William> For purposes of depreciation an ELV is just an RLV with an
William> economic lifetime of one use (conversely, an RLV can be
William> understood to be an ELV with more uses).
I think this is wrong, but I don't know how to articulate it. But if
we goto the other extreme, what is the depreciation of an Airplane
with 10,000 cycles vs one with 20,000 cycles?
Airlines get rid of airplanes sometimes when they are due for a heavy
D check, because it's costly and doesn't add anything to the value of
the plane.
So this would imply that an RLV would also have a cost of
refurbishment. Which we can see from looking at the SRBs from the
shuttle, and the shuttle itself. Both we're reusable, but not cost
effective enough.
But, since you can't reuse an ELV, much less test it before flight at
100% of rated envelope of performance, whereas you can test an
airplane with simple engine on tests, then taxi tests, then high speed
taxi tests, takeoffs at low weights, etc. All those let you expand
the performance envelope without throwing the entire system away.
And without having to stress the system to 100% from the get go. All
those Resuable features have a cost benefit.
William> If the ELV cost X and the RLV has the same unit cost, then
William> after two uses the RLV cost X/2, after 10 uses, it cost
William> X/10. Thus, most of the economic benefit of reuse--compared
William> to expending--is achieved in less than a dozen uses. Going to
William> X/100 gets another 9% off of the per unit depreciation,
William> X/1000 gains 0.9% more, per flight, and so on.
But what are the continuing costs of refurbishment, versus the costs
of building an EV with reliability guarantee.
William> The details matter: RLV's cost more per unit than similar
William> ELV's, the foregone payload "cost" is significant, and, the
William> cost of reuse can be high or low, depending. All of these do
William> not much effect this simple thought experiment: most of the
William> economic benefit of reuse is captured in less than two dozen
William> uses, even for high cost RLV's.
I wonder if the real benefit of RLVs will come when they can return to
the pad with the payload when something goes wrong. This is *way*
down the road I admit. But getting things to the point where it
approaches more of the airliner model will be important.
And like airliners, engines are the driving cost/problem space.
Making them reliable (who remembers the ETOPS expansion that allowed
the birth and growth of the Boeing 777 to do trans-atlantic flights
farther than 60/90/120/180 minutes from the closest airport), all of
which was due to increased engine reliabily and demonstration of that
reliability.
That's the model I think Musk is going for with merlin, so that a
single engine out doesn't cost the mission.
In some ways, home electronics are back to the ELV model. It's so
cheap to make them, that they're almost treated like disposables. But
even then they're tested before being used to find problems.
ELVs are, to me, much more of a light and pray attempt to get
something up and working.
John
