UVSTAR: An imaging spectrograph with telescope for the Shuttle Hitchhiker-M platform

UVSTAR is an EUV spectral imager intended as a facility instrument devoted to solar system and astronomy studies. It covers the wavelength range of 500 to 1250 A, with sufficient spectral resolution to separate emission lines and to form spectrally resolved images of extended plasma sources. Targets include the Io plasma torus at Jupiter, hot stars, planetary nebulae and bright galaxies. UVSTAR consists of a pair of telescopes and concave grating spectrographs that cover the overlapping spectral ranges of 500-900 and 850-1250 A. The telescopes use two 30 cm diameter off-axis paraboloids having focal length of 1.5 m. An image of the target is formed at the entrance slits of the two concave grating spectrographs. The gratings provide dispersion and re-image the slits at the detectors, intensified CCD's. The readout format of the detectors can be chosen by computer, and three slit widths are selectable to adapt the instrument to specific tasks. UVSTAR has internal gimbals which allow rotation of plus or minus 3 deg about each of two axes. Dedicated finding and tracking telescopes will acquire and track the target after rough pointing is achieved by orienting the Orbiter. Responsibilities for implementation and utilization of UVSTAR are shared by groups in Italy and the U.S. UVSTAR is scheduled for flight in early 1995, timed for an opportunity to observe the Jovian system

On the causes of plasmaspheric rotation variability: IMAGE EUV observations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95534/1/jgra20000.pd

Quantifying the azimuthal plasmaspheric density structure and dynamics inferred from IMAGE EUV

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95221/1/jgra22185.pd

The star identification, pointing and tracking system of UVSTAR, an attached payload instrument system for the Shuttle Hitchhiker-M platform

We describe an algorithm for star identification and pointing/tracking of a spaceborne electro-optical system and simulation analyses to test the algorithm. The algorithm will be implemented in the guiding system of UVSTAR, a spectrographic telescope for observations of astronomical and planetary sources operating in the 500-1250 A waveband at approximately 1 A resolution. The experiment is an attached payload and will fly as a Hitchhiker-M payload on the Shuttle. UVSTAR includes capabilities for independent target acquisition and tracking. The spectrograph package has internal gimbals that allow angular movement of plus or minus 3 deg from the central position. Rotation about the azimuth axis (parallel to the Shuttle z axis) and elevation axis (parallel to the Shuttle x axis) will actively position the field of view to center the target of interest in the fields of the spectrographs. The algorithm is based on an on-board catalog of stars. To identify star fields, the algorithm compares the positions of stars recorded by the guiding imager to positions computed from the on-board catalog. When the field has been identified, its position within the guiding imager field of view can be used to compute the pointing corrections necessary to point to a target of interest. In tracking mode, the software uses the past history to predict the quasi-periodic attitude control motions of the shuttle and sends pointing commands to cancel the motion and stabilize UVSTAR on the target. The guiding imager (guider) will have an 80-mm focal length and f/1.4 optics giving a field of view of 6 deg x 4.5 deg using a 385 x 288 pixel intensified CCD. It will be capable of providing high accuracy (better than 2 arc-sec) attitude determination from coarse (6 deg x 4.5 deg) initial knowledge of the pointing direction; and of pointing toward the target. It will also be capable of tracking at the same high accuracy with a processing time of less than a few hundredths of a second

Mars Aeronomy Observer: Report of the Science Working Team

The Mars Aeronomy Observer (MAO) is a candidate follow-on mission to Mars Observer (MO) in the Planetary Observer Program. The four Mariner and two Viking spacecraft sent to Mars between 1965 and 1976 have provided a wealth of information concerning Martian planetology. The Mars Observer, to be launched in 1990, will build on their results by further examining the elemental and mineralogical composition of the surface, the strength and multipolar composition of the planetary magnetic field, the gravitational field and topography, and the circulation of the lower atmosphere. The Mars Aeronomy Observer is intended to address the last major aspects of Martian environment which have yet to be investigated: the upper atmosphere, the ionsphere, and the solar wind interaction region

Long-Term Variation of the Interplanetary H Lyα Glow: Voyager UVS Measurements and Implications for the Solar H Lyα Irradiance

International audienceIn this paper we study interplanetary (IP) Lya data taken with the Voyager 1 and Voyager 2 spacecraft from 1980 to 1995. The coverage in time is equal to about 156 and 220 points yr~1 for Voyager 1 and Voyager 2, respectively, with almost no gaps. The IP Lya data are normalized for spatial changes in the emissivity, which arise from variations in observing geometry, by using a radiative transfer model. The normalized data show the variation of the solar H Lya line-center Ñux during the solar cycle. We compare this variation with the solar H Lya irradiance measurements of integrated Ñux from the Solar Mesosphere Explorer and the Upper Atmosphere Research Satellite/Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), and, when direct solar measurements are not available, we use estimated irra-diances from magnesium and helium indices. The comparison between Voyager IP data and solar data shows that the best agreement is found with the SOLSTICE set of measurements, when no di †erences in the variation of the line-center Ñux and the integrated Ñux are taken into account

Heliospheric boundary in the backscattered solar Lyman-alpha radiation: analysis of Voyager-1/UVS data

International audienceUVS instrument onboard Voyager-1 has been performing measurements of the backscattered solar Lyman-alpha emissions for more than 35 years. Since 2003 when the scan platform movements were stopped, it measures Lyman-alpha radiation in one line of sight close to the upwind direction. The most interesting feature of these data is radial dependence of measured intensity. Namely, Voyager-1 data shows almost constant intensity (after correction for the solar flux variations) between 90 and 115 AU, while the numerical models of global heliosphere and radiative transfer predict decreasing intensity. Between 115 AU (beginning of 2011) and about 124 AU (beginning of 2013), the data show a decrease of the intensity again. This last period corresponds to motion of Voyager-1 in the transition region (Krimigis et al., 2011) before crossing the heliopause at 122 AU in August, 2012 (Stone et al., 2013). This behavior of the Lyman-alpha intensity observed by Voyager can be a tracer of complicated structure of the heliospheric boundary. Plasma instruments onboard Voyagers provide information about charged component of the solar and interstellar winds and energetic particles, while only the UVS data for the Lyman-alpha intensity reflect the distribution of the neutral hydrogen component. Therefore, interpretation of Voyager-1/UVS measurements is critical to understand the complete picture of the interaction between the solar wind and surrounding interstellar matter. In this work we will present preliminary results of analysis of Voyager-1/UVS data in the frame of the kinetic-MHD heliospheric model and radiative transfer code. Possible scenarios for hydrogen distribution consistent with Voyager-1 data will be proposed

Interplanetary Lyman α Observations: Intensities from Voyagers and Line Profiles from HST/STIS

International audienc

UVS-Voyager 1 measurements in the outer heliosphere

The UVS spectrometer on Voyager 1 is still active in 2014. The only line still observed in the spectral range covered by UVS is the HI Lyman alpha transition due to the backscattering of solar photons by H atoms in the outer heliosphere. The background intensity corresponds to a few tens of rayleigh. In 2003, movements of the Voyager 1 scan platforms were stopped and since then the line of sight of UVS has been fixed. It is pointing towards a direction close to the upwind direction. Over the 2003-2010 period, IPH background data have been very constant and followed the variations of the solar illuminating flux at lyman alpha, smoothed by multiple scattering efftects between the sun and the outer heliosphere. After corrrection from solar flux variations, data obtained in this period changed by less than 10% over a distance of more than 20 AU which is difficult to explain with radiative transfer models. However, a change in the radial dependence of the data started in 2011 and lasted until the end of 2013. New measurements in early 2014 show a stabilization and a return to the previous pattern. This needs to be confirmed in the next few months. We will present the UVS-V1 data, and give special attention to possible instrumental effects linked to thermal changes in the Voyager 1 spacecraft as various heaters are switched off. We think that the changes observed since 2011 are not due to instrumental effects. We will also present some ideas that can help us to explain the UVS observations. To do this, it is necessary to modify our current picture of the distribution of hydrogen atoms in the outer heliosphere. These new results have an impact on our understanding of the heliospheric interface

Voyager Measurements of Hydrogen Lyman-α Diffuse Emission from the Milky Way

International audienceDoppler-shifted hydrogen Lyman-alpha (Lyα) emission from galaxies is currently measured and used in cosmology as an indicator of star formation. Until now, the Milky Way emission has not been detected, owing to far brighter local sources, including the H Glow--i.e., solar Lyα radiation backscattered by interstellar atoms that flow within the solar system. Because observations from the Voyager spacecraft, now leaving the heliosphere, are decreasingly affected by the H glow, the Ultraviolet Spectrographs are detecting Lyα diffuse emission from our galaxy. The surface brightness toward nearby star-forming regions is about 3 to 4 Rayleigh. The escape fraction of the radiation from the brightest H II regions is on the order of 3% and is highly spatially variable. These results will help constraining models of Lyα radiation transfer in distant galaxies