Shroud over the SM at launch?

[Everett]

I just had one of those interesting 'wait a second' moments regarding the SM at launch. I'd always figured that the external surfaces of the SM were exposed at launch. The CM, I know, was covered by a boost protective cover that was jettisoned with the escape tower. But the cover didn't cover the SM, and after all that part of the saturn V was silver in photos.

But what about the RCS quads on the SM? I would assume that you wouldn't want them exposed during supersonic flight. Was there some sort of payload shroud over the SM at launch? And if there wasn't, what was done bout the problem of supersonic airflow into the forward facing RCS nozzle, which couldn't be good for the internal mechanism, with the nozzle acting as an air scoop? I assume that some sort of valve to let the air flow through would be a non starter, since that's not something you want in a rocket engine.

I've seen enough pictures of rocket before arriving at the pad to know that they put bright red cloth covers over the nozzles, but they wouldn't hold up in a supersonic airflow. I think. Also, whatever was used would have to work in the event of an abort after tower jettison, since the RCS quads are needed for an abort.

Anybody know the answer?

[Allan F]

There were no shrouds or covers on the RCS quads at launch. The earlier test launces had sensors which showed the aerodynamic loads weren't a problem. The nozzles were covered until some time before launch. I suspect the shape of the BPC diverted the airflow far enough out from the SM to avoid damaging the RCS. Pete Conrad actually expressed concerns that rain before the launch would be a problem with regard to the forward-facing thruster. But it turned out to be just fine.

http://www.hq.nasa.gov/office/pao/History/alsj/a11/ap11-S69-39961HR.jpg

This Picture shows without a doubt that the RCS were uncovered at launch.

[Glom]

It probably helps that the RCS was such a simple system. No pumps to get waterlogged.