Robert W. Bussard proposed a radical idea in the 1960s for a spaceship that could harvest hydrogen from the outside. The high speed of theramjet causes the hydrogen to be in a magnetic field. The energy from the magnetic field is directed towards the rear of the vehicle.
The Bussard Ramjet has been popularized by hard science fiction writers like Larry Niven and Carl Sagan. A team of physicists concluded that Bussard's idea is not practical after analyzing the concept in more detail. This analysis is more of a reality check than a wet blanket, at a time when the possibility of interstellar travel is very much a possibility.
Peter Schattschneider is a physicist and materials science specialist with the University of Vienna and a science fiction author. Albert A. Jackson is a physicist with the Texas-based company. The study about their findings will be published in the journal in February of 2022.
The Bussard Ramjet is an elegant solution for sending crewed missions to other star systems. Nuclear pulse propulsion (NPP) and fusion propulsion had been proposed in the past. These concepts were answers to the fundamental challenges of reaching another star system in a relatively short amount of time. They would need to get up to a fraction of the speed of light.
The methods were considered impractical because of their size, mass, and cost. The detonation of nuclear warheads behind the vehicle was used in Project Orion. A push plate would absorb the force of the detonations and convert them into strength.
Hundreds to thousands of nuclear devices would be needed to achieve 10% speed of light for an ion spaceship. This, in turn, required a very large spaceship and lots of external rocket boosters to get it into space, all of which added up to a prohibitive price tag. There was a problem of radioactive fallout, which would leave a trail in its wake. The Partial Test Ban Treaty of 1963, which forbade nuclear testing in Earth's atmosphere, space, or underwater, made the project impossible.
Project Daedalus called for a two-stage uncrewed probe that would rely on pellets of deuterium or helium to generate power. The energy from the fusion of the pellets would be directed to the rear to create thrust. Most of the mass and volume of the spacecraft was taken up by propellant and propellant tanks.
There is a comparison of the two rockets. Adrian Mann is a credit.
Bussard proposed a variation on the traditional fusion rocket in his proposal paper. The ISM would be used as a source of energy by nuclear fusion and as a working fluid by the Ramjet. The Ramjet did away with bulky propellant tanks and could be much smaller and less massive than the Daedalus concept.
John F. Fishback, a researcher at MIT, wrote the first paper about the magnetic field theoretically in nine years. Fans of science fiction and members of the technical community have been interested in the idea since that time. Peter Schattschneider made the statement in a recent press release.
The idea is worth investigating. Hydrogen is the mostDiluted gas in space at a rate of one atom per cm. You could use the magnetic fields to run a fusion reactor if you were to collect the hydrogen in front of the spacecraft.
Schattschneider and Jackson reexamined the Bussard Ramjet using software developed at the University of Vienna as part of a research project for calculating the fields in electron microscopy. The basic principle of magnetic particle trapping is that particles can be collected in the proposed magnetic field and guided into a reaction chamber.
There are a lot of laser-sail spacecraft in the solar system. Adrian Mann has aTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkia
Their results were a mixed bag. Fishback proposed a magnetic field that is slowly-varying and capable of guiding matter into a fusion reactor. A consistent acceleration of one Earth gravity can be achieved until the speeds are improved. The bad news began when they calculated the magnetic funnel size.
The magnetic field would need to be over 3000 km in diameter to achieve a thrust of 10 million newtons. The field would need to be over 100 million km long to adequately capture and funnel ISM material into the ship. The distance between the Sun and Earth is equivalent to 1AU.
It is not possible for a civilization to engineer such a feat. Bussard's proposal was based on inaccurate ISM density estimates that were shown to be incorrect a decade later. The latest research shows that the technical challenges are not within our reach, even though various reanalyses have indicated that a fusion ramjet could be feasible with lower concentrations of hydrogen in the ISM.
What does this mean for travel? Not much, at least not much that we already suspected. It seems as though the only practical option is to send tiny sailcraft to the nearest stars. In the coming years, Project Dragonfly and other groups will send spaceships to Alpha Centauri and other stars in the hope of achieving interstellar flight in our lifetimes.
The Bussard Ramjet is depicted in an artist's impression. Adrian Mann has aTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkiaTrademarkia
The research into nuclear rockets continues with promising results. Nuclear-electric and nuclear-thermal propulsion are used in this method. The Nuclear Engine for Rocket Vehicle Application (NERVA) uses a reactor to heat hydrogen fuel to create thrust, while the other uses a reactor to charge an inert gas like a Hall-Effect thruster.
The method is expected to become the go-to method for interplanetary missions. Nuclear power will allow for trips from Earth to Mars in 100 days. The Initiative for Interstellar Studies, the British Interplanetary Society, and the Icarus Interstellar are all researching other methods for travel through the stars.
Feasibility studies for generation ships, cryogenic spaceships, and other methods of sending human passengers to colonize other solar systems are included. Even if the travel plans need to be adjusted, the journey continues.
Further reading is about TU Wien.