Have you seen concords cockpit or the sr71 it's all dials and switches I doubt any of it is electronically controlled, even the autopilot heading lock is probably a mechanical system
it doesn't need to calculate thruster burn times and god knows what else
what was the first plane with fly-by wire controls with a computer correcting the movements to keep it stable?
B-2 ?
First flight 17 July 1989
Doubt you could do it with the power of a calculator either
The guidance computer from the Apollo 11 mission ran at 1.024 MHz, about 1/6th of the processing power of a TI-83 calculator
You don't need massive amounts of computational power to do burn times.
They're fairly simple as you know the output of your engines and your mass and other variables (it's basically a case of knowing in advance when to do stuff and for how long)...
A lot of what was done for the moon landings in terms of burn times etc was worked out well in advance on the ground, often with what little computing power was available being there to automate the burn times or assist in speeding up the process for simple stuff.
It's like artillery etc, before the advent of computers they had tables to let the people using it work out the angle, amount of powder etc to hit targets at X range with Y difference in altitude (+/-), and Z wind speed/direction.
Then the early "automated" systems basically let them work it out faster and without having to manually do the math.
IIRC one of the earliest uses of computers in the military was to calculate artilllery barrages so they could do time on target for multiple batteries in minutes, so they could do them on call, rather than having to be very carefully planned well in advance.
You could probably work out the burn times for a rocket to the moon if you know the distance and thrust with an abacus, let alone a slide rule, or even a 1970's/80's calculator.
Remember the early workings for a stable orbit around the earth were done, from memory on pen and paper...
Even today most rocket launches etc have the bulk of the working out done well in advance, with the computers being used to automate the sequence of events, and allow trickier manoeuvres .