Nixon, Conor A; Brasunas, John C; Lakew, Brook; Fettig, Rainer; Jennings, Donald E; Carlson, Ronald; Kunde, Virgil G

RECON No. 20040068207. International Thermal Detectors Workshop (TDW 2003), February 2004, p. 1-12 - 1-15

The Composite Infrared Spectrometer (CIRS) on-board Cassini consists of two interferometers: a conventional Michelson for the mid-infrared; and a Martin-Puplett type in the far-infrared employing wire grid polarizers to split, recombine and analyze the radiation. The far-IR focal plane (FP1) assembly uses two thermopile detectors to measure the final transmitted and reflected beams at the polarizer-analyzer: if one fails, the interferometer can still operate, albeit with a lower efficiency. The combined effect is for good response from 10 to 300/cm, and declining response to 600/cm. This paper will examine in-flight performance of the far-IR interferometer, including NESR and response. Regular noise spikes, resulting from pickup from other electrical sub-systems has been found on the CIRS interferograms, and the removal of these effects is discussed. The radiometric calibration is described, and then we show how the calibration was applied to science data taken during the Jupiter flyby of December 2000. Finally, we discuss signal-to-noise on the calibrated spectra, emphasizing limitations of the current instrument and the potential for improvement in future missions. (Author)

Sittler, EC; Johnson, RE; Jurac, S; Richardson, JD; McGrath, M; Crary, F; Young, DT; Nordholt, JE

Journal of Geophysical Research. A. Space Physics (0148-0227), vol. 109, no. A1, Jan. 2004

Voyager images of the icy satellites of Saturn, Dione and Enceladus, suggest that they may have been geologically active and are not only composed of ice. Recent observations by the Hubble Space Telescope have shown the presence of ozone at both Dione and Rhea, which also implies the presence of molecular oxygen at these bodies. Observations of Ariel, Europa, Ganymede, and Callisto indicate the presence of CO2, so its presence on the Saturnian satellites is also expected. The Cassini Plasma Spectrometer (CAPS) will provide the capability to determine the global composition of these bodies by measuring the pickup ions produced by the ionization of their sputter-produced atmospheres. We will present a model of these atmospheres and associated pickup ions and demonstrate CAPS ability to distinguish the freshly produced picked up ions from the ambient plasma. Such ions are expected to form a ring distribution that will have a uniquely different energy-angle dependence than the ambient plasma ions. In the case of Dione we expect the potential for a moderate strength interaction for which both Voyager 1 and Pioneer 11 spacecraft measured ion cyclotron waves centered on the Dione L shell and near the equatorial plane. SKR radio emissions also displayed emissions occurring at the orbital period of Dione which could indicate some intrinsic activity due to Dione. So again, something interesting may be going on at Dione. Since Enceladus, or material in orbit near Enceladus, may be the source of the E-ring, some surprises may be encountered during its close encounter with the Cassini spacecraft. In the case of Dione we will show that a wake pass at 500 km altitude is more than an order of magnitude better than an upstream pass at 500 km altitude. Pickup ion detection for minor ion species such as NH3(+) is possible for 500 km altitude wake pass but not for 500 km altitude upstream pass at closest approach. For navigation reasons a 100 km pass is not allowed. Therefore it is essential to have a wake pass to maximize the science return for a targeted flyby with Dione. The CAPS observations when combined with magnetometer, plasma wave and energetic particle observations will allow us to estimate the source of ions into Saturn's magnetosphere due to these two bodies and to characterize the nature of the interaction with Saturn's magnetosphere. (Author)

Nixon, C A; Achterberg, R K; Conrath, B J; Irwin, P G J; Fouchet, T; Parrish, P D; Romani, P N; Abbas, M; LeClair, A; Strobel, D

RECON No. 20040081365.

Hydrocarbons such as acetylene (C2H2) and ethane (C2H6) are important tracers in Jupiter's atmosphere, constraining our models of the chemical and dynamical processes. However, our knowledge of the vertical and meridional variations of their abundances has remained sparse. During the flyby of the Cassini spacecraft in December 2000, the Composite Infrared Spectrometer (CIRS) instrument was used to map the spatial variation of emissions from 10-1400 cm(sup -1) (1000-7 microns). In this paper we analyze a zonally-averaged set of CIRS spectra taken at the highest (0.5 cm(sup -1)) resolution, to infer atmospheric temperatures in the stratosphere at 0.5-20 mbar via the v4 band of CH4, and in the troposphere at 150-400 mbar, via the H2 absorption at 600-800 cm(sup -1). Simultaneously, we retrieve the abundances of C2H2 and C2H6 via the v5 and vg bands respectively. Tropospheric absorption and stratospheric emission are highly anti-correlated at the CIRS resolution, introducing a non-uniqueness into the retrievals, such that vertical gradient and column abundance cannot both be found without additional constraints. Assuming profile gradients from photochemical calculations, we show that the column abundance of C2H2 decreases sharply towards the poles by a factor approximately 4, while C2H6 is unchanged in the north and increasing in the south, by a factor approximately 1.8. An explanation for the meridional trends is proposed in terms of a combination of photochemistry and dynamics. Poleward, the decreasing UV flux is predicted to decrease the abundances of C2H2 and C2H6 by factors 2.7 and 3.5 respectively at a latitude 70 deg. However, the lifetime of C2H6 in the stratosphere (5 x 10(exp 9)) is much longer than the dynamical timescale for meridional motions inferred from SL-9 debris (5 x 10(exp 8 s)), and therefore the constant or rising abundance towards high latitudes likely indicates that meridional mixing dominates over photochemical effects. For C2H2, the opposite occurs, with the relatively short photochemical lifetime (3 x 10(exp 7 s)), compared to meridional mixing times, ensuring that the expected photochemical trends are visible. (Author)

Grieger, B; Rodin, AV; Salinas, SV; Keller, HU

Planetary and Space Science (0032-0633), vol. 51, no. 14-15, Dec. 2003, p. 991-1001

In January 2005, the Huygens probe will descent through Titan's atmosphere and the Descent Imager/Spectral Radiometer (DISR) will perform upward and downward looking observations at various spectral ranges and spatial resolutions. One of the subinstruments, the Upward Looking Visible Spectrometer (ULVS), measures the total downward radiation flux including the direct solar beam and also, with a shadow bar over the Sun, the diffuse downward flux. The intensity of the direct solar beam and thus the optical depth can be calculated from the difference of these two measurements. But 10 wide shadow bar also obscures the Solar Aureole Imager (SA) and therefore removes a considerable fraction of the diffuse downward radiation. This fraction can be estimated taking into account the brightness distribution of the SA which is estimated with the Titan Inverse Radiation Model (TIRM). Input to the model are a first guess of the optical depth in dependence on the altitude calculated directly from ULVS measurements and data from another DISR subinstrument, the Solar Aureole Imager SA imager. By assimilating the sparse SA data, TIRM yields a consistent estimate of the scattering phase function and the complete radiance field in dependence on the altitude. By iteratively correcting the initial optical depth estimation using the resultant radiance field and passing it again to TIRM, the model is used to simultaneously solve for optical depths and scattering phase functions. (Author)

Formisano, V; D'Aversa, E; Bellucci, G; Baines, KH; Bibring, JP; Brown, RH; Buratti, BJ; Capaccioni, F; Cerroni, P; Clark, RN

Icarus (0019-1035), vol. 166, no. 1, Nov. 2003, p. 75-84

We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a 'mirror' for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing technique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times. (Author)

Bertotti, B; Iess, L; Tortora, P

Nature (0028-0836), vol. 425, no. 6956, 25 Sept. 2003, p. 374-376

According to general relativity, photons are deflected and delayed by the curvature of space-time produced by any mass (Will, 1993, 2001, 2003; Ciufolini and Wheeler, 1995). The bending and delay are proportional to gamma + 1, where the parameter gamma is unity in general relativity but zero in the Newtonian model of gravity. The quantity gamma - 1 measures the degree to which gravity is not a purely geometric effect and is affected by other fields; such fields may have strongly influenced the early universe, but would have now weakened so as to produce tiny, but still detectable, effects. Several experiments have confirmed to an accuracy of about 0.1 percent the predictions for the deflection (Dyson et al., 1920; Lebach et al., 1995) and delay (Reasenberg et al., 1979) of photons produced by the sun. Here, we report a measurement of the frequency shift of radio photons to and from the Cassini spacecraft as they passed near the sun. Our result, gamma = 1 + (2.1 +/- 2.3) x 10 exp -5, agrees with the predictions of standard general relativity with a sensitivity that approaches the level at which, theoretically, deviations are expected in some cosmological models (Damour and Polyakov, 1994; Damour et al., 1994). (Author)

Altobelli, N; Kempf, S; Landgraf, M; Srama, R; Dikarev, V; Krueger, H; Moragas-Klostermeyer, G; Gruen, E

Journal of Geophysical Research. A. Space Physics (0148-0227), vol. 108, no. A10, Aug. 2003

We report the successful in situ measurement of interstellar dust particles inside the orbit of the Earth with the Cosmic Dust Analyzer (CDA) on the Cassini spacecraft. The impact ionization subsystem of the CDA is similar to the instruments on Ulysses and Galileo. As the heliocentric velocity and the direction of the interstellar dust flux are well known from Ulysses measurements, a combined analysis of the impact charge signals together with geometric and kinematic spacecraft data allowed us to separate interplanetary impacts from interstellar ones. The mean interstellar flux between 0.7 and 1.2 AU derived from our analysis is 2.5 +/- 0.5 u. 10 super -5 m super -2s super -1, in a mass range of 5 u. 10 super -17 kg to 10 super -15 kg which is in good agreement with the interstellar dust flux measured by Ulysses at 3 AU during the same time period . The simultaneous detection of interstellar grains by Ulysses at 3 AU and approximately 1 AU by Cassini proves that big interstellar grains (radius greater than 0.4 micro m), can penetrate deeply into the inner solar system. (Author)

Rodriguez, S; Paillou, P; Dobrijevic, M; Ruffie, G; Coll, P; Bernard, JM; Encrenaz, P

Icarus (0019-1035), vol. 164, no. 1, July 2003, p. 213-227

Simulations of Titan's atmospheric transmission and surface reflectivity have been developed in order to estimate how Titan's atmosphere and surface properties could affect performances of the Cassini radar experiment. In this paper we present a selection of models for Titan's haze, vertical rain distribution, and surface composition implemented in our simulations. We collected dielectric constant values for the Cassini radar wavelength (2.2 cm) for materials of interest for Titan: liquid methane, liquid mixture of methane-ethane, water ice, and light hydrocarbon ices. Due to the lack of permittivity values for Titan's haze particles in the microwave range, we performed dielectric constant (dr) measurements around 2.2 cm on tholins synthesized in laboratory. By combining aerosol distribution models (with hypothetical condensation at low altitudes) to surface models, we find the following results: (1) Aerosol-only atmospheres should cause no loss and are essentially transparent for Cassini radar, as expected by former analysis. (2) However, if clouds are present, some atmospheric models generate significant attenuation that can reach-50 dB, well below the sensitivity threshold of the receiver. In such cases, a 13.78 GHz radar would not be able to measure echoes coming from the surface. We thus warn about possible risks of misinterpretation if a 'wet atmosphere' is not taken into account. (3) Rough surface scattering leads to a typical response of -17 dB. These results will have important implications on future Cassini radar data analysis. (Author)

Lorenz, Ralph D; Biolluz, Gilles; Encrenaz, Pierre; Janssen, Michael A; West, Richard D; Muhleman, Duane O

Planetary and Space Science (0032-0633), vol. 51, no. 4-5, Apr. 2003, p. 353-364

The Radar instrument on the Cassini spacecraft can be used in a passive radiometric mode to map the microwave emission from Titan: these will be the first resolved microwave emission measurements of an icy satellite. Observation plans and the theory for their interpretation is presented: these data should be able to provide crude composition maps of Titan's surface, confirm equator-to-pole temperature gradients without the influence of the atmospheric effects which affect infrared observations and place constraints on surface and subsurface temperature variations. Additionally, passive radiometry will also provide some bistatic reflection measurements, using the sun as a source, which may be used to constrain roughness of ethane seas. (Author)

Abbate, Salvatore F; Armstrong, John W; Asmar, Sami W; Barbinis, Elias; Bertotti, Bruno; Fleischman, Don U; Gatti, Mark S; Goltz, Gene L; Herrera, R G; Iess, L

Gravitational-Wave Detection, Waikoloa, HI, Aug. 23-25, 2002, Bellingham, WA, Society of Photo-Optical Instrumentation Engineers, 2003, p. 90-97

Doppler tracking experiments using the earth and a distant spacecraft as separated test masses have been used for gravitational wave (GW) searches in the low-frequency band(~0.0001-0.1 Hz). The precision microwave tracking link continuously measures the relative dimensionless velocity, Delta v /c, between the earth and the spacecraft. A GW incident of the systems produces a characteristic signature in the data, different from the signatures of the principal noises. For 40 days centered about its solar opposition in December 2001, the Cassini spacecraft was tracked in a search for low-frequncy GWs. Here we describe the GW experiment, including transfer functions of the signals and noises to the Doppler observable, and present noise statistics and compare them with the pre-experiment noise budget. (Author)

Roundhill, I; Roth, D

Spaceflight Mechanics 2003. Vol. 2, Ponce, PR, 9-13 February 2003, San Diego, CA, Univelt, Incorporated, 2003, p. 1391-1406

The Cassini mission will arrive at Saturn in July 2004 to explore the Saturnian system. The navigation team will update the ephemerides of 9 satellites to improve spacecraft navigation and provide information on satellite location for pointing of the spacecraft. This paper outlines the approach used to predict pointing uncertainty when pointing information is generated with a spacecraft prediction and older satellite ephemerides. This modeling is then used to choose times when the satellite ephemerides need to be updated to meet requirements. (Author)

Porco, C C; West, R A; McEwen, A; Del Genio, A D; Ingersoll, A P; Thomas, P; Squyres, S; Dones, L; Murray, C D; Johnson, T V

Science (0036-8075), vol. 299, no. 5612, 7 Mar. 2003, p. 1541-1547

The Cassini Imaging Science Subsystem acquired about 26,000 images of the Jupiter system as the spacecraft encountered the giant planet en route to Saturn. We report findings on Jupiter's zonal winds, convective storms, low-latitude upper troposphere, polar stratosphere, and northern aurora. We also describe previously unseen emissions arising from Io and Europa in eclipse, a giant volcanic plume over Io's north pole, disk-resolved images of the satellite Himalia, circumstantial evidence for a causal relation between the satellites Metis and Adrastea and the main jovian ring, and information on the nature of the ring particles. (Author)

Grieger, B; Lemmon, M T; Markiewicz, W J; Keller, H U

Planetary and Space Science (0032-0633), vol. 51, no. 2, Feb. 193, p. 147-158

During the descent of the Huygens probe through Titan's atmosphere in January 2005, the Descent Imager/Spectral Radiometer (DISR) will perform upward and downward looking measurements at various spectral ranges and spatial resolutions. This internal radiation density could be estimated by radiative transfer calculations for Titan's atmosphere. However, to do this, the optical properties, i.e. volume extinction coefficient, single scattering albedo and scattering phase function - have to be prescribed at every altitude, and these are apriori not known. Herein, an inverse approach is investigated, which retrieves the single scattering albedo and the phase function of the aerosols from DISR observations. The method uses data from a DISR subinstrument, the Solar Aureole imager (SA), to estimate the optical properties of the atmospheric layer between two successive observation altitudes. A unique solution for one layer can in principle be calculated directly from a linear system of equations, but due to the sparseness of the data and the unavoidable noise in the measurements, the inverse problem is ill-posed. The problem is stabilized by the regularization method requiring smoothness of the resultant solution. A consistent set of solutions for all layers is obtained by iterating several times downward and upward through the layers. The method is tested in a simulated radiation density scenario for Titan, which is based on a microphysical aerosol model for the haze layer. Within this scenario, the expected coverage of SA data allows a reconstruction of the angular dependence of the scattering phase function with an explained variance better than 90 pct. (Author)

Mitchell, Robert T

54th International Astronautical Congress of the International Astronautical Federation (IAF), Bremen, Germany, Sep. 29 - Oct. 3, 2003

The Cassini/Huygens mission to Saturn is a joint endeavor by NASA, the European Space Agency, and the Italian Space Agency to conduct an extensive investigation of Saturn, its atmosphere, rings, satellites, and magnetosphere. The spacecraft was launched in October, 1997, and has completed six years of its almost seven year journey to Saturn with nearly flawless performance. On July 1, 2004, it will arrive at Saturn and begin a four-year orbital mission, releasing the Huygens probe in December 2004 to enter the atmosphere of Titan, Saturns largest moon, in January 2005. This paper provides an overview of the mission but focuses primarily on the activities over the past year in preparation for Saturn arrival and beginning the scientific observations to be made in orbit. Details are provided on the completion, validation, and uplink of new on-board flight software, development and testing of the sequences to be used for orbit insertion and relay of the data stream from the Huygens probe as it descends through the atmosphere of Titan, and design and preparation of the science sequences to be performed by the Orbiter. The past year has been a very productive one for the Cassini/Huygens team and, although much remains to be done before arrival, the work is on schedule, the team is highly motivated and performing well, and is looking forward to an exciting and productive mission. (Author)

Tortora, P; Iess, L; Bordi, J J; Ekelund, J E; Roth, D

Advances in the Astronautical Sciences. Vol. 114, Suppl.:Spaceflight Mechanics 2003, pp. 18. 2003

The Cassini spacecraft and its ground segment are currently testing a novel radio frequency multilink technology to perform radio science experiments. During solar conjunctions, this allows the complete removal of the solar plasma noise from the Doppler observables, with benefits also for deep space navigation. This is obtained combining the carrier frequencies of three independent down-links: two of them, a X- and a Ka-band (Kal), are coherent with a X-band up-link, while an additional Ka-band down-link (Ka2), is coherent with a Ka-band up-link. During the June-July 2002 Cassini solar conjunction, this procedure was fully tested for the first time. We show that, using the adopted multifrequency plasma calibration scheme, the standard deviation of the Doppler frequency residuals is reduced up to a factor of 200 over the uncalibrated X-band data. This large improvement in the data quality, revealed by values of the frequency stability previously achieved only during solar oppositions, makes the navigation accuracy of deep space probes nearly independent of the solar elongation angle.

Morabito, D D; Shambayati, S; Finley, S; Fort, D

IEEE Transactions on Antennas and Propagation. Vol. 51, no. 2, pp. 201-219. Feb. 2003

Interplanetary spacecraft, which fly in the ecliptic plane, typically encounter solar conjunctions during their main missions. The communications link between an interplanetary spacecraft and Earth is affected by the charged particles that constitute the intervening solar corona and solar wind. As the Sun-Earth-probe (SEP) angle becomes small (usually < 3 deg for X band or 8.43 GHz), the signal suffers increased degradation. The effects on the received signal include time delay and phase fluctuations due to the fluctuating columnar electron density, which in turn cause carrier lock problems and telemetry data loss. Because of these effects, studies of solar corona charged particle effects on spacecraft signals were conducted to determine strategies for optimizing data return during these periods. The first solar conjunction of the Cassini spacecraft occurred between May 8, 2000 (2000/129) and May 18, 2000 (2000/139). During this period, the Cassini spacecraft was within 3.2 deg of the Sun as seen from Earth with the minimum SEP angle of 0.56 deg occurring on May 13 (2000/134). This solar conjunction occurred prior to the expected peak of the current solar cycle. Coherent dual-frequency X band (8.43 GHz) and Ka band (32 GHz) data were acquired from 3.2 deg to near the minimum SEP angle at 0.6 deg for both ingress and egress. The measurements of amplitude scintillation, spectral broadening and phase scintillation were examined as a function of SEP angle. As expected, these solar effects are significantly less at Ka band than at X band for the same SEP angle. This studys results will be combined with those of other spacecraft solar conjunctions in order to build a statistical database of solar effects as a function of solar elongation angle and phase of the solar cycle. Such studies are useful in the design of telecommunications systems for future spacecraft missions, which may have stringent communication requirements during their solar conjunction phases. (Author)

Bellucci, G; Brown, R H; Formisano, V; Baines, K H; Bibring, J P; Buratti, B J; Capaccioni, F; Cerroni, P; Clark, R N; Coradini, A

Advances in Space Research. Vol. 30, no. 8, pp. 1889-1894. Oct. 2002

We present preliminary scientific results obtained from the analysis of VIMS (Visible and Infrared Mapping Spectrometer) lunar images and spectra. These data were obtained during the Cassini Earth flyby in August 1999. Spectral ratios have been produced in order to derive lunar mineralogical maps. Some spectra observed at the north-east lunar limb show few unusual absorption features located at 0.357, 0.430 and 0.452 micron, the origin of which is presently unknown. (Author)

Lopez-Moreno, J J; Molina-Cuberos, G J; Hamelin, M; Brown, V J G; Ferri, F; Grard, R; Jernej, I; Jeronimo, J M; Leppelmeier, G W; Makinen, T

Advances in Space Research. Vol. 30, no. 5, pp. 1359-1364. Sept. 2002

The HUYGENS Atmospheric Structure Instrument (HASI) was designed to characterize the atmosphere of Titan during the descent of the HUYGENS probe in the framework of the NASA/ESA CASSINI/HUYGENS mission in November 2004. A balloon campaign was conducted in Leon, Spain, in December 1995, in order to test the HASI hardware and software in the terrestrial atmosphere and investigate the influence of the HUYGENS probe on the electrical measurements in a real environment. The subsystems from the HASI instrument, the Pressure Profile, the Accelerometer, the Temperature Profile and the Permittivity, Wave and Altimetry packages with their corresponding sensors, were accommodated on a HUYGENS 1:1 mock-up and launched by a stratospheric balloon crossing a distance of 340 km and reaching a maximum altitude of around 30 km. The Huygens mission at Titan was simulated by a drop test; the probe was separated from the balloon in order to descend to ground dragged by a parachute. Measurements have been performed both in the ascending and descending phases. (Author)

Goldsworthy, B J; Burchell, M J; Cole, M J; Green, S F; Leese, M R; McBride, N; McDonnell, J A M; Mueller, M; Gruen, E; Srama, R; Armes, S P; Khan, M A

Advances in Space Research. Vol. 29, no. 8, pp. 1139-1144. Apr. 2002

The Cassini Cosmic Dust Analyzer (CDA), developed from the Galileo and Ulysses dust instruments with the addition of a Chemical Analyzer, is currently traveling outward from the Earth (collecting data from March 1999 onward) to the Saturnian system (arrival 2004) via Jupiter. The Chemical Analyzer will provide information on the elemental composition of impacting micrometeoroids through impact ionization time-of-flight mass spectrometry. A rigorous calibration program primarily focused upon the Chemical Analyzer is in progress at the University of Kent at Canterbury. A 2-MV Van de Graaff electrostatic accelerator and CDA laboratory model are used to simulate impacts. Acceleration of revolutionary low-density polymer dust particles has enabled an insight into the response of CDA to molecularly bonded material with increasing event velocity. These conducting polymer-coated polystyrene latex particles represent significantly better analogs for carbonaceous cosmic grains than more traditionally accelerated projectiles (e.g., iron) and have enabled complex organic spectra to be produced in the laboratory. The current status of an ongoing program is reported. Three samples are presented, two polypyrrole coated latexes of differing size and one PEDOT-coated latex sample. (Author)

Bird, M K; Dutta-Roy, R; Heyl, M; Allison, M; Asmar, S W; Folkner, W M; Preston, R A; Atkinson, D H; Edenhofer, P; Plettemeier, D

Space Science Reviews. Vol. 104, no. 1-4, pp. 613-640. 2002

A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m/s from the start of mission at an altitude of about 160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed. (Author)

Clausen, K C; Hassan, H; Verdant, M; Couzin, P; Huttin, G; Brisson, M; Sollazzo, C; Lebreton, J P

Space Science Reviews. Vol. 104, no. 1-4, pp. 155-189. 2002

This paper presents a technical description of the elements of the Huygens Probe System. The early in-flight performance of the Probe is briefly discussed. During in-flight testing in 2000, a technical anomaly was found with the Probe-to-Orbiter telecommunication system that required a change in the Huygens mission scenario designed before launch. It also required a change in the Orbiter trajectory during the Probe mission. This change was achieved by modifying the initial Cassini/Huygens orbits around Saturn. (Author)

Cuzzi, J N; Colwell, J E; Esposito, L W; Porco, C C; Murray, C D; Nicholson, P D; Spilker, L J; Marouf, E A; French, R C; Rappaport, N; Muhleman, D

Space Science Reviews. Vol. 104, no. 1-4, pp. 209-251. 2002

Theoretical and observational progress in studies of Saturn's ring system since the mid-1980s is reviewed, focusing on advances in configuration and dynamics, composition and size distribution, dust and meteoroids, interactions of the rings with the planet and the magnetosphere, and relationships between the rings and various satellites. The Cassini instrument suite of greatest relevance to ring studies is also summarized, emphasizing how the individual instruments might work together to solve outstanding problems. The Cassini tour is described from the standpoint of ring studies, and major ring science goals are summarized. (Author)

Fulchignoni, M; Ferri, F; Angrilli, F; Bar-Nun, A; Barucci, M A; Bianchini, G; Borucki, W; Coradini, M; Coustenis, A; Falkner, P

Space Science Reviews. Vol. 104, no. 1-4, pp. 395-431. 2002

The Huygens Atmospheric Structure Instrument (HASI) is a multi sensor package designed to measure the physical quantities characterizing the atmosphere of Titan during the Huygens probe descent on Titan and at the surface. HASI sensors are devoted to the study of Titan's atmospheric structure and electric properties, and to provide information on its surface, whether solid or liquid. (Author)

Henry, C A

Space Science Reviews. Vol. 104, no. 1-4, pp. 129-153. 2002

In October of 1997 NASA launched its largest interplanetary spacecraft to date. The Cassini spacecraft will arrive at Saturn in July 2004 and begin a four year tour of that planetary system. After the spacecraft arrives it will separate into an orbiter and a probe. The Huygens Probe, developed by the European Space Agency, will follow a ballistic trajectory into the atmosphere of the moon Titan. The orbiter will relay signals received from the probe back to Earth and then begin the tour. This article provides an introduction to the design of the Cassini spacecraft. The major engineering functions of mechanical configuration, power generation and distribution, telecommunications, information system, pointing and course correction, and some other miscellaneous design features are discussed. A description of the engineering elements of the Huygens Probe is also provided. (Author)

Lebreton, J P; Matson, D L

Space Science Reviews. Vol. 104, no. 1-4, pp. 59-100. 2002

Huygens is an entry probe designed to descend under parachute through the atmosphere of Titan, Saturn's largest moon, down to the surface. The main Huygens science mission phase occurs during the 2-2.5 h parachute descent. Measurements will also be conducted during the 3 min entry and possibly tip to about one hour on the surface if Huygens survives the landing impact. The Probe's payload comprises six instruments. The Huygens Probe is provided by the ESA for the joint NASA/ESA Cassini/Huygens mission to Saturn and Titan. This paper provides an overview of the Huygens mission and a concise description of the payload as an introduction to the papers which describe the Huygens investigations in this volume. (Author)

Lunine, J I; Soderblom, L A

Space Science Reviews. Vol. 104, no. 1-4, pp. 191-208. 2002

The Saturnian system contains 18 known satellites ranging from 10 km to 2575 km in radius. In bulk properties and surface appearance these objects show less regularity than the sparser Jupiter system. The Galilean-sized moon Titan sports a dense atmosphere of nitrogen and methane which renders surface observations difficult, but also makes this moon intriguing from the standpoints of climate change and exobiology. The Cassini-Huygens mission will make extensive observations of the satellites over a range of wavelengths, as well as using in situ sampling of satellite environments (and in the case of Titan, sampling of atmosphere and surface). The goals of these extensive investigations are to understand the bulk properties of the satellites, their surface compositions and evolution through time, as well as interactions with the magnetosphere and rings of Saturn. This knowledge in turn should provide a deeper understanding of the origin of the Saturnian system as a whole and the underlying causes for the distinctive differences from the Jovian satellite system. (Author)

Matson, D L; Spilker, L J; Lebreton, J P

Space Science Reviews. Vol. 104, no. 1-4, pp. 1-58. 2002

The international Cassini/Huygens mission consists of the Cassini Saturn Orbiter spacecraft and the Huygens Titan Probe that is targeted for entry into the atmosphere of Saturn's largest moon, Titan. From launch on October 15, 1997, to arrival at Saturn in July 2004, Cassini/Huygens will travel over three billion kilometers. Once in orbit about Saturn, Huygens is released from the orbiter and enters Titan's atmosphere. The Probe descends by parachute and measures the properties of the atmosphere. If the landing is gentle, the properties of the surface will be measured too. Then the orbiter commences a four-year tour of the Saturnian system with 45 flybys of Titan and multiple encounters with the icy moons. The rings, the magnetosphere and Saturn itself are all studied as well as the interactions among them. (Author)

Niemann, H B; Atreya, S K; Bauer, S J; Biemann, K; Block, B; Carignan, G R; Donahue, T M; Frost, R L; Gautier, D; Haberman, J A

Space Science Reviews. Vol. 104, no. 1-4, pp. 553-591. 2002

The Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens Probe will measure the chemical composition of Titan's atmosphere from 170 km altitude (about 1 hPa) to the surface (and 1500 hPa) and determine the isotope ratios of the major gaseous constituents. The GCMS will also analyze gas samples from the Aerosol Collector Pyrolyzed (ACP) and may be able to investigate the composition (including isotope ratios) of several candidate surface materials. The GCMS is a quadrupole mass filter with a secondary electron multiplier detection system and a gas sampling system providing continuous direct atmospheric composition measurements and batch sampling through three gas chromatographic (GC) columns. The mass spectrometer employs five ion sources sequentially feeding the mass analyzer. Three ion sources serve as detectors for the GC columns and two are dedicated to direct atmosphere sampling and ACP gas sampling, respectively. The instrument is also equipped with a chemical scrubber cell for noble gas analysis and a sample enrichment cell for selective measurement of high boiling point carbon containing constituents. The mass range is 2 to 141 Dalton and the nominal detection threshold is at a mixing ratio of 10 exp -8. The data rate available from the Probe system is 885 bit/s. The weight of the instrument is 17.3 kg and the energy required for warm up and 150 minutes of operation is 110 Watt-hours. (Author)

Israel, G; Cabane, M; Brun, J F; Niemann, H; Way, S; Riedler, W; Steller, M; Raulin, F; Coscia, D

Space Science Reviews. Vol. 104, no. 1-4, pp. 433-468. 2002

ACP's main objective is the chemical analysis of the aerosols in Titan's atmosphere. For this purpose, it will sample the aerosols during descent and prepare the collected matter (by evaporation, pyrolysis and gas products transfer) for analysis by the Huygens Gas Chromatograph Mass Spectrometer (GCMS). A sampling system is required for sampling the aerosols in the 135-32 km and 22-17 km altitude regions of Titan's atmosphere. A pump unit is used to force the gas flow through a filter. In its sampling position, the filter front face extends a few mm beyond the inlet tube. The oven is a pyrolysis furnace where a heating element can heat the filter and hence the sampled aerosols to 250 or 600 C. The oven contains the filter, which has a thimble-like shape (height 28 mm). For transferring effluent gas and pyrolysis products to GCMS, the carrier gas is labeled nitrogen 15N2, to avoid unwanted secondary reactions with Titan's atmospheric nitrogen. Aeraulic tests under cold temperature conditions were conducted using a cold gas test system developed by ONERA. The objective of the test was to demonstrate the functional ability of the instrument during the descent of the probe and to understand its thermal behavior, that is, to test the performance of all its components, pump unit and mechanisms. In order to validate ACP's scientific performance, pyrolysis tests were conducted at LISA on solid phase material synthesized from experimental simulation. The chromatogram obtained by GCMS analysis shows many organic compounds. Some GC peaks appear clearly from the total mass spectra, with specific ions well identified thanks to the very high sensitivity of the mass spectrometer. The program selected for calibrating the flight model is directly linked to the GCMS calibration plan. (Author)

Tomasko, M G; Buchhauser, D; Bushroe, M; Dafoe, L E; Doose, L R; Eibl, A; Fellows, C; McFarlane, E; Prout, G M; Pringle, M J

Space Science Reviews. Vol. 104, no. 1-4, pp. 469-551. 2002

The payload of the Huygens Probe into the atmosphere of Titan includes the Descent Imager/Spectral Radiometer (DISR). This instrument includes an integrated package of several optical instruments built around a silicon CCD detector, a pair of linear InGaAs array detectors, and several individual silicon detectors. The scientific objectives are (1) measurement of the solar heating profile for studies of the thermal balance of Titan; (2) imaging and spectral reflection measurements of the surface for studies of the composition, topography, and physical processes which form the surface as well as for direct measurements of the wind profile during the descent; (3) measurements of the brightness and degree of linear polarization of scattered sunlight including the solar aureole together with measurements of the extinction optical depth of the aerosols as a function of wavelength and altitude to study the size, shape, vertical distribution, optical properties, sources and sinks of aerosols in Titan's atmosphere; and (4) measurements of the spectrum of downward solar flux to study the composition of the atmosphere, especially the mixing ratio profile of methane throughout the descent. We briefly outline the methods by which the flight instrument was calibrated, relative spectral response, and field of view over a very wide temperature range. The extinction optical depths measured as a function of wavelength are compared to models of the Earth's atmosphere and are divided into contributions from molecular scattering, aerosol extinction, and molecular absorption. The test observations during simulated descents with mountain and rooftop venues in the Earth's atmosphere are very important for solving problems in the calibration and interpretation of the observations to permit rapid analysis of the observations after Titan entry. (Author)

Zarnecki, J C; Leese, M R; Garry, J R C; Ghafoor, N; Hathi, B

Space Science Reviews. Vol. 104, no. 1-4, pp. 593-611. 2002

The design and performance of the Surface Science Package (SSP) on the Huygens probe are discussed. This instrument consists of nine separate sensors that are designed to measure a wide range of physical properties of Titan's lower atmosphere, surface, and sub-surface. By measuring a number of physical properties of the surface, it is expected that the SSP will be able to constrain the inferred composition and structure of the moon's near-surface environment. Although the SSP is primarily designed to sense properties of the surface, some of its sensors will also make measurements of the atmosphere along the probe's entry path and will complement the data gathered by other experiments on the Huygens probe. (Author)

Blanc, M; Bolton, S; Bradley, J; Burton, M; Cravens, T E; Dandouras, I; Dougherty, M K; Festou, M C; Feynman, J; Johnson, R E

Space Science Reviews (0038-6308), vol. 104, no. 1-4, p. 253-346

Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres. These are an 'induced' magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's 'intrinsic' magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific questions concerning the interaction of these two magnetospheres with their environment. The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity and wake, which we call an 'induced magnetosphere'. The Mach number characteristics of this interaction make it unique in the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic field of Titan. Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards, we first describe the region of the main rings and their connection to the low-latitude ionosphere. Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible to address, and hopefully solve, many of these questions. (Author)

Castillo, J; Rappaport, N; Mocquet, A; Sotin, C

Lunar and Planetary Science XXXIII, Houston, TX, Mar.11-15,2002, Houston, TX, Lunar and Planetary Institute, 2002

The authors examine which aspects of Titan's internal structure will be derived from gravity potential measurements by Cassini-Huygens. For that purpose, dynamic Love numbers are computed for various models of the satellite. (Author)

Kazeminejad, B; Lebreton, J-P; Bird, MK; Atkinson, DH

Earth-Like Planets and Moons; Proceedings of the 36th ESLAB Symposium, Noordwijk, Netherlands, June 3-8, 2002, Noordwijk, Netherlands, European Space Agency, 2002, p. 191-199

The Huygens Probe is the ESA-provided element of the joint NASA /ESA Cassini/Huygens mission to Saturn and Titan. The Cassini /Huygens spacecraft was launched on 15 October 1997 and will arrive at Saturn on the 1 July 2004. The Huygens probe will be released on 24 December 2004 and enter the atmosphere of Titan on 14 January 2005. A recently discovered design flaw in the Huygens radio receiver onboard Cassini led to a significant redesign of the mission geometry by both the Huygens and Cassini project teams. In this new scenario the Orbiter will pass Titan at high altitude (i.e., 60,000 km) on the retrograde side of Titan and will trail the Probe by only about 2.1 hours instead of the originally planned 1250 km flyby altitude on the prograde side of Titan and a 4 hour delay time. Among the factors governing the duration and quality of the Cassini/Huygens communication window during the descent is the Probe drift caused by zonal winds. Existing Titan wind models have been reevaluated and compared to recent ground-based observations. Simulations of the Probe entry and descent show a drift from about 300 km up to about 430 km away from the "no wind" landing point, depending on the wind model. At the end of the nominal mission this difference in wind drift (assuming prograde winds) causes a difference of up to 1.7 dB (within a margin of 3 to 4 dB, resulting from the receiver design flaw) in the received SNR. The high sensitivity of the received signal strength to zonal winds and their directions is due to the steep decrease of the Probe antenna gain when the Cassini spacecraft (with the Huygens receiver) as seen from the Probe moves to increasingly higher elevation angles. A simulation of the Probe atmospheric entry phase shows that the zonal wind direction also impacts the shape of the deceleration profile and its peak value. (Author)

Macala, G A

Spaceflight Mechanics 2002; Proceedings of the AAS/AIAA Space Flight Mechanics Meeting. Vol. 1, San Antonio, TX, Jan. 27-30, 2002, San Diego, CA, Univelt, Incorporated, 2002, p. 303-315

This paper presents the architecture and methodology used for the design of the Cassini spacecraft's Reaction Wheel Attitude Controller. Simulation results are presented that predict the pointing performance. Preliminary in-flight pointing performance results are also presented. (Author)

Musso, Ivane; Cardillo, Andrea; Casentino, Orazio

Twenty-Third International Symposium on Space Technology and Science, Matsue, Japan, May 23 - June 2, 2002, Tokyo, Japan, Japan Society for Aeronautical and Space Sciences, 2002, p. 2014-2019

The HASI (Huygens Atmospheric Structure Instrument) is one of the six experiments on board the Huygens probe. It will be released in 2004 by the Cassini mission, started on October 1997, to descend onto Titan, the major moon of Saturn. During the 2001 summer campaign, in the Italian Space Agency's (ASI) "Luigi Broglio" Base in Trapani Milo, a balloon-borne test of this system was made. In this paper the strategy to manage this balloon flight and the strategy that is planned to be used for the second flight during the 2002 campaign are presented. Six hours before the launch, using sounding data, or two days before the launch, using forecast information, a simulation of the flight is made. The ascent trajectory is obtained, taking into account the possible errors of the wind status information and the possible starting free lift variation. A "predicted impact area" is evaluated, and some "preferable impact point" can be designated. An ascending phase control strategy can be planned, taking into account its effects on the recovery phase and, when possible, driving the balloon into a particular recovery area. In order to avoid signal losses of telemetry, housekeeping the position of a mobile TLM/TLC unit is evaluated using the predicted trajectory. (Author)

Antonello, M; Masi, M; Fulchignomi, M; Angrilli, F

4th European Symposium on Aerothermodynamics for Space Vehicles, Capua, Italy, Oct. 15-18, 2001, Noordwijk, Netherlands, European Space Agency, 2002, p. 545-552

The turbulent flow around the Huygens probe is characterized by effects such as flows curvature and separation that introduce changes in the turbulence structure, thus invalidating many of the turbulence models widely used for "simple shear flows." In this work the predictions of the standard k-epsilon model, and the Shih et al. (1993) model are compared with an algebraic model developed by the present authors. This algebraic stress model is a way of accounting for the anisotropy of Reynolds stresses without going to the full length of solving the Reynolds stress transport equations. The aim is to establish which models better evaluate the flow around the Huygens probe during the descent phase. The predictions of the axial force coefficient supplied by the model presented below correlate with the experimental data better than the standard k-epsilon model and the Shih et al. model. (Author)

Chang, Y; O'Neil, J M; McGrath, B E; Heyler, G A; Brenza, P T

Space Technology and Applications International Forum - STAIF 2002; Proceedings; Conference on Thermophysics in Microgravity; Conference on Innovative Transportation Systems for Exploration of the Solar System and Beyond; 19th Symposium on Space Nuclear Power and Propulsion; Conference on Commercial/Civil Next Generation Space Transportation, Albuquerque, NM; 3-6 Feb. 2002. pp. 732-739. 2002

On 15 October 1997 at 4:43 AM EDT, the Cassini spacecraft was successfully launched on a Titan IVB/Centaur on a mission to explore the Saturnian system. It carried three Radioisotope Thermoelectric Generators (RTGs) and 117 Light Weight Radioisotope Heater Units (LWRHUs). As part of the joint National Aeronautics and Space Administration (NASA)/U.S. Department of Energy (DoE) safety effort, a contingency plan was prepared to address the unlikely events of an accidental suborbital reentry or out-of-orbital reentry. The objective of the plan was to develop procedures to predict, within hours, the Earth impact footprints (EIFs) for the nuclear heat sources released during the atmospheric reentry. The footprint predictions would be used in subsequent notification and recovery efforts. As part of a multi-agency team, The Johns Hopkins University Applied Physics Laboratory (JHU/APL) had the responsibility to predict the EIFs of the heat sources after a reentry, given the heat sources' release conditions from the main spacecraft. JHU/APL's other role was to predict the time of reentry from a potential orbital decay. The tools used were a three degree-of-freedom trajectory code, a database of aerodynamic coefficients for the heat sources, secure links to obtain tracking data, and a high fidelity special perturbation orbit integrator code to predict time of spacecraft reentry from orbital decay. In the weeks and days prior to launch, all the codes and procedures were exercised. Notional EIFs were derived from hypothetical reentry conditions. EIFs predicted by JHU/APL were compared to those by JPL and US SPACECOM, and were found to be in good agreement. The Cassini launch contingency effort contributed to mission safety and demonstrated successful cooperation between several agencies. (Author)

Deutsch, L J

2002 IEEE Aerospace Conference Proceedings - Volume 3, Big Sky, MT; 9-16 Mar. 2002. pp. 3-1295 to 3-1302. 2002

NASA's Cassini mission to Saturn carries the European Space Agency's (ESA's) Huygens probe, which it will release shortly before an encounter with Saturn's moon, Titan, a possible location for extraterrestrial life within our Solar System. As it parachutes towards Titan's surface, Huygens will acquire scientific information that will be relayed to Earth through Cassini. Comprehensive testing of this relay radio link was not performed prior to Cassini launch and cannot be done during cruise. A test using NASA's Deep Space Network (DSN) to mimic the probe's signal was performed in 2000 and uncovered an anomaly that, unchecked, would result in nearly complete loss of the Huygens mission. An international team of experts from NASA and ESA was assembled to solve this problem: the Huygens Recovery Task Force (HRTF.) This team, cochaired by the author, performed extensive testing, modeling, and simulation to understand the failure mechanism. Each Huygens science team determined mission impacts for various scenarios based on these results. This led to a suggested modification to the Cassini trajectory that will result in nearly complete data return for Huygens with minimal impact on Cassini. (Author)

Strange, N J; Goodson, T D; Hahn, Y

AIAA/AAS Astrodynamics Specialist Conference and Exhibit, Monterey, CA, Aug. 5-8, 2002

The Cassini spacecraft will arrive at Saturn in 2004, carrying the Huygens probe, which will descend into the atmosphere of Saturn's moon Titan. The beginning of the Cassini tour has been redesigned in order to compensate for the probe relay receiver problem that was discovered during tests in February 2000. An extra 32-day orbit has been inserted at the beginning of the tour, and the orbiter altitude has been increased during the probe delivery flyby. This paper details the changes to the tour. (Author)

Molina-Cuberos, G J; Lopez-Moreno, J J; Rodrigo, R; Schwingenschuh, K

Advances in Space Research. Vol. 28, no. 10, pp. 1511-1516. Nov. 2001

The penetration of the Huygens probe through the atmosphere of Titan in 2004 will provide a unique opportunity to measure the electrical properties of its lower atmosphere. Many studies have been carried out to predict the density of electrons and the distribution of the major positive ions, but there is no recent analysis concerning the electrical conductivity that will be measured by Huygens. In this paper we present predictions of negative and positive conductivity by using the present models of the lower ionosphere. The predicted conductivity is delimited between a minimum and a maximum profile and compared with the capability of the PWA-HASI instrument on board Huygens to measure it. Special attention is paid to the influence of electrophilic species on the conductivity and on the decrease of the negative conductivity depending on the concentration of electrophilic species. We present an analytic expression to calculate the concentration of electrophilic species, if any, depending on the measurements of positive and negative conductivity that will measure PWA-HASI. (Author)

Cravens, TE; Vann, J; Clark, J; Yu, J; Keller, CN; Brull, C

Advances in Space Research (0273-1177), vol. 33, no. 2, p. 212-215

Titan has an atmosphere consisting mainly of molecular nitrogen and methane. Solar extreme ultraviolet and X-ray radiation and energetic electrons from Saturn's magnetosphere interact with the upper atmosphere producing an ionosphere. This paper describes improvements to earlier models of Titan's ionosphere. In particular, we consider in more detail ion production from solar ionizing radiation for solar zenith angles beyond the terminator, and a higher spectral resolution soft X-ray flux is adopted in the ion production rate calculations. We demonstrate that significant photoionization takes place well beyond the terminator. K-shell photoionization is also included, and this process adds Auger electrons to the ionospheric photoelectron spectrum, which we model using the two-stream transport code. Our calculated photoelectron spectrum shows a distinct Auger electron peak near an energy of 400 eV. (Author)

Ledvina, SA; Luhmann, JG; Cravens, TE

Advances in Space Research (0273-1177), vol. 33, no. 2, p. 221-226

The interaction of Titan's ionosphere with the Saturn's magnetospheric plasma was found to be subsonic, superAlfvenic and submagnetosonic. However, the plasma conditions along Titan's orbit are highly variable resulting in a wide range of possible Mach numbers for the interaction. We consider the effect Titan would have on the ambient (or magnetospheric) ion population during a supermagnetosonic interaction, which might occur in the outer magnetosphere. The trajectories of several thousand ions in the vicinity of Titan are calculated using the fields from the output of a three-dimensional MHD model of Titan's plasma interaction. We have simulated the Voyager Plasma Spectrometer (PLS) response to the ambient ions using the determined ion trajectories. These results are compared with the Voyager distribution functions in order to illustrate how upstream conditions might affect the observed distributions, as will likely be observed during the Cassini mission Titan flybys. (Author)

Fischer, G; Tokano, T; Macher, W; Lammer, H; Rucker, HO

Planetary and Space Science (0032-0633), vol. 52, no. 5-6, Apr. 2004, p. 447-458

The search for lightning on Saturn's satellite Titan is one scientific target of the Cassini/Huygens mission. Although Voyager 1 did not detect any radio emissions caused by Titan lightning during its flyby in November 1980, one cannot generally rule out their existence, because of low flash rates or ionospheric radiation blockade. Recently, Tokano et al. (Planet. Space Sci. 49 (2001a) 539) have developed a thundercloud model in Titan's troposphere favoring the existence of Titan lightning due to negatively charged clouds causing temporary electric fields sufficient to initiate cloud-to-ground lightning strokes. In the present investigation we estimate the amount of energy dissipation of such lightning strokes by electrostatic energy considerations similarly to those by Cooray (J. Geophys. Res. 102(D17) (1997) 21, 401). The analysis is based on the cloud charge distribution given by Tokano et al. (2001a), which has a monopole structure or a dipole structure depending on the electrification mechanism. It consists of horizontally homogenous charge layers, whose charge densities depend on the altitude above ground. As results we get the typical charge lowered in a possible Titan lightning stroke and the amount of energy dissipation. For a simulated Titan monopolar cloud charged by electron attachment we found that cloud-to-ground strokes lower about 30 C of charge and dissipate energies about 10 super 10 J. For the modelled bipolar clouds charged by collisional charging these values are a few C of lowered charge and about 10 super 8-10 super 9J of dissipated energy, which are quite similar to typical Earth values. These energies are substantially higher than the energies suggested by Desch and Kaiser (Nature 343 (1990) 442), who concluded from the Voyager data that discharges might be frequent but weak (<10 super 6J). We shortly discuss the detection capability of the Cassini/RPWS (Radio and Plasma Wave Science experiment) for possible Titan lightning strokes taking into account the wave attenuation in the frequency range up to 16 MHz during the propagation through Titan's ionosphere as calculated by Schwingenschuh et al. (Adv. Space Res. 28(10) (2001) 1505). (Author)

Clark, P E; Curtis, S A; Rilee, M L; Cheung, C

RECON No. 20040062010.

The Saturn Autonomous Ring Array (SARA) mission concept is a new application for the Autonomous Nano-Technology Swarm (ANTS) architecture, a paradigm being developed for exploration of high surface area and/or multibody targets to minimize costs and maximize effectiveness of survey operations. Systems designed with ANTS architecture are built from potentially very large numbers of highly autonomous, yet socially interactive, specialists, in approximately ten specialist classes. Here, we analyze requirements for such a mission as well as specialized autonomous operations which would support this application. (Author)

Bernard, J-M; Coll, P; Coustenis, A; Raulin, F

Planetary and Space Science (0032-0633), vol. 51, no. 14-15, Dec. 2003, p. 1003-1011

For several years now, an experimental simulation of Titan's atmosphere has been on going at LISA. A cold plasma is established in a gas mixture representative of the atmosphere of the satellite. In these experiments, more than 70 organic compounds have been identified, including the first identification in this type of experimental simulation of C sub 4N sub 2 already detected in its solid form on Titan, which suggests that the setup correctly mimics the chemistry of Titan's atmosphere. We have carried out the first experimental simulation including O-containing compounds in order to study the influence of the presence of CO on the chemical behavior of Titan's atmosphere. With the help of gas chromatography-mass spectrometry (GC-MS) and infrared spectroscopy (IRS) we can thus determine which minor species still undetected in Titan's atmosphere are likely to be present and understand the complex chemistry of the atmosphere of this satellite. Surprisingly we have identified unpredicted O-containing gaseous compounds, mainly ethylene oxide (also named oxirane, C sub 2H sub 4O). This molecule has been observed in the interstellar medium by observation in the millimeter region (Astrophys. J. 489 (1997) 553; Astron. Astrophys. 337 (1998) 275). On the contrary, the predicted O-compounds (formaldehyde and methanol) have not been identified in this experiment. Furthermore, we have identified NH sub 3 in the gaseous products with an initial mixture of N sub 2 (98 percent) and CH sub 4 (2 percent). The paper describes the experimental device used in this work, in particular the IRS and GC-MS techniques. We also comment the results related to the detection of the O-containing compounds and NH sub 3 and their implications on our knowledge of the chemistry of Titan's atmosphere and on the retrieval of the future Titan data expected from Cassini- Huygens. (Author)

Campbell, DB; Black, GJ; Carter, LM; Ostro, SJ

Science (Washington) (0036-8075), vol. 301, no. 5644, 17 Oct. 2003, p. 431-434

Arecibo radar observations of Titan at 13-centimeter wavelength indicate that most of the echo power is in a diffusely scattered component but that a small specular component is present for about 75 percent of the subearth locations observed. These specular echoes have properties consistent with those expected for areas of liquid hydrocarbons. Knowledge of the areal extent and depth of any deposits of liquid hydrocarbons could strongly constrain the history of Titan's atmosphere and surface. (Author)

Jatvis, K S; Vilas, F; Larson, S M; Gaffey, M J; Dominique, D

Lunar and planetary science XXIX; Proceedings of the 29th Lunar and Planetary Science Conference, Houston, TX; 16-20 Mar. 1998. 1998

Theories for the dichotomous nature of Iapetus, the Saturnian satellite with a dark leading side and a bright trailing side, are reviewed. One theory suggests remnants of Hyperion's precursor body as the darkening agent while another suggests Phoebe's dust as the cause. Spectral studies of the Hyperion and Phoebe surfaces are briefly discussed to assess the plausibility of these theories. (AIAA)

BORONENKO, T S; SHMIDT, I U B

Celestial Mechanics and Dynamical Astronomy. Vol. 48, no. 4, pp. 289-298. 1990

The literal solution of the restricted three-body problem up to the eleventh order with respect to the minor parameter (Boronenko, 1980) is applied to the investigation of the motion of Phoebe, the ninth satellite of Saturn. As distinct from the existing analytical theories of the motion of the satellite, in the present paper the planetary perturbations are taken into account. A comparison with the modern numerical theory of the motion of Phoebe shows that the new analytical theory of the satellite motion represents observations with the same degree of accuracy. (Author)

Goodson, T D; Gray, D L; Hahn, Y; Peralta, F

AIAA Guidance, Navigation, and Control Conference and Exhibit, Boston, MA, Collection of Technical Papers. Pt. 2; 10-12 Aug. 1998. pp. 665-676. 1998

The Cassini mission to Saturn, launched in 1997, is an international effort to study the Saturnian system. Cassini's interplanetary cruise, which will deliver the spacecraft to Saturn in 2004, uses many propulsive maneuvers, both statistical and deterministic; the first few of these have been executed and are reported on herein. The system has performed close to prelaunch expectations and requirements. Additionally, two maneuvers have already been dispensed with, saving fuel and flight team effort. The analysis that led to the cancellation of these maneuvers is summarized and followed by comments on upcoming maneuvers. (Author)