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At least 469 records · Page 26

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NASA NTRS1995

A open loop guidance architecture for navigationally robust on-orbit docking

The development of an open-hop guidance architecture is outlined for autonomous rendezvous and docking (AR&D) missions to determine whether the Global Positioning System (GPS) can be used in place of optical sensors for relative initial position determination of the chase vehicle. Feasible command trajectories for one, two, and three impulse AR&D maneuvers are determined using constrained trajectory optimization. Early AR&D command trajectory results suggest that docking accuracies are most sensitive to vertical position errors at the initial conduction of the chase vehicle. Thus, a feasible command trajectory is based on maximizing the size of the locus of initial vertical positions for which a fixed sequence of impulses will translate the chase vehicle into the target while satisfying docking accuracy requirements. Documented accuracies are used to determine whether relative GPS can achieve the vertical position error requirements of the impulsive command trajectories. Preliminary development of a thruster management system for the Cargo Transfer Vehicle (CTV) based on optimal throttle settings is presented to complete the guidance architecture. Results show that a guidance architecture based on a two impulse maneuvers generated the best performance in terms of initial position error and total velocity change for the chase vehicle.

Chern, Hung-Sheng↗

NASA NTRS1989

Photospheres of hot stars. III - Luminosity effects at spectral type 09.5

Hydrogen and helium line profiles with high signal-to-noise ratios were obtained for four stars of spectral type 09.5 (Alpha Cam, Xi Ori A, Delta Ori A,AE Aur) that form a sequence in luminosity: Ia, Ib, II, V. The basic stellar parameters of these stars are determined by fitting the observed line profiles of weak photospheric absorption lines with profiles from models which include the effect of radiation scattered back onto the photosphere from their stellar winds, an effect referred to as wind blanketing. For these stars, the inclusion of wind blanketing is significant only for the most luminous star, Alpha Cam, for which the effective temperature was shifted about -2000 K relative to an unblanketed model.

Voels, Stephen A.↗

NASA NTRS2004

What Information Theory Says About Best Response and About Binding Contracts

Product Distribution (PD) theory is the information-theoretic extension of conventional full- rationality game theory to bounded rational games. Here PD theory is used to investigate games in which the players use bounded rational best-response strategies. This investigation illuminates how to determine the optimal organization chart for a corporation, or more generally how to order the sequence of moves of the players / employees so as to optimize an overall objective function. It is then shown that in the continuum-time limit, bounded rational best response games result in a variant of the replicator dynamics of evolutionary game theory. This variant is then investigated for team games, in which the players share the same utility function, by showing that such continuum- limit bounded rational best response is identical to Newton-Raphson iterative optimization of the shared utility function. Next PD theory is used to investigate changing the coordinate system of the game, i.e., changing the mapping from the joint move of the players to the arguments in the utility functions. Such a change couples those arguments, essentially by making each players move be an offered binding contract.

Wolpert, David H.↗

NASA NTRS2007

Development of a Human Behavior and Performance Training Curriculum for ISS Astronauts

The paper will describe the DACUM process and summarize the core competencies that were agreed upon, internationally, as important for ISS astronauts. The paper will further discuss the ongoing work being completed by the subgroup, Human Behaviour and Performance Training Working Group, including defining the competencies and behavioural markers. Finally, an overview of remaining work will be provided, including determining which competencies require formal training and which require no formal training, developing training objectives, sequencing the training, and establishing how to assess training effectiveness. DISCUSSION: Designing a common set of goals for behavioural training has been the desire of the SHBP WG since its inception in 1998. This group, along with training specialists and astronauts, are making great strides toward defining these competencies. The road ahead will be exceedingly challenging as training objectives are defined and a training flow is proposed to the MCOP; with proposed ISS crews increasing to six people in the near future, such enhanced behavioural training may be all the more essential for mission success.

VanderArk, Steve↗

NASA NTRSDate not supplied

The Initial Orbit Determination (IOD) Problem With Range, Range-Rate and Angles

The Initial Orbit Determination (IOD) problem has been tacked since Laplace, Euler and Gauss in the service of determining the orbits of planets, asteroids, and comets. The measurements that established the orbit characteristics were angles over long arcs.1 The Space Age brought two new measurement types to bear: range and range-rate.2, 3 Initially these measurements were provided by radars through skin-tracking. Soon, however, transponders allowed better measurement accuracy and availability. To date, there are three types of IOD problems: angles only, range and angles, and range and range-rate. The Orion program exposed the need for an additional capability in the case of an extended loss of communication: when the measurements included antenna angles (azimuth and elevation or right-ascension and declination), range and range-rate. This paper contains the details of this new methodology. We will begin with state determination with range, range-rate and angle measurements. First the state estimate, given a sequence of these four time-synchronized measurements, will be analytically developed. Next the covariance matrix associated with this state estimate will be analytically developed. Finally, these will be verified by Monte Carlo simulations.

Christopher D’Souza↗

NASA NTRS1988

The ribosomal gene spacer region in archaebacteria

Sequences for the spacer regions that separate the 16S and 23S ribosomal RNA genes have been determined for four more (strategically placed) archaebacteria. These confirm the general rule that methanogens and extreme halophiles have spacers that contain a single tRNAala gene, while tRNA genes are not found in the spacer region of the true extreme thermophiles. The present study also shows that the spacer regions from the sulfate reducing Archaeglobus and the extreme thermophile Thermococcus (both of which cluster phylogenetically with the methanogens and extreme halophiles) contain each a tRNAala gene. Thus, not only all methanogens and extreme halophiles show this characteristic, but all organisms on the "methanogen branch" of the archaebacterial tree appear to do so. The finding of a tRNA gene in the spacer region of the extreme thermophile Thermococcus celer is the first known phenotypic property that links this organism with its phylogenetic counterparts, the methanogens, rather than with its phenotypic counterparts, the sulfur-dependent extreme thermophiles.

Non-NASA Center↗

NASA NTRS2001

Analysis of the myosins encoded in the recently completed Arabidopsis thaliana genome sequence

BACKGROUND: Three types of molecular motors play an important role in the organization, dynamics and transport processes associated with the cytoskeleton. The myosin family of molecular motors move cargo on actin filaments, whereas kinesin and dynein motors move cargo along microtubules. These motors have been highly characterized in non-plant systems and information is becoming available about plant motors. The actin cytoskeleton in plants has been shown to be involved in processes such as transportation, signaling, cell division, cytoplasmic streaming and morphogenesis. The role of myosin in these processes has been established in a few cases but many questions remain to be answered about the number, types and roles of myosins in plants. RESULTS: Using the motor domain of an Arabidopsis myosin we identified 17 myosin sequences in the Arabidopsis genome. Phylogenetic analysis of the Arabidopsis myosins with non-plant and plant myosins revealed that all the Arabidopsis myosins and other plant myosins fall into two groups - class VIII and class XI. These groups contain exclusively plant or algal myosins with no animal or fungal myosins. Exon/intron data suggest that the myosins are highly conserved and that some may be a result of gene duplication. CONCLUSIONS: Plant myosins are unlike myosins from any other organisms except algae. As a percentage of the total gene number, the number of myosins is small overall in Arabidopsis compared with the other sequenced eukaryotic genomes. There are, however, a large number of class XI myosins. The function of each myosin has yet to be determined.

NASA Discipline Plant Biology↗

NASA NTRS1976

Wavelengths and levels of the Na I isoelectronic sequence from K IX through Mn XV

The seven spectra K IX through Mn XV have been analyzed and the series limits determined. We present the adopted wavelengths and the derived energy levels and term splittings. The highly ionized atoms were produced in a spark source and recorded mainly on a 3 m grazing incidence spectrograph. Many new lines have been identified and many previously given wavelengths have been revised. All wavelengths have been examined for consistency by least-squares-fitting procedures and other tests. These procedures indicated misidentified lines and incorrect wavelengths which we corrected when possible. A discussion of the errors is given.

Cohen, L.↗

NASA NTRS1993

Progressive matrix cracking in off-axis plies of a general symmetric laminate

A generalized shear-lag model is derived to determine the average through-the-thickness stress state present in a layer undergoing transverse matrix cracking, by extending the method of Lee and Daniels (1991) to a general symmetric multilayered system. The model is capable of considering cracking in layers of arbitrary orientation, states of general in-plane applied loading, and laminates with a general symmetric stacking sequence. The model is included in a computer program designed for probabilistic laminate analysis, and the results are compared to those determined with the ply drop-off technique.

Thomas, David J.↗

NASA NTRS1971

Quantitative results of stellar evolution and pulsation theories.

The discrepancy between the masses of Cepheid variables deduced from evolution theory and pulsation theory is examined. The effect of input physics on evolutionary tracks is first discussed; in particular, changes in the opacity are considered. The sensitivity of pulsation masses to opacity changes and to the ascribed values of luminosity and effective temperature are then analyzed. The Cepheid mass discrepancy is discussed in the light of the results already obtained. Other astronomical evidence, including the mass-luminosity relation for main sequence stars, the solar neutrino flux, and cluster ages are also considered in an attempt to determine the most likely source of error in the event that substantial mass loss has not occurred.

Fricke, K.↗

NASA NTRS1973

Rotations about nonorthogonal axes.

Given a desired three-axis reorientation, it is well known that there are, in general, twelve possible sequences of three successive rotations about orthogonal axes which will perform the reorientation. The present paper determines whether the maneuver can or cannot be accomplished with three successive rotations aobut arbitrary (not necessarily orthogonal) axes. This result is then employed to derive conditions on the axes which insure that every rotation may be so generated. The associated angles of all the possible three-legged slews are exhibited by a closed analytical procedure which requires no assumptions concerning the degree of nonorthogonality nor any approximations. The classical orthogonal case (Euler angles) is then an immediate consequence as a special case of the generalized solution.

Davenport, P. B.↗

NASA NTRS1973

Eigenproblem solution by a combined Sturm sequence and inverse iteration technique.

Description of an efficient and numerically stable algorithm, along with a complete listing of the associated computer program, developed for the accurate computation of specified roots and associated vectors of the eigenvalue problem Aq = lambda Bq with band symmetric A and B, B being also positive-definite. The desired roots are first isolated by the Sturm sequence procedure; then a special variant of the inverse iteration technique is applied for the individual determination of each root along with its vector. The algorithm fully exploits the banded form of relevant matrices, and the associated program written in FORTRAN V for the JPL UNIVAC 1108 computer proves to be most significantly economical in comparison to similar existing procedures. The program may be conveniently utilized for the efficient solution of practical engineering problems, involving free vibration and buckling analysis of structures. Results of such analyses are presented for representative structures.

Gupta, K. K.↗

NASA NTRS1974

Role of man in flight experiment payloads, phase 1

The identification of required data for studies of Spacelab experiment functional allocation, the development of an approach to collecting these data from the payload community, and the specification of analytical methods necessary to quantitatively determine the role of man in specific Spacelab experiments are presented. A generalized Spacelab experiment operation sequence was developed, and the parameters necessary to describe each signle function in the sequence were identified. A set of functional descriptor worksheets were also drawn up. The methodological approach to defining the role of man was defined as a series of trade studies using a digial simulation technique. The tradeoff variables identified include scientific crew size, skill mix, and location. An existing digital simulation program suitable for the required analyses was identified and obtained.

Malone, T. B.↗

NASA NTRS1985

Design of suboptimal regulators for nonlinear systems

An optimal feedback control law is preferred for the regulation of a deterministic nonlinear system. In this paper, a practical, iterative design method leading to a sequence of suboptimal control laws with successively improved performance is presented. The design method requires the determination of an upper bound to the performance of each successive control law. This is obtained by solving a partial differential inequality by means of a linear programming technique. Robustness properties and the application of the design method to the control of a robot manipulator arm are also presented.

Balaram, J.↗

NASA NTRS1986

Application of TIMS data in stratigraphic analysis

An in-progress study demonstrates the utility of Thermal Infrared Multispectral Scanner (TIMS) data for unraveling the stratigraphic sequence of a western interior, North American foreland basin. The TIMS data can be used to determine the stratigraphic distribution of minerals that are diagnostic of specific depositional distribution. The thematic mapper (TM) and TIMS data were acquired in the Wind River/Bighorn area of central Wyoming in November 1982, and July 1983, respectively. Combined image processing, photogeologic, and spectral analysis methods were used to: map strata; construct stratigraphic columns; correlate data; and identify mineralogical facies.

Lang, H. R.↗

NASA NTRS1986

Development of the Spartan 101 navigation and pointing timeline

This paper presents the techniques and analyses that were used to construct the Spartan 101 mission pointing timeline for the Space Shuttle Orbiter-detached portion of its flight. This covers the design process that had to transform requirements and constraints originating from the experimenter, the Space Transportation System, and the payload hardware design into a workable set of pointing instructions sequenced to mission events. The paper will discuss the technical approach used for initial attitude acquisition, determining target visibility, observation scheduling, and calculation of vehicle maneuvers.

Lambros, S. D.↗

NASA NTRS1990

Preliminary Subsystem Designs for the Assured Crew Return Vehicle (ACRV), volumes 1-3

A long term manned facility in space must include provisions for the safety of the crew. The resolution of this need was the design of an Assured Crew Return Vehicle (ACRV). The main focus is on the braking and landing system of the ACRV. This subsystem of the ACRV was divided into three phases. The Phase 1 analysis showed that the use of a tether to aid in the reentry of the ACRV was infeasible due to cost and efficiency. Therefore, a standard rocket would be used for reentry. It was also found that the continental United States was an achievable landing site for the ACRV. The Phase 2 analysis determined the L/D of the vehicle to be 1.8, thus requiring the use of a lifting body for reentry. It was also determined that shuttle tiles would be used for the thermal protection system. In addition, a parachute sequence for further deceleration was included, namely a ringslot drogue chute, a pilot chute, and finally a ringsail main parachute. This sequence was found to be capable of slowing the vehicle to a descent velocity of 9 to 10 m/s, which is the required velocity for aerial recovery. The Phase 3 analysis proved that a Sikorsky CH-53E helicopter is capable of retrieving the ACRV at 5.5 km altitude with minimal g-forces induced on the ACRV and minimal induced moments on the helicopter upon hookup. The helicopter would be modified such that it could stabilize the ACRV close to the bottom of helicopter and carry it to the nearest designated trauma center.

Source record↗

NASA NTRS1990

Image based range determination

Flight vehicles operating at low altitudes such as rotorcraft require range determination schemes for locating the terrain and obstacles. The development of a ranging scheme combining image sequences from vehicle mounted passive imaging sensors and the vehicle motion variables obtained from an on-board inertial navigation system is described. This approach can handle sequences from more than one imaging device. Derivation of the numerical algorithm and the performance results using a laboratory image sequence are given. Other applications of the proposed approach include ranging schemes for autonomous planetary rovers and telerobots.

Menon, P. K. A.↗