Studying a supernova: what the New Robotic Telescope will tell us

Supernovae – exploding stars at the end of their lives – and the black-hole-powered, enormous explosions of gamma ray bursts, are occurring in galaxies all around us.

Even when these phenomena are identified by powerful telescopes, they might only be visible for a matter of minutes, and their transient nature means opportunities to study them are exciting and rare. No sooner have they been identified, and the position of the telescope adjusted, then they quickly become too faint for observation.

But thanks to a high speed, automated approach, this ephemeral display will be the target of the New Robotic Telescope (NRT). The NRT will be able to move to a target in just 30 seconds, making it ten times faster than its predecessor. It will be four times more sensitive too, and these capabilities will give scientists the opportunity to make new discoveries about the universe, capturing the very first seconds of evolution after an explosion.

The NRT advances on the Liverpool Telescope, so called after its 2003 development by Liverpool John Moores University. This telescope is based on La Palma in the Canary Islands, where it benefits from high altitude, stable atmospheric conditions, and low light pollution. The NRT will be based there too, and the project to develop the new telescope is a consortium led by Liverpool John Moores University (LJMU) in partnership with the Institute of Astrophysics of the Canary Islands (IAC) and the University of Oviedo in Spain.

30 seconds to target

The increased sensitivity of the NRT will be a result of its much larger size, with a primary mirror diameter twice as large as its predecessor, increasing up to four metres. The fully automated robotic telescope means that it can remain unstaffed, but the crucial benefit of automation is achieving the 30-seconds time to target. The NRT will receive early warning signals about the presence of astronomical phenomena from telescopes, including those located in space, and automated control will then quickly react to find its target.

A striking design feature of the NRT is its clamshell enclosure. Set to be the largest clamshell style roof of any telescope in the world, this design will help the NRT achieve fast deployment with 360° viewing. To reach the 30-second to target mark, the ability to quickly position the telescope is also crucial. With such a short time window to observe the phenomena, this must be combined with rapid engagement of the telescope’s instrumentation.

This instrumentation will measure different properties of the light coming from space, and it will be installed in an area of the telescope called the focal station. Light travels through the telescope’s optical system and down towards its focus, where it reaches the science fold mirror, the third mirror in the optical path. This mirror is angled at 45° and rotates to reflect the light towards the required instrument. The instrument array, positioned around the focal station, includes spectrographs that can identify aspects such as the target object’s chemical composition, as well as its temperature, mass, luminosity, and even its relative motion – all by measuring a spectrum of the light. The focal station also includes a polarimeter that can identify the angle of the approaching wave of light to identify phenomena like magnetic fields.

Arguably the most desirable location for an instrument is the straight-through port. This is positioned directly below the primary mirror and directly receives the incoming beam of light with no interaction with the science fold mirror. Usually, the straight-through port hosts the instrument that requires the largest field of view of the sky. This is often an imaging camera that carries out photometry, used to explore brightness that can help indicate the nature of supernovae and gamma-ray bursts. The NRT’s straight-through port will either host a camera like this, or a polarimeter, as a straight-through port location can achieve more accurate polarimetric measurements.

Fast and precise mirror control

The ability to switch the light beam to or away from the straight-through port in a matter of seconds is vital to capture the fleeting celestial activity. To prevent obscuration of the light beam, the focal station’s mirror must rapidly move out of the light’s path. This will be achieved by mounting the mirror on a platform that can move laterally at high speed, carried by a linear motion system with a ball screw actuator.

“The mirror and its support structure weigh around 70kg, and we need to move this mass quickly and accurately, within five seconds,” says Adam Garner, Control & Automation Engineer for the NRT at LJMU. “A separate motor and gearbox solution would achieve the required accuracy, but not at the speed we needed, so we specified a direct drive system that directly connects to the ball screw, eliminating the mechanical losses that additional transmission would introduce.”

Adam engaged with maxon’s Young Engineers Program (YEP), which provides engineering expertise and beneficial rates for academic projects. maxon engineer, Ronak Samani, specified a maxon IDX direct drive. Quickly moving the linear stage and its mirror into place also has to be achieved with pinpoint accuracy, and the IDX direct drive ensures micron-level precision.

Direct drive motion solution

This is reached using a design that combines a brushless DC motor with an integrated encoder, as well as a positioning controller that enables smooth modulation of position and speed. The motion system is also controlled with command signals carried over the EtherCAT communications protocol, where real time data exchange optimises precision coordination.

As the NRT operates autonomously, and without maintenance engineers on site, reliability is also crucial. This requirement also extends to the motion system.

“The telescope’s dome will close in bad weather, but the island’s proximity to the Sahara means that after six months of operation, the equipment is covered with a film of dust that can damage the sensitive equipment if it’s allowed to penetrate,” says David Copley, Systems Engineer for the NRT at LJMU.

The direct drive motor’s IP65 rating will seal it from dust and ensure long-term, reliable operation.

Heading to first light

The team is currently lab testing the mechanical control of the focal station’s linear motor, and they aim to complete this aspect around January 2024. This feeds in to the NRT’s overall timeline with ‘first light’, its operational introduction, planned for 2026.

With its speed of reaction, combined with sensitivity, the NRT is set to provide new discoveries on the evolution of the cosmos and our understanding of physics. But the new telescope is also intended to inspire future generations of astronomers.

“The NRT will work as part of the Schools Observatory, giving school pupils around the UK and worldwide the opportunity to make their own observations,” says David. “Via the Schools Observatory, school students currently receive time with the Liverpool Telescope. When it comes online, this will be extended to the NRT too.”