LFO chemical rockets, or LV-N?

[Skorpychan]

As I contemplate my first big Duna mission, I find myself at an impasse. I have two cruise stages ready to go; one with a pair of LV-Ns, and one with the big single-nozzle Kerbodyne chemical rocket.

I have roughly equal DeltaV for both, as calculated with a test mass on top. Cost-effectiveness isn't an issue, because I'm playing on Science mode.

Past experience with nuclear rockets has led to multi-minute burns. 20 or more when dragging a heavy load. I haven't used the Kerbodyne engines for anything huge yet.

The main issue is that the Kerbodyne stack would be pushing the lander instead of pulling it. That's lead to wobbles while using docking ports before.

Edited July 4, 2015 by Skorpychan

[windows_x_seven]

Since the LV-Ns that are actually pulling it, I'd say you use the LV-N this time.

If you haven't launched it yet, though, I'd say you use a Skipper engine.

The Skipper is the only perfect engine.

[Gaarst]

Do not bother using LV-N for a Duna mission if it's just landing, plant a flag and go and if you're not sure about LV-N. Your burns will be longer and you can achieve the mission with LFO with a reasonable sized rocket.

For your Duna mission, Kerbodyne sized engines might not be necessary; as said above, a Skipper will do the job.

However, if you're going elsewhere or moving bigger payloads around, you might want to consider LV-N seriously.

[Dispatcher]

From the sound of things, among my choices would be the Skipper. However, depending on your mission objectives and ship design, you might want to consider the Mainsail or radial mounted Aerospikes.

In previous KSP versions, I always used the LV-N (Nerv). I have yet to attempt an interplanetary mission to evaluate the changes in version 1.0.4. Good luck!

[Edax]

As I contemplate my first big Duna mission, I find myself at an impasse. I have two cruise stages ready to go; one with a pair of LV-Ns, and one with the big single-nozzle Kerbodyne chemical rocket.

I have roughly equal DeltaV for both, as calculated with a test mass on top. Cost-effectiveness isn't an issue, because I'm playing on Science mode.

Past experience with nuclear rockets has led to multi-minute burns. 20 or more when dragging a heavy load. I haven't used the Kerbodyne engines for anything huge yet.

The main issue is that the Kerbodyne stack would be pushing the lander instead of pulling it. That's lead to wobbles while using docking ports before.

Since LV-N's are useless in atmosphere, I think it'll depend on whether you want to stop by Ike. The LV-N will save you a lot of gas in non-atmosphere landings, but if the mission is solely for Duna, they'll be dead weight. That is unless you plan to leave them in orbit for the landing.

Edited July 4, 2015 by Edax

[Skorpychan]

Okay, the big interplanetary engines won't be landing anywhere. I'm hauling a separate lander around for Duna/Ike, as I like to have a reusable cruising stage for my landers.

The big Kerbodyne engine has better ISP and thrust than the Skipper, however, so that was my choice for this mission. And I want to try it out.

At the moment, it looks like I'm going to be sending both, though. I realised that I can't fit a survey scanner on the Kerbodyne rocket because not enough ports, and the LV-N system will be ideal for sending the lab, refinery, miner, and fuel tanks over to set up a station.

And since I have two stages UP there, why not reuse?

[Sharpy]

It also has a much higher mass.

ISp converts to delta-V only with connection of dry to wet weight ratio. If you attach an Oscar-B to a Reliant (ISp 300), you'll get much more delta-V than from Oscar-B attached to Rhino - simply because burning 80kg of fuel can get 1.25 tons of the engine moving way, way faster than the same 80kg accelerating nine tons of metal.

The effect only changes when the wet-dry ratios change. When you are pushing 300 tons of fuel ahead of you, whether you use a 9 ton engine or a 1 ton engine doesn't matter much - but how the engine utilizes that fuel matters a lot.

That, amongst all, makes both LV-N and Skipper not particularly good for short flights, as they both weight 3 tons. Additionally, LV-N *must* be used with LF-only fuel tanks, or all the benefits of the high ISp are totally nullified by abysmal dry-to-wet weight ratio of LF+Ox tanks with oxidizer removed.

[GoSlash27]

I always go with whichever is lightest to put into orbit.

The LV-N doesn't outperform chemical rockets for the same mass until you get out towards Jool, so I'd recommend looking at the LV-909 or Poodle depending on how much payload you're moving.

Best,

-Slashy

[Red Iron Crown]

Since LV-N's are useless in atmosphere, I think it'll depend on whether you want to stop by Ike. The LV-N will save you a lot of gas in non-atmosphere landings, but if the mission is solely for Duna, they'll be dead weight. That is unless you plan to leave them in orbit for the landing.

LV-Ns are only really bad deep in a thick atmosphere, once over 10km on Kerbin and they're delivering about 56Kn at ~790s of Isp. Duna's atmosphere never gets thick enough to significantly affect their efficiency, they are great engines for Duna landers.

Edit: Might also be worth looking at Meithan's mass-optimal engine calculator.

[Laie]

Since LV-N's are useless in atmosphere,

(buzz sound) WRONG!

Duna's atmosphere so thin that nukes still work a treat: even in the deepest valleys, LV-Ns will still have an ISP over 700. TWR may be an issue, but the atmosphere barely matters. By the same token, Terriers and Poodles also work well on Duna.

As to the OP: I'd suggest to deal with the wobble first, that's gonna be annoying even with a LV-N puller configuration. Install KJR or do the suspension bridge: the latter may look silly, but works wonderfully at only a few extra parts.

[Edax]

(buzz sound) WRONG!

Duna's atmosphere so thin that nukes still work a treat: even in the deepest valleys, LV-Ns will still have an ISP over 700. TWR may be an issue, but the atmosphere barely matters. By the same token, Terriers and Poodles also work well on Duna.

As to the OP: I'd suggest to deal with the wobble first, that's gonna be annoying even with a LV-N puller configuration. Install KJR or do the suspension bridge: the latter may look silly, but works wonderfully at only a few extra parts.

It wasn't their ISP in atmosphere I was referring too, it was their low thrust. Very heavy engine with low thrust is a bad combo when trying to get off planets. This is why people use solid fuel when taking off, they have completely horrid ISP, but a good twr, which is specifically need when taking off a planet and countering gravity.

[Red Iron Crown]

It wasn't their ISP in atmosphere I was referring too, it was their low thrust. Very heavy engine with low thrust is a bad combo when trying to get off planets. This is why people use solid fuel when taking off, they have completely horrid ISP, but a good twr, which is specifically need when taking off a planet and countering gravity.

Thrust and Isp are exactly proportional for a given engine. If there is little Isp lost there is also little thrust lost. Duna's low gravity and thin atmo means LV-Ns are a reasonable choice there.

[Requia]

Since LV-N's are useless in atmosphere, I think it'll depend on whether you want to stop by Ike. The LV-N will save you a lot of gas in non-atmosphere landings, but if the mission is solely for Duna, they'll be dead weight. That is unless you plan to leave them in orbit for the landing.

I've launched off Duna with LV-Ns. 'atmosphere' is a bit of an exaggeration, as long as you don't land at the lowest points on Duna you're good.

[Skorpychan]

I'm launching with a Sr docking port on the top of a short stubby lander. LV-Ns won't help.

I've decided that the lander is going with the LFO rocket, and the lab station, the fuel refinery, the fuel miner, and the LFO fuel tank are going with the nuclear stage.

And that I need to design a fuel tanker with a Klaw, so I can harvest all the fuel I left hanging around the Kerbin system launching all that with slightly overbuilt lifters.

[Padishar]

And that I need to design a fuel tanker with a Klaw, so I can harvest all the fuel I left hanging around the Kerbin system launching all that with slightly overbuilt lifters.

If you decide to put a claw anywhere near your save then I suggest you save regularly (with alt-f5 so you can give each quicksave a different name) and often because the claw is notoriously buggy and you will encounter save-breaking problems that will force you to return to an earlier save...

[mrclucks]

lv-n vs lv909(not sure of the difference when it comes to size, I suggest you use Kerbal Engineer Redux) I would only use them as an interplanetary tug. Be sure to utilize peripasis kicks if needed(gradual apoapsis raising)

I would use an engine such as the poodle( an engine with high ISP and relative high thrust) to land and reenter orbit in most planets and/or moons.

If and when you use a stage to go from one planet go another, I suggest you add a probe core to your transfer stage, as well as add at least 1k dv for error