New ion craft using fuel cell

[panzer1b]

Aside from early career, is there any reason to use these over a RTG/solars? It requires fuel, so unless ur mining fuel anyways, i see no reason to use them, solars weigh less, RTGs work 100% of the time period regardless of situation (unless they have been shot off of your vessel by missiles).

Still its a nice addition, even if one that i personally dont think ill be utilizing much.

[r_rolo1]

Very much this. KSP, at its core, is very much a game about managing mass; to trade massful fuel for massless electricity would seem to be a poor choice is almost every scenario.

Well, up to now it is also a game about minimizing part count, for various reasons. There is also the cost angle to consider for career.

Who knows, maybe in some situations it might be a worthwhile approach.

[panzer1b]

Well, up to now it is also a game about minimizing part count, for various reasons. There is also the cost angle to consider for career.

Who knows, maybe in some situations it might be a worthwhile approach.

True, basically teh 2 things that matter for most thing are lowering dry mass (basically anything that isnt fuel), and making whatever ship you have as low part count as humanely possible, all while achieving whateer you want it to do.

Sadly teh whole low part count and low mass doesnt work for armored capital ships and wepons, both of those use too many parts and weigh too much, still, who cares when you can vaporize stuff.

[Commissioner Tadpole]

I don't know if it will be worth it. You're carrying the weight of the fuel cell plus the fuel, which is dead weight most of the time. Solar panels and batteries still look like a better option. And how much the weight of the fuel+cell will compare with rtgs?

I was thinking the same. For an ion engine, it would need a lot of electricity, which would need a lot of fuel, which would lead into a lot of weight, which would need more ion engines, which would need even more electricity, which would need even further more...

[Xyrus]

True, basically teh 2 things that matter for most thing are lowering dry mass (basically anything that isnt fuel), and making whatever ship you have as low part count as humanely possible, all while achieving whateer you want it to do.

Sadly teh whole low part count and low mass doesnt work for armored capital ships and wepons, both of those use too many parts and weigh too much, still, who cares when you can vaporize stuff.

Well, since we don't have a way to dump fuel at the moment maybe you could carry along some empty fuel cells just in case you need to rebalance you're SSTO.

[RoverDude]

I think you folks will enjoy these

[timsfitz]

I'm looking forward to it. Going to be useful for mining I think. Sometimes you can be in the dark for a long while behind Jool, say on Bop. Bop is a good place to set up a mining base given the low gravity.

[Foxster]

It works!

[SpaceSphereOfDeath]

I'm looking forward to it. Going to be useful for mining I think. Sometimes you can be in the dark for a long while behind Jool, say on Bop. Bop is a good place to set up a mining base given the low gravity.

Therefore pol is better.

[CocoDaPuf]

Well, since we don't have a way to dump fuel at the moment maybe you could carry along some empty fuel cells just in case you need to rebalance you're SSTO.

You know, that's actually not a bad idea.

Although alternatively, you could also bring a LV-N engine, as they've been rebalanced to use only liquid fuel, no oxidizer.

But the fuel cell is a lot lighter...

- - - Updated - - -

It works!

And?!

Does it work well? Compared to batteries? Details!

[RoverDude]

Actually... you do have a way to dump fuel

There's a fuel jettison module used on the ore tanks. Note that it is an all or nothing (i.e. it will dump the entire tank contents of either all resources or a specific resource) but I expect you folks are pretty creative

[StainX]

Actually... you do have a way to dump fuel

There's a fuel jettison module used on the ore tanks. Note that it is an all or nothing (i.e. it will dump the entire tank contents of either all resources or a specific resource) but I expect you folks are pretty creative

Well, ore is not fuel

--

Not that bad i must say... and no more "out of EC" on the dark side!

Edit.... i didn't make it very efficient, the xenon ran out way before the LF OX

--

@RoverDude: I have a small suggestion... it would be handy to make fuel cells toggleable in the action groups

Edited May 1, 2015 by StainX

[klgraham1013]

I've wanted this type of generator for so long. Thanks RoverDude! Now I've got a liquid fuel powered rover!

[RoverDude]

Well, ore is not fuel

@RoverDude: I have a small suggestion... it would be handy to make fuel cells toggleable in the action groups

They should be. Also remember they don't push to 100% battery capacity, so if you have solar it will take priority and the fuel cell will kick on and properly throttle only when battery levels drop below 95%

[klesh]

Hey RoverDude. Thank you for being so cool as to be on the actual forums answering actual questions the players of the game have.

[MiniMatt]

Hey RoverDude. Thank you for being so cool as to be on the actual forums answering actual questions the players of the game have.

In big bold text do I second this! This update has brought several frankly awesome new gameplay mechanics to the table and every bit of headscratching has seen me wander to the forums - whereupon and I find thread after thread with really top quality help, advice, suggestions and inspiration provided by RoverDude.

I get that he wrote a good chunk of the new features, but seriously, The Dude abides

[klgraham1013]

Hey RoverDude. Thank you for being so cool as to be on the actual forums answering actual questions the players of the game have.

I'll add a yes to this!

[RoverDude]

Thanks, glad you dig the new toys.

And I am taking a lot of notes along the way, so the dialogue and help is definitely a two way street

[klgraham1013]

RoverDude, was there any discussion on making fuel cells LF powered, as opposed to LF+O powered?

edit: I should probably read through the thread again, just in case.

edit: Using Google, it seems appropriate that fuel cells use both fuels. Disregard this question.

Edited May 1, 2015 by klgraham1013

[DancesWithSquirrels]

Ok, I ran some numbers on this. I may have done things completely wrong, and would appreciate cross-checks, but:

Mass expenditure (xenon) for an ion engine at full thrust: 2000N/(9.81 * 4200) = 0.04854 kg/s

Fuel cell array fuel burn is 0.0025 units/s/e, at 5 kg/unit, or 0.0125 kg/s/e.

Generator mass expenditure (fuel/ox through fuel cell) for an ion engine at full power: 8.7285 * 0.0125 = 0.1091 kg/s.

That's a total mass expenditure of 0.15765 kg/s for 2000N.

Effective Isp for a fuel cell powered ion engine = 2000N/(0.15765 * 9.81) = Isp of 1293 seconds

Tankage and power balance: I figure about 6.5 PB-X150's to a FL-T100 is about right, and a single fuel cell array would power two ion engines.

So - rather better than an LV-N at Isp 800, (Edit: lower engine TWR than LV-N) and I think better combined tank mass fraction than the straight xenon containers (haven't run those numbers, though). On the downside, really low thrust, more complicated fuel tank math. it could be a win in some cases.

Example: Eloo orbit-orbit transfer round-trip (with Kerbin aero-capture) runs about 7500m/s. Add 1000m/s for buffer so 8500 m/s. A ship with an Isp of 1293 and 50% of the mass in fuel would have a delta-V of ~8792m/s, more than sufficient.

Edit: Fuel cell powered ion engines have a TWR = 5.4 (1 array at 0.24 + 2 ion engines at 0.25, thrust of 4kN), compared to (for example) the LV-N at 13.875. But they're not all that heavy, and it might be useful to stack enough of them to get your ship above, say, 1 m/s acceleration, which is my personal threshold of 'too painful to deal with".

Edited May 6, 2015 by DancesWithSquirrels

[FlyingPete]

Could be useful as a backup power source when a base etc is in shadow. Also for missions to the outer planets before you've researched RTGs. Definitely worth some experimentation on hybrid engines too

[quantumpion]

Ok, I ran some numbers on this. I may have done things completely wrong, and would appreciate cross-checks, but:

Mass expenditure (xenon) for an ion engine at full thrust: 2000N/(9.81 * 4200) = 0.04854 kg/s

Fuel cell array fuel burn is 0.0025 units/s/e, at 5 kg/unit, or 0.0125 kg/s/e.

Generator mass expenditure (fuel/ox through fuel cell) for an ion engine at full power: 8.7285 * 0.0125 = 0.1091 kg/s.

That's a total mass expenditure of 0.15765 kg/s for 2000N.

Effective Isp for a fuel cell powered ion engine = 2000N/(0.15765 * 9.81) = Isp of 1293 seconds

Tankage and power balance: I figure about 6.5 PB-X150's to a FL-T100 is about right, and a single fuel cell array would power two ion engines.

So - rather better than an LV-N at Isp 800, (Edit: lower engine TWR than LV-N) and I think better combined tank mass fraction than the straight xenon containers (haven't run those numbers, though). On the downside, really low thrust, more complicated fuel tank math. it could be a win in some cases.

Example: Eloo orbit-orbit transfer round-trip (with Kerbin aero-capture) runs about 7500m/s. Add 1000m/s for buffer so 8500 m/s. A ship with an Isp of 1293 and 50% of the mass in fuel would have a delta-V of ~8792m/s, more than sufficient.

Edit: Fuel cell powered ion engines have a TWR = 5.4 (1 array at 0.24 + 2 ion engines at 0.25, thrust of 4kN), compared to (for example) the LV-N at 13.875. But they're not all that heavy, and it might be useful to stack enough of them to get your ship above, say, 1 m/s acceleration, which is my personal threshold of 'too painful to deal with".

Awesome! Can you compare to the ISP of a solar powered ion craft taking into account the mass of the solar panels for a given amount of xenon/delta-v?

[Red Iron Crown]

Awesome! Can you compare to the ISP of a solar powered ion craft taking into account the mass of the solar panels for a given amount of xenon/delta-v?

Solar panels don't change the Isp, they don't shed any mass. So the Isp for a solar powered ion craft of any size/dV capability is 4200s.

[DancesWithSquirrels]

The Isp is based on thrust and mass expenditure - a solar or RTG powered ion engine will always have an Isp of 4200 as a result. The only thing that changes is the engine T/W ratio, due to the weight of the needed panels/RTGs/generators at whatever distance from Kerbol you are currently located.

Now, if you want the TWR of an RTG powered ion engine, figure 12 RTG's per ion engine, 12*0.08 + 0.25 = 1.21T, for a RTG powered ion engine TWR = 1.65. On the other hand, if you have all massless OX-STAT panels you have a max solar powered ion engine TWR = 8.

I've been thinking about a minimalistic RTG powered ion ship for an Eloo trip, putting more mass into fuel so that I can run a non-optimal but quicker trip. Just haven't done that yet...

Off the top of my head I'm not certain if 1.x isn't adding the formerly 'massless' objects to the total ship mass - anyone? The changes to a more realistic solar power drop-off certainly make solar powered ion ships pretty useless past Dres, now.

[Red Iron Crown]

Physicsless parts now have their masses added to their parent parts, yes.