'Dawn' engine. Useful or useless?

[juanml82]

My issue with ion engines is that there isn't much solar power beyond Dres to power them continuously and, if you're going outwards from Kerbin, you'll have to burn from Kerbin's shadow anyway. That leaves Moho, Eve/Gilly and the Kerbin system to play around with solar powered continuously firing ions.

But there is a lot of fun in figuring out ways to power them without using Gigantors receiving sunlight. As others said, you can limit the burn times to whatever batteries can provide, and slowly recharge the batteries with either rtgs or solar panels barely receiving sunlight. You can use fuel cells and a small amount of LOX, which also allows the usage of small chemical engines for added thrust during take off or landing. Or with mods (Near Future Electrical, MKS and even Mk2 Expansion), you can power them with nuclear reactors. NFE has a 0.625m reactor which weights less than one ton and delivers 60 EC/s which, IIRC, can power four Dawns at once,. That's perfectly fine for a light lander with the MK1 lander can instead of seats.

And if we get into mods and nuclear electric ships, Near Future Propulsion adds a lot more electric engines, with greater thrust and isp, but also much greater power consumption. With NFP, I find the engines with a 400 EC power budget to be the sweet spot when building nuclear electric ships. Anything bigger than than and it's better to stick to the Nerv.

[TheTripleAce3]

22 minutes ago, juanml82 said:

My issue with ion engines is that there isn't much solar power beyond Dres to power them continuously and, if you're going outwards from Kerbin, you'll have to burn from Kerbin's shadow anyway. That leaves Moho, Eve/Gilly and the Kerbin system to play around with solar powered continuously firing ions.

Ion outwards has 2 easy solutions.

1: retrograde kerbin orbit keeps you on the light side for your burn with only a 352m/s dv cost

2: put 2 stacks of 3 oscar-b tanks alongside the main probe and use them while on the dark side of a prograde orbit.

[Mikki]

The Dawn engine can even propell a interplanetary crewtransfervessel as in "The Dunatian" (Link in Sig)

No problem for the tiny things 

[Raptor9]

Another technique, proposed in real-life for the ion-powered Deep-Space Transport to Mars, is use a spiraling trajectory to gradually raise your altitude to a much higher orbit before committing to an interplanetary transfer "burn".

The real-life equivalent wouldn't be quite like this since real ion thrusters are less powerful and KSP only uses patched conics vs N-body, but you get the idea.  Starting orbit in this example was 150x150km orbit, each altitude raising burn is about 3 mins long to minimize cosine losses, and by the time it's you perform the interplanetary ejection, the burn for that final maneuver node will be much shorter than a single (or dual) long ones, as well as having no chance of going behind Kerbin before it's completed.

For capturing into a stable low orbit, around Duna or Eve for example, you set your encounter trajectory at a much higher altitude for a longer insertion burn, and then gradually spiral back down, keeping the alternating altitude-lowering nodes on each side of the planet's terminator.  The only downside is you can't use the Oberth effect, but with the huge Isp of 'Dawn' engines this shouldn't be an issue.

Edited April 7, 2019 by Raptor9
typo

[Fraston]

Miniscule craft in low-gravity, atmosphereless bodies.

[FreeThinker]

For KSP InterstellarExtended I modified the dawn engine to its real thrust power and power usage and added target and orbital thrust resistance allowing you to spiral out or toward a celestial body using only a few newtons combined with high time acceleration.

Edited April 17, 2019 by FreeThinker

[Xurkitree]

Apparently it's far too useful.

[Pthigrivi]

On 4/4/2019 at 9:45 PM, Raptor9 said:

 

This is how I do it, though usually with 3 burns (the 1st, 6th, and 7th nodes on the above image). Nice thing is because there are no night-side burns you barely need batteries, just a solar array matched to your engine consumption. I've used fuel-cells too deeper into the solar system which saves you the trouble and gains you a bit more oberth savings. 

Edited April 17, 2019 by Pthigrivi

[MechBFP]

Personally I find that if you design it properly they are useful, but if you already know how to design a ship properly then you can make a ship that is just as useful (and significantly faster) using chemical engines. So really all they do is waste your time. 

[KerballingSmasher]

On 4/4/2019 at 3:45 PM, Raptor9 said:

Another technique, proposed in real-life for the ion-powered Deep-Space Transport to Mars, is use a spiraling trajectory to gradually raise your altitude to a much higher orbit before committing to an interplanetary transfer "burn".

The real-life equivalent wouldn't be quite like this since real ion thrusters are less powerful and KSP only uses patched conics vs N-body, but you get the idea.  Starting orbit in this example was 150x150km orbit, each altitude raising burn is about 3 mins long to minimize cosine losses, and by the time it's you perform the interplanetary ejection, the burn for that final maneuver node will be much shorter than a single (or dual) long ones, as well as having no chance of going behind Kerbin before it's completed.

For capturing into a stable low orbit, around Duna or Eve for example, you set your encounter trajectory at a much higher altitude for a longer insertion burn, and then gradually spiral back down, keeping the alternating altitude-lowering nodes on each side of the planet's terminator.  The only downside is you can't use the Oberth effect, but with the huge Isp of 'Dawn' engines this shouldn't be an issue.

OH MY HECK! The patience needed for that is unreal! I.e. not me...

[Pthigrivi]

3 hours ago, Kerballing (Got Dunked On) said:

OH MY HECK! The patience needed for that is unreal! I.e. not me...

Like I said you can do this in 3 burns. First two are short, just enough to raise your altitude so the ejection angle crosses your orbital path well outside the planetary shadow. Its only a waste of time if you’ve got a crazy low TWR. 

Edited April 17, 2019 by Pthigrivi