A diffractive solar sail, or diffractive lightsail, is a type of solar sail which relies on diffraction instead of reflection for its propulsion. [1] [2] Current diffractive sail designs use thin metamaterial films, containing micrometer-size gratings based on polarization or subwavelength refractive structures, causing light to spread out (i.e. diffract) and thereby exert radiation pressure when it passes through them. [2] [3]
The idea of using diffraction for a solar sail was first proposed in 2017 by researchers at the Rochester Institute of Technology. [4] This was enabled in part by advances in material design and fabrication (particularly of gratings), and optoelectronic control. [5] In 2019 a diffractive solar sail project from the Rochester Institute of Technlology suggested a solar polar orbit mission with diffractive sails that could reach a higher solar inclination angle and smaller orbital radius than one with reflective sails, reaching NASA's NIAC phase II. [1] [2] [6] In 2022 the NIAC project reached phase III and gained US$2 million of support from NASA, with involvement of researchers from both Johns Hopkins University and the Rochester Institute of Technology. [7] [8]
Reflective solar sail designs tend to consist of large, thin reflective sheets. By the law of reflection, the forces acting on them will always be normal to the sheet surface; the sheets must therefore be tilted during navigation, which poses structure and control challenges, and reduces the power reaching the sail. [2] [5] [7] These in turn can lower reliability, increase mass, and reduce acceleration. [2] Furthermore, reflective sails tend to absorb a reasonable proportion of the light hitting them, causing them to heat up; this can cause structural problems, particularly when the sail is repeatedly heated and then allowed to cool. [5] Also, each photon hitting the sail is used once, i.e. it's either reflected or absorbed. [5]
On the other hand, in a diffractive sail the grating can redirect light even when the sheet directly faces the sun, allowing much more efficient control with maximum power hitting the sail. [5] [2] The diffractive film can be designed to allow for optoelectronic control of the gratings, thereby reducing mass and increasing reliability relative to mechanical control. [2] Since the film is translucent, most of the light just passes through the sail, reducing overall heating. [5] Photons can be reused: either by passing through a second diffraction grating for more thrust, or by going to a solar cell to provide electricity. [8]
Diffraction is the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.
An optical spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the irradiance of the light but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light or a closely derived physical quantity, such as the corresponding wavenumber or the photon energy, in units of measurement such as centimeters, reciprocal centimeters, or electron volts, respectively.
Solar sails are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010.
Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a laser beam and it is either pulsed or continuous. A continuous beam lends itself to thermal rockets, photonic thrusters and light sails, whereas a pulsed beam lends itself to ablative thrusters and pulse detonation engines.
In optics, a diffraction grating is an optical grating with a periodic structure that diffracts light, or another type of electromagnetic radiation, into several beams traveling in different directions. The emerging coloration is a form of structural coloration. The directions or diffraction angles of these beams depend on the wave (light) incident angle to the diffraction grating, the spacing or periodic distance between adjacent diffracting elements on the grating, and the wavelength of the incident light. The grating acts as a dispersive element. Because of this, diffraction gratings are commonly used in monochromators and spectrometers, but other applications are also possible such as optical encoders for high-precision motion control and wavefront measurement.
A laser diode is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction.
XMM-Newton, also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second cornerstone mission of ESA's Horizon 2000 programme. Named after physicist and astronomer Sir Isaac Newton, the spacecraft is tasked with investigating interstellar X-ray sources, performing narrow- and broad-range spectroscopy, and performing the first simultaneous imaging of objects in both X-ray and optical wavelengths.
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle.
A coronagraph is a telescopic attachment designed to block out the direct light from a star or other bright object so that nearby objects – which otherwise would be hidden in the object's bright glare – can be resolved. Most coronagraphs are intended to view the corona of the Sun, but a new class of conceptually similar instruments are being used to find extrasolar planets and circumstellar disks around nearby stars as well as host galaxies in quasars and other similar objects with active galactic nuclei (AGN).
A space blanket is an especially low-weight, low-bulk blanket made of heat-reflective thin plastic sheeting. They are used on the exterior surfaces of spacecraft for thermal control, as well as by people. Their design reduces the heat loss in a person's body, which would otherwise occur due to thermal radiation, water evaporation, or convection. Their low weight and compact size before unfurling make them ideal when space or weight are at a premium. They may be included in first aid kits and with camping equipment. Lost campers and hikers have an additional possible benefit: the shiny surface flashes in the sun, allowing its use as an improvised distress beacon for searchers and as a method of signalling over long distances to other people.
The NASA Institute for Advanced Concepts (NIAC) is a NASA program for development of far reaching, long term advanced concepts by "creating breakthroughs, radically better or entirely new aerospace concepts". The program operated under the name NASA Institute for Advanced Concepts from 1998 until 2007, and was reestablished in 2011 under the name NASA Innovative Advanced Concepts and continues to the present. The NIAC program funds work on revolutionary aeronautics and space concepts that can dramatically impact how NASA develops and conducts its missions.
A distributed-feedback laser (DFB) is a type of laser diode, quantum-cascade laser or optical-fiber laser where the active region of the device contains a periodically structured element or diffraction grating. The structure builds a one-dimensional interference grating, and the grating provides optical feedback for the laser. This longitudinal diffraction grating has periodic changes in refractive index that cause reflection back into the cavity. The periodic change can be either in the real part of the refractive index or in the imaginary part. The strongest grating operates in the first order, where the periodicity is one-half wave, and the light is reflected backwards. DFB lasers tend to be much more stable than Fabry–Perot or DBR lasers and are used frequently when clean single-mode operation is needed, especially in high-speed fiber-optic telecommunications. Semiconductor DFB lasers in the lowest loss window of optical fibers at about 1.55 μm wavelength, amplified by erbium-doped fiber amplifiers (EDFAs), dominate the long-distance communication market, while DFB lasers in the lowest dispersion window at 1.3 μm are used at shorter distances.
The Extreme Ultraviolet Explorer was a NASA space telescope for ultraviolet astronomy. EUVE was a part of NASA's Explorer spacecraft series. Launched on 7 June 1992. With instruments for ultraviolet (UV) radiation between wavelengths of 7 and 76 nm, the EUVE was the first satellite mission especially for the short-wave ultraviolet range. The satellite compiled an all-sky survey of 801 astronomical targets before being decommissioned on 31 January 2001.
An echelle grating is a type of diffraction grating characterised by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore in high diffraction orders. Higher diffraction orders allow for increased dispersion (spacing) of spectral features at the detector, enabling increased differentiation of these features. Echelle gratings are, like other types of diffraction gratings, used in spectrometers and similar instruments. They are most useful in cross-dispersed high resolution spectrographs, such as HARPS, PARAS, and numerous other astronomical instruments.
An electric sail is a proposed form of spacecraft propulsion using the dynamic pressure of the solar wind as a source of thrust. It creates a "virtual" sail by using small wires to form an electric field that deflects solar wind protons and extracts their momentum. The idea was first conceptualised by Pekka Janhunen in 2006 at the Finnish Meteorological Institute.
Vyacheslav Gennadievich Turyshev is a Russian physicist now working in the US at the NASA Jet Propulsion Laboratory (JPL). He is known for his investigations of the Pioneer anomaly, affecting Pioneer 10 and Pioneer 11 spacecraft, and for his attempt to recover early data of the Pioneer spacecraft to shed light on such a phenomenon.
Optical lift is an optical analogue of aerodynamic lift, in which a cambered refractive object with differently shaped top and bottom surfaces experiences a stable transverse lift force when placed in a uniform stream of light.
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail interstellar probes named Starchip, to be capable of making the journey to the Alpha Centauri star system 4.34 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.
A solar gravitational lens or solar gravity lens (SGL) is a theoretical method of using the Sun as a large lens with a physical effect called gravitational lensing. It is considered the best method to directly image habitable exoplanets.
Joel C. Sercel is an American aerospace engineer. He is the inventor of Omnivore Thruster, a new concept of propulsion technology for in-space transportation, of Optical Mining, a technology for extracting raw materials from asteroids, of the Radiant Gas Dynamic method of lunar water harvesting, and of the Sun Flower Power Tower architecture for capturing and converting solar power into electricity to be used in polar lunar regions. As of July 2021, his work and studies have led to eight US patents and seventeen published applications. An asteroid, (46308) Joelsercel, was named after him.
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