AS-201 finally went down in Cape annals as the "scrub and de-scrub" launch. After their many weeks of problem after problem, delay after delay, the launch team began the countdown at midnight, 20 February. Bad weather imposed three holds, two for 24 hours each; and terminal countdown did not get underway until 5:15 p.m., 25 February. It was held at T-266 minutes in the early morning hours of 26 February on account of an Apollo access arm problem. A faulty helium regulator took up the remaining 30 minutes of scheduled hold time. At 35 seconds before liftoff, a nitrogen regulator commenced a high flow purge of the S-IB stage's LOX dome and thrust chamber fuel injector. [See chapter 3-5 for a discussion of this operation.] The reading on the stage's high-pressure nitrogen spheres, normally at 211 kilograms/square centimeter, fell rapidly. At T-4 seconds the pressure dropped below 199 and the automatic sensor stopped the count.28
After some discussion, the launch team decided that the purge of the booster's LOX dome and thrust chamber fuel injector was using most of the nitrogen flow from the ground supply, in effect starving the high-pressure spheres. A technician increased the flow by resetting the pressure on the equipment supplying the nitrogen. At T - 5 minutes, although the nitrogen sphere on the S-IB stage read a satisfactory 203.2 kg/sq cm, Marshall and Chrysler stage engineers requested another hold. Their calculations indicated that, if the low readings on the nitrogen spheres were caused by excessive purge flow or leakage, the existing pressure might not prove sufficient to maintain the minimum needed to pressurize engine gear boxes, actuate LOX and fuel lines, and purge the LOX seal area of the engine turbopumps through stage burnout The stage engineers recommended eliminating the calorimeter purges. These instruments on the base heat shield measured heat radiation from the stage engines. No serious problems in this area were anticipated and the measurement had no influence on the flight, so the purge was expendable. The operation, however, would take longer than the launch window allowed, and the mission was scrubbed.29 But a few members of the launch team refused to quit. Gruene reported later:
A few of my people, including [A. J.] Pickett and [L. E.] Fannin, had an idea that if they could just run one test and convince the [Marshall] people this test was valid, . . . we could still launch the vehicle. We ran the test, de-scrubbed and launched - all in the same day. 30The test involved a simulated liftoff and 150-second flight. The simulation demonstrated that 203.2 kg/sq cm of nitrogen in the high-pressure spheres at liftoff would provide adequate pressure in the spheres at burnout.* Hurried calculations by stage engineers supported KSC's findings, and Marshall engineers then agreed to resume the count at 10:57 a.m.31
The trouble-plagued AS-201 lifted its 585 metric tons off the pad 15 minutes later. During the 39-minute trip down the Eastern Test Range, the S-IVB stage and the main propulsion engine in the service module increased the Apollo's velocity to nearly 29,000 kilometers per hour, a speed greater than manned Apollos would face at reentry. The command module splashed down east of Ascension Island where Navy forces recovered it.32 With the flight a success, KSC released a general sigh of relief. Carlson said later: "We had struggled so long and so hard.... We were all glad to see it go."33
The pad suffered substantial damage from flame and vibration at launch. Three seconds after liftoff, high voltage fuses in the pad area substation vibrated loose from their holders and blew a 300-ampere fuse in the industrial power feeder. LC-34 and other Cape facilities were powerless for an hour. One casualty was the launcher water deluge system. Its failure accounted for much of the fire damage on the pad and nearby structures. The power failure also short-circuited the Eastern Test Range's impact computer B, used by Houston to make an abort decision. Computer B tried to transfer to the alternate power system and failed; the back-up computer came on for six seconds and then quit. As a result, Range Safety could not determine vehicle abort impact points during the first five minutes of flight and Mission Control (Houston) operated without trajectory data.34
* Telemetered flight data confirmed that the residual pressure at S-IB cutoff exactly equalled the prediction.