This reminds me strongly of the Alderson Drive used in the Niven/Pournelle "Mote in God's Eye" universe. As handwaves go, it's pretty good. And I like that it gives an excuse for blockades, ambushes, risky untried routes, and other plot generators.

On Tue, Jun 7, 2016 at 3:55 AM, Richard Aiken <xxxxxx@gmail.com> wrote:
I recently picked up an SF novel that uses something called "gravity slips" to travel FTL. These are explained in the first chapter using the following technobabble:

"This grav pocket was fairly typical - two binary systems and one red giant star served as distant gravity anchors. That meant there were three slip points in the pocket. Gravity slips were formed by the intersection of at least two celestial bodies interacting with each other across a fixed point to the center of their mass. This intersection created a confluence of gravity waves known as a "slip."

"Using the grav impeller, her warship could travel instantaneously from one end of the slip to the other, swooping across light years in a moment. Travelling by gravity slip resulted in a long curving pattern between stars. Ships could also use the smaller gravity slips between stars and their planets, but these routes frequently shifted and were therefore unpredictable. It was also more difficult to detect the smaller slips.

"[Her race] had developed their own gravity impeller independently of the [Evil Empire]. [Their] ancestral scientists had recognized that gravity acted instantly between bodies in the universe no matter what the distance, and could therefore be harnessed for transport. It was a fundamental of physics that when a mass moved, the force of gravity acting on other masses adjusted instantly to the new location of the displaced mass. By harnessing the subquantum field of gravity, ships equipped with grav impellers could move instantly through the slips.

"Each slip ended in a pocket where there was no confluence to ride. The pocket where their squadron currently patrolled was large, because of the masses of the closest stars. Areas of intense gravity, such as pulsars, created longer slips that were more popular routes."

Of course, the above talks around how "grav impellers" work rather than actually explains them, but that's nothing new. It occurred to me that if an impellor ship is restricted to travelling between slip points in normal space and these points are far enough apart, we could end up with a situation similar to requiring a week to jump between stars. But you could follow ships much more easily, as there would be only limited possible routes out of each grav pocket.   

--
Richard Aiken

"Never insult anyone by accident."  Robert A. Heinlein
"I studied the Koran a great deal. I came away from that study with the conviction there have been few religions in the world as deadly to men as Muhammed." Alexis de Tocqueville (1843)
"We know a little about a lot of things; just enough to make us dangerous." Dean Winchester
"It has been my experience that a gun doesn't care who pulls its trigger." Newton Knight (as portrayed by Matthew McConaughey), to a scoffing Confederate tax collector facing the weapons held by Knight's young children and wife.
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