Large area low-cost space solar cell development

A development program to produce large-area (5.9 x 5.9 cm) space quality silicon solar cells with a cost goal of 30 $/watt is descibed. Five cell types under investigation include wraparound dielectric, mechanical wraparound and conventional contact configurations with combinations of 2 or 10 ohm-cm resistivity, back surface reflectors and/or fields, and diffused or ion implanted junctions. A single step process to cut cell and cover-glass simultaneously is being developed. A description of cell developments by Applied Solar Energy Corp., Spectrolab and Spire is included. Results are given for cell and array tests, performed by Lockheed, TRW and NASA. Future large solar arrays that might use cells of this type are discussed

Solar cell development for the power extension package

The PEP is a 32 kilowatt flexible substrate, retrievable, solar array system for use on the Space Shuttle. Solar cell costs will be reduced by increasing cell area and simplifying cell and coverglass fabrication processes and specifications. The cost goal is to produce cells below $30 per watt. Two and ten ohm-cm silicon cells were investigated. In phase I of the cell development program a few thousand candidate cells will be produced and evaluated for utility and quality. In phase II a large number of cells will be fabricated to verify production readiness and cell yields and costs. This schedule is compatible with PEP initial operational capability in 1984. Approximately 140,000 large area (5.9 x 5.9 cm) cells will be required for two PEP solar arrays. The status of the cell development and testing, including a radiation damage test and side-by-side comparison of candidate cell types with pre- and post-irradiation airplane calibration of outer space short-circuit current, is reported

The morphology of the Magellanic Clouds revealed by stars of different age: results from the DENIS survey

The spatial distribution of sources populating different regions of the colour-magnitude diagram (I-J, I) extracted from the DENIS catalogue towards the Magellanic Clouds (DCMC -- Cioni et al. 2000) reveal significantly different morphologies. Each region is associated to a different age group. The Large Magellanic Cloud (LMC) shows an extended circular shape with a prominent, off center bar, a nucleus and irregular spiral arms. The Small Magellanic Cloud shows a perturbated structure with a prominent central concentration of stars. Old and young populations are offset from one another.Comment: 4 pages and 7 figures, accepted for publication in A&A Journal Letter

The AGB population of NGC 6822: distribution and the C/M ratio from JHK photometry

NGC 6822 is an irregular dwarf galaxy and part of the Local Group. Its close proximity and apparent isolation provide a unique opportunity to study galactic evolution without any obvious strong external influences. This paper aims to study the spatial distribution of the asymptotic giant branch (AGB) population and metallicity in NGC 6822. Using deep, high quality JHK photometry, taken with WFCAM on UKIRT, carbon- and oxygen-rich AGB stars have been isolated. The ratio between their number, the C/M ratio, has then been used to derive the [Fe/H] abundance across the galaxy. The tip of the red giant branch is located at K0 = 17.41 \pm 0.11 mag and the colour separation between carbon- and oxygen-rich AGB stars is at (J - K)0 = 1.20 \pm 0.03 mag (i.e. (J - K)2MAS S {\guillemotright} 1.28 mag). A C/M ratio of 0.62 \pm 0.03 has been derived in the inner 4 kpc of the galaxy, which translates into an iron abundance of [Fe/H] = -1.29\pm0.07 dex. Variations of these parameters were investigated as a function of distance from the galaxy centre and azimuthal angle. The AGB population of NGC 6822 has been detected out to a radius of 4 kpc giving a diameter of 56 arcmin. It is metal-poor, but there is no obvious gradient in metallicity with either radial distance from the centre or azimuthal angle. The detected spread in the TRGB magnitude is consistent with that of a galaxy surrounded by a halo of old stars. The C/M ratio has the potential to be a very useful tool for the determination of metallicity in resolved galaxies but a better calibration of the C/M vs. [Fe/H] relation and a better understanding of the sensitivities of the C/M ratio to stellar selection criteria is first required