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NASA NTRS2016

Determination of Celestial Body Principal Axes via Gravity Field Estimation

The determination of physical parameters of celestial bodies provides critical navigational and scientific information. Determining the mass, rotation state, and density distribution is an important task of the navigation team on an operational mission. One representation of the internal density distribution, spherical harmonics, may be leveraged to compute the orientation of the principal axis frame of the celestial body, which in turn informs the dynamics of the body’s motion. Using data from NASA’s Dawn mission to the massive asteroids (1) Ceres and (4) Vesta, a method is proposed that refines the knowledge of the principal axis frame by utilizing estimated spherical harmonic coefficients. Applying an iterative rotation scheme to the solved-for body-fixed frame leads to convergence on a frame that is very close to the actual dynamical principal axis frame.

Takahashi, Yu↗

NASA NTRS2012

Observing Campaign for Potential Deep Impact Flyby Target 163249 (2002 GT)

The Deep Impact spacecraft is currently on course for a Jan. 4, 2020 flyby of the sub-kilometer near-Earth asteroid 163249 (2002 GT). The re-targeting will be complete with a final small maneuver scheduled for Oct. 4, 2012. 2002 GT, which is also designated as a Potentially Hazardous Asteroid (PHA), has a well-determined orbit and is approx 800 m in diameter (H=18.3). Little more is known about the nature of this object, but in mid-2013 it will pass near the Earth, affording an exceptional opportunity for ground-based characterization. At this apparition 2002 GT will be in range of Arecibo. In addition to Doppler measurements, radar delay observations with precisions of a few microseconds are expected and have a good chance of revealing whether the system is binary or not. The asteroid will be brighter than 16th mag., which will facilitate a host of observations at a variety of wavelengths. Light curve measurements across a wide range of viewing perspectives will reveal the rotation rate and ultimately lead to strong constraints on the shape and pole orientation. Visible and infrared spectra will constrain the mineralogy, taxonomy, albedo and size. Along with the radar observations, optical astrometry will further constrain the orbit, both to facilitate terminal guidance operations and to potentially reveal nongravitational forces acting on the asteroid. Coordinating all of these observations will be a significant task and we encourage interested observers to collaborate in this effort. The 2013 apparition of 2002 GT represents a unique opportunity to characterize a potential flyby target, which will aid interpretation of the high-resolution flyby imagery and aid planning and development of the flyby imaging sequence. The knowledge gained from this flyby will be highly relevant to the human exploration program at NASA, which desires more information on the physical characteristics of sub-kilometer near-Earth asteroids.

Pittichova, Jana↗

NASA NTRS2010

Mineralogy and Thermal Properties of V-Type Asteroid 956 Elisa: Evidence for Diogenitic Material from the Spitzer IRS (5-35 Micrometers) Spectrum

We present the thermal infrared (5-35 micrometer) spectrum of 956 Elisa as measured by the Spitzer Infrared Spectrograph ("IRS"; Houck,1.R. et .11. [20041. Astrophys, 1. SuppL 154, 18-24) together with new ground-based lightcurve data and near-IR spectra. From the visible lightcurve photometry, we determine a rotation period of 16.494 +/- 0.001 h, identify the rotational phase of the Spitzer observations, and estimate the visible absolute magnitude (Hv) at that rotational phase to be 12.58 +/- 0.04. From radiometric analysis of the thermal flux spectrum, we find that at the time of observation 956 Elisa had a projected radius of 5.3 +/- 0.4 km with a visible albedo pv = 0.142+/- 0.022, significantly lower than that of the prototype V-type asteroid, 4 Vesta. (This corresponds to a radius of 5.2 +/- 0.4 km at lightcurve mean.) Analysis with the standard thermal model (STM) results in a sub-solar temperature of 292.3 +/- 2.8 K and beaming parameter eta = 1.16 +/- 0.05. Thermophysical modeling places a lower limit of 20 J m(exp -2)K(exp -1)s(exp -1/2) on the thermal inertia of the asteroid's surface layer (if the surface is very smooth) but more likely values fall between 30 and 150 J m(exp -2)K(exp -1)s(exp -1/2) depending on the sense of rotation. The emissivity spectrum, calculated by dividing the measured thermal flux spectrum by the modeled thermal continuum, exhibits mineralogically interpretable spectral features within the 9-12 micrometer reststrahlen band, the 15-16.5 micrometer Si-O-Si stretching region, and the 16-25 micrometer reststrahlen region that are consistent with pyroxene of diogenitic composition: extant diogenitic pyroxenes fall within the narrow compositional range W0(sub 2+/-1)En(sub 74+/-2)Fs(sub 24+/-1). Spectral deconvolution of the 9-12 micrometer reststrahlen features indicates that up to approximately 20% olivine may also be present, suggesting an olivine-diogenite-like mineralogy. The mid-IR spectrum is inconsistent with non-cumulate eucrite as the major component on the surface of 956 Elisa, although cumulate eucrite material may be present at abundances lower than that of the diogenite component. Analysis of new near-IR spectra of 956 Elisa with the Modified Gaussian Model (MGM; Sunshine, J,M., Pieters, C.M., Pratt, S.F.[1990]. J. Geophys. Res, 95 (May), 6955-6966) results in two pyroxene compositions: 75% magnesian low-Ca pyroxene and 25% high-Ca pyroxene. High-Ca pyroxene is not evident in the mid-IR data, but may belong to a component that is underrepresented in the mid-IR spectrum either because of its spatial distribution on the asteroid or because of its particle size. High-Ca pyroxenes that occur as exsolution lamellae may also be more evident spectrally in the NIR than in the mid-IR. In any case, we find that the mid-IR spectrum of 956 Elisa is dominated by emission from material of diogenite- like composition, which has very rarely been observed among asteroids.

Lim, Lucy F.↗

NASA NTRS1982

Astronomical studies of the major planets, natural satellites and asteroids using the 2.24 m telescope

Ground based detection of east-west asymmetries in the Jovian torus, three dimensional models of the plasma conditions in the Jovian torus, rotational variations in methane band images of Neptune, Io's rapid flickering, thermophysical models, the diameters and albedos of the satellites of Uranus from radiometric observations, the diameters of Pluto and Triton, standard stars are discussed.

Jefferies, J. T.↗

NASA NTRS1976

Physical properties of asteroid 433 Eros

Newly available photometric, polarimetric, spectroscopic, thermal-radiometric, radar, and occultation results are synthesized in order to derive a coherent model for Eros. The geometric albedo is 0.19 plus or minus 0.01 at the visual wavelength, and the overall dimensions are approximately 13 by 15 by 36 km. The rotation is about the short axis, in the direct sense, with a sidereal period of 5 hr 16 min 13.4 sec. The pole of rotation lies within a few degrees of ecliptic coordinates 16 deg longitude and beta = +11 deg latitude. Eros is uniformly coated with a particulate surface layer several millimeters thick. It has an iron-bearing silicate composition, similar to that of a minority of main-belt asteroids, and probably identifiable with H-type ordinary chondrites.

Zellner, B.↗

DOE OSTI2024

Physical properties of asteroid Dimorphos as derived from the DART impact

On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid (65803) Didymos. Numerical simulations of the impact provide a means to find the surface material properties and structures of the target that are consistent with the observed momentum deflection efficiency, ejecta cone geometry and ejected mass. Our simulation that best matches the observations indicates that Dimorphos is weak, with a cohesive strength of less than a few pascals, like asteroids (162173) Ryugu and (101955) Bennu. We find that the bulk density of Dimorphos ρ B is lower than ~2,400 kg m – 3 and that it has a low volume fraction of boulders (≲40 vol%) on the surface and in the shallow subsurface, which are consistent with data measured by the DART experiment. These findings suggest that Dimorphos is a rubble pile that might have formed through rotational mass shedding and reaccumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA’s upcoming Hera mission may find a reshaped asteroid rather than a well-defined crater.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1987

Detection of lambda = 2 cm emission from minor planet 704 Interamnia

Results are presented from a study of the 2 cm natural radio emissions from the class U asteroid 704 Interamnia. The study was performed with the NRAO VLA using 26 antennas in a compact hybrid configuration with baselengths from 0.1-2.2 km. The IF scans were centered at 14.97 GHz and 14.92 GHz. A brightness temperature plot is provided for 2 AU distance, assuming a 338 km diam for the asteroid. The scans revealed a surface dust layer at least 3 cm thick. Comparisons with spectra of 15 Eunomia, another rapidly rotating minor planet with a similar diameter reveals that this second object also has a surface dust layer a few centimeters thick.

Webster, W. J., Jr.↗

NASA NTRS2014

Spacecraft Stabilization and Control for Capture of Non-Cooperative Space Objects

This paper addresses stabilization and control issues in autonomous capture and manipulation of non-cooperative space objects such as asteroids, space debris, and orbital spacecraft in need of servicing. Such objects are characterized by unknown mass-inertia properties, unknown rotational motion, and irregular shapes, which makes it a challenging control problem. The problem is further compounded by the presence of inherent nonlinearities, signi cant elastic modes with low damping, and parameter uncertainties in the spacecraft. Robust dissipativity-based control laws are presented and are shown to provide global asymptotic stability in spite of model uncertainties and nonlinearities. It is shown that robust stabilization can be accomplished via model-independent dissipativity-based controllers using thrusters alone, while stabilization with attitude and position control can be accomplished using thrusters and torque actuators.

Joshi, Suresh↗

NASA NTRS2016

A Collision Avoidance Strategy for a Potential Natural Satellite around the Asteroid Bennu for the OSIRIS-REx Mission

The cadence of proximity operations for the OSIRIS-REx mission may have an extra induced challenge given the potential of the detection of a natural satellite orbiting the asteroid Bennu. Current ground radar observations for object detection orbiting Bennu show no found objects within bounds of specific size and rotation rates. If a natural satellite is detected during approach, a different proximity operation cadence will need to be implemented as well as a collision avoidance strategy for mission success. A collision avoidance strategy will be analyzed using the Wald Sequential Probability Ratio Test.

satellite↗

NASA NTRS2016

A Collision Avoidance Strategy for a Potential Natural Satellite Around the Asteroid Bennu for the OSIRIS-REx Mission

bennu↗

NASA NTRS1994

(abstract) Asteroid Radar Astronomy at Goldstone in the 1990s

Since 1990, much effort has been devoted to optimizing Goldstone's capability to study near-Earth objects (NEOs). Three different configurations are now available. The nominal system on the 70-m antenna (DSS 14) uses separate feed horns for transmitting and receiving, and the 15-plus seconds required for transmit-to-receive switching renders the system useless for targets much closer than about 0.025 AU (about 10 lunar distances, about 25 seconds of echo time delay) and unwieldy even for targets twice that far. However, an additional, recently installed single horn system shrinks switching time to about 5 seconds, letting DSS 14 observe NEOs as close as about 5 lunar distances. Closer targets will require two-station observations, with DSS 14 transmitting continuously while DSS 13, a 34-m antenna 22 km away, receives. That configuration, first used for Toutatis, will also be required for delay-Doppler imaging that places thousands of pixels on any NEO whose rotation period P(h) and echo roundtrip time delay RTT (s) satisfy P > RTT. Between January 1990 and June 1994, the Goldstone radar has detected 11 asteroids. During the next 2 years, seven asteroids are scheduled for Goldstane observations. After completion of the Arecibo upgrade, Goldstone will play an important complementary role to that much more sensitive instrument.

asteroids radar Goldstone delay-Doppler imaging Ar↗

NASA NTRS1999

Radar and Optical Observations of Asteroid 1998 KY26

Observations of near-Earth asteroid 1998 KY26 shortly after its discovery reveal a slightly elongated spheroid with a diameter of about 30 m, a composition analogous to carbonaceous chondritic meteorites, and a rotation period of 10.7 minutes, which is an order of magnitude shorter that that measured for any other solar system object.

radar asteroids near-Earth Asteroid 1998 KY26↗

NASA NTRS1988

Speckle interferometry of asteroids. IV - Reconstructed images of 4 Vesta

The images of 4 Vesta obtained by means of speckle interferometric observations on November 16 and 17, 1983, support a 5-hr 20.5-min rotational period. The 4 Vesta visible light curve was approximately matched by the placing of circular 'spots' with 135-km diameter over the three dark and three bright features, followed by the assigning of albedos of 0 to the dark spots and 2 to the bright. The light curve is found to be primarily defined by albedo structure, rather than shape; this results in one maximum and one minimum/rotation, rather than the two of each that would be associated with 4 Vesta's triaxial ellipsoid morphology.

Drummond, J.↗

NASA NTRS2000

Dynamical Reference Frame: Current Relevance and Future Prospects

Planetary and lunar ephemerides are no longer used for the determination of inertial space. Instead, the new fundamental reference frame, the International Celestial Reference Frame (ICRF), is inherently less susceptible to extraneous, non-inertial rotations than a dynamical reference frame determined by the ephemerides would be. Consequently, the ephemerides are now adjusted onto the ICRF, and they are fit to two modern, accurate observational data types: ranging (radar, lunar laser, spacecraft) and Very Long Baseline Interferometry (VLBI) (of spacecraft near planets). The uncertainties remaining in the inner planet ephemerides are on the order of 1 kilometer, both in relative positions between the bodies and in the orientation of the inner system as a whole. The predictive capabilities of the inner planet ephemerides are limited by the uncertainties in the masses of many asteroids. For this reason, future improvements to the ephemerides must await determinations of many asteroid masses. Until then, it will be necessary to constantly update the ephemerides with a continuous supply of observational data.

VLBI (VERY LONG BASELINE INTERFEROMETRY)↗

NASA NTRS1988

Observations of cometary nuclei

Attempts to observe cometary nuclei and to determine fundamental physical parameters relevant to the relationship between comets and asteroids are reviewed. It has been found that cometary nuclei, at least of periodic comets, are bigger and blacker than generally thought as recently as five years ago. Geometric albedos may be typically three percent and typical radii are probably of order 5 km. Nuclei of periodic comets are probably highly prolate unless they are both oblate and rotating about one of the major axes. P/Halley images provide convincing evidence of the existence of mantles discussed in many models. Numerous pieces of evidence suggest a connection between cometary nuclei and A-A asteroids of types D and C.

A'Hearn, Michael F.↗

NASA NTRS1999

Radar Reconnaissance of Near-Earth Asteroids

Groundbased radar observations of NEAs can help identify space resources with commercial potential and can dramatically reduce the cost and risk of the initial spacecraft missions to those objects. The near-Earth asteroid (NEA) population is thought to contain approximately 1500 objects as large as a kilometer, approximately 300,000 as large as 100 meters, and more than 100,000,000 as large as 10 meters. More than 10% of the NEAs are more accessible in terms of mission delta-V (i.e., fuel required) than the Moon, Mars, or the moons of Mars. Fewer than 1000 NEAs have been found, but the discovery rate is increasing rapidly. Once an asteroid is discovered (necessarily by wide-field optical telescopes), radar can provide otherwise unavailable information about its size, shape, spin state, and surface properties if it approaches within the range of the Goldstone (California) or Arecibo (Puerto Rico) radar telescopes. Asteroids generally appear as unresolved points through groundbased optical telescopes, but radar measurements of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity) can yield images with resolution as fine as a decameter. Image sequences that furnish adequate orientational coverage can be inverted to construct geologically detailed 3-D models, to define the rotation state precisely, and to constrain the object's internal density distribution. Estimates of radar scattering properties characterize the surface's cm-to-m-scale roughness as well as its bulk density, which for asteroids depends primarily on porosity and metal concentration. A useful spin-off of radar detection is orbit refinement that simplifies navigation of flyby and rendezvous spacecraft.

Ostro, S. J.↗

NASA NTRS1999

Radar Reconnaissance of Near-Earth Asteroids

Groundbased radar observations of NEAs can help identify space resources with commercial potential and can dramatically reduce the cost and risk of the initial spacecraft missions to those objects. The near Earth asteroid (NEA) population is thought to contain approx. 1500 objects as large as a kilometer, approx. 300,000 as large as 100 meters, and more than 100,000,000 as large as 10 meters. More than 10% of the NEAs are more accessible in terms of mission delta-V (i.e., fuel required) than the Moon, Mars, or the moons of Mars. Fewer than 1000 NEAs have been found, but the discovery rate is increasing rapidly. Once an asteroid is discovered (necessarily by wide-field optical telescopes), radar can provide otherwise unavailable information about its size, shape, spin state, and surface properties if it approaches within the range of the Goldstone (California) or Arecibo (Puerto Rico) radar telescopes. Asteroids generally appear as unresolved points through groundbased optical telescopes, but radar measurements of the distribution of echo power in time delay (range) and Doppler frequency (radial velocity) can yield images with resolution as fine as a decameter. Image sequences that furnish adequate orientational coverage can be inverted to construct geologically detailed 3-D models, to define the rotation state precisely, and to constrain the object's internal density distribution. Estimates of radar scattering properties characterize the surface's cm-to-m-scale roughness as well as its bulk density, which for asteroids depends primarily on porosity and metal concentration. A useful spin-off of radar detection is orbit refinement that simplifies navigation of flyby and rendezvous spacecraft.

Ostro, S. J.↗

NASA NTRS1985

Ellipsoidal geometry in asteroid thermal models - The standard radiometric model

The major consequences of ellipsoidal geometry in an othewise standard radiometric model for asteroids are explored. It is shown that for small deviations from spherical shape a spherical model of the same projected area gives a reasonable aproximation to the thermal flux from an ellipsoidal body. It is suggested that large departures from spherical shape require that some correction be made for geometry. Systematic differences in the radii of asteroids derived radiometrically at 10 and 20 microns may result partly from nonspherical geometry. It is also suggested that extrapolations of the rotational variation of thermal flux from a nonspherical body based solely on the change in cross-sectional area are in error.

Brown, R. H.↗