NASA Researchers Speed Design of Next-Generation Launch Vehicles
09.28.11
With the retirement of the Space Shuttle this year, a new Space Launch System capable of carrying large payloads into orbit will be key to continuing NASA's science and exploration missions.
As NASA embarks on an ambitious new path to develop a next-generation Space Launch System (SLS) both swiftly and affordably, cutting-edge analysis tools will be critical to streamlining the design process while also ensuring the highest possible performance and safety standards.
A team of modeling and simulation experts in the NASA Advanced Supercomputing (NAS) Division is performing advanced aerodynamic simulations that supply critical design performance data more efficiently and accurately than ever before. Using NASA-developed computational fluid dynamics (CFD) codes and supercomputers at the NAS facility, the team is modeling new launch vehicle designs and computing the detailed aerodynamic flows, forces, and interactions that could affect flight performance and safety during launch.
Efficient Design Analysis
"CFD analyses help fine-tune the design process by enabling early optimization of vehicle aerodynamics, and rapid assessment of potential changes or new details," said Cetin Kiris, chief of the NAS Applied Modeling and Simulation Branch at NASA Ames Research Center. "This leads to better initial designs and more efficient design analysis cycles."
Over the past few years, NAS CFD experts have demonstrated the many benefits of CFD for vehicle development through their extensive analyses of the Ares V heavy lift launch vehicle (HLLV, see sidebar). As the vehicle design evolved, the CFD team delivered comprehensive "aerodynamic databases" of forces and loads throughout the launch trajectory, assessed the aerodynamic effects of numerous design characteristics, and developed high-fidelity analyses of complex rocket engine plume physics.
Their results have supplemented limited wind tunnel data, and enabled more conditions and designs to be assessed-all at a fraction of the cost and time required to obtain the data through testing alone.
As the Ares V design solidified, CFD analyses also provided an important first stepping-stone for each design analysis cycle. At the beginning of each design cycle, CFD simulations were used to predict the aerodynamic forces and load distributions needed to support further trajectory adjustments, structural analyses, and other studies. The fast turnaround of the CFD analyses—which could generate the needed aerodynamic data within just a few days, thanks to NAS supercomputing resources and modeling expertise— greatly expedited the design cycle process and helped all teams meet tight design cycle timetables.
Best Practices for Accurate Simulations
NAS CFD experts have also performed comprehensive studies to establish "best practices" for generating accurate CFD simulations of HLLV ascent and plume effects. Accurate simulation of rocket engine plumes is essential for evaluating both the overall aerodynamic environment during ascent, and potential issues such as plume-induced flow separation (PIFS) or excessive heating to the base of the vehicle.
The best practices studies assessed a wide range of analysis criteria, including: grid resolutions, turbulence models, ways of defining the nozzle exit boundary conditions that control the intial outwared plume flow, and levels of physical modeling fidelity such as inviscid, viscous, and multi-species gas models. The analysis methods were then compared and vetted with wind tunnel test data for Ares V and flight data from the Saturn V HLLV to identify the most accurate protocols and help determine uncertainty levels for various modeling fidelities.
"These best practices will provide a valuable foundation for future analyses of the new space launch system vehicle," said Kiris. "They will help ensure consistent and reliable CFD data, and will also enable CFD teams to identify the most efficient level of modeling fidelity needed for different types of studies."
New Tools for Future Vehicles
The NAS team is also developing new computational tools and techniques to simulate launch environments for NASA's future SLS, which will be even more intense than those generated by the Space Shuttle's 7 million pounds of thrust. These analyses predict critical pressure loads and acoustic noise levels during ignition and liftoff to assess the suitability of existing launch facilities for larger vehicles, and to ensure that excessive vibrations won't damage their valuable payloads.
The team's launch environment simulations previously helped NASA determine that the current mobile launch platform would not require costly modifications for the Ares V vehicle, and also provided detailed pressure data that was instrumental in assessing and repairing damage to the flame trench wall that occurred during the STS-124 Space Shuttle launch in May 2008.
Now, CFD experts are developing improved modeling tools and techniques, which will provide even better launch environment data for the Agency's future space launch system.
Role of Supercomputers
Throughout these projects, NAS high-end computing resources have paved the way for more extensive use of CFD in vehicle development, enabling scientists to quickly compute entire aerodynamic databases and analyze many designs and conditions. NAS's continually expanding computing power has spurred ongoing advances in modeling fidelity and techniques by enabling both the large-scale simulations required to resolve highly complex flow physics, as well as the large parameter studies needed to develop sound computational methodologies.
The advances in launch vehicle simulation achieved through these projects, combined with NASA's world-class supercomputing resources, have poised NAS CFD teams to provide cutting-edge design analysis support for NASA's future space launch system. Increasingly powerful computing resources and higher-fidelity CFD models will give designers ready access to more valuable performance data, and will allow them to consider complex design factors with greater accuracy than ever before.
— Lorien Wheeler
411 on HLLVs
Heavy lift launch vehicles (HLLVs) are powerful rockets designed to carry very large, massive payloads into orbit. While the payload capacities of smaller mid-sized launch vehicles generally max out at around 20,000 kg (44,000 lbs), an HLLV could handle 50,000 kg (110,000 lbs) or more depending on the design.
HLLV payloads could include, for example, crewed or un-crewed (robotic) exploration vehicles, scientific instruments, crew habitat or space station components, or large, high-orbit satellites such as communications satellites.
NASA's first HLLV, the retired Saturn V, remains the largest and most powerful rocket flown to date. It was able to lift around 119,000 kg (262,000 lbs) into orbit, and successfully launched both the entire Skylab space station and the Apollo crew module that brought U.S. astronauts to the Moon.
NASA is now embarking on the design of a next-generation heavy lift space launch system (SLS) that will support the Agency's future large-scale science and exploration missions. Potential future missions could include missions to near-Earth objects (NEOs) such as asteroids, lunar missions, scientific research missions, and someday even human exploration missions to Mars.
Related Info
Websites:
Papers:
- Space-Time Accuracy Assessment of CFD Simulations for the Launch Environment
Jeffrey A. Housman and Michael F. Barad
AIAA-2011-3650 Housman, Barad, and Kiris (PDF-9.7MB) - Aerodynamic Database Generation for SRB Separation from a Heavy Lift Launch Vehicle
Marshall R. Gusman and Michael F. Barad
AIAA-2011-3651 Gusman, Kiris, and Barad (PDF-11.3MB) - Best Practices for CFD Simulations of Launch Vehicle Ascent with Plumes
M. Gusman, J. Housman, C. Kiris
AIAA-2011-1054 Aerospace Sciences Meeting (PDF-7.5MB) - Best Practices for Aero-Database CFD Simulations of Ares V Ascent
C. Kiris, et al
AIAA-2011-16 Aerospace Sciences Meeting (PDF-11.8MB)
Contact
Cetin Kiris
NASA Ames Research Center
cetin.c.kiris@nasa.gov
