NASA Ames has a heritage in Entry System Technologies, spanning more than four decades and encompassing modeling of aerothermal environments, critical aerothermal testing capabilities, and Thermal Protection System (TPS) material research, evaluation, selection, and qualification.
NASA Ames expertise and capabilities in Entry System (ES) Technologies are briefly described below.
Advanced Thermal Materials
The focus of future materials development will be durability and performance for acreage, leading edges, seals, and control surfaces for both reusable and ablative materials. Approaches will include graded or multi-layer concepts, new high temperature materials, foams, improved coatings, surface treatments and new and improved composites. This activity could also leverage the extensive research within the Agency in nanotechnology, by investigating the development of a whole new class of TPS materials based on the changes in material properties (such as heat conduction) at the nano-scale.
Enhanced environmental flow modeling and integrated design
The design and selection of advanced thermal materials is dependent upon the aerothermal environment. Existing state-of-the-art methods can predict laminar windward heating to within 20% for only a limited range of conditions, such as Earth reentries from low Earth orbit and low velocity ballistic entries at Mars. However, Lunar and Mars return missions, and outer planet probe missions, experience much higher entry velocities. For these cases the prediction uncertainties are much larger (as high as 50%) due to: a lack of validation of existing aerothermal models for these flow environments; the presence of ablation products in the flow; shock-layer radiation; and flow turbulence. Afterbody heating models have even higher uncertainty, with margins of up to 200%routinely applied to planetary entry probes. The development of high-fidelity aeroheating analysis and its inclusion in an integrated design philosophy will enable full use of the inherent performance capabilities in the ES. An integrated ES design includes: forebody shape optimization with respect to the correct aerothermal environments; entry trajectory optimization considering distributed heating constraints and aerodynamic performance requirements; reliability-based integrated IVHM design; and TPS material performance, thickness and attachments.
Focused Systems Analysis
Functions within this element include risk management, failure modes and effects analysis (FMEA), operations, system health assessment, reliability, maintainability and systems analysis for the ES. The purpose is to determine the risks associated with TPS and ES technologies and to develop mitigation techniques. These risks encompass technical (e.g. impact resistance), schedule-related (turnaround time), and cost-related (frequent replacement) factors.
Risk Mitigation, including traceability from computation to ground test to flight
Future vehicle system optimization will be enabled, with high levels of mission success, through reliability-based design approaches. ES design to date has primarily used a heritage-based approach, employing design procedures used for successful past missions. Although this has resulted in successful missions, the quantitative margin or reliability of these entry designs has been largely unknown. Comprehensive and validated testing and analysis processes are needed to show a clear traceability from ground testing to actual flight environments.
Navigation, Guidance, and Control
An ES that requires maneuvering flight needs the fundamental sensing, prediction, and controls capabilities in navigation, guidance, and control. This need for close integration within the program is even more critical for future entry systems, to enable reconfigurable shapes and multifunctional capabilities such as real-time trajectory tailoring, energy management, and risk-based approaches.
Entry System Health Assessment and Management
Nondestructive evaluation and health monitoring technologies, using advanced wireless sensors, will make future TPS inspection activities more automated, more reliable, and quicker than human inspection, thereby lowering cost and increasing reliability and safety.
Ground Testing & Flight Qualification
Arc jets are used to simulate the aerodynamic heating experienced by spacecraft on atmospheric entry. The Ames Arc Jet Complex is key for customers involved in the three major areas of TPS development: selection, validation, and qualification. With four test bays and the capability of up to 75 MW of power, the Ames Arc Jet Complex is unique in the world (See the separate write-up on this facility).
When a flight vehicle enters a planet’s atmosphere, the Entry System (ES) is the Space Transportation Segment that protects the payload, human or robotic, from the extreme environments experienced during entry. It includes advanced thermal materials, enhanced environmental flow modeling and integrated design, focused systems analysis, risk mitigation (including traceability from ground test to flight), navigation guidance & control, and system health assessment and management. The ES is the biggest risk factor, after Propulsion, for any mission involving entry into an atmosphere. This risk is endemic to the physics of high-speed atmospheric flight. NASA Ames has a heritage in ES, spanning more than four decades. Ames has conceived and led pioneering entry system flight projects, including PAET (world’s first re-entry atmospheric reconstruction experiment), Pioneer Venus (first US entry mission to Venus), Galileo (world’s first entry to a giant planet and fastest entry of a man-made object), and SHARP B1 and SHARP B2 (world’s first hypersonic flight test of ultra-high temperature ceramics). Ames has a history of producing innovations to enhance or enable important NASA missions. Ames has provided TPS technology solutions, along with its integrated approach to TPS materials development, testing, and analysis, and its history in leading innovation. Five Ames-patented TPS inventions are included in the current Orbiter configuration: RCG, gap fillers, LI-2200, FRCI, and TUFI. In addition, an Ames invention, the PICA ablative carbon tile, enabled the Stardust mission, which recently collected comet dust. Another Ames invention, SIRCA ablative tile, significantly enhanced the TPS design of the Mars/Pathfinder, and Mars Exploration Rover vehicles, and was also the baseline material for the leading edges and nose-cap of the X-34 vehicle. Ames is currently designing the TPS for the wing leading edge of the X-37 Orbital Vehicle.