Overview

Exoplanet research and characterization are between the main purposes of the Large Binocular Telescope (LBT) located on Mt. Graham in southeastern Arizona. The telescope’s binocular design combined with impressive adaptive optics provides the large effective aperture, high angular resolution, low thermal background, and exceptional sensitivity for detecting faint objects. The LBT has two identical 8.4m telescopes mounted side-by-side on a common altitude-azimuth mounting.

At the heart of the telescope are a pair of SHARK (System for coronagraphy with High Adaptive optics from R to K band) instruments. The SHARK-NIR (near infrared) and SHARK-VIS (visible light) will be used together to observe exoplanets. Infrared Laboratories designed, manufactured, and tested the dewar for the SHARK-NIR instrument and cooling platform for its HAWAII-2RG detector.

Key Facts

Project: SHARK-NIR Instrument for Large Binocular Telescope
Clients: INAF-Padova and UArizona Steward Observatory
Project Location: United States
Application: Astronomy
IR Labs Product: Customized NDL dual-vessel liquid nitrogen dewar

Large Binocular Telescope using SHARK-NIR instrument

Large Binocular Telescope (LBT), Mt. Graham, Arizona, is an international collaboration of the University of Arizona Steward Observatory in the US, INAF- Astronomical Observatory of Padova in Italy, LBT-Beteiligungsgesellschaft  in Germany, and the Ohio State University Research Corporation, representing the University of Minnesota, University of Virginia, and the University of Notre Dame in the US.

Challenges

There were several thermal management and opto-mechanical requirements that were unique to the SHARK-NIR instrument including:

  • Extended hold time of more than 30 hours: Extended hold time was required throughout the full range of motion including 190⁰ rotation of the instrument and 90⁰ altitude of the telescope at the zenith of its alt-azimuth mount.
  • Maintain an optically centered array during full range of motion: The array needed to be optically centered throughout the full range of instrument and telescope rotation.
  • Evolving adaptive optics (AO) criteria: Understanding of the applied AO evolved during the project, driving several new requirements for the dewar.  Dewar design needed to adapt along with AO.
  • Repeatable demount and precision remount: The dewar needed to be removed manually for convenient servicing and remounted to its precise position.
  • Remote and manual heat switch operation: Telescope users need to operate the heat switch remotely and manually.

Solution

Starting with our founder, Dr. Frank Low, IR Labs has decades of experience in solving challenges in IR astronomy. Our engineering team worked closely with INAF-Padova and Steward Observatory to design, produce and test a customized dewar that met unique specifications of the SHARK-NIR.

To achieve extended hold times the dewar uses a dual vessel configuration. The outer vessel cools the radiation shield to prevent heat transfer to the inner section, maintaining the required 77 K temperature and low background for the HAWAII-2RG detector. In addition, LN2 volume management maintains the required temperatures throughout system travel and extended hold time of more than 30 hours.

The array is required to remain optically centered throughout the instrument’s movement. The traditional support structure that suspends the vessels from only the neck of the dewar would not meet these opto-mechanical requirements. We designed an internal structure to be supported at both ends using low thermal conductivity materials. This sturdy structure holds the array within specification during movement.

The adaptive optics subassembly was being better understood and evolving during the project, driving several new requirements for the dewar including relocating the optical port during manufacturing. These are the challenges of science that we have the experience and service commitment to tackle and adapt to.

For repeatable demounting and precise remounting during servicing, we used the instrument’s weight and center of mass when filled with cryogens, to correctly design and install mounting points and pins for precise remounting.

We designed the heat switch to operate either remotely or manually, allowing for the necessary increased operating temperature at the cold stage, while maintaining a high system hold time.

IR Labs’ experience in cryogenic and optical systems, our understanding of the challenges of IR astronomy, and our adaptability during the project make us a trusted solution provider for unique and challenging projects.

Illustration of two vessel configuration of IR Labs customized NDL dual-vessel liquid nitrogen dewar

Dual vessel configuration and LN2 volume management maintained required temperatures through system travel and extended hold time of more than 30 hours.

Illustration of IR Labs customized NDL dual-vessel liquid nitrogen dewar

The sturdy internal support structure (in blue) will keep the array optically centered throughout the instrument’s full range of motion.

Heat switch in IR Labs customized NDL dual-vessel liquid nitrogen dewar

Heat switch operated by remote motor drive or manual drive.

Customized IR Labs customized NDL dual-vessel liquid nitrogen dewar for SHARK-NIRNDL dual-vessel liquid nitrogen dewar for HARK-NIR

Special fixtures were used during testing and validation at the extreme orientations of the instrument during its full range of motion.