What's the Point of the new Nuclear Engines?

[ubermonkey101]

Hey guys, as the title says, what's the point of the nuclear engines added in .17? They are weaker than the lander engines and yet the nuclear engines are bigger, so how is it useful at all?

[Anomalous_Matter]

They have an extremely high efficiency in space. The idea is that they make complicated, fuel-intensive maneuvers easier than doing them with normal engines.

[Znath]

I did a report on these a long time ago. The idea is that you have a gas superheated in what is essentially an open ended nuclear reactor. The gas expands based on the heat exchange from the nuclear reaction and then you thrust based on that expansion. The benefit being you're not simply burning a fuel to make it heat and expand, you're both heating a gas as well as generating power from the nuclear reactor....

Naturally, the secondary benefit isn't really needed in KSP, but... they are more efficient overall.

On idea was to launch a nuclear powered "space bus" in a high Earth orbit and leave it in orbit any time we would need to reach the moon. Then a shuttle can dock to it, fly to the moon, park the bus in orbit... land... re-dock, and return.

**I may also add that unlike the Kerbal version, there's no radioactive exhaust in the real version...

Though there was a cold-war nuclear powered jet engine that did.

Edited September 21, 2012 by Znath

[ubermonkey101]

Alright, thanks guys!

[phoenix_ca]

Yeah. Just look at that specific impulse! It's a thing of beauty, I tells ya. Though NovaPunch has one with even higher Isp. O.o

[malcheus]

Has anyone gone interplanetary without a nuclear engine?

[Awaras]

Has anyone gone interplanetary without a nuclear engine?

I have managed to land four Kerbals on Duna and return them safely to Kerbin using two ships very similar to the one I posted here:

http://kerbalspaceprogram.com/forum/showthread.php/15763-How-will-you-get-to-one-of-the-planets?p=264926#post264926

Both ships were built with parts that were available in 0.16 (The only modded part was the crewtank and I replaced the old ASAS with the new 2.5m one) and I had plenty of fuel left over both in my lander and in the Kerbin return vehicle...

The lander probably had enough fuel left over after taking off from Duna to land on Ike and go back up but I already decoupled the landing legs.

Edited September 21, 2012 by Awaras

[_Aramchek_]

Has anyone gone interplanetary without a nuclear engine?

I'm on my way to Eve without one, and tbh I think it may be easier without it. The small lander engines are still my favorite.

[Oggula]

I went to Jool, Duna and Eve with the Gimbal engine before I thought of adding Nuclear engines to my transfer stage. Very boring transfer though.

[eljaydub]

I did in my accidental flight to Eve.

[khyron42]

I did the math on this - let's say you strap the largest stock fuel tank to your interplanetary lander, plus a low-thrust engine, and then manage to get that much of the craft out into a solar orbit.

If the engine you installed is an LV-909 engine, it can burn at 50 thrust for 800 seconds. Total thrust produced = 40000. All other stock engines except the nuclear one are equal to that or worse.

The LV-N can burn at 60 thrust for 1200 seconds. Total thrust = 72000 from the same fuel.

That more than makes up for the extra weight of the engine; if you added one more 400L fuel tank to the first example to equal the same weight you'd get 50000 thrust out of it total, so overall efficiency for interplanetary travel is almost 50% higher than the best alternatives. The bigger the overall craft, the better the actual delta-v comparison between the two gets, too - since the mass of the engine becomes less important as the fuel/payload mass increases. The drawback is definitely the really long burns to make orbit changes rather than quick results with the higher-thrust engines.

I think from the math the break-even point was somewhere around a 15 ton craft (after jettisoning everything that was used to launch and start the transfer) counting the lander, fuel, and engine. Below that, the LV-N's extra weight isn't worth lugging around just for the better ISP.

Edited September 22, 2012 by khyron42

[AlternNocturn]

I attached three of these things to one of the big ~2m fuel tanks with three smaller fuel tanks, and the entire assembly was able to circularize my Kerbin orbit, get to Duna, get to Duna's moon Ike, rendezvous with a capsule, and return to Kerbin, and I did it all in the most inefficient way possible and still had enough fuel to safely get back and splashdown. Stick these onto a lander and you won't need a big complicated lander setup with a bunch of fuel tanks just to get off the surface. These things are a virtual godsend. I couldn't imagine doing anything worthwhile without them.

[Arrowstar]

I did the math on this - let's say you strap the largest stock fuel tank to your interplanetary lander, plus a low-thrust engine, and then manage to get that much of the craft out into a solar orbit.

If the engine you installed is an LV-909 engine, it can burn at 50 thrust for 800 seconds. Total thrust produced = 40000. All other stock engines except the nuclear one are equal to that or worse.

The LV-N can burn at 60 thrust for 1200 seconds. Total thrust = 72000 from the same fuel.

That more than makes up for the extra weight of the engine; if you added one more 400L fuel tank to the first example to equal the same weight you'd get 50000 thrust out of it total, so overall efficiency for interplanetary travel is almost 50% higher than the best alternatives. The bigger the overall craft, the better the actual delta-v comparison between the two gets, too - since the mass of the engine becomes less important as the fuel/payload mass increases. The drawback is definitely the really long burns to make orbit changes rather than quick results with the higher-thrust engines.

I think from the math the break-even point was somewhere around a 15 ton craft (after jettisoning everything that was used to launch and start the transfer) counting the lander, fuel, and engine. Below that, the LV-N's extra weight isn't worth lugging around just for the better ISP.

You need to look at the rocket equation. I think you'll find it is...