Private space technology powers up as Ad Astra’s VX-200 lives up to its name:
We are getting ready to fly the VASIMR engine on the International Space Station (ISS). It is a 200-kilowatt plasma rocket, the most powerful rocket ever built to fly in space, and the prototype is being tested on the ground in our facilities in Houston. We have been gradually ramping up the power over many months, and our goal is to reach 200 kilowatts, which is the power level the rocket will run at on the ISS, and we achieved that today. We actually reached 201 kilowatts.
Dr. Franklin Chang-Diaz explains his plasma rocket engine:
VASIMR stands for “Variable Specific Impulse Magnetoplasma Rocket.” It’s a plasma-based electric rocket engine, so it’s different from conventional chemical rockets, which are propelled by the combustion of rocket fuel. VASIMR isn’t based on chemical reactions. Instead, it uses plasma, which is a gas that’s been heated to extremely high temperatures, temperatures approaching that of the Sun. Because it’s so hot, the plasma can’t be handled with any conventional materials. We have to use superconductors to generate electromagnetic fields to contain the plasma, form it into a jet, and guide it out the back of the rocket engine. VASIMR is meant for use in outer space — it won’t replace chemical rockets for launching payloads into orbit.There is a term in rocketry, “specific impulse,” which measures how efficiently a rocket obtains thrust from its propellant. The higher the specific impulse, the more efficient the rocket, and the less fuel it requires. In general, specific impulse increases as a rocket’s exhaust gets hotter. A good chemical rocket’s specific impulse is on the order of about 500. And the specific impulse of the VASIMR and most other plasma-based rockets is in the thousands, even the tens of thousands. So we’re talking about an orders-of-magnitude performance improvement of the rocket. That’s why we go to all the trouble of working with plasma, because there’s a huge payoff in terms of how much fuel you use to get any given payload from point A to point B in outer space.
In all plasma rockets, you have to produce thrust by accelerating the plasma. Other plasma rockets do this with electric current from metallic grids that are immersed in the plasma. Too much plasma flowing past these grids will make them essentially melt, so you can’t go to extremely high power. You can somewhat get around this by making the grids very large, or making arrays of them, but you’re still limited by grid erosion and damage. This means most plasma rockets are inherently low-power devices.
In VASIMR, however, there are no grids. Its plasma is contained by magnetic fields and heated and accelerated by electromagnetic waves. Since no parts of the rocket are immersed in the plasma flow, you can make the plasma very dense and hot and get much better performance.
To reach its full potential, the VASIMR needs nuclear power:
In fact, with the power close to what a nuclear submarine generates, you could use VASIMR to fly humans to Mars in 39 days. A chemical rocket makes the trip in eight months. That’s eight months of exposing your astronauts to debilitating cosmic radiation and weightlessness. By the time they get to where they’re supposed to work, they’re gonna be in bad shape—almost invalids! They’ll have to spend a big chunk of their time just recovering from the trip. That’s simply not a smart way to conduct an exploration program. By not addressing the key problems of limited power and propulsion, NASA is forced to work with extremely complicated and expensive mission architectures that are very limited in capability.
Without nuclear power, how will the VASIMR get deployed?
We signed an agreement with NASA last December to actually mount the VF-200 on the International Space Station in 2012 or 2013. Unfortunately, the space station doesn’t have 200 kilowatts to give us. So what we’ll do is use the solar arrays of the station to charge a battery pack that we’ll carry on board, which will allow us to fire the rocket at 200 kilowatts for up to 15 minutes. We’ll do this again and again for months to qualify the engine in space. In 2013 or 2014, we’ll make clusters of 200-kilowatt engines to give us something close to a megawatt of electricity, and deploy them with a very high-powered solar array. This will be a robotic reusable “space tug” that can refuel or reposition satellites, or even send packages to the Moon at a much lower price. By charging for those services, we hope to bootstrap our way into developing a megawatt-class rocket.
Here’s how the VX-200 might pay for itself:
The ISS has to be reboosted every few months; otherwise it gradually falls and burns up in the atmosphere. These reboosts require about 7 metric tons of rocket fuel per year. How much does it cost to get 7 metric tons of rocket fuel into orbit? $140 million. That’s the bill someone has to pay, each year, just for hauling up the fuel. The 200-kilowatt solar-powered VASIMR can do the same thing with about 320 kilograms of argon gas per year, which still costs about $7 million, but it decreases the price by a factor of 20.
(Hat tip to Nyrath.)