The Analyzer of Space Plasmas and Energetic Atoms (ASPERA), is an ion, electron, and neutral atom analyzer consisting of a neutral particle imager and ion spectrometer mounted on a scanning platform. Its primary scientific objective is to measure the plasma-induced atmospheric escape and the interaction of the solar wind with the martian ionosphere.

Barabash, S., et. al., ASPERA-3: Analyser of Space Plasmas and Energetic Ions
                   for Mars Express, ESA SP-1240, September 2004

Instrument Overview
  ===================
     This is the ASPERA-3 (Analyzer of Space Plasmas and Energetic
     Atoms - 3rd version) instrument description.
 
     Analyzer of Space Plasmas and Energetic Atoms, 3rd version
     ----------------------------------------------------------
     (ASPERA-3)
     ----------
     Abstract. The general scientific objective of the ASPERA-3
     experiment is to study the solar wind-atmosphere interaction and
     characterize the plasma and neutral gas environment in the near-
     Mars space through energetic neutral atom (ENA) imaging and
     local charged particle measurements. The studies to be performed
     address the fundamental question: How strongly do the
     interplanetary plasma and electromagnetic fields affect the
     Martian atmosphere? This question is directly related to the
     problem of Martian dehydration. The ASPERA-3 instrument
     comprises four sensors; two ENA sensors, electron and ion
     spectrometers. The Neutral Particle Imager (NPI) provides
     measurements of the integral ENA flux (0.1 -60 keV) with no mass
     and energy resolution but high angular resolution. The Neutral
     Particle Detector (NPD) provides measurements of the ENA flux,
     resolving velocity (0.1 -10 keV) and mass (H and O) with a
     coarse angular resolution. The electron spectrometer (ELS) is a
     standard top-hat electrostatic analyzer in a very compact
     design. These three sensors are located on a scanning platform
     providing a 4pi coverage (maximum possible). The instrument also
     contains an ion mass composition sensor, IMA (Ion Mass
     Analyzer). Mechanically, IMA is a separate unit connected by a
     cable to the ASPERA-3 main unit. IMA provides ion measurements
     in the energy range 0.01 - 40 keV/q for the main ion components
     H+, H2+, He+, O+, with 20-80 amu/q.
 
    Neutral Particle Imager (NPI)
    -----------------------------
     The Neutral Particle Imager (NPI) provides measurements of the
     integral ENA flux with no mass and energy resolution but with 5
     deg x 11 deg angular resolution. The intrinsic field of view is
     9 deg x 344 deg. The sensor utilizes a graphite surface to
     suppress the UV background. ENAs incident on the surface at a
     grazing angle of 20 deg are reflected and/or cause ion
     sputtering. An MCP stack detects the reflected particles and
     sputtered fragments with a discrete anode.
 
    Neutral Particle Detector (NPD)
    -----------------------------
     The Neutral Particle Detector (NPD) provides measurements of the
     ENA differential flux over the energy range 100 eV - 10 keV
     resolving H and O with a coarse 5 deg x 30 deg angular
     resolution. The sensor consists of two identical detectors each
     with a 9 deg x 90 deg intrinsic field of view. The measurement
     technique is based on a principle similar to NPI. ENAs incident
     on a surface at a grazing angle of 15 deg are reflected and
     cause secondary electron emission. The secondary electrons are
     transported to an MCP assembly, which gives the START signal.
     The reflected ENAs hit the second surface and again produce the
     secondary electrons used to generate the STOP signal. The time-
     of-flight (TOF) electronics give the ENA velocity. The pulse-
     height distribution analysis of the STOP signals is used to
     provide a rough determination of the ENA mass.
 
    Electron Spectrometer (ELS)
    ---------------------------
     The ELectron Spectrometer (ELS) provides electron measurements
     in the energy range 0.01 - 20 keV. The intrinsic field of view
     is 10 deg x 360 deg. The 360 deg aperture is divided into 16
     sectors. The sensor is a standard top-hat electrostatic analyzer
     in a very compact design.
 
    Ion Mass Analyzer (IMA)
    -----------------------
     The Ion Mass Analyzer (IMA) is a separate unit connected by a
     cable to the ASPERA-3 experiment. IMA provides ion measurements
     in the energy range 0.01 - 40 keV/q for the main ion components
     H+, H2+, He+, O+, and for the group of molecular ions 20 < M/q <
     ~80. IMA has a 4.6 deg x 360 deg field of view. Electrostatic
     sweeping performs elevation (+/- 45 deg) coverage. The IMA
     sensor is a spherical electrostatic analyzer followed by a
     circular magnetic separating section. A large diameter MCP with
     a discrete anode images the matrix azimuth x mass.
 
 
  Scientific Objectives
  =====================
    The ASPERA-3 experiment fulfills the Mars Express mission
    objective of studying the interaction of the atmosphere with the
    interplanetary medium by:
 
    * Remote measurements of energetic neutral atoms (ENA) in order
      to
      (a) investigate the interaction between the solar wind and
          Martian atmosphere,
      (b) characterize quantitatively the impact of plasma processes
          on the atmospheric evolution, and
      (c) obtain the global plasma and neutral gas distributions in
          the near-Mars environment.
 
    * in situ measurements of ions and electrons in order to
      (a) complement the ENA images (electrons and multiply-charged
          ions cannot be imaged)
      (b) to study local characteristics of plasma (dynamics and fine
          structure of boundaries), and
      (c) provide undisturbed solar wind parameters necessary for
          interpretation of ENA images.
 
    The scientific objectives of the ASPERA-3 experiment are:
 
    1) Scientific objective: Determine the instantaneous global
          distributions of plasma and neutral gas near Mars
       Associated measurements: ENAs originating from the shocked
          solar wind
       Measurement requirements:  Measure the ENA flux in the energy
          range tens eV - few keV with 4pi coverage. ENA flux >
          10**4/(cm**2-s-keV)
          Measure the upstream solar wind parameters
 
    2) Scientific objective: Study plasma induced atmospheric escape
       Associated measurements: ENAs originating from the inside of
          the magnetosphere
       Measurement requirements: Mass resolving (H / O) ENA
          measurements in the energy range up to tens keV. ENA flux >
          10**3/(cm**2-s-keV)
 
    3) Scientific objective: Investigate the modification of the
          atmosphere through ion bombardment
       Associated measurements: ENA albedo
       Measurement requirements: Mass resolving (H / O) ENA
          measurements in the energy range down to tens eV from nadir
          direction.
          ENA flux > 10**6/(cm**2-s-keV)
 
    4) Scientific objective: Investigate the energy deposition from
          the solar wind to the ionosphere
       Associated measurements: Precipitating ENAs
       Measurement requirements: ENA measurements in the energy range
          tens eV - few keV. ENA flux > 10**4/(cm**2-s-keV)
 
    5) Scientific objective: Search for the solar wind-Phobos
       interactions
       Associated measurements: ENAs originating from Phobos
       Measurement requirements: ENA measurements in the energy range
          tens eV - few keV with 4pi coverage. ENA flux
          > 10**4/(cm**2-s-keV)
 
    6) Scientific objective: Define the local characteristics of the
          main plasma regions
       Associated measurements: Ions and electron measurements of hot
          plasma
       Measurement requirements: Ion and electron measurements in the
          energy range few eV - tens keV with 4pi coverage.
 
  Calibration
  ===========
    Calibration of the ASPERA-3 sensors can be divided up in:
 
    1. Characterization, tests and selection of detectors (MCPs and
       secondary emitting surfaces).
    2. Characterization and final calibration of the integrated
       sensor units.
    3. Functional tests of the sensors in the fully mounted (flight)
       configuration.
 
    All sensor units were fully calibrated, and some preliminary
    functional tests were made in the fully mounted, flight,
    configuration in June 2002. The final functional tests were
    successfully carried out during the retrieval period 18 November
    - 9 December 2002.
 
    The Neutral Particle Imager, NPI, was calibrated in Nov-Dec 2001
    at the IRF ion source in Kiruna. The sensitivity of the
    instrument and the characterization of the acceptance field of
    view were obtained using ions (e.g. N+, H2O+, and H+). The ion
    deflector properties versus energy were calibrated for various
    deflector voltages. The integral efficiency of the secondary
    surface were found to range between 2% and 24% (MCP bias
    dependent). Azimuthal field-of-view slightly broader than nominal
    (13.5 deg). NPI-calibration performance as expected. The ideal
    NPI field-of-view, 4pi, is covered in half a scan of the scanning
    platform.
 
    The Neutral Particle Detector, NPD, is a completely new design
    using secondary emitting surfaces and a geometry that has not
    been flown before. NPD therefore underwent extensive
    characterisation tests and calibrations during the spring of
    2002. The results of the calibrations at the IRF calibration
    facility in Kiruna were very successful, the NPD performance
    surpassing expectations. NPD is even more sensitive than
    expected. The mass and energy resolving capability of the
    instrument were as expected in the energy range ~1 - 10 keV. The
    NPD field-of-view, 2pi, is covered after a scan of the scanning
    platform.
 
    The Electron Spectrometer unit, ELS, was calibrated at MSSL in
    London, fall 2001. The energy resolution was found to be better
    than expected, which is an advantage for studying the narrow
    electron peaks expected as a result of the solar impact on the
    ionosphere and upper atmosphere. The geometric factor is a factor
    of five less than nominal, but the loss of sensitivity is, for
    this mission, considered to be well compensated by the improved
    energy resolution of ELS. Calibrations and tests are considered
    to be successful.
 
    IMA was successfully calibrated January to March, 2002.
    Performance largely as expected, except that the upper energy
    limit was lowered from 40 keV to 30 keV. Mass resolution, an
    energy and angular characteristics also as expected.
 
  Operation of ASPERA-3
  =====================
    The ASPERA-3 experiment contains four sensor units and the
    scanner. Each sensor unit measures different components of the
    near-Mars plasma and can be operated in different modes. To
    handle available power and telemetry resource requirements in the
    most efficient way and to inhibit too large number of individual
    modes, there are eight basic TM modes (macro modes): (1) OFF
    mode, (2) Safe mode, (3) Housekeeping mode, (4) Calibration mode,
    (5) Low mode, (6) Normal mode, (7) High mode, and (8) Burst mode.
 
    (1) OFF mode. The instrument is off although the external heaters
        are on and controlled by the instrument thermistors.
 
    (2) Safe mode. At experiment power switch on, the instrument
        enters to a safe mode. In the safe mode the software is run
        in PROM although the software allows command execution,
        housekeeping TM generation, RAM dumping and jumping to the
        RAM code. The instrument also enters to the safe mode in the
        following cases:
           * the checksum of the RAM code fails
           * watch dog is not reset
        The safe mode is a fully operational mode, and the instrument
        is listening for other commands.
 
    (3) Housekeeping mode. In this mode none of the ASPERA-3 sensors
        are taking scientific data and the DPU delivers housekeeping
        data to OBDH. This mode is to monitor the instrument status.
 
    (4) Calibration mode. In this mode each of the different sensors
        is switched on individually for check-out and in-flight
        calibration purposes.
 
  (5-8) Low, Normal, High, Burst modes. These modes are for the
        scientific data taking. The modes differ from each other in
        the total amount of data produced and the structure of TM
        packages although individual settings defining the sensor
        configurations might be the same for different modes.
 
    The choice of the instrument operational mode for each phase of
    the mission is due to available power and telemetry as well as
    scientific requirements.
 
    The scanning platform has three operational modes: scanning mode,
    stepping mode, and fixed position mode. In the scanning mode, the
    platform performs scans with three pre-selected speeds 32, 64,
    and 128 sec in one 0 deg - 180 deg scan. In the stepping mode the
    platform moves in steps through the angle defined by a command.
    The time the platform rests in each position is also commanded.
    In the fixed position mode the platform moves to a commandable
    position from 0 deg to 180 deg and rests there until the scanner
    mode changes.
 
    All four ASPERA-3 sensors, ELS, NPI, NPD1 and NPD2, IMA, can be
    run independently although the individual sensor bit rates are
    set by a macro command. The raw data are compressed by
    integration over time, energy, azimuth, mass as well as using
    log-compression of 16-bit words to 8-bit words, masking, and
    look-up tables (NPD). The processed and formatted data are loss-
    less compressed by the USES algorithm (Universal Source Encoding
    for Space, CCSDS 111.0-W-2).
 
  Principal Investigator
  ======================
    PI:    Prof. Rickard Lundin
    Co-PI: Dr. Stas Barabash
    Both at Swedish Institute of Space Physics (IRF), Kiruna, Sweden

extracted metadata from PDS3 catalog and
                    modified to comply with PDS4 Information Model

Mars Express Analyzer of Space Plasma and Energetic Atoms

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