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Light Sail Propulsion Could Reach Sirius Sooner Than Alpha Centauri (arxiv.org)
RockDoctor writes: A recent proposition to launch probes to other star systems driven by lasers which remain in the Solar system has garnered considerable attention. But recently published work suggests that there are unexpected complexities to the system. One would think that the closest star systems would be the easiest to reach. But unless you are content with a fly-by examination of the star system, with much reduced science returns, you will need to decelerate the probe at the far end, without any infrastructure to assist with the braking. By combining both light-pressure braking and gravitational slingshots, a team of German, French and Chilean astronomers discover that the brightness of the destination star can significantly increase deceleration, and thus travel time (because higher flight velocities can be used). Slingshotting around a companion star to lengthen deceleration times can help shed flight velocity to allow capture into a stable orbit. The 4.37 light year distant binary stars Alpha Centauri A and B could be reached in 75 years from Earth. Covering the 0.24 light year distance to Proxima Centauri depends on arriving at the correct relative orientations of Alpha Centauri A and B in their mutual 80 year orbit for the sling shot to work. Without a companion star, Proxima Centauri can only absorb a final leg velocity of about 1280km/s, so that leg of the trip would take an additional 46 years. Using the same performance characteristics for the light sail, the corresponding duration for an approach to the Sirius system, almost twice as far away (8.58 lightyears), is a mere 68.9 years, making it (and it's white dwarf companion) possibly a more attractive target. Of course, none of this addresses the question of how to get any data from there to here. Or, indeed, how to manage a project that will last longer than a working lifetime. There are also issues of aiming -- the motion of the Alpha Centauri system isn't well-enough known at the moment to achieve the precise maneuvering needed without course corrections (and so, data transmission from there to here) en route.
This is a Thought Experiment, not a real plan to go anywhere... we aren't going to travel between the stars until we figure out something a whole lot better than chemical rockets and probably FTL drive...
Everything else is just fantasy...
Thought experiments are how you come up with an idea that nobody has thought of before.
Back in the late 1980sI was on an email discussion group for Traveller (a sci-fi RPG). Someone asked why hydrogen fuel (for fusion) was stored as water aboard ships. Someone answered that water stores hydrogen atoms more densely than hydrogen gas, and the energy needed to chemically break off the hydrogen atoms off of water was trivial compared to the energy you could get from fusing them into helium. That spawned a discussion about whether there were other molecules which stored hydrogen even more compactly. Methane (CH4) was an obvious choice - 4 hydrogen atoms per non-hydrogen base, compared to just 2 for water (H2O). But eventually we settled on ammonia (NH4) because it's liquid at room temperature and wouldn't require pressurization or cryogenic storage in a vehicle sharing space with a life support environment for humans.
It's totally useless info right now (and probably the next few decades). But it's something that will be important in the future.