In 1957, I had been playing with Jetex propulsion when Aerojet-General hired me as an engineering aide (age 17), right out of high school. Elmer E. Nelson, general manager of Aerojet in Sacramento, was my mentor, and wisely assigned me to the company's smallest rocket motor project, the 530NS-35 being developed for Radioplane, a division of Northrup. Jack Elias was project engineer on this one-engineer project, and I was soon shadowing him about propellant mixing Line 1, and the small solid-rocket test area near our offices on Line 2.
Jack Elias was solid rocket igniters expert (he had helped develop Alclo pellets), and a natural for the 530NS-35. That motor produced 35-lbf thrust (from long, twin nozzles) for nearly 9-min (530-sec nominal burn time). It propelled the Radioplane RP-76 up to around 75,000-ft and Mach 0.9, reportedly, though at the time all this was stamped "SECRET." The RP-76 was built as a target drone fror Army Nike-Ajax and early Hawk surface-to-air tests (shadows of the ICI drones for His Majesty's Admiralty, during WWII?). And Aerojet built lots of those motors in the late 1950s.
Regretably, I was a bewildered teenager at the time, and though granted a security clearance, the exciting big motors all around captivated my attention: Polaris, Minuteman, Titan I and II were in development next door. I recall little of the grain design, or formulation chemistry, or such vital details. The RP-76 was said to weight only 120-lb, and had a 4-ft 11-in wingspan. If I recall correctly, the motor used an ammonium nitrate (AN) oxidizer, though guanidine nitrate may have been on the scene as well.
Attached is a Smithsonian photo of the Radioplane. An exhaust nozzle can be seen just aft of the wing, silvery metallic in color. The motor itself was about the size (and looks) of an office wastebasket, perhaps 12" in diameter, maybe 15" long, and not at all heavy.