Moonport: A History of Apollo Launch Facilities and Operations|
Beginning the Checkout
Andrew Pickett's Vehicle and Missile Systems Group (part of Zeiler's Mechanical Office) spent the next month installing the accessories of SA-1* and conducting a series of launch vehicle tests. In some, the purpose was to make sure that various components responded correctly to pressure stimuli. Others checked for leaks caused by the barge trip and the subsequent erection of the S-1 stage. The first week the group performed pressure switch functional tests, verifying the pickup and dropout pressures for several hundred switches. The Saturn's 48 nitrogen bottles, which pressurized the RP-1 fuel tanks during flight, were then tested at one-half the operating pressure.
During the second week, the unit checked out the pressurizing and venting capability of the LOX tanks. Air pressure was applied to a switch in the tanks' electrical system. The switch, when functioning properly, would terminate pressurization at a certain level. If excessive pressure built up, a second switch would vent the hypothetical gaseous oxygen. LOX and RP-1 system leak checks followed; in both tests the team pressurized the tanks to about one-half the operating pressure, looking for seal leaks.
Concurrently Pickett's group conducted a series of engine tests. A nitrogen purge of the LOX dome, located at the top of the H-1 engine, served several purposes. A low-level purge, begun prior to propellant loading and continued until shortly before engine ignition, exceeded atmospheric pressure to prevent contaminants from entering the thrust chamber nozzle and flowing up to the injector plate and LOX dome. This also prevented moisture from condensing in the area. If a launch was cancelled, a full-flow nitrogen purge would quickly expel all LOX from the dome to avoid a possible explosion. Similar purges of the liquid-propellant gas generator, LOX injector manifold, and the fuel-injector manifold of the thrust chamber prevented the entry of unwanted substances.
The full-tank pressurization test on 6 September ended the first phase of mechanical checkout. Allowing for the possibility of an explosion while bringing the launch vehicle to full pressure, LOD officials cleared the pad for the Wednesday morning test. The two-hour exercise went smoothly, and that afternoon engineers were back at the launch vehicle for further operations.24
Calibration of the measuring devices that were to report more than 500 flight measurements was a daily operation. Sensing devices such as transducers, potentiometers, thermocouples, and strain gauges measured pressures, propellant flows, temperatures, and vibrations. A signal from one of these sensors, measured in millivolts, was routed to a signal conditioner which amplified the reading until it could be read on a scale of 0.5 volts. The calibration of these signal conditioners, popularly referred to as black boxes, was a major concern of Reuben Wilkinson's Measuring Group (a unit of Sendler's Measuring and Tracking Office). The team sometimes stimulated a sensing device by tapping on a portion of the rocket to cause vibrations or by placing a hot soldering iron near a thermocouple. More often they simulated a signal with an electrical input through an "interrupt box" located between the sensor and the signal conditioner. While calibrating the black boxes, the launch team bypassed the telemetry system. The amplified signal went from the signal conditioner through a series of remote-controlled relays, and then over wires to a measuring station in the base of the service structure. The calibrating equipment in the station normally performed a five-step sequence, checking the reading of each instrument at 0, 25%, 50%, 75%, and 100% of maximum value. After the tests were completed, Wilkinson's team reconnected the measuring and telemetry systems for readings over the radio frequency (RF) links.** The Measuring Group removed faulty instruments from the launch vehicle for further checks at calibration stands or in an instrument-calibration laboratory. The team was also responsible for the blockhouse measuring-station. Here LOD received 100 ground measurements on the rocket and ground support equipment, as well as telemetry data.25
Another of Sendler's units, Daniel McMath's telemetry team, checked out the booster's eight RF links. Seven of the links used the XO-4B package, a proved system from Jupiter flights. The XO-4B was a PAM- FM-FM (pulse amplitude modulated-frequency modulated-frequency modulated) system with 15 channels of continuous data and 54 multiplexed channels.#
The Guidance and Control Division in Huntsville had developed the eighth link to ensure sufficient data channels for the Saturn C-1. The central feature in the new XO-6B was a 216-channel electronic commutating system.## Sub-multiplexers sequentially sampled the same measurements for each of the eight engines. Sub-multiplex 1 might sample "temperature LOX pump bearing" while sub-multiplex 2 sampled "pressure at fuel pump inlet." The main transistorized multiplexer, in turn, sequentially sampled each of the 27 sub-multiplexers. The multiplexer's output was fed to a 70-kilohertz wide-band subcarrier. This frequency permitted the use of a commercially available oscillator that accurately carried the 3600-pulse-per second wave train and utilized existing demodulation equipment. The result was that 216 separate Saturn measurements traveled on one radio frequency.26
McMath's Telemetry Group first tuned the two sets of antennas located at the forward end (top) of the S-1 stage. The six-man team next performed transmitter and power amplifier checks. A third operation, alignment of the subcarrier channels, involved tuning each subcarrier oscillator to its center frequency and band edges. The test also ensured that signal output from the oscillators was of correct amplitude. Midway into the second week the team began verifying telemetry wiring. Data was fed into each line at a break between the measuring and telemetry systems. If range operations permitted, the team conducted an "open loop test," with the RF transmitter radiating the telemetry signal to receivers in the blockhouse and hangar D. But if radiating RE signals would interfere with any other activity in the area, the team operated "closed loop" with the signal going from the telemetry link over wire to the telemetry ground stations. After all eight links were checked out, the team reconnected the measuring and telemetry systems for subsequent tests of the launch vehicle.27
During the first month of checkout, Jim White's Tracking Group worked on the tracking systems for the SA- 1: cameras, UDOP and UDOP Beat-Beat, S-band radar, C-band radar, Azusa, Beat-Beat MKII Telemetry, and Telemetry ELSSE.*** The two radar systems were controlled by the Air Force. The S-band provided position data by tracking the Saturn beacon. The C-band was a backup, should the Saturn beacon fail. LOD had eight UDOP stations in the Cape area, each connected by RE data links to a central recording station in hangar D. The Beat-Beat MKII Telemetry employed two baselines: one set of antennas located south of LC-34 determined whether the rocket made its proper turn out to sea; the other set, southwest of LC-34, ascertained flight path deviations downrange. The UDOP Beat-Beat system would fly on SA-1 as an experimental package.28
White's team employed a test transmitter to check out the UDOP stations. The test team simulated launch vehicle movement by varying the transmitted frequency. A drop in frequency simulated velocity away from the receiving station; conversely, a frequency increase represented rocket movement toward the receiver. These response tests checked the data-link equipment as well as the eight UDOP receiving sets. Preparation of the Beat-Beat systems included "walking the antenna," a basic test, but one which pointed up the importance of the tracking unit's work.### First, antenna connections were broken at one end of the baseline. Then a team member, equipped with a hand antenna and field telephone, walked a certain distance to set up a new baseline. Launch vehicle signals received at the new baseline indicated a theoretical rocket deviation from the previous flight path (read at the old baseline), the degree and direction of the deviation depending on the man's new location. By correlating the deviation and the new baseline, White's team determined whether the Beat-Beat system was functioning properly.29
SA-1 required many modifications of equipment and procedures; as early as the second week the activities report listed among its major events, "engineering changes underway."30 Characteristic of first launches, SA-1 was the most difficult and time-consuming of the Saturn block I launches. Robert Moser altered the schedule, when necessary, at the daily operations meeting in blockhouse 34.31
The scheduling committee planned an RF compatibility test for the midway point in the eight-week checkout (see table 3). The test was a major one for SA-1, marking the first time the vehicle stood alone (service structure removed from pad) for a complete check of the radio systems. Power was applied to the vehicle's RF systems to transmit signals to Cape receiving stations for telemetry, radar, and command and control. The launch team was particularly interested to see if the test would cause any interference in the command destruct system. Earlier launch programs had involved two to four telemetry links. SA-1's eight links increased the possibility of carrier and subcarrier frequencies beating against each other to produce harmonics that would feed back into receiving antennas. The effect might introduce spurious signals into the command destruct system.**** The operations serve both a validation and confidence function, proving each radio channel's performance and demonstrating that no serious interference would enter the destruct system. As an unexpected bonus, the test also demonstrated the launch vehicle's stability. Shortly after removal of the service structure, a sudden September squall subjected the rocket to 48-kilometer-per-hour winds without ill effect.32
TABLE 3. RF INSTRUMENTATION TEST PROCEDURES, SA-1
T-20 (20 minutes prior to launch). 1.M: Telemeter 1, 2, 3, 4, 5, 6, 7 and 8 ON 2.M: Auxiliary Equipment ON 3.M: Azusa ON 4.M: UDOP ON 5.M: C Band beacon to FILAMENT 6.M: S-Band to FILAMENT 7.M: Command Receiver + 1 ON 8.M: Command Receiver + 2 ON 9.M: Telemeter Calibration to PREFLIGHT 10.M: Telemeter Calibration Command to 50% 11.RANGE: Radars ON and away from pad T-18 1.TM-D: Telemeter Recording ON 2.TM-B: Telemeter Recording ON T-17 1.M: C-Band Beacon to B + 2.M: S-Band Beacon to B + T-16 1.M: Telemeter calibration command to 0% for 10 sec. 2.M: Telemeter calibration command to 100% for 10 sec. 3.M: Telemeter calibration command to 0%, 25%, 50%, 75%, 100%, 0% in 2 sec. increments T-15 1.M: Telemeter calibration to INFLIGHT 2.M: Telemeter calibration command ON & OFF 3.RANGE: Command Carrier ON 4.RANGE: Check Azusa and report verbal readout to Test Conductor 5.RANGE: Interrogate C- and S-Band Beacons and report verbal readout to Test Conductor T-12 1.RANGE: Cutoff command on request of Test Conductor 2.RANGE: Destruct command on request of Test Conductor 3.RANGE: Switch transmitters as required by Range and repeat functions 4.RANGE: Secure Command Carrier 5.M: Command Receiver #1 OFF 6. Command Receiver #2 OFF T-10 1.M: Telemeters 1, 2, 3, 4, 5, 6, 7, and 8 OFF 2.M: Auxiliary Equipment OFF 3.TM-D: Telemeter Recording OFF 4.TM-B: Telemeter Recording OFF T-5 1.M: Azusa OFF (or sooner if RANGE readout is complete) 2.M: UDOP OFF T-0 1.M: C-Band Beacon OFF (or sooner if RANGE readout is complete) 2.M: S-Band Beacon OFF (or sooner if RANGE readout is complete)Source: "Saturn Test Procedures, RF Instrumention Test SA-1 (4-LOD-3)," Robert Moser papers. This test format is similar to, but briefer than, most of the several hundred other procedures prepared by LOD for SA-1. Symbols:
M Firing Room Measuring Panel TM-D LOD Telemeter Station Hangar D TM-B Blockhouse 34 Telemeter Station RANGE Items for Test Conductor and Safety Officer
LOD started integrated systems tests in the fifth week of checkout. Overall test (OAT) #1 (mechanical and network) was the first run of the launch vehicle's sequencing system, the relay logic that controlled the last minutes of countdown. OAT #2, a "plugs-drop test," put the vehicle on internal power with ground support disconnected. The key overall test, the guidance and control OAT #3, pulled all systems together in a check verifying the previous five weeks' work. The launch team began preparations for the test Saturday, 23 September. The advance work fell into seven categories: vehicle networks, ground networks, mechanical, electrical support, measuring, RF, and navigation. Vehicle network requirements included the connection and verification of telemeters, calibrators, radars, and 60 test cables, e.g., the Thrust OK Switch Engine #3 test cable. The checkout on Monday morning went well; MSFC officials were increasingly confident that SA-1 would fly.33
By early October the original launch date of the 12th had slipped eight days. On the 4th the launch team conducted the LOX loading test, a major exercise for SA-1 since it represented the first integration of the Cape's cryogenic support equipment with the Saturn vehicle. LOD followed this successful exercise with another plugs-drop test on the 10th. Engine-swivel checks were completed by the end of the week. The launch team began the ninth week of checkout with the simulated flight test, the last major preflight test. Robert Moser's 43-page procedure covered preparations for launch, the last 90 minutes of countdown, and activities for 5 hours after liftoff. The test went well, but MSFC delayed the launch another week while its Saturn Office debated the merits of adding more sensors near the base of the booster to provide additional information on the critical bending during the first 35 seconds of flight. It was finally decided that SA-1's instrumentation was adequate and the launch was set for 27 October. During the last week, LOD completed ordnance fitting (the command destruct system) and repeated the simulated flight test.34
* Both the rocket and the mission carried the designation SA-1.
** According to the Saturn SA-1 Vehicle Data Book. the following types of measurements were made on the SA-1: "propulsion, expulsion, temperature, pressure, strain and vibration, flight mechanics, steering control, stabilized platform, guidance, RE and telemetering signals, voltage, current and frequency, and miscellaneous." Nearly 400 of SA-1's 510 telemetered readings concerned propulsion, temperature, or pressure. F. A. Speer, "Saturn I Flight Test Evaluation," 1st American Institute of Aeronautics and Astronautics Meeting, 29 June-2 July 1964, fig. 4.
# Each telemetry link employed one frequency, e.g., SA-1's link 3 used 248.6 megahertz. Oscillators within that system produced sub carrier channels, referred to as straight channels because they carried continuous data from one sensor. Most measuring instruments, however, shared telemetry time by means of a multiplexer. On the XO-4B links, two 27-channel mechanical commutators provided the multiplex function.
## Commutation in telemetry is sequential sampling, on a repetitive time-sharing basis, of multiple-data sources for transmitting on a single channel.
*** See footnote 3-2.1 for descriptions of Beat-Beat and UDOP. Azusa dated back to the early 1950s and was named after the southern California town where the system was devised. The Azusa ground station determined the vehicle transponder's position by measuring range and two direction cosines with respect to the antenna baselines. ELSSE (Electronic Skyscreen Equipment) was used "to determine angular deviations of the missile from the flight line. The system consists of two ELSSE receivers placed behind the missile equidistant on either side of the backward extended flight line." W. R. McMurran, ed., "The Evolution of Electronic Tracking... at KSC," p. 3.
### According to LOD veterans, an incorrect performance of this test had cost the Air Force its first Thor shot several years earlier. After establishing its new baseline, an inexperienced contractor crew had picked up an LOD test transmitter frequency rather than the Thor's RF . Getting the opposite results from what they expected, the team had rewired the indicating device. When the Thor was launched, the range officer destroyed it unnecessarily, because the Beat-Beat system indicated a westward flight toward Orlando.
**** In a subsequent Saturn I checkout, after additional telemetry links had been added and before LOD adopted a digital command receiver, the launch team had considerable trouble with interference in the command channel.
33. Moser interview, 30 Mar. 1973; "Saturn SA-1 Schedule"; MSFC, SA-1 Flight Evaluation, pp. 7-9; LOD, "Saturn Test Procedures, SA-1 G & C Overall Test #3," Moser papers, Federal Archives and Records Center, East Point, GA, accession 68A1230, boxes 436257, 436259.
34. Moser interview, 30 Mar. 1973; "Saturn SA-1 Schedule"; MSFC, "SA-1 Flight Evaluation," pp. 8-9; George Alexander, "Telemetry Data Confirms Saturn Success," Aviation Week and Space Technology, 6 Nov. 1961, pp. 30-32.