# Hypersonics

As illustrated by NASA’s recent successful landing of Curiosity on Mars, one of the most dangerous and challenging aspects of any planetary exploration mission is a spacecraft's hypersonic entry into a planet's atmosphere. Achieving this goal will involve many missions over the coming years. Perhaps the most dangerous and challenging aspect of any mission is a spacecraft's hypersonic entry into a planet's atmosphere. The physical processes occurring around the spacecraft are quite complex and involve the synthesis of chemical kinetics, quantum mechanics, radiation physics, and ablation effects with fluid dynamics. To further complicate matters, the atmosphere is often rarefied and conventional fluid dynamic analysis is no longer applicable. Such high energy, high speed, rarefied conditions are very expensive and often impossible to reproduce in wind tunnels here on Earth. Actual flight tests are even more expensive and measured data is limited to that collected during the 1960's Mercury, Gemini, and Apollo programs. If numerical simulation can reproduce the experimental data that is available, it can then be used with confidence as a fast and inexpensive design tool for new spacecraft flying new missions.

At low altitudes (below ~80km for Earth) the atmosphere is
sufficiently dense such that molecules undergo a vast number of collisions as
they move over the spacecraft. Under these conditions the gas can accurately be assumed to
behave as a continuum and the Navier-Stokes equations can be solved using
methods from Computational Fluid Dynamics (CFD). CFD methods are very mature and are capable of incorporating advanced
physical models such as chemical and thermal non-equilibrium, radiation, and
even ablation. For very high altitudes (above ~100km for Earth) the atmosphere
is rarefied to the point where molecules undergo far fewer collisions
invalidating the continuum assumptions inherent in the Navier-Stokes equations.
In this regime the most mature numerical method is the direct simulation Monte
Carlo (DSMC) method which is also capable of incorporating advanced physical
models. Since the DSMC method simulates the gas on the molecular scale it
provides accurate results in all regimes, however under continuum conditions,
large numbers of particles and collisions demand impractical computational
resources. Thus, in general, the DSMC method is used to simulate atmospheric
entry at high altitudes and CFD is used at lower altitudes. Of course there is a
large overlap regime in which the flow around the spacecraft exhibits regions of
both continuum flow and non-equilibrium or rarefied flow. For this reason
current research is not only focused on using CFD and DSMC to simulate the
aerothermodynamics of atmospheric entry, but also focuses on incorporating these
methods into a *hybrid* particle-continuum code.

## Current Work:

- Electron Transpiration Cooling
- Kyle Hanquist, PhD Candidate
- Thermochemical Nonequilibrium Modeling in State-Resolved High Fidelity Model
- Daniil Andrienko, Postdoctoral Research Fellow

## Previous Work:

- Hybrid Particle Scheme for Atmospheric Entry Flow Simulation
- Extension of a Hybrid Particle-Continuum Method for a Mixture of Chemical Species
- Scramjet Combustion Chamber Radiation
- Direct Simulation Monte Carlo Modeling of Weakly Ionized Flows
- Mars Entry, Descent, and Landing
- Extension of a Modular Particle-Continuum (MPC) Method for Nonequilibrium, Hypersonic Flows
- Particle Simulations of Continuum/Rarefied Flows
- Hypersonic Interaction Flows
- Sharp Leading Edges
- Plasma-Based Flow Control at Hypersonic Speeds
- Re-entry and Hypersonic Vehicle Plasma Communications System