New Vasimir engine could cut Mars travel to 60-70 days, allow greater rocket fuel economy
DailyTech has covered advances in the field of rocket propulsion and spaceflight. From such theoretical technologies as a laser engine, to actualized devices like ion drives, there are many unique ideas in the field, despite the relatively tight budgets.
The key challenge facing rocket designers is basic physics. Propulsion is determined by two key factors -- how much stuff you throw out the back of the rocket (mass) and how fast that stuff is going (velocity). One of these factors can be relatively low if the other is high to compensate. Thus on one extreme you have the solid-fuel and liquid fuel rockets -- these exit burning chemicals at relatively low velocities (compared to alternative technologies), but they dump large quantities of mass and therefor produce sufficient thrust. On the other extreme you have technologies such as ion drives, which exit a minuscule amount of mass at much higher speeds, to eventually produce a sufficient impulse.
The problem with solid/liquid fuel rockets is that they require massive fuel stockpiles, hence the big fuel tanks. And while they produce enough thrust to reach orbit, their fuel is quickly exhausted. Ion drives, on the other hand, can not reach space without using liquid rockets, so they can only activate after the fact.
However a new technology may soon leave both options in the dust. The new tech is a plasma rocket engine developed by Texas based startup Ad Astra Rocket corporation. The company was founded by former NASA astronaut Dr. Franklin Chang-Díaz, who serves as its chief executive.
The new rocket is named Variable Specific Impulse Magnetoplasma Rocket (VASIMR). A traditional rocket can produce a specific impulse of around 450 seconds, or in other words 1 pound of thrust from 1 pound of fuel for 450 seconds. VASIMR can produce several times this amount, cutting a trip to Mars from 6 to 9 months with conventional rockets down to a mere 2 to 3 months. It could do this by being able to burn fuel continuously the whole trip accelerating on the first half of the journey to Mars and decelerating on the second leg of the journey, preparing to enter orbit.
The rocket consists of three critical units or cells. The first is the plasma generator. It sits deepest into the rocket and consists of a generator which ionizes heated light gases such as hydrogen, creating plasma -- atoms stripped of their electrons. The plasma, at a modest temperature of 10,000 °C, is then pumped into the second unit, the amplifier. In the amplifier cell the plasma is blasted with electromagnetic waves via radio waves. These waves heat the plasma burning hot similar to how food is heated in a microwave. Finally the ultra-hot plasma is channeled in magnetic containment fields to the final cell, the magnetic nozzle. This nozzle is the critical control which controls how much fuel exits, and how fast the exiting plasma is going.
The nozzle also protects the spacecraft from the burning hot plasma. How hot is the plasma exactly?? Well, early estimates are that it will be around 180 million degrees Fahrenheit (100 million degrees Celsius), only about 25,000 times hotter than the burning gases exiting the space shuttle. However, thanks to the magnetic nozzle the plasma can be tamed and channeled into useful impulse.
Dr. Chang-Diaz explains, "Rockets tend to work much better the hotter the exhaust is and the plasma allows you to go to temperatures millions of degrees rather than thousands of degrees in a conventional rocket engine."
In order to accomplish the critical control of the fuel, VASIMR utilizes superconductors to make pumped up magnets. Explains Dr. Chang-Diaz, "To harness the plasma at those temperatures, the only way is…to have a very strong magnetic field to hold it together. The only way to create those fields in a reasonable way in space is with superconductors."
His company, along with NASA, academic partners, and corporate partners developed special superconductors at the Johnson Space Center’s (JSC) Advanced Space Propulsion Laboratory to rise to the occasion. These superconductors have a wide array of applications, but for now the focus is on the plasma engine.
So how close is the engine to deployment? Well after years of hard work, the engine is virtually complete and ready for its first "field test" -- a deployment in space. At the AirVenture show in Oshkosh on July 29, US space agency's administrator Michael Griffin announced to the press that "we are at the end stages of agreeing a co-operative agreement for NASA to test the Vasimir engine on station".
While no timescale was given for the launch, the deal is expected to be signed soon. NASA already signed a broader collaborative agreement with the firm in 2006. The model used in the tests aboard the International Space Station would be a scale model. Nonetheless, it would be critical to gaining final insight to prepare the engine for full deployment.
Plasma rockets are considered by many the best long-range propellant solution besides fusion rockets. As fusion power is still a fledgling research field, plasma may help to fill the gap for many years to come. Past fusion power, only exotic propulsion solutions could possibly yield greater speeds.
To view videos of VASIMR in action, please view the links on Ad Astra Rocket corporation's page visible here.
The engine features a three cell design. The first cell creates plasma from hydrogen at 10,000 deg. C. The next cell heats the plasma with radio waves to approximately 100 million deg. C. The last cell is a nozzle which controls how fast this fuel is let out, protecting the spacecraft and allowing acceleration control. (Source: Ad Astra Space Corporation)
A computer rendering of the engine module. (Source: Ad Astra Space Corporation)
An artist's rendition of three plasma engines burning in space, propelling a spacecraft, perhaps to Mars. (Source: Ad Astra Space Corporation)
The actualized plasma rocket under development at the Johnson Space Center. (Source: Ad Astra Space Corporation)
DailyTech - Commercially Developed Plasma Engine Soon To Be Tested In Space
