Magnetosphere Imaging Instrument (MIMI) on the Cassini Mission to Saturn/Titan

The magnetospheric imaging instrument (MIMI) is a neutral and charged particle detection system on the Cassini orbiter spacecraft designed to perform both global imaging and in-situ measurements to study the overall configuration and dynamics of Saturn’s magnetosphere and its interactions with the solar wind, Saturn’s atmosphere, Titan, and the icy satellites. The processes responsible for Saturn’s aurora will be investigated; a search will be performed for substorms at Saturn; and the origins of magnetospheric hot plasmas will be determined. Further, the Jovian magnetosphere and Io torus will be imaged during Jupiter flyby. The investigative approach is twofold. (1) Perform remote sensing of the magnetospheric energetic (E > 7 keV) ion plasmas by detecting and imaging charge-exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. Such escaping neutrals were detected by the Voyager l spacecraft outside Saturn’s magnetosphere and can be used like photons to form images of the emitting regions, as has been demonstrated at Earth. (2) Determine through in-situ measurements the 3-D particle distribution functions including ion composition and charge states (E > 3 keV/e). The combination of in-situ measurements with global images, together with analysis and interpretation techniques that include direct “forward modeling’’ and deconvolution by tomography, is expected to yield a global assessment of magnetospheric structure and dynamics, including (a) magnetospheric ring currents and hot plasma populations, (b) magnetic field distortions, (c) electric field configuration, (d) particle injection boundaries associated with magnetic storms and substorms, and (e) the connection of the magnetosphere to ionospheric altitudes. Titan and its torus will stand out in energetic neutral images throughout the Cassini orbit, and thus serve as a continuous remote probe of ion flux variations near 20R _S (e.g., magnetopause crossings and substorm plasma injections). The Titan exosphere and its cometary interaction with magnetospheric plasmas will be imaged in detail on each flyby. The three principal sensors of MIMI consists of an ion and neutral camera (INCA), a charge–energy–mass-spectrometer (CHEMS) essentially identical to our instrument flown on the ISTP/Geotail spacecraft, and the low energy magnetospheric measurements system (LEMMS), an advanced design of one of our sensors flown on the Galileo spacecraft. The INCA head is a large geometry factor (G ∼ 2.4 cm² sr) foil time-of-flight (TOF) camera that separately registers the incident direction of either energetic neutral atoms (ENA) or ion species (≥5^∘ full width half maximum) over the range 7 keV/nuc < E < 3 MeV/nuc. CHEMS uses electrostatic deflection, TOF, and energy measurement to determine ion energy, charge state, mass, and 3-D anisotropy in the range 3 ≤ E ≤ 220 keV/e with good (∼0.05 cm² sr) sensitivity. LEMMS is a two-ended telescope that measures ions in the range 0.03 ≤ E ≤ 18 MeV and electrons 0.015 ≤ E≤ 0.884 MeV in the forward direction (G ∼ 0.02 cm² sr), while high energy electrons (0.1–5 MeV) and ions (1.6–160 MeV) are measured from the back direction (G ∼ 0.4 cm² sr). The latter are relevant to inner magnetosphere studies of diffusion processes and satellite microsignatures as well as cosmic ray albedo neutron decay (CRAND). Our analyses of Voyager energetic neutral particle and Lyman-α measurements show that INCA will provide statistically significant global magnetospheric images from a distance of ∼60 R _S every 2–3 h (every ∼10 min from ∼20 R _S). Moreover, during Titan flybys, INCA will provide images of the interaction of the Titan exosphere with the Saturn magnetosphere every 1.5 min. Time resolution for charged particle measurements can be < 0.1 s, which is more than adequate for microsignature studies. Data obtained during Venus-2 flyby and Earth swingby in June and August 1999, respectively, and Jupiter flyby in December 2000 to January 2001 show that the instrument is performing well, has made important and heretofore unobtainable measurements in interplanetary space at Jupiter, and will likely obtain high-quality data throughout each orbit of the Cassini mission at Saturn. Sample data from each of the three sensors during the August 18 Earth swingby are shown, including the first ENA image of part of the ring current obtained by an instrument specifically designed for this purpose. Similarily, measurements in cis-Jovian space include the first detailed charge state determination of Iogenic ions and several ENA images of that planet’s magnetosphere.This revised version was published online in July 2005 with a corrected cover date.     

Gravitation and celestial mechanics investigations with Galileo

The gravitation and celestial mechanics investigations during the cruise phase and Orbiter phase of the Galileo mission depend on Doppler and ranging measurements generated by the Deep Space Network (DSN) at its three spacecraft tracking sites in California, Australia, and Spain. Other investigations which also rely on DSN data, and which like ours fall under the general discipline of spacecraft radio science, are described in a companion paper by Howard et al. (1992). We group our investigations into four broad categories as follows: (1) the determination of the gravity fields of Jupiter and its four major satellites during the orbital tour, (2) a search for gravitational radiation as evidenced by perturbations to the coherent Doppler link between the spacecraft and Earth, (3) the mathematical modeling, and by implication tests, of general relativistic effects on the Doppler and ranging data during both cruise and orbiter phases, and (4) an improvement in the ephemeris of Jupiter by means of spacecraft ranging during the Orbiter phase. The gravity fields are accessible because of their effects on the spacecraft motion, determined primarily from the Doppler data. For the Galilean satellites we will determine second degree and order gravity harmonics that will yield new information on the central condensation and likely composition of material within these giant satellites (Hubbard and Anderson, 1978). The search for gravitational radiation is being conducted in cruise for periods of 40 days centered around solar opposition. During these times the radio link is least affected by scintillations introduced by solar plasma. Our sensitivity to the amplitude of sinusoidal signals approaches 10^-15 in a band of gravitational frequencies between 10^-4 and 10^-3 Hz, by far the best sensitivity obtained in this band to date. In addition to the primary objectives of our investigations, we discuss two secondary objectives: the determination of a range fix on Venus during the flyby on 10 February, 1990, and the determination of the Earth's mass (GM) from the two Earth gravity assists, EGA1 in December 1990 and EGA2 in December 1992.     

IMF connection for energetic protons observed at Ulysses via mid-latitude solar wind rarefaction regions

As Ulysses moved inward and southward from mid-1992 to early 1994 we noticed the occasional occurrence of inter-events, lasting about 10 days and falling between the recurrent events, observed at proton energies of 0.48–97 MeV, associated with Corotating Interaction Regions (CIR). These inter-events were present for several sequences of two or more solar rotations at intensity levels around 1% of those of the neighbouring main events. When we compared the Ulysses events with those measured on IMP-8 at 1 AU we saw that the inter-events appeared at Ulysses after the extended emission (>10 days) of large fluxes of solar protons of the same energy that lasted at least one solar rotation at 1 AU. The inter-events fell completely within the rarefaction regions (dv/dt<0) of the recurrent solar wind streams. The interplanetary magnetic field (IMF) lines in the rarefactions map back to the narrow range of longitudes at the Sun which mark the eastern edge of the source region of the high speed stream. Thus the inter-events are propagating at mid-latitudes to Ulysses along field lines free from stream-stream interactions. They are seen in the 0.39–1.28 MeV/nucleon He, which exhibit a faster decay, but almost never in the 38–53 keV electrons. We show that the inter-events are unlikely to be accelerated by reverse shocks associated with the CIRs and that they are more likely to be accelerated by sequences of solar events and transported along the IMF in the rarefactions of the solar wind streams.     

Ulysses observations of a coronal origin particle event at 32° south heliographic latitutde

A remarkable streaming beam-like particle event of 60 keV-5 MeV ions and of 38–315 keV electrons has been reported previously. This event has been associated with the passage of a Coronal Mass Ejection (CME) over the Ulysses spacecraft on June 9–13, 1993. At this time, the spacecraft was located at 4.6 AU from the sun and at an heliolatitude of 32° south. It was proposed (Armstrong et al., 1994) that the particle injection source could have been of coronal origin. In this study, we analyse the solar activity during this period. We identify a region of solar radio noise storms in the corona and in particular, a flare on June 7 that presents all the required characteristics to produce the hot plasma beam observed in the interplanetary medium.     

红色“飓风”Ⅱ

苏联首次将“飓风”投入战斗是在摩尔曼斯克地区北部。1941年10月到12月间,北方舰队航空兵的第72混合航空团,第78歼击机团和列宁格勒前线的第152、760歼击机团首先参战,战斗在卡累利阿和科拉半岛上空打响。     

红色“飓风”

在整个二战期间，苏联曾经获得了盟过大量的军事援助。英国曾经向苏联提供了２，９５２架“飓风”战斗机，但苏联方面的资料却显示苏联空军一共得到了３，０８２架。造成数量上的差异是由于苏联把作为零备件的一些机体组装成飞机的缘故。本文回忆了这种著名英国战斗机在苏联的传奇经历。摩尔曼斯克上空的第１５１联队 第一架抵达苏联的“飓风’战斗机隶属于英国空军第１５１联队，这个联队下辖第８１和第１３４中队。１９４１年第１５１联队以英国援苏部队的身份进驻摩尔曼斯克（苏联欧洲部分西北部城市，临科拉湾北部，位于巴伦支海入口处…     

Target tracking with a network of Doppler radars

By observing a Doppler signal at several points in space, it is possible to determine the position, velocity, and acceleration of a moving target. Parameter identification for a constant-acceleration motion model is studied, and the Cramer-Rao bound on motion parameter uncertainty is obtained for phaseand frequency-based estimation strategies, with the result that the preferred strategy depends upon the sensor/target geometry and target motion. Direct identification of the constant-acceleration trajectory model from the Doppler signal requires a 9-dimensional nonlinear optimization. Exploiting symmetry in the sensing geometry, a novel trajectory representation is presented which reduces the nonlinear optimization to one in 3 dimensions, with additional parameters obtained by linear identification. Baseball tracking using a network of four Doppler radars is experimentally demonstrated     

Next-Generation Thin-Film Photovoltaics

Future spacecraft and high-altitude airship (HAA) solar array technologies will require high array specific power (W/kg), which can be met using thin-film photovoltaics (PV) on lightweight and flexible substrates [1]. Thin-film array technology, with thin-film specific array support structure, begin to exceed the specific power of crystalline multi-junction arrays with thin-film device efficiencies as low as 8.5% [2]. Thin-film PV devices have other advantages in that they are more easily integrated into HAAs, and are projected to be much less costly than their crystalline PV counterparts. Furthermore, it is likely that only thin-film array technology will be able to meet device specific power requirements exceeding 1 kW/kg (photovoltaic and integrated substrate/blanket mass only).     

Cassini Radio Science

Cassini radio science investigations will be conducted both during the cruise (gravitational wave and conjunction experiments) and the Saturnian tour of the mission (atmospheric and ionospheric occultations, ring occultations, determinations of masses and gravity fields). New technologies in the construction of the instrument, which consists of a portion on-board the spacecraft and another portion on the ground, including the use of the Ka-band signal in addition to that of the S- and X-bands, open opportunities for important discoveries in each of the above scientific areas, due to increased accuracy, resolution, sensitivity, and dynamic range.This revised version was published online in July 2005 with a corrected cover date.     

Comparison of model predictions with LDEF satellite radiation measurements.

Some early results are summarized from a program under way to utilize LDEF satellite data for evaluating and improving current models of the space radiation environment in low Earth orbit. Reported here are predictions and comparisons with some of the LDEF dose and induced radioactivity data, which are used to check the accuracy of current models describing the magnitude and directionality of the trapped proton environment. Preliminary findings are that the environment models underestimate both dose and activation from trapped protons by a factor of about two, and the observed anisotropy is higher than predicted.