S-I
On the 27th of October 1961, the S-I stage lifted off for the first time with less propellant than it could hold. Engineers had reduced the load deliberately. If something failed near the launch pad, less fuel would mean a smaller disaster. A rocket of this size had never flown before. The S-I was the first stage of the Saturn I, developed by Chrysler for NASA's Apollo program. How did Chrysler design and assemble an engine stage for a vehicle that had no precedent in American rocketry? And how did one later S-I launch prompt John F. Kennedy to declare that the United States had overtaken the Soviet Union?
Nine tanks formed the structural core of the S-I stage, all of them drawn from existing missile programs. One was a tank originally designed for the Jupiter ballistic missile, sitting at the center. Eight Redstone missile tanks surrounded it, creating the cluster shape. Four of those Redstone tanks carried liquid oxygen; the other four held RP-1 fuel. Engineers painted the outer tanks in a specific pattern for two purposes. One was thermal: the paint altered the temperature conditions inside each tank. The other was navigational. The contrasting colors created a "roll pattern" that was readable from the ground, letting observers estimate how the stage was rotating during flight. The engines below the tank cluster had a more complex job than simply providing thrust.
Eight H-1 engines powered the S-I stage, arranged in two distinct groups. Four central engines were fixed in place, providing stable, unvarying thrust. The outer four pivoted on gimbals, which allowed them to redirect their thrust in different directions. This technique, known as thrust vectoring, gave the stage directional control. The first four Saturn I missions flew without any fins on the S-I stage. From SA-5 onward, engineers added eight fins to improve stability during the dense lower atmosphere portion of flight. SA-2, the second mission, would add an entirely different experiment to the flight plan.
SA-2 lifted off on the 25th of April 1962. It carried 86,000 kg of water inside dummy upper stages that stood in for a live second stage. At an apogee of 145 km, all of that water was released into the upper atmosphere. Project Highwater, as the experiment was called, studied what happened when a large mass of water entered the near-space environment. SA-3 repeated the test on the 16th of November 1962, releasing the same 86,000 kg at a slightly higher apogee of 167 km. SA-3 was the final Project Highwater mission. SA-4, launched on the 28th of March 1963, was the last Block I flight to carry dummy upper stages. It flew a suborbital trajectory reaching an apogee of 129 km. SA-5, scheduled for January 1964, would introduce a live upper stage for the first time.
SA-5 launched on the 29th of January 1964, carrying the first live S-IV second stage. It was also the first Saturn I mission to reach orbit, inserting its payload into an elliptical path of 760-264 km. The orbiting mass at insertion weighed 38,700 lb (17,550 kg). President John F. Kennedy publicly identified SA-5 as a pivotal point in the Space Race. According to Kennedy, the mission had placed the United States ahead of the Soviet Union in lift capability. The SA-5 hardware remained in orbit for more than two years, decaying on the 30th of April 1966. The mission that followed, SA-6, would carry the first Apollo boilerplate command and service module.
SA-6, launched on the 28th of May 1964, placed an Apollo boilerplate designated BP-13 into an orbit of 204-179 km. That boilerplate decayed just days after launch, on the 1st of June 1964. SA-7, launched on the 18th of September 1964, carried a second boilerplate designated BP-15. SA-7 achieved an orbit of 203-178 km and flew with a payload mass of 36,800 lb (16,700 kg). BP-15 decayed on the 22nd of September 1964, just four days after launch. Three Pegasus micrometeoroid satellites would follow as payloads of the final three S-I missions.
SA-9, launched on the 16th of February 1965, carried the first Pegasus micrometeoroid satellite. The mission also carried the third Apollo boilerplate, designated BP-26. Pegasus 1 entered an orbit of 523-430 km at a mass of 3,200 lb (1,450 kg). It remained in orbit for more than thirteen years, decaying on the 17th of September 1978. SA-8 followed on the 25th of May 1965, becoming the only night launch in the Saturn I program. SA-8 placed Pegasus 2 into an orbit of 594-467 km alongside a fourth Apollo boilerplate, BP-16. The final S-I mission, SA-10, launched on the 30th of July 1965. Pegasus 3 entered an orbit of 567-535 km and decayed on the 4th of August 1969. The boilerplate carried on SA-10, designated BP-9A, did not decay until the 22nd of November 1975, over a decade after its launch.
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Common questions
Who developed the S-I stage of the Saturn I rocket?
The S-I stage was developed by Chrysler for NASA's Apollo program. Its nine-tank structure combined a central Jupiter missile tank with eight surrounding Redstone missile tanks, all drawn from existing hardware.
What engines powered the Saturn I S-I stage and how were they arranged?
Eight H-1 rocket engines powered the S-I stage, burning RP-1 fuel with liquid oxygen as oxidizer. Four central engines were fixed in place, while four outer engines were mounted on gimbals to provide directional control through thrust vectoring.
When did the first Saturn I S-I stage mission launch?
The first S-I mission, SA-1, launched on the 27th of October 1961. The stage flew with a reduced propellant load as a precaution to limit damage if the vehicle failed near the launch pad.
What was Project Highwater on the Saturn I?
Project Highwater was an experiment conducted on two Saturn I test flights, SA-2 and SA-3, that released 86,000 kg of water into the upper atmosphere. SA-2 performed the release at an apogee of 145 km on the 25th of April 1962; SA-3 repeated it at 167 km on the 16th of November 1962.
What did John F. Kennedy say about the SA-5 Saturn I launch?
President Kennedy publicly identified the SA-5 launch as the mission that placed the United States ahead of the Soviet Union in lift capability. SA-5 launched on the 29th of January 1964 and was the first Saturn I mission to reach orbit, at an altitude of 760-264 km.
What were the Pegasus micrometeoroid satellites launched on Saturn I S-I missions?
Three Pegasus micrometeoroid satellites were deployed on the final three S-I missions in 1965: SA-9 in February, SA-8 in May, and SA-10 in July. Each satellite had an orbital insertion mass of 3,200 lb (1,450 kg) and remained in space for years after launch.