In article ,
says...

On 2018-03-13 05:53, Jeff Findley wrote:

BFS. It could be that the first BFS would be similar to Grasshopper or
Enterprise in that it won't have all the systems necessary for
supporting a crew in space. Automated testing only.

Thanks. Hadn't thought of that.

Does the ability to land on Earth absolutely imply the ability to take
off from Earth? (I know BFS is to be able to take off from Mars).

It had better, otherwise what's the point? How else would you do these
short test flights like Grasshopper did.

(I realise the prototype will be empty shell and much lighter so usable
for tests, just curious about whether the ability to take off from Earth
comes automatically with ability to land on Earth).

Why would they do that? The only thing that was grossly wrong on
Grasshopper was the landing gear, which was over engineered so as not to
lose the test article on a relatively "hard" landing. Again, they'll
build it as close to the "real thing" as they can.

Note that is what NASA did with Enterprise. Enterprise was originally
going to be "refitted" to be space-worthy. But the cost was higher than
starting with the Structural Test Article, so that became Challenger.
Enterprise was not built to be a museum piece after the approach and
landing tests.

I know that spaceX has been pushing composite tank size limits by a huge
margin for the first stage. Is the 2nd stage/BFS also beyond current
"commodity" tech for tanks?

They built a full scale tank two years ago and pressure tested it:

http://www.businessinsider.com/space...nk-ocean-ship-
test-2016-11

Asking in a context of wondering how much new tech needs to be ready to
make first flight possible. (aka: how far ahead SpaceX is in developping
the new tech that makes the scaling to BFR possible).

Raptor is the "long pole in the tent", IMHO.

You can do a partial fill for short "hops". Does your car's gas
tank
need to be full to make a trip to the grocery store?

Thinking in terms of keeping the methane liquid long enough in such a
large tank. Will the tanks be pressurized to maintain the methane
liquid, or will it be a "reduce the boiling rate and vent excess
pressure" on pad like for shuttle's ET?

It will almost certainly be cryogenic just like the LOX in order to
maximize density and minimize tank mass.

Note: you car may not worry about fuel sloshing around in a small car
tank, but fuel trucks worry very much about it when the tanks are not
full, which is why they have separate tanks in the big one, and each of
those smaller tanks have baffles to reduce movement as truck
accelerates/brakes/turns.

BFR/BFS isn't a tanker truck, but sloshing is one of the potential
problems. That's why launcher tanks typically have anti-slosh baffles
in them.

Jeff
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