One does not need to do an "economic analysis" to know that bulk
deliveries of a commodity are cheaper than specialized ones, and that
more stages improve transportation efficiency, particularly when they
aren't thrown away. We will be delivering propellant to orbit that is
not mission specific, and whether we put it in a Starship, or a depot,
or a handbasket, doesn't really matter. The days of a single launch
sending a payload to a non-LEO destination, at least as the normal way
of doing things, are coming to a close.
What will happen will happen, regardless of your economic analyses.
On 2019-08-24 16:46, William Claybaugh 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:have
Then why is SpaceX not building a depot?
Is it remotely possible that they have done the same analysis I
done?<simberg@xxxxxxxxxxxxxxx>
Bill
On Sat, Aug 24, 2019 at 5:13 PM Rand Simberg
wrote:is
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
payload
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
thathas
failed to fly because the launcher couldn't carry it; arguing
depot.depots solve a problem that does not exist is simply specious.its
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
you<simberg@xxxxxxxxxxxxxxx>
Bill
On Sat, Aug 24, 2019 at 1:08 PM Rand Simberg
wrote:
We are on the verge of getting a fundamentally different launch
architecture. Probably more than one. I don't understand why
Ithink
that depots are costly.
On 2019-08-24 12:04, William Claybaugh wrote:
Henry:
I’ve reread this post more than a few times and I’m afraid
forneedam
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
any
of the attributes you conjecture and instead plan in future
pro-rataa
fundamentally 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:
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
theamortization
of the cost of the depot plus the pro-rata depreciation of
ondepot plus
the cost of losses.
Propellant in an upper stage costs the price of propellant
specialthe
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
4. Reduced upper-stage launch mass doesn't confer some
thanistank aadvantage,
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
because
Wernher von Braun had quietly built a rather bigger rocket
tothatConstellation'sHouston's
spacecraft mass estimates would have required -- and
troubled history conspicuously included repeated discoveries
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
players--whothis?
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
