New ion craft using fuel cell

[Sharpy]

Fuel Cell Array weighs 0.23t vs 3t of 6 fuel cells, and produces twice as much power as 6 fuel cells.

That means a setup of one array + 2 Dawns will have the same ISp and thrust as one of 12 fuel cells and 2 Dawns in almost half the mass.

Lower mass = higher delta-V.

[Streetwind]

I've actually seen a video featuring a small VASIMR rocket engine that used water a it's propellant (real world). I wonder if anyone has thought of using the output of a fuel cell for the propellant of an ion engine. Interesting discussion.

That depends on how good fuel cells are for supplying power to electric drives IRL. Water is a bad propellant for electric drives, so it only makes sense if fuel cells are so mass efficient that your total dV with fuel cells + bad propellant is better than <other power source> + good propellant.

My gut feeling says: this is several orders of magnitude away from making sense. Googling power to weight ratios, it would seem like space grade solar panels are in the neighborhood of 100 W/kg right now, whereas fuel cells are around 1000 - 1500 W/kg. That sounds favorable until you realize that that is the fuel cell without any fuel, which would add extra mass (both from the fuel itself, as well as from the tankage required). And the weight of the fuel generally dominates the weight of the cell by a significant margin. Also, the power production equipment is only one part of a spacecraft's total mass, but the engine Isp matters for the entire craft.

[Jett_Quasar]

That depends on how good fuel cells are for supplying power to electric drives IRL. Water is a bad propellant for electric drives, so it only makes sense if fuel cells are so mass efficient that your total dV with fuel cells + bad propellant is better than <other power source> + good propellant.

My gut feeling says: this is several orders of magnitude away from making sense. Googling power to weight ratios, it would seem like space grade solar panels are in the neighborhood of 100 W/kg right now, whereas fuel cells are around 1000 - 1500 W/kg. That sounds favorable until you realize that that is the fuel cell without any fuel, which would add extra mass (both from the fuel itself, as well as from the tankage required). And the weight of the fuel generally dominates the weight of the cell by a significant margin. Also, the power production equipment is only one part of a spacecraft's total mass, but the engine Isp matters for the entire craft.

Makes sense, but if all of the mass of fuel for the fuel cell were used as propellant (even if it's not the best) then you should still come out ahead...

JR