NASA Scientific and Technical Aerospace Reports

are added using a monochromatic frame grabber producing a standard NTSC video signal that can be monitored and/or
recorded. The digital approach is more complicated, but maintains the full resolution of the acquisition cameras with the
capabilities to correct the signal image for pixel sensitivity variations and to remove of background light. Prototype circuits
for each scheme are described and example results from the investigation of the vortical flow field above a 75-degree delta
wing presented.
Author
Velocity Measurement; Signal Processing; Doppler Radar
33
ELECTRONICS AND ELECTRICAL ENGINEERING
Includes development, performance, and maintainability of electrical/electronic devices and components; related test equipment; and
microelectronics and integrated circuitry. for related information see also 60 Computer Operations and Hardware; and 76 Solid-State
Physics. For communications equipment and devices see 32 Communications and Radar.
20040111062 Centre National d’Etudes Spatiales, Toulouse, France
An Improved Method for Simulating the Charge of Dielectrics in a Charging Electron Environment
Payan, D.; Catani, J. P.; Reulet, R.; Dirassen, B.; Levy, L.; 8th Spacecraft Charging Technology Conference; March 2004;
15 pp.; In English; See also 20040111031; No Copyright; Avail: CASI; A03, Hardcopy
Due to their dielectric nature and under the effect of the different forms of radiation encountered in space, dielectrics
accumulate electrical charges up to the point where electrostatic discharges may occur. To prevent and avoid harmful
interference due to discharges, their behaviour under irradiation must therefore be investigated in the laboratory before they
are used in space applications. A current and widely used practice is to submit the tested materials to the bombardment of
monoenergetic electron beams. Such a practice ignores the presence in space of a spectrum of electrons with energies reaching
several MeV, and leads solely to surface charging and surface potentials generally higher than those really induced in space.
The new approach used by SIRENE is to build an electron source as similar as possible to the one existing in orbit. This paper
describes the SIRENE facility, which was developed for simulating the spatial geo-stationary environment during great
geomagnetic activity. The range of available electrons goes from 10 to 400 keV. From a monoenergetic electron beam of 400
keV and thanks to a complex diffusion foil (made of several foils of different thicknesses and surface areas) the quantity of
electrons of each energy level present in this particular environment is reproduced. However, it is always possible to work at
lower energy levels in the monoenergetic range, for instance to simulate the inverted gradient mode. This paper provides
information on the spectrum used for testing materials in the geo-stationary environment, and on the potential for adapting it
to other orbits. It also gives the first results demonstrating the interest of this new approach. It also mentions the new
instruments used to measure the surface potential as well as the space charge through the complete thickness of the material.
Author
Dielectrics; Computerized Simulation; Aerospace Environments; Electrostatics
20040111105 Toronto Univ., Ontario, Canada
Embedded-Probe Floating Potential Charge-Discharge Monitor
Balmain, Keith G.; Kremer, P. C.; Dubois, G. R.; Luettgen, A. A. E.; 8th Spacecraft Charging Technology Conference; March
2004; 9 pp.; In English; See also 20040111031; No Copyright; Avail: CASI; A02, Hardcopy
Described is a device that responds to the floating potential of an electrically isolated (or floating ) metal probe embedded
in a dielectric slab and exposed to a source of energetic electrons. With the passage of time, the probe potential becomes
increasingly negative due to the accumulation of electric charge both on it and nearby it in the surrounding dielectric, until
equilibrium is reached between charge influx and charge conduction or emission. The device ultimately would be mounted
on a spacecraft positioned in an energetic-electron environment, typically in geo-synchronous orbit or geo-transfer orbit. The
probe-plus-dielectric configuration would be designed to represent a relevant possible site for electrical breakdown, for
example with the metal probe representing the inner conductor of a coaxial cable or a metallic trace on a printed-circuit board.
A high probe floating potential or an abrupt change in potential would serve as advance warning of a charge accumulation
threat or an electrical breakdown threat in the vicinity of the monitor. Multiple units with probes at different depths would
respond preferentially to electrons with different penetration depths (i.e. different energies), thus conceivably providing data
for correlation with energetic-particle spectra from other instruments on the same satellite or ones nearby. Two designs are
described, one motor-driven and one piezo-vibrator-driven, so that the mechanical movement can generate an electrical signal
suitable for processing because it is proportional to the floating potential. Under high-vacuum exposure to Strontium-90
98