[Sort of Request] Ideas/suggestions for a Moon rocket in RSS

[Gaarst]

So, I want to go to the Moon in RSS.

I have a rocket that should do the job, but it's 170+ parts and kinda overkill, with 3290 tons at launch and 180 tons put to orbit.

I was wondering if anyone had ideas for a rocket design (or improving this one) to reduce part count, as this thing is laggy as hell on my puny laptop.

I also would like to know if it was possible to do it single-core (or at least having less than 5 cores), I'm planning to wait for the 7.5m parts of SpaceY anyway, but I'll still appreciate any suggestion. Note that the 5m lower boosters are actually a single stage, all sides + center boosters decoupling at the same time.

My mods (only relevant ones):

Real Fuels (with corresponding configs and Real Plume)

Joint Reinforcement

SpaceY

Stock Bug Fix Modules

RSS

(I think that's it, my other mods shouldn't act on the rocket)

Thank you for any answer !

EDIT: not 100% sure if that's the right section of the forum, mods please correct if not

[Tank Buddy]

I just started doing the RSS thing aswell.

If you want a smaller rocket, you will need the same amount of ÃŽâ€V but use much less fuel to achieve it.

There are three major things that affect your ÃŽâ€V:

1. Payload Mass
   
2. Fuel and ISP
   
3. Engine and ISP
   

If your payload, i.e. lander + return vessel is too large, your launch vehicle will be similarly massive. Same goes for the TMI stage (mass also dependent on payload); more payload, more pain. For your launch vehicle to be in a single stack, you should use an efficient fuel-motor pair, such as LH2 and INSERT ENGINE NAME HERE. Also make sure you have several vertical stages. The Saturn V has 3 massive stages burnt out by the time it was in a Lunar Transfer Orbit.

Even then, a single stack may be out of your reach depending on the engines you have (I use the stock engines with the RF configs) There are only two things you can do: Decrease your payload mass or increase the ISP of your rocket motors. Since you can only really decrease payload mass, you'd better get working on designing a striped-down lander. If you've read The Martian, you will know you need to get rid of anything unnecessary. But probably not as drastically as in The Martian. You may want to try some variation of the Apollo style for your lander.

For your lander and TMI stage, you will have to pick the fuels that will give you the best bang for you buck (mass). LH2 is not very dense and also has a much higher ISP thank RP-1 or Aerozine 50. You will just need to throw in more tankage if you choose to use it because LH2 is less dense. Keeping with comparisons to the Saturn V, make note that the S-IC (First stage) was fueled by Kerosene and the upper stages LH2. The CSM used MMH because cryogenic fuels would have boiled off, as you probably know.

And lastly, use the lightest motor you can get away with in your upper stages as this will save on payload mass.

Good luck!

[Gaarst]

Thank you for your reply !

I know about all the Isp stuff and have seriously considered using essentially hydrolox, but it is not dense enough so I would have to basically double the tanks size or number (second stage boosters still use hydrolox) and boiloff is a serious issue for a trip to the Moon. For the bottom stage and the core second stage, I use kerolox as it is the densest and I don't care that much about mass. For the third stage, command module and lander (lunar insertion and orbit) I use hypergolics (Aerozine50) as they are not cryogenic, so no boiloff issue and I can wait as long as I want for a transfer window.

Delta-V is not an issue with this design (I have 1500 m/s spare dV on lunar orbit stage, and over 500 m/s extra on both lander and ascent module) so I do not need to worry that much about Isp and which engines to choose.

As I said, my main issue with this design is the part count (>170) that makes it basically a slideshow at launch (add that it is a little wobbly) for my current laptop. Using LH2 would give me better Isp and a less massive rocket, but I would have to use bigger/more tanks, which would either increase the part count or make the rocket taller, so more wobbly (I can use struts, but then again, more parts). So, even if I change this design, I think I will keep using Kerolox and Aerozine.

[Tank Buddy]

If you have extra Delta V you should ditch the extra fuel and tanks. Because of the logarithmic nature of the rocket equation, you may be able to shrink the launch vehicle a decent amount. You have to try to squeeze as much DV from your upper stages if you want to get a single stack. You kinda have to deal with the fact that you need a taller rocket so that is why I don't usually use a LH2 first stage.

I don't know exacly how you get into a parking orbit, but I don't stick around for more than 1 orbit so my TLI stage is usually LH2 like the Saturn V's. Boil-of isn't significant but the mass savings are. Also, what is the mass of your payload you are delivering to the Moon?

[Gaarst]

So far, I could wait a few days in LEO for a transfer window because I did not bother matching the inclination ^^ But anyway, in my current design, the stage that gets me from parking orbit to lunar insertion is also used to circularise the Moon orbit. So anyway, I'll have to wait a few days to get to the Moon, so no hydrolox...

Payload to Moon orbit (lander+command module) is 25 tons.

Anyway, I think I'll redesign my upper stage configuration according to your advices, and see what I can do then for lower stages.

[Tank Buddy]

I actually started a thread because I couldn't find any adequate tutorials on how to get to the Moon. I did figure out that if you set the Moon as target and use KER's "relative inclination" value you can launch straight into an orbit that has the same inclination as the Moon. (Warp until value is 0°: Moon's orbit is directly overhead; follow heading of 90° into orbit) You only have to wait <1 full orbit until you have a window. I will work on a design w/ a 25 ton payload when I get the chance.

[Gaarst]

Ok... so, by some obscure and unknown mathematical manipluations of the rocket equation and a miraculously random yet as miraculously fortunate event, what was supposed to be an small optimisation of my 3200t heavy rocket became a hardcore diet that literally cut its mass in half while still keeping it able to perfectly send its payload to the Moon.

I was so surprised that I reinstalled KER for dV readouts, checked quite a few times that infinite fuel wasn't on and did actually put it to orbit to make sure it was capable of such miracle !

So, the new rocket, Alba Ultra Opt, now weighs a bit over 1600t, and part count went from >170 to 130. If you're interested, .craft file here. (No screenshots for now, I may add some later.)

[Tank Buddy]

Wow! Congratulations! I just downloaded KW Rocketry because if felt like I needed some larger diameter parts.