$8.90/lb to LEO (was The old "big rockets aexpensive" canard)

> Neither one of you is putting actual dollar numbers on the cost for specific missions.

Marginal cost-per-pound to 300 n.m. orbit, averaged over a 10-year program, in January 1963 dollars:

240 launches, recoverable first-stage:

Pessimistic values: $28.60
Optimistic values: $8.90
Most probable values $16.20

http://neverworld.net/truax/Sea_Dragon_Concept_Volume_3.pdf

Those estimates are hampered by ancient guidance hardware, a command module for humans which includes an escape tower, low launch rate, non-use of second-stage rocket body as scrap or tubing for orbital city, small vehicle size (only 506 ft. and 40 million pounds gross lift-off mass), smaller 1963 shipbuilding industry, smaller 1963 Panama Canal capacity, etc.

I believe Mike has cited $0.10/kg for mass-driving from Moon to EML2 (I believe O'Neill in the 70's was his source). A $10 billion lunar mass-driver, paying merely its cost-of-capital at 10%/year, would then need to launch 10 billion kg per year, just to break even. That seems like a lot. Maybe he had been referring to just the electricity costs, at some very-low cost-rate.

> But Mike is dead on correct in saying that high delta v cost more.

He is not correct in ignoring, in his analysis, the myriad relevant Earth-launch-favorable differences between Earth and Luna.

> Making the stages reusable is yet another problem.

It seems to be pretty easy to re-use the first stage when it's a thick-walled pressure-fed rocket, and one is launching it from the ocean. Keeping some pressure in the tank helps protect it during impact. Inflating a big cheap tail-flare also helps protect it by slowing it prior to impact. This is all explained in numerical detail in the two Sea Dragon report pdf's, here:
http://neverworld.net/truax

> The best proposal I know of now is Reaction Engines Skylon.

Even their optimistic cost estimates on their website put the marginal LEO payload-delivery costs higher than those of the Sea Dragon. They cite $2-5 million per launch for "low-value" payloads. "10.5 tonnes to a 460km equatorial spacestation" works out to $86.40-216.00/lb.

They cite a 10-year development period. The Sabre engine looks complicated and expensive and time-consuming to maintain. It has 2 turbopumps (for each of two nozzles?), a circulator pump, an airplane-type air-turbine, and a lot of complex piping. There are 2 of those Sabre engines on each vehicle, so all of that complexity gets multiplied by 2.

If the Skylon actually ends up working, and doing it cheaply, it will be another piece of evidence that launching things from Earth is inherently easy. But the Sea Dragon already proved that on paper, using half-century-old technology and techniques.