© Ted Debosz Space travel: celestial surfers could travel down gravitational tubes to cut fuel use.
Gravitational corridors could help spacecraft travel the solar system like ships carried on ocean currents, making longer and cheaper journeys possible, it has been claimed.
Scientists in the US are trying to map the twisting "tubes" so they can be used to cut the cost of space travel.
Each one acts like a gravitational version of the Gulf Stream, created from the complex interplay of forces between planets and moons.
Depicted by computer graphics, the pathways can look like strands of spaghetti that wrap around planetary bodies and snake between them.
The pathways connect sites called Lagrangian points where gravitational forces balance out.
Professor Shane Ross, from Virginia Tech university, said: "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.
"These are freefall pathways in space around and between gravitational bodies. Instead of falling down, like you do on Earth, you fall along these tubes.
"Each of the tubes starts off narrow and small and as it gets further out it gets wider and might also split.
"I like to think of them as being similar to ocean currents, but they are gravitational currents.
"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."
Riding one of the gravitational currents was unlike exploiting the "slingshot" effect of a planet or moon's gravity, a routine space travel technique, he explained.
"Its not the same as a slingshot," said Prof Ross. "Slingshots don't put you in orbit round a moon, whereas this does."
Just one US mission so far has made use of the concept. The Genesis spacecraft was launched in 2004 to capture solar wind particles and return them to Earth. Following the gravitational pathways allowed the amount of fuel carried by the probe to be cut tenfold.
The mission ended in failure, but only because a parachute failed on landing.
The corridors were especially useful for voyaging between a planet's moons, said Prof Ross, speaking at the British Science Festival at the University of Surrey in Guildford.
"Once you get to another planet that has its own tubes you can use them to explore its moons," he added. "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 trade off was time, he said. It would take a few months to get round the Jovian moon system.
However, interplanetary travel would always require some fuel, Prof Ross pointed out. Attempting to get a free tube ride from Earth to Mars would take thousands of years.
are becoming typical of science journalism in this, the 21st century. Meanwhile, Newton's laws remain unchanged.
Designing trajectories in a planet-moon environment using the controlled Keplerian map
Journal of Guidance, Control, and Dynamics 32(2), 436-443.
Piyush Grover and Shane D. Ross
Engineering Science and Mechanics, Virginia Polytechnic Institute and State University
[Link]
ABSTRACT
Designing fuel efficient trajectories which visit different moons of a planetary system is best handled by breaking up the problem into multiple three-body problems. This approach, called the patched three-body approach has received considerable attention in recent years, and has proved to lead to substantial fuel savings compared to the traditional patched-conic approach. We consider the problem of designing fuel-efficient multi-moon orbiter spacecraft trajectories in the Jupiter-Europa-Ganymede-spacecraft system with realistic transfer times. Fuel-optimal (i.e., near zero fuel) trajectories without using any control are first determined but turn out to be infeasible due to very long transfer times involved. We then describe a methodology which exploits the underlying structure of the dynamics of the two three-body problems, i.e., Jupiter-Europa-Spaceraft and Jupiter-Ganymede-Spacecraft, using the Hamiltonian structure-preserving Keplerian map approximations derived earlier and using small control inputs in the form of instantaneous Delta-Vs to get trajectories with times-of-flight on the order of months rather than several years. A typical trajectory constructed using the control algorithm can complete the mission in about 10% of the time-of-flight of an uncontrolled trajectory.