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Sub keV Atom Reflecting Analyser (SARA)
Scientific Objectives:
SARA will image the Moon surface using low energy neutral atoms as diagnostics in the energy range 10 eV - 3.2 keV to address the following scientific objectives:
  • Imaging the Moon’s surface composition including the permanently shadowed areas and volatile rich areas
  • Imaging the solar wind-surface interaction
  • Imaging the lunar surface magnetic anomalies
  • Studies of space weathering
  • The Moon does not possess a magnetosphere and atmosphere. Therefore, the solar wind ions directly impinge on the lunar surface, resulting in sputtering and backscattering. The kick-off and neutralized solar wind particles leave the surface mostly as neutral atoms. The notable part of the atoms has energy exceeding the escape energy and thus, such atoms propagate along ballistic trajectories. The SARA instrument is designed to detect such atoms with sufficient angular and mass resolution to address the above scientific objectives. SARA is the first-ever energetic neutral atom imaging mass spectrometer.
    Payload Configuration Details:
    The SARA instrument consists of neutral atom sensor CENA (Chandrayaan-1 Energetic Neutrals Analyzer), solar wind monitor SWIM and DPU (Data Processing Unit). CENA and SWIM interface with DPU, which in turn interfaces with the spacecraft. The masses of CENA, SWIM and DPU are 2 kg, 0.5 kg and 2 kg respectively, totaling the SARA mass as 4.5 kg.
    The functional blocks of CENA are shown below: Low-energy neutral atoms enter through an electrostatic charged particle deflector (1), which sweeps away ambient charged particles by a static electric field. The incoming low energy neutral atoms are converted to positive ions on an ionization surface (2), and then passed through an electrostatic analyzer of a specific (“wave”) shape that provides energy analysis and effectively blocks photons (3). Particles finally enter the detection section (4) where they are reflected at grazing incidence from a start surface towards one of several stop micro channel plate (MCP) detectors. Secondary electrons generated at the start surface and the stop pulses from the stop MCP detectors preserve the direction and the velocity of the incident particle.
    SWIM is an ion mass analyzer, optimized to provide monitoring of the precipitating ions. Ions first enter the deflector, which provides selection on the azimuth angle, following a cylindrical electrostatic analyzer. Exiting the analyzer the ions are post-accelerated up to 1 keV and enter the time-of-flight cell, where their velocity is determined by the same principle (surface reflection), as in the CENA instrument.
    SARA is realised through ESA, in collaboration with Swedish Institute of Space Physics, Sweden and Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO. The Data Processing Unit of this payload/ experiment is designed and developed by ISRO, while Swedish Institute of Space Physics develops the payload.
    For Further Information:
    Swedish Institute of Space Physics http://www.irf.se
    University of Bern http://www.space.unibe.ch
    JAXA/ISAS http://www.isas.ac.jp/e/index.shtml
     
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    Last Update
    11 Nov 2008