3 ms·

Note it's probably not useful to "stop and refuel" on any trajectory in space, since there's nothing slowing you down in a vacuum. Space flights are free ballis

Note it's probably not useful to "stop and refuel" on any trajectory in space, since there's nothing slowing you down in a vacuum. Space flights are free ballistic trajectories: you don't consume any fuel on the way, you just coast. A more interesting network would look at gravitational slingshot [0] opportunities between stars -- from their relative motion in the galaxy, or from binary stars (orbiting each other), or exoplanets. Freeman Dyson noticed [1] that if you found a white dwarf binary in its late stage of inspiraling, you could get an absolutely ridiculous slingshot (~2,000 km/s = 0.01c), entirely for free! Unfortunately these are extremely rare, since these orbits quickly decay until the stars collide (possibly causing a Type Ia supernova [2]... so, maybe not so unfortunate). It's interesting to look at how interplanetary probes fly. According to the Cassini engineers for instance [3], the shortest path from the earth to Saturn is go fly around Venus, then come back to Venus a year later, than return to earth... then go to Jupiter first. You could benefit from powered flybys [4] too. There are nearby gravitational wells much deeper than the sun's. Sirius B [5] (the white dwarf) should have an surface escape velocity around 7,000 km/s -- although it'd be rather crazy to engineer a white dwarf flyby (up to 100's of g's of acceleration, 10^10 W/m^2 thermal load). [0] https://en.wikipedia.org/wiki/Gravity_assist https://en.wikipedia.org/wiki/Gravity_assist [1] http://www.ifa.hawaii.edu/~barnes/ast242/Dyson_Machines.pdf http://www.ifa.hawaii.edu/~barnes/ast242/Dyson_Machines.pdf [2] https://en.wikipedia.org/wiki/Supernova#Thermal_runaway https://en.wikipedia.org/wiki/Supernova#Thermal_runaway [3] https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens_timeline https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens_timeli... [4] https://en.wikipedia.org/wiki/Oberth_effect https://en.wikipedia.org/wiki/Oberth_effect [5] https://en.wikipedia.org/wiki/Sirius https://en.wikipedia.org/wiki/Sirius

AllThingsGraph 12y ago
Thanks for the information (fascinating!). A gravitational fly-by of Sirius B would be crazy. Straight-shot trajectory (and/or gravitational assist) would be the simplest way to get the ship there, but other constraints might force one to "stop and refuel": * Energy needed to maintain life for duration of journey (e.g. hibernation) may exceed what you can store in one "charge" for your ship. * Instead of 3D trajectory travel, perhaps the energy needed to "warp" or establish a worm-hole is proportional to the distance being travelled. * Or, perhaps, the reliability and precision of calculated trajectories breaks down after certain distances; forcing a series of "hops" vs. a single trajectory in order to make the journey safe/reliable. * Time may factor in. You may have enough energy, but perhaps components of the ship can't be expected to operate without error/failure for such long times. In that case, "stopping to refuel" might include expected repairs as well. All hand-wavy a bit, but interesting to think about.

AllThingsGraph 12y ago

Thanks for the information (fascinating!). A gravitational fly-by of Sirius B would be crazy. Straight-shot trajectory (and/or gravitational assist) would be the simplest way to get the ship there, but other constraints might force one to "stop and refuel": * Energy needed to maintain life for duration of journey (e.g. hibernation) may exceed what you can store in one "charge" for your ship. * Instead of 3D trajectory travel, perhaps the energy needed to "warp" or establish a worm-hole is proportional to the distance being travelled. * Or, perhaps, the reliability and precision of calculated trajectories breaks down after certain distances; forcing a series of "hops" vs. a single trajectory in order to make the journey safe/reliable. * Time may factor in. You may have enough energy, but perhaps components of the ship can't be expected to operate without error/failure for such long times. In that case, "stopping to refuel" might include expected repairs as well. All hand-wavy a bit, but interesting to think about.