SpaceX Super Heavy booster will have hot gas thrusters instead of nitrogen thrusters for maneuvering in space before reentry. This will be the case before the first orbital flight.
Aiming to have hot gas thrusters on booster for first orbital flight
— Elon Musk (@elonmusk) May 26, 2021
Every Day Astronaut describes hot gas thrusters. They have greater efficiency.
Hot gas in this case means the fuel and prop are stored in gaseous form. They’re stored at high pressures in COPV’s, either from engine tap offs or heat exchangers. Then they reach the thruster chambers as a gas where they combust so they’re efficient.
— Everyday Astronaut (@Erdayastronaut) May 26, 2021
SOURCES- SpaceX, Elon Musk, Everyday Astronaut
Written By Brian Wang. Nextbigfuture.com
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Good news
It would be SpaceXish if they planned to mass produce the hot gas thrusters for all Starship’s maneuvering and just use more of them in a ring for the Artemis Lander Starship or other places they need small methalox engines.
I was wondering if they might switch up to a helium based tridyne system, from cold gas. The performance is intermediate between cold gas and regular bipropellant, but (in theory!) tridyne can be used for tank pressurization.
Tridyne is a mixture of inert gas with hydrogen and oxygen, but little enough of the latter to be incapable of sustaining combustion or detonation. You use it like a cold gas thruster, except that it passes through a catalyst bed in the thruster, which more than negates the temperature drop from expansion. You might call it a "warm" gas thruster.
But they're planning on autologous pressurization, using hot gas bled off the engines to pressurize the tanks. So I guess the helium pressurization was just a temporary thing.
So, what's this about "Nitrogen" thrusters? I thought the Starship was using the same helium system used to pressurize the tanks for the thrusters?