Ion engine burns for interplanetary transfers

[Kermanzooming]

Am I doing my interplanetary burns correctly?

When travelling to Duna and the rest of exterior planets, my escape burn from Kerbin must be done on the night side of the planet to make use of the optimal ejection angle.

This is of course is a problem with ion engines, so right now I'm dealing with it by doing multiple burns in consecutive orbits around Kerbin.

Am I missing something, or it's inevitable due to orbital mechanics to have to burn on the night side?

[Red Iron Crown]

If sunlight is essential, try launching yourself into LKO by heading west rather than east. You will spend a bit more delta V during the ascent but the optimal ejection point will be on the day side when heading to a superior planet like Duna. 

You still might need to split up the burn due to the low TWR of ion stages, if you will forgive a bit of self-promotion here is a link to some precomputed multiple burn ejections I made a while back: 

 

[Palaceviking]

Eve slingshot? 

[bewing]

Grab the ship with a nuclear space tug, and use that to perform the first few minutes of the ejection burn, until you are close to being in the sunlight again? Then let go, and reuse the nuclear tug.

[W. Kerman]

Ion engines, these are not the rockets you want to use, try something like poodle or nuclear. But you have the night\sun thing figured out, I personally use crazy 1400 ton vehicles which launch strait out of SOI of Kerbin at night or day respectively. Cost isn't that big of a deal if you're using an ion drive right?

Edited July 23, 2016 by W. Kerman

[Kermanzooming]

21 hours ago, Red Iron Crown said:

If sunlight is essential, try launching yourself into LKO by heading west rather than east. You will spend a bit more delta V during the ascent but the optimal ejection point will be on the day side when heading to a superior planet like Duna. 

So simple solution and never came to my mind

This is why I enjoy so much this game; it's not about space exploration, it's about solving problems 

[FleshJeb]

On 7/23/2016 at 4:25 AM, Red Iron Crown said:

If sunlight is essential, try launching yourself into LKO by heading west rather than east. You will spend a bit more delta V during the ascent but the optimal ejection point will be on the day side when heading to a superior planet like Duna. 

 

Something like 3500 hours in, and this has never occurred to me. Consider me humbled and delighted.

[Foxster]

Or you could power your ion engines with a fuel cell array, 

[HU5KI3]

On 2.08.2016 at 10:27 AM, Foxster said:

Or you could power your ion engines with a fuel cell array, 

Kinda beats the whole point of using electric engines if you power them with fuel.

[Foxster]

11 hours ago, HU5KI3 said:

Kinda beats the whole point of using electric engines if you power them with fuel.

Umm, not really. They aren't "electric engines", they already use fuel: Xenon. You are just adding a small amount of additional other fuel to that. 

The trade off is that, yes, you have an overall lower Isp but then you don't have to keep some solar cell panels facing the sun all the time, you can make the ship more compact, you can make the ship more rugged and you can explore the outer planets where sunlight is weak. 

[foamyesque]

I wonder what the Isp of a fuel-cell powered ion actually works out to. I should run the math sometime.

 

EDIT:

Mass flow of xenon: 0.0486kg/s

Flow of EC: 8.74 EC/s

Conversion ratio of fuel cells: 72 EC/kg

Mass flow of LFO: 0.121kg/s

Total mass flow: 0.17kg/s

Thrust: 2000N

Exhaust velocity: 11765m/s

Isp: 1200 seconds.

 

I'm actually not sure it's worth it. That's better'n a nuke engine, but xenon tanks have crappy mass ratios, and a nuke gives much better TWR, are cheaper once you account for the cost of fuel cells/solar panels, and can be refuelled by ISRU.

Edited August 14, 2016 by foamyesque

[eddiew]

Maybe worth it for ultra-light probes that can go a very long way on a tank of xenon? A lot of my science orbiters weigh ~5-700kg, slapping a nuke on the back of that is barmy  

You can also consider the LFO tanks and fuel cells to be droppable, I guess. Kick them off as soon as you're out of Kerbin's shadow for the last time and go pure solar from there on.