A fair point:
Let’s start with repetition: the costs associated w/ building and
operating a depot must be paid by the users. It accordingly follows that
propellant at that depot must be higher cost than propellant that does not
carry the amortization, depreciation, overhead and—if for profit—the profit
associated with building and operating that facility.
Is that enough or should I go on? I can actually go on in very
great detail....
Bill
On Sat, Aug 24, 2019 at 6:07 PM DH Barr <dhbarr@xxxxxxxxx> wrote:
At the risk of getting yelled at, what careful economic analysis have YOU
presented to this thread?
Not that I or we are entitled to any such thing, just goose-gander etc.
On Sat, Aug 24, 2019, 6:47 PM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Rand:
They don’t need a depot because they designed their architecture to avoid
it; that appears—to me—to have been a thought choice. I previously reached
similar conclusions in a proprietary study for a former employer.
You’ve a gift for assertion; please, where is the economic analysis that
proves your many claims correct?
Bill
On Sat, Aug 24, 2019 at 5:30 PM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
Because they don't think they need one. That doesn't mean that others
won't find it useful, or even that SpaceX wouldn't if someone else did
it.
We've needed to decouple LEO launch from other destinations for a long
time, and until we do so, we won't drive down the overall costs as much
as possible with rockets. Having a place to leave propellant, whether
excess flight reserve, or just some in the tank because the launch
payload was light, will decrease the cost of propellant on orbit on the
margin, and perhaps quite a bit. The effect of sending everything to
LEO, including propellant, and then departing from there with an
in-space transfer vehicle has the efficiency effect of adding another
stage, that is fully reusable. It's how we would have done things long
ago if we had wanted to build an affordable transportation
infrastructure, but we got sidetracked by Apollo and USAF conservatism,
in which few could imagine not getting to the final destination in a
single launch. Boeing's electric GEO birds are just the first step in a
process that is now underway.
On 2019-08-24 16:16, William Claybaugh wrote:
Rand:
Then why is SpaceX not building a depot?
Is it remotely possible that they have done the same analysis I have
done?
Bill
On Sat, Aug 24, 2019 at 5:13 PM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
The whole point is to replace the existing architecture with one
that is
much more scalable and cost effective. With the coming space
transports
from SpaceX and Blue Origin, and the new smallsat launchers, that is
happening in real time.
On 2019-08-24 14:29, William Claybaugh wrote:
Rand:plainly
I conclude that depots add cost to space flight because they
so do compared to the existing architecture. To date, no payloadhas
failed to fly because the launcher couldn't carry it; arguing thatits
depots solve a problem that does not exist is simply specious.
I am aware that SpaceX is planning to make use of refueling for
planned fully reusable architecture and that plan does appear tolower
their required investment as compared to building a biggerrocket. I
do not understand that their cost would be further lowered bypaying
the cost of a depot; rather, it appears obvious that their costswould
be higher by the amount required to build and operate that depot.<simberg@xxxxxxxxxxxxxxx>
Bill
On Sat, Aug 24, 2019 at 1:08 PM Rand Simberg
wrote:need
We are on the verge of getting a fundamentally different launch
architecture. Probably more than one. I don't understand why you
think
that depots are costly.
On 2019-08-24 12:04, William Claybaugh wrote:
Henry:am
I’ve reread this post more than a few times and I’m afraid I
not able to make sense of it.ignore
If I understand your argument, it is at heart that we should
the 60 plus year existence proof that chemical rockets do not
aany
of the attributes you conjecture and instead plan in future for
isfundamentally different launch architecture.rational
Setting aside the improbability of selling this idea to any
investor or government, I don’t see the point: architecturesthat
require refueling don’t require a depot or it’s costs.<hspencer@xxxxxxxxxxxxx>
Bill
On Fri, Aug 23, 2019 at 2:56 PM Henry Spencer
wrote:the
On Fri, 23 Aug 2019, William Claybaugh wrote:
Propellant at a propellant depot costs the price of thatpropellant on the
ground plus the cost of launching it to LEO plus the pro-rataamortization
of the cost of the depot plus the pro-rata depreciation of thedepot plus
the cost of losses.
Propellant in an upper stage costs the price of propellant on
eitherground
plus the cost of launching it to LEO.
True if:
1. The cost of launching an extra kilogram to LEO is the same
mass.way.
2. There is extra room in the tanks for it.
3. The lower stage has the lift capability to carry its extra
tank a4. Reduced upper-stage launch mass doesn't confer some special
advantage,
like seriously reduced structural mass, that's very important
later.
Which is to say, if it's just a matter of whether to fill the
advantagebit
more, that does indeed usually win. Depots et al show to
when
it's not that simple, when one (or more) of those assumptions
aboutnot
thattrue.
It's appealing to think (or at least claim) that things *are*
decouplesimple.
Trouble is, often they aren't.
For example, an important advantage of depots is that they
LEO
departure mass from launcher payload mass, so violations of
assumptions 2
and 3 don't threaten to sink your project. Should we worry
onlysuch
violations? Yes! They nearly sank Apollo -- which survived
thatConstellation'sbecause
Wernher von Braun had quietly built a rather bigger rocket than
Houston's
spacecraft mass estimates would have required -- and
troubled history conspicuously included repeated discoveries
players--whothis?the
rockets were undersized. Let's see, that's 2 out of NASA's 2
previous
attempts to reach the Moon that had big trouble with those
assumptions --
should we really believe that the current attempt is immune to
Depots are not getting any traction because the key
quietlyare at
OMB and the Space Council--know these facts.
Or because they are getting their briefings from folks who
aren't
discussing the dubious assumptions underlying these "facts".
Henry
