Engineering topics
Atreya, Sushil
Publications and source records attributed to Atreya, Sushil.
Uranus and Neptune Missions: A Study in Advance of the Next Planetary Science Decadal Survey
The ice giant planets, Uranus and Neptune, represent an important and relatively unexplored class of planet. Most of our detailed information about them comes from fleeting looks by the Voyager 2 spacecraft in the 1980s. Voyager, and ground-based work since then, found that these planets, their satellites, rings, and magnetospheres, challenge our understanding of the formation and evolution of planetary systems. We also now know that Uranus- Neptune size planets are common around other stars. These are some of the reasons ice giant exploration was a high priority in NASA's most recent Planetary Science Decadal Survey. In preparation for the next Decadal Survey, NASA, with ESA participation, conducted a broad study of possible ice giant missions in the 2024–2037 timeframe. This paper summarizes the key results of the study, and addresses questions that have been raised by the science community and in a recent NASA review. Foremost amongst these are questions about the science objectives, the science payload, and the importance of an atmospheric probe. The conclusions of the NASA/ESA study remain valid. In particular, it is a high priority to send an orbiter and atmospheric probe to at least one of the ice giants, with instrumentation to study all components of an ice giant system. Uranus and Neptune are found to be equally compelling as science targets. The two planets are not equivalent, however, and each system has things to teach us the other cannot. An additional mission study is needed to refine plans for future exploration of these worlds.
Huygens GCMS Results from Titan
The Huygens Probe executed a successful entry, descent and impact on the Saturnian moon of Titan on January 14, 2005. The Gas Chromatograph Mass Spectrometer (GCMS) instrument conducted isotopic and compositional measurements throughout the two and one half hour descent from 146 km altitude, and on the surface for 69 minutes until loss of signal from the orbiting Cassini spacecraft. The GCMS incorporated a quadrupole mass filter with a secondary electron multiplier detection system. The gas sampling system provided continuous direct atmospheric composition measurements and batch sampling through three gas chromatographic (GC) columns, a chemical scrubber and a hydrocarbon enrichment cell. The GCMS gas inlet was heated to prevent condensation, and to evaporate volatiles from the surface after impact. Data products from the GCMS included altitude profiles of the major atmospheric constituents dinitrogen (N2) and methane (CH4), isotope ratios of 14N/15N, 12C/13C, and D/H, mole fractions of radiogenic argon (40Ar) and primordial argon (36Ar), and upper limits on the mole fractions of neon, krypton and xenon, which were found to be absent. Surface measurements confirmed the presence of ethane (C2H6) and cyanogen (C2N2). Later data products expanded atmospheric profiles to include the surface response of C2N2. C2H6, acetylene (C2H2), and carbon dioxide (CO2). More recent results include the profiles of benzene (C6H6) and molecular hydrogen (H2). The GCMS data are being further analyzed to obtain higher precision results and to identify other trace species ion the atmosphere and evaporating from the surface.
Neptune Polar Orbiter with Probes
The giant planets of the outer solar system divide into two distinct classes: the gas giants Jupiter and Saturn, which consist mainly of hydrogen and helium; and the ice giants Uranus and Neptune, which are believed to contain significant amounts of the heavier elements oxygen, nitrogen, and carbon and sulfur. Detailed comparisons of the internal structures and compositions of the gas giants with those of the ice giants will yield valuable insights into the processes that formed the solar system and, perhaps, other planetary systems. By 2012, Galileo, Cassini and possibly a Jupiter Orbiter mission with microwave radiometers, Juno, in the New Frontiers program, will have yielded significant information on the chemical and physical properties of Jupiter and Saturn. A Neptune Orbiter with Probes (NOP) mission would deliver the corresponding key data for an ice giant planet. Such a mission would ideally study the deep Neptune atmosphere to pressures approaching and possibly exceeding 1000 bars, as well as the rings, Triton, Nereid, and Neptune s other icy satellites. A potential source of power would be nuclear electric propulsion (NEP). Such an ambitious mission requires that a number of technical issues be investigated, however, including: (1) atmospheric entry probe thermal protection system (TPS) design, (2) probe structural design including seals, windows, penetrations and pressure vessel, (3) digital, RF subsystem, and overall communication link design for long term operation in the very extreme environment of Neptune's deep atmosphere, (4) trajectory design allowing probe release on a trajectory to impact Neptune while allowing the spacecraft to achieve a polar orbit of Neptune, (5) and finally the suite of science instruments enabled by the probe technology to explore the depths of the Neptune atmosphere. Another driving factor in the design of the Orbiter and Probes is the necessity to maintain a fully operational flight system during the lengthy transit time from launch through Neptune encounter, and throughout the mission. Following our response to the recent NASA Research Announcement (NRA) for Space Science Vision Missions for mission studies by NASA for implementation in the 2013 or later time frame, our team has been selected to explore the feasibility of such a Neptune mission.
Enhanced acetylene emission near the north pole of Jupiter
The present paper is concerned with observations of acetylene fundamental and hot band vibrational emission lines from the planet Jupiter. It is pointed out that the observation of a polar bright spot in the atmosphere of Jupiter is characterized by an enhancement in the individual lines of C2H2 which can be interpreted as an enhancement in the acetylene abundance. However, a purely thermal effect, on non-LTE phenomena cannot be excluded. The intensity of the observed hot band lines is also consistent with either hypothesis. The reported observations were performed with a cooled Fabry-Perot Grating Spectrometer (FPGS). Observations and instrumentation are considered in detail along with the calculation of synthetic spectra on the basis of a line-by-line computation, and the interpretation of the obtained data.