Question: What would the exhaust of a Fusion Rocket in vacuum look like? I've been putting together some reference images for myself, and have some very helpful ones when it comes to conventional chemical and nuclear-thermal rockets.
This outstanding guide by @nosusuishin compares exactly with SpaceX's Merlin engine (Kerosene and Oxygen)
With the Methane-Oxygen Raptor engine
And with the Hydrogen-Oxygen engines from Apollo 9's upper stage
There's a puff on ignition and then no visible plume.
But I'm trying to figure out the appearance (as best I can) of a fusion rocket. Based on actual fusion plasma we've made and filmed in tokamaks, I expect the color to be somewhere between pink and purple
The colour comes from the fuel, which is basically hydrogen. Hydrogen gives out two different colours, ...
What I'm wondering is: To what extent would there be a visible exhaust plume?
1- Based on what we see with chemical rockets burning hydrogen, I'm tempted to say No Visible Plume, it dissipates too quickly in vacuum.
2- On the other hand, looking at existing plasma thrusters, they do show some plume visible
Though I note that despite the high exhaust velocity, these plumes are still fading to invisibility within a few meters inside a vacuum chamber. (they also have a definite cone shape, not a tighter beam as I have seen some depict)
3- However, I also see artists who have clearly put more thought into their work than I have, showing a long exhaust plume
For example, the excellent FR0S7 https://fr0s7.artstation.com/projects/qJ29Ve
EddyMundy's ENCR and Luminal Flare settings
Likewise the exhaust of the ISVs from James Cameron's Avatar movies
(I understand that the ISVs use Plasma-Core or Afterburning Beam-Core antimatter rockets, this is just an example of a long exhaust plume)
Perhaps this is due to much higher mass-flow rate than the wimpy electric MPD thrusters, but I'm not sure whether you can just scale up the exhaust of a small electric thruster to be proportional to your large rocket.
If anyone has any insight on what a real Fusion Rocket would look like, please let me know
