The shuttle external tank holds 1515 cubic meters, or 107,262 kg, of liquid hydrogen. When combusted with oxygen it liberates 1.295E+13 joules of energy. That's 241.5 kJ per mole of H2.

The exhaust velocity relative to the shuttle main engines is approx. 4500 m/s. The total mass of fuel (LOX + LH2) carried by the shuttle is about 556,505 kg. The total kinetic energy produced is therefore 5.635E+12 joules. The thermodynamic efficiency of the shuttle main engines is therefore approximately 43.51 percent.

Newtons law of action-reaction dictates that half of that energy move the shuttle while the fuel is exhausted in the opposite direction. Therefore the maximum kinetic energy imparted to the non-combustible shuttle components is approx. 2.818E+12 joules.

The total energy (kinetic + gravitational) of an orbiting body is defined by the equation:

E = -(GMm)/(2r)

where,
G = 6.673E-11
M = 5.98E+24
r = h + Re
m = orbiting mass

and where,
h = orbit altitude
Re = earth radius = 6.375E+6 meters

Consequently, the maximum mass that can be lifted to a 300 km orbit is 94,276 kg (94.2 metric tonnes), and the maximum mass that can be lifted to 400 km orbit is 92,864 kg (92.8 metric tonnes).

The empty mass of the external tank (23,805 kg) and the orbiter (45,720 kg) is approximately 69,525 kg. Together with a published payload mass of 19,812 kg gives a total mass of 89,337 kg (89.3 metric tonnes). This comes in just under the theoretical maximum for established operating conditions.

If you were going to operate a private spacecraft fleet with LH2/LOX fuel, electrolyzed from water, you can expect a total system efficiency for the electrolysis plant of around 14 percent. Therefore the space shuttle, with a 19.8-tonne payload capacity and an orbit altitude not much better than 400 km high, would burn the equivalent of 9.25E+13 joules of energy per launch. A 4-gigawatt nuclear powerplant could provide enough energy to electrolyze fuel for 1364 launches annually, if you had that many shuttles running. So, fuel isn't a major concern at the moment.

But if you want to compare ridership with motor vehicles, consider that there are over 44 million motor vehicles sold each year, and in total over 510 million vehicles in operation worldwide. If you could cram 100 people into the space shuttle, you would still have to launch 5.1 million times annually to get the same ridership. This would require 3739 nuclear powerplants, each producing 4-gigawatts of power, continuously producing LOX/LH2 fuel via electrolysis. There are only 232 nuclear powerplants in the world. Even one percent would require more than 37 dedicated powerplants to manufacture fuel. That's alot of water to exhaust into space. Such an approach to space travel may not be just energy-limited, but material-limited as well.

I think a non-rocket based system is needed, for both launch and space propulsion. Solar energy should be employed for both, to create re-usable magnetic field effects or photon impulse to move spacecraft, without expending any onboard material resources. The sun is a 5-billion year power supply, and I think we should make our systems last just as long.