Hacker News Reader

Comment by WinstonSmith84 | Hacker News Reader

> "Pellet-Beam Propulsion for Breakthrough Space Exploration"

More than 250,000AU separate us from Alpha Centauri and at a speed of 500AU in 15 years, that doesn't look very realistic... More realistic is however a faster exploration of the solar system.

View on HN

Pellet beam propulsion can allow fairing efficient travel at 10% c, fast enough to reach Alpha Centauri in a human healthspan, when combined with interstellar plasma braking.

I can only find very high-level descriptions of the pellet-beam approach. What's the advantage of accelerating the pellets after launch via laser ablation versus using a more powerful mass driver to launch the pellets and omitting the laser?

It’s more cost effective, assuming the mass driver is taking most of your budget. Both driver length and force required scale with the square of launch velocity.

Laser beams are only one method of acceleration for the pellets, and not necessarily the most efficient option.

Got me thinking whether capturing asteroids, mining them and shoting pellets with a solar powered automated facility will drive future space exploration. Seems easier than other challenges like terraforming.

But what about navigating on the other end? It would make a terrible first impression if our probe smashed into their version of Voyager.

Hopefully we come up with a good way to test the brakes.

This sounds like a great sci-fi premise. We think we’re being attacked by intergalactic missiles but they’re really just probes sent by a more advanced, albeit clumsy civilization in an attempt to move fast and break things in the name of discovery.

Humanity vehemently debates the meaning of the “attacks” but ultimately decides we must go to war with these aliens. Eventually the aliens do arrive, interested only in peaceful communication. They disarm our arsenal trivially, but understand why we wanted to fight them and apologize for the misunderstanding.

Or after series of misunderstandings they hit the big reset button, sterilize Earth and move on from those aggressive apes.

A bit of a spoiler, but something similar to this happens in Ender's Game.

The interstellar void is not a pure void but is filled with diffuse plasma, the Interstellar Medium. Which, because plasma is electrically conductive at large length scales, you can brake against using gargantuan superconducting coils producing a magnetic field (which induces eddy currents in the plasma, producing a force opposing the direction of motion), slowing down like a magnet dropped into a vertical copper pipe: https://youtu.be/uh0bbW6S3BY?si=kE-1jYagQxGHIVMA

With current technology NASA get 3100s of specific impulse for ion drive, 2.3kw, 92mN. For a larger ship, not just small satellite, it should be doable to increase the voltage and get 10x specific impulse at 10x power with the same thrust. A nuclear reactor without much protection - on a long stick with small screen protecting only direction of the payload - can be something like 5-10kw/kg. That allows to have 90% of the mass to be propellant, and thus reach the speed, in about 30 years of acceleration, of more than 600km/s. With 2 stages, in 60 years with some optimization/etc. we can get 1500km/s, or 800 years to Alpha Centauri.

https://en.wikipedia.org/wiki/Breakthrough_Starshot

Reply on news.ycombinator.com