
SpaceX to Debut Upgraded Falcon 9 on Return to Flight Mission - situationista
http://spacenews.com/spacex-to-debut-upgraded-falcon-9-on-return-to-flight-mission/#sthash.ZmZMNGJu.uxfs&st_refDomain=t.co&st_refQuery=/F3UyTaBjV5
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smoyer
"I want to _stick a landing_ this year"

That's a gymnastics phrase for landing on your feet (with no bounce) during a
dismount and is a pretty appropriate analogy for what they're trying to do
with the Falcon 9 first stage.

To carry the analogy further, the second landing attempt could have been a
"one hop" landing if they'd had a bigger drone ship. The first landing (which
needed a bit more propellant to keep the stage upright) would have succeeded
as a "one step" dismount - if the stage could actually take a step with it's
legs.

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ohitsdom
I wouldn't take that phrase too literally. I take it to mean that she wants
them to actually land a rocket (not necessarily on all feet with no bounce).
The other attempts were "landings", but they blew up. Bounce or no, if they
land the rocket upright, I think that's sticking it.

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ethbro
The problem as I understand it, and I think what smoyer was talking about, is
that there are no other viable landing methods for the rocket than "feet"
first.

Sufficient thrust is only available from the main engines, and those only
point in one direction.

So if it starts to tilt off vertical then the rocket has no way to right
itself after a point (and certainly no way to counteract gravity). Gravity +
tall enough rocket + landing on side = boom (or crumple).

So "stick it or bust"?

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ohitsdom
There are cold gas thrusters on top of the first stage that fire to keep its
balance. If it lands in an uneven manner and starts to tip, those should be
enough to maintain the landing. You can see them working in the video embedded
in the link below. They only didn't work in that instance because the main
rocket motor fired too long at it was too much for the small thrusters.

[http://www.spacex.com/news/2015/06/24/why-and-how-landing-
ro...](http://www.spacex.com/news/2015/06/24/why-and-how-landing-rockets)

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grinich
I think the bigger issue is that idle thrust of a single Merlin engine (which
is used to land the first stage) produces more force than gravity on the
vehicle.

This means it can't "hover" so the final burn must be timed with exact
precision to have ~zero velocity on impact. Doesn't give a lot of room for
error.

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Symmetry
The other side to the upgrade to the Falcon 9 is chilling down the fuel more
than normal so that it shrinks and they can fit more of it in the rocket's
tanks.

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avian
Do you have any reference for that? It seems to me that further cooling
already liquified fuel doesn't give you any noticeable difference in volume.

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mikeash
Why not? According to a random page I found on the internet, kerosene has a
coefficient of thermal expansion of 0.00099 per Kelvin. If you can cool it by
50 degrees then you'll be able to store about 5% more fuel in the same volume
of tank, which is a nice little upgrade.

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akshayB
I just want to see a Klondike Bar in middle of ocean and a pencil on top of
it.

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gadrfgaesgysd
Looks like they are taking the software approach to fixing things.

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creshal
Still an improvement to the Von Braun approach, I'd guess.

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kakali
What's the Von Braun approach? I mean, his work was a model for hardware reuse
and improvement every launch. (I think considering the Atlas, Titan, and
Saturn 1.)

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creshal
V2.

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benihana
> _that features engines with increased thrust, providing an increase in
> performance of about 30 percent._

I'm not a rocket engineer but this sounds like a mind-blowingly good increase.
Is it just that they're early in the development of the engines and since
they're taking an iterative approach this is just low hanging fruit? Even if
that's the case, 30% increase seems impressive.

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VLM
By careful selection of metric goals, impressive results can be achieved with
little change. (this is a summary of modern american corporate process LOL).

So if your metric is pounds of payload delivered to orbit, for example,
rockets are usually pretty heavy compared to the payload delivered so a rather
small improvement in thrust to weight ratio can have seemingly extreme
improvement in pounds delivered. You're still launching a million pounds
sitting on the pad, its just removing a mere 300 pounds of insulation over
than million pound booster means you get 1300 of payload delivered instead of
1000.

Rockets have all kinds of interesting problems with thermal limits and
combustion instability and its very easy to defeat those problems at
considerable weight penalty and then when telemetry consistently shows the
nozzle temp is fine at full flow rate and projections show 80% flow is fine,
then next model has microscopically smaller pipes or whatever. And repeat many
times and next thing you know you've gained quite a bit of performance. Its
hard to add fluid flow baffles to an existing system, but if it works with
existing baffles its usually much easier to slowly remove them.

There is another spacex specific issue that to do the "land on a barge" thing
general opinion is they overspec the marketing numbers to about 30% less. I
don't know how much, if any, current improvement is lowering that to 27% or
whatever. If you were to give up on recycling boosters and one-shot the
booster, the marketed performance specs would go up a bit without any
engineering changes (well other than software to land wouldn't be necessary,
LOL).

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ziedaniel1
I think you're underrating the difficulty of this kind of improvement. Rockets
already have to be extremely well-optimized to reach orbit, so there wouldn't
be the kind of low-hanging fruit like removing 300 pounds of insulation
without side effects. Also, if you want weight reductions to give payload
increases in a 1:1 ratio, the weight has to be taken off of the final stage
(in F9's case, the second stage); removing it from earlier stages gives you
much less benefit.

