Forty-nine years ago this week, the United States successfully conducted the fourth Saturn I test flight designated as Saturn-Apollo No. 4 (SA-4). Launched from LC-34 at Cape Canaveral, Florida on Thursday, 28 March 1963, SA-4 reached an apogee of 70 nm, attained a maximum speed of 3,670 mph and flew 216 nm downrange during the brief 15 minute suborbital mission. The Saturn I measured 180 feet in length, featured a maximum diameter of 21.4 feet and weighed 1,123,600 l bs at lift-off. The first stage propulsion system consisted of an octet of H-1 engines generating a total sea level thrust of 1,600,000 lbs. Nominal burn time was 150 seconds. Part of the early Apollo Program, SA-4 was the last flight to fire just the first stage rocket engines. As with the previous three launches, the primary goal of SA-4 was to validate the structural integrity of the Saturn I vehicle. However, a significant additional objective of SA-4 was to verify the GNC system’s ability to properly handle an engine-out anomaly during first stage operation. As such, one of the H-1 engines was programmed to intentionally shutdown at approximately T+100 seconds. The GNC system did indeed respond properly to this anomaly by rerouting propellants to the remaining seven (7) engines which burned longer to compensate for the loss of thrust. SA-4 also employed a nonfunctional second stage which incorporated the external shape of the ultimate second stage design. This included the presence of vent ducts, fairings, simulated camera pods and various externally-mounted antennae. SA-4 also fired a retrorocket system that would be employed to aid separation of various rocket stages on later flights. Despite dire warnings in some quarters, the shutdown H-1 engine remained intact despite the build-up of heat caused by the lack of cooling propellant flowing around the nozzle. This survivability feature underscored the robustness of the clustered engine concept employed in the Saturn series of space boosters. Interestingly, the engine-out compensation capability demonstrated on SA-4 was in fact successfully employed during a pair of later Apollo missions; Apollo 6 and Apollo 13.