NASA Scientific and Technical Aerospace Reports

onset. In double Maxwellian plasmas, the onset of spacecraft charging depends on the density and temperature of both
distributions. We explain pedagogically the onset of charging in double Maxwellian plasmas. Triple-root jumps in spacecraft
potential can occur.
Author
Spacecraft Charging; Plasmas (Physics); Flux (Rate); Electrons; Critical Temperature; Electron Energy
20040111109 European Space Agency. European Space Research and Technology Center, ESTEC, Noordwijk, Netherlands
Modeling of the Photoelectron Sheath Around an Active Magnetospheric Spacecraft With PicUp3D
Thiebault, Benoit; Hilgers, Alain; Forest, Julien; Escoubet, Philippe; Fehringer, Michael; Laakso, H.; 8th Spacecraft Charging
Technology Conference; March 2004; 7 pp.; In English; See also 20040111031; No Copyright; Avail: CASI; A02, Hardcopy
Emission of photoelectrons by the sunlit surfaces of a spacecraft can affect the plasma environment via the resulting
spacecraft potential but also via the induced space charge. The photoelectron cloud structure around Cluster has been
investigated with the PicUp3D plasma simulation software taking into account the plume of the onboard ion emitter.
Preliminary results are presented related to the shielding of the ion emitter plume by the photoelectron and on the propagation
of the photoelectrons around the spacecraft and along the wire booms. Conclusions are drawn related to the possible influence
of these effects on electrostatic sensors mounted at the end of long (\g40 meters) wire boom antennas.
Author
Photoelectrons; Emitters; Space Charge; Plasmas (Physics); Cloud Physics; Plumes
20040121091 NASA Marshall Space Flight Center, Huntsville, AL, USA
Using Magnetic Fields to Control Convection during Protein Crystallization: Analysis and Validation Studies
Ramachandran, N.; Leslie, F. W.; [2004]; 1 pp.; In English
Contract(s)/Grant(s): NAS8-02096; Copyright; Avail: Other Sources; Abstract Only
The effect of convection during the crystallization of proteins is not very well understood. In a gravitational field,
convection is caused by crystal sedimentation and by solutal buoyancy induced flow and these can lead to crystal
imperfections. While crystallization in microgravity can approach diffusion limited growth conditions (no convection),
terrestrially strong magnetic fields can be used to control fluid flow and sedimentation effects. In this work, we develop the
analysis for magnetic flow control and test the predictions using analog experiments. Specifically, experiments on solutal
convection in a paramagnetic fluid were conducted in a strong magnetic field gradient using a dilute solution of Manganese
Chloride. The observed flows indicate that the magnetic field can completely counter the settling effects of gravity locally and
are consistent with the theoretical predictions presented. This phenomenon suggests that magnetic fields may be useful in
mimicking the microgravity environment of space for some crystal growth ana biological applications where fluid convection
is undesirable.
Author
Crystallization; Proteins; Convection; Magnetic Fields; Fluid Flow; Magnetic Control; Crystal Growth; Gravitational Effects
89
ASTRONOMY
Includes observations of celestial bodies; astronomical instruments and techniques; radio, gamma-ray, x-ray, ultraviolet, and infrared
astronomy; and astrometry.
20040111371 Smithsonian Astrophysical Observatory, Cambridge, MA, USA
RGS Spectroscopy of the Cygnus Loop XA Knot
Mushotzky, Richard F., Technical Monitor; Gaetz, Terrance J.; September 2004; 2 pp.; In English
Contract(s)/Grant(s): NAG5-9978; No Copyright; Avail: CASI; A01, Hardcopy
The observations were performed at the end of April 2002, and the data were received in July 2002. Unfortunately, the
observations were badly compromised by high levels of background radiation; one of the three observations was lost entirely.
Two replacement observations were scheduled for November 2002, and were only made available in January of 2003. A
preliminary analysis of the RGS data has been performed. Analysis of these data is complicated by the extended nature of the
source, and the limited statistics. Nevertheless, examination of the ‘m lambda’ vs. ‘xdsp-corr’ data shows that the bright knot
is visible in C VI Ly-alpha and Ly-beta, the O VII triplet and He-beta, and O VIII Ly-alpha. The dispersed C VI Ly-alpha
image is the first image of the remnant at that energy. The F, I, R components of the O VII triplet can be seen, and the 0 VII
He-beta is distinct from the O VIII Ly-alpha (although the dispersed diffuse emission provides a pseudo-continuum).
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