"The escape velocity from Earth is about 11.186 km/s (6.951 mi/s; 40,270 km/h; 36,700 ft/s; 25,020 mph; 21,744 kn) at the surface."
No other velocity needs be considered, because it is greatest at the surface...
COMPREHEND: If starting at the center of the earth, you would initially only need to overcome the half of the mass beneath you, while the mass above you would aid in your acceleration. Only when reaching the surface would the entire mass of the earth be beneath you and need to be overcome. It would gradually increase to the maximum of 11.186 km/s.
We can calculate for the center of mass only when on or above the surface. Once below the surface all the mass is no longer beneath you..... It is for convenience only because one never launches a ship from below the surface. And regardless of where you launched the ship from, it would only take 11.186 km/s to reach escape velocity.....
No, it is not a matter of convenience that they don’t launch deep underground, like launching at the core or the centre of the Earth.
It is unrealistic, because it is never going to happen.
What you are talking about, isn’t science. It is just pseudoscience conjecture.
Science is about WHAT it is, or WHAT is feasible, or HOW does it work, or HOW would you do it, etc, and once you have the explanation, you would test each and every ones of those questions and explanations.
What you are asking is doing the impossible, which amounts to being highly improbable to achieve.
Seriously, Justatruthseeker, how do you excavate all the way to the centre of Earth and at the same time construct the launch tube?
Do you magically make the tube appear? Or make a wish? Do you pray for the launch tube?
A matter of “convenience only” is an understatement. Your conjectures can never be achieve, so essentially they are pointless with the “what-if” sophistry.
You are forgetting that science have to be something that feasible. Wasting time on something that feasible, is nothing but waste of everyone’s time.