Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

Towards intelligent autonomous control systems: Architecture and fundamental issues

Abstract: Autonomous control systems are designed to perform well under significant uncertainties in the system and environment for extended periods of time, and they must be able to compensate for system failures without external intervention. Intelligent autonomous control systems use techniques from the field of artificial intelligence to achieve this autonomy. Such control systems evolve from conventional control systems by adding intelligent components, and their development requires interdisciplinary research. A hierarchical functional intelligent autonomous control architecture is introduced here and its functions are described in detail. The fundamental issues in autonomous control system modelling and analysis are discussed.

Discovery of an 86 AU Radius Debris Ring around HD 181327

Abstract: HST NICMOS PSF-subtractedcoronagraphicobservationsof HD181327haverevealedthepresenceofaringlike disk of circumstellar debris seen in 1.1 � m light scattered by the disk grains, surrounded by a diffuse outer region of lower surface brightness. The annular disk appears to be inclined by 31N7 � 1N6 from face-on, with the disk major-axis P.A. at 107 � � 2 � . The total 1.1 � m flux density of the light scattered by the disk (at 1B2 < r < 5B0) of 9:6 � 0:8 mJy is 0:17% � 0:015% of the starlight. Seventy percent of the light from the scattering grains appears to be confined in a 36AUwideannuluscenteredonthepeakoftheradialsurfacebrightness(SB)profile86:3 � 3:9AUfromthestar,well beyond the characteristic radius of thermal emission estimated from IRAS and Spitzer flux densities, assuming blackbody grains (� 22 AU). The 1.1 � m light scattered by the ring (1) appears bilaterally symmetric, (2) exhibits directionallypreferentialscatteringwellrepresentedbyaHenyey-Greensteinscatteringphasefunctionwith g HG ¼ 0:30 � 0:03, and (3) has a median SB (over all azimuth angles) at the 86.3 AU radius of peak SB of 1:00 � 0:07 mJy arcsec � 2 .N o photocentric offset is seen in the ring relative to the position of the central star. A low SB diffuse halo is seen in the NICMOS image to a distance of � 4 00 . Deeper 0.6 � m Hubble Space Telescope (HST) ACS PSF-subtracted coronagraphic observationsreveala faint (V � 21:5 mag arcsec � 2 ) outer nebulosityat4 00 < r < 9 00 , asymmetrically brighter to the north of the star. We discuss models of the disk and properties of its grains, from which we infer a maximum vertical scale height of 4Y8 AU at the 87.6 AU radius of maximum surface density, and a total maximum dust mass of collisionally replenished grains with minimum grain sizes of � 1 � mo f� 4MMoon. Subject headingg circumstellar matter — infrared: stars — planetary systems: protoplanetary disks — stars: individual (HD 181327)

Detecting oceans on extrasolar planets using the glint effect

Abstract: Glint, the specular reflection of sunlight off Earth's oceans, may reveal the presence of oceans on an extrasolar planet. As an Earth-like planet nears crescent phases, the size of the ocean glint spot increases relative to the fraction of the illuminated disk, while the reflectivity of this spot increases. Both effects change the planet's visible reflectivity as a function of phase. However, strong forward scattering of radiation by clouds can also produce increases in a planet's reflectivity as it approaches crescent phases, and surface glint can be obscured by Rayleigh scattering and atmospheric absorption. Here, we explore the detectability of glint in the presence of an atmosphere and realistic phase-dependent scattering from oceans and clouds. We use the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional line-by-line, multiple-scattering spectral Earth model to simulate Earth's broadband visible brightness and reflectivity over an orbit. Our validated simulations successfully reproduce phase-dependent Earthshine observations. We find that the glinting Earth can be as much as 100% brighter at crescent phases than simulations that do not include glint, and that the effect is dependent on both orbital inclination and wavelength, where the latter dependence is caused by Rayleigh scattering limiting sensitivity to the surface. We show that this phenomenon may be observable using the James Webb Space Telescope paired with an external occulter.