it might sound weird but IMO if you are going with a "stealth sat" it might make the most sense to go with a highly custom one, where you basically take an asteroid, and mount retractable solar panels, com arrays, and instrument clusters, with camouflaged hatches that cover those things over when it goes into "stealth mode" also having large battery/cap arrays, so that it can at least redeploy the solar panels even after a long idle period say several months to a year or so so that it can effectively reactivate itself without having someone have to go visit it, and give it a "jump start"