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Next step in advancing space travel: Fission rockets

Project Bifrost is an ambitious study examining emerging space technologies that could lay the foundation for future interstellar flights and investigates the utility of fission for future space missions.
An artist's impression of the Project Bifrost fission rocket leaving Earth orbit for an interstellar mission.
An artist's impression of the Project Bifrost fission rocket leaving Earth orbit for an interstellar mission.Adrian Mann
/ Source: Discovery Channel

Project Bifrost is an ambitious study examining emerging space technologies that could lay the foundation for future interstellar flights and investigates the utility of fission for future space missions.

Project Bifrost was initiated by research lead Tabitha Smith (strategic officer of General Propulsion Science) and Brad Appel (program manager of Nuclear Propulsion at General Propulsion Science), working in collaboration with Icarus Interstellar Inc., a nonprofit foundation dedicated to achieving interstellar flight by the year 2100.

WIDE ANGLE: Project Icarus: Reaching for Interstellar Space

Chances are, you own a smart phone or some kind of electronic device with capabilities that would stun even an Apple engineer from 10 years ago. We've come to expect that technology advances at a mind-boggling pace, but just how far has rocket technology advanced in, say, the past three decades?

Not much.

The rockets that sent men to the moon were powered by chemical combustion, which in its most powerful form ignites hydrogen with oxygen. The space shuttle main engine, essentially the state of the art for rocket propulsion, uses the same chemicals.

No doubt, these rockets do their job well for what we ask of them. Send astronauts to the International Space Station? No problem. Send astronauts to the moon? Sure. But, suppose we wanted to dream a little bit bigger, and actually explore the rest of the solar system and beyond. How far can these chemical rockets send us?

Not very far.

It turns out, through the quirky laws of Newtonian mechanics, that the exhaust velocity of a rocket is one of the most important parameters in determining how far it can send a payload. Chemical rockets have fundamental energy limits that give them a maximum exhaust velocity that is too low for most piloted missions with destinations further than the moon.

(Keep in mind we're talking about the huge spaceships that would be required to transport people — chemical rockets can handle the smaller robotic probes.)

PROJECT ICARUS: Which Exoplanet to Visit?

We live in an exciting time in which NASA's Kepler Space Telescope churns out discoveries of new exoplanets — whole other worlds — on a daily basis. Just last month, scientists working with Kepler confirmed that they located a planet orbiting within the 'habitable zone' of its host star — a special region where an Earth-like planet could maintain liquid water on its surface.

You may be tempted to ask how long it would take for us to send a spacecraft over to one of those exoplanets and take a closer look. To answer that question, consider Voyager 1, one of humanity's fastest spacecraft, and certainly the farthest space probe from Earth. If we were to suddenly re-aim Voyager 1 towards one of these new solar systems, it would take more than 70,000 years to reach even the closest of stars.

While interstellar missions may seem like the stuff of science fiction, the technology needed to enable them is currently an active area of research, and novel propulsion systems typically focus on highly energetic reactions as a means to liberate more energy per unit mass of propellant.

Common areas of research include fission rockets, fusion rockets and even antimatter rockets. Project Icarus, for example, is an international group of volunteer scientists and engineers dedicated to working out the challenges of interstellar voyages.

According to Richard Obousy, senior scientist for Icarus, "the technology roadmap to antimatter, or even fusion rockets could easily be decades in the making, but there is one technology that we have available today that represents the critical first step in the long road to the stars, namely fission."

PROJECT ICARUS: What Would an Interstellar Mission Look Like?

The fission rocket being referred to here is the Nuclear Thermal Rocket, or NTR. An NTR uses nuclear fission as an energy source instead of chemical combustion, and uses just hydrogen as a propellant, allowing it to achieve a very high exhaust velocity and high thrust. That's the kind of mind-boggling technology upgrade that means piloted missions to deep space, which are beyond the pale for chemical rockets, suddenly become very feasible.

Beginning this month, Icarus Interstellar Inc., the managing company for Project Icarus, is teaming up with General Propulsion Sciences, a small propulsion research company based in Washington, D.C., for a new effort to pursue the development of NTRs and other fission-based space technologies.

The program, called Project Bifrost, recognizes fission as a crucial stepping-stone technology toward the next generation of space travel, and will take steps to advance the technological maturity of NTRs. In the coming decades, sending humans to Mars is considered by many to be the Holy Grail for space exploration, a mission for which NTRs are ideally suited.

Brad Appel of General Propulsion Sciences frames the situation in more familiar terms: "To look at it another way, imagine you are planning a road trip from New York to Los Angeles and back. Except, there are no gas stations along the way — you need to pack all of the fuel along with you. Using a chemical rocket to send humans to Mars would be like making the road trip in a cement truck. You might barely make it, but it would be one enormous, inefficient and expensive voyage. Using an NTR, however, would be more akin to taking a Prius. It'll make it there comfortably, and it can go a lot further too."

PROJECT ICARUS: How to Navigate Interstellar Space

Priorities in NASA's current space program emphasize developing capabilities to take humans beyond Low Earth Orbit (LEO). And while there are agreements in place between NASA and private companies such as SpaceX to deliver cargo and potentially American astronauts to the International Space Station, few outside of the U.S. government are privately exploring nuclear space technologies for their inevitable use in the future of space exploration.

Private industry has the flexibility to pursue international partnerships, as companies like Rocketdyne and Aerojet have done in the past for propulsion subcontracting work with Russia.

Recently, Tabitha Smith, research lead for Project Bifrost and chief strategic officer of General Propulsion Sciences, was invited to Moscow to become more familiarized with U.S.-Russian business partnerships, and to collaborate with NTR and rocket propulsion colleagues under the auspices of the newly created Russian agency Rossotrudnichestvo — an initiative started by President Dmitry Medvedev to cultivate Silicon Valley-like entrepreneurship and international projects in Russia.

International cooperation is seen as a vital part of future large-scale space projects in the space community at large, as it encourages transparency, expedites completion times and splits costs.

It's worth noting that as with many technologies in space exploration, the 1960s were the golden age for NTRs. Between 1955 and 1973, the U.S. government spent $1.4 billion in an NTR program called Rover/NERVA, anticipating it would be used after Apollo was completed. Although it was ultimately canceled before a flight could be achieved, the program was tremendously successful in proving that NTRs work. The knowledge gained from NERVA remains a vital resource for future NTR development.

This spring, while we mark the 50th anniversary of John F. Kennedy's famous speech to Congress in which he challenged the nation to go to the moon, perhaps it would be useful to reflect upon what he said immediately after declaring that goal: "Secondly, an additional $23 million ... will accelerate the development of the Rover nuclear rocket. This gives promise of some day providing a means for even more exciting and ambitious exploration of space, perhaps beyond the moon, perhaps to the very end of the solar system itself."