[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?

[Chansith]

By the way: is there any comment on the ground rules as set out?

How do wings affect Hnd?

[alimantando]

What about a space lift?
Is that super science?

[AstralRunner]

Space lifts are easily TL 9, given an adequately motivated and organized civilization.

A launch loop might be even cheaper than that, though.

[Chansith]

Originally Posted by alimantando

What about a space lift?

• There are no rules for them in GURPS Spaceships, so they don't provide a suitable basis for a design championship.

• Space lifts are no good for getting to LEO: you can't get off below GEO. And it takes a long time to get to GEO, which might make space lifts unattractive to passengers. Rotorvators, bolo space stations, and even space fountains sound more practical to me.

• Space lifts eat up an awful lot of valuable territory in orbit, besides which they are mind-bogglingly capital-intense, and a very considerable engineering challenge. A beanstalk is equivalent to a suspension bridge with a 24,000-mile span. There might be a long wait before we get one built. We are much closer to building an orbital lighter. It is not clear to me that a space lift will ever be economic: operating costs are much lower than shuttles, but amortisation is through the roof, and there might be prohibitive rental costs on orbital territory.

• Until we design the most cost-effective orbital lighter we don't know what price the space lift will have to compete with. I won't be surprised if at higher TLs lighters (perhaps fusion powered) provide a trip to LEO that is cheaper than a space lift ticket to GEO.

• This design exercise will give us a basic approach to the more general problem of building lighters for trips from ground to low orbit on habitable planets. This will be important in the case of comparatively low-population colony worlds, which don't generate enough traffic to amortise a minimum-scale beanstalk.

[Crakkerjakk]

Laser Launch system is the most cost effective(at low TLs), I believe, but that was in THS, not Spaceships.

Also, by highly radioactiv,e do you mean no orion drives, or no saltwater nuke drives? Orion drives are not that hazardous in terms of fall-out

[Chansith]

Originally Posted by Crakkerjakk

Laser Launch system is the most cost effective(at low TLs), I believe, but that was in THS, not Spaceships.

Also, by highly radioactiv,e do you mean no orion drives, or no saltwater nuke drives? Orion drives are not that hazardous in terms of fall-out

I was particularly thinking of NSWR. Old Bang-Bang hadn't even crossed my mind. I think Orion is currently outlawed by the CTBT, but I might entertain a case that the law might be reformed if the emissions were likely to be negligible.

I am, obviously, considering commercial operations: thousands of passengers per day. Regulators would be concerned with cumulative emissions over myriads of launches, plus of course the possible use of the bombs as bombs.

Have you thought about Daedalus?

[Frost]

The trouble with any sort of pulse system especialy the Daedalus fusion pulse system is the expense of the fuel, I don't currently own spaceships but I suspect that this will prove to be the killer for any sort of Orion/ Daedalus pulse engine in regular service. As the rules of the competion, if not the build system, appear preclude hybrid vehicles such as the Helios designs (two stage vehicles using a chemical first stage and a nuclear second stage) at least at TL 9, nuclear systems may not be all that credible for low tech levels.

[Chansith]

Originally Posted by Frost

The trouble with any sort of pulse system especialy the Daedalus fusion pulse system is the expense of the fuel

Which is not a problem for this exercise: you only have to calculate it, not pay it.

I don't currently own spaceships

It is more or less necessary for participation in this designers' championship.

The PDF is US$9.95, plus which printing and binding my copy cost me about US$4.90. I consider it to have been worth every penny.

As the rules of the competion, if not the build system, appear preclude hybrid vehicles such as the Helios designs (two stage vehicles using a chemical first stage and a nuclear second stage)

The build system certainly doesn't preclude staged vehicles. As for the rules of the competition, if they rule out an economic and practical approach I would be open to changing anything that was unreasonable or opening a Designer's Championship Ia with more relaxed rules.

[Frost]

The PDF is something I am going to get as of payday (the joys of being a student again- only so many hours a week you are physicaly able to work work etc). My coment about the Helios design (nominaly TL 7- at least when it was first proposed) being useless was not about staging but the emmisions problem, using the chemical stage to reach the stratosphere and then using a nuclear sustainer to finish the job seams to violate rule 1 quite thouroughly. Even a closed cycle engine is probably a dead end because of its low thrust, without TL 10+ fusion systems it isn't going to fly.
As of when I get a copy I will try runing up stats for one of the Helios RLV designs using TL 9 materials and components while it will almost certainly not be legal under the competition rules (or sane for that matter) it may provide a useful reference.