Rocket Design Quick‐Guide
Disclaimer: the author prefers specifying a extra transfer stage for high-energy missions (i.e. Deep space and GTO missions). This does not guarantee financial efficiency.
This will get you what payload mass and Delta-V your rocket would need.
Achieving Low Earth Orbit in this category typically requires a velocity of around 9400 m/s on the "rocket side." When transferring payloads to more energetic orbits, such as a transfer orbit to another planet, the Delta-V requirements often exceed 3000 m/s. Consequently, launching a small probe to such destinations, particularly in the early to mid-game phase, usually necessitates packing at least a few tonnes (4-12t) of fuel on the payload side.
Needs a more Delta-V abundant rocket ranging from 9500 m/s to 11600 m/s. Commercial satellites (except tundra and geostationary) and science satellites usually require a moderate amount of Delta-V to get into the targeted orbit. According to the PVG guide, you either coast or use another upper stage(s) to get there. Usually require ~800 kg of LEO payload for most contract purposes.
Requires no more than 9400 m/s on the "rocket side," making it the lowest energy requirement among them all. Typically, only 200 m/s of Delta-V needs to be packed. Payload ranges from 1.5t (Mercury) to 8t (Soyuz) (excluding Apollo and D-2).
Put a Navsat model in VAB. Adjust Nav Payload so that it fits the type of payload mass you want to deliver into LEO. (not using lead because it will cause fairing to be too small)
Slap a fairing base under your dummy payload. Put fairings on it. (turning 2 pedals of fairing to 3 may help dealing with cliping issues)
Put one on. If Delta-V is needed(prefer smaller LC), use separate Avionics on each stage. If lower tooling and integration cost is preferred (most of the case), use one to control the whole rocket.
If you have Douglas, Spam isogrid. If you don't, use Conventional tanks(mostly) . Balloon tanks are only for transfer stages(payload).
Find an upper stage engine (with air-light capability). Basicly higher Isp and lighter upper stage is more optimal so choose the most efficient (and non-HP if possible) one you can choose.
If possible, follow tooled diameters. However, if you haven't decided, don't use too long or too fat tanks unless you have weak gimbal(RD0105) or spin-stabilized stages as this would end up in a higher dry mass(especially on hydrolox and HP stages). After decision, apply the diameter to all parts(fairing, Avionics, and tanks.
You can choose if you want to use shrouds, but some might clip with the fairing structure on the lower stage.
Add truss and move it upwards. Adjust "Extra height". Side attach the engine and offset it back to center so less fairing height adjustments would be made. If you get more than 5000m/s of Delta-V in this phase, it would be quite suboptimal!
Even out the Delta-V packed on each stage.
Try different available engines. Try to use up the full burn time. If Delta-V is not enough, add fuel. If SLT is not enough, add engines. If lower stage have too much deltaV (but total amount of deltaV is still not enough after this whole process, add a stage in between your upper stage and lower stage. Low isp engines(open - cycle hypergols) usually need more staging. Repeat until you are satisfied.
If you have too little SLT, add moar boosters(or relatively, use a drop mass design) as this would keep Delta-V when mass is reduced. Even an engine dump may be useful!
See if theres any large amounts of remaining deltaV after a ride with Mechjeb PVG. If yes, remove some fuel on the "uneven" stage(Delta-V in excess compared to other stages) Happy rocketing!