
SpaceX set to launch ‘used rocket’ - ethbro
http://www.bbc.com/news/science-environment-39437407
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jessriedel
As usual, /r/SpaceX is a treasure trove of information about this launch.

[https://www.reddit.com/r/spacex/comments/62aqi7/rspacex_ses1...](https://www.reddit.com/r/spacex/comments/62aqi7/rspacex_ses10_official_launch_discussion_updates/)

[https://www.reddit.com/r/spacex/](https://www.reddit.com/r/spacex/)

Here's the SpaceX press kit:

[http://www.spacex.com/sites/spacex/files/finalses10presskit....](http://www.spacex.com/sites/spacex/files/finalses10presskit.pdf)

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H4CK3RM4N
I'm always amazed at how different /r/SpaceX and /r/Tesla are from the rest of
Reddit.

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TulliusCicero
People often lump different subreddits together too much. /r/gaming and
/r/games are both ostensibly about video games but their content and culture
are very different from each other.

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sealjam
I find the difference between r/golang and r/node quite marked.

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blhack
Could anybody here comment on the differences between spacex's engine, and the
engines on the space shuttle?

I was under the impression that SpaceX was trying to make the first re-usable
rocket stage, but I've recently found out that that isn't true. The space
shuttle already holds that title.

I'm also kindof curious why they decided to go with a vertical-landing-design,
instead of putting some wings on it and having it glide home like the shuttle
did. Is that a weight-concern? Aerodynamics, mabye, but couldn't the wings be
articulated in the same way that the landing legs are right now?

(I will admit some ignorance in this field. I'm definitely a fan, but I'm
definitely not a historian or a rocket scientist)

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pdelbarba
The engines have minor differences, namely that the space shuttle used fully
closed cycle engines while the falcon 9 does not. All this means though is
that the efficiency is slightly lower because some of the propellant is burned
and the combustion product dumped overboard to power the turbo pumps that push
the rest of the propellant into the main combustion chamber. While this
reduces efficiency, this makes the engine somewhat easier to design and I
believe the next gen spacex engines will have this feature.

The vertical landing design is actually really smart because it allows a
relatively un-aerodynamic object to get back to the ground without adding
heavy wings and fairings. Rockets don't actually like having fins when they go
up since the dynamic pressures get to be extremely high. Rather, they opt for
gimbaled engines to steer (this also helps when there's no atmosphere to steer
with). The only downside to this approach is that some of the fuel has to be
retained for the return trip, though this is a relatively small fraction. The
other huge issue you have to deal with when gliding back is having some sort
of landing gear in addition to the control surfaces. You can put wheels on it
but that's a lot of weight and if you land it horizontally, without the
pressure of the propellant keeping the body rigid, it will most likely
crumple.

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greglindahl
F9 FT can launch ~ 5.3 metric tons to GTO with landing, or ~ 8 metric tons
without. I'm not sure if I'd call that a relatively small penalty. It does
allow SpaceX to launch most GTO satellites. I expect Block 5 will do a bit
better.

~~~
itp
I think both views are essentially correct. It is a relatively small fraction
of the fuel load, but thanks to the impact of the rocket equation, that
relatively small fraction translates (as you are pointing out) to a sizable
difference in payload to a given orbit.

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the8472
It is interesting that they are confident enough to launch it with a
commercial payload instead of doing a test flight with a dummy second stage.

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manicdee
The static fire yesterday was enough proof for SpaceX that everything is
working as expected. After that the major undetected flaws will show up some
time from launch through MECO :D

SpaceX will no doubt discover new failure modes that nobody has thought of up
till now (and thus were not looking for, and thus did not detect).

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foota
In a static fire the rocket is "tied down" to the ground. Do you know how the
stress profile presented by this differs from a real launch?

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manicdee
Vastly different, but the most likely point of failure is the moving parts, as
tested in the static fire.

Other parts that failed had been successfully used in flight so a "dummy
launch" would have provided no certainty other than "everything worked this
time."

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aerovistae
Fingers crossed. In theory it shouldn't be any more dangerous than a first-
time rocket, given that they've examined every inch of it and deemed it
flawless. If it weren't flawless, obviously they wouldn't be trying to fly it.
So we're just hoping there isn't some unanticipated source of entropy, so to
speak. As always.

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nether
Not to be pedantic, but it's not possible to inspect an entire rocket for all
defects because so many of them are microscopic and internal (not on the
surface of a solid part). These can be analyzed and predicted with fatigue
models in aggregate with varying levels of certainty. This comprises the
fascinating field of fatigue analysis.

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SEJeff
While you're correct, you're not pedantic enough. Using X-rays to validate the
most critical engine parts has been done for literally years and is a
relatively boring and old part of "rocket science". Don't expect SpaceX to
spend some serious cash on this and techniques such as this (MRI and sonic /
ultrasound tech comes to mind).

Source: a good friend of mine is a structural engineer for Aerospace
Corporation (a rocket scientist if you will) and I'm an avid r/SpaceX reader.

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unwind
Uh, you meant "Don't expect SpaceX _not_ to ...", or "Expect SpaceX to ...",
right? I had a negation parse error.

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SEJeff
Well played sir, well played, and yes! :)

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benmorris
I'm pretty stoked we are staying right next to Jeti park on spring break and
are planning on watching this launch tonight from the beach. We've got to see
one other Delta IV launch, but really looking forward to seeing this one. We
just missed OCSILY heading out to landing zone, but I got a good view of the
parking spot and unloading area.

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TeMPOraL
The BBC article doesn't use the word "today" anywhere in the text, nor does it
provide a date. Does "X set to do Y later" in journalism-speak mean "later
today" instead of "later somewhen"? Is this another idiosyncrasy like using
commas instead of "and"?

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newhere420
In Britain, you commonly use it in that form. For example, we might say "want
to do X later?".

Perhaps it's just British?

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freehunter
I feel like it's a little different when you speaking to someone versus in a
news article. I could read the article tomorrow and be very confused, but I
won't hear you say those words tomorrow unless you actually mean tomorrow.

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woodandsteel
Looks like SpaceX is going to sell the rocket:

[https://losangeles.craigslist.org/lac/for/6067287590.html](https://losangeles.craigslist.org/lac/for/6067287590.html)

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andromeda__
The incumbents said it couldn't be done...

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InclinedPlane
It's pretty common for people to make a hard problem out to be much more
difficult than it actually is if they have a track record of failing to tackle
it. The reality is that the problem is not that terribly difficult, all things
considered. That's not to diminish SpaceX's achievement, what they've done is
genius. But their genius is primarily in avoiding falling into the common trap
of optimizing an expendable rocket to the detriment of any hope of easy and
beneficial reuse of part of it. And indeed the most logical optimizations of
expendable rockets tend to push the design in precisely that direction, so it
takes a considerable amount of sticktoitiveness to avoid that pitfall.
Additionally, they figured out how to do reusable R&D very effectively and
cheaply (by using commercial launches to subsidize most of the costs).

Together this has led them to success, but any space-faring nation or
organization with a few billion dollars sitting around could have achieved the
same thing, they just didn't have the courage or foresight to do so. Indeed,
Blue Origin will probably follow along and reproduce the same achievement in
orbital rocketry within the next 5 or 10 years or so. And I expect others to
follow as well, once a model that can be easily copied has become established
and its advantages proven.

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ygra
I guess the fact that it hasn't been done so far is in part due to lack of
technology (bot materials and processing power) and the lack of necessity.
Space programs have been purely national affairs for a long time and cost for
the rather few launches was not really an issue. Even more so when the
launcher was developed off ICBMs where development costs were already paid for
with a military budget.

And, well, as long as no cheaper competitor comes along it doesn't matter if
launch prices are high since whoever _needs_ to launch something just _has_ to
pay them.

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nickik
Well it was done. The Space Shuttle was this exact idea. The problem was just
that it did not work and nobody wanted to try it again.

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brogrammer2
Hello,

If this launch is successful, how much money SpaceX would have saved by using
a 'used rocket' instead of a new one?

~~~
ygra
No one knows for now, as refurbishment costs are a big unknown (and I don't
think SpaceX will release those numbers at this point). The cost of the first
stage is a significant part of the overall rocket cost, though, considering
it's the largest part, and it has 90 % of the engines (each of which costs
about a million already).

Since they took four months to refurbish this stage it may have cost quite a
bit to do so for now. But they're learning and Block 5 to debut later this
year will have lots of changes based on what they learned.

~~~
simonh
In fact optimizing the Falcon 9 for first stage re-use has lead it down a very
different development path from most modern launchers.

On an expendable architecture the priority is saving weight on the second
stage, because every kilogram saved there saves many kilograms for the first
stage. So pound for pound the second stage usually costs more than the first
stage. Also the cheapest way to build a first stage is with one or just a few
big engines. Both these optimization criteria are reversed for a re-usable
design. In the Falcon 9 the first stage is re-used while the second stage
isn’t, so that’s the stage you want to spend your money on. Also a few big
engines can’t be throttled low enough or gimbaled precisely enough for a
landing burn. Even the using just one of the relatively small engines in the
Falcon 9 can’t be throttled low enough to hover. Hence the Falcon 9 has many
smaller engines to give it a much greater range of thrust settings and better
attitude control.

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jlebrech
reusability is the key to commodity rockets. look at the car and how
depreciation works, people will own a rockets after 5 owners for a
ridiculously cheap price. at that point fuel will be the number one cost issue
and the fuel source will charge.

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usrusr
Expect used rockets to be about as comparable to used cars as used cars are
comparable to used chewing gum.

~~~
jlebrech
you're right, it'll be companies buying used rockets.

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jlebrech
methane fuel is what we desperately need now, methane is the number one danger
to our atmosphere and burning it is the most ecofriendly way of disposing of
it.

~~~
simonh
I'm pretty sure any methane fuel they use will be manufactured for the purpose
rather than extracted from the atmosphere. That means there's bound to be some
leakage.

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jlebrech
leakage is happenening here
[http://siberiantimes.com/ecology/casestudy/news/n0681-now-
th...](http://siberiantimes.com/ecology/casestudy/news/n0681-now-the-proof-
permafrost-bubbles-are-leaking-methane-200-times-above-the-norm/)

we could extract this before it get's into the atmosphere.

~~~
simonh
The Russians happen to have a shiny new launch complex in Siberia. Just
saying.

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jlebrech
smart move

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ivanb
When you launch single-use rockets every next one is more advanced and
reliable than the previous one. It includes some of the error corrections that
were found during previous launches. This is an often ignored point.

I highly doubt that reusable rockets would be economically viable at our
current state of material technology. We need better materials for the engines
and the tanks to make them reusable. Even airplanes have to be retired when
they still look new just because they've been through multiple
pressurization/depressurization cycles and accumulated microfissures. Of
course they are not even close to the levels of stress sustained by rockets.

~~~
JshWright
I think your point is weakened a bit by the fact that SpaceX is both the only
company flying a rocket designed for re-usability, as well as the company that
is iterating their design far faster than any of their competitors.

SpaceX has had trouble getting approved for Air Force launches in the past
because they "tweak" the design of Falcon 9 too often. They had to commit to
NASA to fly seven launches of a "fixed" design (what SpaceX is calling "Block
5") before they will be allowed to fly crewed missions (for NASA).

