Terrestrial Plume – Surface Interaction Studies for VTVL Launch Vehicles

Space Shuttle launches routinely caused erosion and “liberation” of large chunks of launch pad concrete. Substantial erosion is still visible under some heritage AFRL Rocket Laboratory (RQR) Apollo engine test stands. The severity of the damage seen in such cases has raised concerns regarding potential impacts on infrastructure, facilities, and surrounding communities from launching and landing rockets vertically on terrestrial surfaces. However, plume-induced concrete pad erosion is a challenging multi-physics problem involving coupled compressible flow and material morphology in response to intense heating. Understanding how and to what degree this degradation happens is essential to ensuring that the vertical launch and landing (VTVL) phases critical to reusable operations can happen in a responsible and safe manner. Vertical landings on selected surfaces have been demonstrated by several companies, Space X has landed its Falcon 9 vehicle first stage hundreds of times, including on offshore barges. Recently, Blue Origin successfully landed its New Glenn first stage on a similar barge. The ability to do so reliably significantly reduces the cost of commercial launch operations. However, an open question in all these operations is how successful would stage recovery operations be for a landing on an alternate, less vetted surface in case the primary site were unavailable, say due to rough seas. The recently concluded AFRL Deployable In-Situ Rocket Test (DIRT) program was an experimental effort to address that concern and characterize risks. The DIRT project generated and interpreted data of the effects of rocket plume impingement on multiple potential landing surfaces. The DIRT test apparatus used a heritage solid rocket motor (SRM) configuration, specifically the 70lb BATES (BAllistic Test and Evaluation System) motor which generates approximately 4000 lbf thrust. The motor was arranged to fire vertically downward on surfaces at fixed elevations, simulating landing approach and launch departure environments. A suite of instruments was used to gather visual, thermal, and other data from the surface during motor firing. The test campaign is discussed, including some relatively unique data which the robust design of the DIRT rig made possible to obtain. Erosion profiles, visible and IR videographic imaging of material surfaces during the tests and concrete internal temperature data from recent tests are discussed.