This is a massive water vapor cloud from the latest RS25 hotfire on the A1 engine test stand at the NASA Stennis Space Center. This water vapor is formed when the hot exhaust plume from the RS25 hits the water that is spraying through the flame diverter and causes it to rapidly vaporize into a gigantic cloud. Often times the vapor cloud condense into rain and will have localize rain cells. For this hotfire the wind was just right and it rained on us. The RS25 (AKA Space Shuttle Main Engine) testing is being conducted in preparation for delivery of engines to NASA’s Space Launch System (SLS) for the Artemis program. Current thrust produced by the RS25 is north of 400,000 lbf with 452 seconds ISP.
Thank you to the test director at SSC for letting me use the video I took of the hotfire!