Beam me to the stars: Scientists propose new interstellar propulsion method

Wasnt this a concept like 10 years ago? i thought someone sent out a probe that used a laser to propell it. Or at least i remember it being discussed somewhere

So, at first glance this appears to be the same laser-lightsail concept that’s been around for decades now, only they want to use an electron beam instead of a laser beam. The claim is that an electron beam can become self-focusing due to some relativistic effects and interaction with the interstellar medium, in a way that’s not possible with lasers.

So far so good, but. . . They seem very unclear on what’s going to happen when this beam reaches the spacecraft. With a laser it would simply reflect off a lightsail and provide direct propulsion. This article is vague about how energy from the beam would be used to propel the craft, using “some kind of propellant or reaction mass”. That right there sounds like an enormous disadvantage compared to a light sail.

Also, they are talking about getting it up to 10% of the speed of light. That is not particularly ambitious in comparison with some interstellar lightsail schemes that I’ve seen discussed.

For those wondering what makes this different from other beam propelled probe concepts like Break Through Star Shot, this concept is for an electron beam rather than a laser. And the thing that’s new about is that most people dismissed electrons beams as too short ranged due to the particles repelling each other and spreading out. However the authors have taken a confinement trick from particle accelerators and think it might work in space, which could make electron beams even longer ranged than lasers. The key insight being that space is not perfectly empty, there is small traces of gas and charged plasma in it, and as the relativistic beam punches through that, it will interact magnetically.

> As the electron beam passes through the plasma, it sees a magnetic field due to passing by the ions left behind from the space plasma; that magnetic field creates a force that pulls the electron beam together, effectively squeezing the beam and preventing it from spreading apart. “That’s called a ‘relativistic pinch,'” said Greason. “If this all works right, we can hold the beam together in space a very long distance — thousands of times the distance from Earth to the sun — and that would provide the power to accelerate a spacecraft.”

> In their paper, the duo calculated that an electron beam traveling at these speeds could generate enough power to propel a 2,200 lb (1,000 kg) probe — about the same size as Voyager 1 — up to 10% of the speed of light. This would enable it to reach Alpha Centauri in just 40 years, a significant improvement over the current 70,000 years it would take.

> Greason argues that examples of these pinched relativistic beams already exist in deep space, such as jets of charged particles released by black holes, indicating it is hypothetically possible. “But can we produce those kinds of conditions artificially?” he asked. “Will the sun’s own magnetic field break up the beam? How would we get the electron beam started? These are all questions that remain.”

The space journalist Frasier Cain also has [a great interview](https://youtu.be/E74Kg8NpCyE?si=jL1ao8wjo7Zv_Kgw) with one of the authors of the paper, where they go over the concept and mission design in much more detail.