Ultra-Stable Struts

Ultra-Stable ALLVAR Alloy athermalized struts eliminate the need for costly and long-lead telescope components by compensating for positive CTE of other materials. This tunable CTE innovation flips the design paradigm on its head by enabling telescope engineers to dictate a support structure’s CTE by matching materials in a specific operating temperature range, thus athermalizing the system.

Zero thermal expansion metering structures for telescopes can be achieved using negative thermal expansion ALLVAR Alloys. This prototype was built during a NASA SBIR Phase II.


ALLVAR Alloys offer a new material solution for thermally stable structures. ALLVAR Alloy 30:

  • Has a axial Coefficient of Thermal Expansion (CTE) of -30.0ppm/°C at room temperature.
  • Has a positive CTE in the radial direction (similar in magnitude to Aluminum), allowing for compliant mounting of optical elements.
  • Negative Thermal Expansion (NTE) can control the CTE of a component. By selecting the correct length of NTE alloy relative to other components, the CTE of the overall strut length is tunable to a specific value, including zero.
  • Exhibits mechanical and material properties similar to other Titanium alloys.
  • Can be machined like many other metals, tolerances of ±0.001” are easily achievable.
  • Available in both round bar and tube formats; ALLVAR Alloy 30 is a natural fit for the design and fabrication of strut components, lens barrels, and lens-to-focal plane stand-offs.

Value Propositions

For more cost-sensitive designs and programs, these tailored CTE rods can reduce engineering design time, simplify optic manufacturing and alignment, and offer ultra-high stability of telescope support structures . When ALLVAR Alloy 30 is used in telescope support structures, it has the following effects:

  • Reduced Coefficient of Moisture Expansion (CME) effects and bake-out requirements by replacing some or all carbon fiber composite components.
  • Reduced carbon fiber composite scrap components by tuning the CTE of carbon fiber tubes whose CTE is out of specification.
  • Enable a design-specific zero-CTE crossing determined by the application’s operating temperature.
  • In-situ CTE tunability without changing strut’s metering length.
  • Increased structural stiffness by eliminating nested or tube-in-tube athermalizing designs.

Getting technical

These struts were designed and manufactured as part of a NASA SBIR Phase II project titled “Ultra-Stable ALLVAR Alloy Strut Development for Space Telescopes.” The CTE and stability of each strut were measured to quantify variability between struts. A stability of 2 pm/√Hz was achieved for the individual struts with a CTE of 0.6 ppm/°C. The manufacturing consistency was very high with a standard deviation of 0.05 ppm/°C between each strut.

In order to achieve this low CTE, ALLVAR Alloy 30’s negative CTE was tuned to counteract the positive CTE of each of the other components in the series.  

Zero thermal expansion struts were created using negative thermal expansion allvar ,titanium 6-4, a286 stainless steel, and invar 36.

Ultra-Stable Strut Related Posts

Learn more about these ultra-stable struts and the work being done on this application in the ALLVAR blog series.

Products Available

ALLVAR offers a range of products that can help suit your project or program needs – either by providing semi-finished material in round bar or tube form, or fully machined parts to print. Maximum sizes are 2.25” round bar and 3.00” out diameter tube up to 10 feet in length.

ALLVAR Alloy 30 can also be machined into custom products or components best suited for your specific product or project. Our team of engineers at ALLVAR are on hand to provide design support, machine parts to print, and discuss the technical details of your project. If it is beyond our own expertise, we will collaborate with one of our many partners experienced in designing and machining these negative thermal expansion alloys. Utilizing groundbreaking materials and streamlined design strategies for your next project is sure to bring up a lot of questions. Not sure if ALLVAR is a good fit for your project? Please contact us. We would be happy to discuss negative thermal expansion Alloy 30’s applicability for your application.

Knowledge is Power

Our ALLVAR University video series offers a deeper dive into designing with ALLVAR Alloy 30. These specific videos offer more information related to the ultra-stable strut application.

Contact Us Today to Revolutionize Your Thermal Performance

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