Liquid-mirror space telescope
A space telescope using a rotating liquid mirror and artificial gravity.
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A liquid-mirror space telescope is a proposed design for a reflecting telescope in space where the main mirror is made from a reflective liquid, such as mercury. Instead of using Earth’s gravity to shape the spinning liquid into a parabola, the telescope would create its own artificial gravity. Several configurations have been suggested. One involves spinning a mirror assembly and a counterweight (which might hold the camera) to generate centripetal force.
Another uses a hollow, spinning torus, with the camera at its center; a flat mirror could be added to allow the telescope to point in different directions without changing the spin axis. A balloon design spins a reflective liquid inside a flexible envelope, which deforms into a parabolic shape, with an internal flat mirror directing light to the concave surface. A fourth option uses a spacecraft under constant acceleration from an ion thruster, carrying a rotating liquid mirror aligned with the direction of travel; the spacecraft can be steered to aim the mirror anywhere.
History
Other methods to create the parabolic shape include using magnetic fields on a viscous, partially magnetic liquid, relying on internal pressure or surface tension, or letting the liquid solidify after shaping to form a solid mirror. The main advantage is cost: a liquid mirror would be much cheaper to build than a conventional glass mirror of similar size, making very large space telescopes more feasible. In April 2022, NASA announced the Fluidic Telescope Experiment (FLUTE) on the ISS, part of Axiom Mission 1 astronaut Eytan Stibbe’s research.
This tested liquid lenses by injecting water with polymers in microgravity, using buoyancy to cancel gravitational forces, then hardening the shape with UV light or temperature. A 2025 study from the Technion in Israel found that maneuvering the telescope to point at different targets would cause tiny ripples on the mirror’s surface, but the effect would be very slow, and the inner 80% of the aperture would remain optically usable even after ten years of regular operation.
Quick Facts
- Primary reflector material
- reflecting liquid such as mercury
- Artificial gravity methods
- twirled pail
- half toroid
- balloon
- continuous-acceleration rocket
- Other parabolic shaping methods
- magnetic fields
- internal pressures or surface tension
- cooling to solidify
Facts from the source article.
Background
The concept includes several designs. In the twirled pail design, a pair of objects—one the mirror assembly and the other a counterweight possibly containing a camera assembly—are spun up to induce centripetal acceleration on the surface of the mirror assembly. The half toroid design spins a hollow torus to maintain centripetal acceleration against the inside wall, with the camera assembly in the center; the torus width is arbitrarily large, and optional pieces include a large flat mirror in the center to allow randomly orienting the mirror without frequently changing the axis of spin.
Design
The balloon design uses a balloon with reflective liquid on the inside that is spun up and deforms into a parabolic shape, with a flat mirror on the inside reflecting light to the concave surface. The continuous-acceleration rocket design accelerates a spacecraft by an ion thruster or similar, producing constant linear acceleration; the spacecraft carries a rotating liquid mirror with its axis parallel to the direction of acceleration, and the spacecraft can be accelerated in any direction so the mirror can be aimed in any direction.
Other possibilities for inducing a parabolic shape include magnetic fields on a viscous and partially magnetic liquid; internal pressures or surface tension effects on a reflective liquid; or creating the telescope while the reflective surface is liquid but depending on cooling effects to solidify the surface and then using that as the telescope main mirror.
In April 2022, NASA reported they would conduct the Fluidic Telescope Experiment (FLUTE) on the ISS as part of Axiom Mission 1 astronaut Eytan Stibbe's research portfolio. The research would test liquid lenses by using water injected with polymers in microgravity, utilizing buoyancy to even gravitational forces and cause weightlessness, to be later hardened by UV light or temperature in orbit. A 2025 study by the Technion in Israel concluded that while maneuvering the telescope to point at different points in space will cause tiny ripples on the surface of the mirror, the effect would be very slow, and the inner 80% of the aperture will still be optically functional even after 10 years of regular operation.
Frequently Asked Questions
What is a liquid-mirror space telescope?
It is a proposed reflecting-telescope design whose primary mirror is a reflective liquid, typically mercury, rather than a solid optical surface. Because there is no Earth gravity in orbit to pull the liquid into a parabola, the telescope must generate its own artificial gravity through spinning or sustained acceleration.
How does a liquid-mirror space telescope shape its mirror in microgravity?
Several configurations have been outlined: a 'twirled pail' setup spins the mirror assembly against a counterweight, a hollow spinning torus holds the camera at its center, and a continuous-acceleration rocket uses steady thrust to press the liquid into a parabola. Alternative shaping ideas include magnetic fields, internal pressures, surface tension, or simply cooling the liquid until it solidifies in the correct form.
More in Telescope Types
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Liquid-mirror space telescope (CC BY-SA 4.0).
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