Josef Fischer

Investigation of the Composition of Solar and Interstellar Matter Using Solar Wind and Pickup Ion Measurements with SWICS and SWIMS on the Ace Spacecraft

The Solar Wind Ion Composition Spectrometer (SWICS) and the Solar Wind Ions Mass Spectrometer (SWIMS) on ACE are instruments optimized for measurements of the chemical and isotopic composition of solar and interstellar matter. SWICS determines uniquely the chemical and ionic-charge composition of the solar wind, the thermal and mean speeds of all major solar wind ions from H through Fe at all solar wind speeds above 300 km s−1 (protons) and 170 km s−1 (Fe+16), and resolves H and He isotopes of both solar and interstellar sources. SWICS will measure the distribution functions of both the interstellar cloud and dust cloud pickup ions up to energies of 100 keV e−1. SWIMS will measure the chemical, isotopic and charge state composition of the solar wind for every element between He and Ni. Each of the two instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made with SWICS and SWIMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition, SWICS and SWIMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; (vii) the physics of the pickup process of interstellar He in the solar wind; and (viii) the spatial distribution and characteristics of sources of neutral matter in the inner heliosphere.

The Toroidal Imaging Mass-Angle Spectrograph (TIMAS) for the POLAR Mission

The science objectives of the Toroidal Imaging Mass-Angle Spectrograph (TIMAS) are to investigate the transfer of solar wind energy and momentum to the magnetosphere, the interaction between the magnetosphere and the ionosphere, the transport processes that distribute plasma and energy throughout the magnetosphere, and the interactions that occur as plasma of different origins and histories mix and interact. In order to meet these objectives the TIMAS instrument measures virtually the full three-dimensional velocity distribution functions of all major magnetospheric ion species with one-half spin period time resolution. The TIMAS is a first-order double focusing (angle and energy), imaging spectrograph that simultaneously measures all mass per charge components from 1 AMU e−1 to greater than 32 AMU e−1 over a nearly 360° by 10° instantaneous field-of-view. Mass per charge is dispersed radially on an annular microchannel plate detector and the azimuthal position on the detector is a map of the instantaneous 360° field of view. With the rotation of the spacecraft, the TIMAS sweeps out very nearly a 4π solid angle image in a half spin period. The energy per charge range from 15 eV e−1 to 32 keV e−1 is covered in 28 non-contiguous steps spaced approximately logarithmically with adjacent steps separated by about 30%. Each energy step is sampled for approximately 20 ms;14 step (odd or even) energy sweeps are completed 16 times per spin. In order to handle the large volume of data within the telemetry limitations the distributions are compressed to varying degrees in angle and energy, log-count compressed and then further compressed by a lossless technique. This data processing task is supported by two SA3300 microprocessors. The voltages (up to 5 kV) for the tandem toroidal electrostatic analyzers and preacceleration sections are supplied from fixed high voltage supplies using optically controlled series-shunt regulators.

A high precision calibration system for the simulation of cometary gas environments

For the calibration of comet mass spectrometers a novel calibration system was designed to simulate the neutral gaseous atmosphere of comets. The facility consists of a fully automated three-chamber ultra-high vacuum system with a separate gas mixing unit. The molecular beam technique is used for the simulation of the dynamic environment of comets. The gas mixing unit allows one to produce molecular beams and static environments of pure water vapour, of mixtures of water vapour and minor gas constituents and also of a wide range of other gases which are expected in the environment of comets. The uniqueness of this system lies in its emphasis on accuracy and long term stability both in the static and in the molecular beam mode. Of particular interest is the determination of the absolute pressure for all gases in the range below 10 -6 mbar and the determination of the molecular beam characteristics. Although it is optimized for cometary environments, the calibration system is, by virtue of its versatility, well suited for the calibration of various space instruments over an extended parameter range.

Design and manufacture of a lightweight reflective baffle for the BepiColombo Laser Altimeter

The BepiColombo Laser Altimeter (BELA), part of the payload of the European Space Agencys BepiColombo mission, is designed to point a telescope with a 200-mm aperture toward a surface that can reach 700 K. Furthermore, direct sunlight can shine into the instrument at angles of 38 deg from the boresight. At Mercury, the solar flux can exceed 14 kW m−2. A baffle for such conditions must both reduce straylight to the best possible extent and minimize the heat load to the spacecraft, i.e., the sum of absorbed visible light and infrared flux. We describe the design and manufacture, including coating, of a reflective baffle. The baffle is made by diamond turning of aluminum and has a clear aperture of 200 mm, about 300-mm length, and a mass of 716 g.

Solar Wind Monitoring with SWIM-SARA Onboard Chandrayaan-1

The SARA experiment aboard the Indian lunar mission Chandrayaan-1 consists of two instruments: Chandrayaan-1 Energetic Neutral Analyzer (CENA) and the SolarWind Monitor (SWIM). CENA will provide measurements of low energy neutral atoms sputtered from lunar surface in the 0.01–3.3 keV energy range by the impact of solar wind ions. SWIM will monitor the solar wind flux precipitating onto the lunar surface and in the vicinity of moon. SWIM is basically an ion-mass analyzer providing energy-per-charge and number density of solar wind ions in the energy range 0.01–15 keV. It has sufficient mass resolution to resolve H+ , He++, He+, O++, O+, and >20 amu, with energy resolution 7% and angular resolution 4:5° × 22:5. The viewing angle of the instrument is 9° × 180°.Mechanically, SWIM consists of a sensor and an electronic board that includes high voltage supply and sensor electronics. The sensor part consists of an electrostatic deflector to analyze the arrival angle of the ions, cylindrical electrostatic analyzer for energy analysis, and the time-of-flight system for particle velocity determination. The total size of SWIM is slightly larger than a credit card and has a mass of 500 g.