Rediscovering Electric Propulsion

[NGTOne]

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):

[Madrias]

I don't use a lot of Ion propelled craft (At least, not in stock form. I increase the thrust, but reduce the ISP of the engines to make them more fuel inefficient), but the handful of small probes I've set up to encounter planets while I eat lunch have done the job needed.

Honestly, I prefer the Probodobodyne Ant Engine. 1.5 units of thrust doesn't sound like much, but if you couple it with a few other engines to get it to space, it's sufficient as a last-gasp engine for your probes to send them hurtling into the black.

That Rockomax small red radial engine is a lot of fun for cruising around in small vehicles, too.

As for Ion engines, I've found their best purpose is as a downforce engine on my rovers to keep them on the surface of low gravity moons. Yes, they're obnoxious for power consumption, but they make up for it with stupidly low fuel usage.

[SpacedCowboy]

And you've got 8 junior labs going on there because ????

[KerbMav]

And you've got 8 junior labs going on there because ????

(the Jool rendezvous burn is ongoing):

Because he will need them.

Whenever I experiment with the ion drive, I end up with something very timeconsuming and therefore (for me) unsatisfying.

I once managed to burn a "sail ship" (for the big solar panels) to Mun and even establish orbit, but ... nah ...

[Streetwind]

@OP: I really like the adapter you got going at the end there. What is is built of? It's difficult to see but it seems like there's 16 engines on there. The top part is an upside down Rockomax quad adapter, but how are the engines affixed to it? Also, how heavy is that craft compared to the 8 kN of thrust it's getting? The engines alone are 4 tons, and all those RTGs can't be lightweight either.

As far as electric propulsion goes, some mods can give you a lot of extra options. RLA has some half-size radial attached ion thrusters, and a 1.25m part that combines 4 regular ion thrusters. Both of these exactly maintain the TWR and other stats of the stock ion thruster, if you're concerned about balance. Next to that, it also brings arcjets and resistojets, which are almost exact ion thruster clones except that they trade thrust potential for Isp (1kN/2100 and 2kN/1050 respectively). They too come in radial and quadmount variants. The only downside is that they don't get those fancy HotRockets effects without manually extending the configs

If you feel more adventurous, you can try the Near Future Propulsion pack. It adds many different electric engine systems, most of which are quite honestly overpowered compared to stock. But even if you don't want these, there's parts in there which can greatly enhance your stock ion thruster experience, such as a large selection of multiadapters specifically for small engines (there's a 2.5m --> 8x 0.625m + 1x 1.25m one there, so with RLA's quad thruster you could fit 12 ions on a regular 2.5m part without having to resort to exotic part clipping). There's also a trio of lower profile inline battery parts that let you get large amounts of EC into a craft wthout having to stack huge battery towers (and yes, they maintain the stock "weight per EC"). This is especially great for probes which you want to keep small, but still able to operate power-draining equipment (and the electric propulsion to some degree) while they're in the shadow of whatever they're orbiting. Also, bigger solar panels beyond the size of the Gigantor, and onboard nuclear reactors for power production as an alternative to spamming RTGs everywhere.

I've actually been building a lot of unmanned probes with the help of the two above mods (and a generous helping of the nerfbat in case of Near Future, courtesy of ModuleManager). Kerbin and both its moons have electrically powered mapping/prospecting satellites in orbit, a fourth one is on its way to Moho ahead of future manned missions, and the other planets and moons will get their own when the transfer windows roll around. And I'm planning a kethane ferry for shipping between a mine on Minmus and a processing station in Kerbin orbit that will likely be using one or two VASIMR plasma drives configured to very high specific impulses. After all, fuel efficiency is important on ferries that transfer something meant to be processed into fuel, so it makes sense to go electric here. Also, pushing the empty ferry out to Minmus should not require much thrust, and escaping back to Kerbin with a full load and aerobraking avoids overly long burns on the return too.

Edited February 17, 2014 by Streetwind

[DunaRocketeer]

Indeed, that is a nice ship there! As soon as I unlock the rtg's in my career mission I think I'll try something similiar. I'm still messing around with ion powered transfer stages - I'm about to use four ion engines to get my crewman back from Duna, and I agree, I think it'll be engrossing.

[ZodiaK]

here is my mid-mission Ion probe, Yutu I.

http://imgur.com/gallery/XXTqt

[ZodiaK]

has anyone ever been out to eeloo from LKO to LEO only on Ions?

[KerbMav]

has anyone ever been out to eeloo from LKO to LEO only on Ions?

No, and I have no inclination to do so any time soon! That short trip to the Mun was enough ... my only other try to go interplanetary used normal engines to escape and had to wait over a Kerbin year for an opportunity for a low dV-return on the opposite side of Kerbol.

(Although now that you placed that inception into my mind again, I will surely try again and bite my desk half way through my escape burn at Kerbin ...)

The secret has to be to built as light as possible?

[ZodiaK]

mmh. I agree. my Yutu mission's ap is at desired height, now trying to circularise.

[Streetwind]

I would summarize the secrets with:

- minimalism in construction; it doesn't need to be pretty, it needs to be functional and light

--- don't overfuel, calculate your dV and only bring what you need; that Isp isn't just for show

- solar panels for missions to Dres and below; use as small panels as possible in large amounts, only go larger if you run out of attachment space

--- RTGs for Jool and Eloo

- electric buffer storage is lightweight and can allow longer burns even if your power income is below the draw of the thruster(s)

--- everytime you use a girder, you could be using a battery bank instead, which weighs less and gives you buffer

- escape burn in 8-10 min bursts around your periapsis, do other missions while it loops back around; keeps burntime boredom down and exploits Oberth effect

--- have a good eye when to start capture burns (usually well outside of SoI)

--- bring a good book

[Levelord]

has anyone ever been out to eeloo from LKO to LEO only on Ions?

With the current time warp, waiting for the craft to coast to Eeloo is kinda pushing it. Does anyone know of a mod that allows higher time warp?

[Red Iron Crown]

I want to like ion engines, I really do. The high Isp is awesome, as is the challenge of designing ships with enough electrical power to run them.

But I just can't take the ridiculously long burn times for any sort of useful payload. I have a job, a wife, kids, social life, etc so my time to play KSP is finite. A multi-hour ion burn, even with time compression, is not a good use of that time. I'd rather be designing/building something, or warping to the next maneuver node, or landing, or anything more interesting.

If we had enough time compression to bring the burns down to 5 mins or so of real time, then I would probably use them more.

[Streetwind]

Look at RLA then for a balanced alternative (see post #5). Try the arcjet at 1 kN thrust, 2100 Isp. Half the burn time, you just need to bring a little more fuel. But Xenon is so light that it barely adds anything to the craft's weight.

Edited February 17, 2014 by Streetwind

[Aphox]

Mornin', folks. I've cleaned up the thread a bit, so don't mind the missing posts. Let's keep in cool in here and stay on-topic.

[NGTOne]

@OP: I really like the adapter you got going at the end there. What is is built of? It's difficult to see but it seems like there's 16 engines on there. The top part is an upside down Rockomax quad adapter, but how are the engines affixed to it? Also, how heavy is that craft compared to the 8 kN of thrust it's getting? The engines alone are 4 tons, and all those RTGs can't be lightweight either.

The "adapter" is just a Rockomax short adapter with some Clamp-o-tron Jr. docking ports surface-attached to it at 8x symmetry (there are, in fact, 16 of them), with the engines attached to those. I could probably have crammed in another 8, but I knew this thing would be a massive energy sucker as it was. As for mass, the fully fuelled probe clocks in at about 22.7 tons, with a TWR just below 0.04. It can burn for about 55 seconds at a stretch using the two Z-4Ks in the top section, and then it needs to wait about 8 minutes to recharge fully.

Here's a better view of the engine section:

And a view of how the engines are attached:

[Levelord]

I have two questions,

1. What mod gives those ion engines those effects?

2. Are those RTGs enough to power all of those ion engines at full power? O_o

[Streetwind]

That engine cluster honestly is really, really beautiful. I need to try something like that. Well, as good as I can make it without part clipping, anyway. My craft always end up looking a terribly utilitarian patchwork of randomly colored parts stuck together...

EDIT:

The engine trail mod is HotRockets. And the RTGs are not enough, as he wrote he can burn 55 seconds until the buffer is dry, which then needs 8 minutes to refill.

Maybe one could attach a solar array to a decoupler and use it to be able to burn continuously for the initial ejection, then discard the array when the craft is underway (as it becomes ineffecient way out at Jool anyway).

Edited February 17, 2014 by Streetwind

[NGTOne]

Maybe one could attach a solar array to a decoupler and use it to be able to burn continuously for the initial ejection, then discard the array when the craft is underway (as it becomes ineffecient way out at Jool anyway).

I toyed with using solar arrays, but they didn't actually contribute much during ground testing, and having them permanently attached added an extra 1.5 tons (and dropped my dV by 700 m/s).

[Levelord]

Maybe one could attach a solar array to a decoupler and use it to be able to burn continuously for the initial ejection, then discard the array when the craft is underway (as it becomes ineffecient way out at Jool anyway).

It might also help having the science bays being able to jettison themselves after use. Since it's an unmanned mission I assume there isn't going to be a science lab, so the used up science experiments aren't re-usable. They'd end up as dead weight after transmission. I dont see any parachutes or langing gears on the craft, so I also assume that he isn't going to bring it back to kerbin for recovery.

[NGTOne]

The goal is actually recovery, rather than transmission (I don't do transmission missions if I can help it). There's a docking port on the nose of the ship, where it's meant to dock with a manned craft on return to Kerbin.

[zarakon]

The best advice I have for using ion engines: Look up the DynamicWarp mod. Combined with normal physics warp you can burn at 8x or 16x speed

[ArmchairGravy]

I just don't have the patience for ion drives. Heck, I barely have the patience for LV-N's. Give me TWR or give me death!

[jmiki8]

I use ion engines for fine tuning/backup on my satellites, like this one, deployed using a spaceplane. For that purpose they work very well, I don't even bother putting other kinds of engines on, when it comes to the final-final stage on probes.

Edited February 17, 2014 by jmiki8

[CaptainArchmage]

Before moving to career mode, I build some heavy ion-powered spacecraft. There was a three-kerbal spacecraft to Eve using the large command pod with five ion engines, many batteries and solar panels, and a lot of the xenon tanks. I used this to get to Eve in about 20 days, not just during a Hoffman transfer launch window. This required a burn of over two hours.

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.