George:
Citations? I have found nothing that remotely resembles a careful economic
analysis.
Be careful about what you think others think: I know no one in my
acquaintance who thinks SLS will “succeed” as a launch vehicle. At best,
it will prove so expensive that a very expensive cost reduction
program—lead by guess which NASA center—will be required to fix the cost.
Bill
On Sat, Aug 24, 2019 at 5:26 PM George Herbert <george.herbert@xxxxxxxxx>
wrote:
They exist, but the establishment disbelieve the assumptions.
Which is fine. We disbelieve SLS will succeed. If we’re both right it’s
going to suck. We can only test fairly if we’re both right.
-George
Sent from my iPhone
On Aug 24, 2019, at 3:43 PM, William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Peter:
Hand wavy unquantified “advantages” do not wash with the folks who ask my
advice.
If there exists a careful quantified estimate of the economic value of the
“benefits” of a depot which compelling demonstrates that the present value
of the economic “benefits” are greater than the present value of all the
costs of a depot then I would be extremely interested in seeing that
analysis.
In the telling absence of any such careful economic analysis I am going to
continue to advise that depots appear to increase the cost of space travel.
Bill
On Sat, Aug 24, 2019 at 3:13 PM Peter Fairbrother <peter@xxxxxxxxxx>
wrote:
On 24/08/2019 19:02, William Claybaugh wrote:
Peter:
If building a depot requires the development of a lower cost propellant
only launcher than that is a further argument against a depot since it
further increases the required investment.
Eh? Just send it up in eg a Falcon 9 first and second stage. As there is
no payload the unused fuel in the second stage will be plentiful.
No payload shroud, so it will need a new hat - but that's all.
I concur that there is a “depot” that is indistinguishable from
refueling from a tanker and that such a depot has little or no
amortization, depreciation, overhead, or profit charges.
You’re correct that overhead and profit should be added to the cost of
propellant at a depot, but that just seems to be gilding the lily....
To go back to your original post:
"Propellant at a propellant depot costs the price of that propellant on
the ground plus the cost of launching it to LEO plus the pro-rata
amortization of the cost of the depot plus the pro-rata depreciation of
the depot plus the cost of losses.
Propellant in an upper stage costs the price of propellant on the ground
plus the cost of launching it to LEO [plus profit and overhead]."
Hmmmm, in the second part, are you referring to launching propellant in
eg a Falcon upper stage with no payload? I got the impression not, that
you were referring to launching propellant as an integral part of a
payload - but I may be wrong.
Accepting that cost analysis, still in many cases propellant at a
propellant depot can be cheaper than propellant in an upper stage.
Why? Because the cost of launching it to LEO in a Falcon second stage,
{which makes up 90% of the cost and is the only real cost of interest -
the rest can be ignored as lost in petty cash}, can easily be cheaper
than the cost of launching it in an upper stage. Suppose you want a half
load?
Another advantage or two of a depot is that you can aggregate propellent
loads from several propellent launches before you send up the payload
with the rockets to use the propellent, so you can guarantee
availability when you launch the main payload without worrying about
vagaries like failed propellent launches or launch delays.
And you can have tugs. Yes that's some new hardware, but it means that
the propellent launches (and payloads) don't have to have their own
manoeuvre and vernier thrusters.
The main disadvantage of a depot is of course its fixed orbital plane.
Equatorial seems sensible, but there are other possibilities.
Peter Fairbrother
