Here's a handy trick, especially for computers with lower-speed connections: Open a collection (Hubble, Spitzer, etc.) and then play it as a slide show (Explore.Play collection as slide show).
This will fill your cache with the images for each of those items, and give you the surrounding stellar background as well. Subsequent visits to any of those objects will be much faster.
You can do a similar thing with tours with Guided Tours.Auto Repeat.
Enjoy!