Going to the moon was one thing; going to Mars will be quite another. The distance alone is intimidating. While the moon is 238,855 miles away, the distance to Mars is between 33 million and 249 million miles. The propulsion systems that got us to the moon just won't work.
Taylor Hampson, a master's student in the Department of Nuclear Science and Engineering (NSE), is well aware of the problem. It's one of the many reasons he's excited about his NASA-sponsored research into nuclear thermal propulsion (NTP).
The technique uses nuclear energy to heat a propellant, like hydrogen, to an extremely high temperature and expel it through a nozzle. The resultant thrust can significantly reduce travel times to Mars, compared to chemical rockets. "You can get double the efficiency, or more, from a nuclear propulsion engine with the same thrust. Besides, being in microgravity is not ideal for astronauts, so you want to get them there faster, which is a strong motivation for using nuclear propulsion over the chemical equivalents," Hampson says.
Understanding nuclear thermal propulsion
It's worth taking a quick survey of rocket propulsion techniques to understand where Hampson's work fits.
There are three broad types of rocket propulsion: chemical, where thrust is achieved by the combustion of rocket propellants; electrical, where electric fields accelerate charged particles to high velocities to achieve thrust; and nuclear, where nuclear energy delivers needed propulsion.
Nuclear propulsion, which is only used in space, not to get to space, further falls into one of two categories: nuclear electric propulsion uses nuclear energy to generate electricity and accelerate the propellant. Nuclear thermal propulsion, which is what Hampson is researching, heats a propellant using nuclear power. A significant advantage of NTP is that it can deliver double the efficiency (or more) of the chemical equivalent for the same thrust. A disadvantage: cost and regulatory hurdles. "Sure, you can get double the efficiency or more from a nuclear propulsion engine, but there hasn't been a mission case that has needed it enough to justify the higher cost," Hampson says.
Until now.
With a human mission to Mars becoming a very real possibility - NASA plans on sending astronauts to Mars as early as the 2030s - NTP might soon come under the spotlight.
"It's almost futuristic"
Growing up on Florida's Space Coast and watching space shuttle launches stoked Hampson's early interest in science. Loving many other subjects, including history and math, it wasn't until his senior year that Hampson cast his lot into the engineering category. While space exploration got him hooked on aerospace engineering, Hampson was also intrigued by the possibility of nuclear engineering as a way to a greener future.
Wracked by indecision, he applied to schools in both fields and completed his undergraduate degree in aerospace engineering from Georgia Tech. It was here that a series of internships in space technology companies like Blue Origin and Stoke Space, and participation in Georgia Tech's rocket team, cemented Hampson's love for rocket propulsion.
Looking to pursue graduate studies, MIT seemed like the next logical step. "I think MIT has the best combination of nuclear and aerospace education, and is really strong in the field of testing nuclear fuels," Hampson says. Facilities in the MIT Reactor enable testing of nuclear fuel under conditions they would see in a nuclear propulsion engine. It helped that Koroush Shirvan , associate professor of NSE and Atlantic Richfield Career Development Professor in Energy Studies, was working on nuclear thermal propulsion efforts with NASA while focusing most of his efforts on the testing of nuclear fuels.
At MIT, Hampson works under the advisement of Shirvan. Hampson has had the chance to pursue further research in a project he started with an internship at NASA: studies of a nuclear thermal propulsion engine. "Nuclear propulsion is itself advanced, and I'm working on what comes after that. It's almost futuristic," he says.
Modeling the effects of nuclear thermal propulsion
While the premise of NTP sounds promising, its execution will likely not be straightforward. For one thing, with NTP, the rocket engine won't start up and shut down like simple combustion engines. The startup is complex because rapid increase in temperatures can cause material failures. And the engines can take longer to shut down because of heat from nuclear decay. As a result, the components have to continue to be cooled until enough fission products decay away so there isn't a lot of heat left, Hampson says.
Hampson is modeling the entirety of the rocket engine system - the tank, the pump, and more - to understand how these and many other parameters work together. Evaluating the entire engine is important because different configurations of parts (and even the fuel) can affect performance. To simplify calculations and to have simulations run faster, he's working with a relatively simple one-dimensional model. Using it, Hampson can follow the effects of variables on parameters like temperature and pressure on each of the components throughout the engine operation.
"The challenge is in coupling the thermodynamic effects with the neutronic effects," he says.
Ready for more challenges ahead
After years of indecision, delaying practically every academics-related decision to the last minute, Hampson seems to have zeroed in on what he expects to be his life's work - inspired by the space shuttle launches many years ago - and hopes to pursue doctoral studies after graduation.
Hampson always welcomes a challenge, and it's what motivates him to run. Training for the Boston Marathon, he fractured his leg, an injury that surfaced when he was running for yet another race, the Beantown Marathon. He's not bowed by the incident. "I learned that you're a lot more capable than you think," Hampson says, "although you have to ask yourself about the cost," he laughs. (He was in crutches for weeks after).
A thirst for a challenge is also one of the many reasons he chose to research thermal nuclear propulsion. It helps that the research indulges his love for the field. "Relatively speaking, it's a field in need of much more advancement; there are many more unsolved problems," he says.
