Painting is 90% preparation and 10% painting.
Think of primer as the glue that holds wallpaper on.
After all your prep is done ..... one final light coat of primer should be applied. It should be even with no light spots or runs.
Now you have a nice surface for the the finish coat to "grip" on, much like wallpaper must grip via the glue.
lighter colors like yellow will not look good or be even colored, if applied to a splotchy undercoat of primer.
So if you are using that much primer on a small rocket, I suspect that you are using it as a filler trying to work out imperfections. There are other products for that.
The general course of action is a filler on spirals, sanded smooth, followed by primer. Then inspection, if needed more filler on missed spots, then sanding smooth. Several coats of primer applied, then sanded smooth, if you hit cardboard...stop... you have gone to far. Re-apply primer.
Finally an even coat of primer, left to dry/cure for several days. [if it smells like paint, it isn't dry enough to sand] al light sanding to knock off any grit or bugs .....followed by your finish coat.
If you sand to much of the primer off, the result is usually fuzzes raised in the cardboard and you must start over at square one.
The discussion of proper painting technique is a long one riddled with many practices by many different painters.
BUT there is really only one that works and most are not willing to take the time & effort to learn. Like I said 90% preparation.
I have done large projects that required 3-4 days of filling and sanding 6-8hrs a day for an hour or so of actual paint application.
I can show you how to paint a rocket correctly in a few hours, it would take days of typing to explain it. I'm sure there will be a ton of different "ways" shortly.
Search the forums this has been discussed in length with great detail on "how to"