THE PARKING ORBIT
As the Agena separated from the Atlas booster vehicle, it was programmed to pitch down almost 15 degrees, putting it roughly parallel with the local horizon. Then, following a brief coasting period, the Agena engine ignited at 1:58.53 a.m. and fired until 2:01.12 a.m. Cut-off occurred at a predetermined value of velocity. Both the Agena and the spacecraft had now reached a speed of approximately 18,000 miles per hour and had gone into an Earth orbit at an altitude of 116.19 statute miles.
The second stage and the spacecraft were now in a “parking orbit,” which would allow the vehicle to coast out to a point more favorable than Cape Canaveral for blasting off Mariner for Venus.
During the launch, Cape radar had tracked the radar beacon on the Agena, losing it on the horizon at 2:00.53 a.m. Radar stations at Grand Bahama Island, San Salvador, Ascension, the Twin Falls Victory ship, and Pretoria (in South Africa) continued to track down range. Meanwhile, Antigua had “locked on” and tracked the spacecraft’s radio transponder and telemetry from 1:58 to 2:08 a.m. when it went over the Antigua horizon.
Mariner II is accelerated to Earth-escape velocity and out of orbit near St. Helena. Rotation of earth causes flight path to appear to double back to west over Africa.
The sequence of events in the launch phase of the Mariner flight to Venus.
EVENT 1. LIFTOFF 2. ATLAS BOOSTER ENGINE CUTOFF 3. ATLAS SUSTAINER ENGINE CUTOFF 4. ATLAS VERNIER ENGINE CUTOFF 5. SPACECRAFT SHROUD EJECTION 6. ATLAS-AGENA B SEPARATION 7. AGENA B FIRST IGNITION 8. AGENA B FIRST CUTOFF 9. AGENA B SECOND IGNITION 10. AGENA B SECOND CUTOFF 11. SPACECRAFT SEPARATION 12. INITIATE AGENA YAW MANEUVER 13. COMPLETE AGENA YAW MANEUVER 14. EXPEL UNUSED AGENA PROPELLANT
The second coasting period lasted 16.3 minutes, a time determined by the ground guidance computer and transmitted to the Agena during the vernier burning period of Atlas. Then, Agena restarted its engine and fired for a second time. At the end of this firing period, both the Agena and Mariner, still attached, had been injected into a transfer trajectory to Venus at a velocity exceeding that required to escape from the Earth’s gravity.
The actual injection into space occurred at 26 minutes 3.08 seconds after liftoff from the Cape (2:19.19 a.m., EST) at a point above 14.873 degrees south latitude and 2.007 degrees west longitude. Thus, Mariner made the break for Venus about 360 miles northeast of St. Helena, 2,500 miles east of the Brazilian coast, and about 900 miles west of Angola on the west African shore.
During injection, the vehicle was being tracked by Ascension, telemetry ship Twin Falls Victory, and Pretoria. Telemetry ship Whiskey secured the spacecraft signal just after injection and tracked until 2:26 a.m. Pretoria began its telemetry track at 2:21 and continued to track for almost two hours, until 4:19 a.m.
Injection velocity was 7.07 miles per second or 25,420 miles per hour, just beyond Earth-escape speed. The distance at the time of injection from Canaveral’s Launch Complex 12 was 4,081.3 miles.
The Agena and Mariner flew the escape path together for another two minutes after injection before they were separated at 2:21 a.m. Agena then performed a 140-degree yaw or retro-turn maneuver by expelling unused propellants. The purpose was to prevent the unsterilized Agena from possibly hitting the planet, and from following Mariner too closely and perhaps disturbing its instruments.
Now, Mariner II was flying alone and clear. Ahead lay a journey of 109 days and more than 180 million miles.