On Aerogel

Ethan Wong

January 3rd, 2025

It’s 2025, and one of the things I’m most excited to see happen this year is how space companies or researchers creatively manufacture and integrate aerogel into various tasks, such as more components for lunar or Mars missions. They’ve already used aerogel in creative ways thus far, as I’ll mention later in the article.

But what is aerogel, and how do you make it?

Aerogel is a solid composed of around 99.8% air and silica (silicon dioxide) and has nearly the same density of air; because of this, it currently holds the title for the lightest solid, and is super interesting to look at (almost transparent, but not 100%). This manufactured material is an excellent insulator, withstanding temperatures upwards of 3000 degrees Fahrenheit according to NASA. For reference, this is a little higher than the melting point of pure iron. Aerogel can additionally absorb sound, and is capable of absorbing high-energy impacts/shock absorption–a process in which high-impact collisions lose a majority of their (kinetic) energy. 

So how was aerogel first made, and how is it produced today? In the May 16th, 1931 Nature Publishing Group, Dr. Kistler published “Coherent Expanded Aerogels and Jellies,” a short publication which highlighted how liquid in gels could be replaced. In his experiment, Dr. Kistler, Charles Learned and Professor J.W. McBrain set out to determine whether a liquid in a jelly jar could be reduced to a gas without any damage or alterations to its structure. They swapped out the water in the gel (jelly-like consistency from jelly jar) with a “low critical temperature” liquid with the intention of transitioning the liquid to its gaseous state. Alcohol worked well. They maintained higher pressure in the jelly jar to ensure zero liquid evaporation. After turning into a gas, they let the gas escape while the jelly solid remained intact. With this process, they essentially removed the liquid and preserved the gel. 

Almost one hundred years later, technology has provided scientists with better methods of creating aerogel. So it’s clear, making aerogel works by extracting the liquid from the silica gel such that around 99% of the gel’s original volume is maintained. These silica gels are produced through sol-gel chemistry. The reason aerogel is amazingly heat-resistant and a good insulator is because the air molecules are encased in a layer of silica that makes it hard for heat to get through the large cloud of air (air is bad at heat transfer). 

But back to my original statement, I’m excited and curious to see if, and how aerogel is utilized this year in aerospace technologies and research. In the past, aerogel has already been involved in numerous initiatives.

NASA utilized aerogel on a spacecraft to take a sample of a comet and return it to Earth. The mission, Stardust, launched in 1999, and collected Wild-2’s comet material in 2004. The aerogel was used to interfere with the fast-moving particles of Wild-2 and trap them as the particles went through part of the aerogel before stopping inside the substance. Aerogel is perfect for this task, as it won’t damage the particles’ structure nor alter their chemical compositions.

And while I hope to see more usage of aerogel in future missions to the Moon and Mars, scientists have already approached this substance as a solution for some of their technology. In an attempt to make Mars more habitable, scientists have reasoned with different solutions such as terraforming. However, in the 2019 report,“Enabling Martian Habitability with Silica Aerogel via the Solid-State Greenhouse Effect” by Robin Wordsworth, Laura Kerber, and Charles S. Cockell, they propose aerogel as a solution. Their research suggests humans can use 2-3cm thick silica aerogel and no internal heat source in order to block UV radiation, raise the temperature past the melting point of water (increase around 50 degrees Celsius), and be able to transmit enough light for photosynthesis to occur. They found that aerogel was a fit material to replicate the Earth’s atmosphere’s ability to reflect UV radiation but absorb sunlight (heat). The team’s setup included a low reflectivity base with silica aerogel above. The base essentially absorbs solar energy so it won’t reflect and bounce back into the aerogel layer and ruin the data. They insulated the setup so that no external circumstances or heat could interfere with the system, and used a solar simulator to replicate the sunlight on Mars. Temperature was measured with thermistors, and they also positioned a thermal camera above the aerogel to scan heat distribution. Their paper is short, and I highly encourage those reading this to look through it, if interested.

Aerogels can also be used for shielding on vehicles by providing thermal insulation, and can most likely do a good job at protecting electronics onboard spacecraft when combined with other material barriers. They’re even added to spacesuits for extra insulation without adding additional weight. However, aerogels might not be useful for shielding by itself, as the solid is brittle and not suitable for descent conditions. But I’ll continue to keep an eye open for any major aerogel-related news.