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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Bennu Shape Model Validation Methods and Results

The OSIRIS-REx Independent Shape Modeling Team, staffed by the Jet Propulsion Laboratory (JPL), has used stereophotoclinometry (SPC) to produce a three-dimensional shape model of Bennu. The SPC process is informed by (but is separate from) orbit determination, so it is important to ensure that the resulting shape model is consistent with all available spacecraft tracking data. Specifically, checking the shape model’s consistency with LIDAR measurements can illuminate any discrepancies, because LIDAR measurements are highly correlated with the shape model. This study focuses on the JPL experience with these LIDAR measurements and the greater context of the shape model validation process.

Lauretta, Dante S.↗
NASA NTRSDate not supplied

On-board Limb-based Shape Modeling for Small Body Navigation

Missions to small bodies within our solar system are becoming more frequent. Generally, shape models of the target body are required to perform proximity operations as demonstrated by the OSIRIS-REx, Hayabusa2, and Rosetta missions. However, these missions required image downlinking to create high-resolution models on the ground. In some missions, especially small-sats, there may be data downlink data constraints, resulting in the inability to provide the large number of images needed for high-resolution shape models. A solution to this is the ability to generate shape models on-board during the approach to the target or initial proximity surveying. Current work implements a limb-based shape model routine that is able to be executed on a Raspberry Pi 1, which is similar to the processing capability to the flight computer on OSIRIS-REx, and that does not require low phase angle geometries. Initial shape model results generated from Bennu approach (Nov 2-3, 2018) show that the limb-based shape model agrees well with a 75-cm SPC shape model generated after Preliminary Survey; Results are: min difference -7.047m, max difference 17.347m, mean 1.122m, and RMS 3.219m. Further scenarios are presented herein.

Limb-based↗
NASA NTRS1994

(abstract) Asteroid 4769 Casalia: Intrepretation of Optical Lightcurves Using a Radar-Derived Shape Model

A 167-parameter, 3-D shape model of Castalia, obtained from inversion of delay-Doppler images, constrained the object's subradar latitude on the date of the observations by defining an annular sky region that contains Castalia's pole. We have used the shape model and nominal Hapke parameters for S asteroids to model Castalia lightcurves obtained at Table Mountain Observatory on August 23-25, 1989, at solar phase angles ranging from 58(deg) to 90(deg). This investigation defines the projected pole's azimuthal orientation around the radar line of sight and therefore yields a least-squares estimate of the orientation of Castalia's north or south pole; there is insufficient geometric leverage to distinguish the rotation sense or to estimate values of Hapke parameters. The model lightcurves match the TMO data surprisingly well, given the modest number of shape parameters in the model and the fact that part of the asteroid was not seen by the radar.

asteroid Castalia shape radar 3-D model optical li↗
NASA NTRS1993

The generation and use of numerical shape models for irregular Solar System objects

We describe a procedure that allows the efficient generation of numerical shape models for irregular Solar System objects, where a numerical model is simply a table of evenly spaced body-centered latitudes and longitudes and their associated radii. This modeling technique uses a combination of data from limbs, terminators, and control points, and produces shape models that have some important advantages over analytical shape models. Accurate numerical shape models make it feasible to study irregular objects with a wide range of standard scientific analysis techniques. These applications include the determination of moments of inertia and surface gravity, the mapping of surface locations and structural orientations, photometric measurement and analysis, the reprojection and mosaicking of digital images, and the generation of albedo maps. The capabilities of our modeling procedure are illustrated through the development of an accurate numerical shape model for Phobos and the production of a global, high-resolution, high-pass-filtered digital image mosaic of this Martian moon. Other irregular objects that have been modeled, or are being modeled, include the asteroid Gaspra and the satellites Deimos, Amalthea, Epimetheus, Janus, Hyperion, and Proteus.

Simonelli, Damon P.↗
NASA NTRS2008

A Faceted Shape Model Approach to Altimetry and Velocimetry for Irregularly Shaped Bodies

Range and velocity sensors based on lidar or radar with multiple beams are often used to measure the altitude and velocity, respectively, of a spacecraft above a targetbody. A difficulty that arises when navigating about small bodies such as asteroids or comets, is that the notion of altitude is largely obscured by the irregular shape of the target surface. This paper develops a method to incorporate the multibeam altimeter and Doppler velocimeter measurements into the on-board spacecraft state estimator by using information from a faceted shape model representation of the target body surface.

state estimation↗
NASA NTRS2020

Osiris-Rex Shape Model Performance During the Navigation Campaign

The Navigation Campaign of the OSIRIS-REx mission began when the first image of Bennu was recorded by the PolyCam high-resolution imager on Au-gust 17, 2018. In the ensuing months, two teams began building shape models based on imagery taken during the Approach and Preliminary survey phases to be used for the transition to landmark navigation in the Orbital A phase. The orbit determination team began analyzing and characterizing the performance and errors associated with each shape model delivery working closely to iterate on the next shape model delivery. By the end of Orbital A, shape models produced by the Altimetry Working Group and JPL exceeded pre-launch performance re-quirements. This paper provides a summary of the analysis performed during operations.

Leonard, Jason M.↗
NASA NTRS2018

Application of Machine-Learning Algorithms for On-Board Asteroid Shape Model Determination

The Application of Machine-learning Algorithms for On-board Asteroid Shape Model Determination project will develop an innovative system for spacecraft navigation to expand the capability of small spacecraft to meet the critical challenges associated with small-body exploration. Such challenges include accurate navigation in a microgravity environment and precision targeting of particular locations on an asteroid surface for sample collection. This on-board system will cut the computational "umbilical" back to Earth-currently necessary for the generation of a global shape model that requires thousands of images with sufficient resolution and adequate variation of incidence and emission angles, processed manually by a team of experts on Earth for several months. Small satellites have limited bandwidth and are unable to downlink the data volume required for this processing, restricting their ability to perform deep-space asteroid exploration.

Machine learning algorithms↗
NASA NTRS2008

Multibeam Altimeter Navigation Update Using Faceted Shape Model

A method of incorporating information, acquired by a multibeam laser or radar altimeter system, pertaining to the distance and direction between the system and a nearby target body, into an estimate of the state of a vehicle upon which the system is mounted, involves the use of a faceted model to represent the shape of the target body. Fundamentally, what one seeks to measure is the distance from the vehicle to the target body.

Bayard, David S.↗
NASA NTRSDate not supplied

A Solar Sail Shape Modeling Approach for Attitude Control Design and Analysis

Solar sails operating in the space environment experience deformations in sail shape that result in relatively large disturbance torques which dictate the required performance of the spacecraft attitude control and momentum management systems. These deformations are driven by thermal loads on the booms (due to uneven solar heating), manufacturing and assembly tolerances, and variations in membrane tension. The Solar Cruiser spacecraft utilizes a four-quadrant sail design with four 30-meter length booms and four triangular sail membranes, creating a square sail structure of >1600 m2. Medium-fidelity mesh models were developed based on a characteristic deformed shape. A series of parametric studies were conducted using this shape paradigm to determine worst-case deformed sail shapes which produce bounding disturbance torques. A large database of shapes was produced, and the forces and moments induced by each individual shape were calculated using a Rios-Reyes reduced order generalized sail model. Two were selected as reference worst-case shapes for the Solar Cruiser mission: one which produced the highest pitch/yaw root-sum-squared (RSS) torque, and one which produced the highest roll torque. The results showed that the worst-case shapes at high solar incidence angles induce significantly higher (2-10x) disturbance torques than an ideal, flat-plate sail. Even with considerable safety margins, assuming an ideal sail is unlikely to sufficiently bound the disturbances, which is critical when designing the attitude control system and sizing actuators. Accurate sail shape modeling methodologies should therefore be employed on future solar sail missions.

Solar Sail↗
NASA NTRSDate not supplied

A Solar Sail Shape Modeling Approach for Attitude Control Design and Analysis

Solar sails operating in the space environment experience deformations in sail shape that result in relatively large disturbance torques which dictate the required performance of the spacecraft attitude control and momentum management systems. These deformations are driven by thermal loads on the booms (due to uneven solar heating), manufacturing and assembly tolerances, and variations in membrane tension. The Solar Cruiser spacecraft utilizes a four-quadrant sail design with four 30-meter length booms and four triangular sail membranes, creating a square sail structure of >1600 m2. Medium-fidelity mesh models were developed based on a characteristic deformed shape. A series of parametric studies were conducted using this shape paradigm to determine worst-case deformed sail shapes which produce bounding disturbance torques. A large database of shapes was produced, and the forces and moments induced by each individual shape were calculated using a Rios-Reyes reduced order generalized sail model [1]. Two were selected as reference worst-case shapes for the Solar Cruiser mission: one which produced the highest pitch/yaw root-sum-squared (RSS) torque, and one which produced the highest roll torque. The results showed that the worst-case shapes at high solar incidence angles induce significantly higher (2-10x) disturbance torques than an ideal, flat-plate sail. Even with considerable safety margins, assuming an ideal sail is unlikely to sufficiently bound the disturbances, which is critical when designing the attitude control system and sizing actuators. Accurate sail shape modeling methodologies should therefore be employed on future solar sail missions. References [1] L. Rios-Reyes and D. J. Scheeres, “Generalized Model for Solar Sails,” Journal of Spacecraft and Rockets, Vol. 42, Jan. 2005, pp. 182–185, 10.2514/1.9054.

Solar Sail↗
NASA NTRS2014

Constraints on Vesta's Interior Structure Using Gravity and Shape Models from the Dawn Mission

We use the shape and gravity field of Vesta determined from observations of the Dawn spacecraft to place constraints on the asteroid's interior structure. We compute a three-layer interior structure model by minimizing the power of the residual gravity anomaly. The densities of the mantle and crust are based on constraints derived from the Howardite-Eucrite-Diogenite (HED) meteorites. Vesta's present-day shape is not in hydrostatic equilibrium. The Rheasilvia and Veneneia impact basins have a large effect on Vesta's shape and are the main source of deviation from hydrostatic shape. Constraining a pre-giant-impact rotation rate and orientation of the spin axis from an ellipsoidal fit to the parts of Vesta unaffected by the giant impacts, and using the theory of figure, we can constrain the shape of the core. Our solution for Vesta's crust-mantle interface reveals a belt of thick crust around Rheasilvia and Veneneia. The thinnest crust is in the floor of the two basins and in the Vestalia Terra region. Our solution does not reveal an uplift of the crust-mantle boundary to the surface in the largest basins. This, together with the lack of olivine detected by the Visible and Infrared Spectrometer (VIR) data in Rheasilvia and Veneneia, indicates that Vesta's presumed olivine mantle was either not brought to the surface by these large impacts or was covered by ejecta from subsequent impacts.

Interiors↗
NASA NTRS2008

Estimating Small-Body Gravity Field from Shape Model and Navigation Data

This paper presents a method to model the external gravity field and to estimate the internal density variation of a small-body. We first discuss the modeling problem, where we assume the polyhedral shape and internal density distribution are given, and model the body interior using finite elements definitions, such as cubes and spheres. The gravitational attractions computed from these approaches are compared with the true uniform-density polyhedral attraction and the level of accuracies are presented. We then discuss the inverse problem where we assume the body shape, radiometric measurements, and a priori density constraints are given, and estimate the internal density variation by estimating the density of each finite element. The result shows that the accuracy of the estimated density variation can be significantly improved depending on the orbit altitude, finite-element resolution, and measurement accuracy.

Covariance Analysis↗
NASA NTRS2022

Controls on Greenland Moulin Geometry and Evolution From the Moulin Shape Model

Nearly all meltwater from glaciers and ice sheets is routed englacially through moulins, which collectively comprise approximately 10–14% of the efficient englacial–subglacial hydrologic system. Therefore, the geometry and evolution of moulins has the potential to influence subglacial water pressure variations, ice motion, and the runoff hydrograph delivered to the ocean. We develop the Moulin Shape (MouSh) model, a time-evolving model of moulin geometry. MouSh models ice deformation around a moulin using both viscous and elastic rheologies and models melting within the moulin through heat dissipation from turbulent water flow, both above and below the water line. We force MouSh with idealized and realistic surface melt inputs. Our results show that variations in surface melt change the geometry of a moulin by approximately 30% daily and by over 100% seasonally. These size variations cause observable differences in moulin water storage capacity, moulin water levels, and subglacial channel size compared to a static, cylindrical moulin. Our results suggest that moulins are significant storage reservoirs for meltwater, with storage capacity and water levels varying over multiple timescales. Representing moulin geometry within subglacial hydrologic models would therefore improve their accuracy, especially over seasonal periods or in regions where overburden pressures are high.

Moulin↗
NASA NTRSDate not supplied

Astrometric Reduction of Phoebe Using a Digital Shape Model

The Cassini Imaging Science Subsystem (ISS) has provided the most spectacular images of the Saturnian system [1] and these observations constitute a fundamental dataset of high accuracy and exceptionally long-time span for the purpose of astrometry [2]. Several elaborate astrometric efforts using Cassini ISS data have demonstrated their use for the development and maintenance of the Saturnian satellite ephemerides and have been critical in improving our understanding of their secular orbital evolution and interior properties[3].Astrometric efforts using images with well-resolved bodies often employ limb-based methods for center finding; this is proven to be robust for satellites with a uniform ellipsoidal shape. However, systematic biases are of concern for bodies that deviate considerably from tri-axial ellipsoids(e.g., moons with irregular shapes and/or extensive features such as craters, ridges, slumps and grooves). To help understand such biases, we used the Goddard Image Analysis and Navigation Tool (GIANT) [4,5]to improve the astrometric reduction of these moons. Here we apply the method to Phoebe (Saturn IX).

V Viswanathan↗