Publications (55) View all
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Article: The New Horizons Radio Science Experiment (REX)
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ABSTRACT: The New Horizons (NH) Radio Science Experiment, REX, is designed to determine the atmospheric state at the surface of Pluto and in the lowest few scale heights. Expected absolute accuracies in n, p, and T at the surface are 4⋅1019m−3, 0.1Pa, and 3K, respectively, obtained by radio occultation of a 4.2 cm-λ signal transmitted from Earth at 10–30kW and received at the NH spacecraft. The threshold for ionospheric observations is roughly 2⋅109 e− m−3. Radio occultation experiments are planned for both Pluto and Charon, but the level of accuracy for the neutral gas is expected to be useful at Pluto only. REX will also measure the nightside 4.2 cm-λ thermal emission from Pluto and Charon during the time NH is occulted. At Pluto, the thermal scan provides about five half-beams across the disk; at Charon, only disk integrated values can be obtained. A combination of two-way tracking and occultation signals will determine the Pluto system mass to about 0.01 percent, and improve the Pluto–Charon mass ratio. REX flight equipment augments the NH radio transceiver used for spacecraft communications and tracking. Implementation of REX required realization of a new CIC-SCIC signal processing algorithm; the REX hardware implementation requires 1.6 W, and has mass of 160g in 520cm3. Commissioning tests conducted after NH launch demonstrate that the REX system is operating as expected.Space Science Reviews 04/2012; 140(1):217-259. · 3.61 Impact Factor -
Article: Vertical structure of the Venus cloud top from the VeRa and VIRTIS observations onboard Venus Express
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ABSTRACT: Cited By (since 1996): 4, Export Date: 6 August 2012, Source: ScopusIcarus 01/2012; 217(2):599-609. · 3.38 Impact Factor -
Article: Polarization in Bistatic Radar Probing of Planetary Surfaces: Application to Mars Express Data
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ABSTRACT: Spacecraft-to-ground bistatic radar provides a straightforward method for surveying planetary surfaces on scales of importance to landers and rovers. Centimeter wavelengths, currently in use for deep-space telecommunications, interact with surface structure of similar to somewhat larger scales. For the quasi-specular component of scattering and for surfaces uniformly illuminated by monochromatic signals from an orbiting or flyby vehicle, the echo Doppler dispersion is proportional to the root mean square (rms) surface slope. When the specular condition occurs within 10°-20° of the Brewster angle, the surface dielectric constant can be derived from relative echo power measured simultaneously in orthogonal polarizations and the Fresnel reflection laws. Cross spectra, computed from outputs of the orthogonally polarized receivers, may be used to calculate a complete description of the polarization properties of the scattered fields. Application to planetary studies requires accurate amplitude and phase calibration of the polarization channels, including correction for any leakage between the two receiving paths, such as from imperfectly isolated antenna feeds. We illustrate these techniques using Mars Express results from “Stealth” (Medusae Fossae), a region on Mars that has not previously been detected by Earth-based radar, and from a long profile including Acidalia Planitia. Single-location Stealth observations support previous conclusions that the surface is rough and porous (dielectric constant ≈ 1.4). But the longest experiment (in which the specular point was followed for an hour) yields relatively high dielectric constants (2.8), suggesting that the model is incomplete. The surface of Acidalia Planitia has low dielectric constants ( ≈2.6) over 60-90 W at 50 N and higher values (≈3.6) as the specular point moves south and crosses the equator.Proceedings of the IEEE 06/2011; · 6.81 Impact Factor -
Article: On the Mass of CoRoT-7b
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ABSTRACT: The mass of CoRoT-7b, the first transiting superearth exoplanet, is still a subject of debate. A wide range of masses have been reported in the literature ranging from as high as 8 M_Earth to as low as 2.3 M_Earth. Although most mass determinations give a density consistent with a rocky planet, the lower value permits a bulk composition that can be up to 50% water. We present an analysis of the CoRoT-7b radial velocity measurements that uses very few and simple assumptions in treating the activity signal. By only analyzing those radial velocity data for which multiple measurements were made in a given night we remove the activity related radial velocity contribution without any a priori model. We demonstrate that the contribution of activity to the final radial velocity curve is negligible and that the K-amplitude due to the planet is well constrained. This yields a mass of 7.42 +/- 1.21 M_Earth and a mean density of rho = 10.4 +/- 1.8 gm cm^-3. CoRoT-7b is similar in mass and radius to the second rocky planet to be discovered, Kepler-10b, and within the errors they have identical bulk densities - they are virtual twins. These bulk densities lie close to the density - radius relationship for terrestrial planets similar to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal structure more like Mercury than the Earth.05/2011; -
Article: Images of Asteroid 21 Lutetia: A Remnant Planetesimal from the Early Solar System
Science 01/2011; 334:487-490. · 31.20 Impact Factor
