[AR] Re: Faster Space Transport? (was Re: Zubrin,

  • From: Rand Simberg <simberg@xxxxxxxxxxxxxxx>
  • To: arocket@xxxxxxxxxxxxx
  • Date: Sun, 25 Aug 2019 09:13:29 -0700

The problem with SLS is not its size; Super-Heavy/Starship will be much larger. The problem with SLS is that it is not a launch system, but a jobs program.

On 2019-08-24 23:55, Peter Fairbrother wrote:

On 25/08/2019 01:13, William Claybaugh wrote:
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

No, it does *not* follow - you are comparing apples and oranges.

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.


Efficient propellent loads would all be alike - they are lumps the
size of the propellent launcher. Suppose the customer wants half a
load, or ten?

The on-orbit operations are different for tankers and depots. They
require different launch hardware, with different launch costs.

So no, you cannot make that simplistic comparison, and your conclusion
that propellant at a depot must be higher cost does not follow.


Plus, you are ignoring the other benefits of a depot. It doesn't have
to be just a fuel depot, it can do other things too. Like assemble a
very large mission craft from launch-size parts, then fill it and send
it on its way. If you have tugs there then the parts can be dumb and
immobile.

I think that a depot is actually economic and inevitable, but I am not
trying to show that here - only to show that your argument is
fallacious.



As to your implicit/explicit assumption that bigger is cheaper on a
mass-to-LEO  basis. True with caveats [1] for smallsat launchers vs
Falcon, and for Falcon heavy vs Falcon9 - but compare Falcon vs SLS
...

Bigger can be better. But there is such a thing as too big.

Suppose the customer wants a thousand-ton-at-LEO mission. Are you
going to build a thousand-ton launcher for one mission? Plus a
thousand-ton launchpad? Or assemble the mission in parts, in orbit?

SLS is just too big to be economic. And the economics of space have
changed markedly (eg with SpaceX and the upcoming Blue Origin) since
it was commissioned. It is past time to remember the sunk cost fallacy
and cancel it.


[1] like do-it-now , customer-specified orbits etc - if there were no
non-mass-related advantages in smallsat launchers then no-one would
use them :)



Peter Fairbrother

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