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That was how the interstellar ship¹ in The Sparrow by Mary Doria Russell worked. For the first half of the trip they accelerated at 1g, then the ship rotated an
by dhosek 4y ago
That was how the interstellar ship¹ in The Sparrow by Mary Doria Russell worked. For the first half of the trip they accelerated at 1g, then the ship rotated and they decelerated at 1g for the second half of the trip.
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1. Which was actually a hollowed-out asteroid and used the asteroid itself as propellant to achieve continuous acceleration and deceleration for the trip. One of the better attempts at providing a plausible mechanism for interstellar travel. Good enough that I neither declared it magic nor spent a long time thinking that it wouldn’t work.²
2. Doubtless someone will reply here with a detailed explanation of why it wouldn’t work.
- rsynnott 4y agoRequires a magic-based energy source; the usual problem with this sort of thing.
- tomrod 4y agoWhy would an ion thruster engine not be feasible?
- throwaway09223 4y agoThe X3 ion engine has a weight of 230kg and a thrust of 5.4N. This is about 500 times less force than is needed to propel the engine forward at 1g (even if we pretend the entire rest of the spaceship doesn't exist - in reality it would need to be thousands of times more powerful) Ion engines cannot currently produce anywhere close to this level of force. Adding more engines won't help because each engine can't even push its own weight at one gravity.
- hinkley 4y agoELI5: Ion engines are the slowest tortoise you can imagine and to feel like gravity you need the hare.
- mateo1 4y agoIt's just barely feasible with fusion energy densities. To accelerate a million tons to 0.1c you need as much kinetic energy as is theoretically contained in a million tons of hydrogen you'll fuse. Maybe with antimatter, but traveling so fast causes a ton of other issues, like every single particle you encounter is also traveling at ~0.1c.
- deleted 4y ago[deleted]
- titanomachy 4y agoThis checks out! Kinetic energy = 0.5 mv^2, where v = 0.1c => E = 0.005mc^2 (relativistic effects not too important at this speed). Fusing a kilo of hydrogen converts ~6g to energy; at E = mc^2, that's 0.006mc^2. So the energy needed to accelerate a given mass of hydrogen to 0.1c is almost exactly equal to the energy produced by fusing that hydrogen.
- hinkley 4y agoI believe the math works out such that any slag you create while refining construction or fuel materials needs to be launched out the back of the ship as fast as you can (frequency and velocity) so that you're not accelerating it along with the rest of the rock. Though probably not exactly straight out the back, since that would create a navigation hazard for the next ship...
- hinkley 4y agoAchieving a given acceleration takes a certain amount of force per unit of mass. If one made the (dangerous) assumption that the propulsion system doesn't wear out over time, then it's more plausible to assume that at the beginning of the voyage you would achieve less than 1g, hopefully ramping up fast enough to keep atrophy to a moderate risk. Toward the end, as the asteroid gets lighter, you would run the engines at less than 100% for comfort. In this scenario the acceleration phase continues well past the halfway point. And even without magic engines, any acceleration to match velocity with the destination doesn't need to be cancelled out, so the first 'half' of the trip is going to be slightly longer than the back half, even if you could do 1g the whole way (which the rocket equation has some problems with).