Stardust

Description

Stardust is developing particles for SAI that it suggests would be safer than sulphates – the most studied potential material for SAI. The company is seeking to patent these particles, which are composed of silica and calcium carbonate. It plans to secure government contracts to manufacture, disperse, and monitor these particles in the stratosphere.

According to reporting from Politico in 2025, a 2023 pitch deck shared with potential investors stated that Stardust had already conducted outdoor experiments using “test particles” at low altitudes. These experiments were not previously revealed to the public.

In an email to SRM360, Stardust described their previous outdoor activities as “measurement equipment system checks”, involving commercially available materials such as the white smoke used in air shows. They said these do not constitute outdoor SRM experiments in their view.*

There are also reports of planned experiments, which would aim to test Stardust’s particles inside modified jets flying at a height of 18 km (about 11 miles). Rather than releasing the particles, air from the stratosphere would be sucked into the jet, where the experiment would take place. However, according to later reporting, the company has no current plans to conduct outdoor tests.

* We have included this experiment in our tracker in accordance with our criteria, given that it appears to have been intended to advance SRM deployment capabilities, it related to an SRM approach capable of producing substantial global cooling, and it involved testing equipment outdoors.