If you're a NASA engineer, you get to play with a lot of awesome toys, like these furious mini-rockets. They are models of the Space Launch System (SLS) core stage engines, "scaled down to just 2 per cent of the actual size of the flight hardware".
[M]odels of the SLS core stage RS-25 engines and solid rocket boosters have been designed, built and hot-fire tested at sea-level conditions by Marshall Space Flight Center engineers, in close collaboration with Calspan-University of Buffalo Research Center Inc. in Buffalo, N.Y. The replicas will provide data on the convective heating environments that the base of the vehicle will experience upon ascent. The models were developed for base heating testing scheduled for this summer. When completed, SLS, NASA's new rocket, will be one of the biggest, most powerful rockets ever built.