In article , bthorn64
@suddenlink.net says...

On Wed, 26 Oct 2011 08:14:03 -0400, Jeff Findley
wrote:

MPLM cargo is a bit more than 9,000 kg. Dragon up-mass is 6,000 kg and
down-mass is 3,000 kg. In crew mode, Dragon supports up to 7
passengers.

I don't believe Dragon is going to get anywhere near 6,000kg mass to
ISS. Its shape and volume just don't lend themselves to it. I'll be
happy to be proven wrong, though.

That's the capacity SpaceX is advertising. Agreed that in practice,
this could be different.

Again, ISS assembly is complete. There is no requirement to
duplicate
shuttle's ability to deliver entire station modules to ISS. The
requirement is cargo deliveries (and later crew rotation flights) .

I'm not the one who compared Dragon's cost to Shuttle's cost. Alan
opened that door, so the defense of Shuttle is allowed.

In any case, I think we're living dangerously in having no 'large
upmass' capability for Station. Are you really so certain there won't
be another SARJ failure or something else requiring a big spare part
that NASA has no way to launch anymore?

And there is still talk of Node 4 to fly as an "exploration node" to
ISS.

I'd think that Delta IV Heavy or Falcon Heavy could loft large masses to
ISS when used in conjunction with a Dragon service module or the service
module that Orbital Sciences is using on their ISS resupply craft. The
Russians have done the same thing with a Progress service module to
deliver their docking modules to ISS (launched on a Soyuz launch
vehicle). That and they've used TKS derived service modules to deliver
large station modules (launched on Proton). Certainly the US can do the
same.

Dragon Payload Volume: 10 m3 (350 ft3) pressurized and 14 m3 (490 ft3)
unpressurized compared to MPLM's pressurized volume of 31 m3. MPLM has
about a 3 to 1 advantage in volume.

I think it will be closer to 4 to 1 when you factor in volume that has
to be set aside for the hatch, etc., in a basically conical structure.
I said before, Dragon will run out of room (volume) long before it
runs out of mass. I stand by that, but will be happy to admit I was
wrong if SpaceX pulls it off.

The other part of the 6 to 1 is the mass carried in addition to the
MPLM by the Shuttle. Such as CMGs or ammonia tanks on the MPESS, and
all the water delivered from Shuttle's fuel cells, which was
substantial, not counted as Shuttle cargo, and counted as pure cargo
by all other cargo haulers.

So you weren't looking at a specific STS mission carrying an MPLM when
you came up with your 6:1 ratio?

Obviously the shuttle's unpressurized volume is huge, but again, we're
talking ISS resupply missions, not assembly missions, so volume isn't
quite as critical.

Whoever said resupply only involves internal stowage? Kibo and
Columbus were both built with external science equipment in mind, and
now there is very little opportunity to fly external experiments. What
little external capacity HTV has will likely end up being used for
critical replacement parts like CMGs or ammonia tanks.

Very little opportunity? I think not. HTV is flying and has provisions
for unpressurized cargo. Dragon does as well (14 m3 volume for
unpressurized cargo). I'm not sure about OSC's vehicle...

Total program cost for the shuttle was $196 billion in 2011 dollars.
There were 135 missions (including the two which destroyed Challenger
and Columbia) so the cost per flight was $1.45 billion dollars.

While that's true, Shuttle in an operational sense didn't cost that
much. We already had Shuttle, we didn't have Falcon 9/Dragon. It
wasn't going to cost $1.45 billion per flight out of NASA's budget at
the time NASA was deciding whether or not to extend Shuttle. It was
$700 million or so out of the U.S. Treasury per flight each year in
2006-2010. (It was a little higher than that, but I think we must
assume that other "space support" budget would continue to exist if
Shuttle were replaced by Dragon.)

$700 million for one Shuttle flight versus, call it one Manned Dragon
flight at $140 million each and four or five Cargo Dragons at, what
$100 million each? The numbers get interesting.

While the numbers are "interesting", shuttle isn't flying anymore.
Commercial competition for ISS resupply is the capitalist way to go
about moving forward. Costs should drop as competition should spur the
commercial providers to innovate in a way that the prior single source
cost-plus contracts did not.

You're not a socialist, are you? ;-)

If Dragon really does take six flights to replicate a typical shuttle
crew rotation and resupply mission (I doubt it would), each Dragon
flight would need to cost more than $240 million dollars.

I think $150-200 million is probably going to be the ballpark for
Manned Dragon, and I think that's a bargain. They currently claim $140
million, if I heard right, but Falcon 1 and 9 have both busted their
budgets in the past (they are still very cheap, I'm not claiming
otherwise, just not as cheap as they originally hinted they would be).
If SpaceX ends up on the high side at $200 million, is losing
Shuttle's huge upmass, downmass, and impressive in situ
construction/repair capability, and the option to fly other missions
like another Hubble repair (looking all the more desirable now that
Webb has completely screwed the pooch) really worth $40 million?

It will be interesting. SpaceX is working hard on making Falcon 9's
first stage reusable. Even if they fail at this, reusable boosters for
Falcon Heavy (a much easier problem to solve) would make 1/2 of the
stages reusable, which means well over half of the engines could be
reused per launch. Reusability could be a huge game changer for SpaceX
both in terms of improved reliability and reduced cost.

If the number
is four Dragon flights to equal a typical MPLM flight, then SpaceX only
needs to cost less than $360 million dollars.

I think they'd have to screw up a lot, or be NASA regulationed to
death to hit that high. Unfortunately, both are completely within the
realm of possibility.

True, but to me, this is still better than SLS. The one silver lining
to NASA screwing the pooch on Ares I and Orion is that they *have* to
rely on commercial providers for ISS resupply. If Ares I and Orion were
flying, NASA might have given a single finger salute to the commercial
providers and continued along the socialist path of US government only
vehicles flying to ISS.

I'm betting SpaceX can come in with costs lower than that if it's
successful in reusing Dragon multiple times, which is the plan.

I'm betting they might be able to lower costs, but they won't actually
cut their prices. Mr. Musk is still a capitalist at heart. He'll lower
his prices only so far to win contracts, no farther.

Kind of a moot point since shuttle is retired. Comparing Dragon to
Progress and Soyuz (or ATV or HTV) is a better choice.

Just reponding originally to Alan, who compared one apple (Dragon) to
a bushel of apples (Shuttle.)

Ok.

Jeff
--
" Ares 1 is a prime example of the fact that NASA just can't get it
up anymore... and when they can, it doesn't stay up long. "
- tinker