This tough question links to the NASA YouTube video NASA 60th: How It All Began which shows a lot of really nice, historical file footage and stills.

At about 01:56 there is a still of an engineer standing next to what looks like a sounding rocket, or a model of one, that is transparent. Behind the engineer is an inflatable, metallized balloon, smaller, but similar to the ones shown in the question Did Echo 2 remain spherical without requiring gas pressure? If so, how is this known to be true?, and it looks like an un-inflated balloon is stowed in a compartment of the transparent rocket as well.

Most likely, the rocket is transparent because it is just a model, but I am still wondering what that thing is that looks like a nozzle, pointing up, in the cone.

below: Screen shot from the NASA YouTube video NASA 60th: How It All Began.

Click for full size.