Showing papers by "David E. Smith published in 2006"
TL;DR: In this paper, the authors examined the further possibility of constraining the thickness of the icy shell in the case where a liquid ocean exists, by combining measurements of tidal gravity obtained from tracking an orbiting spacecraft with measurements of vertical tidal surface displacements obtained from a precise onboard altimeter.
Abstract: [1] It has been shown previously that measurements of tides on Jupiter's moon Europa can be used to determine whether there is a liquid ocean beneath this moon's icy outer shell. In this paper we examine the further possibility of constraining the thickness of the icy shell in the case where a liquid ocean exists, by combining measurements of tidal gravity obtained from tracking an orbiting spacecraft with measurements of vertical tidal surface displacements obtained from a precise onboard altimeter. By simulating a 1-month Europa mapping mission we demonstrate that this combination of tidal measurements would provide a much better estimate of ice thickness than could be obtained using either tracking or altimeter measurements alone. The thickness value inferred from the combined data would also require an estimate of the shear modulus of Europa's icy shell. This introduces an additional uncertainty in the thickness estimate that is approximately proportional to the uncertainty in the inverse of the shear modulus.
93 citations
University of California, Los Angeles1, Max Planck Society2, Los Alamos National Laboratory3, University of Hawaii4, University of Maryland, College Park5, University of Tennessee6, Free University of Berlin7, Brown University8, Goddard Space Flight Center9, University of Arizona10, Massachusetts Institute of Technology11
TL;DR: Dawn, the ninth Discovery mission, is a journey to the main belt asteroids Vesta and Ceres to attempt to understand the building blocks of the solar system and the processes occurring at the solar solar system's earliest epoch as discussed by the authors.
26 citations
21 May 2006
TL;DR: In this article, a ground-based Nd:YAG laser was detected in Mars orbit, at with the MOLA instrument on-board the Mars Global Surveyor spacecraft on September 28, 2005, at distance of 80.1 Mkm.
Abstract: Over 500 pulses transmitted from a ground-based Nd:YAG laser were detected in Mars orbit, at with the MOLA instrument on-board the Mars Global Surveyor spacecraft on September 28, 2005, at distance of 80.1 Mkm.
20 citations
21 Aug 2006
TL;DR: In this article, the authors analyzed X-band radio tracking observations of the Mars Odyssey spacecraft during its aerobraking phase (October 2001-January 2002) using the precision orbit determination software GEODYN, and obtained estimates of the spacecraft orbital energy lost during each periapsis pass due to atmospheric drag.
Abstract: We analyzed X-band radio tracking observations of the Mars Odyssey spacecraft during its aerobraking phase (October 2001–January 2002). Using the precision orbit determination softwareGEODYN,we obtained estimates of the spacecraft orbital energy lost during eachperiapsis pass due to atmospheric drag.Wealso recovered atmospheric density values at each periapsis, assuming simple exponential atmospheric models. Our measurements are in good agreement with the time series from the Odyssey accelerometer instrument, but they are dependent on the a priori scale height used. Using the accelerometer-derived periapsis densities and the precision orbit determination-derived frictional loss of orbital energy, we calculated new scale heights. Each represents the effective scale height of the atmosphere near periapsis for each aerobraking pass. Our results are consistently 1:7 0:7 km greater than the published accelerometer values. The accelerometermeasurements have higher spatial and temporal resolutionwhen they are available, but these results provide a data set useful for engineering and navigational purposes, to assess variability in the Martian middle atmosphere.
1 citations