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Drake, V. A.

Publications and source records attributed to Drake, V. A..

2 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Coded aperture devices for viewing extended objects from space

Coded aperture sensors for photons or energetic neutral atoms (ENAs), which incorporate FOV limiters and subdivide the object field into a number of elements which is smaller than the number of detector pixels, are described. A least squares fit to the data is made in reconstructing the object field. To evaluate the optics and reconstruction algorithms, two 'breadboard' sensors have been constructed, one based on a film camera and the other upon a UV-light sensitive microchannel plate detector system. Results obtained thus far show that the concept is viable, and no special difficulties should be encountered in adapting the detector geometries to neutral particle imaging systems. Charged particle deflection plates could be incorporated into the region between the FOV limiter and the aperture, or installed ahead of the limiter.

Curtis, C. C.↗
NASA NTRS1992

H Ly-alpha transmittance of thin foils of C, Si/C, and Al/C for keV particle detectors

A class of instruments designed for remote sensing of space plasmas by measuring energetic neutral atoms (ENA) uses a thin foil as both a signal generator and a light shield. An ENA imager must look directly at the ENA source region, which is also usually an intense source of H Ly-alpha (1216 A) photons. It is desirable to minimize the energy threshold for ENA detectors, at the same time maximizing the blocking of H Ly-alpha. Optimizing filter design to meet these two contrary requirements has led us to measure the transmittance of thin C, Si/C, and Al/C foils at H Ly-alpha. Our results indicate that (1) transmittance of less than 0.0007 can be achieved with 7 micro-g/sq cm Si on 1.7 micro-g/sq cm C; (2) an Si/C composite foil with a thin carbon layer is more effective in blocking UV radiation while having the lowest energy threshold of all the foils measured; and (3) transmittance of Si/C foils of known Si and C thicknesses cannot be accurately predicted, but must be measured.

Drake, V. A.↗