Editing Saturn I SA-3 (section)

== Objectives ==

=== Primary ===

The main objectives of SA-3 were much the same as the previous two Saturn I flights in that it was primarily a test of the first-stage booster (S-I) and its H-1 engines. According to the NASA report ''Results of the Third Saturn 1 Launch Vehicle Test Flight'', SA-3 aimed to test four areas: the booster, the ground support equipment, the vehicle in flight, and Project Highwater.<ref name="thirdsaturn1964" />{{rp|3}}

The test of the booster involved the propulsion system, structural design, and control systems. The ground support test involved the facilities and equipment used in the launch, including propellant systems, automatic checkout equipment, launch platform, and support towers. The vehicle in flight test measured aeroballistics, which confirmed values of aerodynamic characteristics such as stability and performance; propulsion, which ensured the engines could provide enough thrust to propel the vehicle at the correct velocity and trajectory, as well as provide data on the performance of all eight engines during flight; structural and mechanical, which provided measurements of the vehicle's stress and vibration levels through all phases of flight; and guidance and control, which demonstrated that spacecraft systems could accurately provide orientation and velocity information.<ref name="thirdsaturn1964" />{{rp|3}}

The fourth objective, Project Highwater, was an experiment previously flown on [[Saturn I SA-2|SA-2]]. This involved the intentional release of ballast water from the second and third stages which allowed scientists to investigate the nature of Earth's [[ionosphere]], as well as [[noctilucent cloud]]s and the behavior of ice in space.<ref name="Woodbridge1965" />

For Project Highwater, tanks in SA-3's dummy upper stages were filled with {{convert|192528|lb}} of water, approximately {{convert|22900|USgal}}, which was used to simulate the mass of future Saturn payloads.<ref name="thirdsaturn1964" />{{rp|3, 66}} The water was divided roughly in half between the two dummy stages. When the terminate command was sent to the rocket, [[primacord]] charges split both stages longitudinally, instantly releasing its load of water.<ref name="Woodbridge1965" /> The experiment was tracked by cameras and other equipment on the ground and in aircraft.<ref name="miami19621117" /> Observers at Cape Canaveral reported that the ice cloud was visible for about three seconds and was "several miles across".<ref name="montreal19621117" /><ref name="miami19621117" />

NASA declared all engineering goals of the flight as achieved,<ref name="nssdc-sa3" /> despite occasional issues with telemetry during flight and some measurement data being unusable or only partially usable.<ref name="thirdsaturn1964" />{{rp|3}} Project Highwater on SA-3 was also declared successful,<ref name="thirdsaturn1964" />{{rp|3}} though again, telemetry issues produced questionable results.<ref name="nssdc-sa3" />

=== Special ===

The NASA ''Results'' report states that ten special tests were included in the SA-3 flight, all focused on technologies and procedures intended for use on future Apollo missions.

;Propulsion
As mentioned earlier, SA-3 was the first Apollo flight to carry a full load of propellant, compared to earlier flights that carried approximately 83% of maximum capacity. This had the effect of testing the rocket's reaction to slower acceleration and extended first stage flight time.<ref name="Benson1978" /> Also on this mission, the outboard engines were allowed to fire until depletion of the rocket's [[liquid oxygen]] (LOX), rather than the timed cut-offs of previous flights.<ref name="Flight19621122" />

SA-3 also featured the first use of [[retrorocket]]s on Apollo hardware. These were the only functional part on SA-3 of what would become the S-I/S-IV stage separation system, which would separate the two stages in later missions. These four small solid rockets were located 90 degrees apart around the top of the S-I stage, with their nozzles aimed up. At 2 minutes 33.66 seconds after launch, the rockets fired for about 2.1 seconds. A minor misalignment of the rockets caused a 4.3 degree per second roll of the vehicle, which caused the spacecraft's ST-90 and ST-124P inertial platforms to fail after 15 degrees of rotation. This was considered incidental to the flight and did not impact mission success.<ref name="thirdsaturn1964" />{{rp|17–18}}

;Instrumentation
The [[ST-124-M3 inertial platform|ST-124P inertial platform]] ('P' for prototype) was a component of the guidance and control system, and contained [[gyroscope]]s and [[accelerometer]]s that fed information to control computers.<ref name="thirdsaturn1964" />{{rp|32}} Once out of the atmosphere, this information provided steering signals to the gimbaled engines.<ref name="Bilstein1996" /> During SA-3, this platform was an inactive component; while functioning and monitored during the flight, it had no control over the vehicle, and was used only to compare performance with the then-standard ST-90 platform, which was also an inactive component for the flight.<ref name="thirdsaturn1964" />{{rp|1, 29}} For this mission, both platforms were located on the interstage between S-I and S-IV;<ref name="Flight19621122" /> [[Saturn IB]] and [[Saturn V]] vehicles would have one on the [[Saturn V Instrument Unit|Instrument Unit]] atop the S-IVB stage.<ref name="Seltzer1963" />

Two new transmitters were included on SA-3. The pulse code modulated (PCM) data link transmitted digital data, which would be vital to providing automated spacecraft checkout and launch procedures on future flights.<ref name="Benson1978" /> The unit operated with high signal strength, indicating that it would provide very accurate data.<ref name="thirdsaturn1964" />{{rp|60}} An [[ultra high frequency]] (UHF) radio link was also tested on SA-3. It would be used to transmit sensor measurements which could not be effectively transmitted at lower frequencies.<ref name="Benson1978" /> The system performed satisfactorily, and post-flight documentation indicated engineers may expand its role for future telemetry transmission.<ref name="thirdsaturn1964" />{{rp|60}}

A Block II antenna panel was tested during flight. Located between propellant tanks, it provided stronger and more consistent signal strength than the Block I panel.<ref name="thirdsaturn1964" />{{rp|60}}

Temperature measurements of the S-IV dummy stage and interstage fairing were carried out with eighteen temperature probes, called [[thermocouple]]s. These were used to detect temperature changes around protuberances on the stage's skin and in the area of the retrorockets during operation. For the S-IV stage, temperatures were within expected levels, though a [[heat transfer|heating rate]] around twice that predicted was encountered. On the interstage, during retrorocket firing, a maximum temperature of {{convert|315|C|F|abbr=on}} was seen, indicating something unknown may have caused an abnormally high reading.<ref name="thirdsaturn1964" />{{rp|53}}

;Engineering and ground equipment
A single panel of Block II M-31 heat shield insulation, along with one of the spacecraft's [[calorimeter]]s, was mounted on the base of the first stage by the engines. This test measured [[heat flux]] through the new insulation compared to the material normally used on Saturn I Block I flights.<ref name="thirdsaturn1964" />{{rp|49–51}}

A dynamic pressure study was conducted for the [[Centaur (rocket stage)|Centaur]] program, in which two aluminum panels were mounted to the payload adapter atop the S-V stage and equipped with 11 pressure sensors. This study was performed due to the failure of the first Centaur vehicle flown, suspected to result from an adverse pressure environment around the shoulder of the vehicle. The test found that a very low pressure region formed just behind the shoulder while the vehicle was at Mach 0.7.<ref name="Garcia1964" />

Finally, a new {{convert|240|ft|0|adj=on}} umbilical tower and Block II swing arm were used for the first time in preparation for future Block II Saturn I flights.<ref name="thirdsaturn1964" />{{rp|66}}<ref name="Flight19621122" />