A multi-part series on the history of NASA's Apollo missions.
Reaching the moon required a mammoth launch vehicle – the Saturn V. Standing 363 feet and weighing 6 million pounds when fully fueled, the Saturn V dwarfed anything previously launched.
The Saturn V had three stages. Stage 1, called the S-IC, was 138 feet long and 33 feet in diameter. It had five F-1 engines. Each engine generated just over 1.5 million pounds’ thrust, giving the Saturn a lift off thrust of 7.6 million pounds. The power output of the S-IC was about 160 million horsepower. Liquid oxygen and RP-1 kerosene fueled the F-1s. The S-IC held 3,307,855 pounds (346,372 gallons) of liquid oxygen and 1,426,069 pounds (212,846 gallons) of RP-1. The stage consumed these propellants in two minutes and forty seconds..
The second stage, or S-II, also had five engines, but they were much smaller, the J-2. Burning liquid oxygen and liquid hydrogen, each J-2 produced a thrust of 200,000 pounds to give the S-II a thrust of 1 million pounds. The S-II held 821,022 pounds (85,973 gallons) of liquid oxygen and 158,221 pounds (282,555 gallons) of liquid hydrogen.
A single J-2 powered the third and final stage, the S-IVB. The S-IVB contained 192,023 pounds (20,107 gallons) of liquid oxygen and 43,500 pounds (77,680 gallons) of liquid hydrogen. The S-IVB stage provided the final boost into earth orbit for the Apollo spacecraft and then propelled it towards the Moon.
Such a gigantic rocket needed a unique suite of ground facilities, so NASA built Launch Complex 39, which had two launch pads. Complex 39 introduced the mobile concept of launch preparations to the American space program. Previously, technicians assembled rockets and their payloads vertically on the pad, leaving the vehicles exposed to the weather for weeks or even months before launch. Apollo needed a new approach, where the rocket and spacecraft could be assembled and “stacked” indoors then transported to the launch pad in a vertical position.
NASA constructed a gargantuan building, the Vehicle Assembly Building (VAB), for Saturn V assembly and check out. Measuring 716 feet long by 518 feet wide and 525 feet tall, the VAB could accommodate four rockets at one time. The VAB had a volume of 129,482,000 cubic feet and covered 343,500 square feet of floor space. The building foundation rested on 4,225 steel pilings driven 150 to 170 feet into the ground, to the bedrock. Each piling was 16 inches in diameter.
The Launch Control Center (LCC) for Pads 39A and B adjoined the VAB. This, too, was a radical departure from past launch pad architecture. The Apollo launch control center looked more like a glass-front office building than one of the older, igloo shaped concrete blockhouses.
Saturn Vs were stacked on a mobile launch platform in the VAB. Moving the Saturn and its mobile platform from the VAB to the launch pad required a huge tracked vehicle, the Crawler Transporter. Maximum speed for the transporter was about one mile per hour when loaded. An unfueled Saturn V and mobile launch platform weighed 6,000 tons; the Crawler Transporter by itself weighed 3,000 tons!
Launch Pads 39A and B were three and a half miles from the VAB. A special 131-foot wide roadbed topped with river rock from Alabama connected the assembly building and launch pads. The rocks helped distribute the load on the transporter bearings and reduced friction during steering. It took about six hours to reach the pad, because maximum speed was not maintained throughout the trip.
On November 9, 1967, NASA launched Apollo 4, the first flight test of the Saturn V. With the Saturn V, NASA adopted a philosophy of “all up testing.” That meant all three stages of the rocket were functional. Previously, the first flight of a new multistage rocket only had the first stage live. Only after the first stage’s performance was verified were live upper stages added. George Mueller, who headed NASA’s Office of Manned Space Flight, advocated testing all three stages on the first flight, as a measure to save both time and money. Mueller’s judgment had been correct; Apollo 4 was a success.
The next flight nearly derailed the entire schedule. The second unmanned Saturn V test, Apollo 6, lifted off on April 4, 1968. There were problems with all three stages. The first stage exhibited longitudinal instability, called “pogo” oscillations. Two of the S-II stage’s five engines quit early due to ruptured propellant lines caused by the oscillations, requiring the remaining three to burn longer than planned. The third stage engine also had to burn longer to make up for the loss of power. As a result, Apollo 6 entered an elliptical orbit rather than the circular parking orbit desired. When it came time to restart the S-IVB engine, it refused to fire again. At least the spacecraft performed well throughout its ten-hour flight. Despite this positive note, NASA managers did not view the flight as a success because of the booster problems
The most serious implication of the booster problems was that another unmanned test might be needed, something that would wreck NASA’s timetable for reaching the Moon. NASA solved the pogo problem by redesigning some propellant lines and injecting helium gas into the liquid oxygen prevalves. The problems with the second and third stage engines were corrected with modifications to the propellant lines, Everyone was so confident the fixes would succeed that the Saturn V was cleared to carry a live crew on its next flight.
Next month’s installment of the “Season of Apollo” series will feature the 50th anniversary of Apollo 8, the first voyage around the Moon.