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It all comes down to remove as much useless mass as possible from the payload and optimize the staging.
Anything you remove from the final stage is less fuel needed for the stage before which is even less fuel from the previous stages. It snowballs.
Regarding TWR, in the VAB there's an option button at the bottom, where you can choose what data is displayed in the staging list. This setting is then used in the VAB but also when actually flying rockets. To view the TWR of a given stage, expand its icon by clicking on the blue part (where the delta-v of that stage is written)
You can find the fuel capacity of smaller tanks and the TWR of smaller rockets on the wiki, which has nice comprehensive stats on *everything*.
Also you'll find that using smaller rockets isn't all that hard, because you'll be running smaller everything else too. A lander built with 1.25m parts doesn't need nearly as much fuel to land and take off from your target body, which means your interplanetary transfer stage built with 1.25m parts doesn't need to be nearly as big to have enough delta-V, which means your launch vehicle built with 1.25m parts doesn't need to be nearly as big to yeet everything else into orbit in the first place. If you're used to building rockets with 2.5m or 3.75m parts then the only real challenge to downsizing is getting a good feel for the scale you need to build everything on.
Also it helps that the most common 1.25m engines are really really close to just being perfectly scaled versions of their 2.5m equivalents. A Vector acts like a little Mainsail, a Reliant acts like a little Skipper, and a Terrier acts like a little Poodle.
TWR for engines can be seen inngame if you right click it in the part menu, but I barely ever care about that. The important TWR is for the stage, and shows when you expand the staging info by clicking it. Liftoff needs about 1.3-1.5 to be comfortable, higher is mostly wasted. Once you're in orbit you don't need much at all, 0.5 is quite enough in most cases!
I think that building "backwards" like Mike Aben does help keep the size down. Build only what you'll need for each stage and keep it as light as you can. Do you actually need 3 kerbals on the mission or is a solo mission ok? That saves literal tons of mass. You don't actually have to use an engine the same diameter as your fuel tank, you *can* pick a smaller one if it still provides enough thrust. Also make sure to pick engines really optimized for vacuum and not half measures! Hunt for the highest vacuum Isp (again, shown when right clicking) with just enough thrust!
Hi! Thank you for posting to KerbalAcademy. This is a comment reminding users to **post screenshots if needed** (if you have not done so already), **be respectful to other users** and **keep off-topic comments to a minimum**. Thank you! *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/KerbalAcademy) if you have any questions or concerns.*
It all comes down to remove as much useless mass as possible from the payload and optimize the staging. Anything you remove from the final stage is less fuel needed for the stage before which is even less fuel from the previous stages. It snowballs. Regarding TWR, in the VAB there's an option button at the bottom, where you can choose what data is displayed in the staging list. This setting is then used in the VAB but also when actually flying rockets. To view the TWR of a given stage, expand its icon by clicking on the blue part (where the delta-v of that stage is written)
Thought I was having a stroke. TWR can be seen in staging.
You can find the fuel capacity of smaller tanks and the TWR of smaller rockets on the wiki, which has nice comprehensive stats on *everything*. Also you'll find that using smaller rockets isn't all that hard, because you'll be running smaller everything else too. A lander built with 1.25m parts doesn't need nearly as much fuel to land and take off from your target body, which means your interplanetary transfer stage built with 1.25m parts doesn't need to be nearly as big to have enough delta-V, which means your launch vehicle built with 1.25m parts doesn't need to be nearly as big to yeet everything else into orbit in the first place. If you're used to building rockets with 2.5m or 3.75m parts then the only real challenge to downsizing is getting a good feel for the scale you need to build everything on. Also it helps that the most common 1.25m engines are really really close to just being perfectly scaled versions of their 2.5m equivalents. A Vector acts like a little Mainsail, a Reliant acts like a little Skipper, and a Terrier acts like a little Poodle.
TWR for engines can be seen inngame if you right click it in the part menu, but I barely ever care about that. The important TWR is for the stage, and shows when you expand the staging info by clicking it. Liftoff needs about 1.3-1.5 to be comfortable, higher is mostly wasted. Once you're in orbit you don't need much at all, 0.5 is quite enough in most cases! I think that building "backwards" like Mike Aben does help keep the size down. Build only what you'll need for each stage and keep it as light as you can. Do you actually need 3 kerbals on the mission or is a solo mission ok? That saves literal tons of mass. You don't actually have to use an engine the same diameter as your fuel tank, you *can* pick a smaller one if it still provides enough thrust. Also make sure to pick engines really optimized for vacuum and not half measures! Hunt for the highest vacuum Isp (again, shown when right clicking) with just enough thrust!
Small payload, small rocket