Four Contemporary Issues Concerning Ionospheric Plasma Flow to the Magnetosphere

Space Science Reviews - In this review, we examine four specific questions/issues of contemporary interest within the overall topic of ionospheric plasma outflow into the magnetosphere. These four...     

Graviresponses in fungi.

Although the orientation of mycelial hyphal growth is usually independent of the gravity vector, individual specialised hyphae can show response to gravity. This is exemplified by the sporangiophore of Phycomyces, but the most striking gravitropic reactions occur in mushroom fruit bodies. During the course of development of a mushroom different tropisms predominate at different times; the young fruit body primordium is positively phototropic, but negative gravitropism later predominates. The switch between tropisms has been associated with meiosis. The spore-bearing tissue is positively gravitropic and responds independently of the stem. Bracket polypores do not show tropisms but exhibit gravimorphogenetic responses: disturbance leads to renewal of growth producing an entirely new fruiting structure. Indications from both clinostat and space flown experiments are that the basic form of the mushroom (overall tissue arrangement of stem, cap, gills, hymenium, veil) is established independently of the gravity vector although maturation, and especially commitment to the meiosis-sporulation pathway, requires the normal gravity vector. The gravity perception mechanism is difficult to identify. The latest results suggest that disturbance of cytoskeletal microfilaments is involved in perception (with nuclei possibly being used as statoliths), and Ca2(+)-mediated signal transduction may be involved in directing growth differentials.     

Effect of clinostat rotation on differentiation of embryonic bone in vitro.

We have investigated the effect of changes in the gravity vector on osteoblast behaviour, using the clinostat set at 8 rpm. Two sources of osteoblasts were used: secondary cultures of fetal rat bone cells, and the rat osteosarcoma line 17/2.8 (ROS). Cell number was determined by incubation with 3-(4,dimethyl-2yl)-2,3 diphenyl) tetrazolium bromide (MTT) and measurement of optical density at 570 nm (OD). Alkaline phosphatase activity was detected by standard cytochemical methods. Dividing cells were localised by labelling dividing nuclei with Bromodeoxyuridine (BrdU), detected by immunofluorescence. Cell culture was initiated at densities between 1-4x10(4) cells ml-1. Growth rates in all cultures during the first 48 hours exposure to clinostat rotation were less than in stationary controls. After 3 days, ROS cell numbers were 35% lower, and calvarial cells 39% lower than their respective controls. Alkaline phosphatase activity in calvarial control cultures was uniformly present in characteristically polygonal cells, but after culture in the clinostat the enzyme was present sporadically, and the cells were cuboid. There was also no BrdU uptake in nuclei, but it was present in cell cytoplasms. We conclude that the clinostat decreases cell numbers and cell division. Both cell shape and the distribution of alkaline phosphatase activity in calvarial cell cultures were also affected. This implies that changes in the gravity vector can affect osteoblasts directly, without interaction with other cell types.     

Precise orbit determination and sea-surface topography from ERS-1

Results of ERS - 1 orbit refinement procedures for long-arcs are summarised with particular reference to gravity field modelling and sea-surface topography. Long arcs from the three day and thirty - five day repeat cycles have been used to refine the earth's gravity field constrained by the JGM- 2 covariance matrix and simultaneously to solve for the quasi - stationary sea - surface topography. Orbital computations are presented for arcs not included within the refinement process with improvements identified through rms of fit to laser, altimeter and single satellite crossover data. Additional results utilising dual crossovers with TOPEX / POSEIDON in a full dynamic process are also presented. In particular, reference is made to the relative altimeter biases between the respective satellites and the characteristics of the orbital adjustment through inclusion of dual crossover data.     

Confluence of navigation, communication, and control in distributedspacecraft systems

This research details the development of technologies and methodologies that enable distributed spacecraft systems by supporting integrated navigation, communication, and control. Operating at the confluence of these critical functions produces capabilities needed to realize the promise of distributed spacecraft systems, including improved performance and robustness relative to monolithic space systems. Navigation supports science data association and data alignment for distributed aperture sensing, multipoint observation, and co-observation of target regions. Communication enables autonomous distributed science data processing and information exchange among space assets. Both navigation and communication provide essential input to control methods for coordinating distributed autonomous assets at the interspacecraft system level and the intraspacecraft affector subsystem level. A technology solution to implement these capabilities, the Crosslink Transceiver, is also described. The Crosslink Transceiver provides navigation and communication capability that can be integrated into a developing autonomous command and control methodology for distributed spacecraft systems. A small satellite implementation of the Crosslink Transceiver design is detailed and its ability to support broad distributed spacecraft mission classes is described     

Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission

The New Horizons instrument named Ralph is a visible/near infrared multi-spectral imager and a short wavelength infrared spectral imager. It is one of the core instruments on New Horizons, NASA’s first mission to the Pluto/Charon system and the Kuiper Belt. Ralph combines panchromatic and color imaging capabilities with SWIR imaging spectroscopy. Its primary purpose is to map the surface geology and composition of these objects, but it will also be used for atmospheric studies and to map the surface temperature. It is a compact, low-mass (10.5 kg) power efficient (7.1 W peak), and robust instrument with good sensitivity and excellent imaging characteristics. Other than a door opened once in flight, it has no moving parts. These characteristics and its high degree of redundancy make Ralph ideally suited to this long-duration flyby reconnaissance mission.     

IBEX—Interstellar Boundary Explorer

The Interstellar Boundary Explorer (IBEX) is a small explorer mission that launched on 19 October 2008 with the sole, focused science objective to discover the global interaction between the solar wind and the interstellar medium. IBEX is designed to achieve this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock, (2) How are energetic protons accelerated at the termination shock, (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail, and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The answers to these questions rely on energy-resolved images of energetic neutral atoms (ENAs), which originate beyond the termination shock, in the inner heliosheath. To make these exploratory ENA observations IBEX carries two ultra-high sensitivity ENA cameras on a simple spinning spacecraft. IBEX’s very high apogee Earth orbit was achieved using a new and significantly enhanced method for launching small satellites; this orbit allows viewing of the outer heliosphere from beyond the Earth’s relatively bright magnetospheric ENA emissions. The combination of full-sky imaging and energy spectral measurements of ENAs over the range from ～10 eV to 6 keV provides the critical information to allow us to achieve our science objective and understand this global interaction for the first time. The IBEX mission was developed to provide the first global views of the Sun’s interstellar boundaries, unveiling the physics of the heliosphere’s interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries.     

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) on the New Horizons Mission

The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) comprises the hardware and accompanying science investigation on the New Horizons spacecraft to measure pick-up ions from Pluto’s outgassing atmosphere. To the extent that Pluto retains its characteristics similar to those of a “heavy comet” as detected in stellar occultations since the early 1980s, these measurements will characterize the neutral atmosphere of Pluto while providing a consistency check on the atmospheric escape rate at the encounter epoch with that deduced from the atmospheric structure at lower altitudes by the ALICE, REX, and SWAP experiments on New Horizons. In addition, PEPSSI will characterize any extended ionosphere and solar wind interaction while also characterizing the energetic particle environment of Pluto, Charon, and their associated system. First proposed for development for the Pluto Express mission in September 1993, what became the PEPSSI instrument went through a number of development stages to meet the requirements of such an instrument for a mission to Pluto while minimizing the required spacecraft resources. The PEPSSI instrument provides for measurements of ions (with compositional information) and electrons from 10 s of keV to ～1 MeV in a 160°×12° fan-shaped beam in six sectors for 1.5 kg and ～2.5 W.     

A new algorithm for the formation of ISAR images

A new technique for implementing the enhanced image processing (EIP) algorithm for the formation of inverse synthetic aperture radar (ISAR) images is presented. The EIP algorithm is required when, during the formation of an image, scattering centers on a target move out of range and/or Doppler resolution cells. This phenomenon is common for high resolution imagery of practical-sized targets. The method presented is based entirely on the fast Fourier transform (FFT) and therefore does not require the interpolation schemes that are prevalent in the standard EIP implementation. A brief review of the theory of radar imaging is presented to establish the notation for the work. Following the presentation of the new algorithm, a simple example is given to demonstrate the effectiveness of the new technique. In addition work is presented that demonstrates the processing required to reduce the sidelobes in imagery generated by the EIP technique     

Tradeoff between Picture Element Dimensions and Noncoherent Averaging in Side-Looking Airborne Radar

An experiment was performed to determine the effect on radar image interpretation of: 1) rectangular instead of square pixels, and 2) spatial resolution in the presence of noncoherent averaging. The result is a proof of the hypothesis that interpretability of images is determined by a "spatial-gray-level (SGL) resolution volume" that is the product of the range resolution, the azimuth resolution, and a gray-level resolution. The last is defined as the ratio of the value exceeded 10 percent of the time to that exceeded 90 percent of the time for a chi-square distribution having twice as many degrees of freedom as the number of independent samples averaged. Since the area of the pixel enters, rather than explicit dependence on range or azimuth resolution, rectangular pixels are as interpretable as square pixels having the same area. The SGL accounts for the effect of reduction in fading on interpretability. The numerical interpretability assigned by experienced image interpreters asked to look for specific classes of targets was found to fall exponentially with increasing SGL volume, with a scale determined by the class of target. The experiment showed that, for most of the tasks assigned to the interpreters, the interpretability is reduced to 37 percent for a fully focussed synthetic-aperture radar (SAR) (1-look) for a 10-m (33-ft) square pixel. With an infinite number of samples averaged, the comparable square-pixel dimension is 48 m (157 ft). This is consistent with results obtained using LANDSAT images of about 60-m resolution.