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Comment by Retric | Hacker News Reader

I don't know about propulsion ect, but IMO the best approach without magic levels of technology or antimatter is going to look something like:

2 stage craft, first stage uses solar sail to shift into a highly parabolic orbit that goes from close to the sun into the and back out to the ort cloud. Passengers meet up with craft as it's heading toward the sun on final passage. And ignite rocket near sun for maximum gravity assist on it's final flight through the solar system.

PS: Probes get's to skip the docking part of the trip.

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Could you explain the gravity assist portion a bit more please? A gravity slingshot only works when you transition from a regime dominated by one body (sun for example) to a regime dominated by another body moving relative to it (Jupiter for many outbound probes).

I guess you could use a scheme similar to Cassini where you're doing multiple gravity assist swings off anything at all to get every last erg of thrust but my gut feeling is that you're not gaining much relative to the delta v needed for your complete voyage.

It would make for a fun app though. Design your own Interstellar Mission!

I believe he's talking about the Oberth effect.

Consider the total kinetic energy of a spacecraft in free fall (in orbit) and after a delta V has been applied. When farthest away from the Sun the KE after the spacecraft has finished firing its rocket will be proportional to (low-v + delta-v)^2, whereas if the firing is done at closest approach to the Sun the KE will be proportional to (high-v + delta-v)^2. You'll get a 2free-fall-speeddelta-v energy boost, so being at the highest relative speed possible to start is definitely advantageous, since this KE boost will translate into higher final speeds as well.

> It would make for a fun app though

Like this one? http://orbit.medphys.ucl.ac.uk/

Orbiter is a space sim with accurate orbital mechanics (including the Oberth effect ;).

It's a lot of fun. You can use realistic current vehicles for accuracy, or unrealistic ones with huge power-to-weight for fun.

Why you exclude antimatter? I think it has the most perspective as the energy source of the starship, now scientist can hold antimatter for minutes, until we'll have other technologies for star travel - they will learn to create much more of it and hold it for much longer.

Keeping ~10^6th protons contained for minutes is a long way from 10^28th protons contained for years. Anyway even with antimatter you are still bound by the E=V^2 problem so launching a large ship at 1g for 2 months might be possible with anti matter but the energy requirements become insane. For that matter generating atimatter is ridiculously inefficient, if you had perfect containment and converted the all the world electricity production into antimatter using current methods you would not be able to launch a bottle rocket let alone a useful ship.

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