# Propulsion in space... what color are the flames?
**URL:** https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188
**Category:** Factual Questions
**Created:** [July 13, 2003, 5:50pm UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188 "2003-07-13T17:50:38Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@IBBen](https://boards.straightdope.com/u/IBBen)
#### Post date: [July 13, 2003, 5:50pm UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188/1 "2003-07-13T17:50:38Z")
Someone asked me this question recently and all I’ve got to draw on is the Hollywood interpretation.
So, what color do rockets burn in a vacuum?
Thanks,
Ben
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### Author:  [@raygirvan](https://boards.straightdope.com/u/raygirvan)
#### Post date: [July 13, 2003, 6:17pm UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188/2 "2003-07-13T18:17:28Z")
According to [badastronomy.com](http://www.badastronomy.com/bad/tv/foxapollo.html#flame), the standard hydrazine / dinitrogen tetroxide type have an invisible flame.
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### Author:  [@Ale](https://boards.straightdope.com/u/Ale)
#### Post date: [July 14, 2003, 3:12am UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188/3 "2003-07-14T03:12:06Z")
Ion propulsion engines have a faint blue glow, at least the ones that use Xenon. AFAIK
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### Author:  [@Ale](https://boards.straightdope.com/u/Ale)
#### Post date: [July 14, 2003, 3:17am UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188/4 "2003-07-14T03:17:27Z")
Thinking about it a bit more; LOX/LH engines should have invisible flame as long as the nozle doesn´t have an ablative coating; LOX querosene (as the main engines on Apollo XI) have a bright orange/white flame. Solid propellants make some nice fireworks.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [July 14, 2003, 4:12am UTC](https://boards.straightdope.com/t/propulsion-in-space-what-color-are-the-flames/188188/5 "2003-07-14T04:12:16Z")
The color of the flame/exhaust depends on the type of rocket, as already pointed out. It would look pretty much the same regardless of whether it’s in air or vacuum. [This Shuttle photo](http://science.ksc.nasa.gov/shuttle/missions/sts-101/images/medium/KSC-00PP-0656.jpg) clearly shows the faint blue flames from LH/LOX (liquid hydrogen and liquid oxygen) rockets on the orbiter as well as the brilliant white exhaust of the solid rocket boosters. The OMS (Orbital Maneuvering System) engines used for orbital corrections use MMH/N2O4 (monomethylhydrazine and nitrogen tetroxide). [This image](http://images.jsc.nasa.gov/iams/images/pao/STS5/10060996.jpg) ([caption](http://images.jsc.nasa.gov/images/pao/STS5/10060996.htm)) shows the Shuttle OMS engine firing, though I believe this photo was taken at “night” with a high sensitivity camera.
The _smoke_ would look very different in vacuum. With a hydrogen rocket, the exhaust (water vapor) wouldn’t condense into a visible smoke at all. Even if it did, it would disperse quickly instead of billowing.