13.1 WEATHER CONDITIONS
Cumulus clouds existed in the launch complex area with tops at 15 000 feet 20 minutes prior to the scheduled launch and with tops at 18 000 feet 10 minutes later. During this time, the ground-based electric field meters clearly showed fluctuating fields characteristic of mildly disturbed weather conditions. Since the mission rules do not allow a launch through cumulus clouds with tops in excess of 10 000 feet, a 40-minute hold was required before a permissible weather situtation existed. At launch, the cloud bases were at 4000 feet with tops to 10 000 feet. The launch under these conditions did not enhance the cloud electric fields enough to produce a lightning discharge, thus providing further confidence in the present launch mission rules.
13.2 ATMOSPHERIC ELECTRICITY EXPERIMENTS
As a result of the lightning strikes experienced during the Apollo 12 launch, several experiments were performed during the launch of Apollo 13 and Apollo 14 to study the effects of the space vehicle on the atmospheric electrical field during launch. Initially, it was hoped that the effects could be related simply to the electrical-fieldenhancement factor of the vehicle. However, the results of the Apollo 13 measurements showed that the space vehicle produced a much stronger electrical field disturbance than had been expected and also produced some lowfrequency radio noise. This disturbance may have been caused by a buildup of electrostatic charges in the exhaust cloud, charge buildup on the vehicle, or a combination of both of these sources. To define the origin and the carriers of the charge, additional experiments were performed during the Apollo 14 launch to study the electric field phenomena in more detail, to measure radio noise, and to measure the temperature of the Saturn V exhaust plume, which is an important parameter in calculating the electrical breakdown characteristics of the exhaust. The preliminary findings of these experiments are given here. When analyses of data have been completed, a supplemental report will be issued (appendix E) .
13.2.1 Electrical Field Measurements
Atmospheric electrical field measurements were made by the New Mexico Institute of Mining and Technology and the Stanford Research Institute at the locations shown in figure 13-1. In addition, a field measuring instrument (field mill) was installed on the launch umbilical tower to detect any charge buildup on the vehicle during ignition and the initial seconds after lift-off. Accurate timing signals, which were not available on Apollo 13, were provided to most of the field measurement equipment locations on Apollo 14. Time-lapse photographs of the launch cloud were n1so taken to aid in the interpretation of the data. Like Apollo 13, the Apollo 14 launch produced a significant electrical disturbance in the field mill records (fig. 13-2). Although the data are still being analyzed, some preliminary observations can be made.
During the Apollo 13 launch, the instruments at sites west of the launch complex registered a smooth positive field increase, succeeded by a less pronounced negative excursion. For Apollo 14, the negative excursion was not evident; however, the field variations occurred at approximately equivalent times for both launches. The positive excursion was approximately five times greater for Apollo 13 than for Apollo 14, and reached maximum when the space vehicle was at altitudes greater than 1000 meters. This observation, coupled with the fact that the maximum electric fields were observed downwind on both launches makes it unlikely that the space vehicle charge was the dominant factor but, rather, that the positively charged clouds were the dominant sources of the electric fields.
During lift-off, the swiftly moving exhaust clouds are channeled both north and south through the flame trough. The principal cloud which moved through the north end of the flame trough was composed largely of condensed spray water and contained.a positive charge of approximately 50 millicoulombs and a field of approximately 4000 volts/meter (Site 2 of fig. 132). The cloud that exhausted to the south had much less water and contained about a 5-millicoulomb negative charge. The,cloud also appeared to contain solid particulate matter which rapidly fell out.
The field mill on the launch umbilical tower indicated a small positive value (<400 volts/meter) a few seconds after liftoff. Model measurements using a 1/144-scale model of the launch umbilical tower and the Apollo/Saturn vehicle indicated that, in this configuration, the launch umbilical tower field and the vehicle potential are related by volts/ field = 20 meters. Thus, the vehicle potential is less than 8000 volts (400 x 20). A comparison of the launch umbilical tower record with the data from the other sites indicates that the charge on the vehicle appears to be less than 1 millicoulomb.
13.2.2 Radio Noise Measurements
Narrow-band radio receivers operating at frequencies of 1.5, 6, 27, 51, and 120 kHz were located at camera pad 5 (field mill site 11) together with a broadband detector. As in the case of Apollo 13, signals were detected at several different frequencies, but the time behavior of different frequency components was not the same during the two launches.
The loop-antenna data (fig. 13-3) indicate a large increase in noise on the 1.5-kHz and 6-kHz channels 3 seconds after engine ignition, while the noise on the 51-kHz channel did not begin until 2 seconds after liftoff (about 11 seconds after ignition). Initially, it appeared that the 1.5- and 6-kHz data might not represent radiated electromagnetic noise, rather, microphonic noise generated by some component of the system such as the loop antenna preamplifier. Preliminary data from the electric dipole antenna at camera pad 5, however, indicate the same general behavior, and as the two antenna systems use separate amplifiers, it appears that the data are valid. An abrupt cessation of the 1.5- and 6-kHz noise by both systems prior to the loss of the 51-kHz noise is not understood and further studies of the noise data are presently being made.
13.2.3 Plume Temperature Measurements
The temperature characteristics of the Saturn V exhaust plume were studied from a site about 5 miles west of the launch complex using a twochannel radiometer system operating at 1.26 and 1.68 microns. The radiometers viewed a narrow horizontal section of the exhaust plume which, in turn, provided temperature as a function of distance down the plume as the vehicle ascended vertically. Figure 13-4 shows the measured plume temperature as a function of distance behind the vehicle. These results are now being used to improve the theoretical calculations of the electrical characteristics of the exhaust plume. It appears that the plume may be a reasonable electrical conductor over a length of some 200 feet. This result is consistent with the low value of vehicle potential when the vehicle is passing the launch umbilical tower field meter since, at that time, the vehicle is probably still effectively connected electrically to earth. (Reference 10 contains additional information concerning plume temperature measurements.)
13.3 LAUNCH VEHICLE SUMMARY
The seventh manned Saturn V Apollo space vehicle, AS-509, was launched on an azimuth 90 degrees east of north. A roll maneuver was initiated at 12.8 seconds that placed the vehicle on a flight azimuth of 75-558 degrees east of north. The trajectory parameters from launch to translunar injection were close to nominal with translunar injection achieved 4.9 seconds earlier than nominal.
All S-IC propulsion systems performed satisfactorily. Total propellant consumption rate was 0.42 percent higher than predicted with the consumed mixture ratio 0.94 percent higher than predicted. Specific impulse was 0.23 percent higher than predicted.
The S-II propulsion system performed satisfactorily. Total propellant flow rate was 0.12 percent below predicted and specific impulse was 0.19 percent below predicted. Propellant mixture ratio was 0.18 percent above predicted. The pneumatically actuated engine-mixture-ratio control valves operated satisfactorily. Engine start tank conditions were marginal at S-II engine start command because of the lower start tank relief valve settings caused by warmer-than-usual start tank temperatures. These warmer temperatures were a result of the hold prior to launch.
The S-IVB stage engine operated satisfactorily throughout the operational phase of first and second firings and had normal shutdowns . The S-IVB first firing time was 4.1 seconds less than predicted. The restart at the full-open propellant utilization valve position was successful. S-IVB second firing time was 5.5 seconds less than predicted. The total propellant consumption rate was 1.38 percent higher than predicted for the first firing and 1.47 percent higher for the second firing. Specific impulses for each were proportionally higher.
The structural loads experienced were below design values. The maximum dynamic pressure period bending moment at the S-IC liquid oxygen tank was 45 percent of the design value. The thrust cutoff transients were similar to those of previous flights. The S-II stage center engine liquid oxygen feedline accumulator successfully inhibited the 14- to 16-hertz longitudinal oscillations experienced on previous flights. During the maximum dynamic pressure region of flight, the launch vehicle experienced winds that were less than 95-percentile January winds.
The S-IVB/instrument unit lunar impact was accomplished successfully. At 82:37:52.2 elapsed time from lift-off, the SIVB/instrument unit impacted the lunar surface at approximately 8 degrees 5 minutes 35 seconds south latitude and 26 degrees 1 minute 23 seconds west longitude, approximately 150 miles from the target of 1 degree 35 minutes 46 seconds south latitude and 33 degrees 15 minutes west longitude. Impact velocity was 8343 ft/sec.
The ground systems, supporting countdown and launch, performed satisfactorily. System component failures and malfunctions requiring corrective action were corrected during countdown without causing unscheduled holds. Propellant tanking was accomplished satisfactorily. Damage to the pad, launch umbilical tower, and support equipment was minor.
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