Prelaunch activities, countdown and launch for Nimbus 3 satellite

Hahn, A. C.

English

NASA Technical Reports Server

VII. LAUNCH OPERATIONS 
by Alvin C. Hahn 
P RELA UN CH ACTlV IT I ES 
The major prelaunch activities at the Western Test Range (WTR) are shown in 
table VII-I. During the tests problems were satisfactorily resolved as discussed in the 
following paragraphs. 
Thorad electrical connector X-rays. - NASA directed that an X-ray examination be 
made of 99 of the readily accessible and flight critical connectors on the Thorad. The 
results of this inspection indicated that 23 of the connectors were suspect, and these 
were opened for  further inspection, cleaning, o r  rework. 
Thorad turbopump torque test. - An out of specification variation in the running 
torque was observed while the turbine in the turbopump was being manually rotated. 
The second stage nozzle of the turbine assembly was repositioned and the turbopump 
was retested satisfactorily. 
Thorad single-propellant flow. - The liquid-oxygen propellant valve for vernier 
engine No. 1 indicated leakage and was replaced. The fuel depletion float switch stuck 
in the high position and was replaced. A regulation circuit in the ground power supply 
fo r  the ground inverter malfunctioned and was  replaced. 
Thorad dual-propellant flow. - The fuel depletion float switch stuck in the high 
position and was replaced. An expansion joint in the liquid-oxygen transfer line to the 
booster leaked and was retorqued. 
COUNTDOWN AND LAUNCH 
The countdown for the first launch attempt of the Thorad-Agena-Nimbus III began 
on April 10, 1069, concurrent with the countdown of a United States Air Force mission 
which had launch priority. The Nimbus III countdown started at 1123 Pacific standard 
time (PST) and proceeded as planned to the start of Agena propellant tanking. At this 
time the status of the Air Force mission was  reevaluated. The results of the evaluation 
indicated that the countdown for  the Air Force mission was continuing successfully 
toward i t s  scheduled launch. Consequently, the Nimbus ITI countdown was  terminated. 
The countdown for the second launch attempt began at 1123 PST on April 11, 1969. 
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The countdown proceeded without significant problems until 2234 PST when the fuel leak 
detector (Aerospace Ground Equipment) for the Agena showed the presence of fuel 
vapors. The cause of the vapors could not be determined and the launch attempt was 
terminated at 0022 PST on April 12, 1969. Pressure checks after countdown termination 
and propellant unloading showed a small leak through the vent port of the fuel propellant 
isolation valve. The gas leakage rate observed during the pressure check was determined 
to  be within specification limits. A plastic tube and bottle was  attached to  the vent line 
on the fuel propellant isolation valve so that the actual fluid leakage rate of fuel could be 
checked during the next scheduled countdown. 
The final countdown fo r  launch was initiated at 1124 Pacific standard time on 
April 13, 1969. Early completion of the launch vehicle tasks through mobile service 
tower removal permitted early tanking of the Agena and provided a 2-hour check on the 
leakage rate through the vent port of the fuel propellant isolation valve. Only a trace of 
fuel had collected in the bottle after the 2-hour period, and the plastic tubing and bottle 
were removed. No significant problems occurred during the countdown. Lift-off, 
5.08-centimeter (2-in. ) motion, occurred at 2354:03.136 Pacific standard time on 
April 13, 1969. 
Date 
1/17/69 
2/19/69 
3/19/69 
3/30/69 
3/ 30/6 9 
4/01/69 
4/03/69 
4/10/69 
4/11/69 
4/13/69 
TABLE W - I .  - MAJOR PRELAUNCH 
Event 
Thorad Arrival at Vandenberg AFB 
Agena Arrival at Vandenberg AFB 
Spacecraft Arrival at Vandenberg AFB 
Thorad-Agena Mate 
Thorad -Agena Erection 
Agena-Spacecraft Mate 
Simulated Launch 
First Launch Attempt 
Second Launch Attempt 
Launch 
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Launch Operations: Prelaunch Activities

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