Reports/Apollo 17/Saturn V flight evaluation/4 Trajectory

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[edit] 4.1 Summary

The vehicle was launched on an azimuth 90 degrees east of north. A roll maneuver was initiated at 13.0 seconds that placed the vehicle on a flight azimuth of 91.504 degrees east of north. In accordance with preflight targeting objectives, the translunar injection maneuver shortened the translunar coast period by 2 hours and 40 minutes to compensate for the launch delay so that the lunar landing could be made with the same lighting conditions as originally planned. The reconstructed trajectory was generated by merging the following four trajectory segments: the ascent phase, the parking orbit phase, the injection phase, and the early translunar orbit phase. The analysis for each phase was conducted separately with appropriate end point constraints to provide trajectory continuity. Available C-Band radar and Unified S-Band (USB) tracking data plus telemetered guidance velocity data were used in the trajectory reconstruction. The trajectory variables from launch to Command and Service Module (CSM) separation are discussed below and, in general, were close to nominal. Because the S-II Outboard Engine Cutoff velocity was higher than nominal, earth parking orbit insertion conditions were achieved 4.08 seconds earlier than nominal. Translunar Injection (TLI) conditions were achieved 2.11 seconds later than nominal with altitude 5.8 kilometers greater than nominal and velocity 5.1 meters per second less than nominal. CSM separation was Commander initiated 57.9 seconds earlier than nominal resulting in an altitude 306.1 kilometers less than nominal and velocity 91.7 meters per second greater than nominal.

[edit] 4.2 Trajectory Evaluation

[edit] 4.2.1 Ascent Phase

The ascent phase spans the interval from guidance reference release through parking orbit insertion. The ascent trajectory was established by using telemetered guidance velocity data as generating parameters to fit tracking data from six C-Band stations (Meritt Island, Patrick Air Force Base, Grand Turk, Bermuda FPQ-6, Bermuda FPS-16M and Antigua) and two S-Band stations (Merritt Island and Bermuda). Approximately 13 percent of the C-Band tracking data and 42 percent of the S-Band tracking data were not used because of inconsistencies. These values are consistent with past experience. The launch portion of the ascent phase (liftoff to approximately 20 seconds) was established by constraining integrated telemetered guidance accelerometer data to the best estimate trajectory. Actual and nominal altitude, surface range, and crossrange for the ascent phase are presented in Figure 4-1. Actual and nominal space-fixed velocity and flight path angle during ascent are shown in Figure 4-2. Actual and nominal comparisons of total non-gravitational accelerations are shown in Figure 4-3. The maximum acceleration during S-IC burn was 3.87 g.

Mach number and dynamic pressure are shown in Figure 4-4. These parameters were calculated using meteorological data measured to an altitude of 86.3 kilometers (31.5 n mi). Above this altitude, the measured data were merged into the U.S. Standard Reference Atmosphere. Actual and nominal values of parameters at significant trajectory event times, cutoff events, and separation events are shown in Tables 4-1, 4-2, and 4-3, respectively. All trajectory parameters were close to nominal throughout ascent. The space-fixed velocity was 25.6 m/s (84.0 ft/s) higher than predicted at the end of S-II powered flight. This difference is somewhat greater than usual and is discussed in Section 6.3.

[edit] 4.2.2 Parking Orbit Phase

Orbital tracking was accomplished by the NASA Manned Space Flight network. Three C-Band stations (Merritt Island, Antigua and Carnarvon) provided four data passes. Six S-Band stations (Goldstone, Bermuda, Texas, Merritt Island, Hawaii and Ascension) furnished eight additional tracking passes.

Velocity data generated by the ST-124M guidance platform were used to derive the orbital non-gravitational acceleration (venting) model. The parking orbit trajectory was obtained by integrating a comprehensive force model (gravity plus venting) with corrected insertion conditions forward to T6 at 10,978.65 seconds (03:02:58.65). The insertion conditions were obtained by using the force model and a differential correction procedure to fit the available tracking data.

A comparison of actual and nominal parking orbit insertion parameters is presented in Table 4-4. The groundtrack from insertion to S-IVB/CSM separation is given in Figure 4-5. All orbital trajectory variables were close to nominal.

[edit] 4.2.3 Injection Phase

Figure 4-5. Launch Vehicle Groundtrack

The Injection phase spans the interval from T6 to TLI and was established in two parts (T6 to 11,500 seconds and 11,500 seconds to TLI). The first part was obtained by fitting data available from one C-Band station (Carnarvon) and three S-Band stations (Texas, Goldstone, and Merritt Island). The second part was obtained by integrating a state vector taken from the first part at 11,500 seconds (03:11:40) through second burn and constraining the integration to a final TLI state vector taken from the early translunar orbit trajectory. Telemetered guidance velocity data were used as generating parameters for both parts.

• Figure 4-1. Ascent Trajectory Position Comparison
• Figure 4-2. Ascent Trajectory Space-Fixed Velocity and Flight Path Angle Comparisons
• Figure 4-3. Ascent Trajectory Acceleration Comparison
• Figure 4-4. Dynamic Pressure and Mach Number Comparisons
• Table 4-1. Comparison of Significant Trajectory Events
• Table 4-2. Comparison of Cutoff Events
• Table 4-3. Comparison of Separation Events
• Table 4-4. Parking Orbit Insertion Conditions

Comparisons between the actual and nominal space-fixed velocity and flight path angle are shown in Figure 4-6. The actual and nominal total non-gravitational acceleration comparisons are presented in Figure 4-7. The lower than nominal velocity and acceleration shown in Figures 4-6 and 4-7, respectively, are due to the heavier S-IVB stage resulting from the 4.0 seconds early first S-IVB cutoff. The actual and nominal S-IVB second guidance cutoff conditions are presented in Table 4-2. The slightly longer than nominal burn compensated for the heavier S-IVB stage and resulted in near nominal conditions at cutoff.

[edit] 4.2.4 Early Translunar Orbit Phase

The early translunar orbit trajectory spans the interval from translunar injection to S-IVB/CSM separation. Tracking data from one C-Band station (Carnarvon) and one S-Band station (Ascension) were fitted using the procedure outlined in 4.2.2. The actual and nominal translunar injection conditions are compared in Table 4-5. The S-IVB/CSM separation conditions are presented in Table 4-3(b). The large differences at CSM separation were due to the earlier than nominal separation time which was Commander initiated.

• Figure 4-5. Injection Phase Space-Fixed Velocity and Flight Path Angle Comparisons
• Figure 4-7. Injection Phase Acceleration Comparison