Are you placing the spacecraft object using a file downloaded from the web. It is probably a raster file (jpeg, gif, tiff etc.) rather than a vector file (svg, eps etc.) which may be why you are seeing the jaggies. Raster images are based upon bit maps and use more space and are not easily enlarged or reduced without distortion. Vector graphics allow smooth transitions however they are re-sized.
You could try re-sizing the object in the PSE Editor: