Gregory's ServerThe Space Shuttle had a large teleprinter onboard so the astronauts could receive text documents. We want to get it working, but first some reverse engineering... 1/13
Ken Shirriff
36 comments
Ken Shirriff
The teleprinter is absurdly heavy (~60 pounds) considering that every pound launched on the Shuttle cost $30,000. Moreover, it will overheat if left on for more than 20 to 30 minutes. I find it hard to imagine this was the best printer option available. 3/13
Ken Shirriff
The right side of the teleprinter has four complex circuit boards: a CPU board with a Motorola 6800 (photo), a memory board, a communications board, and a printer driver board. Fortunately, these boards are somewhat documented: https://radionerds.com/index.php/AN~UGC-74 4/13
Ken Shirriff
The left side has three circuit boards, specific to the Space Shuttle. They interface to the Space Shuttle's systems so it can receive messages through the Shuttle's audio system. I reverse-engineered these boards. 5/13
Ken Shirriff
This board receives audio, amplifies it, and applies a 900 Hz high-pass filter. It also has some control logic. 6/13
Ken Shirriff
The bits are encoded with two frequencies (Frequency-Shift Keying, FSK). This board uses a 64-bit shift register as a delay line to convert the 3600 Hz or 7200 Hz tones to bits. It also generates timing and control signals from the crystal. 7/13
Ken Shirriff
The final board applies a 400 Hz low-pass filter to the output and sends the serial data stream to the communication board. It also has carrier detection, control logic, and regulated +5 and +12 volt power supplies. 8/13
Ken Shirriff
There is a lot of control logic on these boards to power up the teleprinter when a message comes in and then power it off so it doesn't overheat. 9/13
Ken Shirriff
The boards use standard ICs, but they mostly have weird military part numbers, making reverse engineering annoying. 10/13
Ken Shirriff
The military teleprinter took all sorts of protocols: ASCII, Baudot, 45.5 to 1200 baud, but the Shuttle takes just one (unspecified) After reverse-engineering the boards, I think I know what type of signal it needs (ASCII, even parity, 1 stop bit, 600 baud, 3600/7200 Hz). 11/13
Ken Shirriff replied to Ken
Hopefully we can get the teleprinter to print. But first we'll need to do some maintenance. A rubber roller turned to goo that was soaked up by the paper. (Sorry, no photo.) So we'll need to replace that. Stay tuned... 12/13
Ken Shirriff replied to Ken
Thanks to Marcel for letting https://twitter.com/Curious_Marc, https://twitter.com/TubeTimeUS, and me work on this system. 13/13
tjhowse replied to Ken
@kenshirriff Incredible stuff! Please keep us posted on your progress! Did that type of print head/drum work by rotating to present a facet with the desired symbol in the desired place then transferring it to paper via a ribbon and hammer? If so, that is wild. NASA must've decided it was worth the weight budget to ship up this incredibly device. The frame looks like cast iron! I bet the symbol drum weighs a few kilograms by itself.   
Mister Sterling
@kenshirriff Crazy. Makes me think if the rack for the printer was settled in the mid 70s and no one thought it was worth fighting for a newer, lighter printer as delays pushed the first launch to 1981. I can totally see the NASA and the Rockwell-Boeing-Lockheed Martin guys saying, "sure it's heavy, but we have these things printing away in B-52s for decades now. It's been field tested." *I'm spitballing that B-52s have these. But I do know that B-52s have text printers. 
Christian Berger DECT 2763
@kenshirriff Didn't those get replaced by a system that could also reproduce graphics? 
Brad Bell
@kenshirriff I wonder if this shares any code with my 1980ish 6800-based portable terminal and integrated spark printer 😄 
Joe Cooper 💾
@kenshirriff I would have sent one of these and saved a few hundred thousand dollars.  
penguin42
@kenshirriff Yeh it's a weird choice isn't it; impact dot matrix machines had been around for a while at that point; a DECwriter or an Epson MX would surely have worked.
danimrich
@kenshirriff One wonders why they didn't use a thermal printer, for example. (Yes, they were commercially available back then.) 
Penguin
@kenshirriff Worked for US DoD in late 1960’s on teletype communication for field offices in Vietnam. Printer tech hadn’t gone too far past that used for law enforcement & newspapers in the 1940’s, there was little incentive for improvement since no-one had a computer at home. And military use meant much heavier components & associated parts.
joelion
@kenshirriff they put that 60lb monstrosity on the Shuttle, but the Apollo astronauts had to use a modified hand held camera with no view-finder, to save weight, in the Saturn rockets? 🤨
Peter Evans
@kenshirriff I imagine the strongest constraint was to avoid Drops In Space floating all around the middeck. #microgravity
Urwumpe
@kenshirriff not so absurd if you remember that this printer was selected at some point between 1973 and 1975, and thus had to be on the market before and had to survive intense vibrations and accellerations. NASA could have designed a lighter printer instead, but who'd paid for this? Later, this "interim" printer was replaced by lighter and cheaper gear. But it stayed as backup until 1998. 
MrEmerson
@kenshirriff makes me think how many rolls of paper and ink must be stocked for each launch. 
Ari [APz] Sovijärvi
@kenshirriff Curiously to this day some planes have printers on them for weather reports and stuff. Recall seeing one on an older 747.  |
The teleprinter was based on the military's AN/UGC-74, heavily modified to receive data over the Shuttle's audio system. It's more like a line printer than a Teletype, using a spinning drum and a row of hammers to print each line. 2/13