Ashley M. Korzun

High Mass Mars Entry, Descent, and Landing Architecture Assessment

As the nation sets its sight on returning humans to the Moon and going onward to Mars, landing high mass payloads ( 2 t) on the Mars surface becomes a critical technological need. Viking heritage technologies (e.g., 70 sphere-cone aeroshell, SLA-561V thermal protection system, and supersonic disk-gap-band parachutes) that have been the mainstay of the United States’ robotic Mars exploration program do not provide sucient capability to land such large payload masses. In this investigation, a parametric study of the Mars entry, descent, and landing design space has been conducted. Entry velocity, entry vehicle conguration, entry vehicle mass, and the approach to supersonic deceleration were varied. Particular focus is given to the entry vehicle shape and the supersonic deceleration technology trades. Slender bodied vehicles with a lift-to-drag ratio (L=D) of 0.68 are examined alongside blunt bodies with L=D = 0.30. Results demonstrated that while the increased L=D of a slender entry conguration allows for more favorable terminal descent staging conditions, the greater structural eciencies of blunt body systems along with the reduced acreage required for the thermal protection system aords an inherently lighter vehicle. The supersonic deceleration technology trade focuses on inatable aerodynamic decelerators (IAD) and supersonic retropropulsion, as supersonic parachute systems are shown to be excessively large for further consideration. While entry masses (the total mass at the top of the Mars atmosphere) between 20 and 100 t are considered, a maximum payload capability of 37.3 t results. Of particular note, as entry mass increases, the gain in payload mass diminishes. It is shown that blunt body vehicles provide sucient vertical L=D to decelerate all entry masses considered through the Mars atmosphere with adequate staging conditions for the propulsive terminal descent. A payload mass fraction penalty of approximately 0.3 exists for the use of slender bodied vehicles. Another observation of this investigation is that the increased aerothermal and aerodynamic loads induced from a direct entry trajectory (velocity 6.75 km/s) reduce the payload mass fraction by approximately 15% compared to entry from orbital velocity ( 4 km/s). It should be noted that while both IADs and supersonic retropropulsion were evaluated for each of the entry masses, congurations, and velocities, the IAD proved to be more mass-ecient in all instances. The sensitivity of these results to modeling assumptions was also examined. The payload mass of slender body vehicles was observed to be approximately four times more sensitive to modeling assumptions and uncertainty than blunt bodies.

Development of Supersonic Retropropulsion for Future Mars Entry, Descent, and Landing Systems

Recent studies have concluded that Viking-era entry system deceleration technologies are extremely difficult to scale for progressively larger payloads (tens of metric tons) required for human Mars...

A Survey of Supersonic Retropropulsion Technology for Mars Entry, Descent, and Landing

This paper presents a literature survey on supersonic retropropulsion technology as it applies to Mars entry, descent, and landing (EDL). The relevance of this technology to the feasibility of Mars EDL is shown to increase with ballistic coefficient to the point that it is likely required for human Mars exploration. The use of retropropulsion to decelerate an entry vehicle from hypersonic or supersonic conditions to a subsonic velocity is the primary focus of this review. Discussed are systems-level studies, general flowfield characteristics, static aerodynamics, vehicle and flowfield stability considerations, and aerothermodynamics. The experimental and computational approaches used to develop retropropulsion technology are also reviewed. Finally, the applicability and limitations of the existing literature and current state-of-the- art computational tools to future missions are discussed in the context of human and robotic Mars exploration.

Comparison of Inviscid and Viscous Aerodynamic Predictions of Supersonic Retropropulsion Flowfields

Supersonic retropropulsion, or the initiation of a retropropulsion phase at supersonic freestream conditions, is an enabling decelerator technology for high-mass planetary entries at Mars. The current knowledge on supersonic retropropulsion is largely derived from exploratory development efforts prior to the Viking missions in the 1960s and early 1970s, predominantly sub-scale wind tunnel testing. Little literature exists on analytical and computational modeling approaches for supersonic aerodynamic-propulsive interactions at moderate thrust levels and flight-relevant conditions. This investigation presents a discussion of the relevant flow physics to provide insight into the effectiveness of inviscid and viscous computational analysis approaches in consistently and accurately capturing the relevant flow physics. Preliminary computational results for a blunt body with two retropropulsion configurations are compared with experimental data for the location of prominent flow features and surface pressure distributions. This work is intended to provide an initial discussion of the challenges facing the computational simulation of supersonic retropropulsion flowfields.

Development of Supersonic Retro-Propulsion for Future Mars Entry, Descent, and Landing Systems

1 ____________________________________________ * Aerospace Engineer, Atmospheric Flight & Entry Systems Branch, MS 489, Karl.T.Edquist@nasa.gov, Senior Member. † Aerospace Engineer, Atmospheric Flight & Entry Systems Branch, MS 489, Member. ‡ Propulsion Systems Engineer, Propulsion Systems Branch, MS EP4. § Senior Engineer, Aeroscience & Flight Mechanics Division, MS EG5, Member. ¶ Systems Engineer, Entry, Descent, and Landing Systems and Advanced Technologies Group, MS 321-220. # Research Scientist, Aerothermodynamics Branch, MS 230-2, Member. ** Aerospace Engineer, Systems Analysis Branch, MS 258-1, Member. †† Graduate Research Assistant, Daniel Guggenheim School of Aerospace Engineering, Student Member. Development of Supersonic Retro-Propulsion for Future Mars Entry, Descent, and Landing Systems

Conceptual Modeling of Supersonic Retropropulsion Flow Interactions and Relationships to System Performance

Supersonic retropropulsion is an entry, descent, and landing technology applicable to and potentially enabling high-mass missions required for advanced robotic and human exploration on the surface of Mars. For conceptual design, it is necessary to understand the significance of retropropulsion configuration on an entry vehicle’s static aerodynamic characteristics and the relation of this configuration to other vehicle performance metrics. This investigation developed an approximate model for the supersonic retropropulsion flowfield to assist in evaluating the impact of design choices on the vehicle’s drag characteristics for flight-relevant conditions and scales. This model was used to explore the impact of operating conditions, required propulsion system performance, propulsion system composition, and vehicle configuration on the integrated aerodynamic drag characteristics of full-scale vehicles for Mars entry, descent, and landing. The forebody aerodynamic drag and axial force characteristics of vehicle...

Performance Characterization of Supersonic Retropropulsion for Application to High Mass Mars Entry, Descent, and Landing

Prior high-mass Mars EDL systems studies have neglected aerodynamic-propulsive interactions and performance impacts during the supersonic phase of descent. The goal of this investigation is to accurately evaluate the performance of supersonic retropropulsion with increasing vehicle ballistic coefficient across a range of initiation conditions relevant for future high-mass Mars landed systems. Past experimental work has established supersonic retropropulsion trends in static aerodynamics as a function of retropropulsion configuration, freestream conditions, and thrust. From this experimental database, an aerodynamic-propulsive interactions model is created. EDL system performance results are developed with the potential aerodynamic drag preservation included and excluded during this phase of flight for comparison against prior studies. The results of this investigation demonstrate the significance of aerodynamic drag preservation as a function of retropropulsion initiation conditions, characterize mass optimal trajectories utilizing supersonic retropropulsion, and compare propulsion system requirements with existing propulsion systems and systems under development for future exploration missions.

Computational Aerodynamic Predictions of Supersonic Retropropulsion Flowfields

Supersonic retropropulsion, or the initiation of a retropropulsion phase at supersonic freestream conditions, is an enabling decelerator technology for high-mass planetary entries at Mars. Supersonic retropropulsion relies on retrothrust to decelerate the vehicle. A thrust-driven interaction of underexpanded jet flow with the shock layer of a blunt body alters the aerodynamic characteristics of the vehicle. Little literature exists on analytical and computational modeling approaches for supersonic aerodynamic-propulsive interactions at moderate thrust levels and flight-relevant conditions. This investigation is an exploratory application of a steady, turbulent computational approach to supersonic retropropulsion flowfields using modern and historical test cases. The results obtained from this approach agree reasonably well with experimental data for the locations of the bow shock, stagnation point, and Mach disk for a retropropulsion configuration with a single nozzle at the nose. The surface pressure dis...

Supersonic Aerodynamic Characteristics of Blunt Body Trim Tab Configurations

Trim tabs are aerodynamic control surfaces that can allow an entry vehicle to meet aerodynamic performance requirements while reducing or eliminating the use of ballast mass and providing a capability to modulate the lift-to-drag ratio during entry. Force and moment data were obtained on 38 unique, blunt body trim tab configurations in the NASA Langley Research Center Unitary Plan Wind Tunnel. The data were used to parametrically assess the supersonic aerodynamic performance of trim tabs and to understand the influence of tab area, cant angle, and aspect ratio. Across the range of conditions tested (Mach numbers of 2.5, 3.5, and 4.5; angles of attack from -4deg to +20deg; angles of sideslip from 0deg to +8deg), the effects of varying tab area and tab cant angle were found to be much more significant than effects from varying tab aspect ratio. Aerodynamic characteristics exhibited variation with Mach number and forebody geometry over the range of conditions tested. Overall, the results demonstrate that trim tabs are a viable approach to satisfy aerodynamic performance requirements of blunt body entry vehicles with minimal ballast mass. For a 70deg sphere-cone, a tab with 3% area of the forebody and canted approximately 35deg with no ballast mass was found to give the same trim aerodynamics as a baseline model with ballast mass that was 5% of the total entry mass.

Testing of the Trim Tab Parametric Model in NASA Langley's Unitary Plan Wind Tunnel

In support of NASA’s Entry, Descent, and Landing technology development efforts, testing of Langley’s Trim Tab Parametric Models was conducted in Test Section 2 of the NASA Langley Unitary Plan Wind Tunnel. The objectives were to generate quantitative aerodynamic data and qualitative surface pressure data for computational validation and aerodynamic database development. Six-component force and moment data were measured on 38 unique blunt-body trim tab configurations at Mach numbers of 2.5, 3.5, and 4.5, angles of attack from -4° to +20°, and angles of sideslip from 0° to +8°. Configuration parameters investigated in this study were forebody shape, tab area, tab cant angle, and tab aspect ratio. Pressure sensitive paint was used to provide qualitative surface pressure distributions for a subset of these flow and configuration variables. Over the range of parameters tested, the effects of varying tab area and tab cant angle were found to be much more significant than varying tab aspect ratio relative to key aerodynamic performance requirements. Qualitative surface pressure data supported the integrated aerodynamic data and provided information to aid in future analyses of localized phenomena for trim tab configurations.