Call this a thought experiment.
Spacecraft to Earth orbit and beyond are traditionally launched by means of one or more rocket engines. The fundamental principle is that a rocket moves by expelling the vapour from a high-energy combustion. This energy is adequate to move the rocket as well as anything (within reason!) in physical proximity….
The obvious limitation of this approach is that the spacecraft a rocket may carry is a miniscule fraction of the combined mass of the rocket and its fuel.
Say that a spacecraft launched is capable of human-rated re-entry. What is the typical proportion of its re-entry propellant and heat-shield as a fraction of
- total payload, and
- launch vehicle propellant mass?
(The figures will probably vary from one launch engine to another; an approximate range will suffice in the answer. E.g. 3% to 5% of payload, and 0.9% to 1.2% of propellant mass.)