Experimental data obtained in June 2012 on Ad Astra’s VX-200 high power VASIMR® engine prototype showed an improvement in efficiency at intermediate values of specific impulse (Isp) below the 5000 sec optimal point demonstrated in late 2010. A new optimized performance model that shows approximately a 10% improvement in engine efficiency over a wide Isp range. Short for Variable Specific Impulse Magnetoplasma Rocket, VASIMR® works with plasma, an electrically charged gas that can be heated to extreme temperatures by radio waves and controlled and guided by strong magnetic fields. VASIMR can be 10-30 times more efficient with fuel than a chemical rocket. VASIMR has 15 to 200 times more thrust than current ion engines.
Constant Power Throttling is made possible by changing the relative fraction of power going to the first stage (helicon) and second stage (ion cyclotron heating (ICH)) systems and simultaneously changing the rate at which the propellant gas is fed into the engine. For high thrust, power is routed predominantly to the helicon with propellant consumed at a relatively high rate, producing more ions at lower exhaust velocity (low Isp). For high Isp, more power is diverted to the ICH while less power and propellant are being fed to the helicon with concomitant reductions in thrust.