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:
I conclude that depots add cost to space flight because they plainly
so do compared to the existing architecture. To date, no payload has
failed to fly because the launcher couldn't carry it; arguing that
depots solve a problem that does not exist is simply specious.
I am aware that SpaceX is planning to make use of refueling for its
planned fully reusable architecture and that plan does appear to lower
their required investment as compared to building a bigger rocket. I
do not understand that their cost would be further lowered by paying
the cost of a depot; rather, it appears obvious that their costs would
be higher by the amount required to build and operate that depot.
Bill
On Sat, Aug 24, 2019 at 1:08 PM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
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 needany
of the attributes you conjecture and instead plan in future for arational
fundamentally different launch architecture.
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
notwhen
it's not that simple, when one (or more) of those assumptions is
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
Constellation'sLEO
departure mass from launcher payload mass, so violations of
assumptions 2
and 3 don't threaten to sink your project. Should we worry about
such
violations? Yes! They nearly sank Apollo -- which survived only
because
Wernher von Braun had quietly built a rather bigger rocket than
Houston's
spacecraft mass estimates would have required -- and
this?
troubled history conspicuously included repeated discoveries that
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
quietly
Depots are not getting any traction because the key players--whoare 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
