Ever watch the fueling of the Apollo rockets during the Moon launch days? Notice the frost and ice, amidst the fog? When you fill a rocket, there is a pressure change as you are filling a volume (P=nVRT).
The Vessel will get cold.
We can see that; just like they can see ours.
Oh, I understand that...what I wonder is: How do we know WHAT is in the payload? If they’ve got one of these ‘super-EMP’ weapons, how do we know? It might be a harmles dummy payload, or it might be a USA-ending weapon. How would we know?
Uh...That should be PV=nRT. And the frost you see on those rockets comes from the liquid oxygen and/or liquid hydrogen part of the propellant.
1) The Apollo rockets used LOX/Kerosene for the first stage, and LOX/LH2 for the second and third stages. LOX and LH2 frost the vents on their containers when filled, because LOX and LH2 are COLD. LOX ~ 90K, LH2 ~ 20K. The frost has nothing to do with pressure changes while filling a volume.
2) The North Korean Taepodong missile is powered by nitric acid/kerosene. Neither of these is cold, but both are liquid. There may be detectable venting of gases, but it won't be the frost and fog of a Saturn V.
3) US ballistic missiles (currently Minuteman III and Trident II) are solid fueled.