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Physicists Unveil Radical Plan to Send a Probe Beyond Interstellar Space...and out if our solar system...

Getting a spacecraft to another star is a monumental challenge. However, that doesn't stop people from working on it. The most visible groups currently doing so are Breakthrough Starshot and the Tau Zero Foundation, both of whom focus on a very particular type of propulsion-beamed power.
https://www.sciencealert.com/physicists-...llar-space

Chairman of Tau Zero's board, Jeffrey Greason, and Gerrit Bruhaug, a physicist at Los Alamos National Laboratory who specializes in laser physics, takes a look at the physics of one such beaming technology – a relativistic electron beam – how it might be used to push a spacecraft to another star.


There are plenty of considerations when designing this type of mission. One of the biggest of them (literally) is how heavy the spacecraft is.

Electron Beam Graph
Depiction of the electron beam statite used in the study. (Greason & Bruhaug)
Breakthrough Starshot focuses on a tiny design with gigantic solar "wings" that would allow them to ride a beam of light to Alpha Centauri. However, for practical purposes, a probe that small will be able to gather little to no actual information once it arrives there – it's more of a feat of engineering rather than an actual scientific mission.

The paper, on the other hand, looks at probe sizes up to about 1,000 kg – about the size of the Voyager probes built in the 1970s. Obviously, with more advanced technology, it would be possible to fit a lot more sensors and controls on them than what those systems had.

But pushing such a large probe with a beam requires another design consideration – what type of beam?.

Breakthrough Starshot is planning a laser beam, probably in the visible spectrum, that will push directly on light sails attached to the probe. However, given the current state of optical technology, this beam could only push effectively on the probe for around 0.1 AU of its journey, which totals more than 277,000 AU to Alpha Centauri.

1. [b]Even that minuscule amount of time might be enough to get a probe up to a respectable interstellar speed, but only if it's tiny and the laser beam doesn't fry it. At most, the laser would need to be turned on for only a short period of time to accelerate the probe to its cruising speed. A different approach to providing power for only a brief period of time, not do over a longer period? This allow more force to build up  to allow a much beefier probe to travel at respectable percentage of the speed of light. [/b]
   
2. [b]Here plenty of challenges with that kind of design as well. First would be beam spread – at distances more than 10 times the distance from Sun to Earth, how would such a beam be coherent enough to provide meaningful power?[/b]
   

Most of the paper goes into detail about this, focusing on relativistic electron beams. This mission concept, known as Sunbeam, would use just such a beam.

Utilizing electrons traveling at such high speeds has a couple of advantages. First, it's relatively easy to speed electrons upto around speed of light – at least compared to other particles. Since they all share same negative charge, will likely repel each other, diminishing the beam's effective push. discovered in particle accelerators known as relativistic pinch. Essentially, due to the time dilation of traveling at relativistic speeds, there isn't enough relative time experienced by the electrons to start pushing each other apart to any meaningful degree.

Calculations show such a beam could provide power out to 100 or even 1,000 AU, well past the point where any other known propulsion system would be able to have an impact. It shows at end of the beam powering period, a 1,000 kg probe can moving as fast as 10% of the speed of light – allowing it to reach Alpha Centauri in a little over 40 years.

https://www.sciencealert.com/physicists-...llar-space