Re: Book, Single Stage to Orbit

George William Herbert wrote:
>>>[...]
>>
>>No, because a similar sized LAP can only carry 1/4 the payload; so you 
>>only launch as much payload per unit time.
>>
>>In fact I found an expendable LAP can only carry 1/4 the payload of an 
>>expendable TSTO of the same size/GLOW/dry mass.) A reusable LAP would be 
>>even worse.
> 
> You're not looking at the things that make LAPs useful.
> Mass is not the figure of merit; cost is.

Careful here, probably not. Price perhaps or more likely: *profit*.

That's why payload is important, because it provides income that leads 
to profit; and that's why I'm concerned about a 4x reduction in income 
per flight. My gut feel is that the profit margin isn't necessarily a 
factor of 4 over cost in the first place.

> A LAP platform plus stage to orbit has one complex
> vehicle and one simpler one, one low maintenance and
> low performance one, etc.  The LAP will be cheaper to
> design (by far), cheaper to operate from an operational
> perspective due to simpler recovery, lower performance
> requirements so lower stress and more robust, etc.
> Traded off against that is the larger GLOW for the
> combined vehicle, and correspondingly higher propellant
> masses and costs.

I think that this is, or may be, swamped by the 4x reduction in income 
per flight.

> There are also strong suspicions that there are
> LAP/nearlySSTO solutions where it is in fact a
> lot cheaper, despite the GLOW and propellant
> costs...

Maybe. I'm not totally convinced.

The other, perhaps better way to go is to differentiate the market and 
command a higher price per kilogram- it may not matter if it is 4x more 
expensive if it means you can launch a spy sat every half an hour or 
something. If having a well designed, simple LAP can do that, then it 
might be a preferred system after all. Or something.

> The devil is in the details.  You have to
> make common assumptions about design parameters
> and then compare apples and apples.

Sure. But this payload reduction seems to be rather important, and I was 
getting the impression people aren't completely getting the implications 
of this particular architecture.

> -george william herbert
> [email protected]