Imagine a space telescope with a mirror stretching 50 meters across! That’s larger than the width of a UK soccer field and nearly eight times wider than the James Webb Space Telescope. Now imagine that this enormous mirror is made not of precisely manufactured glass segments, but of liquid floating in space. This might sound like science fiction but it's the cutting edge concept behind the Fluidic Telescope (FLUTE), a joint NASA-Technion project that could revolutionise how we explore the universe.
The challenge of building ever larger space telescopes has reached a technological bottleneck. Even the James Webb Space Telescope, with its 6.5-meter segmented mirror, pushed the limits of what could be folded into a rocket and deployed in space. Scaling this approach to the tens of meters needed to directly image Earth like exoplanets seems impossible with current methods.
Enter the liquid mirror solution. In the microgravity environment of space, a thin film of liquid naturally forms a perfect spherical surface due to surface tension, the shape needed for a telescope mirror. The FLUTE concept proposes using this phenomenon to create mirrors that would be impractical or impossible to manufacture using traditional solid materials.
But there's a catch: even if such a mirror could be created, what happens when the telescope needs to slew from one astronomical target to another? New research led by Israel Gabay and colleagues at Technion has tackled this fundamental question through sophisticated mathematical modelling and experimentation. Their work reveals both the promise and the challenges of liquid space telescopes.
The team developed the first comprehensive theoretical model describing how a liquid mirror behaves when subjected to the angular accelerations of telescope slewing manoeuvres. Using advanced mathematical techniques they created analytical solutions that predict exactly how the liquid surface will deform during and after telescope movements.
Their findings are both encouraging and sobering. When a 50 meter liquid telescope with a 1 millimetre thick mirror performs typical slewing manoeuvres, the surface does indeed deform, with disturbances reaching several micrometers at the edges. However, these deformations propagate inward extremely slowly, taking years to reach the telescope's center.
The key insight is that not all of the mirror needs to remain perfect. Even after 10 years of operation involving daily slewing manoeuvres, the inner 80% of the aperture remains adequately formed. This is well within the tolerance for high quality space optics.
The research reveals that telescope operators would need to manage a "manoeuvring budget”, or the total amount of slewing the telescope can perform before deformations compromise its optical performance. Interestingly, the study found that multiple small manoeuvres in different directions can sometimes produce better results than single large movements, as they create more symmetric deformation patterns that are easier to correct optically.
To validate their theoretical predictions, the researchers conducted ingenious laboratory experiments using microscopic liquid films and contactless electromagnetic forces to create controlled deformations. Despite the vast difference in scale the mathematical framework successfully predicted the observed liquid dynamics.
The implications extend beyond just building bigger telescopes. Liquid mirrors could enable space telescopes that reshape themselves for different observational tasks, correct their own optical aberrations, or even self repair from micrometeorite damage. The research suggests that such telescopes could maintain functionality for decades, with the possibility of "reset" procedures to restore the original mirror shape when needed.
As space agencies plan the next generation of telescopes for the 2030s and beyond, the FLUTE concept represents a shift from the precision manufacturing process to precision fluid dynamics. While challenges remain, particularly in the engineering systems needed to contain and control the liquid in space, this research demonstrates that the fundamental physics is sound.