Most effective way of getting heavy stuff into orbit?

[ray]

So, I'm currently playing a modded career mode. That means I'm limited on part choice, but I've always had this issue to some extent or another even in sandbox.

I have built a rather heavy moon lander that I designed for the purpose of landing on the Mun & Minmus in order to deploy a small rover, which it carries, to search for a suitable landing site for a base as well as to conduct research. The lander itself weighs about 18 tons.

I can get it into orbit if I use my launcher stage (which consists of solid fuel boosters) to get me out of the atmosphere, followed by using the majority of my transfer stage. This, however, means I don't have the delta V to get to the mun (and especially minmus) and back without having to tap into my lander's fuel reserves, which is designed specifically to have enough delta v to land and return from minmus (which I tested using hyperedit).

18 tons is not a lot of weight all things considered, but it's posing enough of a challenge that I am having immense trouble designing a rocket suitable enough to get this into orbit.

I have some pictures below of my current design.

https://imgur.com/a/R169Z30

Is the issue simply because of the weight of my lower stages? How do I effectively design a rocket that will lift this lander to orbit and to minmus?

I have been to the mun and minmus several times before with crewed and uncrewed missions, but this particular vehicle is designed to be a more permanent and cargo-based transporter for my mun/minmus missions to carry supplies (USI life support) and equipment to the mun/minmus, which my earlier landers were absolutely incapable of doing.

[Quizzical]

I generally start with the payload that I have in mind and the location of where it's supposed to go. The location generally means in some particular orbit about some particular body. Figure out how much delta-v it will take to go from launch pad to destination. It takes about 3400 m/s to get to a low Kerbin orbit, and you can compute what it takes to go from low Kerbin orbit to your intended destination.

Take your payload and make a new stage to deliver it. Add about as much mass in fuel tanks as the mass of your payload, and then enough engines to get a reasonable thrust to mass ratio. That won't get you all the way to your destination, but see how much delta-v it gives you.

Then do it again. See if that's enough delta-v to reach your destination. If not, then do it again. And again, until you've got enough stages and enough delta-v. At that point, add some boosters for a first stage to give you some excess delta-v in case you're not as efficient as you hoped, and you're ready to go.

The very first liquid fuel stage needs to function at sea level, which limits your choices. Mammoths are the best if you're building something big. For smaller rockets where a single mammoth would be overkill, use a mainsail, skipper, swivel, or whatever is appropriate to your rocket size.

For subsequent liquid fuel stages, you generally want upper stage boosters that are efficient in a vacuum. You won't be out of Kerbin's atmosphere entirely by the time you fire the second liquid fuel stage, but even an altitude of 15 km is enough to make the deleterious effects of air pressure negligible. For big stages, use however many rhino engines it takes to make the thrust to weight ratio reasonable. For smaller stages where a single rhino is overkill, use wolfhounds for moderate-sized rockets, or a single poodle, cheetah, terrier, or spark if even a single wolfhound is overkill.

For your third and later liquid fuel stages, you're probably going to be in space. At that point, nerv engines are an option. I usually avoid them because the very low thrust means very long burns, which is annoying. But for the largest of rockets, you basically have to use them in order to make the first stage fit on the launchpad.

You'll generally want clydesdale boosters for big rockets, or maybe something smaller for smaller rockets. For small rockets, you might not even use solid fuel boosters at all.

Here's the biggest launch vehicle that I've got:

https://steamcommunity.com/sharedfiles/filedetails/?id=2248217170

That has to deliver several hundred tons to a low orbit about Laythe. On the launch pad, it comes to 10820 tons.

[AoD_lexandro]

Launch stage is just too weak. You need more power and fuel. The SRB engines are too big, and the main stage is too small. SRB are only really used to give you the kick to get off the pad. The rest of the thrust comes from the main stage.

Use a bigger scale tank, more of them in a long pipe and put the best engine you have on the bottom. Also consider using some fairings to reduce drag from all the bits sticking out. Oh and align your engines properly. Having the SRB so far up causes a lot of thrust loss from bad placement.

[ulzgoroth]

I recently boosted a somewhat heavy fuel depot platform (with 22.5 tons of LF tank as the main payload) into LKO using only up to Skippers. It's a bit of a sluggish launcher but it worked nicely.
https://steamcommunity.com/sharedfiles/filedetails/?id=2410805195
Three asperagus-staged Skippers, plus four Thumpers to boot it off the pad. The platform itself has a Poodle and needed to use it a little to complete orbital circularization, but only a little.

Probably a mainsail would be an improvement but I didn't have the tech points handy.

Rather heavy - I had to upgrade to the level 3 launchpad.

[MangoMan]

is this a return trip? how to move a huge payload is something like the fundamental problem of space travel. the solution is to dwarf the payload with fuel mass. the later fuel and engine techs make this a lot easier to do.

for 18 tons of payload I can get just about 7500 vacuum dV without the later techs, though it's pushing it quite a bit. it's probably doable if you're just delivering the 18 tons, but not returning it. (it's probably possible, just will take a lot of fine tuning.)

6x Thoroughbred -> 2x Rockomax Jumbo + Twin-Boar -> 1x Rockomax Jumbo + Poodle -> 18 ton payload.

checking my saves, something I called "stupid big" at a similar tech level, not knowing if I could make the trip was only a 10 ton payload. (though I did make the trip with dV to spare).

[ray]

Originally posted by Quizzical:

Take your payload and make a new stage to deliver it. Add about as much mass in fuel tanks as the mass of your payload, and then enough engines to get a reasonable thrust to mass ratio. That won't get you all the way to your destination, but see how much delta-v it gives you.

What would be a good thrust to weight ratio? I think that is likely where I am running into issues the most.

Originally posted by Quizzical:

The very first liquid fuel stage needs to function at sea level, which limits your choices. Mammoths are the best if you're building something big. For smaller rockets where a single mammoth would be overkill, use a mainsail, skipper, swivel, or whatever is appropriate to your rocket size.

So, the first LFO stage should kick off on launch? I typically just used solid boosters to get up further out of the atmosphere before engaging anything LFO-related. But I will keep this in mind if that's what you were implying.

Originally posted by AoD_lexandro:

Launch stage is just too weak. You need more power and fuel. The SRB engines are too big, and the main stage is too small. SRB are only really used to give you the kick to get off the pad. The rest of the thrust comes from the main stage.

Use a bigger scale tank, more of them in a long pipe and put the best engine you have on the bottom. Also consider using some fairings to reduce drag from all the bits sticking out. Oh and align your engines properly. Having the SRB so far up causes a lot of thrust loss from bad placement.

Those 4 SRBs usually send my apoapsis up to a LKO altitude, around 70-90 KM depending how I do my gravity turn. Then I usually just try to burn to circularize. Orbit isn't too much of an issue, it's moreso getting to the mun/minmus. But I will keep this in mind and try to restructure accordingly. Also, what would be a good placement for SRBs? I currently have them located at the center of mass of the lander + the main stage, I figured that would be the best placement for them, but I could easily be wrong.

Also I don't have bigger scale tanks, those are the biggest ones I've got, equivalent to rockomax tanks.

Originally posted by ulzgoroth:

I recently boosted a somewhat heavy fuel depot platform (with 22.5 tons of LF tank as the main payload) into LKO using only up to Skippers. It's a bit of a sluggish launcher but it worked nicely.
https://steamcommunity.com/sharedfiles/filedetails/?id=2410805195
Three asperagus-staged Skippers, plus four Thumpers to boot it off the pad. The platform itself has a Poodle and needed to use it a little to complete orbital circularization, but only a little.

I will keep this design in mind and be sure to check it out once I get back to redesigning the launcher.

[AoD_lexandro]

I try to always have my SRB in line with the main drive (ie all level at the bottom). If you note the DV window when moving them up and down, you can see the DV and TWR change as the thrust is better placed and improves the flight profile.

[Quizzical]

Originally posted by ray:

Originally posted by Quizzical:

Take your payload and make a new stage to deliver it. Add about as much mass in fuel tanks as the mass of your payload, and then enough engines to get a reasonable thrust to mass ratio. That won't get you all the way to your destination, but see how much delta-v it gives you.

What would be a good thrust to weight ratio? I think that is likely where I am running into issues the most.

Originally posted by Quizzical:

The very first liquid fuel stage needs to function at sea level, which limits your choices. Mammoths are the best if you're building something big. For smaller rockets where a single mammoth would be overkill, use a mainsail, skipper, swivel, or whatever is appropriate to your rocket size.

So, the first LFO stage should kick off on launch? I typically just used solid boosters to get up further out of the atmosphere before engaging anything LFO-related. But I will keep this in mind if that's what you were implying.

Originally posted by AoD_lexandro:

Launch stage is just too weak. You need more power and fuel. The SRB engines are too big, and the main stage is too small. SRB are only really used to give you the kick to get off the pad. The rest of the thrust comes from the main stage.

Use a bigger scale tank, more of them in a long pipe and put the best engine you have on the bottom. Also consider using some fairings to reduce drag from all the bits sticking out. Oh and align your engines properly. Having the SRB so far up causes a lot of thrust loss from bad placement.

Those 4 SRBs usually send my apoapsis up to a LKO altitude, around 70-90 KM depending how I do my gravity turn. Then I usually just try to burn to circularize. Orbit isn't too much of an issue, it's moreso getting to the mun/minmus. But I will keep this in mind and try to restructure accordingly. Also, what would be a good placement for SRBs? I currently have them located at the center of mass of the lander + the main stage, I figured that would be the best placement for them, but I could easily be wrong.

Also I don't have bigger scale tanks, those are the biggest ones I've got, equivalent to rockomax tanks.

I generally want a thrust to weight ratio of around 1.5 on the launch pad, which goes up as you burn fuel without losing thrust. In subsequent stages, you generally don't want your thrust to weight ratio to go very far below 1.0 before you reach a stable orbit.

Once you're in a stable orbit, your thrust to weight ratio can go much lower. The problem with very little thrust is that you end up with annoyingly long burns. I usually want at least 5 m/s^2 of acceleration just to prevent burns from being unreasonably long. Hour-long burns usually won't cause your rocket to explode, but they are pretty boring to watch, even at 4x physics warp.

I generally recommend using both liquid fuel rockets and solid fuel boosters at the very start, unless your rocket is pretty small. Have thrust start at max, then slowly lower the throttle as you ascend to keep the thrust to weight ratio from getting too high. The solid fuel rockets will go all out until they're out of fuel, of course, but you can throttle back the liquid rockets to keep the thrust to weight ratio reasonable, which likely means around 2 or so in Kerbin's lower to mid atmosphere.

If done properly, the solid fuel boosters will run out of fuel long before your first stage liquid rockets. At that point, you stage to drop the solid fuel rockets, while letting the liquid rockets keep burning. You probably also max the throttle on the liquid fuel rockets at this point to make up for losing the thrust from the solid boosters.

When you drop the solid fuel boosters, you want the liquid fuel rockets to still offer a thrust to weight ratio of around 1, as you still need to reach space. You should be going up pretty fast by this point, and also well into your gravity turn, so you could reach space with a considerably lower thrust to weight ratio, but it's inefficient to spend too long fighting against gravity.

[GunsForBucks]

https://steamcommunity.com/sharedfiles/filedetails/?id=2262699227

https://steamcommunity.com/sharedfiles/filedetails/?id=2111705328

https://steamcommunity.com/sharedfiles/filedetails/?id=2111825135

[Wobbly Av8r]

Lot of different ideas above but relative to your original post I would highly recommend you take a look at the Twin-Boar heavy lift system. I have no problem lifting 18t - 19t into LKO with nothing more than a Twin-Boar and an additional Jumbo-64 tank. (The Twin-Boar is available to you since you have a Mainsail attached to your system and they are in the same node of the Tech Tree)

There are other advantages of the Twin-Boar such as ease of recovery, if that's your thing, but not necessary. One important thing to remember about using the Twin-Boar is that you need to accelerate it as quickly as possible to Mach 1 (~330 m/s in the low Kerbin atmosphere) and then the thrust to drag ratio will get heavy payloads into LKO.

[GunsForBucks]

https://steamcommunity.com/sharedfiles/filedetails/?id=2093842945

I like the twin boars too

[Wobbly Av8r]

Originally posted by GunsForBucks:

I like the twin boars too

Yeah you do! LOL!

I love your "No Holds Barred" approach to spaceflight - it's impressive and I always look forward to seeing what the GFB Bureau has on the drawing board!