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UmbraSpaceIndustries / FTT

Freight Transport Technologies
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Star Lifter Under-powered #124

Open jamieT06 opened 8 years ago

jamieT06 commented 8 years ago

So either kerbal engineer is wrong or a X200 and a poodle has almost double the delta v of a GNR-2500 nuclear engine and the hydrogen tank. To get more delta v I need a cluster tank which is incredibly more expensive and even then it isn't much.

Kerbas-ad-astra commented 8 years ago

The rocket equation doesn't just depend on the specific impulse of an engine. It also depends on the ratio of fuel mass to total spacecraft mass. Hydrogen is pretty lightweight compared to LFO, and a GNR-2500 is quite heavy compared to a Poodle, so I'm not surprised that LFO does better in the case of a fuel tank plus an engine. However, if you're sending large craft on interplanetary missions (e.g. a colony ship), then the mass of the engine doesn't matter as much anymore (since the payload itself is already much heavier), and the difference in efficiency has a much larger impact.

The ideal choice of engine depends a lot on the kind of mission.

jamieT06 commented 8 years ago

I was trying to make a cruise/colony ship and it was over 100t for the main section. I was testing a full drive section and not just a tank and engine.

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On Tue, Apr 12, 2016 at 8:31 AM, Kerbas-ad-astra notifications@github.com wrote:

The rocket equation doesn't just depend on the specific impulse of an engine. It also depends on the ratio of fuel mass to total spacecraft mass. Hydrogen is pretty lightweight compared to LFO, and a GNR-2500 is quite heavy compared to a Poodle, so I'm not surprised that LFO does better in the case of a fuel tank plus an engine. However, if you're sending large craft on interplanetary missions (e.g. a colony ship), then the mass of the engine doesn't matter as much anymore (since the payload itself is already much heavier), and the difference in efficiency has a much larger impact.

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