W. D. Smythe

California Institute of Technology, Pasadena, California, United States

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Publications (177)295.4 Total impact

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    ABSTRACT: The JPL Rapid Mission Architecture (RMA) capability is a novel collaborative team-based approach to generate new mission architectures, explore broad trade space options, and conduct architecture-level analyses. RMA studies address feasibility and identify best candidates to proceed to further detailed design studies. Development of RMA first began at JPL in 2007 and has evolved to address the need for rapid, effective early mission architectural development and trade space exploration as a precursor to traditional point design evaluations. The RMA approach integrates a small team of architecture-level experts (typically 6-10 people) to generate and explore a wide-ranging trade space of mission architectures driven by the mission science (or technology) objectives. Group brainstorming and trade space analyses are conducted at a higher level of assessment across multiple mission architectures and systems to enable rapid assessment of a set of diverse, innovative concepts. This paper describes the overall JPL RMA team, process, and high-level approach. Some illustrative results from previous JPL RMA studies are discussed.
    Aerospace Conference, 2011 IEEE; 04/2011
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    ABSTRACT: At the request of the Satellites Panel of the National Research Council (NRC) Planetary Science Decadal Survey, a Rapid Mission Architecture (RMA) study of possible missions to Saturn's moon Enceladus was conducted at the Jet Propulsion Laboratory in January and February of 2010. This was one of many studies commissioned by this NRC Decadal Survey. In this study, 15 Enceladus mission architectures were examined that spanned a broad range of potential science return and total estimated mission cost.
    Aerospace Conference, 2011 IEEE; 04/2011
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    ABSTRACT: Comet Odyssey is a proposed New Frontiers mission that would return the first samples from the surface of a cometary nucleus. Stardust demonstrated the tremendous power of analysis of returned samples in terrestrial laboratories versus what can be accomplished in situ with robotic missions. But Stardust collected only 1 milligram of coma dust, and the 6.1 km/s flyby speed heated samples up to 2000 K. Comet Odyssey would collect two independent 800 cc samples directly from the surface in a far more benign manner, preserving the primitive composition. Given a minimum surface density of 0.2 g/cm3, this would return two 160 g surface samples to Earth. Comet Odyssey employs solar-electric propulsion to rendezvous with the target comet. After 180 days of reconnaissance and site selection, the spacecraft performs a "touch-and-go'' maneuver with surface contact lasting 3 seconds. A brush-wheel sampler on a remote arm collects up to 800 cc of sample. A duplicate second arm and sampler collects the second sample. The samples are placed in a return capsule and maintained at colder than -70 C during the return flight and at colder than -30 C during re-entry and for up to six hours after landing. The entire capsule is then refrigerated and transported to the Astromaterials Curatorial Facility at NASA/JSC for initial inspection and sample analysis by the Comet Odyssey team. Comet Odyssey's planned target was comet 9P/Tempel 1, with launch in December 2017 and comet arrival in June 2022. After a stay of 300 days at the comet, the spacecraft departs and arrives at Earth in May 2027. Comet Odyssey is a forerunner to a flagship Cryogenic Comet Sample Return mission that would return samples from deep below the nucleus surface, including volatile ices. This work was supported by internal funds from the Jet Propulsion Laboratory.
  • W. D. Smythe, R. Nelson, M. D. Boryta
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    ABSTRACT: Ammonia has been suggested as a probable source for sustaining Titan's thick nitrogen-dominated atmosphere. Ammonia is believed to be important to maintaining nitrogen in Titan's atmosphere. Ammonia is seen in clouds in the atmospheres of Jupiter and Saturn, but has yet to be detected on any of the satellites. This may be because all forms of NH3 are unstable in the ambient conditions of the satellites surfaces or that its spectral features are altered by other components of the surface, and have not been identified. It has recently been demonstrated[1] that brightening occurs in Titan's atmosphere that is transient on the time-scale of months. The spectral shape of the brightening is more consistent with that of the transient apparition of a pure ammonia frost than of an ammonia monohydrate or ammonia dihydrate frost. However, the phase behavior of the ammonia water system has peritectics at compositions of 1:1 and 1:2. These hydrate forms would be expected to dominate if the frost, or the reservoir from which the frost was derived had any water present. Physical mechanisms for producing measurable quanitities of anhydrous ammonia can include chemical dehydration or dehydration of the vapor phase - but it is challenging to store significant quantities of the anhydrous material because of the phase behavior in the solid state. [1] Nelson, R.M., et al. Saturn's Titan: Surface Change, Ammonia, and Implications for Atmospheric and Tectonic Activity., Icarus, 199, pp. 429-441, 2009 This work was performed at JPL under contract to NASA
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    ABSTRACT: In 2007 a JPL rapid mission architecture (RMA) analysis team identified and evaluated a broad set of mission architecture options for a suite of scientific exploration objectives targeting the Saturnian moon Enceladus. Primary science objectives were largely focused on examination of the driving mechanisms and extent of interactions by the plumes of Enceladus recently discovered by Cassini mission science teams. Investigation of the architectural trade space spanned a wide range of options, from high-energy flybys of Enceladus as a re-instrumented expansion on the Cassini mission, to more complex, multi-element combinations of Enceladus orbiters carrying multiple variants of in-situ deployable systems. Trajectory design emerged as a critical element of the mission concepts, enabling challenging missions on Atlas V and Delta IV-Heavy class launch vehicles. Various Enceladus Flagship-class mission concepts identified were analyzed and compared against several first-order figures of merit, including mass, cost, risk, mission timeline, and associated science value with respect to accomplishment of the full set of science objectives. Results are presented for these comparative analyses and the characterization of the explored trade space.
    Aerospace conference, 2009 IEEE; 04/2009
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    ABSTRACT: Titan is known to have a young surface. Here we present evidence from the Cassini Visual and Infrared Mapping Spectrometer that it is currently geologically active. We report that changes in the near-infrared reflectance of a 73,000 km2 area on Titan (latitude 26° S, longitude 78° W) occurred between July 2004 and March of 2006. The reflectance of the area increased by a factor of two between July 2004 and March–April 2005; it then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again, establishing a new maximum. Thereafter, it trended downward for the next three months. Detailed spectrophotometric analyses suggest these changes happen at or very near the surface. The spectral differences between the region and its surroundings rule out changes in the distribution of the ices of reasonably expected materials such as H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of NH3 frost over a water ice substrate. NH3 has been proposed as a constituent of Titan's interior and has never been reported on the surface. The detection of NH3 frost on the surface might possibly be explained by episodic effusive events occur which bring juvenile ammonia from the interior to the surface. If so, its decomposition would feed nitrogen to the atmosphere now and in the future. The lateral extent of the region exceeds that of active areas on the Earth (Hawaii) or Io (Loki).
    Icarus 02/2009; DOI:10.1016/j.icarus.2008.08.013 · 2.84 Impact Factor
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    ABSTRACT: The VIMS instrument on the Cassini spacecraft observes the surface of Titan through spectral 'windows' in its atmosphere where methane, the principal absorbing gas is transmitting. We previously have used VIMS to document changes in spectral reflectance and that have occurred on Titan's surface during Cassini's orbital tour at (latitude 26S, longitude 78W), (AGU spring meeting 2007). Having removed the possibility that the observed changes are either an atmospheric phenomenon or are the result of viewing angle (phase) effects, we conclude that physical changes in the chemistry or structure of the surface must be occurring. The size of the region suggests it may exceed the size of the largest active volcanic areas in the solar system. We now have explored additional sections of Titan's surface and have developed new techniques for locating surface changes over time. While some additional candidate areas for surface activity are suggested, confirmation is possible with the support of additional instruments on the Cassini Orbiter, particularly the radar instrument. The principal difficulty in implementing a coordinated program of observations with both instruments is due to the radar instrument's higher spatial resolution but small footprint on the surface relative to VIMS. In addition, the two instruments can not be used simultaneously on the same pass. Overlapping coverage will only be available after repeated flybys during Cassini's extended mission. This work done at JPL/CALTECH under contract with NASA
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    ABSTRACT: On several occasions during its orbital tour the Cassini spacecraft has flown between the sun and Saturn in such fashion that the zero phase point passed through the rings. The Visual and Infrared Mapping Spectrometer (VIMS) recorded spectral image cubes (0.4< ? <5.2μm) that showed the opposition effect (OE) at zero phase. The OE is a spike in the reflected light observed near 0o phase when it is displayed as a function of phase angle. This is the first time the OE has been resolved for small areas on the rings. Previous work has shown that the OE arises from two distinct processes, shadow hiding (SHOE) and coherent backscattering (CBOE). The SHOE process causes an OE by the elimination of shadows cast by regolith grains upon one another as phase angle decreases. The CBOE process causes an OE by constructive interference between photons traveling in opposite directions along the same path within the medium. SHOE is expected to dominate the contribution to the OE in absorbing media where multiple scattering of photons is not significant. CBOE is expected to dominate the contribution to the OE in highly reflective media with much multiple scattering. We have made spectral scans the VIMS images that traverse the zero phase point. We selected narrow spectral bands that reflected a variety of wavelengths and reflectance levels. In this way, phase curves of the ringlet were obtained for each band. We have compared these data to data we acquired in the laboratory using the JPL long arm goniometer where we measured the phase curve of particulate materials that simulate the surface of Saturn's ring particles. We argue here that the OE is due to coherent backscattering because: 1) The theoretical CBOE function fit to the data is excellent. 2) The OE width is extremely narrow 3) The angular width of the peak increases with wavelength. CBOE theory also predicts that the width depends on the transport mean free path (TMFP) in the medium. We find that the OE is caused by coherent interactions between sub-particles in the outer layers of the ring particles, and that these sub-particles are of the order of 20-40 μm in size. A portion of this work was performed at JPL under contract with NASA
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    ABSTRACT: We present the motivations and objectives of a new experimental cryo-ices initiative at JPL. This is a joint effort among experimentalists and theorists at JPL, in collaboration with specialists in ice properties.
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    ABSTRACT: The bidirectional reflectance of a powder of spherical particles predicted by exact numerical solutions of the radiative transfer equation are more forward scattering than laboratory measurements, because the particles are more backscattering in a regolit
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    ABSTRACT: A report on the implementation and testing of the Mars Borehole IR spectrometer. This spectrometer is designed to fit within a Mars drill, providing near real-time monitoring of the composition of the borehole wall.
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    ABSTRACT: The near-infrared reflectance of a 73,000 km2 area on Titan changed between July 2004 and March of 2006. The reflectance of the region (latitude 26S, longitude 78W) increased twofold between July 2004 and March-April 2005. It then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again to a new maximum. It then declined for the next three months. Detailed analyses indicate that the brightenings are a surface phenomenon, making these the first changes seen on Titan’s surface. The spectral differences between the region and its surroundings rule out the ices of H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of ammoniated materials. NH3 has been proposed as a constituent of Titan’s interior but not its surface or atmosphere. This transitory NH3 spectral signature is consistent with occasional effusion events in which juvenile ammonia is brought to the surface. Its decomposition may feed nitrogen to the atmosphere. The size of the region suggests it may exceed the size of the largest active volcanic areas in the solar system.
    38th Lunar and Planetary Science Conference; 01/2007
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    ABSTRACT: The Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini Saturn Orbiter returned spectral imaging data as the spacecraft undertook six close encounters with Titan beginning 7 July, 2004. Three of these flybys each produced overlapping coverage of two distinct regions of Titan's surface. Twenty-four points were selected on approximately opposite hemispheres to serve as photometric controls. Six points were selected in each of four reflectance classes. On one hemisphere each control point was observed at three distinct phase angles. From the derived phase coefficients, preliminary normal reflectances were derived for each reflectance class. The normal reflectance of Titan's surface units at 2.0178 μm ranged from 0.079 to 0.185 for the most absorbing to the most reflective units assuming no contribution from absorbing haze. When a modest haze contribution of τ=0.1 is considered these numbers increase to 0.089–0.215. We find that the lowest three reflectance classes have comparable normal reflectance on either hemisphere. However, for the highest brightness class the normal reflectance is higher on the hemisphere encompassing longitude 14–65° compared to the same high brightness class for the hemisphere encompassing 122–156° longitude. We conclude that an albedo dichotomy observed in continental sized units on Titan is due not only to one unit having more areal coverage of reflective material than the other but the material on the brighter unit is intrinsically more reflective than the most reflective material on the other unit. This suggests that surface renewal processes are more widespread on Titan's more reflective units than on its less reflective units.We note that one of our photometric control points has increased in reflectance by 12% relative to the surrounding terrain from July of 2004 to April and May of 2005. Possible causes of this effect include atmospheric processes such as ground fog or orographic clouds; the suggestion of active volcanism cannot be ruled out.Several interesting circular features which resembled impact craters were identified on Titan's surface at the time of the initial Titan flyby in July of 2004. We traced photometric profiles through two of these candidate craters and attempted to fit these profiles to the photometric properties expected from model depressions. We find that the best-fit attempt to model these features as craters requires that they be unrealistically deep, approximately 70 km deep. We conclude that despite their appearance, these circular features are not craters, however, the possibility that they are palimpsests cannot be ruled out.We used two methods to test for the presence of vast expanses of liquids on Titan's surface that had been suggested to resemble oceans. Specular reflection of sunlight would be indicative of widespread liquids on the surface; we found no evidence of this. A large liquid body should also show uniformity in photometric profile; we found the profiles to be highly variable. The lack of specular reflection and the high photometric variability in the profiles across candidate oceans is inconsistent with the presence of vast expanses of flat-lying liquids on Titan's surface. While liquid accumulation may be present as small, sub-pixel-sized bodies, or in areas of the surface which still remain to be observed by VIMS, the presence of large ocean-sized accumulations of liquids can be ruled out.The Cassini orbital tour offers the opportunity for VIMS to image the same parts of Titan's surface repeatedly at many different illumination and observation geometries. This creates the possibility of understanding the properties of Titan's atmosphere and haze by iteratively adapting models to create a best fit to the surface reflectance properties.
    Planetary and Space Science 12/2006; 54(15-54):1540-1551. DOI:10.1016/j.pss.2006.06.014 · 1.63 Impact Factor
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    ABSTRACT: Significant regional changes in the near-infrared reflectance of a 2800 km2 area on Titan occurred between July 2004 and March of 2006. The reflectance increased by a factor of two between July 2004 and March-April of 2005; it then decreased to the July 2004 level by November 2005. By late December 2005 the reflectance had surged again, slightly exceeding its earlier maximum. It then decreased in reflectance in the three following months through mid-March 2006. This behavior is inconsistent with tropospheric clouds of the type observed at Titan's South pole and high mid-latitudes. Application of a comprehensive radiative transfer model indicates that it is unlikely to be caused by a ground fog and most likely occurred at Titan's surface. This is the first direct evidence of short-term surface change on Titan. Inspection of the spectral differences between the spot and its surrounding terrain rules out changes in the distribution of the ices of H2O, CO2, and CH4 as the cause. However, the spectral change is consistent with what would be expected from NH3 frost. Interpretations include changing surface deposits due to abrupt tectonic or volcanic activity. This is the first evidence for currently active tectonic processes such as volcanism on Titan. This work done at JPL/CALTECH under contract with NASA
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    ABSTRACT: Spectra and optical constants of ammonia frost are used to assess the detectability of ammonia frost viewed through Titan's atmospheric windows in the spectral range 1-5 µm.
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    XXXVII Lunar and Planetary Science Conference; 01/2006
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    ABSTRACT: The National Research Council's solar system exploration decadal survey identified Jupiter's moon Europa as its highest-priority destination for near-term exploration. Voyager and Galileo missions to the Jupiter system provided evidence consistent with a subsurface ocean on Europa, which is of great interest as a potential abode for extraterrestrial life. This paper describes a conceptual flagship-class Europa orbiter concept that was assumed to launch as early as 2012, arriving at Europa approximately 8 years later using inner solar system gravity assists to reach Jupiter. Jupiter's intense radiation environment limits the mission duration at Europa to 30 days for this study, though the duration is a result of multiple trades and is by no means fixed. The Europa subgroup of the outer planets assessment group identified six primary science objectives for this concept. An ~150-kg instrument suite selected for the study addresses those objectives. Large heliocentric distances, high power levels required, and especially the harsh Jovian radiation environment drove the selection of radioisotope thermoelectric generators (RTGs) for all onboard electrical power, with the excess heat aiding spacecraft thermal control. Mass and architecture trades were performed using different spacecraft trajectories, launch vehicle types, radioisotope power systems, and mission durations. The study shows that new mission constraints allow a scientifically compelling Europa orbiter mission that might also deliver a Europa lander
    Aerospace Conference, 2006 IEEE; 01/2006
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    ABSTRACT: On May 20 2005 the Cassini spacecraft flew between the sun and Saturn on a trajectory such that the zero phase point passed through the rings The Visual and Infrared Mapping Spectrometer VIMS recorded a number of spectral image cubes 0 4 lambda 5 2 mu m that showed the opposition effect OE at zero phase The OE is a spike in the reflected intensity observed near 0 o phase when it is displayed as a function of phase angle This is the first time the OE has been resolved for small areas on the rings Previous work has shown that the OE arises from two distinct processes shadow hiding SHOE and coherent backscattering CBOE The SHOE process causes an OE by the elimination of shadows cast by regolith grains upon one another as phase angle decreases The CBOE process causes an OE by constructive interference between photons traveling in opposite directions along the same path within the medium SHOE is expected to dominate the contribution to the OE in absorbing media where multiple scattering of photons is not significant CBOE is expected to dominate the contribution to the OE in highly reflective media with much multiple scattering Using the individual image cubes a total of 32 areas containing 4 pixels each were selected that lay along the same ringlet as the opposition point and bracketed it in phase angle Because water ice is a major component of the rings the spectra are predominantly that of water Within each spectrum 9 narrow spectral bands were chosen to reflect a variety of wavelengths and reflectance levels In this
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    ABSTRACT: Most regolith reflectance models are based on two assumptions: (1) radiative transfer (RT) theory is valid, and (2) the fundamental scatterers of the medium are its particles, which scatter independently (the fundamental scatterer assumption - FSA). These assumptions give good results when applied to suspensions of well-separated particles comparable to or smaller than the wavelength Î&Gt;. However, serious questions have arisen regarding their applicability to close-packed media of particles larger than Î&Gt;. In a major continuing study we have measured the bidrectional reflectances of several well-characterized powders using the JPL goniometric photopolarimeter, which is capable of measuring reflectances in linearly and circularly polarized light between 0.05 - 22 °. From our results we infer the following: 1. RT-FSA models give good results when used to calculate the reflectance functions of close packed particulate media at phase angles greater than a few degrees. Evidently coherent effects between particles can be neglected. 2. For media of perfect spheres with diameters > Î&Gt;, models of the coherent backscatter opposition effect (CBOE) peak based on the RT-FSA assumption predict photon transport mean free paths L consistent with laboratory results. 3. For media of large irregular particles L's deduced from the measured CBOE widths are much smaller than predictions of RT-FSA models. Exactly what the CBOE is measuring in these materials is unclear, although scattering by small, closely-spaced surface and interior imperfections is a good candidate. 4. Much of the light that contributes to the CBOE is scattered from the top layer. 5. The diffraction peak of a large isolated particle does not exist when the particle is in a powder. These conclusions have strong implications for understanding planetary surfaces and Saturn's ring particles. The latter are discussed in a companion paper. Rresearch sponsored by the Planetary Geology and Geophysics program of NASA.
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    XXXVII Lunar and Planetary Science Conference; 01/2006

Publication Stats

1k Citations
295.40 Total Impact Points

Institutions

  • 1991–2009
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 1990–2005
    • University of Pittsburgh
      • Department of Geology and Planetary Science
      Pittsburgh, PA, United States
  • 1974–2001
    • University of California, Los Angeles
      Los Ángeles, California, United States