The 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.
Oddly 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.
It looks like the <code> tag is the problem. I guess the Android Chrome code font doesn't include those special characters. I took out the <code> tag and now the characters render on Android (at least for me).
>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.
The 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.)
Most 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.)
I 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.
The 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.)
Maybe in the space shuttle surroundings, white/black/grey are more common than yellow so a printout in yellow could be spotted more easily. May not be the main reason but a useful side effect of the color.
The incremental cost refers to one shuttle flight divided by pounds.
I think what OP was asking is - given shuttle already had a mission with some spare payload capacity, how much did it cost to bring one more pound into space? I think this question has a relevancy to the fact the printer was surprisingly heavy and came with a lot of paper. I'm not sure if there's a good way to calculate this though.
Its a bit of a nonsense calculation anyway. Fundamentally the shuttle's engines had a maximum thrust they could generate, and there's no amount of money that could easily change that. That dictates the maximum shuttle + crew + payload weight and it's just a question of how you parcel that out. Include a heavy printer, and you constrain the maximum crew and/or payload. (There was one flight, recently covered on HN - https://en.wikipedia.org/wiki/STS-93 - where they flew with fewer crewmembers because the payload was so heavy).
Greetings 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.
The 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.
Is 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?
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.
It 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
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)
I'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.
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.
Was 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.
No 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.
Were 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?
Most 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.
>Were commercially available dot-matrix or daisy-wheel printers toxic or flammable?
It’s not a binary but spectrum. For example military has a long list of standards for wires. The ships/tanks/planes use different wiring than your house does. That doesn’t mean our wires are toxic and flammable but they are probably more toxic/flammable than the application calls for.
And here is the problem: there was no off the shelf printer that met their exact requirements on paper. It’s possible some of the printers were similar quality but they were not certified to same standard.
So NASA would call a printer company and ask “does your printer self extinguish? What about in 100% oxygen? What about inrush current? Does the motor stall and what are the protections?”.
The printer company would not want to spend the time/energy on that vs what nasa would be willing to pay for 5-10 printers.
There were several classified shuttle missions. In those missions their link capacity was severely degraded and had to run through encrypted military rather than open NASA civilian channels.
This became an issue on STS-27 where they were unable to inspect tile damage with high resolution imaging because of these limitations. The astronauts on this mission were not at all pleased with the situation, and they had good reason not to be, as an entire tile had become dislodged by foam during the ascent.
Vibration 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.
How 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?
You'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.
How 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.
The 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.
Most 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/ 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 :-)
The 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.
This 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 ....
We 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.
My 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.
I'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.
> And when shuttle was developed, printers barely existed. Both inkjet and laser desktop printers were introduced commercially 1-3 years before the shuttles first flight in 1981, and weren’t very reliable yet. Desktop printers still aren’t as reliable as a teletype or dot matrix printer. There’s a reason airlines use dot matrix for printing flight manifests at the gate.
Ink plotters, teleprinters, and fax machines ruled the world. But plotters are dreadfully slow at writing text. Radio fax machines may have been viable if they were rugged enough. But they probably weighed as much as the teletype and were much slower - only real advantage is printing diagrams and photos.
In 1981, maybe, but there's a long time lag between design and flight for spacecraft. Cheap/light/sturdy dot matrix printers weren't yet available in the 1970s when the Shuttle was being designed. Nor had the idea of using commercial/off-the-shelf (COTS) components yet taken root. That would come years after the STS was already built and in service.
Fair point. But not so "last minute" that a pre-existing military design couldn't be investigated and reworked, custom print heads cast, etc. That puts it back to...what? 1979 or 1980? In that era, "let's build it to our exacting specifications, high tolerances, and unique mission requirements" pervaded NASA / aerospace engineering and procurement. However much we admire it today, COTS was not their way, and wouldn't be for at least another decade.
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?
And imagine how cool that matrix printer sound would be ringing out against the walls of the shuttle in space. Cyberpunk as hell. I miss dot matrix printers so much.
A line printer sounds nothing like a dot matrix printer. They're much, much louder, and it's a continuous buzzing noise, like a chainsaw. Also, the output appears at a similar speed to a dot matrix doing a form feed.
While the sound of a dot matrix printer can be kind of therapeutic - I remember debugging by printing, where the sound of printing and the time waiting could be used to mentally debug the problem, so you almost knew where the bug was without even looking at the print out, a line printer is the complete opposite as it's so loud it's distracting and the output gets spat out so quickly you don't have much, if any thinking time!
Probably not a concern in federal acquisition, but it's an interesting point that Centronics pretty much only built the print head and control electronics. The rest was built by Brother in Japan, as a modification of their electronic typewriter mechanism. Printing really was a very Japan-dominated industry at the time.
Brother's relationship with Centronics fell apart pretty much one model later, and now Brother is the printer company and Centronics is long gone.
There's more to the story of the Centronics printer connector. Centronics was a subsidiary of Wang Laboratories, producer of Wang word processors and computers. They had 20,000 surplus connectors from one of their earlier calculator products, so they reused the connectors for their printers, creating a de facto standard.
An Wang was one of the inventors of core memory (it's complicated). He sold his core memory patent to IBM and used the money to create Wang Laboratories, eventually becoming a billionaire.
Yeah 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.
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.