[Spaceships] Designers' Championship I: ground to LEO

[Chansith]

Using the spaceship design rules in GURPS Spaceships, without superscience, what is the cheapest way to provide a shuttle service between the ground and low Earth orbit, at TL 9? At TL 10? At TL 11?

Ground rules:

1. Orbital lighters must not release highly-radioactive exhaust into Earth's atmosphere.
2. Lighters must carry their passengers from a spaceport on Earth's surface to a ship or space station in a ninety-minute prograde equatorial orbit (ie. at an altitude of 170 miles, heading east at circular orbit velocity), and then return to a spaceport on Earth's equator. For simplicity, treat the circular orbit velocity at LEO as 4.85 miles per second, and the rotation of the Earth as providing 0.25 miles per second, requiring the engines to provide 4.6 miles per second of delta-v to do the job.
3. Earth may be assumed to have no more than two suitable spaceports, one in Ecuador at an altitude of 15,000 feet and possibly one on Sumatra at 9,000 feet. Headway on the service must therefore be an integer multiple of 45 minutes.
4. Embarkation and disembarkation may be assumed to require ten minutes each, and refuelling (if necessary) may be assumed to be completed within twenty minutes, so that the lighter must spend 20 minutes docked to the ship and twenty minutes on the ground in each duty cycle.
5. A lighter may be assumed be in service for 7 300 hours per year.
6. Lighter crew work 1,920 hours per year, of which 5% is administrative overhead, so the flight crew wage bill for the operation is wages for four crews.
7. Lighter crew is a comfortable job.
8. Lighters work at an average load factor of 75% (ie. on average, quarter of the seats are empty).
9. The commercial real return on capital is 5% per annum.
10. Depreciation on an orbital lighter is 4% per annum, straight-line (for accounting convenience).
11. Basic insurance of an orbital lighter is 1% per annum. Operational insurance is 0.001% per round trip to orbit, times 3 if the lighter's Hnd is +3, times six for Hnd +2, times ten for Hnd +1, times 15 for Hnd +0.
12. The servicing cost on an orbital lighter is 0.01% of the cost of engine and fuel tanks, per round trip.
13. Fuel costs are as given on Spaceships p. 46.
14. In the case of a vehicle that is not winged, it will be assumed that supporting the vehicle against gravity will reduce available delta-v from V to V' = V * {square root of (A-squared - 1)} / A, where A is the acceleration of the vehicle.

What is the most cost-effective ground-to-orbit lighter you can build at each TL, without superscience?

How are things different on a backwoods colony planet where there is only a liner in orbit 10% of the time, and where there is only one spaceport?