On Mon, 12 Sep 2016 17:26:25 -0400, JF Mezei
wrote:

On 2016-09-12 13:14, wrote:

http://www.techinsider.io/blue-origi...rockets-2016-9



Is there commercial demand for such a heavy lifter?

There will be, now that there are two (maybe three, but I suspect
Falcon Heavy will eventually be replaced by variants of SpaceX's BFR.)
Comsats are about to get a lot bigger.

Or are its hopes
pinned on governmentds funding the assembly of a large mars expedition
ship, at which point a heavy lifter can be of use to bring the large
modules with fewer flights?

It looks like SpaceX (Mars) and Blue Origin (Orbital Tourism, strong
hints about Lunar Tourism with their talk of New Armstrong) will be
their own core customers. They'll pick up commercial contracts along
the way just due to their price points, and will likely establish new
markets. Space Solar Power just became much more realistic (although
it will still need oil to spike again.)

Secondly, what is the advantage of having a 3rd stage as oppposed to
making a bigger tank for 2nd stage for longer burn with same delta-V ?

You don't lug the extra drymass of the larger stage on missions that
don't need it. The third stage might also have other uses in the
future (lunar tug? orbital tanker?) He might plan on recovering Stage
2 in New Glenn Mk.II.

Since both second and 3rd stages are single engine, I don't see much of
an advantage of having 3 stages since you end up pushing one extra
engine and all extra weight to orbit.

If LOX/LH2 is so much more efficient than LOX/LNG, why not make second
stage LOX/LH2 ?

It would have to be bigger/heavier. Bezos might (probably does?) also
have Stage 2 reusability in mind for down the road, so he's saving
mass for that application.

Brian