Can ionic thrusters be used as a secondary propulsion system for rockets?

[x1892]

what if ionic thrusters being used as a secondary propulsion system for rockets once they reach space, after using jet engines for the initial atmospheric ascent?

 

[anuttarasammyak]

I know that ionic thruster is widely used for asteroid exploration, as well as satellite orbit maintenance and attitude control.　Are you asking more than that ?

 

[hemran55]

what if ionic thrusters being used as a secondary propulsion system for rockets once they reach space, after using jet engines for the initial atmospheric ascent?

Yes in principle, but not as a practical replacement for the main rocket engine. Ion thrusters have extremely high specific impulse but very low thrust, so they ae useful for gradual acceleration once in space, not for launching from Earth. A rocket could use conventional propulsion to reach orbit and then use ion thrusters for long duration acceleration or station keeping. The main limitation is that ion engines need electrical power and may take a very long time to produce a significant change in velocity.

 

[Filip Larsen]

Using a pure air-breathing engine, like a jet engine, combined with an ion engine to launch and establish low earth orbit would leave a large gap in thrusting requirements to establish orbit. From launch, a jet engine cannot put apogee outside the atmosphere and even if it could a (feasible) ion engine cannot raise perigee out of the atmosphere in time before reentry.

However, there have been plenty of research for engine designs that potentially could enable single-stage to orbit vehicles, e.g such as SABRE.

 

[mfb]

Ion thrusters are routinely used on spacecraft - sometimes only to maintain their orbit, but many spacecraft now also use it to raise their orbit. It means the rocket can deploy the spacecraft in a lower orbit, which means you can build a larger spacecraft (or launch more satellites per launch).

Attaching ion thrusters to a rocket stage doesn't do anything useful - you would only use it once the chemical propellant is exhausted, but then you want to discard the stage to save mass anyway.

 

[BobG]

what if ionic thrusters being used as a secondary propulsion system for rockets once they reach space, after using jet engines for the initial atmospheric ascent?

Yes, they can, provided the spacecraft at least reached space.

They have been used as a secondary propulsion system when the chemical thrusters don't perform as well as planned. The ion thrusters designed for station keeping can finish the job of getting the satellite into its desired orbit.

There are some downsides to that. The satellite's lifetime is shortened because they used stationkeeping fuel to finish getting it into orbit. The thrusters will also have to burn for a very long time to get the desired delta-Vs and may actually be damaged. For geostationary orbits, that would limit where the satellite could be stationed. Usually, all the stationkeeping maneuvers are in the same direction, so the satellite would have to be stationed in a location where the damaged thruster wouldn't be used.

They've also been used to finalize the orbit by plan - where the orbit is high enough, but needs to be circularized.

And I'd note that rockets don't typically use jet engines for launch and transfer orbits. Jet engines require air to work. Rockets use chemical thrusters that mix a propellant with an oxidizer to obtain a very strong reaction that sends the fuel out the back of the thruster at an extremely high rate of speed.

Typical chemical thrusters have specific impulses of around 250 seconds - the fuel exits the thruster at around 2500 meters/second (around 5000 mph).

Ion thrusters have specific impulses of around 3500 - the fuel exits the thruster at around 35,000 meters/second (around 70,000 mph).