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The scientific objective of the nanosatellite Munin is to collect data of the auroral activity over both the northern and southern poles. The satellite has been developed by Swedish Institute of Space Physics under international cooperation. The purpose of the Munin project is both to achieve the scientific objectives and to show that it is possible to achieve such objectives by a very small satellite. A passive magnetic attitude control system is used to stabilize Munin along the direction of an intensity vector of the local geomagnetic field. The paper presents the development of the attitude control system and gives a brief discription of the tools and algorithms used for the attitude determination.

Data from the Astrid-2 satellite taken between April and July 1999 show several examples of dense ion clouds in the 0.1–2 keV energy range inside the inner mag-netosphere, both in the northern and southern hemispheres. These inner magnetospheric ion clouds are found predomi-nantly in the early morning sector, suggesting that they could have originated from substorm-related ion injections on the night side. However, their location and density show no cor-relation with Kp, and their energy-latitude dispersion is not easily reproduced by a simple particle drift model. There-fore, these ion clouds are not necessarily caused by substorm-related ion injections. Alternative explanations for the ion clouds are the direct solar wind injections and up-welling ions from the other hemisphere. These explanations do not, however, account for all of the observations.Key words. Magnetospheric physics (energetic particles, trapped; magnetospheric configuration and dynamics; storm and substorms)

The paper describes the passive magnetic attitude control system developed for the Swedish nanosatellite MUNIN, its composition, and the results of the mathematical modeling of the satellite motion around its center of mass under the effects of external torques and control by this attitude control system. The satellite MUNIN is to be oriented along the local vector of intensity of the geomagnetic field. The problems, which are expediently considered hereafter are formulated too.

We investigate how the two geostationary spacecraft, Meteosat-3 and Tele-X, are affected by the space environment, as characterized by Dst, Kp, and energetic electron flux (> 2 MeV, EEF). Neural network models are developed to predict spacecraft anomalies 1 day ahead. It is found from superposed epoch analysis that the spacecraft anomalies frequently occurred during the recovery phase of geomagnetic storms and that the space environment during the last 4–6 days preceding an anomaly contributes statistically the most to the anomaly occurrence. We find from network prediction (1) that when training is only on Meteosat-3, Kp, Dst, and the EEF, respectively, give the total prediction rate of 79%, 73%, and 62% for Meteosat-3 (both anomalies and non-anomalies) and the total prediction rate of 64%, 66%, and 67% for Tele-X; (2) that when training is only on Tele-X, Kp, Dst, and the EEF, respectively, give the total prediction rate of 57%, 58%, and 51% for Meteosat-3 and the total prediction rate of 70%, 71%, and 74% for Tele-X; (3) that Kp is the optimal environment parameter to correlate with the anomalies on both Meteosat-3 and Tele-X. It is revealed from the anomaly local time distribution, superposed epoch analysis, and network prediction that Meteosat-3 was more subject to surface charging than to internal dielectric charging, and that Tele-X was more subject to internal dielectric charging than to surface charging. The developed neural network models can be used to predict times with higher risks for anomalies in real-time from ACE data.

Observations of energetic neutral atoms (ENA) in the energy range 26- 52 keV are reported from four occasions during geomagnetically disturbed periods. The data were acquired by the ENA imager flown on the Swedish microsatellite Astrid in a 1000 km circular orbit with 83 deg inclination. The ENA imager separates charged particles from neutrals through an electrostatic deflection system in the energy range between 0.1 and 114 keV. ENA images obtained from vantage points in the polar cap and in the afternoon magnetic local time (MLT) hours looking into the antisunward hemisphere show intense ENA fluxes (approx. 10(exp 4)/sq cm sr s over 26-37 keV) coming from the dusk region and low altitudes (approx. 300 km). The morphology shows no relation to local magnetic field excluding the possibility of charged particle detection. It is concluded that the source of these ENAs are precipitating/mirroring ions from the ring current/trapped radiation interacting with the exobase on auroral L-shells and in the dusk region. The observed ENA fluxes show a relation with Kp and Dst geomagnetic indices. The observed ENA spectrum from a geomagnetic storm on February 8, 1995, is investigated in more detail and compared to the parent ion spectrum obtained by the Defense Meteorological Satellite Project (DMSP) satellite, Fl2, during the same period on L = 6 +/- 2 around dusk. The observed ENA spectral slope is used to derive the parent ion spectral temperature. The derived ion temperatures range is 3.0 - 6.0 keV for H and 4.5 - 8.5 keV for O. The higher of these ion temperatures comes closest in agreement to the extrapolated DMSP spectrum leading us to favor O over H as the species of the detected ENAS. It is shown that the detected ENAs must have been produced at L greater than or equal to 6 to reach the detector without atmospheric attenuation and that the main energy dependence of the ENA spectrum, apart from the parent ion spectrum, is governed by the energy dependence of the charge exchange cross section between ions and exospheric oxygen.

The Rosetta spacecraft will rendez-vous with comet Wirtanen round 2011 and will study it for a period of nearly two years, thus providing a unique opportunity to monitor its behaviour over a wide range of distances from the Sun. A plasma and wave package, the Rosetta Plasma Consortium, RPC, will be part of the Rosetta orbiter payload. RPC is a highly integrated package that consists of five sensors: the Langmuir Probe, LAP, the Ion and Electron Sensor, IES, the Ion Composition Analyzer, ICA, the Fluxgate Magnetometer, MAG, and the Mutual Impedance Probe, MIP. RPC also includes the common instrument control, spacecraft interface, and power management unit, PIU, plus the Electrical Ground Support Equipment, EGSE. The prime objectives of RPC are to investigate: (1) the physical properties of the cometary nucleus and its surface, (2) the inner coma structure, dynamics, and aeronomy, (3) the development of cometary activity, and the microscopic and macroscopic structure of the solar-wind interaction region as well as the formation and development of the cometary tail. In addition, the planned asteroid, possibly Otawara and Siwa, flybys will provide an excellent opportunity to study in detail the physics of the solar wind-asteroid interaction. The magnetic and electric conductivity properties of the asteroid will also be studied.

The magnetosphere of Mercury differs in several aspects from that of the other Earth-like planets in our solar system. For instance, the lack of a dense atmosphere and ionosphere implies a different solar-wind magnetosphere interaction compared to that of for example the Earth. However, the solar wind interaction with Mercury might be strongly dependent on a tenuous, but yet significant, exoionosphere. Indeed, the scale sizes and the time constants are different from that of the Earth's magnetosphere, but the large-scale solar wind energy and mass transfer and the intrinsic plasma acceleration processes near Mercury may have very much in common with plasma processes near the Earth. In this report we discuss potential ion acceleration and plasma outflow processes at Mercury in context with results obtained from observations of ion acceleration and outflow in the Earth's magnetosphere and topside ionosphere. We conclude that the acceleration and outflow processes at Mercury, although present in a more extreme environment compared to the other Earth-like planets, are expected to have many similarities with the acceleration and outflow processes near the Earth. Furthermore, we demonstrate that charge-exchange processes in the Hermean magnetosphere are expected to be rather efficient, resulting in “bright flashes” of energetic neutral atom (ENA) generation regions in the nightside atmosphere of Mercury and subsequent loss of magnetospheric plasma. A future mission to Mercury should therefore, besides appropriate plasma experiments, also incorporate ENA imaging experiments.

The generation of energetic neutral atoms (ENA) through charge exchange processes between hot (≥ 1 keV) plasma and cold ( D st ≈−80 nT). The equatorial ion distribution is modeled by a 13 parameter model using a three component (H, He and O) Chamberlain exosphere model with parameters from the MSISE90 extended thermospheric model. The equatorial ion distribution, deduced from the ENA-images through forward modeling is located at MLT (magnetic local time) 1900 hours and occupies L-shell 4–6. Very low ENA fluxes were detected at energies >37 keV. It is suggested that the ENAs are produced by precipitating/mirroring ions on auroral/subauroral field lines coming from the near Earth current sheet charge exchanging with exospheric neutrals at near-exobase altitudes (300–400 km).

The microsatellite Astrid carried the first instrument (PIPPI, Prelude in Planetary Particle Imaging) specifically designed to perform energetic neutral atom (ENA) imaging. It made measurements from a low altitude (1000 km) polar orbit in the energy range ∼13–140 keV. The ENA images, obtained from near-pole vantage points, adequately reflect general morphological features of the ring current such as a global dawn — dusk asymmetry. The detected ENA peak fluxes (500 – 2000 cm−2s−1sr−1keV−1 for 26 – 37 keV) and structure of the ENA images correlate well with magnetospheric activity throughout the entire data set. The Astrid results demonstrate a considerable potential for ENA imaging from low altitude polar orbits. High ENA fluxes, large angular size of the generation region and simultaneous sampling over all local times are major advantages of such imaging.

Plasma and magnetic field data from circular orbits of the Phobos 2 spacecraft near Mars are examined to provide a description of the plasma properties of inner regions of the Mars magnetosheath and the boundary layer/plasma mantle. The data are analyzed in the VB coordinate system, which is reasonable for draping magnetospheres of nonmagnetized planets and comets. It is shown that a boundary almost impermeable for protons is formed. The ion composition changes at this boundary, and a transition layer dominated by planetary ions is observed. The characteristics of the magnetosheath plasma is drastically changed near this ion composition boundary. A strong drop of the proton bulk velocity is accompanied by an increase of the proton temperature and intense fluxes of planetary ions. In dependence of the solar wind dynamic pressure and other factors, radius of the “magnetospheric cavity”, virtually void of solar wind plasma varies from 4500 to 9500 km. During time intervals of very high solar wind dynamic pressure, the cavity, divided up in lobe cells, is almost degenerated. The comparison of positions of different magnetospheric boundaries identified earlier from single-instrument measurements shows their collocation.

On February 21, 1994, both Geotail and LMP 8 satellites detected an interplanetary plasma cloud with intense interplanetary magnetic field (IMF>50 nT) and high dynamic pressure (> 50 nPa). Du ...

An asteroid belt mission is being studied by Swedish space authorities in cooperation with Russian, European, and American partners. The mission will perform a survey of the inner solar system with an emphasis on cosmogonic issues, i.e. it will study the importance of plasma processes in the formation and evolution of the solar system. For this purpose the asteroid belt will be visited several times to enable close studies of these primordial bodies, and their interaction with the solar wind. Cosmogony issues to be studied include detailed measurements of the solar wind aberration and its relation to plasma angular momentum transfer, electric current structures in interplanetary space and near small bodies, surface properties of asteroids, and interaction between the heliosphere and interstellar neutrals. Selection of asteroids to be visited will be done so that a variety of taxonomic types, shapes and sizes can be studied. A comet flyby during the mission may also be performed. The mission will carry charged particle and field instruments, a neutral particle imager, a dust/micrometeroid detector, and planetology instrumentation (including infrared and visible imagers) to fully investigate these processes which may shed light on the question of how the solar system has evolved. The mission calls for a small autonomous spacecraft with high reliability and an advanced payload. The platform concept studied has a dry mass of 150 kg, and a payload mass of 44 kg. Hannes is being studied with a planned launch in mid 2002 with Venus and Earth gravity assist maneuvers before the first asteroid encounter in early 2004. The mission is named after the late Nobel laureate Hannes Alfven.

Measurements with the Sondre Stromfjord incoherent scatter radar, co-ordinated with the observations by the Freja satellite, have been performed during three campaigns, April 1993, February 1994, and May–June 1994. Radar signatures of various types of magnetosheath particle injections in the cusp-cleft region are investigated. The measurement days represent very different geomagnetic conditions, from very quiet to a Kp index of 7+. On three occasions both Freja and the radar detected the cusp. A unique cusp signature is found for a relatively stable cusp, distinguishing it from the many other soft precipitation features seen around noon. The signature includes extremely high electron temperatures in a latitudinally well-defined region with a sharp equatorward border, some F region electron density enhancement, ion outflow, and mainly poleward plasma flow. Enhanced ion temperatures are also seen in the vicinity of, but not exactly coincident with, the electron temperature enhancements. Other day side precipitation features observed with an intense soft component are narrow arcs, which usually have an accompanying accelerated electron component of several hundred eV to some keV energy. These are typically seen in, or bordering, convection regions where the plasma flow vorticity implies upward field-aligned currents.

We show examples of newly found fine structures in low-energy (< 1 keV) ion distribution inside the ring current/radiation belt region. They are, from equatorward to poleward, (1) wedge-like energylatitude dispersion of high intensity oxygen, (2) irregular field-aligned low-energy (

We have calculated the proton and the oxygen velocities in the nightside magnetosheath of Mars utilising the particle observations made by ASPERA onboard the Phobos 2 spacecraft. The O+ observations can be divided into three classes according to the velocities and locations: the “central tail”, the “energetic”, and the “slowly moving” O+ ions. A detailed study of the energetic O+ ions shows that they are related to non-typical magnetic field conditions.

The Hot Plasma Experiment, F3H, on board Freja is designed to measure auroral particle distribution functions with very high temporal and spatial resolution. The experiment consists of three different units; an electron spectrometer that measures angular and energy distributions simultaneously, a positive ion spectrometer that is using the spacecraft spin for three-dimensional measurements, and a data processing unit. The main scientific objective is to study positive ion heating perpendicular to the magnetic field lines in the auroral region. The high resolution measurements of different positive ion species and electrons have already provided important information on this process as well as on other processes at high latitudes. This includes for example high resolution observations of auroral particle precipitation features and source regions of positive ions during magnetic disturbances. The Freja orbit with an inclination of 63° allows us to make detailed measurements in the nightside auroral oval during all disturbance levels. In the dayside, the cusp region is covered during magnetic disturbances. We will here present the instrument in some detail and some outstanding features in the particle data obtained during the first months of operation at altitudes around 1700 km in the northern hemisphere auroral region.

Observations by the Freja satellite at altitudes of about 1700 km in the auroral zone sometimes show energization of both light and heavy ions to characteristic energies of up to about 50–100 eV. This ion heating is often associated with lower hybrid waves, and also with wave emissions at lower frequencies. No obvious decrease of electric field wave power below the proton gyrofrequency, reported by other spacecraft at similar altitudes, is observed in the regions of intense ion heating. Furthermore, localized density depletions associated with lower hybrid waves have not been detected in these regions. We present a preliminary model where waves observed during an event in the evening-side auroral zone are used to explain the observed ion energies.

The experiments on board Freja are designed to measure auroral particle energization processes with very high temporal and spatial resolution. One main scientific objective is to study ion heating transverse to the magnetic field lines in the auroral region. The Freja orbit with an inclination of 63° allows us to make detailed measurements in the nightside auroral oval during all disturbance levels. We concentrate here on two different observations of transverse ion energization at an altitude of about 1700 km in the northern hemisphere auroral region. The three-dimensional ion mass spectrograph has shown that both heavy and light ions are heated to energies most often in the range from a few eV to some hundred eV. Transversely heated ions are, however, also seen up to the present high energy limit of the hot plasma instrument, 4.5 keV. Ion conics are produced in regions with anisotropic electron fluxes as well as in regions of intense keV proton precipitation. Waves above the lower hybrid frequency are observed in the events presented in this report. These waves may play an important role in the ion heating process. The Freja data indicate that the waves are generated in different ways in these events. Thus, this preliminary investigation confirms that several scenarios are needed to explain the heating of ionospheric plasma and shows some of the possibilities for future studies.

Radar measurements in the cusp region, in close conjunction with the Freja satellite, show evidence of the ionospheric signature of the cusp. The intense low-energy fluxes of ions and electrons associated with the cusp, and seen with the satellite, produce a distinct region of enhanced electron density and electron temperature in the ionospheric F-region. The ionization due to the precipitating ions is rather weak, of the same order of magnitude, and maximizing at the same altitude, as the solar EUV ionization. That due to the electrons is much stronger, maximizes at higher altitude and is clearly identifiable in this case. This is partly because of the unusually high altitude of the cold, EUV and convection controlled F-region, creating a distinct height difference as compared to the precipitation region, and partly because ion outflow prevents the cold daytime plasma from convecting into the precipitation region. A narrow region of high ion temperatures most likely indicating strong electric fields is seen within the precipitation region but is not coincident with the most intense precipitation. The equatorward boundary of the precipitation region is seen to move equatorward, while the convection of the plasma within the region is poleward.

In this paper the authors discuss observations by the ion composition mass spectrometer on Freja of injection events into the polar cusp. The time and energy resolution of the instrument allows it to resolve multiple injection events, from an altitude of roughly 1700 m. The satellite can intersect the polar cusp when it is displaced southward, which is primarily due to interaction with a south directed interplanetary magnetic field.

The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M/q=4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He+ from ionisation within the Martian helium corona. The particles had typical energies of either more than 10 keV or about 500 eV. The former correspond to ion pickup in the solar wind and the latter might be ions extracted from the upper ionosphere by an electric field. The observed density of pickup He+ ions was 0.02–0.1 cm−3 and the He+ density in the plasmasheet was of 0.2–0.7 cm−3. According to a recent model of the Martian neutral atmosphere [Moroz et al, 1991], the He+ density could reach 0.2 cm−3 at the Phobos orbit. Such values give mass densities comparable to those of the solar wind. Thus, helium may play a role in the solar wind mass loading process near Mars.

3-dimensional (3D) proton velocity data measured by the ASPERA mass spectrometer onboard the Phobos-2 spacecraft are presented. The mass spectrometer was capable of providing 3D plasma distribution data by scanning through the 4π space, but most of the time its own scanner was switched off, and only 2D data have been presented so far. Because the spacecraft was often spinning around its Sun-pointing axis, the specific data treatment presented in this paper gives a possibility to restore the full angular coverage and obtain 3D vectors of the proton velocity near Mars for the first time. For the circular orbits analysed in this work the flow was deflected at the bow shock and almost stopped at a boundary termed the magnetopause. The main features of the flow and the location of the boundary are compared with a gas-dynamic model of the flow. In general, the model and data are in good agreement. Other observed effects, possibly associated with reflected and pick-up ions, non-thermal proton population, and/or mass loading, which are not taken into account in the gas dynamic model, are discussed.

The measurements carried out by the plasma spectrometer ASPERA, on-board the Phobos 2 spacecraft show that the Martian bow shock is characterized by a sudden increase of ionization of the neutral corona. It acts as a source of new ions that can strongly modify the process of ion heating behind the shock front. The loss of momentum of solar wind protons due to their interaction with exospheric ions may lead to an increase in the effective scale of the obstacle.

The measurements carried out on the spacecraft Phobos-2 have revealed that the plasma sheet of the Martian magnetosphere consists mainly of ions of planetary origin, accelerated up to ∼ 1 keV/q. Such an acceleration may result from the action of magnetic shear stresses of the draped field, the ion energy increasing toward the center of the tail where magnetic stresses are stronger. The energy gained by heavy ions does not depend on their mass and are proportional to the ion charge. The mechanism of the ion acceleration is related with the generation of a charge separation electric field, which extracts ions from “ray” structures in the Martian tail.

Hot plasma measurements from the Soviet Phobos-2 spacecraft in the Martian magnetosphere suggests that the solar wind interaction with Mars is cometary-like, with mass loading of the solar wind and ion pick-up occuring also outside the subsolar bow-shock. The interaction is characterized by a pronounced decrease of the solar wind speed inside what has been termed the mass-loading boundary (MLB). Well outside the MLB, the ion pick-up process acts in a normal sense. There ions pick up approximately the solar wind velocity - independent of mass. Inside the MLB, the momentum loss of solar wind ions is more pronounced - heavy ions of Martian origin taking up most of the solar wind ion maximum flux. The heavy mass-loading of solar wind ions in the innermost part of the Martian boundary layer (near the magnetopause) leads to a loaded ion pick-up. The process can be understood as internal loading of an MHD-dynamo, propelled by a driver plasma - the solar wind. The ASPERA ion composition and momentum data is consistent with such a pick-up process. Inside the magnetopause ions of Martian origin are accelerated up to energies close to those of the solar wind protons. The authors propose two types ofmore » acceleration processes, one similar to that acting within the Earth's auroral acceleration region (acting in the presence of an ambient magnetic field), another pick-up process acting within a limited spatial region.« less

This paper surveys satellite observations (Viking, Interball-2, and Munin) and possible models of bulk plasma transfer phenomena from the magnetosheath to the inner magnetosphere in non-cusp dayside regions. Mid-altitude satellites show a variety of such phenomena in the inner magnetosphere. Some of them are also identified by low-altitude satellites for the first time, and the observations suggest that most of those events are transient ones through various segments of the dayside magnetopause within very short time intervals. The responsible mechanism for most injection events appears to be neither spontaneous reconnection nor pressure pulse-driven penetration. There are many possible models, although very conceptional, that can deal with such non-ideal behavior of plasma. A variety of observations and models for both non-cusp and cusp injections suggest that one cannot uniquely define one location as open or closed geomagnetic field region as magnetohydrodynamics (MHD) does, and that we need a fuzzy definition of openness with analogue (0 to 2) values. A value more than unity (extra-open) means accessibility of ionospheric ions to the magnetosheath.

Micro and nano-satellites are important tools to explore and test new ideas and various new devices for space missions without spending extreme amounts of money. The actual launch cost per kilogram payload on a micro or nano-satellite can be as high or even higher than ordinary satellites but the turn around time and quick responses are extremely important. The HUGIN project is a nano-satellite (less than 10 kg) explicitly designed to test magnetic coils and adaptive artificial neural network (ANN) algorithms for attitude control purposes. A small PC video camera is also included and if the control function is successful then also tests of adaptive image processing using other ANN and biologically inspired methods will be performed.

The Munin satellite (Figure 1) is set to become the first of a new type of monitoring spacecraft. Using modern technology, this very small satellite (mass ≈ 5 kg) will have all the necessary functions needed to support its specific scientific mission: monitoring of the auroral activity on both the northern and southern hemispheres. With Munin we can now usher in a fleet of monitor spacecraft to cost-effectively provide global monitoring, and at the same time have a large degree of student involvement on different levels.

The Swedish microsatellite ASTRID was launched by a Russian Cosmos rocket on January 24, 1995 into a 1000 km circular orbit with 83° inclination. Besides the main objective of technological demonstration, imaging of energetic neutral atoms (ENAs) was attempted. The imager detected ENA in the energy range 0.1 -140 keV utilizing two different techniques. Neutrals of the energy 13 - 140 keV were recorded by 14 solid state detectors with the total field of view 5°x322°. For half a spin (∼1.5 s) of the ASTRID spacecraft, almost all of space was covered with an angular resolution 2.5° × 25°. Less energetic neutrals of ∼0.1 - 70 keV were converted on a graphite target into secondary particles which then were detected by a microchannel plate with 32 anodes. A fraction of primary neutrals was directly reflected towards the sensor. This technique provided the total ENA flux with an angular resolution 4.6° × 11.5°. The instrument weight is 3.13 kg. Successful operation of the instrument during the first 5 weeks of the mission provided the first ENA images of the ring current at low altitudes.

The Automatic Space Plasma Experiment with a Rotating Analyzer (ASPERA) measurements on board the Phobos 2 spacecraft gave, for the first time, a three-dimensional (3-D) picture of the proton flow around Mars. The measurements from the circular orbits of Phobos 2 are well suited to study the bow shock at the terminator region, the nightside magnetosheath, and the tail region. Moreover, measurements from the elliptical orbits offer dayside magnetosheath data. In this work, all circular orbits (11) where there was enough information for 3-D velocity calculations are analysed. The solar wind deflection at the bow shock and the disappearance of the flow near the optical shadow of Mars are found to be typical features on all circular orbits. A dawn-dusk asymmetry is detected in many cases as well. When the results are compared to a gasdynamic model, the locations of the observed boundaries and the general behavior of the flow are found to be quite consistent with the model. The region where proton particle flux decreases significantly, referred to as a magnetopause near the optical shadow of Mars, was typically found near the magnetic field maximum. The magnetopause was thus inside the so-called magnetic tail boundary, which is defined to be at the broad magnetic minimum between the bow shock and the central current sheet. The magnetic tail boundary may be related to the O+ pick-up ions because the mass loading boundary also lies between the shock and the magnetopause. Because the proton flow may behave differently in the dayside than in the nightside magnetosheath, the 3-D velocities are calculated on two elliptical orbits as well. However, in these cases the nature of the flow is not possible to determine as reliably as near the terminator.

The Ion Mass Imager (IMI) is a light-weight ion mass composition instrument for the Japanese Planet-B mission to be launched to Mars in 1998. The objective of the Planet-B mission is to study the Martian environment with emphasis on the upper atmosphere interaction with the solar wind. IMI measures positive ions with energies between 10 eV/q and 35 keV/q and with a mass resolution high enough to resolve the most important ion species (H+, He++, He+, O++, O+, O2+). The instrument has a 360° field-of-view aperture and uses the spacecraft spin to cover almost the full unit sphere to obtain three-dimensional distribution functions every 4 s (half a spacecraft spin period). Particles are energy-filtered by a spherical electrostatic analyzer, and then mass-analysed by the magnetic separation method. The ions hit a microchannel plate assembly with a position sensitive anode divided into 32 mass channels. Together with 16 angular sectors, this system “images” the direction of motion and mass of ions. A pre-acceleration voltage of 0–4000 V is used to select the mass range, e.g., modes optimized for light ions (up to O+) and heavy ions (O+ to charged dust grains). A loss-less data compression algorithm is used in the in-flight processing software to optimize the amount of data that can be returned from Mars.

The effect of microtubule antagonist (MA) colchicine and its two non-MA derivatives beta-lumicolchicine and gamma-lumicolchicine on the phagocytosis of yeast cells by glass-adherent monocytes were studied with a fluorescence quenching technique which allowed a distinction between the adherence and engulfment phases of phagocytosis. The engulfment of yeast cells was depressed by colchicine (p = 0.031) but not by the lumicolchicines. The adherence of yeast cells to the monocytes, on the other hand, was depressed by gamma-lumicolchicine (p = 0.028). The colchicine effect suggests that cytoplasmic microtubules play a role in the engulfment process whereas the lumicolchicine effect suggests a role of nucleoside transport over the cell membrane in the adherence process of phagocytosis.

The role of the cortical actomyosin-like contractile system in monocyte phagocytosis was studied by means of inhibition with cytochalasin B. Monocyte phagocytosis of yeast cells was assayed with a fluorescence extinction technique of surface-located phagocytosis which distinguishes between adherence and ingestion phases of total phagocytosis. Cytochalasin B, 10 micrograms/ml, inhibited monocyte phagocytosis by 20-30%. The cytochalasin inhibition was significant and restricted to the ingestion phase. The finding supported the hypothesis that the contractile structures of the cell have a contributory role in IgG-mediated monocyte phagocytosis on a surface. It is suggested that the cytochalasin effect reflected the role of chemotaxis in monocyte phagocytosis assayed by the present technique.

Mononuclear cells from peripheral blood were incubated with phytohemagglutinin (PHA) for 24-72 hours. The cells formed dense cell clusters with firm cell-to-cell attachment and signs of cell communication, proliferation and differentiation. At the end of a 72-hour period of incubation, the test preparations were treated for 90 minutes with the classical microtubule antagonist Colcemid and the new microtubule antagonist taxol. Taxol produced approximately twice as many mitoses as Colcemid. Chromosomes in taxol-blocked mitoses appeared to be more contracted than chromosomes in Colcemid-blocked mitoses. It is suggested that one beneficial side effect of Colcemid preparation of chromosomes is stretching due to microtubule disassembly.