Goldstone Radar Research Articles

Radar and Lightcurve Observations and a Physical Model of Potentially Hazardous Asteroid 1981 Midas

Abstract We report observations of the Apollo-class potentially hazardous asteroid 1981 Midas, which passed 0.090 au from Earth (35 lunar distances) on 2018 March 21. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights) and from NASA’s Goldstone Deep Space Communications Complex on March 19 and 21. Optical lightcurves were obtained by other observers during four apparitions (1987, 1992, 2004, and 2018), which showed a rotation period of 5.22 hr. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck, which, at its thinnest point, is about 60% of the width of the largest lobe. We also confirm the lightcurve-derived rotation period and show that Midas has a pole direction within 6° of ecliptic longitude and latitude (λ, β) = (39°, −60°) and dimensions of (3.41 ± 9%) × (1.90 ± 11%) × (1.27 ± 29%) km. Analysis of gravitational slopes on Midas indicates that nearly all of the surface has a slope less than the typical angle of repose for granular materials, so it does not require cohesion to maintain its shape. In addition, we measured a circular polarization ratio of 0.83 ± 0.04 at Arecibo’s 13 cm wavelength, which is the highest seen to date for any near-Earth asteroid with visible and near-infrared spectral type V.

Goldstone Radar Observations of Horseshoe-orbiting Near-Earth Asteroid 2013 BS45, a Potential Mission Target

Abstract We report radar observations of near-Earth asteroid 2013 BS45 obtained during the 2013 apparition. This object is in a resonant, Earth-like orbit, and it is a backup target for NASA’s NEA Scout mission. 2013 BS45 belongs to the Arjuna orbital domain, which currently has ∼20 discovered representatives. These objects tend to be small and difficult to characterize, and 2013 BS45 is only the third Arjuna object observed with radar to date. We observed 2013 BS45 on three days at Goldstone (8560 MHz, 3.5 cm) between 2013 February 10 and 13. The closest approach occurred on February 12 at a distance of 0.0126 au. We obtained relatively weak echo power spectra and ranging data at resolutions up to 0.125 μs (18.75 m px−1). The Doppler broadening of the echo power spectra strongly suggests an upper bound on the rotation period of 1.9 minutes. The radar data, in combination with an assumption that the asteroid’s radar albedo is no higher than that of metallic NEA 1986 DA, constrain the equivalent diameter to 15 m ≤ D ≤ 38 m. The circular polarization ratio is 0.21 ± 0.06, which implies a near-surface that is relatively smooth on decimeter spatial scales. We bounded the OC radar albedo to η OC ≥ 0.09 and the optical albedo remains relatively unconstrained at 0.05 ≤ p V ≤ 0.35. The Yarkovsky acceleration has not been detected but, due to the object’s rapid rotation, would be dominated by a seasonal component whose direction and magnitude depends on the currently unknown pole orientation and thermal inertia.

A Complex for Carrying Out Radar Observations of Near-Earth Objects

The Institute of Applied Astronomy of the Russian Academy of Sciences and the Goldstone Deep Space Communications Complex regularly conduct intercontinental radar observations of near-Earth objects using a 70-m DSS-14 antenna as a transmitter and the 32-m RT-32 radio telescopes of the Quasar VLBI network as receivers. To carry out the observations, the existing complex for reception, conversion, and recording of signals from the RT-32 radio telescopes has been adapted and special software for scheduling observations and processing echo signals has been developed. Since 2015, echoes from the 2011 UW158, 2003 TL4, 2003 YT1, 2003 BD44, and 2014 JO25 asteroids have been recorded. The power spectra of the echoes from these asteroids have been obtained and analyzed.

Deep space

Beam waveguide antennas, each 34 m in diameter, lit up against the early-dawn sky at the Goldstone Deep Space Communications Complex in the Mojave Desert in California, US.

Goldstone radar imaging of near-Earth Asteroid 2003 MS2

We report radar observations of near-Earth Asteroid (NEA) 2003 MS2 with Goldstone (8560MHz, 3.5cm) on June 28, 29, and July 4, 2003, shortly after the asteroid’s discovery. Delay-Doppler images with resolutions as fine as 19m/pixel reveal an unusually angular object with pronounced facets. The longest sequence of images was obtained on July 4 when the asteroid rotated ∼140deg in 2.7h. During this interval, bandwidths varied by a factor of ∼1.5 and indicate that 2003 MS2 is an elongated object. The rotation and bandwidth variations evident in the radar images are consistent with the 7h rotation period and the 0.7 magnitude lightcurve amplitude reported by Muinonen et al. (Muinonen, K. et al. [2007]. Spins, shapes, and orbits for near-Earth objects by Nordic NEON. In: Milani, A., Valsecchi, G.B., Vokrouhlický, D. (Eds.), Near Earth Objects, our Celestial Neighbors: Opportunity and Risk. Cambridge University Press, Cambridge, pp. 309–320). If we adopt the 7h period, then the maximum and minimum bandwidths place lower bounds on the pole-on dimensions of (0.33×0.19)km/cosδ, where δ is the unknown subradar latitude. The radar and photometric observations by Muinonen et al. constrain the pole directions to (λ, β)=(20±20deg, 0±40deg) and (200±20deg, 0±40deg). The circular polarization ratio of 0.31±0.02 is comparable to that of 25143 Itokawa, suggesting a similar degree of near-surface roughness at decimeter spatial scales.

Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations

We determine the three-dimensional shape of near-Earth Asteroid (101955) Bennu based on radar images and optical lightcurves. Bennu was observed both in 1999 at its discovery apparition, and in 2005 using the 12.6-cm radar at the Arecibo Observatory and the 3.5-cm radar at the Goldstone tracking station. Data obtained in both apparitions were used to construct a shape model of this object. Observations were also obtained at many other wavelengths to characterize this object, some of which were used to further constrain the shape modeling. The lightcurve data, along with an initial determination of the rotation period derived from them, simplified and improved the shape modeling.Below we briefly describe the observations and shape modeling process. We discuss the shape model and the implications for the possible formation and evolution of this object. We also describe the importance and limitations of the shape model in view of the fact that this object is the target of the OSIRIS-REx spacecraft mission.

Locating the LCROSS Impact Craters

The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated \sim9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft's trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of -84.6796\circ, -48.7093\circ, with a 1{\sigma} un- certainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is -84.719\circ, -49.61\circ, with a 1{\sigma} uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region.

Debris flux comparisons from the Goldstone Radar, Haystack Radar, and Hax Radar prior, during, and after the last solar maximum

The continual monitoring of the low Earth orbit (LEO) debris environment using highly sensitive radars is essential for an accurate characterization of these dynamic populations. Debris populations are continually evolving since there are new debris sources, previously unrecognized debris sources, and debris loss mechanisms that are dependent on the dynamic space environment. Such radar data are used to supplement, update, and validate existing orbital debris models. NASA has been utilizing radar observations of the debris environment for over a decade from three complementary radars: the NASA JPL Goldstone radar, the MIT Lincoln Laboratory (MIT/LL) Long Range Imaging Radar (known as the Haystack radar), and the MIT/LL Haystack Auxiliary radar (HAX). All of these systems are highly sensitive radars that operate in a fixed staring mode to statistically sample orbital debris in the LEO environment. Each of these radars is ideally suited to measure debris within a specific size region. The Goldstone radar generally observes objects with sizes from 2 mm to 1 cm. The Haystack radar generally measures from 5 mm to several meters. The HAX radar generally measures from 2 cm to several meters. These overlapping size regions allow a continuous measurement of cumulative debris flux versus diameter from 2 mm to several meters for a given altitude window. This is demonstrated for all three radars by comparing the debris flux versus diameter over 200 km altitude windows for 3 nonconsecutive years from 1998 to 2003. These years correspond to periods before, during, and after the peak of the last solar cycle. Comparing the year to year flux from Haystack for each of these altitude regions indicate statistically significant changes in subsets of the debris populations. Potential causes of these changes are discussed. These analysis results include error bars that represent statistical sampling errors.

Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980–1995

We report detailed results of Arecibo and Goldstone radar observations of 30 mainbelt asteroids (MBAs) during 1980–1995. In addition to estimates of radar cross section, radar albedo, and circular polarization ratio, we obtain new constraints on pole direction for several asteroids, with those for 21 Lutetia being particularly restrictive. We carry out statistical analyses of disk-integrated properties (radar albedo and polarization ratio) of all 37 radar-observed MBAs. M asteroids seem to have higher radar albedos and a wider range of albedos than do asteroids from the other taxonomic classes; there is no evidence that C and S MBAs have different albedo distributions; and there is some suggestion, worthy of future study, that primitive B, F, G, and P asteroids are not as radar-bright as C and S objects. There is no statistically significant evidence that different taxonomic classes have different polarization ratio distributions, despite suggestions to the contrary based on visual inspection of these distributions. The similarity between the C and S albedo distributions implies similar near-surface regolith bulk densities. The hypothesis of ordinary chondritic composition for the S-class asteroids is reasonably consistent with the radar data, provided that these asteroids have typical lunar porosities. Nevertheless, it is possible that some of these targets have high-porosity regoliths of stony-iron composition. Our M-class sample presumably contains both metallic objects (such as 216 Kleopatra and, probably, 16 Psyche) and less metallic objects.

Radar observations of space debris

Our radar monitoring of small Earth-orbiting debris at NASAs Goldstone Tracking Station has been extended to an altitude of 3200 km. Many of the observed particles lie in clusters ; the largest of which appears to be remnants of the West Ford Needles, launched over 3 decades earlier, and originally designed to have reentered the Earths atmosphere long ago.

Shape of Asteroid 433 Eros from Inversion of Goldstone Radar Doppler Spectra

We use new analysis techniques to constrain the shape of 433 Eros with Goldstone radar data obtained during the asteroid's close approach in 1975. A previous analysis of these data (Ostro, Rosema, and Jurgens, 1990,Icarus84,334–351) used estimates of the echo's spectral edge frequencies as a function of asteroid rotation phase to constrain the convex envelope of Eros' pole-on silhouette. Our approach makes use of the echo's full Doppler-frequency distribution (effectively ∼15 times more echo data points) and is thus capable of constraining shape characteristics, such as concavities, within this convex envelope. The radar echoes are weak and north-south ambiguous, which limits the accuracy of our models. We present two different approaches, perturbations to an ellipsoid and successive approximations, that help to quantify the model uncertainties and identify features that are likely to be real. Both approaches yield models that are tapered along their lengths, with one or more prominent concavities on one side but not the other. We do not have sufficient information to determine the exact nature of the concavities, and in particular, whether they are craters, troughs, or bends in Eros' overall shape. The pole-on silhouette of the successive approximation model is shaped like a kidney bean, which resembles a nearly pole-on optical image derived from speckle interferometry (Drummond and Hege, 1989, inAsteroids II(R. P. Binzell, T. Gehrels, and M. S. Matthews, Eds.), pp. 171–191, Univ. of Arizona Press, Tucson); however, we cannot exclude shapes, such as the perturbation model, with more than one large concavity. Variations in the pyroxene/olivine ratio over Eros' surface have been inferred from visual and infrared observations (Murchie and Pieters, 1996,J. Geophys. Res.101,2201–2214). Correlating these variations with our shape information, we find that the side with concavities is relatively px-rich compared with the more rounded opposing side.

Radar detection of the nucleus and coma of comet hyakutake

Radar observations of comet Hyakutake (C/1996 B2) made at the Goldstone Deep Space Communications Complex in California have detected echoes from the nucleus and from large grains in the inner coma. The nucleus of this bright comet was estimated to be only 2 to 3 kilometers in diameter. Models of the coma echo indicate backscatter from porous, centimeter-size grains ejected anisotropically at velocities of tens of meters per second. The radar observations suggest that a comet's activity may be a poor indicator of its size and provide evidence that large grains constitute an important component of the mass loss from a typical active comet.

The NASA engineering model: A new approach

A computer-based semi-empirical orbital debris model has been developed which combines direct measurements of the environment with the output and theory of more complex orbital debris models. It approximates the environment with 6 different inclination bands. Each band has a unique distribution of semi-major axis, for near circular orbits, and a unique perigee distribution, for highly elliptical orbits. In addition, each inclination band has unique size distributions which depend on the source of debris. Collision probability equations are used to relate the distributions of orbital elements to flux on a spacecraft or through the field of view of a ground sensor. The distributions of semimajor axis, perigee, and inclination are consistent with the U.S. Space Command catalogue for sizes larger than about 10 cm, taking the limitations of the sensors into account. For smaller sizes, these distributions are adjusted to be consistent with the flux measured by ground telescopes, the Haystack radar, and the Goldstone radar as well as the flux measured by the Long Duration Exposure Facility (LDEF) and the Space Shuttle. The computer program requires less than 1 second to calculate the flux and velocity distribution for a given size debris relative to an orbiting spacecraft.

Radar Observations of Asteroids 1 Ceres, 2 Pallas, and 4 Vesta

Asteroids 1 Ceres, 2 Pallas, and 4 Vesta were observed with the 13-cm Arecibo radar and the 3.5-cm Goldstone radar during several apparitions between 1981 and 1995. These observations help to characterize the objects' surface properties. Echoes from Ceres and Pallas are ∼95% polarized (μC= σSC/σOC≈ 0.05) in the sense expected for specular (mirror) reflection yet broadly distributed in Doppler frequency, thus revealing surfaces that are smoother than the Moon at decimeter scales but much rougher (rms slopes > 20°) on larger scales. Slopes on Ceres appear to be somewhat higher when viewed with the 3.5-cm wavelength, a trend that is observed for the terrestrial planets and the Moon. In contrast, echoes from Vesta are significantly depolarized, indicating substantial near-surface complexity at scales near 13 cm (μC= 0.24 ± 0.04) and 3.5 cm (μC= 0.32 ± 0.04), which is probably a consequence of Vesta's relatively strong basaltic surface material and may be a signature of large impact features inferred to be present on the surface.The low radar albedos of Ceres (σOC= 0.042 ± 0.006) and Pallas (σOC= 0.075 ± 0.011) are in the range expected for surfaces with a carbonaceous chondrite mineralogy. Pallas' distinctly higher albedo implies a ∼35% higher surface density, which could result from a lower regolith porosity and/or a higher specific gravity (zero-porosity density). Given a porosity of 45%, the specific gravities of the surface materials on Ceres and Pallas would be ∼2.3 and ∼3.0 g cm−3, respectively, which would be consistent with (1) the presence of an additional silicate component on Pallas' surface (as inferred from spectroscopic observations) and (2) recent mass estimates, which suggest a higher mean (volume-averaged) density for Pallas than for Ceres.

Optical-radar imaging of scale models for studies in asteroid astronomy

During the past five years, delay-Doppler radar has become the primary technique for studying the structure of Earth-crossing asteroids. None of these objects has yet been visited by spacecraft, so ground-truth test cases are lacking. A laboratory system is described that provides optical-radar images at 0.1-mm resolution. These data are analogous to the highest-resolution asteroid radar images currently available and provided realistic test cases for developing signal-processing techniques. The system can be thought of as a 1/188,000 scale model of the Arecibo radar, or a 1/52,800 scale model of the Goldstone radar.

Soil-Geomorphic Assessments of Neotectonism at Venus II Antenna Dish Site, Goldstone Deep Space Communications Complex, San Bernardino County, California

Soil-Geomorphic Assessments of Neotectonism at Venus II Antenna Dish Site, Goldstone Deep Space Communications Complex, San Bernardino County, California

Efficiency measurement techniques for calibration of a prototype 34-meter-diameter beam-waveguide antenna at 8.45 and 32 GHz

Efficiency measurements at 8.45 and 32 GHz (X- and Ka-bands) have been carried out on a new 34-m-diameter beam-waveguide antenna now in use at the NASA/JPL Goldstone Deep Space Communications Complex. The use of portable test packages enabled measurements at both the Cassegrain and the beam-waveguide focal points. Radio sources (quasars and Venus) were used as calibrators, and updated determinations of flux and source size correction were made during the period of the measurements. Gain and efficiency determinations as a function of elevation angle are presented, and the effects of the beam-waveguide system and antenna structure are clearly seen. At the beam-waveguide focus, an 8.45-GHz peak efficiency of 72.38% was measured; at 32 GHz, 44.89% was measured.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rings of Earth

The authors have used the planetary radar at the Jet Propulsion Laboratory's Goldstone Tracking Station to monitor small particles of orbital debris. This radar can detect metallic objects as small as 1.8 mm in diameter at an altitude of 600 km. The results of the first set of observations show a flux (at 600 km) of 6.4 objects per square kilometre per day, of equivalent size of 1.8 mm or larger. Forty percent of the observed particles appear to be concentrated into one or two orbits. An orbital ring with the same inclination as the radar (35.1 degrees ) is suggested. However, an orbital band with the much higher inclination of 66 degrees is also a possibility. Neither explanation is without difficulty.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Valley systems on Tyrrhena Patera, Mars: Earth-based radar measurements of slopes

Eight new topographic profiles across the Martian volcano Tyrrhena Patera have been obtained between latitudes 20.0° and 25.1°S from radar data collected by the JPL Goldstone Radar System in 1988. These profiles, which have a reproducible accuracy of better than 150 m, show the volcano to rise ∼1.5 km above the plains of Hesperia Planum to the east, and to have an average height-to-diameter ratio of ∼1:340. The maximum slopes of the flanks appear to be ∼3.0°. The slopes on the northern flanks of Tyrrhena Patera (0.2 to 3.0°) bear little correlation with the width (1.7 to 5.2 km) or depth (∼200 to 300 m) of valley systems found in that area. This suggests that erosion by gravity-driven flows was not responsible for valley formation and that other factors, such as spatial or temporal variations in the volume of ground water released by sapping, or strength differences in the materials comprising the surface units of the volcano, controlled the geometry and locations of the valleys.

Radio Frequency Interference Survey over the 1.0 - 10.4 GHz Frequency Range at the Goldstone - Venus Tracking Station

Plans are currently being made to carry out a comprehensive, all-sky search for radio signals of extraterrestrial origin. The survey will employ the Goldstone tracking station near Barstow, California, and other sites in the northern and southern hemispheres. The principal parameters of this survey are given in Table 1. In preparation for this search, we have constructed a radio spectrum surveillance system (RSSS), and made a series of measurements of the RFI environment at the Goldstone-Venus tracking station. We describe in this paper the receiving system used (Crow et al. 1985), and the results of a low-sensitivity survey performed during February 16-24,1987.