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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Vertical Spin Tunnel Testing and Stability Analysis of Multi-Mission Earth Entry Vehicles

Multi-Mission Earth Entry Vehicles (MMEEVs) are blunt-body vehicles designed with the purpose of transporting payloads from space to the surface of the Earth. To achieve high reliability and minimum weight, MMEEVs avoid using limited-reliability systems, such as parachutes, retro-rockets, and reaction control systems and rely on the natural aerodynamic stability of the vehicle throughout the Entry, Descent, and Landing phases of flight. Testing in NASA Langley's 20-FT Vertical Spin Tunnel (20-FT VST), dynamically-scaled MMEEV models was conducted to improve subsonic aerodynamic models and validate stability criteria for this class of vehicle. This report documents the resulting data from VST testing for an array of 60-deg sphere-cone MMEEVs. Model configurations included were 1.2 meter, and 1.8 meter designs. The addition of a backshell extender, which provided a 150% increase in backshell diameter for the 1.2 meter design, provided a third test configuration. Center of Gravity limits were established for all MMEEV configurations. An application of System Identification (SID) techniques was performed to determine the aerodynamic coefficients in order to provide databases for subsequent 6-degree-of-freedom simulations.

Glaab, Louis J.↗
NASA NTRS1972

Nutational stability of a dual-spin satellite under the influence of applied reaction torques.

The nutational stability of a dual-spin satellite under the influence of an applied reaction torque is analyzed. It is assumed that since the solar paddle attachments to the hub of the spacecraft are not rigidly locked, the effect of the solar panels can be replaced by a constant reaction torque acting on the hub of the spacecraft. This could result in the satellite having an equilibrium motion about an axis displaced from the nominal axis of symmetry. The variational equations of motion are developed about such an equilibrium position using the SAS-A spacecraft as a model. Energy dissipation on the rotor as well as the main body is included. This nonautonomous set of differential equations are linearized and transformed to an autonomous set using the Lyapunov Reducibility Theorem. The stability of the kinematically similar system is examined numerically using representative SAS-A parameters for the case when either pair of solar panels is assumed to be loosely attached. Stability is verified for small system nutation angles (0.1 degree) although the time constant associated with the least damped mode is approximately one order of magnitude larger than that for the SAS-A system without the influence of the reaction torques.

Bainum, P. M.↗
NASA NTRS1974

Passive dual spin misalignment compensators

A combination dual-spin gyroscopically stabilized device is described having a spinning rotor and a non-spinning platform. Two substantially lossless mechanical resonators, resonant at the spin frequency, are orthogonally positioned on the platform for compensation for the disturbing torque acting on the platform due to rotor misalignment.

Donohue, J. H.↗
NASA NTRS1984

Stability of a dual-spin spacecraft with spherical dampers

The present investigation is concerned with the stability characteristics of a specific dual-spin satellite configuration marked by a high degree of symmetry. The configuration includes a platform and a rotor. Both components contain arbitrarily located internal spherical dampers. The symmetry of the system configuration makes it possible to illustrate clearly the relationship between Routhian analysis, energy sink analysis, and digital simulation of the full nonlinear equations. Although the dual-spin spacecraft configuration contains energy dissipating devices on both platform and rotor, it is still possible to employ the rigorous, but relatively simple, Routh stability method. This method, unlike Floquet theory, has the potential of producing closed-form stability criteria. The energy sink method is capable of providing a closed-form stability criterion. Numerical simulation is a necessary requirement in the latter stages of design when the realistic perturbation environment must be considered.

Laskin, R. A.↗
NASA NTRS1958

Low-speed stability and control and spinning characteristics of dynamic models of the X-15 airplane

Paper summarizes the results of low-speed dynamic-model studies of the X-15 aircraft. The investigation included flight tests of a 1/7-scale model in the Langley full-scale tunnel and also in free-gliding flight using a recently developed radio-control technique. In order to interpret and evaluate some of the flight test results, static and dynamic force tests were conducted to determine the low-speed stability and control parameters for angles of attack from 0 degree to as high as 90 degrees. Preliminary tests also have been made in the Langley 20-foot free-spinning tunnel to determine the developed spin and recovery characteristics. Inasmuch as the lower rudder will be jettisoned sometime during the subsonic glide, the investigation has included tests with the lower rudder both on and off.

Hewes, Donald E↗
NASA NTRS1959

Investigation of the Stability of Very Flat Spins and Analysis of Effects of Applying various Moments Utilizing the Three Moment Equations of Motion

Based on linearized equations of motion utilizing only the three moment equations and assuming only flat-spin conditions, it appears that contemporary designs (with the moment of inertia about the wing axis I(sub Y) considerably greater than the moment of inertia about the fuselage axis I(sub X) having positive values of C(sub l, sub p) (rolling-moment coefficient due to rolling) or positive values of C(sub l, sub beta) (rolling-moment coefficient due to sideslip) will probably not have a stable spin in the flat-spin region near an angle of attack of 90 deg. If the damping in pitch in flat-spin attitudes is zero, stable flat-spin conditions may not be possible on an airplane having the mass primarily distributed along the wings. The effect of moving ailerons with the spin or the effect of applying a positive pitching moment producing recovery for contemporary fighter designs will be greatest for large negative values of C(sub n, sub beta) (yawing-moment coefficient due to sideslip). In addition, for a certain critical value of positive C(sub n, sub beta), the rolling moment applied by moving ailerons with the spin or the application of a positive pitching moment will have no effect on reducing the spin rate.

Klinar, Walter J.↗
NASA NTRS1972

Stability and CMG wobble damping of flexible, spinning space stations.

Consideration of the uncontrolled vehicle stability and control moment gyro (CMG) wobble damping of two typical modular-spinning-space-station configurations. General stability trends are established as a function of structural parameters. Results of investigations using a unique CMG wobble damping concept are presented, and requirements are formulated. Modifications to the basic control law required as a result of structural flexibility are described. The majority of the analyses were performed with the aid of a digital simulation of the flexible body dynamics. The description of the vehicles, the flexible body simulation, and the CMG wobble damping concept are presented. Previously established theory is supported insofar as the stabilization and control problems associated with a minimum inertia type spinning spacecraft are shown to be significantly greater than those of a maximum inertia vehicle. For example, the maximum inertia configuration investigated is stable for all structural flexibility conditions studied, while the stability of the minimum inertia configuration is dependent upon the distribution of energy dissipating material throughout the structure.

Berman, H.↗
NASA NTRS1998

Liquid Motion in a Rotating Tank Experiment (LME)

The Liquid Motion Experiment (LME), which flew on STS 84 in May 1997, was an investigation of liquid motions in spinning, nutating tanks. LME was designed to quantify the effects of such liquid motions on the stability of spinning spacecraft, which are known to be adversely affected by the energy dissipated by the liquid motions. The LME hardware was essentially a spin table which could be forced to nutate at specified frequencies at a constant cone angle, independently of the spin rate. Cylindrical and spherical test tanks, partially filled with liquids of different viscosities, were located at the periphery of the spin table to simulate a spacecraft with off-axis propellant tanks; one set of tanks contained generic propellant management devices (PMDs). The primary quantitative data from the flight tests were the liquid-induced torques exerted on the tanks about radial and tangential axes through the center of the tank. Visual recordings of the liquid oscillations also provided qualitative information. The flight program incorporated two types of tests: sine sweep tests, in which the spin rate was held constant and the nutation frequency varied over a wide range; and sine dwell test, in which both the spin rate and the nutation frequency were held constant. The sine sweep tests were meant to investigate all the prominent liquid resonant oscillations and the damping of the resonances, and the sine dwell tests were meant to quantify the viscous energy dissipation rate of the liquid oscillations for steady state conditions. The LME flight data were compared to analytical results obtained from two companion IR&D programs at Southwest Research Institute. The comparisons indicated that the models predicted the observed liquid resonances, damping, and energy dissipation rates for many test conditions but not for all. It was concluded that improved models and CFD simulations are needed to resolve the differences. This work is ongoing under a current IR&D program.

Deffenbaugh, D. M.↗
NASA NTRS1980

Aircraft equilibrium spin characteristics

Program provides analytic solutions to nonlinear equations of motion describing spin conditions. Stability characteristics also are determined. Program can be used to study effects of aerodynamic and inertial parameters on spin and could be modified to compute equilibrium conditions for steady maneuvers. Program is written in FORTRAN IV for batch execution on CYBER 173.

Adams, W. M., Jr.↗
NASA NTRS2005

CORRELATED ERRORS IN EARTH POINTING MISSIONS

Two different Earth-pointing missions dealing with attitude control and dynamics changes illustrate concerns with correlated error sources and coupled effects that can occur. On the OrbView-2 (OV-2) spacecraft, the assumption of a nearly-inertially-fixed momentum axis was called into question when a residual dipole bias apparently changed magnitude. The possibility that alignment adjustments and/or sensor calibration errors may compensate for actual motions of the spacecraft is discussed, and uncertainties in the dynamics are considered. Particular consideration is given to basic orbit frequency and twice orbit frequency effects and their high correlation over the short science observation data span. On the Tropical Rainfall Measuring Mission (TRMM) spacecraft, the switch to a contingency Kalman filter control mode created changes in the pointing error patterns. Results from independent checks on the TRMM attitude using science instrument data are reported, and bias shifts and error correlations are discussed. Various orbit frequency effects are common with the flight geometry for Earth pointing instruments. In both dual-spin momentum stabilized spacecraft (like OV-2) and three axis stabilized spacecraft with gyros (like TRMM under Kalman filter control), changes in the initial attitude state propagate into orbit frequency variations in attitude and some sensor measurements. At the same time, orbit frequency measurement effects can arise from dynamics assumptions, environment variations, attitude sensor calibrations, or ephemeris errors. Also, constant environment torques for dual spin spacecraft have similar effects to gyro biases on three axis stabilized spacecraft, effectively shifting the one-revolution-per-orbit (1-RPO) body rotation axis. Highly correlated effects can create a risk for estimation errors particularly when a mission switches an operating mode or changes its normal flight environment. Some error effects will not be obvious from attitude sensor measurement residuals, so some independent checks using imaging sensors are essential and derived science instrument attitude measurements can prove quite valuable in assessing the attitude accuracy.

Steve Bilanow↗
NASA NTRS1980

Configuration effects on satellite charging response

The paper presents a computer study of the response of various spacecraft configurations to a charging environment in sunlight using the NASCAP code. Configuration features considered include geometry, type of stabilization, and overall size. The most striking configuration effect observed is that type of stabilization. A spinning spacecraft is expected to exhibit slower charging of its structure but to develop larger electric field stresses across shaded insulation than is an identical spacecraft which is three-axis stabilized. Data from the ATS-5 and ATS-6 spacecraft are presented and discussed.

Purvis, C. K.↗
NASA NTRS1984

Effects of the motions of a platform-mounted payload on the nutational stability of a dual-spin spacecraft - A Galileo case study

In the presence of spacecraft nutation, tracking of an inertially fixed target by the Galileo scan platform requires the use of two control loops to move the scan platform and the stator in such a way as to compensate for spacecraft motion. The effect of these control loops on spacecraft nutational stability is examined using an eigenvalue analysis approach as well as several computer analysis packages. It was found that the actions of these control loops tend to drive nutation to the point of neutralizing, and even overpowering the damping actions of the spacecraft nutation damper, for pointing directions close to the spacecraft's poles. Stable and unstable zones are mapped out for two sets of spacecraft mass properties, and contributions of rotor asymmetry and stator flexibility are also discussed.

Man, G. K.↗
NASA NTRS1971

Nutational stability of a dual-spin satellite under the influence of applied reaction torques

It is assumed that since the solar paddle attachments to the hub of the spacecraft are not rigidly locked, the effect of the solar panels can be replaced by a constant reaction torque acting on the hub of the spacecraft. This could result in the satellite having an equilibrium motion about an axis displaced from the nominal axis of symmetry. The variational equations of motion are developed about such an equilibrium position using the SAS-A spacecraft as a model. Energy dissipation on the rotor as well as the main body is included. This nonautonomous set of differential equations are linearized and transformed to an autonomous set using the Liapunov reducibility theorem. The stability of the kinematically similar system is examined numerically using representative SAS-A parameters for the case when either pair of solar panels is assumed to be loosely attached. Stability is verified for small system nutation angles (0.1 degree).

Bainum, P. M.↗