С одной стороны пишут так:
The S-IC/S-II staging sequence for AS-510 differed markedly from earlier missions. On previous flights, the interstage, or skirt, a 4.9-metre tall ring matching the 10-metre diameter of the S-IC and S-II that it sits between,
carried solid-fuel rockets which fired shortly after the first stage separated to settle the S-II propellants in their tanks. AS-501 and AS-502 had eight of these ullage rockets, while AS-503 to AS-509 had four. They were deleted from the Apollo 15 launch vehicle, along with four of the eight retro rockets built into the conical engine fairings around the base of the S-IC, in order to save weight and increase payload
Но с другой стороны там же ниже:
Despite deliberately coasting for longer than usual
between separation and S-II ignition , the distance between the two stages was less than engineers had planned and the blast of hot gases from five J-2s against the top of the empty stage disabled a telemetry package...
Staging of the S-IC and S-II is technically described as a "dual plane separation," as the vehicle is cut across two geometrical planes. The first plane is between the skirt and the S-IC, with
the S-II engines starting 1.1 seconds later .
Я тут посмотрел циклограмму при запуске Скайлеба - самый последний Сатурн-5. Так вот - это норма когда НАЧАЛО подготовки J-2 к запуску начинается через секунду ПОСЛЕ разделения. Так что никаких горячих стартов.
S-IC Engine 1 and 3 Cutoff 158.2
S-IC Engine 2 and 4 Cutoff 158.2
Begin Time Base 3 158.2
S-IC/S-II Separation 159.9
S-II Engine Start Sequence Command 160.6
Короче говоря - видно просто утка американцев. Малость приврали. Скорее всего пороховики были, может быть их поставили меньше количество, или уменьшили время импульса. ИМХО никаких радикальных горячих/минометных стартов