Originally Posted by Chas Russell

If I recall correctly, the "booster" motors had a short delay and ignited a length of theralite to start the upper stage motor. Never did it so don't know how reliable that technique was. The big issue today is the unavailability of thermalite. The little that I have, for "historical" purposes, is probably unreliable. Usually the thermalite was sheathed in teflon tubing which greatly increased its burn rate.

Chas