MSC-07631 02. Status checks and countdown

Cernan

Ground communications with the spacecraft and all the launch preps for a nominal on-time launch went well. There were no spacecraft anomalies or problems during the launch prep. All systems checked out well. Controls and displays went well through T minus 30 seconds, when there was an automatic sequencer hold due to a potential problem that the ground support equipment saw on S-IVB pressurization. However, to the best of my knowledge, the S-IVB was GO on the cockpit displays. The S-IVB pressures were nominal, but, nevertheless, we had an automatic hold in the sequencer at T minus 30 seconds. From then on, for 2 hours and 40 minutes, we had a series of 20-minute recycles. I don't know exactly how many now. Did we ever get down to 8 minutes one time in the count?

Evans

No. Once we got started below 20 minutes, we went all the way.

Cernan

The problem turned out to be apparently in the software of the ground support equipment. The workaround was caught up, checked out through the Cape and Marshall, and once the count picked up, we had two azimuth updates.

Evans

We had two azimuth updates, because the first recycle was more than 20 minutes, wasn't it? It was more than 20 minutes and we recycled to that point and then they found out that they weren't going to be able to pick it up again in 20 minutes. And we stopped at 20 minutes and made the second azimuths.

Cernan

The point here being, both azimuth updates in the spacecraft went well. The CMP put them in the computer. The computer took it. I watched the IMU torque, After each one of those, they had to reset the GDC, which worked fine. So we launched with a good GDC following the platform. The only difference was a small roll angle, and it was reversed, because we had gone through 90° on the azimuth change. But that didn't really bother anything because the roll came in on time in a reverse direction. It was a small roll that culminated in just a few seconds.

The count and lift-off, through the yaw and the roll program, were nominal once we got through T-0.

Distinction of sounds in launch vehicle sequence countdown to lift-off - I think the only thing that really comes across in there is that at some point you get a good vibration. At some point in the countdown, you get a good vibration as you're sitting up there. It's not part of the CSM's operation, so you're not sure what's going on. And this happened in the CDDT and, of course, all we did was check and find out we were doing something with the booster.

Evans

When they ran through some gimbaling programs.

Cernan

The major portion of the launch count has to do with checking out the systems, so the commander stays very busy and many times on separate loops. The entire EDS system checked out very well. We only checked it out once in the initial count and during most of the recycle we stayed in EDS AUTO and then we de-armed EDS AUTO but still maintained a manual EDS capability to abort during that recycle time. We picked EDS AUTO as part of the T minus 20 recycle for final lift-off.

Edits and errors by Eric Hartwell are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 license. The original NASA material is copyright-free.