Simulating Dream Chaser® Spacecraft Aerodynamics: Subsonic through Hypersonic

Overview

Sierra Nevada Corporation’s (SNC) reusable Dream Chaser® spacecraft will transport cargo to the International Space Station starting in fall 2021, as part of NASA’s Commercial Resupply Services missions. During entry, descent, and landing, Dream Chaser will fly through Mach numbers ranging from above 20, about 15,224 miles per hour, to less than 0.4—roughly 304 mph—as it lands on a runway. Vital to the success of Dream Chaser is the accurate characterization of aerodynamic forces on the airframe and control surfaces during atmospheric flight. Additional aerodynamic interactions occur at hypersonic velocities due to Reaction Control System (RCS) firings. Predictions of aerodynamic forces and RCS aerodynamic increments were all modelled using extensive computational fluid dynamics (CFD).

Project Details

Wind tunnels and CFD methods are now complementary tools in the development of aerodynamic and aerothermal databases. Using wind tunnel data as anchoring data, we developed and expanded the Dream Chaser databases using thousands of aerodynamic and aerothermal predictions, a host of NASA-developed CFD packages, including FUN3D, CART3D, and DPLR (Data Parallel Line Relaxation); and the Direct Simulation Monte Carlo (DSMC) Analysis Code, DAC97. These simulations were run using NASA’s Pleiades and Endeavour supercomputers at NASA Ames Research Center.

Results and Impact

These CFD predictions were used heavily in the development of aerodynamic and aerothermal preflight databases. These databases are used by SNC’s Guidance, Navigation and Control (GN&C) for preflight predictions and control analysis and by thermal designers in the development of the Thermal Protection Systems (TPS) used to protect the vehicle during re-entry.

Why HPC Matters

The partnership with NASA allowed the SNC team access to vast computing resources and resulted in CFD simulations of thousands of unique cases along the Dream Chaser entry, descent, and landing (EDL) trajectory. Using the Pleiades and Endeavour supercomputers at the NASA Advanced Supercomputing (NAS) facility, the SNC aerodynamic team performed approximately 20,000 high-fidelity CFD simulations to calculate the aerodynamic forces and moments acting on the Dream Chaser vehicle, control surface interactions, and aerodynamic increments by firing RCS thrusters throughout EDL. These simulations have required tens of millions of core-hours, and store multiple terabytes of data on NAS systems. None of this would have been possible without the help and resources of the NAS Division.

What's Next

In fall 2021, Dream Chaser will launch on its first voyage to the International Space Station (ISS) from Kennedy Space Center (KSC), the first of six missions. Each mission will conclude with the return of valuable experiments from the ISS, returning to the Space Shuttle Landing Facility at KSC. NASA is planning to capture images of the Dream Chaser during its first return flight using Scientifically Calibrated In-Flight Imagery technology. It is expected the heating observations will be coupled with extensive CFD, along the Best Estimated Trajectory, to calibrate thermal predictions and update thermal databases after the flight. The long term benefit to NASA would be increased payload capability to and from the ISS through improvements to the Dream Chaser spacecraft.

More Information

• Sierra Nevada Corporation’s Dream Chaser Achieves Successful Free Flight at NASA Armstrong
• See the poster for this demonstration (PDF, 1.1MB). As shown in the NASA booth at SC19.
• Download the demonstration slide deck (PPSX, 263.8MB) as presented in the NASA booth at SC19. Click "Read Only" after launching presentation.