In article , nospam@
127.0.0.1 says...

Jeff Findley wrote:
Because recovering them intact attached to the first stage would allow
them to "gas and go", which is always going to be cheaper than re-
integrating the engines on essentially a new launch vehicle.


...[snip covered territory]...

Also note that one of the biggest advantages of reusing an entire stage
is that it helps with reliability. You can test fly a reusable stage
without risking an actual payload. But, every flight of an expendable
vehicle is the first flight for that copy of the hardware, so any
problem which crops up with the hardware could lead to a launch failure
and loss of payload.

A "gas and go" option would be ideal, however as addressed in the
"Grasshopper" thread it would seem we are talking about a nearly vertical
trajectory for the 1st stage. Then what? Coming down on chutes until nearly on
the ground and then restart a few of the Merlins for the final 1000 ft or so?

I would think it would coast downward (near terminal velocity for the
relatively "fluffy" stage) and relight the center engine fairly late in
the descent to save on fuel.

Coming down solely on engine power seems like a lot of wasted fuel to be
taking along on the 'up' leg.

After killing the horizontal velocity and being put on a trajectory back
to the launch site, I'd think that either the engine will be deeply
throttled down during the rest of the descent (or perhaps completely
off) until needed for final deceleration and landing. Fairly low
terminal velocity is an advantage of landing on a planet with a fairly
dense atmosphere.

I'd be particularly interested in whatever the cross-range capability of this
is. I mean what about winds aloft on the descent? The aerodynamics seem mind
boggling to me.

With the big heavy engines in the base, I'd think a long stage like this
would naturally come down engines (and landing gear) towards the ground.
It's essentially a really big lawn dart! :-)

As for landing, with a big enough engine, you can do pretty much
anything you want. ;-)

You mention the complications of changing the 1st stage to handle ejecting the
engines from the tankage and I agree with that, but this plan sounds just as
complex if not more so to me.

Almost to the point of my saying ... pie -- sky....

Which is why you start with Grasshopper. You fly a bit, tweak things a
bit, and fly some more. What impresses me most about SpaceX is their
willingness to actually build, test, and fly hardware on a regular
basis. There are some things you just can't learn in simulations.

When was the last time you saw one of the big government contractors
build and fly something as big as one of their first stages just to test
a few things?

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