JF Mezei wrote on Sun, 26 May 2019
14:01:35 -0400:

On 2019-05-26 12:09, Fred J. McCall wrote:

Because that's more complicated and requires a tanker vehicle that's
capable of refueling it. In other words, YOUR way takes longer, costs
more, and is more expensive to operate. Perhaps NASA has a job for
you?


SpaceX already has the software for Dragon2 to dock to another ship.


You say this like you have a point. You don't.


SpaceX is already planning on-in-orbit refueling and originally set to
go to mars by 2024. Surely the refueling mechansims are already in
development?


You say this like you have a point. You don't.


Surely those mechanisms could be fitted/tested on Falcon based vehicles
before BFR/BFS are in service?


Gee, USAF already knows how to do in flight refueling of aircraft.
Boeing already knows how to build supersonic aircraft. Surely all
that stuff could be fitted/tested on Piper Cub based vehicles?


Also, if a Falcon Stage 2 were sent up with a large tank for itslef in
lieu of any payload. Could the actual payloads launched separately then
dock/attach to it and the bit-tanker Stage2 then act as the CDM to bring
all the hardware between LEO and Moon ?


Unlikely and I'm not going to go to the effort to do the math to prove
or disprove it. It's your loony idea. YOU prove whether it will work
or not.


Or is the extra fuel needed for LEO-Gateway trip with all the hardware
attached to it (lander, ascent, transfer) too much to be carried to LEO
by a Falcon Heavy in single launch?

Using a Stage 2 with big fuel tanks would eliminate the need for fuel
transfers.


OK, but even Falcon Heavy cannot get a second stage to LEO with more
than about 54 tonnes of fuel on board in lieu of cargo. So that's
what I've got to get from LEO out to Gateway. I have to take the dry
mass of the second stage (a little under 4 tonnes), the mass of the
Ascent and Descent Elements (if we assume something about the mass of
the old LEM that's around 15 tonnes, give or take; using NASA numbers
for something more modern with more people you get 24-28 tonnes), and
the mass of the Transfer Element (which NASA thinks comes in around
12-15 tonnes). So the total mass you need to get to the Gateway from
LEO comes in at around 40-45 tonnes with 54 tonnes of fuel on a stage
with an Isp of 348 seconds. Getting from LEO to L2 is around 3400 m/s
delta-v. The kludge vehicle can manage a little over 2900 m/s of
delta-v.

You can't get there the way you're proposing, even using a pair of
Falcon Heavy launches. If you assume you can fully fuel the Falcon
second stage, you can get a little under 4100 m/s and you can. But
you need a second stage that can 'dock' to your other assembled
components, that can be refueled on orbit (you need at least 80 tonnes
of propellant aboard), and a 'tanker stage' that can refuel it. You
need three Falcon Heavy launches to get all this up there. Easier and
cheaper to change no vehicles, load the three pieces on separate
Falcon Heavy, and make three Falcon Heavy launches.

Will you stop proposing stupid **** now?


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn