BUMAX provided the customer TNO with critical fasteners that overcame their galling issues
TNO has developed an Adaptive Secondary Mirror for NASA’s Infrared Telescope Facility (IRTF) in Hawaii. The IRTF is a 3m infrared telescope located at an altitude of around 4,200m at the summit of Mauna Kea on the island of Hawaii. Designed for maximum performance in the infrared portion of the spectrum, it takes advantage of the excellent visibility, minimal water vapour and low thermal background that characterise the atmosphere above Mauna Kea. The University of Hawaii and the University of California Santa Cruz realised the secondary mirror upgrade project.
During the integration phase, a manufacturing error required TNO to immediately find a fastener solution so that the integration could proceed.
“We realised that some of the holes in the supporting structure of the secondary mirror assembly had been machined to the wrong dimension,” explains Arjo Bos, Systems and Mechanical Lead Engineer at TNO. “We tried standard A4 screws but had immediate issues with galling. We needed a fast solution to overcome our galling issue with an extremely tight schedule and some dependencies with other projects.”
Delivery and assembly within 24 hours
TNO contacted Pim Oome, the BUMAX Business Development Manager for the Benelux region, who quickly understood their needs and placed an expedited order. Within 24 hours of contacting BUMAX, TNO had received a batch of BUMAX® DX 129 EPK screws at their facility in Delft and had installed them in the secondary mirror assembly.
“BUMAX saved the day at a point in our project when we needed to have no delays,” claims Matias Kidron, Project Manager at TNO. “The next-day delivery of the screws was quite a feat and was greatly appreciated by our entire project team and enabled us to stick to our schedule.”
Anti-galling properties
This application’s BUMAX® DX 129 EPK fasteners were a special variant of the BUMAX standard high-performance DX 129 product grade. DX 129 EPK benefits from even higher surface hardness, making them almost impervious to galling. DX129 EPK also has the advantage of lower surface roughness and a cleaner finish to the fasteners, which eliminates the need for any potential additional lubrication in applications where contamination or outgassing may be of concern.
The high-strength nature of BUMAX® DX 129 EPK screws was not essential, but it is an appreciated property by TNO.
“Quickly obtaining anti-galling screws was the most important thing for us, but the high strength properties of the BUMAX fasteners is a nice bonus that gives us a piece of mind when astronomers are integrating the mirror,” says Bos.
Adaptive secondary mirror allows clearer ground-based astronomy.
TNO’s adaptive secondary mirror, with a diameter of 244 mm, was installed at the IRTF in April 2024. The mirror is based on hybrid variable reluctance actuator technology, which uses small actuators behind it to push and pull it to deform its shape. This allows the mirror to correct for the distortion of the atmosphere, ensuring the IRTF’s view of celestial bodies is as sharp and detailed as possible.
“At TNO, we have a long history of working with adaptive secondary mirrors with a proven track record in the lab, but we have been looking forward to demonstrating our innovative technology on a telescope,” says Bos. “We would certainly use BUMAX screws for other critical connections where galling is an issue, and high strength is desirable. This goes beyond our telescope projects at TNO to include other potential space-related applications that we are working on, such as satellite instruments that undergo extreme force during launch,” concludes Bos.
A solution for the world’s largest optical telescope
BUMAX screws have also been used on the European Southern Observatory Extremely Large Telescope (ESO ELT) in Chile, which required a high-strength, corrosion-resistant solution.