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.

  1. 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].

  1. 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?

  • 1
    That speed wouldn't make them immune to having to follow geodesics, even light itself does that. There's an interesting (if not strictly relevant to the question) extra-galactic map of gravity that the milky-way is gliding through in anything but a straight line. Commented May 18, 2023 at 9:25
  • 2
    Any curve from an object travelling at 0.2 light would have to get really close to a planetary body/star to curve enough to be significantly visible at solar system scale, I think. Just like how gravity lensing with light works. Commented May 18, 2023 at 9:29
  • 3
    @Spencer - The comment clarifies that Ahmed Tawfik didn't really mean 100% unaffected by gravity, just not enough of a curve "to be significantly visible at solar system scale" (OP should be edited to reflect that). If you look at photons, even if they get close enough to the sun to graze the surface, the bending of their path due to gravity is only about 1.75 arcseconds, where 1 arcsecond is 1/3600 of a degree, not visible to human eyes if you use a typical type of coordinate system for planetary motions. Assuming 0.2c would be similar, did author get physics wrong or some other explanation?
    – Hypnosifl
    Commented May 18, 2023 at 17:35
  • 3
    @Spencer I think it was probably meant as a question of whether there was any in-universe explanation for something that seems unrealistic in real-world terms, sort of like asking if there is an in-universe explanation for why Star Wars ships make sound in space or bank when turning.
    – Hypnosifl
    Commented May 18, 2023 at 18:44
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    @Jiminy Cricket True that even at relativistic speeds, geodesics will be followed by freely falling bodies but only by freely falling bodies. Ships under acceleration are not freely falling bodies and do not follow geodesics. Additionally, when you're moving at 0.2c, geodesics look very, very straight. (At those not-really-relativistic speeds, good old Sir Isaac's theory describes motion pretty well.)
    – Mark Olson
    Commented May 18, 2023 at 21:34

3 Answers 3

  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,
  • There is just one path for the fleet. Singular, not plural. There are no estimates, just solid course picking optimal way across the star system with a star and other objects (no mention if these are planets). Fleet is not travelling under power because it is low on fuel. Fleet was going in-system for a time for several reasons, mainly due to indecision through which jump point to exit, but even if it was chosen right away, the course change would be at the last possible moment to not give it away to either pursuit or picket too soon.
    – AcePL
    Commented May 19, 2023 at 0:10
  • One path for the fleet if you use a simplified center of mass modeling. But with hundreds of ships, and shuttles moving around, attaching to auxiliary ships, dealing with maintenance (particularly main propulsion), the true model is one line per ship, with projected changes. And recall, in every case the modeling reflects only the current ship as a ‘fixed’ point. In reality, every object is moving. There is no absolute reference.
    – Kristian H
    Commented May 19, 2023 at 13:38
  • But I am not refering to any hypitheticals, but tho the actual situation in every case OP quotes. These ines are actual routes for the fllet or it's detachments. OP also dails to include a lot of context to quotes, making your answer irrelevant, or at least grossly incomplete. I point that out in my abwer, but OP seems to miss the point. Repeatedly.
    – AcePL
    Commented Dec 10, 2023 at 12:29

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.

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    We know the speed they travel at: 20% of light speed. So I think that counts pretty close to "straight really hard", hence my question. Commented May 19, 2023 at 22:05
  • @AhmedTawfik Relatively speaking, yes, 20% c is fast. But even at that speed you're still affected by gravity. Why spend the extra fuel to take an apparent straight path when you can have considerable savings by letting gravity assist you. The lost fleet isn't in great shape, and not all the ships can travel at the same speed.
    – Xantec
    Commented May 20, 2023 at 8:11
  • Also, when intercepting any moving object in space you want to align your trajectory to match the target's. Instead of burning straight to where it will be and then having it whiz passed you when you get there, you'll want to come along side it, which means your path will naturally appear to be a curve from where you were to being parallel with the target.
    – Xantec
    Commented May 20, 2023 at 8:15
  • For your first point, Mercury's orbit at around 50 million km (radius) from the sun is at 50km/s. 0.2c is 60,000km/s. In order to have a similar effect to Mercury's orbit, ships at 0.2c would need to get to 50,000km from the barycenter, which is inside the Sun. Secondly, only one example of the three above are when the fleet is retreating from the initial encounter. Commented May 20, 2023 at 9:38
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    (cont.) But for a given planetary mass and distance of closest approach (say, just outside the planet's surface), the change in angle will be smaller the faster the initial velocity--as I mentioned in comments on the OP, a light ray that gets very close to the surface of the sun will have its path shifted by only 1.75 arcseconds, where 1 arcsecond = 1/3600 of a degree. A ship moving at 0.2c will have a larger angle shift than a light ray on the same initial trajectory, but I expect the angle change would still be pretty minute if it's swinging by the surface of something like a gas giant.
    – Hypnosifl
    Commented May 20, 2023 at 16:45

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.

  • Are you saying jump points are typically on directly opposite sides of the sun, so the shortest path would go through the inside of the sun? If not, just the fact that they are the same plane of the ecliptic wouldn't seem to be sufficient to conclude the shortest (geodesic) path between them would go through the sun. And while gravitational slingshots with planets may be useful for speeds of real space vehicles I doubt they would be much use for something moving at 0.2c, or shift its path to a degree noticeable by human eyes (see my comment on the OP about the tiny deflection of light by sun).
    – Hypnosifl
    Commented May 19, 2023 at 0:43
  • @Hypnosifl If you haven't read the books, jump points are always on the outskirts of a system, light-hours from the star. And no, sometimes there are multiple jump points and IIRC never are they mentioned to be exactly opposite, and even if so, they won't cause 'long curves' at the speeds mentioned, but rather course corrections about the star, which typically would've been mentioned in the text. Commented May 19, 2023 at 9:49
  • @AhmedTawfik After reading your edits I see the source of your confusion. My answer still stands, but amended. Let me offer you a clue: how does a starship maneuver in space? Especially when travelling at 0.2c?
    – AcePL
    Commented May 19, 2023 at 12:14
  • @AcePL I'm really appreciative of your patience! I can take your explanation, but it doesn't fit with my second and third examples, where it is expected that the ships are accelerating at maximum load yet curves are used to describe trajectories across light-minutes. Additionally, ships apparently can reach .2c in minutes, which means at max acceleration the curve should completely flatten out, leaving no "long curves". Commented May 19, 2023 at 13:50
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    The discussion in comments here was getting pretty long, so I've moved the comments to a chatroom. Please continue the discussion there in chat. (I've deleted most of the comments from this post, but I've tried to preserve the most important ones, and all of them are preserved in the chatroom.)
    – Rand al'Thor
    Commented May 22, 2023 at 8:42

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