This device extends and reacts a 25-foot long metal boom, with a scientific instrument at the end, a gamma ray spectrometer that needs to be at a distance from the spacecraft when making its measurements.
SPAR is the Canadian Aerospace company that made the Canadarm for NASA. It took a bit of hunting before I found reference to their work on Apollo, in a presentation at the CASI 18th Astronautics Conference:
“1955: George Klein invented the Storable Tubular Extendible member (STEM) at the National Research Council in Ottawa. DHC (later spun off as SPAR Aerospace) developed this as a product, sold into many space applications. Used on Gemini and Apollo spacecraft. E.g., used to deploy and retract gamma‐ray spectrometer and mass spectrometer instrument from Service Module Instrument Bay on Apollo 15, 16”
Here is a page dedicated to this STEM mechanism, which reminds me of the retractable arm on the Viking lander (like a metal tape measure that can be deployed into a rigid arm from a spool).
It says “Engineering Test Specimen Qual Unit” in big red lettering. From the Metal tag on the Boom:
Item Name: Boom Actuating Mechanism
Control Number: ME 190-0
Manufacturer: Spar Aerospace Products Ltd.
Serial Number: 103240000010
Part Number: 5965F13
Type: 2” B-STEM
Date of Manufacture: Feb. 71
The actuator stickers have NAS-9 contract and NAA control numbers on them.
The frame is stamped V37-551600-11 06362PAD5793, and V37-551192, and V37-551011-401 A CHG 06362AAJ8251 DR/MR S023473-1.
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