Electronics in the Saturn V Booster - Page 1
Forum section: electronics / general

author: calzap
author_rank: Frequent Contributor
timestamp: June 20, 2025, 06:11:48 pm
content: I recently visited the U.S. Space & Rocket Center in Hunstville, Alabama. It’s definitely worth a visit if you’re in the area. Among the exhibits was an entire Saturn V rocket and separate detailed display of the first-stage booster engine. Included in the exhibit was some of the electronics that were part of the booster.Part of the exhibit was core memory. See 1.jpg pic. I used PDP and Burroughs computers in the ‘70s that had core memory. It was bulky and slow (about 1usec cycle at best). It did have the advantage of retaining its values when power was removed. Replacement of core with semiconductor memory was a big advance.More interesting were the computer logic and control boards. See 2.jpg and 3.jpg pics. The white squares are IBM ULDs (Unit Logic Devices). These are ceramic packages containing multiple silicon dies (one transistor or two diodes) and thin-film resistors. I assume the reddish squares are capacitors and blue circles are coils. Curious that they are rated by impedance. And I assume the black tubular devices are resistors and the small brownish rectangles are capacitors. If anyone has more definitive info, please post. The whole computer was cooled by circulating liquid through the frame with cold plates extending between circuit boards.References:https://en.wikipedia.org/wiki/Launch_Vehicle_Digital_Computerhttps://en.wikipedia.org/wiki/Solid_Logic_Technology

author: EPAIII
author_rank: Super Contributor
timestamp: June 21, 2025, 01:18:54 pm
content: I wandered through the outdoor Saturn V which is sideways and separated into stages back in the late 60s. It is immense!I am sure you are correct about the white, ceramic devices. There were 0.050" pitch, DIP packages back then and these are certainly some. But they certainly are composit devices, not ICs. Individual parts were mounted on one ceramic substrate which had the printed conductors and the other one was cemented on top for protection. I doubt that there were any integrated parts beyond two diodes or transistors on the same chip; some ICs were around in the late 60s but the Saturn was designed earlier and probably didn't use them.Red/orange squares are capacitors, 1uF, 25 Volts, just like today.The blue circles/cans could be coils, electrolytic capacitors, or transistors to drive the various lines in the memory grid. More likely coils with the transistors in the white ceramic packages. Some relays were mounted in cans, but I see no reason for relays here. The numbers seem to be just OEM part numbers to me.The black, axial devices could be resistors, capacitors, coils, or even diodes. I don't see any polarity markings.The brown guys sure look like resistors but I don't recall seeing any like that, back then.Lots of adhesive potting compound to fight the vibration.When they talk about the "right stuff", this is a real big reason for needing it.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: June 21, 2025, 07:10:40 pm
content: Most of the electronics in a Saturn V are in the Instrument Unit that sits between the top of the S-IVB third stage and the lunar module adapter. It had the same diameter as the third stage and was about 1 meter high. All of the IU's components were mounted on the inside perimeter of the IU and components that generated significant amounts of heat were mounted on cold pads that were cooled by sublimating water ice to space.The Launch Vehicle Digital Computer, built by IBM, is a triply redundant 26-bit computer that processed data bit-serially. It was clocked at 2.048 MHz and executed around 12,000 instructions per second. Memory was magnetic core 13 bits wide and up to 32K 26-bit words were supported. The LVDC used 2's complement arithmetic, unlike the Apollo guidance computer, which used 1's complement.The LVDC did not control the vehicle directly. It interfaced to an analog Flight Control Computer (FCC) via the Launch Vehicle Data Adapter (LVDA) to which it sent attitude control commands (2 second main loop with a secondary loop running 25 times per second).The IMU was the ST-124M stabilized platform containing gyros and accelerometers mounted on three gimbals. Initial alignment was via an optical system that used infrared beams from a theodolite mounted at ground level about 600 meters from the launch pad. Guidance was "released" at T-17 seconds in the countdown (Jack King, the NASA public affairs officer who was the announcer during launches, noted this event with the phrase "guidance is internal"). The gyros spun on nitrogen gas bearings and the IU had a spherical tank that supplied N2 to the IMU.The IMU also had radio command receivers and telemetry transmitters. Power during flight was provided by four 28V silver-zinc batteries, each with a capacity of 300 AH.Active guidance started after the first stage was jettisoned. Prior to that, guidance was open-loop via a stored program that did not use input from the IMU. Active guidance "converges" about 45 seconds after second stage ignition.

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 07:52:34 pm
content: Quote from: Sal Ammoniac on June 21, 2025, 07:10:40 pmWhy?

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: June 21, 2025, 08:07:09 pm
content: Quote from: iMo on June 21, 2025, 07:52:34 pmBecause during the first stage burn the vehicle was flying through the densest part of the atmosphere and frequent attitude corrections made by active guidance could have imposed aerodynamic loads that may have affected the structural integrity of the vehicle, especially as the stack passed through max-Q.The stored program performed a roll maneuver as soon as the vehicle cleared the tower to orient the stack on the correct launch azimuth, and then it initiated a pitch program to pitch the stack over to the correct attitude for achieving orbit. As soon as the second stage ignited, the LVDC started closed-loop guidance as the stack was already above most of the atmosphere.