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February 20, 2007

VASIMR progress

Ad Astra rocket is making progress towards a VASIMR rocket The variable specific impulse magnetoplasma rocket (VASIMR) is a hypothetical form of spacecraft propulsion that uses radio waves and magnetic fields to accelerate a propellant. Current VASIMR designs should be capable of producing specific impulses ranging from 10,000-300,000 m/s (1,000-30,000 seconds) - the low end of this range is comparable to some ion thruster designs.

In 2006, the VX-50 (50kw) test bed was successfully operated at 50kw with a modified 70kw high power solid state RF transmitter from Nautel Ltd of Halifax N.S., Canada, instead of the much heavier tube amplifier technology employed in the past. Compact and light weight high power RF technology is critical to a successful space application. The company successfully demonstrated efficient operation of the
engine with the noble gases Neon and Argon, propellants respectively 1/10 and
1/50 the cost of the traditional Xenon used in most plasma rockets.

The VX-50 test bed has now been retired to make way for the more powerful (100kW) VX-100 already in its early phases of test and checkout. This new system will be used in the first half of 2007 to develop the components and critical data set required for the first VASIMR TM flight-like prototype, the 200kw class superconducting VX-200, which will be operating by the end of 2007.

In-space testing is targeted for 2011. The company, which has an exclusive license to the original Vasimr patents under a privatization agreement with NASA (AW&ST Jan. 30, 2006, p. 12), has added new intellectual property in the past year. The Vasimr engine uses radio waves to heat propellant gas to extremely high temperatures, producing exhaust velocities in the 40-50-km./sec. range.

The VASIMR rocket is intended to be powered by a vapor core nuclear reactor (VCR) with magneto-hydrodynamic (MHD) conversion to electricity -- thus VCR-MHD -- and that the vapor used is a mix of uranium tetrafluoride (UF4) and potassium fluoride (KF), to optimise ionisation in the MHD channel.

The VCR-MHD operates at over 2000K (2600K inlet, 1550K outlet). Specific mass, depending on design details, is between 0.4 to 0.6 kg/kWe. This would be about 40-60 tons for 100MWe.

Power (MWe) 100 (from ~455 MWth)
Reactor (MT) 15.75
Shield (MT) 9.86
Radiators (MT) 2.53 (~355 MWth)
Structural (MT) 3.25
Pumps (MT) 3.09
MHD Gen. (MT) 5.05
Total (MT) 39.52
Sp. Mass 0.39 kg/kWe
Conversion eff. 22%

Although ultrahigh temperature gas core reactors (GCRs) or vapor core reactors (VCRs) are the way of the future, these advanced nuclear reactors have not been successfully taken from the drawing board and scaled laboratory experiments into prototype design. The order of magnitude specific mass reduction in VCR/MHD systems is achieved by combing the fuel and heat transport medium into one and by using an ultrahigh MHD Rankine cycle.

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