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By Maury Wood, VP, Strategic Marketing, Vicor
Deep space exploration has captured the imagination for generations, driven by humanity’s desire to understand the origins of the Universe. It’s a journey of constant discovery and inspiration for Italy’s Microgate and its customers. Established in 1989 by brothers Vinicio and Roberto Biasi, Microgate built its early reputation providing highly accurate timing devices for professional sports and racing events. Driven by a focus on extreme precision, the company soon expanded its technology to space exploration, building upon Roberto’s advanced training in adaptive optics, which inspired the design for a linear motor-driven control system for massive earth-based telescope installations.
Enabling deep space exploration with colossal telescopes
The European Southern Observatory (ESO) is an intergovernmental, ground-based astronomy research organization comprising 16 member states and is working with Microgate to build the adaptive mirror for the next and largest generation of Extremely Large Telescopes (ELTs).
Figure 1: Microgate builds the highly sophisticated adaptive-optics mirror for the ESO Extremely Large Telescope. The optics, powered by high-density DC-DC converter modules, correct for atmospheric disturbances to extract more light, achieving higher resolution imaging.
ELTs use primary mirrors with diameters in the 30-meter range – or in the case of the ESO-ELT an even more impressive 39-meter diameter. The objective of these telescopes is to capture light from the distant past to learn more about the early Universe. This requires a large primary mirror to collect the very few photons that can be captured from distant stars and galaxies. Unlike the Hubble or James Webb space telescopes, this Earth-based method of exploring deep space has several advantages. Ground telescopes have an advantage of size – the largest is 23 times bigger than the Hubble. Ground telescopes can also be located anywhere on the planet and are easily upgradeable using the latest technology, while their counterparts in space are far more difficult to maintain and upgrade once launched.
ESO’s existing telescopes have made several ground-breaking discoveries possible. Using the organization’s facilities, astronomers tracked the movement of stars in the extreme gravitational field at the center of our galaxy, delivering convincing evidence that a supermassive black hole exists there. This discovery was recognized with the 2020 Nobel Prize in Physics.
Figure 2: ESO’s telescopes helped Andrea Ghez and Reinhard Genzel win the Nobel Prize in Physics in 2020 for the discovery of the supermassive black hole in the Milky Way’s galactic center.
Adaptive optics enhance visibility by compensating for wavefront aberrations
The ESO-ELT is situated atop Cerro Armazones in Chile’s Atacama Desert at an altitude of about 3,000 meters. The site selection for these installations was strongly dependent on the quality of visible light.
This is because, as light passes through the atmosphere, it is subject to a disturbance known as a wavefront aberration. Using Microgate technology, the captured light is reflected from the primary to a secondary, adaptive mirror, which is physically deformed to re-establish what is known as a “plane” wavefront. In the case of the ESO-ELT project, Microgate delivers all of the real-time control hardware and software to mechanically deform the mirror and physically manipulate the incoming wavefront to correct for these atmospheric disturbances and improve the image quality.
The ability to control the mirror’s geometric shape requires the use of contactless, linear voice-coil motors that conceptually are similar to a loudspeaker (see a short video demonstration).
Figure 3: The secondary or adaptive mirror is made of highly specialized glass with a thickness of about 1.9 millimeters. The copper coils represent the linear motors.
The adaptive mirror is 2.4 meters in diameter and is made of highly specialized glass with a thickness of 1.9 millimeters. The voice-coil motors are driven by a precise current driver and a series of co-located permanent magnets. These are glued to the back of the mirror and provide the force to deform the glass. This process is performed across the entire surface of the adaptive mirror using 5,316 motors, each with an inter-axis distance, or pitch, of about 30 millimeters.
The adaptive mirror physically floats on the magnetic field generated by the voice-coil motors. Each coil allows a dedicated control current to locally deform the mirror and correct the shape. This is achieved by using an equivalent number of highly-sensitive capacitive, or position, sensors with an accuracy in the nanometer (millionth of a millimeter) range. Using electronics operating at a frequency of about 100 kHz, Microgate engineers can completely redefine the shape of the mirror in one millisecond.
Once the gap has been measured, FPGA-based processors apply the correct commands to the mirror in real time and bring the control error to zero. The result is an extremely sharp and clean image that is rendered without having to launch a telescope into space.
“The process requires extreme precision to correct the wavefront aberrations,” said Gerald Angerer, Microgate’s lead hardware development engineer. “As a result, we can improve the image resolution significantly.”
High-density power modules are mission critical to honing adaptive optics
The energy challenges to achieve such image precision are considerable. For example, accurate thermal management of the adaptive optics system is critical and requires all exposed surfaces to be kept close to ambient temperature to avoid local turbulence. To compensate, Microgate uses a direct-expansion gas cooling system to thermally dissipate the motor-control electronics. Other cooling materials, such as water or glycol, have been excluded, because even a small loss of coolant onto the primary mirror could cause catastrophic damage to the entire telescope.
The power challenge is made even more difficult by the limited space available for any power delivery solution, given the constraints imposed by housing thousands of motors in a confined space. A previous option required remote DC-DC converters to bring power to the motors with relatively long and complex wiring.
To streamline the approach, Microgate chose the Vicor DCM3623 series DC-DC power module. The power-system board is now mounted on the underside of the gas-cooled cold plate, and each DCM3623 powers up to 36 motor channels, eliminating complicated wiring. “Vicor’s high-efficiency and high-power density modules are very compact and reliable and take up very little space on the circuit board,” said Angerer. “These miniaturized power converters are the best option for us. We have been using them for more than 10 years and there is currently no comparable substitute.”
Figure 4: Microgate uses the Vicor DCM3623 series DC-DC power module to mechanically deform the mirror and physically manipulate the incoming wave-front to correct for these atmospheric disturbances. The process is mission critical in enabling the telescope’s optics to produce stronger light and higher image quality.
High-density power modules deliver other benefits over alternative solutions:
- Power density: Compact and extremely dense to meet the intense power demands of the ELT mirrors in a very confined space.
- Efficiency: Reduce energy/heat losses helps stabilize the temperature of the optical system, which otherwise could experience performance degradation or distorted optics.
- Fast transient response: A stable output voltage within a wide frequency band ensures precise motor operation even under fast step-load variations.
- Low electromagnetic noise: EMI interference can disturb the focusing system, resulting in loss of image quality.
Exploring new frontiers of deep space to enrich our world
Microgate is committed to deep space exploration through the instantaneous, precise manipulation of exceptionally complex mirrors. Vicor power modules are enhancing the optics of these next-generation telescopes with high power density and reliability. Through a process of continuous experimentation, Microgate is collaborating with Vicor and other world-class partners to deliver mission critical power electronics to organizations like the European Southern Observatory.
“Unlocking the secrets of deep space is difficult,” said Angerer. “These new discoveries are re-writing our history books and redefining the way we think about the human race and where we fit into the Universe. It’s very challenging, and we are grateful to be working with some great partners to achieve our goals.”
About Vicor: Vicor is the leader in high-performance power modules, enabling customer innovation with easy-to-deploy modular power system solutions for power delivery networks that provide the highest density and efficiency from source to point-of-load. We continuously advance the density, efficiency and power delivery capabilities of our power modules by staying on the forefront of distribution architectures, conversion topologies and packaging technology. Vicor serves customers in enterprise and high-performance computing, industrial equipment and automation, robotics, UAVs, electric vehicles and transportation, satellites, and aerospace and defense.
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