

SpaceX CRS-4 Launch - CoachRufus87
https://www.youtube.com/watch?v=7YkCh7uOw1Y

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ChuckMcM
Interesting internal shot of what I presume is the fuel tank? Clearly some
sort of liquid. I note that the Wikipedia page [1] had this one as an F9R
mission but the rocket did not include the landing legs. In theory the next
mission they will try to re-land the first stage on something solid. I am so
looking forward to that.

[1]
[http://en.wikipedia.org/wiki/List_of_Falcon_9_launches](http://en.wikipedia.org/wiki/List_of_Falcon_9_launches)

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rrmm
That's what it looked like to me. I wonder what they wanted from that shot;
looking for slosh, remaining fuel, or how the remainder of the fuel influences
the momentum of the craft after engine cut-off?

If it's something operational, I'm kind of surprised that they would show that
on the public stream.

~~~
ChuckMcM
It is entirely unclear to me how they 'pick' what are the things they put into
the feed. I have wondered if the initial decision to stop doing live coverage
of launches was to enable more operational stuff to be done "live" but hard to
know.

One of the more interesting parts of the ULA discussion of on orbit refueling
capacity was how you might "settle" the tanks. Gravity does that wonderfully,
and of course while you're accelerating you have it covered, but when you want
to 'restart' you are in a microG environment and the fuel might not be at the
end of the tank where you want it. Simple pressurization doesn't help, the
fluid gets evenly distributed in the volume. Not much help. A fuel bladder
might work but you'd something that was very light and compressed well. I also
discussed with one of the ULA folks a movable "piston" on one end of the tank.
Basically do it like a pneumatic cylinder without the rod, You just pushed it
to the other end. He pointed out that there aren't any pneumatics that work
with hydrogen. It is just too "small" a molecule for wall seal to hold. That
leaves things like spinning to create a centripetal 'hold' on the fuel with a
narrower 'top' than bottom so that an axially spinning tank will accumulate
fuel to the bottom. Ok for payloads, not great for astronauts though.

~~~
rrmm
Traditionally, they use ullage motors, right?
([http://en.wikipedia.org/wiki/Ullage_motor](http://en.wikipedia.org/wiki/Ullage_motor)).

Perhaps they could dock with it a little harder than is strictly necessary or
use a maneuvering thruster burn.

It seems like it'd be easier to use non-cryogenic fuels (hypergolics, or
kerosene + LO2) which may make the piston idea workable. How do they keep
cryogenic fuels cool in space in the long term? good insulation and vent a
little of it off regularly?

