Several years back while watching one of the UFO shows on the History channel they interviewed a military spokesman from Groom Lake.
He made it pretty clear that there are few “open air” secrets in today’s world. There are just too many satellites taking too many pictures for anything on the ground to be a secret for very long. They track satellites and know when they’re overhead. If they want to do anything secret they do it in the few minutes they have without sat coverage, they do it underground of they camouflage it somehow.
That's how India managed to evade detection when they blasted five nukes in the Thar Desert, in 1998. The trick is in satellite location espionage, including of those satellites that are shielded from being detected from Earth.
Like sticking the nose of one aircraft out of one end of the hangar and the tail out the other?
We used to have a travel pod that we hung all sorts of antenna's off of, put on rad and radar warning tags, and would hang it off the wing of one of our jets whenever we knew the Soviets were at the fenceline taking pictures.