Low thrust maneuvers

[LordCorwin]

Hello, I have some generic questions regarding Low thrust maneuvers.

1) I want to do a "small" ammount of delta-v using some ionic thrusters (say 20m/s). Assuming I have to do the maneuver at instant t0, when it is the best moment to start it?

2) I suppose I cannot apply the same answer in case of big delta-vs, can I? The time required to achieve the required delta-v is so big that in the meantime the rocket angle changes alot compared to the required ejection angle. So how do you plan your transfer maneuvers when using ionic thrusters?

Thanks

[cantab]

1) The most commonly accepted approach is to try and burn equal times before and after the nominal manouvre. Except when landing, then you need to finish the burn by the nominal time or you'll crash.

2) If your burn will take too long, sometimes you can split it. Do some one orbit, go round the primary, do some more. There's a limit though, since your ejection burn has to be single.

[LordCorwin]

Ok, so small ammount, then circularize the orbit, then another ammount, etc...

I understand that the game doesn't allow to use rockets when time-accelerating even when using ionic thrusters, right? So we cannot plan trajectories with continuous acceleration - deacceleration for extended periods.

Thanks!

[cantab]

Don't circularise.

Let's say you need 1200 m/s to depart LKO for Duna, but that's going to take 12 minutes of burning. Set up your manouvre node, but only start burning two minutes before and keep until two minutes after. Note down how much is left to burn - around 800 m/s or so. Delete the node and set a new one at the next periapsis for that amount. Make one (elliptical) orbit, then do the same thing again. Make another orbit, another burn, and you should be on course for Duna.

[Murph]

Ok, so small ammount, then circularize the orbit, then another ammount, etc...

I understand that the game doesn't allow to use rockets when time-accelerating even when using ionic thrusters, right? So we cannot plan trajectories with continuous acceleration - deacceleration for extended periods.

Thanks!

You can use physics warp, as long as all craft within physics range are small and simple enough (quite likely if you're talking ion engines). Physics warp does kinda amplify any control inputs though, so best to do those at 1x, and push it up when holding on steady course and thrust. Also, don't go straight to 4x from 1x, unless you know it's safe to do so â€â€.take it up 1 level at a time and watch for any wobble, etc, for a few seconds. I've got away with using 2x even on larger things with nuclear engines.

[LordCorwin]

Ok, makes sense. With eliptical orbit you still maintain a high speed in periapsis, not needed to spend energy circularizing. Also put the periapsis at the ejection point to achieve the highest speed. Thanks a lot!

[LordCorwin]

You can use physics warp, as long as all craft within physics range are small and simple enough (quite likely if you're talking ion engines). Physics warp does kinda amplify any control inputs though, so best to do those at 1x, and push it up when holding on steady course and thrust. Also, don't go straight to 4x from 1x, unless you know it's safe to do so â€â€.take it up 1 level at a time and watch for any wobble, etc, for a few seconds. I've got away with using 2x even on larger things with nuclear engines.

I'll take it into account too. Thanks!

[von Ziegendorf]

Try this: the tool I made (self-advertisement, lol)

[Sirrobert]

Ok, makes sense. With eliptical orbit you still maintain a high speed in periapsis, not needed to spend energy circularizing. Also put the periapsis at the ejection point to achieve the highest speed. Thanks a lot!

Exactly.

The higher your speed, the cheaper it will be the next time. That's why you want to make your ejection burn in a low orbit

[LordCorwin]

Try this: the tool I made (self-advertisement, lol)

Thanks, I will check your tool. Sorry, I missed the thread!

Cześć!

Lord