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
According to badastronomy.com, the standard hydrazine / dinitrogen tetroxide type have an invisible flame.
Ion propulsion engines have a faint blue glow, at least the ones that use Xenon. AFAIK
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.
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 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 (caption) 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.