JF Mezei wrote:

On 2017-12-22 18:26, Fred J. McCall wrote:

You'd have to design a new upper stage that allowed refueling plus a
tanker stage to refuel it from. If you could refuel it, the existing
RP1/LOX upper stage might even have the capability for lunar work. But
we're talking hardware that would be, as yet, only a gleam in
someone's eye, unlike SLS.


What about the possibility of sending a the parts separately, but
already fueled such that refueling is not necessary?


Not enough grunt.


Launch 3rd stage, service module, lander and capsule as separate launchs
(perhaps combining capsule with lander), assemble pre-fueled components
in orbit then go to the moon.


You're talking an entire new stage, then. That's certainly an
alternative to refueling a stage.


You could also potentially combine 3rd stage with service module to
reduce the weight of extra engine and use service module (with bigger
tanks) for TLI.


So now you need a bigger Service Module engine, as well, and you're
taking a bunch of excess dry mass into lunar orbit.



I think BFR Spaceship might be too heavy for other boosters, but you
could just use it with BFR. BFR Spaceship refueled in orbit is the
whole works. It can fly to the Moon, land, take off, and return to
Earth.


Reality check question: Apollo managed to get a capsule that fell from
the Moon to re-enter earth. NASA got Shuttle to re-enter earth from as
high as Hubble orbit. Space-X has gotten Stage-1 to re-enter from
suborbital speed/altitude. (same with Virgin Galactic).

Considering BFR will be a long fat stick instead of capsule or "space
plane", how does it expect to re-enter at high speeds and remain
structurally sound?


The same way anything else does.


Is this a question of using engines to slow down such that re-entery
interface is done engine first like Falcon 9 stage-1 and engines firing
long enough to slow it down to sub orbital speeds before hitting
atmosphere?


BFR Spaceship is intended to come in nose-first. They even added some
little delta fins to give it better stability.


Would coming back from Mars create far higher speeds than coming back
from the Moon, or would "catching up to Earth" result in slower speeds?


You can still kill most of the velocity with aerobraking. BFR
Spaceship has a low enough density on return that a normal PICA-X heat
shield on the underside is sufficient. Shuttle needed the special
tiles because it was large, dense, and flying using wings and lifting
body shape (all of which add drag and increase heat loads when
reentering).


--
"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