NASA is exploring the properties of a metal alloy that shrinks as it is heated, as boffins in its Astrophysics Division think it may be needed if the planned Habitable Worlds Observatory (HBO) is to succeed.
Readers doubtless know that metals expand when heated. As explained in a NASA blog post that’s a problem for space telescopes because if their components warm and expand it can mean that the shape of their mirrors change in ways that make it harder to conduct observations.
NASA has already developed materials that compensate for those effects and used them in the James Webb Space Telescope and in the Nancy Grace Roman Space Telescope that the aerospace agency intends to launch in 2027.
The HBO, NASA’s next space ‘scope project after the Nancy Grace Roman, will need even more resilient materials.
To understand why, the post explains how to observe exoplanets.
“As light passes through a planet’s atmosphere or is reflected or emitted from a planet’s surface, telescopes can measure the intensity and spectra (i.e., ‘color’) of the light, and can detect various shifts in the light caused by gases in the planetary atmosphere. By analyzing these patterns, scientists can determine the types of gases in the exoplanet’s atmosphere.”
Observing those shifts is no easy matter, “because the exoplanets appear very near their host stars when we observe them, and the starlight is one billion times brighter than the light from an Earth-size exoplanet.”
That means the Habitable Worlds Observatory “will need a contrast ratio of one to one billion (1:1,000,000,000).”
To achieve that contrast ratio, the HBO will need to be 1,000 times more stable than the James Webb telescope.
Which is why NASA scientists and a company called ALLVAR are investigating a “negative thermal expansion” (NTE) alloy that shrinks when heated.
According to NASA’s post, “A 1-meter-long piece of this NTE alloy will shrink 0.003 mm for every 1° C increase in temperature.”
“Because it shrinks when other materials expand, ALLVAR Alloy 30 can be used to strategically compensate for the expansion and contraction of other materials,” NASA’s post states.
Tests have delivered promising results: ALLVAR apparently built a test mirror mounted on struts of a titanium alloy that expands when heated and struts made with Alloy 30. Both alloys performed as expected, with Alloy 30 offsetting the expansion in the titanium alloy to produce a stable mirror.
NASA thinks the tests also showed Alloy 30 “enabled enhanced passive thermal switch performance and has been used to remove the detrimental effects of temperature changes on bolted joints and infrared optics.”
Space boffins are therefore considering how to use Alloy 30 in many other space scenarios.
You might want to consider using it, too, as NASA wrote “ALLVAR developed washers and spacers are now commercially available to maintain consistent preloads across extreme temperature ranges in both space and terrestrial environments.” ®