Author here for your Apollo questions :-)

Great article. I'd never thought about a spacecraft ADI having a third axis. Sadly, a nitpick - Bill Lear's F-5 autopilot was not, as far as I can tell, in any way connected to the Northrop F-5 fighter jet.

Thanks. You are correct about the F-5 autopilot, so I fixed that. It turns out that it was used in planes such as the C-47, C-60, C-45, and B-26, but is unrelated to the F-5.

>The Command Module for Apollo used a completely different FDAI (flight director-attitude indicator) that was built by Honeywell.

That's surprising. Was there any requirement that necessitated them to be different parts, or it's just because different suppliers were chosen by Grumman/North American?

It's probably a combination of different suppliers being chosen, and everyone wanted a piece of the pie. But it's annoying when I figure out how something works in the Lunar Module and then discover that the Command Module is completely different. Not to mention that the Saturn V is a whole different world.

I remember a similar thing from the, IIRC, F-104.

I mainly remember this because he refers to it as the 'frappin 8 ball' in the Apollo 13 movie, if my memory serves.

Yes, in the movie, Lovell says "What's the frappin' attitude?" as the 8-ball rolls out of control. The actual Apollo 13 transcript has nothing like that, interestingly enough.

Links: https://archive.org/details/apollo1319959231994/page/n92/mod... https://www.nasa.gov/wp-content/uploads/static/history/alsj/...

same here, he sure does

Back in the day, this would be have been a good homework assignment for an EE analog controls class.

That's a 'kunst' of UI (a gem?). One look and you instantly know the orientation of your craft.

As an amateur astro-pilot (1000h in KSP and 200+ in Flight of Nova, both flight simulators with realistic orbital mechanics) I'd like to say that in modern cockpit of the fusion propelled ships in FoA, the one thing I'm missing from Apollo-style flight instruments of KSP is the Nav-Ball.

The jet-fighter-like "ladder" style attitude meter can't be read with just one look. You need to focus to see the numbers next to the ladder steps. And then another look at the compass for a full reading. 3s of focus (away from controlling the ship) vs. 0.5 (that your subconscious has most likely already interialized).

To put that 3s into perspective, according to ship readings, Apollo 11 had <20s fuel left when it touched down on the moon.

This was actually mentioned in a recent talk by Freya Holmér --- I believe this one:

https://www.youtube.com/watch?v=hUlvxaQBW78

Brings me back to playing Kerbal Space Program

kens - Are the collectors of the output transistors on the amplifier boards connected to the metal can? I can see from the photo that the heatsinks don't touch (there's a gap between them for the capacitors). Did they use nylon screws to prevent an electrical path through the frame?

Unfortunately, I don't have the FDAI handy to check this.

For TO-5 bipolars, it was common for the collector to be connected to the case. I wouldn't say that's universally true but I don't recall any exceptions off the top of my head.

Ken once again proves he's one of the greatest publishers on Hacker News.

I wonder if that simulator was OV-095 at SAIL.

https://spaceflightblunders.wordpress.com/2017/03/31/ov-095-...

EDIT: Ah. It almost certainly was:

https://www.superstock.com/asset/oct-astronauts-frederick-ri...

There are many different Shuttle simulators. The simulator photo in my post is one of the Shuttle Mission Simulators (SMS), now at Stafford Museum in Oklahoma. The Shuttle Avionics Integration Laboratory (SAIL) is a different simulator for avionics testing (rather than astronaut training) and is currently in Houston.

The strong impression I always get from the entire Apollo program is "they didn't know it couldn't be done at the level of technology available, so they did it anyway".

  > 3. The FDAI's signals are more complicated than I described above. Among
  > other things, the IMU's gimbal angles use a different coordinate system from
  > the FDAI, so an electromechanical unit called GASTA (Gimbal Angle Sequence
  > Transformation Assembly) used resolvers and motors to convert the
  > coordinates.

I'm so glad I work in software.

1960s technology, designed and made in the USA. It seems that people back then were far more clever at making do with what they had.