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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

The Moving Group Targets of the Seeds High-Contrast Imaging Survey of Exoplanets and Disks: Results and Observations from the First Three Years

We present results from the first three years of observations of moving group (MG) targets in the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) high-contrast imaging survey of exoplanets and disks using the Subaru telescope. We achieve typical contrasts of (is) approximately10(exp 5) at 1" and (is) approximately 10(exp 6) beyond 2" around 63 proposed members of nearby kinematic MGs. We review each of the kinematic associations to which our targets belong, concluding that five, beta Pictoris ((is) approximately 20 Myr), AB Doradus ((is) approximately 100 Myr), Columba ((is) approximately 30 Myr), Tucana-Horogium ((is) approximately 30 Myr), and TW Hydrae ((is) approximately 10 Myr), are sufficiently well-defined to constrain the ages of individual targets. Somewhat less than half of our targets are high-probability members of one of these MGs. For all of our targets, we combine proposed MG membership with other age indicators where available, including Ca ii HK emission, X-ray activity, and rotation period, to produce a posterior probability distribution of age. SEEDS observations discovered a substellar companion to one of our targets, kappa And, a late B star. We do not detect any other substellar companions, but do find seven new close binary systems, of which one still needs to be confirmed. A detailed analysis of the statistics of this sample, and of the companion mass constraints given our age probability distributions and exoplanet cooling models, will be presented in a forthcoming paper.

SEEDS high-contrast imaging survey of exoplanets↗
NASA NTRS2017

Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag

The ability to re-enter the atmosphere at a desired location is important for spacecraft containing components that may survive re-entry. While impact point targeting has traditionally been initiated through impulsive burns with chemical thrusters on large vehicles such as the Space Shuttle, and the Soyuz and Apollo capsules, many small spacecraft do not host thrusters and require an alternative means of impact point targeting to ensure that falling debris do not cause harm to persons or property. This paper discusses the use of solely aerodynamic drag force to perform this targeting. It is shown that by deploying and retracting a drag device to vary the ballistic coefficient of the spacecraft, any desired longitude and latitude on the ground can be targeted provided that the maneuvering begins early enough and the latitude is less than the inclination of the orbit. An analytical solution based on perturbations from a numerically propagated trajectory is developed to map the initial state and ballistic coefficient profile of a spacecraft to its impact point. This allows the ballistic coefficient profile necessary to reach a given target point to be rapidly calculated, making it feasible to generate the guidance for the decay trajectory onboard the spacecraft. The ability to target an impact point using aerodynamic drag will enhance the capabilities of small spacecraft and will enable larger space vehicles containing thrusters to save fuel by more effectively leveraging the available aerodynamic drag.

propagation↗
NASA NTRS2011

Autonomous rover traverse and precise arm placement on remotely designated targets

Exploring planetary surfaces typically involves traversing challenging and unknown terrain and acquiring insitu measurements at designated locations using arm-mounted instruments. We present field results for a new implementation of an autonomous capability that enables a rover to traverse and precisely place an arm-mounted instrument on remote targets. Using point-and-click mouse commands, a scientist designates targets in the initial imagery acquired from the rover’s mast cameras. The rover then autonomously traverses the rocky terrain for a distance of 10 – 15 m, tracks the target(s) of interest during the traverse, positions itself for approaching the target, and then precisely places an arm-mounted instrument within 2-3 cm from the originally designated target. The rover proceeds to acquire science measurements with the instrument. This work advances what has been previously developed and integrated on the Mars Exploration Rovers by using algorithms that are capable of traversing more rock-dense terrains, enabling tight thread-the-needle maneuvers. We integrated these algorithms on the newly refurbished Athena Mars research rover and fielded them in the JPL Mars Yard. We conducted 43 runs with targets at distances ranging from 5 m to 15 m and achieved a success rate of 93% for placement of the instrument within 2-3 cm.

Volpe, Richard↗
NASA NTRSDate not supplied

Guidance, Navigation, and Control for Laser-Based Non-Cooperative Target Detumbling

Orbital debris is a well known and growing problem presenting risks to the future of spaceflight. Many pieces of debris are defunct satellites or rocket upper stages. These large objects could generate an exponentially growing cloud of debris should they be involved in a collision, i.e., Kessler Syndrome. Future orbital debris remediation efforts often propose perturbing the orbit of these large targets to mitigate risk. These plans often involve non-cooperative rendezvous. In the absence of active control, the targets are expected to be tumbling which makes rendezvous a dangerous prospect. In this work we describe a guidance, navigation, and control system for a contactless non-cooperative target detumbling methodology which will significantly increase the safety of non-cooperative rendezvous. An onboard laser generates thrust on the target by ablating its surface material. This thrust is used to control target attitude. Our guidance, navigation, and control system is able to estimate relative pose, target the laser, and maintain formation flight during the detumbling process. The system is validated with Monte Carlo simulation in a variety of scenarios.

Guidance↗
NASA NTRSDate not supplied

Optimal Sensor Mobility Design for Target Tracking with Distributed Sensing, Communication and Computing Infrastructure

The paper presents an airborne target tracking approach with data fusion from distributed stationary and mobile sensor network transmitted through a wireless/wired communication network and using a distributed computing infrastructure. To obtain high quality measurements, sensor flight platforms' positions and orientations are optimized with respect to the available target's position and velocity estimates, and a formation control strategy is applied to derive desired trajectories for the flight platforms. As sensors move, the communication network topology switching is determined using the worst-case approach to handle uncertainties in the target's and sensors' positions, which alters communication delays for sensors' data transmission to computing centers. An optimal data migration algorithm is periodically applied to determine these communication delays for each sensor and the optimal location with minimum end-to-end latency for the target tracking algorithm execution, which is based on adaptive information fusion from multi-modal mobile and stationary sensors inside an Extended Kalman Filter framework. The approach is validated in a desktop simulation environment using synthetic sensor data generated for a simulated target's flight.

Distributed sensing↗
NASA NTRSDate not supplied

Generalized Linear Targeting For Cislunar Flight

An important element of Artemis and NASA’s campaign to explore the Moon is the autonomous onboard two-level targeter (TLT) used during all cislunar flight phases. The function of the TLT is to autonomously recompute the burn targets for the upcoming burn (or multiple burns) in response to navigation and vehicle dispersion providing a solution that meets all of the trajectory constraints. Although the TLT has been utilized previously as a ground-based planning tool, and flown onboard during the Artemis I mission, it’s complexity and iterative nature make is difficult to incorporate into and support rapid analyses such as robust optimal trajectory design applications where speed is essential. In this paper, a set of generalized linear targeting algorithms that mimics many of the properties of the TLT is derived. The generalized algorithms can handle single or multiple impulsive maneuvers, with multiple constraints at multiple fixed or variable times. A linear targeting algorithm for finite burn maneuvers is also derived. The generalized linear targeting algorithms are exceptionally fast and easy to implement in Monte Carlo analysis, linear covariance (LinCov) analysis, and robust optimal trajectory design. Several cislunar flight examples are provided.

Linear Covariance Analysis↗
NASA NTRS1968

Penetration of electrons and associated bremsstrahlung through aluminum targets

This paper contains a brief description of Monte Carlo programs designed to calculate the transport of fast electrons and associated bremsstrahlung through extended media. Two applications are discussed: (1) transmission of electrons through plane-parallel targets, and (2) emergence of secondary bremsstrahlung from such targets. It is shown that the predicted results are in reasonably good agreement with recent experiments for electron beams with energies up to 8 MeV incident normally on aluminum targets. Extensive new calculated data for transmission and thick-target bremsstrahlung production are presented for aluminum targets exposed to an isotropic electron flux.

M. J. Berger↗
NASA NTRS1972

Apollo experience report: Development of guidance targeting techniques for the command module and launch vehicle

The development of the guidance targeting techniques for the Apollo command module and launch vehicle is discussed for four types of maneuvers: (1) translunar injection, (2) translunar midcourse, (3) lunar orbit insertion, and (4) return to earth. The development of real-time targeting programs for these maneuvers and the targeting procedures represented are discussed. The material is intended to convey historically the development of the targeting techniques required to meet the defined target objectives and to illustrate the solutions to problems encountered during that development.

Yencharis, J. D.↗
NASA NTRS1973

Launch window definition for sky target experiments.

This paper is a brief report on the computer program developed for the Extraterrestrial Physics Barium Ion Cloud (BIC) Project. The mathematical analysis developed for the program along with its programing characteristics are pointed out to show that this program is adaptable to similar sky target projects. Definite viewing constraints are specified so that the chosen ground tracking stations can photograph the behavior of the sky target after its release. Viewing factors include the illumination of the target by the sun, the relative elevation look angle to the target from each tracking station, the solar and lunar depression angles at each tracking station, and the total sky background brightness of the target relative to each tracking station. Numeric values are assigned to each factor through program input. The program output is flexible so that the results of the window calculations can be studied to the depth required.

Michaud, N. H.↗
NASA NTRS1978

Simulator method and apparatus for practicing the mating of an observer-controlled object with a target

A servo controlled target replica, and a surface bearing a computer generated line drawing of an object are individually viewed by separate television cameras allowing a two-dimensional composite of the target replica and the object to be displayed on a monitor simulating what an observer would see through a window in a spacecraft. The target replica is coded along one self coordinate axis in such a way that the distance of an elemental area on the target along the axis is capable of being remotely readout by a television camera. A third television camera responsive to the code reads out this information by which the Z-coordinate, relative to the observer, can be calculated, on-line with the scan, for the contents of each picture element of the scene televised by the target camera.

Polstorff, W. K.↗
NASA NTRS1984

Probability of error and radiometric resolution for target discrimination in radar images

A straightforward statistical analysis is presented of the problem of discriminating between two distributed targets in a radar image. The probability of making an error is calculated as a function of the target contrast, the number of samples averaged to form each observation, and the system noise. In the absence of system noise, it is observed that a target contrast of 1 dB could not be detected with less than 10 samples averaged; it is also seen that the error probability is sensitive to the number of samples averaged, as expected. Setting the target contrast at the radiometric resolution, a comparison is made of different definitions for this resolution. The comparison shows that each definition yields a different error probability, ranging from less than 0.05 to 0.35. Attention is also given to the effect of system noise, and it is shown that thermal noise does not have a significant effect on the error probability for a fixed target contrast.

Frost, V. S.↗
NASA NTRS1985

Self-Identifying Reflecting Targets

Proposed scheme for target identification requires no radiation of energy by target itself. Instead, target alters light beam reflected from itself back to interrogating station in unique way. Interrogator then identifies target from its signature impressed on returned beam. Selfidentifying target useful in surveying, navigation, and remote monitoring (for example, of mountain-climbing parties.)

Frazer, R. E.↗
NASA NTRS1985

Polyvinyl alcohol coating of polystyrene inertial confinement fusion targets

An inertial confinement fusion (ICF) target made of polystyrene is first levitated in an acoustic field. The surface of the target is then etched using an appropriate solution (e.g., cyclohexane) to enhance the wetting characteristics. A specially prepared polyvinyl alcohol solution is atomized using an acoustic atomizer and deposited on the surface of the target. The solution is air dried to form a thin coating (2 microns) on the target (outside diameter of about 350-850 microns). Thicker coatings are obtained by repeated applications of the coating solutions. Preliminary results indicate that uniform coatings may be achievable on the targets with a background surface smoothness in the order of 1000 A.

Annamalai, P.↗
NASA NTRS1988

Deep space target location with Hubble Space Telescope (HST) and Hipparcos data

Interplanetary spacecraft navigation requires accurate a priori knowledge of target positions. A concept is presented for attaining improved target ephemeris accuracy using two future Earth-orbiting optical observatories, the European Space Agency (ESA) Hipparcos observatory and the Nasa Hubble Space Telescope (HST). Assuming nominal observatory performance, the Hipparcos data reduction will provide an accurate global star catalog, and HST will provide a capability for accurate angular measurements of stars and solar system bodies. The target location concept employs HST to observe solar system bodies relative to Hipparcos catalog stars and to determine the orientation (frame tie) of these stars to compact extragalactic radio sources. The target location process is described, the major error sources discussed, the potential target ephemeris error predicted, and mission applications identified. Preliminary results indicate that ephemeris accuracy comparable to the errors in individual Hipparcos catalog stars may be possible with a more extensive HST observing program. Possible future ground and spacebased replacements for Hipparcos and HST astrometric capabilities are also discussed.

Null, George W.↗
NASA NTRS1987

Step tracking shrinking targets

Four models describing how people might acquire targets that dynamically vary in size were examined; two that described movement speed as a simple function of target size (either initial or final) and two that described movement speed as a function of the predicted size of the targets at a fixed time in the future (one was referenced to the beginning of the reaction time phase, and the other to the end of this phase). It was found that movement time was best described as a function of a size prediction made at the end, rather than the start, of the reaction time phase. Subjective workload ratings primarily reflected the total amount of time needed to acquire the targets rather than the time pressure imposed by the diminishing size of these targets.

Johnson, Walter W.↗
NASA NTRS1989

Robotic Target-Tracking Subsystem

Position and orientation of target measured in six degrees of freedom. Robotic vision subsystem measures relative position and orientation of specially designed target. Uses standard image-processing algorithms implemented directly in circuitry instead of computer programs. This feature makes it possible to extract complete sets of target-tracking data from successive image frames at rate of 30 frames per second. Five bright circles of target positioned in such way that video images of them processed into data on position and orientation of target relative to camera. Subsystem useful in industrial assembly operation requiring automatic joining of parts initially oriented and moving randomly.

Shawaga, Lawrence M.↗
NASA NTRS1988

Unified approach for two-target game analysis

A two-target differential game is defined from the outset by a qualitative (game-of-kind) formulation. The solution of such a game is the decomposition of the space of admissible initial conditions into zones of different outcomes: two winning zones, one for each player, the zone of nowinning (draw) and (if the intersection of the two target sets is not empty) a zone of eventual mutual winning (mutual kill). In this paper it is shown that the solution of any two-target game can be constructed, based on solving first two single-target pursuit-evasion games of kind (one for each target set) in a systematic way.

Shinar, J.↗
NASA NTRS1989

Reflectance characteristics of reference materials used in lidar hard target calibration

Lidar hard target calibration is discussed, emphasizing the transfer target methodology. Characteristics of example calibratrion target surfaces are described in light of four reflectance mechanisms, specular, diffuse, retroreflection, and off-specular reflectance. The ideal transfer target is one which can be described as entirely diffusely reflecting, i.e., Lambertian. Correction for retroreflection is required when using the flowers of a sulfur transfer target at CO2 laser wavelengths. Corrections for specular and retroreflection for the integrating sphere are negligible; however, the off-specular reflectance of rough metal surfaces used in the integrating spheres is only qualitatively compared with the diffuse reflectance of flowers of sulfur.

Haner, David A.↗