2y agoSomewhere between when this was originally written and when it was delivered to your browser the text here was destroyed. I don't see how that's the fault of Chrome or Android.
- Narishma 2y agoIt works fine in Firefox.
- tialaramex 2y agoYup. I was mistaken about the problem.
- Stratoscope 2y agoOddly enough, Chrome on my Samsung S24 Ultra renders them OK here on HN, but not on Ken's page. Chrome on Windows and Ubuntu and Safari on iOS are the opposite: OK on the page, not here. Character encoding is such fun! Update: Ken, if you see this, it's specifically the characters encoded with numeric entities that have the problem on my devices. I used the Chrome dev tools to replace these with the actual characters on my Windows and Ubuntu devices and they rendered OK.
- deleted 2y ago[deleted]
- skylanh 2y agoAuthor font family: normal normal 14px Arial, Tahoma, Helvetica, FreeSans, sans-serif; News YC font-family: Verdana, Geneva, sans-serif; Per https://unicode.scarfboy.com/ https://unicode.scarfboy.com/ these are the characters (formatting issues are expected): U+03B8 θ GREEK SMALL LETTER THETA U+2713 CHECK MARK U+203E ‾ OVERLINE U+2191 ↑ UPWARDS ARROW U+2193 ↓ DOWNWARDS ARROW U+007E ~ TILDE U+03B1 α GREEK SMALL LETTER ALPHA U+03B2 β GREEK SMALL LETTER BETA U+0394 Δ GREEK CAPITAL LETTER DELTA U+03D5 ϕ GREEK PHI SYMBOL Specific characters that aren't showing up: U+2713 CHECK MARK, U+203E ‾ OVERLINE, U+2191 ↑ UPWARDS ARROW, U+2193 ↓ DOWNWARDS ARROW, U+03D5 ϕ GREEK PHI SYMBOL Arial contains most of these, Verdana does not. That's the limit of my knowledge of webified things.
- Taniwha 2y agoThis was a drum printer, the other common fast printed from the same era was a chain printer, essentially the same mechanism with a row of hammers one for each column and a chain of characters that would get whacked on as it sped past the hammers, they were really fast! The reason why they probably didn't choose a chain printer for the shuttle is likely because they had a failure mode where if the chain broke it would tend to fly out one side of the printer and through the wall - our operators were cautioned not to stand beside it ....
- dugmartin 2y agoWe had to get printouts from the mainframe for my freshman CS class and they came out of a chain printer. It was in the next room separated by a set of cubbyholes for the printouts and it sounded terrifying when it was printing, even 20 feet away.
- michaelcampbell 2y agoMy college had a chain printer in "the computer lab" (obsolete now, but not everyone HAD a home computer then). The "joke" in the lab was to run a or write a program that printed a line of "-" or "=" with no newline so it would overstrike and eventually shear the paper, and often cause the printer to jam. This was especially 'funny' on Sunday nights, when printed programs for courses were due before class on Mondays.
- jonsen 2y ago?: "Since the word processor was irrelevant to the Shuttle, I wonder why this card wasn't removed to reduce weight." !: "We obtained access to a Shuttle teleprinter (probably a development system that remained on the ground)"
- creativenolo 2y ago~£59~