The stupid bobcat engines can't lift my Gemini!

[Drepface]

WHYYYYYYY!
i removed some fuel and IT STILL WONT GO

[Chibbity]

TWR is too low?

Where are you testing it?

What works on the Mun, won't work on Kerbin obviously.

[ScarfacE]

As Chibbity already said, your Thrust to Weight Ratio (TWR) is too low. So you can try a better engine or loose weight in upper stages. You can also try some advanced staging methods:

https://www.youtube.com/watch?v=_0o1CB0hRDQ

I would recommend that you install MechJeb as well. You can toggle a screen that shows the current Delta V, this helps on building the rockets.

https://forum.kerbalspaceprogram.com/index.php?/topic/154834-131-anatid-robotics-mumech-mechjeb-autopilot-270-08-january-2018/

[Chibbity]

Get KER instead, all the same info; none of the autopilot BS.

https://forum.kerbalspaceprogram.com/index.php?/topic/17833-130-kerbal-engineer-redux-1130-2017-05-28/

Works in 1.4.1

[RoofCat]

read thrust kN on engines, multiply ship mass by 10 (9.81) for Kerbin launch. See which one is bigger. If thrust is bigger, you will lift off. If weight (mass*gravity) is higher, you obviously won't. You can see mass in bottom right corner clicking on info icon. Adding one zero at the end shouldn't be too hard :)
Very useful during building stuff.

[Technicalfool]

One of the missions includes a Titan II GLV and an Agena target vehicle that you can use as a simple example on how to create a Gemini-alike that's capable of getting to and from a 300km orbit with enough fuel (just about) to maneuver and dock with.

The two craft should be located in (KSP directory)\GameData\SquadExpansion\MakingHistory\Missions\Meet Me in Zero G\Ships\VAB. Copy them from there into your save's VAB directory and you will be able to load them from within a non-mission game save (assuming you have the parts unlocked, if in career/science modes).

[ScarfacE]

Originally posted by Chibbity:

Get KER instead, all the same info; none of the autopilot BS.

https://forum.kerbalspaceprogram.com/index.php?/topic/17833-130-kerbal-engineer-redux-1130-2017-05-28/

Works in 1.4.1

Ohh KER is working with 1.4.1?... I still prefer MechJeb cause I always install it and I don't want to install an additional mod for Delta V and TWR stats. Later in the game, I don't wanna fly every single mission and I actually learned a lot of maneuvering etc. from MechJeb.