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Gravitational Currents Could Slash Fuel Needed For Space Flight
Hugh Pickens writes "BBC reports that scientists are mapping the gravitational corridors created from the complex interplay of attractive forces between planets and moons that can be used to cut the cost of journeys in space. 'Basically the idea is there are low energy pathways winding between planets and moons that would slash the amount of fuel needed to explore the solar system,' says Professor Shane Ross from Virginia Tech. 'These are free-fall pathways in space around and between gravitational bodies. Instead of falling down, like you do on Earth, you fall along these tubes.' The pathways connect Lagrange points where gravitational forces balance out. Depicted by computer graphics, the pathways look like strands of spaghetti that wrap around planetary bodies and snake between them. 'If you're in a parking orbit round the Earth, and one of them intersects your trajectory, you just need enough fuel to change your velocity and now you're on a new trajectory that is free,' says Ross. 'You could travel between the moons of Jupiter essentially for free. All you need is a little bit of fuel to do course corrections.' The Genesis spacecraft used gravitational pathways that allowed the amount of fuel carried by the probe to be cut 10-fold, but the trade off is time. While it would take a few months to get around the Jovian moon system using gravitational currents (PDF), attempting to get a free ride from Earth to Mars on the currents might take thousands of years."
For example, this old article discusses the same concept.
The vast majority of fuel usage is simply getting out of orbit. I imagine this would be musch more useful for vehicles that are simply motoring around the solar system, but not dropping to the planet, or even going into LEO.
Depends on your time horizon. Millions of years, no. Human time horizons, however, we can handle.
A good, modern, numerical integrator at quadruple precision can handle the Sun, planets, and hundreds of asteroids with very small numerical errors (microns over decades). Bigger errors are introduced by observational uncertainty, primarily in the masses of the asteroids. But, even with that, errors are 100's of meters over decades.
The "tubes" are unfortunately only "tubular" through four-dimensional spacetime. In three-dimensional space, they're just a spot (a LaGrange point) that moves around as the various bodies orbit. If you are trying to move faster than that, then you're essentially leaving the tube and entirely to navigate spacetime on your own power.
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Just thought I'd add another clarifying point.
It's often hard to visualize this, but even though a gravity current path (the minimum energy path) in a 6-d manifold (position+velocity) has time-varying velocity 3d velocitu (because the path isn't straight in 3d space it implies some acceleration from a 3d perspective), the velocity change is still essentially zero energy because sometimes the energy for the required velocity changes can come from gravity interaction itself (imagine a "valley" of some sort in a 6-d manifold), although some may require being very near the optimal path (imagine a "ridge" of some sort in a 6-d manifold) and thus require small corrections to prevent "butterfly-effects" from pushing the spacecraft further away from the optimal path (which these small course corrections are still better than fighting gravity all the way to the destination).