Honda conducts successful launch and landing of experimental reusable rocket

Here is the video which they should have put in the post:

https://global.honda/content/dam/site/global-en/topics-new/c...

I'm accustomed to seeing large plumes of chemicals coming out the other end in my minds eye when I think about rocket launches. This looks "clean" coming out the exhaust.

Why is that? Is it due to the nature of chemicals it uses?

Several reasons. It's filmed in daylight, so any flame or exhaust will be less visible. The rocket engine is much smaller than anything that would go on an orbital booster, so there's less exhaust than what'd you see for an orbital launch. Also it's looks like it's a hydrolox rocket (using liquid hydrogen and oxygen as fuel), which has the least visible flame. The combustion product is almost entirely water vapor. Methalox (methane + liquid oxygen) is the next cleanest, which emits water, CO2, and a little bit of soot. Kerolox (RP-1 and oxygen) is the most common propellant used today, and it emits a significant amount of soot.

Solid boosters put out the most visible exhaust, as burning APCP[1] emits solid particles of metal oxides. Also some rockets (mostly Russian, Chinese, and Indian) use unsymmetrical dimethylhydrazine + dinitrogen tetroxide, which emits a reddish-orange exhaust. Both compounds are toxic, as is the exhaust.

1. https://en.wikipedia.org/wiki/Ammonium_perchlorate_composite...

I doubt it's hydrogen, because the color looks off (blue, rather than pink), and because it'd be a poor fit for a small R&D project. They're not optimizing for performance-at-all-costs on this.

Ethanol/oxygen is my guess. Blue, and also very little soot.