Interstellar Bussard Ramjet Undergoes New Analysis

The advanced propulsion concept known as the Bussard Ramjet has undergone a new analysis to determine its feasibility. And according to the team behind the second look, the concept is sound. But, they add, the physical dimensions of the innovative interstellar drive may make it an impossible feat of engineering.


Space is incredibly vast, with distances between star systems measured in light years. As such, hopes of humans traveling the cosmos have been met with the stark realities of propulsion, time and distance. In the 1960s, Robert Bussard proposed a type of ramjet that could collect the occasional hydrogen atom hanging out in interstellar space and use it for nuclear propulsion. The idea was particularly attractive since it didn’t need to bring along any fuel, but instead gathered fuel along the way.

Now, a group of researchers has taken a fresh look at the Bussard Ramjet to see if this type of nuclear propulsion system could indeed take humans into the cosmos.


“Since (Bussard’s 1960s paper), the idea has not only excited science fiction fans,” says Professor Peter Schattschneider, one of the study’s co-authors in a press release announcing their analysis, “but has also generated a great deal of interest in the technical and scientific astronautics community.”

“In interstellar space there is highly diluted gas, mainly hydrogen – about one atom per cubic centimeter.” explains Schattschneider. “If you were to collect the hydrogen in front of the spacecraft, like in a magnetic funnel, with the help of huge magnetic fields, you could use it to run a fusion reactor and accelerate the spacecraft.”

To actually perform their analysis of this highly theoretical concept, Schattschneider and fellow researcher Albert Jackson used software developed by the Vienna Technical University to calculate electromagnetic fields in electron microscopy.

And as the press release notes, “the physicists were able to use it to show that the basic principle of magnetic particle trapping actually works. Particles can be collected in the proposed magnetic field and guided into a fusion reactor.”

“In this way, considerable acceleration can be achieved – up to relativistic speeds,” the release adds.

Unfortunately, when those researchers tried to calculate the actual size of the magnetic funnel needed to make the drive work, the concept began to fall apart.

Specifically, they determined that achieving a thrust of 10 million newtons, which is about twice the main propulsion of NASA’s retired Space Shuttle, the magnetic funnel that collects the interstellar hydrogen atoms would need a diameter of nearly 4,000 kilometers.

A civilization that is technically advanced enough might be able to pull of the gargantuan feat, the researchers concede. However, they also found that the length of that funnel would have to be somewhere in the neighborhood of 150 kilometers in length. For comparison, that is about the same distance as the Earth to the Sun.


With results published in the journal Acta Astronautica, the researchers determined that a space drive 150 kilometers long is nearly impossible to consider, much less construct. Put more simply, as the pair of researchers who conducted the analysis did in the same press release, “it is now apparent that the ramjet drive, while an interesting idea, will remain merely part of science fiction.”

The research duo also points out that this does not completely rule out interstellar travel, but simply the Bussard Ramjet. “If we want to visit our cosmic neighbours one day,” they say, “we will have to come up with something else.”

Fortunately for Debrief readers, advanced propulsion concepts are regularly covered. So even if this particular space drive is impossible, some other revolutionary concept may one day become a reality, including exotic designs that may even send humans to the stars.

Follow and connect with author Christopher Plain on Twitter: @plain_fiction