The Lost Fleet's descriptions of trajectories as 'curves' at 20% of light speed

Question

I find it strange when reading descriptions of trajectories/fleet movements in The Lost Fleet that they're commonly described as curves.

A few examples

1. From Relentless, chapter 2:

On the display, the projected path of the Alliance fleet curved in a graceful arc through the empty reaches of [redacted for spoilers] Star System.

2. From Resolute (Outlands), chapter 1 (context: urgency was required here):

Along with the [ship names and count redacted for spoilers] the Alliance ships accelerated away from their former orbit and the rest of the Alliance fleet, their path through space a long curve that would intercept the path of [another ship redacted for spoilers].

3. From Guardian (Beyond the Frontier), chapter 1 (context: combat intercept)

The [ship A, name redacted] had started out at the hypernet gate and was now on a track curving outward toward one of the several jump points [...]. [Another] flotilla had only been a couple of light-minutes from the gate, closer to the star and slightly above the gate, and had kicked out its [ships redacted] on flatter, faster curves, which intercepted the path of the [ship A] long before it could reach safety.

For the first example, clearly not combat maneuvers nor avoidance of threats here as the system is described as empty. Since fleet movements typically are at 0.2 c, I would expect any movement to be a straight line and unaffected by gravity or even starting momentum once the initial acceleration is complete.

As for the second example, a "long curve" would be inefficient for an urgent travel. Acceleration at start from a completely tangential trajectory would not produce a long curve, and avoiding the star would result in a bend due to course correction around it, rather than a long curve.

As for the third example, it is clear from the text that the author recognises faster movement/acceleration as flatter trajectories. And acceleration is implied to reach .2c within minutes, and not hours (the typical duration of travel in-system) hence not producing a curve.

This is at odds to the Expanse and Ben Bova books where torchships are described as 'point and shoot' trajectories, even though those don't even reach a significant fraction of light speed.

So, why are trajectories/fleet movements described as curves in The Lost Fleet?

Answer 1

1. Some the curves of the refer to projected paths are estimates. Due to relativistic distortions, while estimates are possible, there MUST be error terms. As described in many of the battle scenes, late changes, too late for the enemy to see and react to make the difference. They 'feel' Geary had was as much psychological / playing chicken, to change when they had the advantage. It was best seen in the battles with the Enigma race, where the quantum computer worms had been disabled, and Geary used infected auxiliary ship systems to model what the enigma saw, and projections of what the might / should do based on the 'engagement' envelopes.

2. Unpowered projectiles (rocks) would need to take into account gravity when fired from significant distances, and travel of the target. It might approach a straight line, but isn't.

3. Point to point travel under power, might also approach a straight line, but that is going to be rare for a lot of reasons.

• Targeting runs may have many course changes, it is (as noted on many occasions) terribly wasteful to abruptly change direction, but rather to maintain velocity (real or relative) requires curving changes in trajectory. Consider a car changing lanes at speed in a freeway,
• Also, in many of the populated systems, there was enough traffic to require traffic rules, lanes, that would be created to minimize cost, either time or distance, particularly for bulk haulers,

Answer 2

Interestingly I never took mental notice of the courses being described as curves when reading this series. Thinking about it now, the most reasonable explanation is that the courses are planned to account for the influence of gravity. Rather than burning excessive fuel to move in a literal straight line through a gravity well, they instead plot a parabolic course that will let gravity help them and curve around to the target point.

As an exaggerated example, imagine you want to hit a point 50 feet from you with a ball. You could throw the ball straight really hard, or you could more easily loft it high and let gravity bring it back.

Answer 3

Moving through space in The Lost Fleet universe, that is mostly empty, and where non-empty spots would be suns, planets, moons etc., involves great distances and days of time, when inside a solar system or in jump space between them.

In our case we're talking about the Fleet consisting of hundreds of ships, which are military designs, meaning highly maneuverable and fast units, heavily armed and armored in some cases, which means they will have a lot of mass. Propelling that mass requires a lot of energy. Energy generation requires fuel.

In order to propel such a starship to, say, 0.2c requires significant energy and the higher the acceleration the more fuel it requires.

But in space there is nothing to slow that vessel down. So, what it has to do to change direction? Or better yet: turn around left and down?

Exactly: basically exactly the same thing it did to attain the speed and direction along the plotted course in the first place, and twice that if it is "3-D" turn-around.

But if we want that ship to not be constantly subject to stresses of high-g maneuvering (and it is said in the books that any ship can basically loose propulsion under maximum load), we have to do low-g maneuvering.

Which literally means that instead of turns of radius of hundreds of kilometers, there will be turns with radius of hundreds of thousands of kilometers... Which will look on the plots like lines "curved in a graceful arc"...

So, bottom line is still the answer I gave initially: fuel conservation. Also to avoid unnecessary engineering casualties due to stress of constantly travelling at maximum power. So to also conserve spare parts, to avoid delays and more fuel consumption to slow down in order to keep formation. And not to leave anyone behind.