Calculating distance to stop

nozmajner
Posts: 846
Joined: Mon Jul 01, 2013 3:25 pm
Location: Budapest HU

Re: Calculating distance to stop

Post by nozmajner » Sat Apr 29, 2017 4:52 pm

I can confirm this, but I wouldn't consider this a bug. I tested a bit differently.
I accelerated away from earth with different thrusters:
Main: 9430 km/s top speed
Retro: 1960 km/s
Belly: 2680 km/s
Side: 1790 km/s
Even with gravity losses, there shouldn't be that much of a difference, if the EVs are the same.
If you are using anything but your mains, it's quite visible that the speed buildup is quite slower as the depletion of the deltaV reserve. (Should build/deplete at the same rate, and it does if you use your mains)

Not sure if it was present in the game before, and the new deltaV gauge is what made this visible or it's something new.

But. I actually asked for this a while ago, but with the possibility to set EVs by hand for each direction. My reasoning is that different engines don't necessarily have the same EV, especially because in real life the relationship between thrust and EV are inversely proportional. (Either efficient or strong)
Like: As a ship engineer/designer you want your belly thruster to be able to lift the ship from the pad, but don't want to put in another of those very powerful and efficient (and most likely big, heavy, expensive and power hog) engines, since you won't really use them that much during travel. So you put a less efficient, lighter, but stronger one.

I think the main problem is, that it's not not readily visible how it's calculated, so it's quite unpredictable. It seems that it's calculated with the thrust proportions, but not sure. Like: "engine is this weaker, then it should be this efficient too".
And that this isn't directly visible to the player, no info to incorporate into the decision to use those other engines for course correction or just rotate the ship a bit instead for it.

Bugbear
Posts: 21
Joined: Sun Jan 11, 2015 3:45 am

Re: Calculating distance to stop

Post by Bugbear » Sun Apr 30, 2017 8:08 am

I suppose it does make sense that engines of different thrust output should have different efficiencies / exhaust velocities (I assume that's what you mean by EV).

If that's the case, then a consequence of this is that long duration burns are to be done only by the main thruster (not saying this is a good or bad thing).

The distance to stop calculations for reverse thruster burns will need to be fixed to take into consideration the different engine efficiencies. Given the current difference in engine efficiencies, we have the state where the reverse thruster will be limited by available propellant, rather than the available distance to stop, so if the reverse thruster has 20% the efficiency of the main thruster, and if total delta-v is 10000km/s (just keeping the maths simple here), then the reverse thruster can at most contribute 2000km/s delta-v. If the ship is travelling faster than this, then using the main thruster is the only option for effecting a meaningful change in velocity.

I've no problem with having different efficiencies for different engine outputs, but perhaps the difference in efficiency can be made less dramatic.

kennworl
Posts: 37
Joined: Thu Jul 13, 2017 9:54 am
Location: Melbourne, Australia

Re: Calculating distance to stop

Post by kennworl » Mon Jul 17, 2017 1:12 pm

Well, maybe the braking thrusters are only 20% efficient compared to the main thrusters.

Bugbear
Posts: 21
Joined: Sun Jan 11, 2015 3:45 am

Re: Calculating distance to stop

Post by Bugbear » Thu Aug 24, 2017 6:25 am

(I really don't move fast)

I've done more playing / testing of the latest build and UI. I've been able to adapt my travel style to account for the significantly superior main thruster efficiency.

It now goes: enter system. Select the planet that hosts my destination. Main thruster to 4000-6000km/s (depending on how much H2 I've got left in the hold). Flip around and wait for the distance to stop indicator to go green. Decelerate and make course adjustments to ensure that I keep my destination on target. Arrive at destination planet and enter a 10km orbit above the surface or atmosphere (whichever is closer). All going well I still have a few hundred km/s delta-v, which is more than enough for the remaining course corrections. From this point I switch to 'follow prograde' and use all directional thrusters to alter my orbit (Kerbal Space Program tutorials are really useful here) so that I eventually travel over my destination starport. And then just because I want to give my graphics card a bit of a workout, (if I'm orbiting an airless rock) drop my altitude to <1km and skim the surface at a few km/s until I reach my destination.

impaktor
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Joined: Fri Dec 20, 2013 9:54 am
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Re: Calculating distance to stop

Post by impaktor » Thu Aug 24, 2017 6:50 am


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