Direct evidence for chromospheric evaporation in a well-observed compact flare

We have observed the flare of 1980 May 7 1456 UT with several Solar Maximum Mission instruments, in coordination with the Sacramento Peak Observatory Vacuum Tower Telescope. From the X-ray data we determine the total amount of plasma at T > 2 × 10⁶ K, commonly attributed to chromospheric evaporation. From Hα we have determined the amount of plasma that has been evaporated from the chromosphere. We find that enough material has been evaporated from the chromosphere to account for the X-ray plasma. Taken together, the Hα, soft and hard X-ray images suggest that chromospheric evaporation is driven both by flare accelerated electrons, during the impulsive phase, and conduction, during the thermal phase.     

A proposed Comet Nucleus Penetrator for the Comet Rendezvous Asteroid Flyby mission

Among the major objectives of NASA's program of space exploration is a better understanding of the origin and evolution of the solar system. Crucial to this objective is the study of comets, which are thought to be the most primitive, pristine bodies remaining in the solar system. The importance of the study of comets has led NASA to plan a mission to rendezvous with comet Tempel 2 in 1997. Critical to the understanding of comets will be measurements of the nucleus material to determine its elemental and isotopic composition, its mechanical properties, and its thermal state and properties. This paper describes a proposal for a Comet Nucleus Penetrator to accomplish these measurement goals. The Comet Nucleus Penetrator will implant instruments into the comet's nucleus beneath a probable volatile-depleted surface mantle into material more representative of the bulk composition of the nucleus.     

The first decade of regular observation of land transformation from space

Data for all of the landmass of Canada has been received and archived since the launch of LANDSAT-1 in July 1972. This data has been used in a number of mapping and monitoring programs such as: revising topographic maps, mapping forest fire burns, mapping the variability of water levels in shallow prairie lakes and sloughs, evaluating rangeland conditions, mapping sedimentation levels due to natural phenomena or human activities, monitoring the environmental effects of major hydro electric projects.     

Dynamic Modeling of Brushless dc Motors for Aerospace Actuation

A discrete time model for simulation of the dynamics of samarium cobalt-type permanent magnet brushless dc machines is presented. The similation model includes modeling of the interaction between these machines and their attached power conditioners. These are transistorized conditioner units. This model is part of an overall discrete-time analysis of the dynamic performance of electromechanical actuators, which was conducted as part of prototype development of such actuators studied and built for NASA-Johnson Space Center as a prospective alternative to hydraulic actuators presently used in shuttle orbiter applications. The resulting numerical simulations of the various machine and power conditioner current and voltage waveforms gave excellent correlation to the actual waveforms collected from actual hardware experimental testing. These results, numerical and experimental, are presented here for machine motoring, regeneration and dynamic braking modes. Application of the resulting model to the determination of machine current and torque profiles during closed-loop actuator operation were also analyzed and the results are given here. These results are given in light of an overall view of the actuator system components. The applicability of this method of analysis to design optimization and trouble-shooting in such prototype development is also discussed in light of the results at hand.     

Hematopoietic responses under protracted exposures to low daily dose gamma irradiation.

In attempting to evaluate the possible health consequences of chronic ionizing radiation exposure during extended space travel (e.g., Mars Mission), ground-based experimental studies of the clinical and pathological responses of canines under low daily doses of 60Co gamma irradiation (0.3-26.3 cGy d-1) have been examined. Specific reference was given to responses of the blood forming system. Results suggest that the daily dose rate of 7.5 cGy d-1 represents a threshold below which the hematopoietic system can retain either partial or full trilineal cell-producing capacity (erythropoiesis, myelopoiesis, and megakaryopoiesis) for extended periods of exposure (>1 yr). Trilineal capacity was fully retained for several years of exposure at the lowest dose-rate tested (0.3 cGy d-1) but was completely lost within several hundred days at the highest dose-rate (26.3 cGy d-1). Retention of hematopoietic capacity under chronic exposure has been demonstrated to be mediated by hematopoietic progenitors with acquired radioresistance and repair functions, altered cytogenetics, and cell-cycle characteristics. Radiological, biological, and temporal parameters responsible for these vital acquisitions by hematopoietic progenitors have been partially characterized. These parameters, along with threshold responses, are described and discussed in relation to potential health risks of the space traveler under chronic stress of low-dose irradiation.     

Magnetic structure of the boundary layer

It now appears that magnetospheric convection is driven by both magnetic reconnection and ‘viscous’ dragging of closed flux tubes acting in varying proportions but with reconnection being, on the average, the predominant cause. But the action of the closed flux tubes of the low latitude boundary layer seems predominant in driving system 1 field aligned currents and discrete auroras. A search of ISEE boundary layer data for the magnetic shear effects associated with field aligned currents has revealed, on some occasions, a ‘reverse draping’ of boundary layer field lines whose cause might be plasma entry around the cusps, a north-south asymmetry in current flow to the polar regions, or magnetic reconnection at high latitudes. Observed asymmetries in the nature and distribution of boundary layer encounters suggest that the boundary layer and/or the plasma mantle may differ substantially at the dawn and dusk sides of the magnetosphere and that there may be seasonal dependencies of their properties.     

Meteorological satellites and cooperative programs

Satellite data are available to meteorological centers around the world in two forms: (1) real-time reception directly from the spacecraft to the users; (2) processed data via the Global Telecommunications System (GTS). Real-time data is broadcast by satellites operated by both the U.S. and the U.S.S.R. From the NOAA series, Automatic Picture Transmission (APT) has been in wide use for 19 years. High Resolution Picture Transmission (HRPT) has been available to users with more sophisticated receiving equipment for the past 10 years. The Meteor satellites have been broadcasting for over 10 years. From the geostationary satellites (GOES), specialized products are broadcast via weather facsimile (WEFAX), and for users with very sophisticated ground systems, real-time geostationary images are available. Derived data, i.e., vertical temperature soundings of the atmosphere, etc., are routinely available on the GTS. The characteristics, utility, current utilization and future developments of these services will be reviewed and discussed.