Squeezing more delta-v out

[Mmmmyum]

I've been getting this right for the last hour, basically building a manned Lunar lander. I tried to do it as is common in stock, and that's a one part lander/return, but I found that the amount of fuel needed for that would be impractical (Much like NASA did).

I use RSS, so I need around 2k more delta-v out of that. Is there a way of getting that out of the Service Propulsion System without making the ascent stages too big? That's a two stage lander with a total of 5km/s of delta-v.

Again, I'm using RSS so stock methods of building are out.

[TechnicalK3rbal]

Take of the battery, add an RTG. Use a command seat instead of a lander can. Add a large reaction wheel instead of the RCS. You could probably also do it with just one ehat shield.... Just try to make it smaller.

[Mmmmyum]

Take of the battery, add an RTG. Use a command seat instead of a lander can. Add a large reaction wheel instead of the RCS. You could probably also do it with just one ehat shield.... Just try to make it smaller.

I would but I like realism, also docking with a reaction wheel would be... Interesting. Another problem is a seat doesn't have oxygen

[WafflesToo]

You can probably ditch the poodle... terrible TWR.

5km/s of dV is needed? Lemme play with it some and I'll be back.

[Traches]

The poodle isn't a great engine-- very heavy. Could you cluster LV-909s to get a lighter descent stage on your lander? Or use one of the KW rocketry engines? (vesta, maybe.) That'll directly give you more dV from your service module, and you also might be able to bring less fuel in your lander, which will help further.

Edit: also, that blue thing that looks like an RCS tank isn't actually an RCS tank is it?

[Spica]

You should be using MMH and N2O4 for the SPS on the Command module. LH2's density is too low to support a high delta v with that heavy lander on top. Even though MMH and N204's ISP is much lower, you will get more delta v out of your CSM. However, it is heavier, so you may need a bigger launcher.

Spica

[bsalis]

Probably a single 909 will do for the lander.

Smaller batteries and a couple of the smallest surface mount solar panels should cut down on weight.

The capsure for re-entry only needs two of those parachutes, not three.

[Mmmmyum]

You should be using MMH and N2O4 for the SPS on the Command module. LH2's density is too low to support a high delta v with that heavy lander on top. Even though MMH and N204's ISP is much lower, you will get more delta v out of your CSM. However, it is heavier, so you may need a bigger launcher.

Spica

I think that will do it. Always wondered why MMH and N2O4 existed, never thought that it had a higher density (leading to more of the rocket's mass being fuel).

EDIT: What was gained in the CSM was lost in the ascent stage, delta-v gain was only around 50m/s in total

Also that blue thing is an oxygen tank.

And as for the size of the launcher, this has 13k delta-v (shown with fairings jettisoned):

Edited December 10, 2013 by Mmmmyum

[Mr.Rocket]

What i would say is, use aerospike engines. They're my favorite as they add so much more delta-v while still being powerful. Only negative is you can't have a decoupler in them.

[makinyashikino]

What i would say is, use aerospike engines. They're my favorite as they add so much more delta-v while still being powerful. Only negative is you can't have a decoupler in them.

This, Aerospikes are crazy efficent.

[Taki117]

I think that will do it. Always wondered why MMH and N2O4 existed, never thought that it had a higher density (leading to more of the rocket's mass being fuel).

EDIT: What was gained in the CSM was lost in the ascent stage, delta-v gain was only around 50m/s in total

Also that blue thing is an oxygen tank.

And as for the size of the launcher, this has 13k delta-v (shown with fairings jettisoned):

0_0 dear god man! Build out not up! instead of building a crazy tall rocket, build rings of boosters (They don't have to be asparagused, but it would help) I'm not expert on RSS (Never played with it) but it seems to me like you need larger boosters on your ascent stage, and probably more of them. Also, it might be a tad more realistic to put your lander behind your CSM instead of in front. This is just a few things that I've noticed.

[Traches]

0_0 dear god man! Build out not up! instead of building a crazy tall rocket, build rings of boosters (They don't have to be asparagused, but it would help) I'm not expert on RSS (Never played with it) but it seems to me like you need larger boosters on your ascent stage, and probably more of them. Also, it might be a tad more realistic to put your lander behind your CSM instead of in front. This is just a few things that I've noticed.

While the OP has taken it to the extreme, with FAR you definitely don't want to build out. It makes for inefficient, flip-happy rockets. A couple of strap-on boosters wouldn't hurt though...

Edited December 11, 2013 by Traches

[Mmmmyum]

Well the CSM now has 2.4k delta-v, most of which will be used to break into Munar orbit, although it will be a lot lighter for the return with no lander being carried. I'm starting to think I'll need NovaPunch's 5m rockets, which is going to push the limits of a 332bit address space a bit...

EDIT: Also just noticed there are no results for anyone doing a manned Mars mission with RSS when I google it, that's something I've been thinking of planning

Edited December 11, 2013 by Mmmmyum

[SRV Ron]

Do a single Kerbal Mun mission. The rocket is so much simpler that the direct approach can easily be done, even in the limited parts available in the demo.

[Ralathon]

Cut down on the Service module's weight. You don't need that much oxygen to keep your guys alive for the 2 weeks it takes to do a mun mission so dump the big O2 tank and use 2 or 3 small radial tanks instead. Also, use less fuel for the service module. MMH+N2O4 is great for reaction mass but it is also heavy, you want to use as little as possible. IIRC you only need about 700m/s of dV to get captured into a low circular mun orbit and the same to escape. So you can probably get away with having only 1.2km/s of dV in that service module (Since the lander doesn't have to come back).

Your lander can also use some weight watching. Use smaller legs and rethink the fuel tanks. You only need 1.7km/s to get from the munar surface to a low orbit and your current configuration seems overkill for that.

Those things combined should limit your weight enough for the 3th stage to boost you into a munar transfer.

[M5000]

Now, I'm not horribly familiar with the RSS mod, so I have a question, and then if the question is answered with the result I am expecting, a possible solution.

Does the RSS mod automagically change the specific impulse of the engines to realistic values, to match the planet sizes? IIRC, the stock values for engines, as well as what most mods are balanced for, are significantly inefficient compared to real-world counterparts.

If it does not account for the difference in Isp, why not modify it yourself? You've built quite a large rocket there and, while I understand that the Saturn V was also huge to get to the Moon, I believe that it may be able to be done with a smaller rocket, or at least one that's a bit shorter.

That's kind of my personal aversion toward the RSS mod, in that I often see people creating massive, Saturn-V/SLS sized launchers to put like, 10 tons into LKO, due to the anemic engines that would work fine in stock KSP, yet are very underpowered or inefficient in RSS. It's just not realistic at all.

However, I may be entirely misguided as I'm not horribly familiar with the RSS mod, but it seems that it, in fact, does not influence the specific impulse of engines.

So, that may be something to consider if you truly are going for realism. You might be able to get away with a much smaller (shorter) rocket.

[Ralathon]

Now, I'm not horribly familiar with the RSS mod, so I have a question, and then if the question is answered with the result I am expecting, a possible solution.

Does the RSS mod automagically change the specific impulse of the engines to realistic values, to match the planet sizes? IIRC, the stock values for engines, as well as what most mods are balanced for, are significantly inefficient compared to real-world counterparts.

If it does not account for the difference in Isp, why not modify it yourself? You've built quite a large rocket there and, while I understand that the Saturn V was also huge to get to the Moon, I believe that it may be able to be done with a smaller rocket, or at least one that's a bit shorter.

That's kind of my personal aversion toward the RSS mod, in that I often see people creating massive, Saturn-V/SLS sized launchers to put like, 10 tons into LKO, due to the anemic engines that would work fine in stock KSP, yet are very underpowered or inefficient in RSS. It's just not realistic at all.

However, I may be entirely misguided as I'm not horribly familiar with the RSS mod, but it seems that it, in fact, does not influence the specific impulse of engines.

So, that may be something to consider if you truly are going for realism. You might be able to get away with a much smaller (shorter) rocket.

The RSS mod doesn't adjust engine values. The Modular Fuel Tanks mod does however. Also note that it isn't the ISP of the KSP engines that is the problem. The stock values for ISP are pretty realistic. It is engine weight. Even the best engines in KSP only ever manage a TWR of 25 due to their own weight. In real life you can easily have a rocket engine lift 100 times its own weight because they aren't that heavy. This is why Apollo missions worked the way they did while you're better off using a single stage lander for munar missions in KSP: The weight of the extra engines wasn't that much of an issue for Apollo while it would be a massive payload increase for KSPers.

But if you use the proper config file for Modular Fuels it adjust the engine weight to be a lot more realistic. So it shouldn't pose issues for the OP. It is purely overengineering weighing him down by the looks of it.

[Pds314]

RSS - where nobody makes SSTOs and escaping Earth/Kerbin is as tough as escaping Eve from sea-level in Stock.

[Spica]

You may want to consider using kerbal joint reinforcement to stop that wobble, also, get stretchytanks or novapunch so you can use 5m diameter parts. That will enable you to have a more realistic saturn V, and more lifting capacity.

[Pds314]

Now, I'm not horribly familiar with the RSS mod, so I have a question, and then if the question is answered with the result I am expecting, a possible solution.

Does the RSS mod automagically change the specific impulse of the engines to realistic values, to match the planet sizes? IIRC, the stock values for engines, as well as what most mods are balanced for, are significantly inefficient compared to real-world counterparts.

If it does not account for the difference in Isp, why not modify it yourself? You've built quite a large rocket there and, while I understand that the Saturn V was also huge to get to the Moon, I believe that it may be able to be done with a smaller rocket, or at least one that's a bit shorter.

That's kind of my personal aversion toward the RSS mod, in that I often see people creating massive, Saturn-V/SLS sized launchers to put like, 10 tons into LKO, due to the anemic engines that would work fine in stock KSP, yet are very underpowered or inefficient in RSS. It's just not realistic at all.

However, I may be entirely misguided as I'm not horribly familiar with the RSS mod, but it seems that it, in fact, does not influence the specific impulse of engines.

So, that may be something to consider if you truly are going for realism. You might be able to get away with a much smaller (shorter) rocket.

Actually, if you look at some of space-X's engines, they are dramatically LESS efficient than even a mainsail. Of course, they also have TWRs of 100+.

Remember, IRL, methane has a MAXIMUM Isp of around 380 seconds. Space-X's new Raptor engine will have an Isp of about that and will have 2940 kN of thrust.

But all RP-1 rocket engines are dramatically less efficient. Space-x's Merlin 1-D engines only have an Isp of 311 and 720 kN of thrust. Granted, that is pretty good for an engine weighing less than an LV-909, but still, not nearly as high Isp as the Skipper, the obvious Kerbal equivalent to this engine.

The only chemical fuel with better performance than that is LH2-LO2 fuel. This was used for all but the first stage of the U.S. Space Team's Up Goer Five, but the problem is that it isn't very dense and requires immensely low temperatures to store.

Cold wet sky bag air used for burning is very good at escaping its can by jumping between the bits of the can and needs a strong cooler to keep wet. still, it moves ten and five times ten hundred feet in a second out of the place where all of the fire comes out. This is two tens and a three parts in a hundred better than air for burning that is taken out of the ground and smells like really bad flying animal baby boxes at your house or when you break wind. Normal places where all of the fire comes out of that use sky bag air are four tens and a six parts in a hundred better than those that use the stuff they burned in lights before houses had power. So over all, this game has a pretty good form of how well the places where all of the fire comes out of work.

[Mmmmyum]

I've been looking for a mod that increased the thrust for RSS (I'm looking at you, mod devs). I'd just edit configs but I like the game to be balanced. All of it points to the lander being too heavy and the CSM being overkill. I'll try using less oxygen (have no idea how much they'd use in the trip so I brought extra), and a lighter lander (the 2.5m fuel tank was chosen to help balance, but a 1.25m tank will do) along with lighter tanks