Low thrust time warp

[frisch]

I understand the problems with simply speeding up the physics warp. The result though is that ion drives are to boring to use - start up the drive then return many hours later. For basic KSP that isn't so bad - you can do everything with Nervas, but for real scale its quite difficult to do an outer planet mission without an electric drive. (there are some wonderful ones in add-on packs).

My suggestion is to have a special delta-V maneuver. The ship needs to be some distance from any object (say 1 million Km). Then you can apply an "instant" delta-V up to the amount of fuel carried. MechJeb calculates available delta-V so the data is probably available.

This would let you do a launch and escape using conventional (chemical or nuke) drives. Warp to 1M km, then use an ion drive. Its not "cheating", the result will be almost the same as if you had turned on the ion drive, then let the computer run for a day or two.

You could of course still use ion drives normally if you want.

[Mr Shifty]

It actually wouldn't be the same. Low thrust applied over a long period of time leads to different (often spiral shaped) trajectories. As you're thrusting, your vessel is rotating around the sun, even if it's not in the SOI of any near planet. As it rotates around the sun, the angle of the thrust relative to your prograde direction will change, and your trajectory will curve away from normal gravitational contour lines.

What you're asking for is essentially a high-ISP impulse engine. There's a reason we don't have those in the game; they're not realistic.

[rkman]

It actually wouldn't be the same.

I think the "special delta-V maneuver" would not be different that what a maneuver node already shows. The only hack would be that under timewarp that particular craft would not follow traditional orbital patched conics but instead would follow the trajectory initially shown by the maneuver node. When the burn time has passed it switches to regular patched conics, fuel is subtracted, done.

What you're asking for is essentially a high-ISP impulse engine. There's a reason we don't have those in the game; they're not realistic.

Ion engines are high-ISP impulse and realistic.

The reason why in ksp they are still nearly useless in spite of being over-powered is that ksp can't do high timewarp under thrust.

[frisch]

If you are far from any gravitational bodies so that during the burn time for an ion engine (say 1 day) your distances don't change significantly then applying the delta-V all at once, or slowly gives almost the same result (good enough for a game anyway). Close in to a planet then there is a big difference and setting ion engines to higher thrust WOULD be cheating. If you require a large distance then its not a cheat.

Imagine you are going to Jupiter. You get to earth escape with conventional engines. Then you start the ion drive. The trip takes years, so once you are away from the earth (using Oberth effect WOULD be cheating), it really doesn't matter if the burn takes 5 minutes or 5 days.

The problem is that while real astronauts on a 5 year trip don't mind waiting 5 days, if you are playing KSP it is REALLY DULL. It means that a correctly designed rocked (eg low thrust) makes for very dull game play - you need to start thing, then set alarms etc.

For normal KSP it doesn't matter - you can get everywhere and back (except EVE) easily with conventional and NERVAs. For real scale though, doing outer planet missions really only makes sense with high impulse drives, or you are sending your kerbals on multi decade missions.

So a X1000 physics time warp is the "right" answer, but its technically difficult to do in the game. I'm suggesting a kludge that has roughly the same effect .

[cpast]

Real ion missions also don't take 5 days to do a burn, after which they coast to the target. They actually run for a substantial portion of the mission. If you're trying to make ions like real ions, you cannot do it the way you suggested - real ion engines are so very much lower thrust than KSP ions (even before the bump, KSP had ions giving 500 N of thrust; for real ions, 5 N is massive thrust, and in-service designs typically have under 1 N of thrust) that you literally cannot model missions using KSP's point-impulse maneuver nodes - two-impulse Hohmann trajectories are not achievable, period, and the craft instead follows a radically different non-ballistic trajectory.

KSP is bad at this, because all the tools are designed for rapid burns (maneuver nodes in particular are inapplicable to brachistochrone trajectories ion craft have to use in real life; the calculations used for planning those missions are fundamentally different to the system implied with maneuver nodes). Given that the proper way would involve a ton of work to implement a special mode just for long-burn missions, and that only one stock engine would even possibly do those long-burn missions, it's probably not worth it.

Now, gameplay does take precedence over realism, but that only applies if ions are an issue and/or useless in stock KSP. Squad has limited dev time; that's best spent working on things that make the game better for the most people, not things that are mostly just relevant to people playing with one particular mod.

[frisch]

Fair enough that you need to concentrate on the core game. Personally I found ion drives to be useless or boring in the standard game. The very long burn times make them dull to use, and you don't really need the high delta-V for any missions anyway.

BTW, the various realism mods are quite impressive, I hope they make it into the mainstream game some day (maybe as a purchased extra). You are probably aware that someone is working on a better physics integrator that will make accurate warps with low thrust engines work correctly. The amount of highly technical work the modders are doing is amazing.