In the basement of the energy wing of the Engineering Quad, past a long, white tunnel, down two flights of stairs and through a set of double doors, is a postcard with the message, "Greetings from Mars."
The postcard hangs on the wall of a lab — the Electric Propulsion and Plasma Dynamics Lab (EPPDyL) — in which research is conducted that may help put a man on Mars. And a grant from NASA just moved that research one step closer to completion.
Over the summer, the National Aeronautics and Space Administration awarded a three-year, $4.4 million contract to Edgar Choueiri, EPPDyL director and associate professor of mechanical and aerospace engineering, to develop a more advanced rocket capable of sending people or heavy cargo to other planets.
"We're going into a whole other level of funding and involvement," Choueiri said. "It's very exciting. We're working on the types of engines that will be the mainstay of future important missions."
In white and orange stainless steel tanks engineered to simulate the vacuum of outer space, Choueiri and his team test their inventions — called plasma thrusters — in the hopes of increasing efficiency and eventually reaching a design suitable for interplanetary flight.
"These advanced-electric propulsion technologies, once developed and proven, would help enable a new class of ambitious robotic and human exploration missions not possible with existing propulsion technologies," said Ray Taylor, acting deputy director of NASA's Project Prometheus, which is funding the research, in a July press release.
Choueiri, who is leading a team that includes scientists at NASA's Glenn Research Center, Jet Propulsion Laboratory and Marshall Space Flight Center, as well as at the University of Michigan and the Worcester Polytechnic Institute, hopes that a rocket will be ready for space as early as 2010.
Plasma Thrusters
The original impetus for plasma thrusters comes from pioneering studies by the early-20th century Russian scientist Konstantin Tsiolkovsky. Tsiolkovsky's rocket equation shows that the more quickly fuel is released from a rocket, the less fuel needed to propel the rocket a given distance. In other words, to make a fuel-efficient rocket, it is important to have a fast exhaust velocity.
That is where plasma thrusters come in. In current chemical rockets, a slow three to four kilometer-per-second exhaust velocity means that up to 70 percent of the rocket must be filled with fuel, Choueiri said. This leaves very little room for cargo, scientific instruments and people.
"There's a few guys sitting up top, and the rest is fuel," Choueiri said. "It's very, very fuel-hungry."
Plasma rockets, however, use a more advanced technology to increase exhaust velocity, and therefore save fuel. In fact, in these rockets, there is no real fuel, and no burning is required for energy.
Instead, plasma is actually a gas — Choueiri uses lithium — that has been heated or electrified until it resembles a soup of ions or electrons. These ionized gases, which make up the vast majority of the visible universe and can be observed in such phenomena as lightning bolts and the aurora borealis, behave differently from neutral gas.
One of the most important of these differences is that plasma, unlike gas, is affected by magnetic fields. Thus, by using electromagnetic forces, Choueiri is able to propel the plasma from the rocket at much higher speeds than in conventional rockets, up to 60 kilometers-per-second — 15 times faster than chemical rockets.
As demonstrated in the rocket equation, this increased velocity translates into greater fuel efficiency. In this case, it means only ten percent of a rocket will need to be propellant, Choueiri said, providing large savings in space and weight from the current chemical rockets. And these savings may allow rockets to carry people to Mars.
"Because of their very high exhaust velocities compared to chemical thrusters, plasma thrusters are very fuel efficient and can allow humans to go to Mars," Choueiri explained.
Indeed, Choueiri added, "the further you want to get, the more efficient the plasma thrusters become."
Beyond human exploration
But plasma thrusters could be useful in ways beyond the human exploration of other planets. For example, satellites could benefit from the technology.
Currently, Choueiri said, satellites in geosynchronous orbit, like telecommunications satellites, avoid natural drift and keep aligned with the Earth by frequently firing chemical rockets.
These rockets use up an enormous amount of fuel, all of which must be carried up to the satellite at huge expense.
In other words, "much of what you're paying to go on the Internet is actually for lifting the propellant to keep the satellite in position," Choueiri said.
Plasma rockets, on the other hand, would be "smaller, cheaper and require less propellant," he added, possibly saving corporations and consumers large sums of money.
Future directions
In addition to the Alfa2 project — the one NASA just funded — Choueiri is entering two NASA competitions in the next month.
One is a $30 million co-investigation with Boeing to develop a facility to test the lifespan of the plasma thrusters.
"No one will fly one of these rockets before there are many tests to determine how long they last," Choueiri said.
The other is a $6 to 10 million project involving a propulsion concept that "didn't exist two years ago," Choueiri said.
"I don't get as excited solving problems on things that have been around for a long time," he added. "To me, that's not as exciting as inventing something totally new."
Both projects were recently selected out of a pool of about 4,000 short pre-proposals, Choueiri said. He now has to complete longer proposals to submit to NASA for final consideration.
Whether or not the proposals are accepted, however, Choueiri will keep busy. And maybe 10 years from now, the rockets will leave the whitewashed basement of the E-quad and travel 140 million miles to where things are a bit more colorful.
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