They are pressure fed hydrazine monopropellant thrusters. They are incredibly reliable. Keep in mind that Voyager 1 doesn't have reaction wheels or any other me

They are pressure fed hydrazine monopropellant thrusters. They are incredibly reliable. Keep in mind that Voyager 1 doesn't have reaction wheels or any other method for controlling its attitude other than its thrusters, and it's 3-axis stabilized. The original thruster set fired thousands of times over a nearly 4 decade period and now the backup thruster set is being rotated into use.