1. The SRL5a and 5b-GFPPT used the same type of large surface flash-over spark plugs that were originally used in the SRL4-GFPPT. With a larger outer electroderadius, however, the SRL5a and 5b-GFPPT used eight igniters where the SRL4-GFPPT used only four. In the third and fourth iteration of the SRL5-GFPPT, the type of spark plug was changed to the same same semi-conductor spark gap ignitor used in the LES 8/9 APPT. These ignitors require a lower break down voltage without any extra propellant mass flow. The breakdown voltage for normal operation ofthe smaller semi-conductor spark-gap ignitor is w 1000 V which is much smaller than what was required for the original larger surface breakdown plugs, w 5000 V. The SRL5c-GFPPT also went through changes in the discharge initiation circuitry to try to balancethe energy distributed between each plug. All the spark plugs in each SRL-GFPPT are connected in parallel to a discharge initiation capacitor that is charged once foreach pulse. More details on changes to the discharge initiation circuitry will be provided in section 6. All versions and iterations of the SRL-GFPPT used the same solid-state control modulator and could be fired at energy levels between 3-10 J at rates up to 4 kHz. Typically six pulseswere fired per burst, however, this number can be set to higher levels depending on the desired thrust level. The discharge initiation power is produced by a separate high voltage supply. On every version of the SRL-GFPPT so far, the inner electrode is at a positive potential (anode) and the outer electrode is held at ground potential (cathode). The main discharge capacitors are mounted directly to the electrodes and the gaps between the conductors are kept at a minimum to reduce the initial inductance to 5-10 nH.
2. 150-100-