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All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Six-degree-of-freedom program to optimize simulated trajectories (6D POST). Volume 1: Formulation manual

The basic equations and models used in a computer program (6D POST) to optimize simulated trajectories with six degrees of freedom were documented. The 6D POST program was conceived as a direct extension of the program POST, which dealt with point masses, and considers the general motion of a rigid body with six degrees of freedom. It may be used to solve a wide variety of atmospheric flight mechanics and orbital transfer problems for powered or unpowered vehicles operating near a rotating oblate planet. Its principal features are: an easy to use NAMELIST type input procedure, an integrated set of Flight Control System (FCS) modules, and a general-purpose discrete parameter targeting and optimization capability. It was written in FORTRAN 4 for the CDC 6000 series computers.

Brauer, G. L.↗
NASA NTRS1976

Six-beam models in radiative transfer theory

A critical analysis is given of the applicability of six-beam models to radiative transfer in particulate materials. The method of introducing transverse scattering in these models is shown to cause fundamental difficulties in the case of physically plausible phase functions; in particular, the effective absorptivity is abnormally large and thus results in incorrect reflectances and transmittances. Six-beam calculations for several media are compared with accurate solutions, with Chu-Churchill two-beam results, and with a simple modification to the Eddington approximation, the last being generally superior over a wide range of conditions.

Meador, W. E.↗
NASA NTRS1978

Concentration-response data on toxicity of pyrolysis gases from six synthetic polymers

Concentration-response data are presented on the toxic effects of the pyrolysis gases from six synthetic polymers on Swiss Webster male mice, using a toxicity screening test method. The polymers consisted of one sample each of polycarbonate and polystyrene, and two samples each of polyethylene and acrylonitrile-butadiene-styrene (ABS). All six samples were evaluated using the rising temperature program, and three samples were evaluated using the fixed temperature program. The pyrolysis gases from polycarbonate, polyethylene, and ABS appeared to exhibit the concentration-response relationships commonly encountered in toxicology. The polystyrene sample gave variable results; probably due to poor reproducibility of the essentially anaerobic pyrolysis. Carbon monoxide seemed to be the principal toxicant in the pyrolysis gases from polycarbonate and polyethylene, but did not appear to be the principal toxicant in the pyrolysis gases from ABS.

Hilado, C. J.↗
NASA NTRS1979

Six collapses

The self-consistent dynamical development of six stellar systems, started from rotating spherical configurations, has been studied by means of a fully three-dimensional n-body integration. The six examples had different initial angular velocities and velocity dispersions. All settled down into prolate bars rotating about a short axis within two initial rotation periods. The bars are long-lived, robust, and stable. Bars are the natural form toward which rapidly rotating stellar dynamical systems develop, instead of the flattened axisymmetric disks that had been expected. The early stages of each collapse are reasonably well described by a theoretical model according to which a collapse passes through a sequence of rigidly rotating, uniform-density spheroids. The first significant departures from spheroidal form were axisymmetric in all cases. Rings formed in some examples, sheets in others, with transition cases between these extremes. Nonaxisymmetric forms developed from these intermediate stages.

Miller, R. H.↗
NASA NTRS1981

Amino acids of the Murchison meteorite. I - Six carbon acyclic primary alpha-amino alkanoic acids

Six of the seven chain isomers of six-carbon acyclic primary alpha-amino alkanoic acids (leucine isomers) have been either identified or confirmed in hot-water extracts of the Murchison meteorite using combined gas chromatography-mass spectrometry (GC-MS) and ion exchange chromatography. 2-Amino-2-ethylbutyric acid, 2-amino-2,3-dimethylbutyric acid, pseudoleucine, and 2-methylnorvaline were positively identified by GC-MS. These amino acids have not been previously reported to occur in natural materials and may be uniquely meteoritic in origin. The presence of leucine and isoleucine (including the diastereoisomer, alloisoleucine) was confirmed. Peaks corresponding to norleucine were seen by ion-exchange and gas chromatography but characteristic mass spectra were not obtained. The alpha-branched chain isomers in this series are quantitatively the most significant. These results are compared with literature data on amino acid synthesis by electrical discharge and Fischer-Tropsch-type catalysis. Neither model system produces an amino acid suite that is completely comparable to that found in the Murchison meteorite.

Cronin, J. R.↗
NASA NTRS1981

Experimental results with a six-degree-of-freedom force-reflecting hand controller

Control experiments performed using an isotonic joystick connected to a six degree-of-freedom manipulator equipped with a six dimensional force-torque sensor at the base of the manipulator end effector are described. The preliminary control experiments were aimed at the investigation of the human operators' ability to command and control forces in different directions by varying the information conditions and the values of the feedforward and feedback command gains in the bilateral control loop. The main conclusions are: (1) a quantified graphic display of force-torque information can considerably enhance the operator's ability to perform a quantitatively sharp force-torque control, and (2) there seems to be a task dependent optimal combination of the feedforward and feedback command gain values which provide a dynamically smooth and stable bilateral control performance.

Bejczy, A. K.↗
NASA NTRS1982

Modal petrology of six soils from Apollo 16 double drive tube core 64002

Petrographic data form six size fractions for six samples of Apollo 16 drive tube section 64002 show source rocks similar to those of core 60009. Analysis of modal data from the 64002 core show that the upper three and lowest core soils are mature and have similar maturation histories, while the two middle soils are submature and have histories that are similar to each other but unlike those from the aforementioned soils. In all of these soils, mixing has dominated over reworking, and appears to involve two mature soils distinguished by differing source rocks and an immature, plagioclase-rich soil which is correlated with larger clasts of chalky, friable breccia. These breccias and the plagioclase-rich soil are tentatively associated with the Descartes Formation.

Houck, K. J.↗
NASA NTRS1983

The photometric variability of solar-type stars. III - Results from 1981-82, including parallel observations of thirty-six Hyades stars

A photometric survey of main-sequence stars in the Pleiades, Hyades, and Malmquist Field, to investigate variability among solar-type stars, had been continued at Cloudcroft Observatory for a second season. Possibly six of 40 Pleiades stars, two (possibly six) of 49 Hyades stars and possibly four of 42 stars in the Malmquist Field are found to be variable. Parallel observations of Hyades stars were obtained also at Lowell Observatory. These measurements, which achieved better precision, reveal significiant variations in eleven (possibly 16) of 36 Hyades stars, all of spectral type F7 V-K2 V. Agreement between the two surveys is acceptable. The two seasons of the Cloudcroft survey show that changes in the mean annual brightness of the Hyades stars accompany changes in the amplitude of their short-term variability, in the sense that a star tends to become fainter as its variability increases and vice versa. Color effects are absent.

Radick, R. R.↗
NASA NTRS1984

Six Degrees of Freedom Control with Each Hand?

For some time man has made six degree of freedom inputs to a pair of dextrous manipulators using both hands simultaneously by the use of the master/slave concept. The advent of the microprocessor has the potential to make the master/slave concept redundant by replacing the master with a mathematical model. All spacecraft to date, including the space shuttle, that were flown in six degrees of freedom were controlled by using both hands, the left hand controlling translation and the right rotation. Almost inevitably the same principle was applied to the CANADARM. At the instigation of NASA the development of a device whereby both translation and rotation could be combined allowing full control with one hand was developed. The development and testing of the device, and the extension of its application into spaceflight control are described. Also the concept of an adaptable workstation for multi-maniipulator and spacecraft flight control is discussed.

King, M. L.↗
NASA NTRS1983

Comparing attitude control effectiveness for actuators on two bodies of a six body model of a flexible spacecraft with that for actuators restricted to a single body

A ten rigid body model of a prototype flexible space platform was approximated by a six body model to facilitate comparison of attitude control effectiveness for actuators on two bodies with control effectiveness for actuators restricted to a single body of the same model. Actuators and sensors were found to be required on two of the six bodies for effective attitude control.

Chichester, F. D.↗
NASA NTRS1986

Six degree-of-freedom LIVE isolation systems, part 1

A Total Main Rotor Isolation System (TRIS) was analyzed, designed, fabricated, and bench tested for the reduction of main rotor vibration levels transmitted to the helicopter fuselage. The TRIS consists of a six degree-of-freedom passive system using six Liquid Inertia Vibration Eliminator (LIVE) units developed by Bell Helicopter Textron. The objective of the program is to develop a helicopter isolation system that will achieve 90% (or greater) isolation at minimum weight with no degradation in vehicle stability, handling qualities, alignment tolerance, and reliability or maintainability.

Halwes, D. R.↗
NASA NTRS1988

Color-magnitude diagrams for six metal-rich, low-latitude globular clusters

Colors and magnitudes for stars on CCD frames for six metal-rich, low-latitude, previously unstudied globular clusters and one well-studied, metal-rich cluster (47 Tuc) have been derived and color-magnitude diagrams have been constructed. The photometry for stars in 47 Tuc are in good agreement with previous studies, while the V magnitudes of the horizontal-branch stars in the six program clusters do not agree with estimates based on secondary methods. The distances to these clusters are different from prior estimates. Redding values are derived for each program cluster. The horizontal branches of the program clusters all appear to lie entirely redwards of the red edge of the instability strip, as is normal for their metallicities.

Armandroff, Taft E.↗
NASA NTRS1990

Blackbody absorption efficiencies for six lamp pumped Nd laser materials

Utilizing high resolution spectra, the absorption efficiencies for six Nd laser materials were calculated as functions of the effective blackbody temperature of the lamp and laser crystal size. The six materials were Nd:YAG, Nd:YLF, Nd:Q-98 Glass, Nd:YVO4, Nd:BEL, and Nd:Cr:GSGG. Under the guidelines of this study, Nd:Cr:GSGG's absorption efficiency is twice the absorption efficiency of any of the other laser materials.

Cross, Patricia L.↗
NASA NTRS1991

Analysis and design of a six-degree-of-freedom Stewart platform-based robotic wrist

The kinematic analysis and implementation of a six degree of freedom robotic wrist which is mounted to a general open-kinetic chain manipulator to serve as a restbed for studying precision robotic assembly in space is discussed. The wrist design is based on the Stewart Platform mechanism and consists mainly of two platforms and six linear actuators driven by DC motors. Position feedback is achieved by linear displacement transducers mounted along the actuators and force feedback is obtained by a 6 degree of freedom force sensor mounted between the gripper and the payload platform. The robot wrist inverse kinematics which computes the required actuator lengths corresponding to Cartesian variables has a closed-form solution. The forward kinematics is solved iteratively using the Newton-Ralphson method which simultaneously provides a modified Jacobian Matrix which relates length velocities to Cartesian translational velocities and time rates of change of roll-pitch-yaw angles. Results of computer simulation conducted to evaluate the efficiency of the forward kinematics and Modified Jacobian Matrix are discussed.

Nguyen, Charles C.↗
NASA NTRS1991

A new active virtual pivot six-degree-of-freedom hand controller for aerospace applications

During 1989 a new six-degree-of-freedom (6-DOF) active hand controller concept was designed and constructed based on the concept of a virtual pivot. This concept, labeled VPHC, was first demonstrated in a 1985 study and a patent was issued in 1990. Operator control input occurs via a force/torque sensor rigidly mounted to the handgrip. Sensed force/torque signals are used by microprocessors to generate motor drive control for each of six independently controlled motors mounted on the three-legged mechanism. The control microprocessor uses input biasing and rate-feedback motor controllers to generate the sensed feel of virtual springs and deadbands found in more conventional designs. An important advantage of this design is that the location of the virtual pivots, reflective forces and torques, breakout force levels, sensed spring rates, and operating modes, can be changed simply by changing the software. This approach yields an autonomous VPHC that can easily adapt itself to an individual operator (by software extension). A proof-of-concept version has been demonstrated, and further improvements are currently being studied and implemented.

Marshall, William C.↗
NASA NTRS1991

Ar-40/Ar-39 ages of six Apollo 15 impact melt rocks by laser step heating

Fifteen high resolution (21-51 step) Ar-40/Ar-39 age spectra are obtained for six Apollo 15 impact melt rocks of different compositions, using a continuous laser system on submilligram subsamples and on single crystal plagioclase clasts. Four of the six samples gave reproducible age spectra with well-defined intermediate temperature plateaus over 48 percent or more of the Ar-39 released; the plateaus are interpreted as crystallization ages. Samples 15304,7,69, 15294,6,21 and 15314,26,156 gave virtually identical plateau ages whose weighted mean is 3870 + or - 6 Ma. These three melt rocks differ in composition and likely formed in three separate impact events.

Dalrymple, G. B.↗
NASA NTRS1993

Six degrees of freedom vibration isolation using electromagnetic suspension

Experimental data are presented for modeling an electromagnet. Control laws are considered with and without flux feedback and with position and orientation information of the suspended body. Base motion and sensor noise are the principal disturbances. Proper selection of the geometrical operating point minimizes the passive coupling above the bandwidth of the control and filtering can attenuate the high frequency content of sensor noise. Six electromagnets are arranged in a configuration which optimizes the load support and provides control over all six degrees of freedom of the suspended body. The design is based on experimental data generated with a specially designed test facility. Application for suspension of a gravity wave antenna is discussed.

Lee, Sang-Il↗
NASA NTRS1993

A two cable, six link boom crane for lunar construction

This paper presents the conceptual design and analysis of a modified crane boom and cable suspension which provide contro1 over all six degrees of freedom of a payload. Two cables pass around pulleys to form six links between the payload and boom. A linearization of the pulley mechanics was derived to create finite element models of the system. The models were experimentally verified and used to explore variations of the suspension geometry. Several crane concepts which use the suspension are discussed and illustrated.

Taylor, Robert M.↗