Lynn Poole gives a brief history of aviation propulsion. Dr. William Avery, of Johns Hopkins University's Applied Physics Lab, describes how techniques of flight have changed from the Chinese rocket of 1232 AD to the ramjet. Isaac Newton's equal and opposite principle was the basis for jet propulsion, and its first use was in jet-assisted takeoffs, which allowed shorter runways. Dr. Avery shows a diagram of a solid fuel rocket consisting of propellant grain, nozzle, and warhead and contrasts it with a liquid propellant rocket consisting of rocket fuel and oxidizer tanks, combustion chamber, warhead, and valves and pumps. He notes that liquid fuel rockets are more subject to failure than solid fuel ones. Dr. Avery briefly describes the work of rocket pioneers Tsiolkovskiy, Goddard, and Oberth. Further research in the field resulted in the air-breathing engine during World War II, pulse jet engine (loud and limited in speed), turbojet engine by Briton Frank Whittle, and ramjet engine, first proposed by Rene Lorin in 1910 but requiring supersonic speed. Dr. Avery describes the key components of the ramjet: the diffuser, fuel system, and combustor. He then explains graphs comparing the ramjet and turbojet in four areas of performance and limitations: thrust per unit frontal area, specific fuel impulse, thrust per unit weight, and speed and altitude limits, proving ramjet the more economical to use. In concluding, Dr. Avery shows how a 1970 airliner with both turbojet and ramjet engines will look and operate.