Survey of Blunt Body Dynamic Stability in Supersonic Flow
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paper_title: Dynamic stability of vehicles traversing ascending or descending paths through the atmosphere

paper_content:

From Summary: "An analysis is given of the oscillatory motions of vehicles which traverse ascending and descending paths through the atmosphere at high speed. The specific case of a skip path is examined in detail, and this leads to a form of solution for the oscillatory motion which should recur over any trajectory. The distinguishing feature of this form is the appearance of the Bessel rather than the trigonometric function as the characteristic mode of oscillation."
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paper_title: Motion of a ballistic missile angularly misaligned with the flight path upon entering the atmosphere and its effect upon aerodynamic heating, aerodynamic loads, and miss distance

paper_content:

From Summary: "An analysis is given of the oscillating motion of a ballistic missile which upon entering the atmosphere is angularly misaligned with respect to the flight path. The history of the motion for some example missiles is discussed from the point of view of the effect of the motion on the aerodynamic heating and loading. The miss distance at the target due to misalignment and to small accidental trim angles is treated. The stability problem is also discussed for the case where the missile is tumbling prior to atmospheric entry."
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paper_title: Stability of ballistic reentry bodies

paper_content:

Report discussing various features of the stability of ballistic reentry shapes, including considerations for ballistic-missile and manned-satellite reentry capsules. Attainment of satisfactory stability of reentry bodies with subsonic terminal velocities was not found to be too difficult, but undesirable features that may cause marginal stability characteristics may be introduced in an effort to minimize weight. Reentry bodies with supersonic terminal velocities have fewer stability issues.
---
paper_title: Dynamic stability of vehicles traversing ascending or descending paths through the atmosphere

paper_content:

From Summary: "An analysis is given of the oscillatory motions of vehicles which traverse ascending and descending paths through the atmosphere at high speed. The specific case of a skip path is examined in detail, and this leads to a form of solution for the oscillatory motion which should recur over any trajectory. The distinguishing feature of this form is the appearance of the Bessel rather than the trigonometric function as the characteristic mode of oscillation."
---
paper_title: Motion of a ballistic missile angularly misaligned with the flight path upon entering the atmosphere and its effect upon aerodynamic heating, aerodynamic loads, and miss distance

paper_content:

From Summary: "An analysis is given of the oscillating motion of a ballistic missile which upon entering the atmosphere is angularly misaligned with respect to the flight path. The history of the motion for some example missiles is discussed from the point of view of the effect of the motion on the aerodynamic heating and loading. The miss distance at the target due to misalignment and to small accidental trim angles is treated. The stability problem is also discussed for the case where the missile is tumbling prior to atmospheric entry."
---
paper_title: Stability of ballistic reentry bodies

paper_content:

Report discussing various features of the stability of ballistic reentry shapes, including considerations for ballistic-missile and manned-satellite reentry capsules. Attainment of satisfactory stability of reentry bodies with subsonic terminal velocities was not found to be too difficult, but undesirable features that may cause marginal stability characteristics may be introduced in an effort to minimize weight. Reentry bodies with supersonic terminal velocities have fewer stability issues.
---
paper_title: Dynamic stability of vehicles traversing ascending or descending paths through the atmosphere

paper_content:

From Summary: "An analysis is given of the oscillatory motions of vehicles which traverse ascending and descending paths through the atmosphere at high speed. The specific case of a skip path is examined in detail, and this leads to a form of solution for the oscillatory motion which should recur over any trajectory. The distinguishing feature of this form is the appearance of the Bessel rather than the trigonometric function as the characteristic mode of oscillation."
---
paper_title: Motion of a ballistic missile angularly misaligned with the flight path upon entering the atmosphere and its effect upon aerodynamic heating, aerodynamic loads, and miss distance

paper_content:

From Summary: "An analysis is given of the oscillating motion of a ballistic missile which upon entering the atmosphere is angularly misaligned with respect to the flight path. The history of the motion for some example missiles is discussed from the point of view of the effect of the motion on the aerodynamic heating and loading. The miss distance at the target due to misalignment and to small accidental trim angles is treated. The stability problem is also discussed for the case where the missile is tumbling prior to atmospheric entry."
---
paper_title: Parameters Influencing Dynamic Stability Characteristics of Viking-Type Entry Configurations at Mach 1.76

paper_content:

Free-oscillation tests of three Viking-type blunt conical configurations were conducted in a wind tunnel to determine the important variables influencing their dynamic stability characteristics at Mach 1.76. The effects of sting geometry are shown to be significant at low angles of attack, while the effects of cross plane motions and tunnel vibration characteristics appear to be negligible. Variation of the reduced-frequency parameter and model base geometry caused significant effects in the data. An approximate technique was developed for converting effective data from either forced-oscillation or free-oscillation tests to values based on the instantaneous angle of attack.
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paper_title: Overview of Orion Crew Module and Launch Abort Vehicle Dynamic Stability (Invited)

paper_content:

With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re- orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft.
---
paper_title: Parameters Influencing Dynamic Stability Characteristics of Viking-Type Entry Configurations at Mach 1.76

paper_content:

Free-oscillation tests of three Viking-type blunt conical configurations were conducted in a wind tunnel to determine the important variables influencing their dynamic stability characteristics at Mach 1.76. The effects of sting geometry are shown to be significant at low angles of attack, while the effects of cross plane motions and tunnel vibration characteristics appear to be negligible. Variation of the reduced-frequency parameter and model base geometry caused significant effects in the data. An approximate technique was developed for converting effective data from either forced-oscillation or free-oscillation tests to values based on the instantaneous angle of attack.
---
paper_title: Overview of Orion Crew Module and Launch Abort Vehicle Dynamic Stability (Invited)

paper_content:

With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re- orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft.
---
paper_title: Dynamics of planetary probes - Design and testing issues

paper_content:

Interest in planetary probes has increased significantly in the last few years. Many of the proposed missions will use aeroassist for the capture and descent phases of the missions. This use of aeroassist will put a greater demand on having accurate aerodynamics for these vehicles. Reviews are presented of some of the aerodynamic requirements with particular emphasis on dynamic stability as well as the aerodynamic testing requirements and with particular attention on the use of the ballistic range.
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paper_title: Dynamic Support Interference

paper_content:

Available experimental results are reviewed and organized to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing. Configurations involving bulbous bases, mass addition, boundary-layer transition near the base, and hypersonic low-density flows are shown to be particularly sensitive to sting interference effects. Transverse rod support interference occurs at all Mach numbers depending on oscillation amplitude and/or trim angle of attack. The postulated flow model predicts that cylindrical and flared stings can have opposite interference effects in agreement with experimental observations. An analytical method of correcting the wind-tunnel results for dynamic support interference is proposed.
---
paper_title: Overview of Orion Crew Module and Launch Abort Vehicle Dynamic Stability (Invited)

paper_content:

With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re- orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft.
---
paper_title: Dynamic Support Interference

paper_content:

Available experimental results are reviewed and organized to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing. Configurations involving bulbous bases, mass addition, boundary-layer transition near the base, and hypersonic low-density flows are shown to be particularly sensitive to sting interference effects. Transverse rod support interference occurs at all Mach numbers depending on oscillation amplitude and/or trim angle of attack. The postulated flow model predicts that cylindrical and flared stings can have opposite interference effects in agreement with experimental observations. An analytical method of correcting the wind-tunnel results for dynamic support interference is proposed.
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paper_title: Dynamic Support Interference

paper_content:

Available experimental results are reviewed and organized to provide a logical explanation of aerodynamic support interference for dynamic wind-tunnel testing. Configurations involving bulbous bases, mass addition, boundary-layer transition near the base, and hypersonic low-density flows are shown to be particularly sensitive to sting interference effects. Transverse rod support interference occurs at all Mach numbers depending on oscillation amplitude and/or trim angle of attack. The postulated flow model predicts that cylindrical and flared stings can have opposite interference effects in agreement with experimental observations. An analytical method of correcting the wind-tunnel results for dynamic support interference is proposed.
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paper_title: Unsteady embedded Newton-Busemann flow theory

paper_content:

An unsteady, embedded Newton-Busemann flow theory is developed by extending the unsteady NewtonBusemann flow theory of Hui and Tobak to blunt bodies, incorporating the embedded Newtonian flow concept of Seiff and Ericsson. In this theory the unsteady surface pressure includes the Newtonian impact part plus Busemann's centrifugal correction. Applications to dynamic stability of blunt bodies of revolution show that 1) the centrifugal pressure is just as important as the impact part and must not be neglected and 2) with its inclusion the complete theory is in good agreement with existing experiments for high Mach number flow.
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paper_title: Comparison of predictions and experimental data for hypersonic pitching motion stability

paper_content:

The stability of oscillatory motions of vehicles flying at hypersonic Mach numbers is of considerable relevance to their initial design. Methods are needed for quick and accurate predictions of stability and control that are applicable over a wide range of body shapes, angles of attack, and flow conditions without the need to resort to computationally time-consuming numerical flowfield calculation methods. The purpose of this paper is to present experimental and theoretical data concerning the static and dynamic pitching stability of pointed and blunted 10 deg semiangle cones and a double-flared hyperballistic shape. Although Newtonian theory gives inadequate accuracy of prediction, inviscid embedded Newtonian theory, which accounts for the reduced dynamic pressure and lower flow velocity in the embedded flow downstream of the strong bow shock, is shown to provide surprisingly good agreement with experimental data over a wide range of conditions. Comparisons with experimental results show that the broad flow features associated with nose bluntness, angle of attack, and center of gravity position and their effect on static and dynamic stability are well described in regimes not containing flow structural change. However, in some cases discrepancies exist between the predictions and experimental observations, and these have been attributed to a variety of viscous-flow phenomena involving boundary-layer transition and flow separation, including complex lee-surface vortical flows.
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paper_title: Generalized unsteady embedded Newtonian flow

paper_content:

An analysis is presented which extends the previously developed unsteady embedded Newtonian theory down to finite supersonic Mach numbers. It is found that Mach number can have a very large influence on the stability characteristics of slender blunted cones, and that there exist cone angle-nose bluntness combinations for which these Mach number effects are minimized. The computed effects of nose bluntness on static and dynamic stability derivatives are in excellent agreement with available experimental data. This also holds true for the highly nonlinear effects of angle of attack.
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paper_title: Estimation of dynamic stability coefficients for aerodynamic decelerators using CFD

paper_content:

A method for performing dynamic simulations of entry vehicles is developed. This capability uses existing infrastructure within the US3D flow solver, developed for doing fluid structure interaction (FSI) simulations, to allow for up to six degree of freedom (6DoF) simulations. Inviscid, free-to-oscillate simulations of the Mars Science Laboratory (MSL) capsule at Mach2.5and3.5are used to evaluate di↵erent data reduction methods. It is found that many simulations may be required to get reliable data. The computed pitch damping coecients show comparable trends to ballistic range data, though they di↵er in magnitude, particularly at high angles of attack. Preliminary viscous simulation results are presented, and show improved agreement with experimental data compared to the inviscid analysis.
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paper_title: Dynamic Viscous Simulations of Atmospheric-Entry Capsules

paper_content:

Viscous, free-oscillation simulations with the OverĔow solver are used to predict the aerodynamic behavior of non-liĕing capsule shapes in the supersonic speed regime. Computations using hybrid Reynolds-averaged Navier-Stokes turbulence models are examined for two novel atmospheric-entry capsule conđgurations: an idealized inĔatable decelerator concept, and the Orion Crew Module. ăe simulation results are validated against nonlinear aerodynamic models determined from free-Ĕight ballistic-range data analysis. For the Orion Crew Module, two separate methods of reducing identical range data, along with common models tested in separate range facilities, are included. ăe computations demonstrate the efficiency and accuracy of dynamic simulations for developing a nonlinear aerodynamic performance database. Analysis indicates that the typical nonlinear, bluff-body behavior is characterized by a rate-dependent dynamic response, which is not currently accounted for in common aerodynamic models.
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paper_title: Reduced-Frequency Approach for Calculating Dynamic Derivatives

paper_content:

A novel method of calculating dynamic stability derivatives using Computational Fluid Dynamics is presented. This method uses a non-linear, reduced-frequency approach to simulate the response to a forced oscillation using a single frequency component at the forcing frequency. This provides an order of magnitude improvement in computational e ciency over similar time-dependent schemes without loss of generality. The reduced-frequency approach is implemented with an automated Cartesian mesh scheme. This combination of Cartesian meshing and reduced-frequency solver enables damping derivatives for arbitrary flight condition and geometric complexity to be e ciently and accurately calculated. The method is validated for 3-D reference missile and aircraft dynamic test configurations through the transonic and high-alpha flight regimes. Comparisons with the results of time-dependent simulations are also included.
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paper_title: Dynamic Analysis of Atmospheric-Entry Probes and Capsules

paper_content:

A Computational Fluid Dynamics analysis of the dynamics of probe and capsule shapes at supersonic flight conditions is performed using an automated, inviscid Cartesian-mesh scheme. This analysis uses static and dynamic free-oscillation simulations to develop static and dynamic aerodynamic coecients for three configurations: the Viking, Genesis, and Mars Exploration Rover capsules. These computed coecients are compared against data reduced from ballistic-range free-flight testing. A comparison of data reduction methods for capsule shapes from computational simulations and range data is included. Free-flight simulations agree well with available flight data for both fully-coupled simulations and aerodynamic database fly-throughs based on the developed aerodynamic coecients. A sensitivity analysis of the aerodynamic coecients for trajectory simulations at constant altitude is included.
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paper_title: Dynamic stability of high-drag planetary entry vehicles at transonic speeds.

paper_content:

The transonic dynamic stability of one 70° and two 60° half-angle cone configurations has been investigated in a continuous flow wind tunnel using free-flight techniques. The parameters varied were Mach number and oscillation amplitude for the approximate ranges of 0.6 to 2.0 and 0° to 15°, respectively. The test data show two marked effects: 1) a decrease in dynamic stability at transonic speeds relative to that exhibited in the subsonic and supersonic regimes, and 2) transonic dynamic stability data sensitive to oscillation amplitude. Generally, measured coefficients were destabilizing for angles of attack less than 10° and stabilizing at greater amplitudes. The effect of using these data in a six-degree-of-freedom computer program to generate oscillation envelopes and corresponding dynamic stability data for a simulated Mars entry trajectory is demonstrated.
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paper_title: Transonic and low supersonic static and dynamic aerodynamic characteristics of the Stardust sample return capsule

paper_content:

The successful deployment of the parachute recovery system for the Stardust sample return mission requires an understanding of the static and dynamic aerodynamic characteristics in the supersonic and transonic speed range. Aerodynamics obtained in a ballistic range at Mach num0ers 1.2 to 2.8 and angles of attack to 30 degrees are presented. The observed motion histories indicated a limit cycle of between 25 and 30 degrees. The major contributor to this was the pitch damping which was highly nonlinear with angle of attack, being dynamically unstable at small angles and dynamically very stable at higher angles. Introduction Experimental Setup The deployment of a parachute or the direct landing of a passive probe on the surface of a planet presents some unique requirements from an aerodynamic standpoint. The sample return capsule for the Stardust mission is an example of these requirements (Ref. 1). Here a parachute is to be deployed in the low supersonics or transonic speed range, but the vehicle must also be capable of direct impact at small angles of incident to the normal to ensure that the payload package is undamaged in case of parachute deployment problems. The ballistic range tests were conducted in the Aeroballistic Research Facility of the Air Force Laboratory, Armament Directorate, located at Eglin Air Force Base, Florida. The ballistic range is a one atmosphere range with 50 orthogonal shadowgraph stations distributed over 200 meters, Ref. 2. The models were fired from a 80 millimeter smooth bore powder gas gun at a nominal velocity of 1 km/set. In the course of the flight down the range the velocity decayed to about 0.4 km&c. Hence data were obtained for Mach numbers from 2.8 to 1.2. The dynamics of entry into a planetary atmosphere are such that after maximum dynamic pressure the pitching amplitude envelope normally begins to grow. The extent of this growth is dependent on the aerodynamic characteristics and the inertial properties of the vehicle, and in many cases these characteristics can lead to a large amplitude limit cycle. This paper will examine the aerodynamic and trajectory characteristics of the Stardust sample return capsule in the low supersonic to transonic speed range as determined from ballistic range tests. Three models were tested with the same external geometry shown in Fig. 1 but with three different center of gravity positions. The models were made of steel to make them as heavy as possible to keep the velocity losses to a minimum. The nominal physical properties for the models with the three different center of gravity positions are shown in Table I. Also shown for reference are the properties of the full scale vehicle. The measured physical properties for the 10 models tested are shown in Table II and the test conditions, number of observed stations and distance flown are shown in Table III. * Consultant, Associate Fellow ALAA + Aerospace Engineer, Aerothermodynatnics Branch, Experimental Data Senior Member AIAA $ Vice President of Engineering, Senior Member AIAA This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. The data consists of 10 sets (tests) of 40-45 orthogonal shadowgraph images and the corresponding times that the shadowgraphs were taken. A typical range shadowgraph is shown in Fig. 2. For im..-.
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paper_title: Dynamic Stability Tests of Spinning Entry Bodies in the Terminal Regime

paper_content:

Analytical studies indicate that rolling blunt entry vehicles are susceptible to angle-ofattack divergence in the terminal regime. To investigate this problem, an experimental program was conducted where models were spun up and dropped inside the 500-ft-high Vehicle Assembly Building at Cape Kennedy. The angle-of-attack motion was recorded photographically, and from these data the dynamic stability coefficient was determined. The data confirm the results of the analytic studies and suggest that the dynamic stability coefficient increases, in a favorable way, as the roll rate increases.
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paper_title: Dynamic stability of high-drag planetary entry vehicles at transonic speeds.

paper_content:

The transonic dynamic stability of one 70° and two 60° half-angle cone configurations has been investigated in a continuous flow wind tunnel using free-flight techniques. The parameters varied were Mach number and oscillation amplitude for the approximate ranges of 0.6 to 2.0 and 0° to 15°, respectively. The test data show two marked effects: 1) a decrease in dynamic stability at transonic speeds relative to that exhibited in the subsonic and supersonic regimes, and 2) transonic dynamic stability data sensitive to oscillation amplitude. Generally, measured coefficients were destabilizing for angles of attack less than 10° and stabilizing at greater amplitudes. The effect of using these data in a six-degree-of-freedom computer program to generate oscillation envelopes and corresponding dynamic stability data for a simulated Mars entry trajectory is demonstrated.
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paper_title: A Study of the Motion and Aerodynamic Heating of Missiles Entering the Earth's Atmosphere at High Supersonic Speeds

paper_content:

A simplified analysis of the velocity and deceleration history of missiles entering the earth's atmosphere at high supersonic speeds is presented. The results of this motion analysis are employed to indicate means available to the designer for minimizing aerodynamic heating. The heating problem considered involves not only the total heat transferred to a missile by convection, but also the maximum average and local time rates of convective heat transfer.
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paper_title: Dynamic Stability Tests of Spinning Entry Bodies in the Terminal Regime

paper_content:

Analytical studies indicate that rolling blunt entry vehicles are susceptible to angle-ofattack divergence in the terminal regime. To investigate this problem, an experimental program was conducted where models were spun up and dropped inside the 500-ft-high Vehicle Assembly Building at Cape Kennedy. The angle-of-attack motion was recorded photographically, and from these data the dynamic stability coefficient was determined. The data confirm the results of the analytic studies and suggest that the dynamic stability coefficient increases, in a favorable way, as the roll rate increases.
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paper_title: Drag and stability of Mars probe/lander shapes.

paper_content:

An experimental program has been conducted in ballistics ranges to investigate the aerodynamic characteristics of three candidate NASA configurations for a Mars probe/lander: a blunted 60° half-angle cone, a spherical segment, and a blunted tension shell. The drag, staticand dynamic-stability coefficients were determined in air for Mach numbers from 0.6 to 13. At supersonic and hypersonic Mach numbers, the drag coefficients corrected to zero angle of attack were slightly higher for the spherical-segment configuration than for the other two shapes. All three configurations were statically stable. The dynamic-stability coefficients for the 60° half-angle cone and spherical-segment configurations were stabilizing in the supersonic and hypersonic region. Destabilizing dynamic-stability coefficients were measured for all three configurations in the transonic region.
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paper_title: Stability of ballistic reentry bodies

paper_content:

Report discussing various features of the stability of ballistic reentry shapes, including considerations for ballistic-missile and manned-satellite reentry capsules. Attainment of satisfactory stability of reentry bodies with subsonic terminal velocities was not found to be too difficult, but undesirable features that may cause marginal stability characteristics may be introduced in an effort to minimize weight. Reentry bodies with supersonic terminal velocities have fewer stability issues.
---
paper_title: Parameters Influencing Dynamic Stability Characteristics of Viking-Type Entry Configurations at Mach 1.76

paper_content:

Free-oscillation tests of three Viking-type blunt conical configurations were conducted in a wind tunnel to determine the important variables influencing their dynamic stability characteristics at Mach 1.76. The effects of sting geometry are shown to be significant at low angles of attack, while the effects of cross plane motions and tunnel vibration characteristics appear to be negligible. Variation of the reduced-frequency parameter and model base geometry caused significant effects in the data. An approximate technique was developed for converting effective data from either forced-oscillation or free-oscillation tests to values based on the instantaneous angle of attack.
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paper_title: Oscillation of Supersonic Inflatable Aerodynamic Decelerators at Mars

paper_content:

This paper examines the dynamic stability of a notional Mars entry vehicle augmented with an attached supersonic inflatable aerodynamic decelerator (SIAD) deployed at Mach 5. Dynamics of the attached isotensoid and tension cone SIAD configurations are compared using an explicit solution to the planar equations of motion. A current experimental database of flexible isotensoid and tension cone static aerodynamics is employed in the simulation. Pitch-damping data from the Mars Science Laboratory (MSL) ballistic range tests is parameterized and applied to the SIAD-augmented portion of flight. The Mach number at which safe parachute deployment can occur depends on the amplitude of pitch oscillation, so the sensitivity of this metric to the parameterized pitch-damping behavior is determined. Pitch dynamics yielding unacceptable parachute staging conditions are quantified to inform SIAD configuration selection and design. These exploratory results are used to recommend a general strategy for measuring the pitch dynamics of SIAD-augmented blunt vehicles in ground testing facilities.
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paper_title: Overview of Orion Crew Module and Launch Abort Vehicle Dynamic Stability (Invited)

paper_content:

With the retirement of the Space Shuttle, NASA is designing a new spacecraft, called Orion, to fly astronauts to low earth orbit and beyond. Characterization of the dynamic stability of the Orion spacecraft is important for the design of the spacecraft and trajectory construction. Dynamic stability affects the stability and control of the Orion Crew Module during re-entry, especially below Mach = 2.0 and including flight under the drogues. The Launch Abort Vehicle is affected by dynamic stability as well, especially during the re- orientation and heatshield forward segments of the flight. The dynamic stability was assessed using the forced oscillation technique, free-to-oscillate, ballistic range, and sub-scale free-flight tests. All of the test techniques demonstrated that in heatshield-forward flight the Crew Module and Launch Abort Vehicle are dynamically unstable in a significant portion of their flight trajectory. This paper will provide a brief overview of the Orion dynamic aero program and a high-level summary of the dynamic stability characteristics of the Orion spacecraft.
---
paper_title: Reduced-Frequency Approach for Calculating Dynamic Derivatives

paper_content:

A novel method of calculating dynamic stability derivatives using Computational Fluid Dynamics is presented. This method uses a non-linear, reduced-frequency approach to simulate the response to a forced oscillation using a single frequency component at the forcing frequency. This provides an order of magnitude improvement in computational e ciency over similar time-dependent schemes without loss of generality. The reduced-frequency approach is implemented with an automated Cartesian mesh scheme. This combination of Cartesian meshing and reduced-frequency solver enables damping derivatives for arbitrary flight condition and geometric complexity to be e ciently and accurately calculated. The method is validated for 3-D reference missile and aircraft dynamic test configurations through the transonic and high-alpha flight regimes. Comparisons with the results of time-dependent simulations are also included.
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paper_title: Low-Speed Aerodynamics of a Planetary Entry Capsule

paper_content:

Results of an investigation of the global aerodynamic coefe cients and e ow characterization around an Apollostyle capsule model at low speed are presented. Flow features were ascertained quantitatively with laser Doppler velocimetry, digital particle image velocimetry, and hot-wire measurements, as well as qualitatively by e ow visualizations. The study revealed a meandering vortex ring around the capsule, well-organized streamwise vortices whose maximum vorticity increased in the recirculating wake before decaying farther downstream, as well as a complex array ofe ow separation and reattachmentfeatures. A numberofparticularitiesin the e owe eld have been identie ed as potential candidates for triggering the onset of vehicle instability. Based on these e ndings, a modeling approach is proposed.
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paper_title: Parameters Influencing Dynamic Stability Characteristics of Viking-Type Entry Configurations at Mach 1.76

paper_content:

Free-oscillation tests of three Viking-type blunt conical configurations were conducted in a wind tunnel to determine the important variables influencing their dynamic stability characteristics at Mach 1.76. The effects of sting geometry are shown to be significant at low angles of attack, while the effects of cross plane motions and tunnel vibration characteristics appear to be negligible. Variation of the reduced-frequency parameter and model base geometry caused significant effects in the data. An approximate technique was developed for converting effective data from either forced-oscillation or free-oscillation tests to values based on the instantaneous angle of attack.
---
paper_title: Drag and stability of Mars probe/lander shapes.

paper_content:

An experimental program has been conducted in ballistics ranges to investigate the aerodynamic characteristics of three candidate NASA configurations for a Mars probe/lander: a blunted 60° half-angle cone, a spherical segment, and a blunted tension shell. The drag, staticand dynamic-stability coefficients were determined in air for Mach numbers from 0.6 to 13. At supersonic and hypersonic Mach numbers, the drag coefficients corrected to zero angle of attack were slightly higher for the spherical-segment configuration than for the other two shapes. All three configurations were statically stable. The dynamic-stability coefficients for the 60° half-angle cone and spherical-segment configurations were stabilizing in the supersonic and hypersonic region. Destabilizing dynamic-stability coefficients were measured for all three configurations in the transonic region.
---
paper_title: Dynamics of planetary probes - Design and testing issues

paper_content:

Interest in planetary probes has increased significantly in the last few years. Many of the proposed missions will use aeroassist for the capture and descent phases of the missions. This use of aeroassist will put a greater demand on having accurate aerodynamics for these vehicles. Reviews are presented of some of the aerodynamic requirements with particular emphasis on dynamic stability as well as the aerodynamic testing requirements and with particular attention on the use of the ballistic range.
---
paper_title: The utilization of low speed facilities in transonic stability of reentry vehicles research - An evaluation

paper_content:

The customary practice of utilizing low speed facilities to extract flow characteristics of reentry vehicles in transonic regimes is examined. Using the Apollo capsule as a generic reentry configuration, the similarity between its wake in incompressible and compressible regimes is assessed from static measurements of lift, drag, pitching moment, surface pressure, wake size and periodicity of the wake flow at four nominal Mach numbers ranging from that of essentially incompressible to Mach 0.9. The results to date indicate that, for vehicle orientations of practical interest in which the heat-shield is facing the freestream, sufficient similitude is noted to warrant such an extrapolation at least as an exploratory tool in devising strategies for wake modification. Additional utility of low speed tests in acquiring wake features of an oscillating vehicle is conceptually feasible and discussed. Introduction A reentry capsule is shaped to be blunt so as to survive the intense aerodynamic heating in the hypersonic portion of the flight. However, during the transonic and subsonic phases of the reentry in what might be considered as off-design conditions, the vehicle faces a more pronounced stability and control problem. The dynamic vortex formation typical of the blunt body wake flow at the aforementioned speed regimes produces unsteady loading on the vehicle, and can sometimes thereby affect its handling characteristics severely. It is therefore important to determine the stability characteristics of the vehicle so as to ensure proper and timely deployment of parachutes prior to the onset of instability, as well as having a well documented *NSF-NATO Postdoctoral Fellow, Member AIAA. Associate Professor. 'Doctoral Candidate, Student Member AIAA. Research Engineer. Copyright © 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. description of the flow-field in order to understand the associated fluid mechanics. The importance and difficulties in characterizing the unsteady wake in studying the stability of a reentry vehicle are illustrated and discussed in further details in Ref. 1. In the context of vehicle stability and parachute deployment issues which take place in high subsonic and transonic regimes, the flow-field characterization around and in the near-wake of a reentry capsule is often extracted from low speed tests where both visualization and detailed diagnostics can be carried out more readily. The utilization of a low speed facility to extrapolate flow-field information of a reentry capsule at higher Mach numbers, although attractive in many perspectives and often implemented, is a practice that deserves a methodical examination. Using the Apollo capsule as a representative shape of planetary reentry vehicles, the present paper presents the results of a first series of experiments conducted at the von Karman Institute (VKJ) in assessing this issue of fundamental and practical importance by comparing the global aerodynamic quantities and the flow structures of a non-oscillating capsule in the incompressible, high subsonic and transonic regimes. These findings would lead to a disclosure of the degree of similarity in the flow-field of the various regimes, as well as contributing to the fundamental knowledge of three-dimensional bluff body flow with compressibility effect. In the case of a two-dimensional symmetric or three-dimensional axisymmetric body in free flow at zero lift, the associated global time-averaged wake characteristics are strongly dependent of the drag exerted by the body as this quantity represents an integral of the wake motion. In the event of a lifting body, it is expected that the lift would play its role and manifest itself ultimately in the wake as well. Similarly on a more refined scale, the details of the flow around the body, which could at least be partially revealed by surface pressure measurements, constitute the initial distribution of vorticity shed downstream of the body thereby 1 American Institute of Aeronautics and Astronautics Copyright© 1998, American Institute of Aeronautics and Astronautics, Inc. influencing the microscopies of the wake both on a time-averaged and temporal basis. With the above in mind, the global aerodynamic quantities lift, drag and moment coefficients about the center of gravity were measured at four different Mach numbers. As for the comparison of flow quantities, the investigation included surface pressure distributions as well as optical diagnostics around and in the near-wake of the capsule. In addition, the temporal characteristic of the flapping wake motion was mapped out. All of the subsonic and transonic measurements had been conducted in the VKI-S1 facility whereas their incompressible counterparts were measured in three separate low speed wind tunnels: VKI-L7, L7+ and L2A. The details of the various facilities are found in Ref. 2 Experimental Setup The Apollo Command Module Block I configuration with no protuberances was selected to represent a generic reentry vehicle in this investigation. A drawing of this configuration, with the various dimensions normalized with the maximum diameter (i.e., heat-shield) of the model, is shown in Figure 1. The model is at a =180° as illustrated, with the freestream flow in the direction from right to left. A clockwise rotation corresponds to the direction of decreasing angle of attack. Depending on the particular test, the model was supported either one-sided cantileverly or on both sides with a transverse rod through the theoretical center of gravity location shown in Figure 1. In this mounting arrangement the pitching moment at the model's theoretical center of gravity is therefore measured directly. The additional pertinent details for the various tests are tabulated in Table 1. Fig. 1 A scaled drawing of the Apollo model. Table 1: Summary of Test and Mounting Conditions in Various Facilities L7+
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Title: Survey of Blunt Body Dynamic Stability in Supersonic Flow

Section 1: Introduction
Description 1: Provide background on the importance of studying the dynamic stability of blunt bodies in supersonic flow, including historical context and current significance.

Section 2: Vehicle Design and Mission Implications
Description 2: Discuss how vehicle design and mission requirements influence dynamic stability characteristics and the importance of minimizing oscillation amplitude.

Section 3: Governing Equations of Motion
Description 3: Examine the differential equations governing the pitching motion of entry vehicles, and explore their analytical applications for predicting dynamic stability.

Section 4: Structure of a Blunt Body Wake
Description 4: Analyze the flow features and pressure forces in the wake of blunt bodies that contribute to dynamic instability.

Section 5: Experimental Techniques for Characterizing Damping
Description 5: Review various experimental methods used to determine the dynamic stability characteristics of blunt bodies, including forced oscillation, free oscillation, free flight wind tunnel, and ballistic range testing.

Section 6: Sting Effects on Dynamic Testing
Description 6: Evaluate the influence of sting configurations on experimental results and explore methods to minimize their interference.

Section 7: Overall Deficiencies in Testing Capabilities
Description 7: Summarize the limitations and uncertainties associated with current experimental techniques for testing dynamic stability.

Section 8: Semi-Empirical Impact Methods
Description 8: Describe the development and application of semi-empirical methods for predicting dynamic stability, including embedded Newtonian techniques.

Section 9: Computational Fluid Dynamics (CFD)
Description 9: Discuss advancements and challenges in using CFD to predict the dynamic stability of blunt bodies, including recent efforts and shortcomings.

Section 10: Vehicle Design Parameters and Dynamic Stability
Description 10: Investigate the influence of several key vehicle design parameters, such as center of gravity location, roll rate, forebody cone angle, nose radius, shoulder geometry, boundary layer trips, and aftbody effects, on dynamic stability.

Section 11: Environmental Parameters and Dynamic Stability
Description 11: Explore the impact of environmental parameters like Mach number, Reynolds number, Strouhal number, and specific heat ratio on the dynamic stability of blunt bodies.

Section 12: Physical Mechanisms
Description 12: Discuss proposed physical mechanisms behind dynamic stability, including pitching moment hysteresis and flow separation and reattachment.

Section 13: Conclusions
Description 13: Summarize key findings, acknowledge existing challenges, and suggest directions for future research in the field of blunt body dynamic stability.

Section 14: Acknowledgements
Description 14: Recognize contributions and support from individuals and organizations that facilitated the research presented in the survey.