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VASIMR® (Variable Specific Impulse Magnetoplasma Rocket)

Space Propulsion Technology     First Flight Unit    Development Status    References

VASIMR is an electro-magnetic thruster concept for spacecraft propulsion under development at Ad Astra Rocket Company (AARC) of Webster, Texas. It uses radio waves to ionize and heat a propellant and magnetic fields to accelerate the resulting plasma to generate thrust. It is one of several types of spacecraft electric propulsion systems. 1)

Background / Company History 2)

1973: As a graduate student at the Massachusetts Institute of Technology (MIT), Franklin Chang Díaz studied the behavior of super-hot gases, called plasmas, as part of the quest for controlled thermonuclear fusion: the process that powers the sun and the stars as a source of power on Earth.

1977: Franklin Chang Díaz's PhD Thesis involved the controlling and ducting of million degree plasmas, in magnetic structures called magnetic mirrors.

1982: Franklin Chang Díaz published a paper entitled “A Supersonic Gas Target for a Bundle Diverter Plasma”, which led to the concept for a plasma rocket, which initially was called the “Hybrid Plume Plasma Rocket.” The first written disclosure of the VASIMR® engine was witnessed by NASA colleagues in Dr. Chang’s Log Book.

1983: First VASIMR®propulsion experiment was conducted at MIT on the magnetic mirror plasma device.

1989: First VASIMR® patent is acquired.

1990s: Important refinements are introduced to the rocket concept, including the use of the “helicon” plasma source, which replaced the initial plasma gun originally envisioned and made the rocket completely “Electrodeless”, an extremely desirable feature to assure reliability and long life.

1995: The advanced Space Propulsion Laboratory (ASPL) was founded at NASA's Johnson Space Center, in Houston. The first plasma experiment in Houston was conducted using microwave plasma source. Collaborations with University of Houston, University of Texas at Austin, Rice University and other academic research institutions were established.

1998: The first helicon plasma experiment was performed at the ASPL. A decision was made regarding official name of the VASIMR® engine and the VASIMR® experiment (VX). The VX-10 operated a helicon discharge up to 10 kW RF power.

2002: The third VASIMR patent is granted. The VX-25 and VX-50 experiments operated to 25 kW and 50 kW power, respectively.

2005: Major breakthroughs were obtained at the ASPL including full and efficient plasma production, and acceleration of the plasma ions in the second stage of the rocket.

Ad Astra Rocket Company is incorporated in Delaware. Ad Astra and NASA signed first Space Act Agreement to privatize the VASIMR®Technology. Franklin Chang Díaz retires from NASA after 25 years of service as an astronaut. Ad Astra's Board of Directors is formed, and Franklin Chang Díaz takes the helm as Chairman and CEO.

2006: AARC opens the Costa Rica subsidiary in the city of Liberia, Guanacaste on the campus of EARTH University. AARC-Costa Rica performs first helicon plasma experiment on the VX-CR device utilizing argon propellant.

2007: The VX-100 VASIMR® experiment demonstrates efficient plasma production with an ionization cost below 100 eV/ion. The VX-100 plasma output is tripled over the prior record of the VX-50. AARC moves out of NASA NBL (Neutral Buoyancy Laboratory) facility to its own building in Webster, TX. NASA's Johnson Space Center and Ad Astra sign a second Space Act Agreement.

2008: The large vacuum chamber becomes operational and VX-200i generates the first plasma in the new facility. NASA and Ad Astra sign the Space Act Agreement for a flight test of a VASIMR® engine onboard the International Space Station.

2009: The VX-200 superconducting magnet arrives enabling plasma operation at an FR power of 200 kW for the first time.

2010: Record VX-200 performance (72% efficiency) is achieved at 200 kW.

2011: A detailed throttle table is created for the first stage of the VX-200 using both argon and krypton. The VX-200 plasma plume is mapped in detail during high vacuum conditions.

2012: The VX-200 demonstrates enhanced performance and efficient constant power throttling.

Franklin Chang Díaz serves as company President and CEO. Franklin Chang Díaz invented the VASIMR® concept, and has been working on its development since 1979. The VASIMR® technology began in The Charles Stark Draper Laboratory in Cambridge Massachusetts and continued at the MIT Plasma Fusion Center before the project moved to the Johnson Space Center in 1994.

Ad Astra Rocket was incorporated on January 14th, 2005 when the VASIMR® concept was privatized from NASA. AARC is headquartered 3 miles to the west of the NASA Johnson Space Center and about 25 miles south of the city of Houston.




Space Propulsion Technology

The VASIMR® engine is a new type of electric thruster with many unique advantages. In a VASIMR® engine, gas such as argon, xenon, or hydrogen is injected into a tube surrounded by a magnet and a series of two radio wave (RF) couplers The couplers turn cold gas into superheated plasma and the rocket’s magnetic nozzle converts the plasma thermal motion into a directed jet. 3)

Principles of operation: The primary purpose of the first RF coupler is to convert gas into plasma by ionizing it, or knocking an electron loose from each gas atom. It is known as the helicon section, because its coupler is shaped such that it can ionize gas by launching helical waves. Helicon couplers are a common method of generating plasma. After the helicon section, the gas is now "cold plasma", even though its temperature is greater than the surface of the Sun (5800 K). The plasma is a mixture of electrons and ions (the atoms they were stripped from). The newly formed electrons and ions carry charge and may then be contained by a magnetic field shielding the rocket core from the plasma. The second coupler is called the ICH (Ion Cyclotron Heating) section. ICH is a technique used in fusion experiments to heat plasma to temperatures on the order of those in the Sun's core (10 million K). The ICH waves push only on the ions as they orbit around the magnetic field lines resulting in accelerated motion and higher temperature.

Thermal motion of ions around the magnetic field lines is mostly perpendicular to the rocket's direction of travel and must be converted into directed flow to produce thrust. The rocket uses a magnetic nozzle to convert the ions orbital motion into useful linear momentum resulting in ion speeds on the order of 180,000 km/hr (112,000 mph).

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Figure 1: VASIMR® works with plasma, an electrically charged gas, heated to extreme temperatures by radio frequency (RF) waves, and controlled and guided by strong magnetic fields, which also provide insulation. Plasma rockets, such as VASIMR®, have an extremely low fuel consumption and much higher power and/or performance as compared to other electric or chemical rockets. VASIMR® offers economic and operational advantages in satellite deployment, re-boost, refurbishment, and end-of-life disposal. With the proper nuclear-electric power source, VASIMR® could enable much faster and safer human and robotic transportation in deep-space where solar power is insufficient (image credit: AARC)

VASIMR® Engine Compared to Other Electric Thrusters

The VASIMR® engine has three important features that distinguish it from other plasma propulsion systems:

• The VASIMR® engine has the ability to more widely vary its exhaust parameters (thrust and specific impulse) in order to optimize mission requirements resulting in the lowest trip time with the highest delivered payload for a given fuel load.

• The VASIMR® engine uses electromagnetic (RF) waves to create and energize the plasma within its core. In this way, the VASIMR® engine has no physical material electrodes in contact with the hot plasma. The lack of electrodes results in greater reliability, longer life, and enables a much higher power density than competing ion and Hall thruster.

• The VASIMR® engine is able to process a large amount of power, meaning that it can then generate a larger amount of thrust. This larger thrust capability promises to make the VASIMR® engine useful for moving large payloads around low Earth orbit, transferring payloads from the Earth to the Moon, and transferring payloads from the Earth to the outer solar system. The VASIMR® technology is also highly scalable, meaning that higher power versions can be easily designed; making human missions powered by electric propulsion a reality.

Power sources

One of the key challenges in developing the VASIMR® engine is supplying power to it. A high-power electric thruster requires a lot of electricity, and generating that in space may require some engineering innovations. Below is a discussion of two options.

Solar power: Solar power can be efficiently used for near-Earth VASIMR® missions, such as drag compensation for space stations, lunar cargo transport, and in-space refueling. Recent advances in solar array technology show a significant increase in solar power utilization (up to an order of magnitude).

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Figure 2: Illustration of a solar powered lunar tug concept using two VASIMR® engines (image credit: AARC)

Nuclear power

A nuclear reactor has a very large amount of energy per unit mass; a reactor core has the highest energy density of any useful energy source on earth. This high energy density and scalability make nuclear reactors an ideal power source in space. A nuclear-electric powered spacecraft could dramatically shorten human transit times between planets and propel robotic cargo missions with a very large payload. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse (less than 1000 seconds). A VASIMR® propelled, nuclear-electric powered spacecraft promises to make fast human missions a reality.




First Flight Unit

The VF-200TM engine is the first flight unit of the VASIMR® engine. It will be tested in space where the thrust and performance can be measured without the limitations of ground-based space simulation chambers. The VF-200TM will consist of two 100 kW thruster units side-by-side. 4)

The VF-200TM engine is being designed to reach the steady-state operating temperature to prove that it is capable of operating indefinitely for future missions. Ad Astra has proposed a flight test on the International Space Station (ISS) that could use small amounts of electrical power from the ISS to charge a large battery pack capable of powering the thrusters for approximately 15 minutes at full power during each pulse. Other space testing approaches are being considered, including a dedicated special purpose free flyer or an existing space test platform.

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Figure 3: Concept of the VASIMR® Aurora ISS payload, including VF-200TM engine, mounted on the International Space Station (image credit: AARC)

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Figure 4: Another view of the VASIMR® Aurora ISS payload concept mounted on the International Space Station (image credit: AARC)




Development status of Ad Astra’s VASIMR® Plasma Rocket

July 22, 2021: Ad Astra Rocket Company’s VASIMR® VX-200SS Plasma Rocket has completed 88 hours of continuous operation at 80 kW at the company’s Texas laboratory near Houston. In doing so, the company establishes a new high-power world endurance record in electric propulsion. The test also demonstrates the maturity of the VASIMR® engine technology as a competitive option for high-power in-space electric propulsion with either solar or nuclear electric power. Electric rockets operating above 50 kW/thruster are considered “high-power.” 5)

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Figure 5: Photo of the VX200 engine (photo credit: Ad Astra Rocket Company)

- The test began at 12:50 pm (CST) last Monday July 12 and ended Friday, July 16 at 4:55 am (CST). The firing stopped only 12 hours shy of its intended duration of 100 hours due to a spurious temperature sensor located in the test support equipment and not on the rocket structure. The rocket, however, was performing normally and all indications were that, were it not for this faulty sensor, it would have met and exceeded the 100- hour goal. Ad Astra believes the 88-hr test provides objective and sufficient evidence that the VASIMR® engine has met the intent of the high-power endurance goal set by NASA.

- “The test is a major success, the culmination of years of trial-and-error testing and painstaking attention to detail and a handsome reward for the team’s tenacity and dedication,” said Franklin R. Chang Díaz, Ad Astra’s chairman and CEO and a decorated former NASA astronaut. “With a new set of engine modifications already in the manufacturing stage, we’ll now move to demonstrate thermal steady state at 100 kW in the second half of 2021,” he added.

- The VASIMR® engine is unique in that it retains the high power of a chemical rocket but with ten times the fuel efficiency. As such, it is an excellent candidate for a host of applications, ranging from high-payload solar-electric robotic commercial cargo and resupply missions in cis-lunar space, to fast human missions to Mars and beyond with NEP (Nuclear-Electric Propulsion).

- The growing importance of NEP missions for which VASIMR® is ideally suited is reflected in the language of the 2022 Bill submitted by the Committee on Appropriations for Commerce, Justice, Science and Related Agencies of the US House of Representatives, which states that “... at least $10,000,000 shall be utilized to begin a systematic approach to Nuclear Electric Propulsion ...,” and “Within 180 days of the enactment of this Act, NASA, in coordination with other relevant Federal departments and agencies such as the Department of Energy, shall submit a multi-year plan for in-space propulsion-system demonstration for NEP.”

- “It is absolutely inspiring to see how much Franklin Chang Díaz and the Ad Astra team have been able to accomplish and advance in the years that I have known them. This technology has major potential to revolutionize the space industry,” said U.S. Congressman Brian Babin, Ranking Member of the House Space and Aeronautics Subcommittee. “Ad Astra’s small but dedicated team is a true testament of perseverance and continuing to invest in advanced technologies such as VASIMR® is critical if we want to remain a country that leads in space exploration,” he added.

- The company’s main goal is for the VASIMR® engine to demonstrate thermal steady-state operation at increasingly higher power levels. This condition calls for all the temperatures of the engine’s critical components to be stably maintained by the engine’s thermal management system.

- “The ability to operate continuously at 80 kW is exciting because we are so close to our 100-kW design goal and needing to focus on upgrading just a few components,” said Dr. Matthew Giambusso, Ad Astra Senior Research Scientist, and leader of experiment operations. “The rapid sequence of successful tests of the last few weeks have been thrilling,” he added.

- Major advances in the design of this system have been achieved in experimental campaigns lasting days to weeks, each followed by a period of inspection, disassembly, and improvement. This rapid prototyping is the basis for Ad Astra’s approach to mature the VASIMR® technology quickly and provide a competitive high-power electric propulsion option for both public and private customers.

- The thermal management of the VASIMR® engine is uniquely challenging, as temperatures from millions of degrees in the rocket’s plasma core to near absolute zero in the superconducting magnet, located a few tens of centimeters away, must be carefully controlled. This, of course, in the vacuum environment where the engine must operate. These stringent requirements have required Ad Astra to develop innovative manufacturing and assembly techniques to meet unusual thermal and electromagnetic constraints within the available engine envelope. “Getting the great diversity of materials to work in harmony in the environment we subject the engine to has presented major manufacturing challenges we have had to overcome,” said Mr. Lawrence “DJ” Dean, Ad Astra’s head of manufacturing.

• July 9, 2021: Ad Astra Rocket Company has shattered another major record for long-duration/high-power firing of its VASIMR® VX-200SS plasma engine, and in doing so, further advancing the technology of powerful and fuel-efficient electric rockets. Electric rockets operating above 50 kW/thruster are considered “high-power.” 6)

- On Wednesday, June 30, building on a succession of earlier tests this year, of increasing duration and power, the company completed a record-breaking test of the engine, operating at a power level of 82.5 kW for 28 hours, far longer than any other high-power firing to date. The tests are ongoing at the company’s Texas research facility near Houston.

- The VASIMR® engine is unique in that it retains the high power of a chemical rocket but with ten times the fuel efficiency. As such, it is an excellent candidate for a host of applications, ranging from high-payload solar-electric robotic commercial cargo and resupply missions in cis-lunar space, to fast nuclear-electric human missions to Mars and beyond.

- “We are extremely proud of the Ad Astra team. Their technical excellence, tenacity and dedication are reflected in this accomplishment. No other electric plasma rocket, at these power levels and technology readiness, has reached the VASIMR® engine’s combination of power and endurance achieved to date,” said Franklin R. Chang Díaz, Ad Astra’s chairman and CEO and a decorated former NASA astronaut. “We could have easily surpassed the 28-hour record but chose to stop our test to give the team a much-needed rest and a chance to celebrate the July 4th holiday,” he added.

- Ad Astra has been steadily approaching the 100-kW/100-hours milestone set by NASA without detracting from the company’s main objective: the demonstration of thermal steady-state control of the engine at high power. This condition calls for all the temperatures of the engine’s critical components to be successfully controlled by the engine’s thermal management system.

- “With a mixture of innovation and determination, our small team has developed unique engineering and manufacturing capabilities for the steady-state VASIMR® engine that have made the recent success possible,” said Dr. Matthew Giambusso, Ad Astra Senior Research Scientist, and leader of experiment operations. “We have more work to do to reach the design power of 100 kW, but these last few weeks have demonstrated significant progress,” he added.

- Major advances in the design of this system have been achieved in experimental campaigns lasting days to weeks, each followed by a period of inspection, disassembly, and improvement. This rapid prototyping is the basis for Ad Astra’s approach to mature the VASIMR® technology quickly and provide a competitive high-power electric propulsion option for both public and private customers.

- The thermal management of the VASIMR® engine is uniquely challenging, as temperatures from millions of degrees in the rocket’s plasma core to near absolute zero in the superconducting magnet, located a few tens of centimeters away, must be carefully controlled. This, of course, in the vacuum environment where the engine must operate.

• January 23, 2000: 7) A new generation radio-frequency (RF) Power Processing Unit (PPU) for the VASIMR® engine, built for Ad Astra Rocket Company by Aethera Technologies Ltd. of Canada, has completed a full-power test in vacuum at Ad Astra’s Texas facility near Houston. The test, conducted on January 20, involved operating the unit in hard vacuum and thermal steady state at its full power rating of 120 kW. As part of the test, the PPU was also subjected to the magnetic field of the VASIMR® engine to verify that there is no magnetic effect on the PPU performance.

- With this test, Ad Astra successfully completed one of the three remaining major technology milestones in the NextSTEP Partnership Program contract with NASA for the maturation of the VASIMR® engine. With these results, the VASIMR® system is now fully positioned at technology readiness level (TRL) 5; that is, all critical engine components have now been operated at full power in a relevant environment under vacuum.

- A critical component of the two-stage VASIMR® engine, the RF PPU provides the RF energy needed to efficiently heat the rocket’s argon propellant in the high-power second stage. A similar, lower power RF PPU will be used in the first stage to ionize the propellant. The resulting high-temperature plasma accelerates in the magnetic nozzle to provide rocket thrust.

- At a maximum rated power of 120 kW and weighing only 53 kg, the VASIMR® RF PPU is as much as 10x lighter than that of competing electric thrusters and its advanced semiconductor-based design produces greater than 97% DC-to-RF power efficiency. Such remarkable performance has now been demonstrated in vacuum and in proximity to the VASIMR® engine’s magnetic field.

- The development of the RF PPUs is supported by Ad Astra Rocket Company and the Canadian Space Agency (CSA). CSA’s support is part of a contribution agreement under the Space Technology Development Program (STDP) announced by the CSA on May 25, 2018 and expands the international dimension of the VASIMR® project.

- Two milestones now remain in Ad Astra’s queue and are planned for completion this spring. These involve long-duration 100 kW firings of the VX-200SS VASIMR® test article; one for 5-6 hours to demonstrate thermal control of the engine and a second, for 100 hours, to estimate component life. Upon completion of these milestones, Ad Astra will move to the next technology maturation phase: the development of a TRL-6 VASIMR® engine for a space test.

- “Watching the test was like a dream with all parameters maintaining very comfortable margins. What seemed like an easy test was a testimony to the quality of the teams that developed and tested this beautiful piece of equipment,” says Jared Squire, Senior VP Research. “The environmental requirements for vacuum and magnetic field were key requirements for the RF PPU and having a successful result on the first test was a big achievement for the design teams” said Tim Hardy, Chief Technology Officer at Aethera. “We’re looking forward to continuing positive outcomes as the Ad-Astra team prepares the VASIMR® engine for a space test,” he added.

- About Aethera: Located in Halifax, N.S., Aethera Technologies Limited develops innovative technology and provides related services for its clients with a focus on Radio Frequency (RF) power for aerospace, communications, scientific and industrial applications including dielectric heating. Aethera is committed to transforming ideas into a competitive advantage for our clients.

- About CSA's Space Technology Development Program: CSA’s Space Technology Development Program (STDP) supports innovation for the growth of the Canadian space sector and aims to reduce technological unknowns. Contracts are issued to Canadian organizations for the development of technologies to support future needs of the Canadian Space Program, while non-repayable contributions are awarded to Canadian organizations to support the development of innovative technologies with strong commercial potential.

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Figure 6: Some of the Ad Astra team members who supported the RF-PPU testing pose in front of the open vacuum chamber at the company's Texas facility. The RF-PPU and part of the test hardware can be seen in background (upper center). The main VX-200SS test article fills the upper right portion of the image (image credit: Ad Astra Rocket Company)

• August 20, 2019: A new generation radio-frequency (RF) Power Processing Unit (PPU) for the VASIMR® engine, built by Aethera Technologies Ltd. of Canada, has completed a series of full power acceptance tests at Ad Astra Rocket Company’s Texas facility near Houston. The unit completed these tests on August 12 by operating in a thermal steady-state with no anomalies at its full power rating of 120 kW. The RF PPU is now ready to be incorporated into Ad Astra’s vacuum facility so that it can be tested with the VX-200SSTM VASIMR® prototype. These tests are part of Ad Astra’s ongoing program under the NASA NextSTEP partnership contract. 8)

- The RF PPU is a critical component of the VASIMR® engine, providing the RF energy needed to efficiently ionize and heat the argon propellant in the rocket. The resulting high temperature plasma is accelerated in the magnetic nozzle to provide thrust.

- Aethera has developed an RF PPU with >97% electrical-to-RF power efficiency, using advanced semiconductors and incorporating the capability to operate in vacuum and in close proximity to the VASIMR® engine’s magnetic field. In addition, at 52 kg, the new VASIMR® RF PPU is about 10 x lighter than the PPU’s of competing electric thrusters.

- The development of the RF PPU is being supported by Ad Astra Rocket Company, and The Canadian Space Agency (CSA). CSA’s support is part of a contribution agreement under the Space Technology and Development Program (STDP) announced by the CSA on May 25, 2018. The CSA funding contribution highlights Canada’s long-term view regarding the importance of high-power electric propulsion in humanity’s gradual evolution beyond low Earth orbit (LEO) and gives the project an added international flavor.

- “We are extremely pleased with the results of these tests,” said Dr. Franklin R. Chang Díaz, CEO of Ad-Astra Rocket Company. “The Aethera and Ad Astra teams have worked very hard and very well together to achieve this important milestone, and we look forward to the road ahead with excitement and optimism,” he added.

- “We are extremely pleased to be a part of the VASIMR® team and to have the opportunity to develop state-of-the-art equipment for the space industry” expressed Tim Hardy, Chief Technology Officer at Aethera. “The new RF PPU full power testing is an extremely positive result on the way to achieving a flight qualified rocket” he added.



1) “Variable Specific Impulse Magnetoplasma Rocket,” Wikipedia, URL: http://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket

2) http://www.adastrarocket.com/aarc/history

3) http://www.adastrarocket.com/aarc/VASIMR

4) http://www.adastrarocket.com/aarc/VF-200

5) ”VASIMR VX-200SS Plasma Rocket Completes Record 88-hour High-power Endurance Test,” Ad Astra, Press Release, 22 July 2021, URL: https://www.adastrarocket.com
/pressReleases/2021/20210722-PressRelease.pdf

6) ”AD Astra Rocket Company shatters power and endurance record in recent tests of the VASIMR® VX-200SS plasma rocket,” Ad Astra Press Release, 9 July 2021, URL: https://www.adastrarocket.com/pressReleases/2021/20210709-PressRelease.pdf

7) ”Aethera’s New RF Power Processing Unit for the VASIMR® Engine Successfully Completes Full Power Vacuum and Magnetic Field Tests at Ad Astra Rocket Company’s Texas Facility,” AD AstraPress Release, 23 January 2020, URL: https://www.adastrarocket.com//pressReleases/2020/AdAstraPressReleaseJan232020_final_photo.pdf

8) ”Aethera’s New RF Power Processing Unit for the VASIMR® Engine Completes Full Power Acceptance Tests at Ad Astra Rocket Company’s Texas Facility,” Ad Astra Press Release, 20 August 2019, URL: https://www.adastrarocket.com/pressReleases/2019/20190820-AdAstra-Aethera.pdf


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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