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Plasma rocket could revolutionize space travel

BY STEPHEN CLARK

SPACEFLIGHT NOW

Posted: June 1, 2010



The headquarters of Ad Astra Rocket Co. doesn't catch the eye, at least until you step inside. Inside an unsuspecting warehouse in suburban Houston, hidden behind a streetcorner strip mall, a team of elite engineers and enterprising physicists is busy developing a high-tech plasma rocket designed to carry humanity to the stars. Founded in 2005, the company accomplishes most of its work just a few minutes from Johnson Space Center, the home of Mission Control. The company's main project is the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR, a highly-efficient space engine running on electricity and argon gas instead of conventional solid or liquid propellants. Franklin Chang-Diaz, the project's chief architect, says the VASIMR engine is the most flight-ready high-power electric propulsion system anywhere in the world. "It is transformational technology that we are developing," Chang-Diaz said. "It always has been my view that chemical approach to space transportation really was not going to get us very far."

The VASIMR ground engine fires during testing in May. Credit: Stephen Clark/Spaceflight Now



Chemical rocket engines require spacecraft to carry all of its propellant during its mission. The VASIMR engine burns small amounts of argon gas, one of the most stable elements on the periodic table. But one of the most revolutionary features of the VASIMR design is its reliance on electricity, a renewable resource in space. "It's very robust, but in order to get beyond the moon, and move on to Mars and beyond, we really need completely new transportation technology," Chang-Diaz said. "We view the VASIMR as the workhorse for that transportation infrastructure." Electrically-powered plasma rockets could cut travel times for missions across the solar system. One concept championed by Chang-Diaz involves a 39-day mission to Mars, but it assumes leaps in nuclear energy production in space. Originally bankrolled by NASA, the VASIMR project has gone from the drawing board to reality since the plasma rocket research was privatized in 2005. Inside Ad Astra's laboratories in Houston and Costa Rica, rocket designers have pushed the VASIMR engine closer to flight. "In five years, we've made some pretty big jumps, in terms of power capability and the efficiency of the plasma source," said Tim Glover, Ad Astra's director of development. NASA measures emerging technologies on a readiness scale from 1 to 10. "When the technology is ready to fly is when you get to a level 6," Chang-Diaz said. "Level 7 is the actual flight." The VASIMR engine is already at level 6, according to Chang-Diaz, who has worked on plasma rocket technology since the 1970s. "I always felt there was a way to use that high-temperature plasma to develop a rocket engine that could go a lot faster than the rockets that we have today," Chang-Diaz said. But Chang-Diaz was sidetracked by a second career as an astronaut after his selection by NASA in 1980. The 60-year-old is one of only two space fliers to complete seven missions on the final frontier. In between training for space shuttle missions, Chang-Diaz led plasma research first at the Massachusetts Institute of Technology, then at NASA's Johnson Space Center. But NASA decided to cancel advanced propulsion research to pay for the Constellation program to return humans to the moon, forcing the work into the private sector in 2005. "Facing such dire possibilities on our project, I proposed to NASA that we privatize it," Chang-Diaz said. "Much to my amazement, they agreed that it would be a good idea. That's how Ad Astra Rocket Co. was born, out of a privatization agreement with NASA, where the laboratory that I used to lead was transformed into a private entity." Chang-Diaz secured investments from the United States, Europe and his native Costa Rica summing several tens of millions of dollars, a figure he says is ten times more than NASA ever spent on the project. The company now employs about 40 workers in Houston and Costa Rica. The influx of funding has propelled the VASIMR engine from a readiness level of 2 to 6 since the laboratory was privatized. "That happened in five years, and we only got from 0 to 2 in 25 years," Chang-Diaz said. "It's been a very drastic progress in the last five years. That's what happens when you have money." But the Obama administration's proposal to cancel the Constellation program and refocus NASA on nurturing new technologies for solar system exploration has put VASIMR in the limelight. "President Obama has decided that NASA needs to go back to its roots and continue to fund projects of advanced technology," Chang-Diaz said. "We've almost come full circle, and we find ourselves at the point where NASA is interested again."

A diagram of the VASIMR engine. From right to left, the argon gas is injected into the engine, the gas is ionized in the engine's first stage, super-heated in the second stage, then directed through the nozzle by superconducting magnets. Credit: NASA



And Chang-Diaz's cozy friendship with NASA chief Charles Bolden doesn't hurt either, Glover said. Chang-Diaz flew with Bolden on two shuttle flights and remain close friends today. "Charlie and I are very good friends," Chang-Diaz said. "I think he's got the right approach in bringing people together. He certainly has the right personality and the right level of technical knowledge." Bolden has cited VASIMR as an example of the new technologies NASA should be pursuing. "One thing that will help will be to let somebody like Dr. Franklin Chang-Diaz or somebody who's studying ion engines help us develop a game-changing interplanetary engine that will cut the time to go to Mars in half," Bolden said in a news conference earlier this year. Ad Astra officials say they welcome NASA interest in the project, but they insist on continuing the engine's development in the private sector. "I don't want to put NASA in the critical path because you never know what's going to happen with NASA," Chang-Diaz said. "I wouldn't consider it very reliable at this moment." Ad Astra is currently testing a two-stage ground version of the VASIMR engine inside a vacuum chamber in Houston. The 200-kilowatt engine, called the VX-200, looks nothing like a conventional rocket engine. The powerplant lacks the combustion chamber found on contemporary boosters. The company successfully tested the ground engine to its 200-kilowatt design standard in late 2009, but those power levels were only achieved in short bursts lasting just a fraction of a second. Engineers plan more testing of the VX-200 to eventually accomplish longer firings. Ground testing so far has relied on low-temperature superconducting coils, but more ambitious demonstrations in space will use more durable materials capable of withstanding much higher temperatures and longer burn durations. "The high-temperature superconducting tape is an enabling technology to us," Glover said. Plasma inside the VASIMR engine is constrained by the powerful coils of a superconducting magnet, a key technological breakthrough that binds the engine together by accelerating the super-heated plasma to produce propulsive force. The engine's argon fuel first passes through the assembly's first stage, where the gas is ionized as electrons are stripped from argon atoms. The first stage, also called the helicon section, heats the gas to about 10,000 Kelvin, or 17,540 degrees Fahrenheit, said Jared Squire, Ad Astra's director of research. "It's the same thing you do in a steam engine, where you first boil water to make steam," Squire said. "You're heating the gas, and that's where the plasma is formed." The VASIMR engine's second stage applies more electromagnetic power to the plasma in a process called ion cyclotron heating. The plasma spills out of the engine nozzle at more than 110,000 mph. The exhaust can reach temperatures of up to 1.8 million degrees Fahrenheit, according to Squire. Officials plan to work out the kinks in the technology before launching flight engines to the International Space Station by 2014 for an orbital demo. Glover said the station tests will use two engines operating at 100 kilowatts. The 10,000-pound engine package will be launched on one of the commercial cargo carriers being developed by SpaceX and Orbital Sciences.

An early concept of the VASIMR engine on the International Space Station. Credit: NASA



VASIMR's opportunity to fly on the space station came through a Space Act Agreement signed with NASA in 2008. The contract, which does not include an exchange of funds, stipulates Ad Astra and NASA must pass through five milestones before the test flight. The parties already completed a payload integration agreement, and the next step will be the VASIMR engine's preliminary design review in 2011. Ad Astra hopes the VASIMR engine could be used to reboost the space station after it completes its demonstration objectives. "If the ISS is really extended well into the 2020s, then the international partners might agree they would like to do reboost using electric propulsion," Glover said. "You would likely have to wait until present agreements to do reboost with [Europe and Russia] are ending, then you could say Ad Astra has already demonstrated this system on the ISS. Why don't we consider how much money we could save by moving this back and using it for reboost?" Glover said such a move would save the station program $200 million and 7 metric tons of propellant each year. That money and mass could be diverted for other scientific experiments aboard the complex. But Ad Astra has set its sights even higher than Earth orbit. The company believes the VASIMR will make voyages to Mars and asteroids a reality. It just so happens those places are the new destinations for NASA's human exploration plans, which would bypass the moon, for now. "We have to get to Mars fast," Chang-Diaz said. "It can't take six, or seven, or eight months to get to Mars. That is just asking for trouble." Even if chemical rockets get humans to Mars, the program will be unsustainable because of the lengthy journey and high cost, according to Chang-Diaz. "These engines that we're developing are inherently high-power engines. These aren't little thrusters, these are very powerful engines, which can scale up to tens of megawatts," Chang-Diaz said. Those megawatt-class engines will be required for any substantial presence in the solar system. The 200-kilowatt engine now under development is best suited for work in Earth orbit or in multi-engine clusters. But is a 39-day manned trip to Mars really possible? Ad Astra says yes, with caveats. It would require major advancements in nuclear power and a departure point somewhere high above Earth.

Ad Astra's concept for a VASIMR-powered spacecraft on the way to Mars. Credit: Ad Astra



"The ship for a 39-day mission to Mars is not that much different than a 747 jumbo jet, in terms of power," Chang-Diaz said. "When they hear we want to use a 200-megawatt ship to go to Mars, people cringe and wring their hands, and say how are you going to get that much power?" Current technology can't produce enough electricity in space to drive multiple megawatt-class high-power plasma engines for weeks at a time. "That takes a really lightweight power supply, around 1 kilogram per kilowatt, which is probably ultimately doable," Glover said. According to Glover, the most important measure for the efficiency of plasma engines is the weight-to-power ratio, or the number of kilograms needed to generate a kilowatt of electricity. Flat panel solar arrays today have a ratio of about 20 kilograms, or 44 pounds, for every kilowatt of power they produce. The best nuclear reactors designed for spaceflight have a specific mass of about 45 kilograms, or nearly 100 pounds. The Pentagon and Boeing Co. are developing a next-generation solar array aimed at reaching a weight-to-power ratio of 7 kilograms per kilowatt, according to the Defense Advanced Research Projects Agency. Engineers predict nuclear power generators will reach an efficiency of a few kilograms per kilowatt within a couple of decades. Even if 39-day trips to Mars are still a distant dream, Ad Astra officials are confident the journey time for smaller missions can be cut by more than half by the 2020s with imminent breakthroughs in solar array technology. "While solar technology is very impressive and it can be used to do some technology demonstrations soon, it's not going to get us very far. Ultimately, you need to have nuclear power if you want to do big things out there."





