Skinny Flat Lenses Might Unleash a Revolution in House Telescopes
Because of the legal guidelines of physics, there are two fundamental guidelines about telescopes. The primary is that the larger your major lens or mirror, the upper the decision of your telescope. The second is that lenses and mirrors need to be curved to focus gentle into a picture. So, if you need an area telescope delicate sufficient to see the atmospheres of distant exoplanets, Your telescope goes to want a big curved mirror or lens. However neither of this stuff is technically true, as a newly proposed telescope design demonstrates.
The necessities for high-resolution telescopes are actual, however there are methods to get round them a bit. For instance, trendy optical telescopes use giant mirrors, that are tough to fabricate in actually giant sizes. Because of this new observatories use a mix smaller of hexagonal mirrors as an alternative of a single giant one. Even the James Webb House Telescope makes use of a number of mirrors in tandem. With optical telescopes, the mirrors are all clustered collectively, however they don’t need to be.
The mandatory dimension of your mirror depends upon the wavelengths of sunshine you employ. The wavelengths of optical gentle are on the order of some hundred nanometers, so even a 4-meter huge mirror offers you a really detailed view of the heavens. Radio wavelengths are a lot bigger, on the order of millimeters to a number of meters, and a radio mirror would should be kilometers huge to create a high-resolution picture. So trendy radio telescopes such because the Atacama Massive Millimeter Array (ALMA) use an array of antenna dishes. By combining the info by way of a course of often called correlation, an array can work as a single giant digital telescope. Radio astronomers have used this method to create the Earth-sized Occasion Horizon Telescope (EHT), which may observe a supermassive black gap in one other galaxy.
Two dozen telescopes may very well be launched as flatpack cargo. Credit score: Daniel Apai/College of Arizona
Optical observatories can even use an array of telescopes to create a big digital one, however the a lot shorter wavelengths of seen gentle make it tough to do on Earth. Even the smallest floor vibration can shift your telescopes out of alignment. However in house vibration isn’t a big drawback, so we may construct giant optical arrays and launch them into orbit. There are a number of engineering challenges, however one massive one is that telescopes with curved lenses or mirrors are heavy, making it cost-prohibitive to launch dozens of them.
Enter the Nautilus House Observatory (NSO). The proposed mission plans for an array of 35 8-meter telescopes. Working collectively as a single digital telescope array, the NSO can be able to analyzing the atmospheres of greater than a thousand Earth-like worlds. Fairly than utilizing curved mirrors, every telescope would use a big lens. However as an alternative of utilizing a heavy curved lens, every would use a flat one.
A daily curved lens vs a flat Fresnel lens. Credit score: Wikimedia consumer Pko
That is potential due to a bodily trick. Though lenses do need to be curved to focus gentle, it’s solely the floor of the lens that does the refraction. You don’t want all of the thick materials behind the curved floor, so you may simply have rings of curved sections with a flat backing. This trick was first popularized by French physicist Augustin-Jean Fresnel and is now known as Fresnel lenses. Fresnel lenses had been first utilized in lighthouses, however are actually utilized in the whole lot from overhead projectors to VR headsets. They are often made so skinny you may even get ones which are versatile plastic sheets. The explanation they haven’t been utilized in optical astronomy is that their segmented design typically produces photos which are too fuzzy for telescopes. The NSO proposal has overcome this problem by making a Fresnel lens with out fuzzy photos.
Fairly than merely utilizing ringed sections of a curved lens floor, the brand new design makes use of a posh etched sample on the lens that takes benefit of optical diffraction. Because of this, gentle is targeted on a single level, permitting for a pointy picture. This design scales, so that giant lenses can nonetheless be flat and light-weight.
Utilizing this lens design, the NSO telescopes might be a lot lighter than standard house telescopes. The telescopes can be folded right into a flatpack in order that dozens of telescopes may very well be launched directly, making the observatory cost-effective. Will probably be a long time earlier than the Nautilus House Observatory may very well be constructed and launched. However this proposal exhibits that sooner or later space-based telescope arrays shall be a strong instrument for astronomers.
Reference: Apai, Dániel, et al. “A thousand earths: a really giant aperture, ultralight house telescope array for atmospheric biosignature surveys.” The Astronomical Journal 158.2 (2019): 83.