Link: NASA’s longshot bet on a revolutionary rocket may be about to pay off

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This is really neat! Coincidentally, back when I was in highschool I did an Aerospace Scholars program at JSC. Our project was a Mars mission, and we opted to outfit our carrier vessel with Vasimr engines because "By the time this mission is feasible, it is our hope that propulsion technology will have developed to the point where this is a viable option." I just had a flash of clarity remembering that line from our final report/presentation.
I remember reading about ion engines a few years back and thinking how cool it is that they look like what we've always imagined in sci-fi movies and shows.
VASIMR is a plasma engine of sorts if I am not mistaken.

There used to be (And maybe still is) a mod for KSP that modeled all the different types of engines like that. It was called "Near Future Propulsion". Cool mod.
200kW = thrust of a C engine?

EnginePower (kW)Thrust (N)Specific Impulse (s)Propellant
PPS-1350 Hall Thruster
NSTAR Ion Engine
(Deep Space 1)
NEXT Ion Engine
VASIMR® VX-20020055000Ar (Optional:
D, N, Xe)

link for above chart:
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For anyone who is a little in the dark about specific impulse and want to think about it in a simple manner, it is basically the equivalent of fuel economy for rocketry.

Comparing the VASIMR to a BP motor is like comparing a contemporary Formula1 car engine to one of the cast iron internal combustion engines that signaled the demise of the steam age in that regard. But yes, approximately the same thrust...
They say just hook it to a solar array.
200kw to get 5N... How many square miles of array would it take to push spaceship?
Especially out by Jupiter.

The article does state that solar power past Mars isn't feasible and would have to be a nuclear reactor.
Robert Zubrin of the Mars Society (also wrote The Case for Mars) has stated that the Vasimr Engine is over-rated and that an ion engine would be better. There was talk a few years ago about testing the Vasimr engine on the ISS, but I have not heard anything more about this.
RTGs would make a nice power source. But getting radio-anything into orbit makes many people nervous.
What's the difference between VASIMR and an 'ion' engine?

The VASIMR is more like magnetic plasma device, where the plasma is confined and directed along magnetic field lines. The plasma, although ionized at a high temperature, is on a whole electrically neutral. On the other hand the ion engine uses electrically charged plates to accelerate the positive ions to high speed. Electrons are injected downstream after the ions have left the engine. I am thinking that Zubrin's objection is that the power requirements for the VASIMR engine are quite a bit higher as Post# 6 shows. One of the claimed advantages of the VASIMR engine is that the thrust can be throttled to relatively high levels.
VAS takes more juice, Ion uses more mass IIRC. Depending on the mission profile, it's yet another design study tradeoff.