Simulating the SLS Sound Suppression Water System

NASA’s next-generation Space Launch System (SLS) for deep space exploration consists of four RS-25 liquid rocket engines and two five-segment solid rocket boosters (SRBs). At ignition, the SRBs create a significant over-pressure event, known as the Ignition Over-Pressure (IOP) event. The IOP event experienced in the first space shuttle flight (STS-1) in 1981 damaged the space shuttle orbiter and motivated significant design changes to the launch pad at NASA’s Kennedy Space Center. The RS-25 liquid rocket engines aboard the SLS, along with the SRBs, also create a very significant acoustic environment that, if not mitigated, can harm the SLS launch vehicle. An Ignition Over-Pressure/Sound Suppression (IOP/SS) water system was developed to reduce the amplitude of both the IOP event and the acoustic environment caused by the firing of the RS-25 engines and the SRBs.

Simulation of the IOP/SS system projecting water during ignition, depicted by a light blue isosurface under the Space Launch System’s RS-25 liquid engines. Note the undesirable water splash upward between the two north and south engine banks. (Jeff West, NASA Marshall)

Mitigation of the IOP and acoustic environment relies on proper design of the IOP/SS system. One of several important aspects of the design is the placement of the water spray so that it reduces pressure and sound within the launch environment while not interfering with the nominal operation of other subsystems in the vicinity of the water system, such as the RS-25 engines, the SRBs, and Hydrogen Burn-off Igniter (HBOI) systems. The volume of fluid (VOF) model developed using the Loci-STREAM computational fluid dynamics (CFD) software program provides the ability to simulate the placement of water within the IOP/SS system. The Loci-STREAM-VOF program was developed at NASA’s Marshall Space Flight Center to enable the use of high-performance computing for the VOF algorithm.

A detailed CFD model of the launch pad was developed, including the IOP/SS water system and the lower portions of the SLS launch vehicle, consisting of 82 million volume cells. The Loci-STREAM-VOF CFD program was then used to perform an unsteady simulation of the IOP/SS water system. This CFD simulation — the first of its kind — was used to determine the optimal placement of the water for reducing IOP and acoustic amplitudes, and maintaining operation of the other subsystems.

The CFD simulations of the initial designs identified water projection patterns that adversely interacted with both the SRBs and the HBOI subsystems. Based on the simulation results, the design of the IOP/SS system was significantly altered to avoid these problems while still performing its intended mitigation function. The CFD simulations also determined that the IOP/SS system was creating an air entrainment effect, or waterfall effect, which interfered with the intended operation of the HBOI subsystem. In this case, an HBOI system design change was devised that accommodated the waterfall effect. As a result, the IOP/SS and HBOI systems are expected to operate as intended during an SLS launch — avoiding expensive redesigns and schedule delays that would have occurred if these problems had been detected much later during full-scale testing activities.

The elevation of Greenland’s ice bed is a major factor in accurately projecting the evolution of the ice sheet. Fortunately, the Ice Sheet System Model (ISSM) can be used to approximate the bed topography. This image gives the elevation of the bed in meters.

Projecting Sea Level Rise

The ability to accurately project sea level rise (SLR) in a changing climate is of paramount importance to mitigate its socio-economic impacts. One of the most significant contributions to SLR comes from freshwater fluxes (evaporation and precipitation) originating in the melting polar ice sheets of Greenland and Antarctica. Understanding and projecting the evolution of these ice caps is a priority for the global science community.

A team at NASA’s Jet Propulsion Laboratory (JPL) and the University of California at Irvine (UCI) has developed open-source Ice Sheet System Model (ISSM) software to assimilate remote sensing data into projections of the water mass for both Greenland and Antarctica. The ISSM team aims to accurately assess the future contribution of freshwater fluxes to the ocean, and understand how this contribution will impact SLR in the coming decades.

Accurately modeling the evolution of ice sheets involves complex physical processes that are still not fully understood, and requires a significant amount of computing power. Furthermore, large amounts of input data (coming from various sources such as regional climate models) need to be processed. To address these issues, ISSM is used. The state-of-the-art finite element model takes full advantage of a wide range of high-performance computing (HPC) environments. The HPC element is essential for dealing with the degrees of freedom that arise as a result of the huge problem domain and complex equations that govern ice flow.