The thrusters weâ€™ve used to visit the moon are no good for traveling to Marsâ€”they simply canâ€™t carry enough fuel. But one of the new ways NASA is exploring for sending astronauts into deep space just got a boost.
Jason Cassibry, an engineer at the University of Alabama at Huntsville, thinks nuclear power may be the answer. “If you took 1 kilogram of fusion fuel and burned it, it would exceed the energy of 1 kilogram of petroleum by at least a million times,” he says. Cassibry estimates that 30 to 40 years from now pulsed-fusion-propulsion systemsâ€”which would use small nuclear explosions to generate thrustâ€”could carry humans on a round-trip journey to Mars in just six months, as opposed to two or three years in a rocket-based craft.
Yes, viable fusion technology has always seemed 5 or 10 or 50 years away. And the concept of pulsed-fusion propulsion is several decades old but still speculativeâ€”itâ€™s low on NASAâ€™s “Technology Readiness” scale. But that may change soon: The University of Alabama recently acquired a powerful new machine that will enable researchers to put pulsed-fusion ideas to the test.
“Thereâ€™ve been a lot of papers, a lot of theory, but these will be the first laboratory experiments,” says Robert Adams, an advanced propulsion technologist at NASAâ€™s Marshall Space Flight Center, who is working with Cassibry to begin developing pulsed-fusion technologies. “Everything weâ€™ve done so far shows that there are no real show-stoppers when it comes to pulsed-fusion propulsion. It is orders of magnitude better than anything thatâ€™s out there now. Itâ€™s really important at this point that we stop talking about it and start testing.” …
Cassibry imagines attaching a large reactor on the back of a human transport vessel. Similar to how the piston of a car compresses fuel and air in the engine, the reactor would use electrical and magnetic currents to compress hydrogen gas. That compression raises temperatures within the reactor up to 100 million degrees Câ€”hot enough to strip the electrons off of hydrogen atoms, create a plasma, and fuse two hydrogen nuclei together. In the process of fusing, the atoms release more energy, which keeps the reactor hot and causes more hydrogen to fuse and release more energy. (These reactions occur about 10 times per second, which is why itâ€™s “pulsed.”) A nozzle in the reactor would allow some of the plasma to rush outward and propel the spacecraft forward.
Cassibry says the acceleration of such a thruster wouldnâ€™t pin an astronaut to the back of his seat. During shuttle liftoff, rocket boosters generate a thrust of about 32 million newtons. In contrast, the pulsed-fusion system would generate an estimated 10,000 newtons of thrust. But rocket fuel burns out quickly while pulsed-fusion systems could keep going at a “slow” but steady 24 miles per second. Thatâ€™s about five times faster than a shuttle drifting around in Earth orbit….