These next-generation large space observatories would study the highest priority astrophysics targets, including first generation stars - the first to shine and flame out after the Big Bang - early galaxies, and Earth-like exoplanets. These observatories could help address one of humanity's most important science questions: "Are we alone in the universe?"
Like a carry-on suitcase, payloads launching to space need to stay within allowable size and weight limits to fly. Already pushing size limits, the state-of-the-art 21 foot (6.5 meter) aperture James Webb Space Telescope needed to be folded up origami-style - including the mirror itself - to fit inside the rocket for its ride to space. The aperture of an optical space observatory refers to the size of the telescope's primary mirror, the surface that collects and focuses incoming light.
The aperture for the space observatory envisioned by FLUTE researchers under the current concept would be approximately 164 feet (50 meters) in diameter - half as long as a football field.
Conventional technology for making optical components for telescopes is literally a grind. It involves an iterative process of sanding and polishing solid materials, such as glass or metal, to shape the precise curved surfaces of lenses and mirrors needed. Using current technologies, scaling up space telescopes to apertures larger than approximately 33 feet (10 meters) in diameter does not appear economically viable.
FLUTE's novel cost-effective technology approach, in contrast, takes advantage of the way fluids naturally behave in microgravity.
All liquids have an elastic-like force that holds them together at their surface. This force is called surface tension. It's what allows some insects to glide across water without sinking and gives water droplets their shape.
On Earth, when droplets of water are small enough - 0.08 inches (2 millimeters) or smaller - surface tension overcomes gravity, and they remain perfectly spherical, much like droplets of morning dew beading into tiny spheres on plant leaves. If a droplet grows much larger, it gets squished under its own weight. But in space, where fluids are free-floating, unhindered by gravity, even large amounts of liquids assume the most energy efficient shape possible, a perfect sphere.
Liquids can cling to surfaces due to a physical property called adhesion. In microgravity, if a sufficient amount of liquid is made to adhere to the interior surface of a circular, ring-like frame, the liquid will stretch across the inside of the frame and naturally form a curved shape - called a spherical section - thanks to surface tension.
By using the right volume of liquid, it is possible to make the surface of the liquid curve inward instead of bulging outward. If the liquid is reflective, that inwardly curved surface can serve as a telescope mirror.
FLUTE would launch liquids to space as the raw material to make optical components in orbit. The primary mirror would form within a huge circular frame and remain in liquid state with an extremely smooth surface for collecting light. FLUTE's technology approach is theoretically able to scale up to very large sizes. The technology could potentially enable telescopes with apertures measuring 10 times - or even 100 times - larger than telescopes to-date.
A unique feature of the liquid mirror would be its ability to self-repair if damaged in space. For instance, if a micrometeorite impacts the mirror's surface, it would naturally heal itself within a short period of time.
The FLUTE team has conducted small-scale experiments in shaping lenses from liquids in different environments: First using neutral buoyancy space analog conditions in a ground laboratory and then in a series of parabolic microgravity flights and aboard the International Space Station.
With the support of a NASA Innovative Advanced Concepts (NIAC) Phase I award, the team is working to analyze options for the key components of a fluid telescope observatory, further develop the mission concept, and create an initial plan for a subscale small spacecraft demonstration in low-Earth orbit.
Enabling the Next Generation of Large Space Observatories
The future of space-based UV/optical/IR astronomy requires ever larger telescopes. For example, the highest priority astrophysics targets, including Earth-like exoplanets, first generation stars, and early galaxies, are all very faint, which presents a challenge for current and next generation telescopes. Larger telescopes are one of the main (if not the main) way to address this issue.
One of the more important science questions Are we alone in the Universe? has been asked for thousands of years and features prominently in the Astro2020 decadal survey. We are fortunate to live at a time when technologies finally exist to begin answering it. Over the last three decades, a number of methods have been used to identify potentially habitable planets around other stars.
James Webb Space Telescope (JWST) will perform some spectroscopic measurements of transiting exoplanet atmospheres, perhaps even detecting biomarker gases. The next NASA Astrophysics flagship mission (Roman) will do direct imaging spectroscopy of exoplanets, but it is not specifically designed for potentially habitable planets. The follow-on flagship recommended by the Astro2020 survey is planned to directly image 25 potentially Earth-like planets. However, the number of exoplanets on which life could be detected by the Astro2020 flagship is strongly limited by its aperture, which is planned to be ~6 m.
With mission costs depending strongly on aperture diameter, scaling current space telescope technologies to aperture sizes beyond 10 m does not appear economically viable. The 6-m Astro2020 flagship would already strain NASAs budget and its launch date is expected to be later than most astronomers would like (first half of the 2040s), largely driven by the substantial expected cost. Without a breakthrough in scalable technologies for large telescopes, future advances in astrophysics may slow down or even completely stall. Thus, there is a need for cost-effective solutions to scale space telescopes to larger sizes.
We propose a mission concept for a space observatory with a large-aperture (50-meter) unsegmented primary mirror suitable for a variety of astronomical applications. The mirror would be created in space via a novel approach based on fluidic shaping in microgravity, which has already been successfully demonstrated in a laboratory neutral buoyancy environment, in parabolic microgravity flights, and aboard the International Space Station (ISS). Theoretically scale-invariant, this technique has produced optical components with superb, sub-nanometer (RMS) surface quality. In the Phase I study we will analyze suitable options for the key components of the 50-m observatory, develop its detailed mission concept, and create an initial plan for a subscale small spacecraft demonstration in low Earth orbit (LEO).
Related Links
Fluidic Telescope (FLUTE): Enabling the Next Generation of Large Space Observatories
Stellar Chemistry, The Universe And All Within It
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