This happens to me too, most any time my sim explores space or woohoos in the rocket. It hasn't mattered what level my sim's skill is, what rocket I use or what upgrades my rocket has. The quick fix I use is just to have the sim change clothes using a mirror or dresser or even clicking on the space the sim should be. Before I figured out that just changing clothes would fix it, I had the sim shower to bring them back. It doesn't fix the underlying issue, but at least you can see your sim.