r/spaceflight • u/The-Author • 6d ago
Could plasma propulsion be used for orbital insertion burns?
I'm aware that ion propulsion is too weak to do things that involve changing velocities quickly (like launching a spacecraft from the surface of a planet) but what about plasma propulsion?
Chemical rockets can create thrust measured in kilo-newtons for a few seconds but plasma propulsion can exert around 1-10 Newton's of thrust per engine for a lot longer than chemical rockets. So would it be possible to use plasma propulsion but just let it burn for longer to make up for the low thrust?
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u/rocketwikkit 6d ago
If you were launched into supersynchronous orbit and you burned the EP from the instant you were released, you could get a measurable increase in your perigee. But it wouldn't be the difference between being in orbit or not.
A normal orbital insertion burn can't be arbitrarily long. If you get launched into low earth nearly-orbit like 400 by -400km, there's about fifteen minutes where you can do a circularizing burn, and no EP is going to be strong enough to do that.
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u/cjameshuff 6d ago
If the launch vehicle can get the spacecraft on a trajectory that gives it enough time to perform the burn to orbit with a plasma thruster, it can probably get it all the way to a lower orbit that means the thruster just has to do orbit raising.
This doesn't mean the lower orbit has to be a long-lived one. SpaceX routinely puts Starlinks into orbit at a low altitude where they have a short lifetime if they fail to properly deploy their solar panels and start raising their orbits.
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u/entropy13 6d ago
Like from a suborbital launch? Not even close. You could use it to circularize after a transfer burn up to GEO (assuming perigee is above the mesosphere) but there's a reason they don't do that too often. You can only run near apogee and although mass is expensive in space time is also money and every day your multi million dollar satellite isn't in position is another day it isn't providing the services you were willing to pay all that money for, either for paying customers or for your own purposes. They remain a good choice for station keeping, for slowly raising or lowering an orbit and for certain deep space interplanetary transfer burns but not much else.
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u/mfb- 6d ago
Multiple GEO satellites have circularized their orbits with ion thrusters. Yes, it takes longer, but you end up with a much larger useful satellite in orbit because you don't need it to be 50% propellant.
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u/entropy13 6d ago
Like I said, they don't do it too often. It happens sometimes, and for some satellites its worth the wait and added complexity but its the exception not the rule.
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u/Martianspirit 2d ago
You need to specify what the ion propulsion would be used for. SpaceX launched a batch of Starlink sats into a too low orbit. The ion thrusters could not fight against the atmospheric drag and the sats deorbited after a short time. So probably not feasible on Earth.
I am hoping for sending probes to the outer planets with a nuclear power source and ion propulsion to achieve orbit insertion from interplanetary cruise at Uranus, Neptun, Pluto.
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u/The-Author 1d ago
I was thinking for missions from Earth to Mars and beyond. Usually, chemical rockets are used for the "instantaneous" velocity changes to put the vehicle on the right trajectory but I was wondering if plasma propulsion would suffice. It would be a way to save on mass.
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u/Martianspirit 1d ago
Using to get payload out of LEO has to big problems.
You lose the advantage of the Oberth effect, which means you need a lot more delta-v.
You spend a lot of time inside the Van Allen Belt. Which is too much radiation for crew. So not suitable for crew.
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u/Beli_Mawrr 6d ago
KSP is lying to you. I used to work in this space. We had a microwave plasma thruster, and our burn times were measured in days for ~500m/s orbital changes. Long story short, it's going to burn up long before it is anywhere near orbit if plasma is its main thruster.