
After giving up the wait for Dream Chaser, which should arrive at some point in 2025, ULA is instead going to use a mass simulator along with some experiments and demonstrations to ease the vehicle's passage to US Space Force certification.
I have an (excessive?) dislike for this term: unless there is new physics involved, it doesn't simulate mass, it IS mass. It's like referring to an airworthy aircraft as a flight simulator.
My apologies to ULA if it is actually a very small box with several sets of switches and dials on the side, with labels "inertial", "passive gravitational", and "active gravitational".
(The term "inert payload", further up the article, is better.)