Rediscovering Electric Propulsion

[Streetwind]

That's because travel time can be timewarped away in an instant, long transfer burns cannot. Short routes are a niche application, usually relevant when playing with life support mods that require you rescuing stranded Kerbals on a tight schedule.

[ZodiaK]

*phew* my Asteroid mission is finally finished! read about it here: http://imgur.com/gallery/VmIgV

[Brapness]

Personally I've been using ion engines more these days. My particular favourite was a rover mission to Duna. Full science package (except for goo and materials) and still only 2 tonnes. It gets launched on my shuttle, propels itself to Duna on an ion engine and then jettisons the gigantor solar panel and ion engine as it enters the atmosphere and lands on parachutes (Its wheels did break on landing but seeing as Duna has no biomes yet that wasn't a major issue, once it does get biomes I will certainly repeat the mission with more chutes).

[Cyst]

I've built a -considering it was ion propelled- pretty huge craft and I pointed it to Jool, to Vall to be more precise.

The whole thing was built up by nothing but solar panels, generators, solar panels, a cockpit for 3, solar panels and...did I mention solar panels? I've duct taped 63 (9x7) stock ion engines on it. Well, it was pretty fast, actually, considering the 0.5 thrust of each, and considering the size it was pretty lightweight too. Using damned robotics (for the panels to face exactly the sun) I managed to sustain all the engines with enough juice. I managed to have a pretty damn low orbit around vall and "landed" on it using only kerbals on EVA (don't try it, seriously...) 2 died, the third landed but couldn't go back, it ran out of EVA fuel. So yeah, it's fun to screw around with ions in my opinion but it is also time consuming.

[Streetwind]

*phew* my Asteroid mission is finally finished! read about it here: http://imgur.com/gallery/VmIgV

Nice mission report! Nicely designed spacecraft too.

[LordQ]

One point of electric propulsion is to cut down on travel time as much as possible. However, most people seem to use ion propulsion just for Hoffman windows.

What sort of trajectory would you recommend for ion engines?

[NERVAfan]

I use ions for when I want tons of delta-v, and build the craft very small. I sundived a probe with an ion engine about a week ago; I'll probably build another one to try to get solar escape velocity soon.

[ZodiaK]

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my asteroid mission.

[Levelord]

my asteroid mission.

That is one sexy engine configuration.

[DunaRocketeer]

^...and a very cool mission to boot

[ZodiaK]

@levelord thanks!

@dunarocketeer boot?

[KerbMav]

http://en.wiktionary.org/wiki/to_boot

Only a few posts more in here and I am in for another go at ions, I feel it ...

[ZodiaK]

ah okay. I'm not the best at phrases

Edited February 18, 2014 by ZodiaK

[Gnipu]

Total hijack.

[ZodiaK]

what do you mean, total Hijack? I just posted my example of ion drive utilization.

[KerbMav]

I think he just wanted to throw another phrase at you, regardless of whether it is 100% applicable now or not.

[NERVAfan]

OK, I just built that solar escape probe, 0.57 tons (0.51 with empty tank). 9 parts: HECS core + one 700-unit xenon tank + ion engine + six OX-4L 1x6 solar panels.

I got the solar escape with about 7-8 units (out of 700!) of Xenon left, but I didn't do everything the most efficiently (wasn't totally at periapsis when I started the burn, and I noticed that I'd been burning a bit off prograde too). Still, it's pretty borderline.

[m4rt14n]

I've toyed with the idea of building ion-powered spacecraft before, but I never really bothered with them because of the low TWRs and the need to wait for my batteries to recharge between burns. But today, I finally built and launched an ion-powered Jool probe (see below) because of a window that coincidentally opened up right after an Eve mission. Flying it is actually more engrossing than I had thought it would be, and designing it forced me to do things a bit differently. Anyways, what I'm wondering is:

a) Do many people bother with ion-powered spacecraft? Feel free to comment on your own experience/experiments with them.

Of those who do, does anyone have any tips for building bigger ones (for manned interplanetary missions)?

And, of course, a pic of the ship in question as it's leaving Kerbin (the Jool rendezvous burn is ongoing):

http://i.imgur.com/c4b99xX.png

Nice Blue exhausts... How many parts do you have in that ship? Looks like a lag magnet on my comp....

[NGTOne]

Nice Blue exhausts... How many parts do you have in that ship? Looks like a lag magnet on my comp....

This particular probe has 247 parts in flight, and 332 parts on the pad. The vast majority are xenon tanks.

[Rarity]

As much as I love electricity and would happily go through the hurdles of building an all electric craft, stock Ions are useless. With only one xenon tank, probe core, solar panels, batteries, etc. there's still next to zero TWR no matter HOW many engines you stack on. And you get diminishing returns by adding more engines because they have mass. Eventually, assuming you had the electricity to feed them, you'll have so many engines on your craft that they'd eat a single xenon tank faster than a Mainsail on a donut.

[NGTOne]

Or you could just do this (my experiment in stock-only manned electric craft, built for an upcoming Moho window):

Showing off the engine array. 64 PB-IONs at full bore, pushing just shy of 100 tons of spaceship.

240,000 liters of xenon. Hope it's enough (Kerbal Engineer did NOT play nice, so I don't actually know how much dV this thing has).

This mission is for a manned, close-range flyby of Moho, to grab the high- and low-orbit science points and return to Kerbin.

Edited February 19, 2014 by NGTOne

[m4rt14n]

Whats the TWR on that?

[Zephram Kerman]

I suppose you could simply set MechJeb to execute a transfer node, then walk away for a few minutes hours days years. The resulting orbit would look something like this:

I also suppose Vesta gets about as much attention these days.

edit: image credit: http://solarsystem.nasa.gov/educ/lesson-view.cfm?LS_ID=1252

[Monty_Droppings]

Or you could just do this (my experiment in stock-only manned electric craft, built for an upcoming Moho window):

Showing off the engine array. 64 PB-IONs at full bore, pushing just shy of 100 tons of spaceship.

http://i.imgur.com/6rxef9O.png

240,000 liters of xenon. Hope it's enough (Kerbal Engineer did NOT play nice, so I don't actually know how much dV this thing has).

http://i.imgur.com/OcWVV4x.png

This mission is for a manned, close-range flyby of Moho, to grab the high- and low-orbit science points and return to Kerbin.

Could I have the craft file for that? And whats the part count that looks absolutely nuts.

[Rodyle]

Or you could just do this (my experiment in stock-only manned electric craft, built for an upcoming Moho window):

Showing off the engine array. 64 PB-IONs at full bore, pushing just shy of 100 tons of spaceship.

http://i.imgur.com/6rxef9O.png

240,000 liters of xenon. Hope it's enough (Kerbal Engineer did NOT play nice, so I don't actually know how much dV this thing has).

http://i.imgur.com/OcWVV4x.png

This mission is for a manned, close-range flyby of Moho, to grab the high- and low-orbit science points and return to Kerbin.

Since xenon is 10 liters to the kilo, assuming a craft weighing 100 tonnes: expect around 11 km/s out of it.

As much as I love electricity and would happily go through the hurdles of building an all electric craft, stock Ions are useless. With only one xenon tank, probe core, solar panels, batteries, etc. there's still next to zero TWR no matter HOW many engines you stack on. And you get diminishing returns by adding more engines because they have mass. Eventually, assuming you had the electricity to feed them, you'll have so many engines on your craft that they'd eat a single xenon tank faster than a Mainsail on a donut.

It's not as bad as you think. You need per engine (roughly) 127 kilos of solar panels (1x6 ones) to run them at full throttle. That gives you a maximum sustainable thrust to mass ratio of 1,3. It's possible to get quite close to this and still have around 6 to 7 km/s. On the other hand, at this point, you might as well use nuclear engines. They give the same amount of thrust (or more), the same amount of delta v and have the advantage of not being dependent on where the sun is.

Edited February 19, 2014 by Rodyle