exhaust divergence. A significant portion of that 40% was waste heat (see energy conversion efficiency). Managing and rejecting that waste heat is critical. Between April and September 2009, 200 kW tests were performed on the VX-200 prototype with 2 tesla superconducting magnets that are powered separately and not accounted for in any "efficiency" calculations. During November 2010, long duration, full power firing tests were performed, reaching steady state operation for 25 seconds and validating basic design characteristics. Results presented in January 2011 confirmed that the design point for optimal efficiency on the VX-200 is 50 km/s exhaust velocity, or an I of 5000s. The 200 kW VX-200 had executed more than 10,000 engine firings with argon propellant at full power by 2013, demonstrating greater than 70% thruster efficiency relative to RF power input. VX-200SS In March 2015, Ad Astra announced a $10 million award from NASA to advance the technology readiness of the next version of the VASIMR engine, the VX-200SS to meet the needs of deep space missions. The SS in the name stands for "steady state", as a goal of the long duration test is to demonstrate continuous operation at thermal steady state. In August 2016, Ad Astra announced completion of the milestones for the first year of its 3-year contract with NASA. This allowed for first high-power plasma firings of the engines, with a stated goal to reach 100hr and 100 kW by mid-2018. In August 2017, the company reported completing its Year 2 milestones for the VASIMR electric plasma rocket engine. NASA gave approval for Ad Astra to proceed with Year 3 after reviewing completion of a 10-hour cumulative test of the VX-200SS engine at 100kW. It appears as though the planned 200 kW design is being run at 100 kW for reasons that are not mentioned in the press release. In August 2019, Ad Astra announced the successful completion of tests of a new generation radio-frequency (RF) Power Processing Unit (PPU) for the VASIMR engine, built by Aethera Technologies Ltd. of Canada. Ad Astra declared a power of 120 kW and >97% electrical-to-RF power efficiency, and that, at 52 kg, the new RF PPU is about 10x lighter than the PPUs of competing electric thrusters (power-to-weight ratio: 2.31 kW/kg) In July 2021, Ad Astra announced the completion of a record-breaking test for the engine, running it for 28 hours at a power level of 82.5kW.