munroburton wrote:There was a particularly telling scene in the Shadow of Saganami, after Hexapuma transits to Lynx and Helen Zilwicki is ordered to compute a least-time hyperspace route to Spindle.
She tell us that she forgot to account for velocity loss on downward translations at the academy and that added 60 hours to the total voyage time.
Shadow of Saganami Ch.8 wrote:She felt a small trickle of satisfaction as she realized the same thing would have happened here, if she'd simply asked the computers to plot a course along the most powerful gravity waves, because one strong section of them never rose above the Gamma bands, which would have required at least three downward translations. That would not only have cost them over sixty percent of their base velocity at each downward translation, but Hexapuma's maximum apparent velocity would have been far lower in the lower bands as well.
She punched in waypoints along the blinking green line of her rough course as the computer refined the best options for gravity waves and the necessary impeller drive transitions between them.
This clearly shows us that even ships with Iota-capable hyperdrives can't use them all the time. If those Gamma-limited grav waves are fairly common, then that might explain why most freighters don't go beyond Delta - they'd end up losing more overall time and base velocity through undesirable ping-pong translations.
Plus, wear and tear: every additional band accessed incurs two translations - one to get there and one to get back down. A freighter which never goes to the delta bands will only ever need six bands of translations(three up, three down) with none mid-course.
To go to Iota and back - that's a base figure of twenty translations, so usage is more than three times heavier to start with under
optimal conditions. Being forced down to Gamma and then going back up to Iota
once adds twelve translations.
That scene bugs me just a little because I have trouble believing a starship's nav comp doesn't have an built-in option for "least time"; so why would she even have been considering the possibility of manually searching for routes starting with "stick to strongest 'waves" instead of starting with "least time"?
I could still see someone making the operator error of asking for the wrong thing. Like assuming what they asked for and what they wanted were the same; for example asking a car's GPS for least distance in an erroneous assumption that that will always provide least time.
Also, I'd be surprised if the nav computers of any starship would calculate a route without automatically factoring in acceleration times and velocity loss. But I also see why they'd have routing options to minimize time outside grav waves; and it's on the operator to ask for the optimization they actually want (and then double check the nav comp's suggestions)
Though for a school assignment it makes total sense to make students to calculate transit times, including accounting for velocity drop, "by hand" to ensure they understand the concepts and can apply it if they have to. But that's the sort of thing that it's trivial for the nav comp to automatically include when outside a school setting.
So I assume that if Helen
had told the computer to stick to the strongest grav waves that it would have given her an accurate arrival time; but (apparently) wouldn't have pointed out that by picking a fuel efficient route she'd actually picked a slower one. So she'd have failed in her task of calculating a least time route; but I have to believe that the arrival time the computer spit out would have been correct had they taken that slower route and used the default assumed acceleration settings.
But like I said, it does make sense for nav comps to also include the option to minimize time outside 'grav waves even at the expense of (some) transit time. Freighters do prefer that due not only to the extra ~10x acceleration they enjoy within a grav wave
[1] but they also save fuel
[2], and it's somewhat safer as apparently rogue waves can't be a factor when you're already in a 'wave. So they'd probably accept
some extra transit time in order to minimize the amount of time they need to spend outside of grav waves. But even there I'd have trouble imagining a freighter picking a grav wave in the Alpha bands over going "cross country" under impeller in the Delta bands; their trip would take about 35 times longer and I can't see the fuel savings justifying that.
(Maybe dropping to Gamma to ride a wave could be justified; but even that drops a merchants max effective time c from 1089 to 736.5; a pretty big drop if you're there long. And that's over and above the velocity losses you take during each transition up and down)
[1] Letting them spend less time working up to their maximum cruise velocity
[2] Can siphon power from the 'wave and throttle down or even power off the fusion reactor.