If it were to become apparent that dangerous changes in global climate were inevitable, despite greenhouse gas controls, active methods to cool the Earth on an emergency basis might be desirable. The ...concept considered here is to block 1.8% of the solar flux with a space sunshade orbited near the inner Lagrange point (L1), in-line between the Earth and sun. Following the work of J. Early Early, JT (1989) J Br Interplanet Soc 42:567-569, transparent material would be used to deflect the sunlight, rather than to absorb it, to minimize the shift in balance out from L1 caused by radiation pressure. Three advances aimed at practical implementation are presented. First is an optical design for a very thin refractive screen with low reflectivity, leading to a total sunshade mass of ≈20 million tons. Second is a concept aimed at reducing transportation cost to $50/kg by using electromagnetic acceleration to escape Earth's gravity, followed by ion propulsion. Third is an implementation of the sunshade as a cloud of many spacecraft, autonomously stabilized by modulating solar radiation pressure. These meter-sized "flyers" would be assembled completely before launch, avoiding any need for construction or unfolding in space. They would weigh a gram each, be launched in stacks of 800,000, and remain for a projected lifetime of 50 years within a 100,000km-long cloud. The concept builds on existing technologies. It seems feasible that it could be developed and deployed in ≈25 years at a cost of a few trillion dollars, <0.5% of world gross domestic product (GDP) over that time.
A 600 m 2 array of 6.5 m telescopes at the lunar pole Angel, Roger
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
2024-May-09, 2024-05-09, Letnik:
382, Številka:
2271
Journal Article
Recenzirano
Odprti dostop
The proposed lunar telescope for optical and infrared astronomy aims at very large aperture, 600 m
, at a fundable cost. It comprises an array of 18 separate telescopes, each of 6.5 m aperture. The ...200 m diameter array will be located within 1/2° (15 km) of a lunar pole on approximately level ground, with a perimeter screen deployed to provide shade and cooling to cryogenic temperature. The 500 m diameter screen will allow unobscured access down to 8° elevation. All 18 telescopes will reflect light into a central beam combiner to form a single image covering wavelengths from 0.4 µm to 10 µm. The initial instrument complement will include high-resolution and multi-object spectrographs to exploit the single combined field of view of two arcminute diameter, with the diffraction limited resolution of 6.5 m aperture. Scientific applications include the search for molecular biosignatures in transiting exoplanets, and the study of galaxy evolution using red-shifted spectra to beyond
= 10. The array cost, including delivery to the Moon by SpaceX Starship for installation using lunar base infrastructure, is around $10 billion, similar to that of the 25 m
JWST. To test the concept, first a single prototype 6.5 m unit would be operated at the lunar south pole. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.
A 600 m2 array of 6.5 m telescopes at the lunar pole Angel, Roger
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
05/2024, Letnik:
382, Številka:
2271
Journal Article
Recenzirano
Odprti dostop
The proposed lunar telescope for optical and infrared astronomy aims at very large aperture, 600 m2, at a fundable cost. It comprises an array of 18 separate telescopes, each of 6.5 m aperture. The ...200 m diameter array will be located within 1/2° (15 km) of a lunar pole on approximately level ground, with a perimeter screen deployed to provide shade and cooling to cryogenic temperature. The 500 m diameter screen will allow unobscured access down to 8° elevation. All 18 telescopes will reflect light into a central beam combiner to form a single image covering wavelengths from 0.4 µm to 10 µm. The initial instrument complement will include high-resolution and multi-object spectrographs to exploit the single combined field of view of two arcminute diameter, with the diffraction limited resolution of 6.5 m aperture. Scientific applications include the search for molecular biosignatures in transiting exoplanets, and the study of galaxy evolution using red-shifted spectra to beyond z = 10. The array cost, including delivery to the Moon by SpaceX Starship for installation using lunar base infrastructure, is around $10 billion, similar to that of the 25 m2 JWST. To test the concept, first a single prototype 6.5 m unit would be operated at the lunar south pole. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'.
High-contrast coronagraphic imaging of the immediate surrounding of stars requires exquisite control of low-order wave-front aberrations, such as tip-tilt (pointing) and focus. We propose an ...accurate, efficient, and easy to implement technique to measure such aberrations in coronagraphs which use a focal plane mask to block starlight. The coronagraphic low-order wave-front sensor (CLOWFS) produces a defocused image of a reflective focal plane ring to measure low-order aberrations. Even for small levels of wave-front aberration, the proposed scheme produces large intensity signals which can easily be measured, and therefore does not require highly accurate calibration of either the detector or optical elements. The CLOWFS achieves nearly optimal sensitivity and is immune from noncommon path errors. This technique is especially well suited for high-performance low inner working angle coronagraphs. On phase-induced amplitude apodization (PIAA)-type coronagraphs, it can unambiguously recover aberrations which originate from either side of the beam shaping introduced by the PIAA optics. We show that the proposed CLOWFS can measure sub-milliarcsecond telescope pointing errors several orders of magnitude faster than would be possible in the coronagraphic science focal plane alone, and can also accurately calibrate residual coronagraphic leaks due to residual low-order aberrations. We have demonstrated 10-3l/D pointing stability in a laboratory demonstration of the CLOWFS on a PIAA-type coronagraph.
An optical/infrared telescope of 20-100 m aperture located on the Moon would be able to observe objects 100 to 1,000 times fainter than the proposed next generation of space telescopes. The infrared ...region of the spectrum is particularly important for observations of objects at redshifts z > 7. The apparent simplicity and low mass of a liquid mirror telescope, compared with a traditional pointable glass mirror, suggest that the concept should be considered further. A previously proposed liquid mirror telescope, based upon a spinning liquid metallic alloy, is not appropriate for infrared applications, which will require a liquid below 130 K. Here we report the successful coating of an ionic liquid with silver. The surface is smooth and the silver coating is stable on a timescale of months. The underlying ionic liquid does not evaporate in a vacuum and remains liquid down to a temperature of 175 K. Given that there are ∼106 simple and ∼1018 ternary ionic liquids, it should be possible to synthesize liquids with even lower melting temperatures.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
As the solar electricity market has matured, energy conversion efficiency and storage have joined installed system cost as significant market drivers. In response, manufacturers of flat-plate silicon ...photovoltaic (PV) cells have pushed cell efficiencies above 25%-nearing the 29.4% detailed-balance efficiency limit-and both solar thermal and battery storage technologies have been deployed at utility scale. This paper introduces a new tandem solar collector employing a "PVMirror" that has the potential to both increase energy conversion efficiency and provide thermal storage. A PVMirror is a concentrating mirror, spectrum splitter, and light-to-electricity converter all in one: It consists of a curved arrangement of PV cells that absorb part of the solar spectrum and reflect the remainder to their shared focus, at which a second solar converter is placed. A strength of the design is that the solar converter at the focus can be of a radically different technology than the PV cells in the PVMirror; another is that the PVMirror converts a portion of the diffuse light to electricity in addition to the direct light. We consider two case studies-a PV cell located at the focus of the PVMirror to form a four-terminal PV-PV tandem, and a thermal receiver located at the focus to form a PV-CSP (concentrating solar thermal power) tandem-and compare the outdoor energy outputs to those of competing technologies. PVMirrors can outperform (idealized) monolithic PV-PV tandems that are under concentration, and they can also generate nearly as much energy as silicon flat-plate PV while simultaneously providing the full energy storage benefit of CSP.
Balance‐of‐system costs now dominate the installed cost of photovoltaic systems, causing the annually averaged module efficiency to become a primary system cost driver. The resulting continued push ...towards higher module efficiencies, coupled with the dominance of single‐axis tracking in the utility‐scale PV market, may create an opportunity for a low‐concentration tandem module technology. Here, we demonstrate such a tandem, using the “PVMirror” concept, on the mini‐module scale. The tandem couples a (concentrating) silicon PVMirror having an aperture area of 156.25 cm2 with a gallium arsenide receiver to achieve 29.6% efficiency with respect to the outdoor global irradiance. Unlike most concentrating technologies, the silicon PVMirror collects some of the diffuse light, but the tandem would nevertheless achieve 31% efficiency in the absence of diffuse light, as in a laboratory measurement. The same tandem technology can be implemented with a wide‐bandgap thin‐film PVMirror and silicon receiver—a potentially cost‐competitive combination—when efficient wide‐bandgap cells have been developed.
We present a low‐concentration “PVMirror” tandem concept based on single‐axis tracking. Though a concentrating technology, it collects diffuse light, as the primary optic is a PV module. We demonstrated this tandem concept by using a silicon mini‐module as a PVMirror and a gallium arsenide mini‐module as a receiver and hit 29.6% efficiency with respect to the outdoor global irradiance, which is the highest‐efficiency silicon‐based tandem reported with an area larger than 5 cm2 (the aperture of our tandem is 156 cm2).
Glass solar reflectors, similar to those widely used to concentrate sunlight in solar thermal plants, form the basis for REhnu's HCPV generators. Multijunction cells are housed in small, upgradeable ...units at each mirror focus.
We describe a polar Moon base habitat using direct solar energy for construction, food production and atmospheric revitalization. With a growing area as large as 2000 m
, it could provide for 40 or ...more people. The habitat is built like the ancient Roman Pantheon, a stone structure with a top circular oculus, bringing in focused sunlight that is spread out to crops below. The conical, corbelled structure is built from cast regolith blocks, held in compression despite the large internal atmospheric pressure by a regolith overlayer 20-30 m thick. It is sealed on the inside against leaks with thin plastic. A solar mirror concentrator used initially to cast the building blocks is later used to illuminate the habitat through a small pressure window at the oculus. Three years of robotic preparation of the building blocks does not seem excessive for a habitat which can be expected to last for millennia, as has the Treasury of Atreus made by similar dry-stone construction. One goal of returning to the Moon is to demonstrate the practicality of long-term human habitation off the Earth. The off-axis, paraboloidal reflecting mirror is rotated about the vertical polar axis in order to direct horizontal sunlight downward to a focus. In this way, the heavy materials needed from Earth to build and power the habitat are largely limited to the solar concentrator and regolith moving and moulding equipment. By illuminating with a reflector rather than with electricity, the solar collection area is 20 times smaller than would be needed for PV cells. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades'.
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