Jeff Findley wrote on Sun, 26 May 2019
08:43:17 -0400:

In article ,
says...

Jeff Findley wrote on Sat, 25 May 2019
08:47:58 -0400:

In article ,
says...

On 2019-05-24 06:34, Jeff Findley wrote:

Because if you look at the damn picture of the proposed time-line that's
all over online, *none* of the stages of the lunar lander are launched
by SLS. They're *all* launched on *separate* commercial launch
vehicles.

Are the separate launches all going to "Gateway" to deliver their
hardware, or would there be LEO dockings involved before the combined
parts get to Gateway ?

Everything possible goes to Gateway in order to justify its existence.
The only exception would be uncrewed landers with surface instruments,
robotic rovers, or modules/supplies to be prepositioned on the surface
for longer term crewed missions.


Well, there's that and there's the problem that if you combine
everything in LEO now you need an upper stage with enough grunt to get
the whole works to where it's going all at once. Sending little
pieces is easier. That's one of the 'justifications' for doing a
Gateway is to give an 'assembly area' to send pieces too without
having to send them all at once.

NASA is trying its best not to need LEO refueling. But, if they ever
get to the point where they're reusing crewed lander ascent stages and
transfer stages (Gateway to LLO), they'll need to be doing similar
refueling at Gateway.


True, but the 'argument' there is that everyone is docked up to
Gateway and 'tended' in order to refuel.


Ultimately, we need in orbit refueling to perform missions that are
bigger than Gateway/lunar surface. Whether that first refueling happens
in LEO (likely with cryogenics) or at Gateway (likely with hypergolics),
it's got to happen sooner or later. One of those approaches gets us
ready to go to Mars while the other simply doesn't.

NASA is making all the wrong long term investments in order to justify
SLS/Orion to the greatest extent possible. So that means delaying the
development of refueling and descoping that development to hypergolics
instead of cryogenics. NASA is deliberately choosing a path which
delays any "exploration" beyond the moon.


I think folks going to Gateway will do what Blue Origin has done and
opt for LH2/LOX engines, so it will be cryo either way. It will be
large volume 'mild cryo' in LEO (Starship) or deep cryo (LH2/LOX) at
Gateway. The big 'delay' in exploration beyond the Moon is that I
think the NASA plan assume in situ fuel manufacturing on the Moon
before they go for deep space. Deep Space exploration vehicles would
fly to Gateway, refuel with lunar LH2 and LOX, and depart. This makes
some sense in that getting fuel up from the Moon is much 'cheaper'
energetically than boosting it up from Earth, but it impacts your Mars
infrastructure as well, since now your in situ fuel factory there has
to find ice and make LH2/LOX out of water rather than making LOX and
liquid methane out of the atmosphere.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw