

Recovering SpaceX’s Falcon 9 Ocean Landing Video - kilroy123
http://www.nasaspaceflight.com/2014/06/recovering-falcon-9-ocean-landing-video-done/

======
mikeknoop
Raw video:
[https://www.youtube.com/watch?v=7m8H8OlJ3o8](https://www.youtube.com/watch?v=7m8H8OlJ3o8)

Recovered video:
[https://www.youtube.com/watch?v=CjZ33C9JZTM](https://www.youtube.com/watch?v=CjZ33C9JZTM)

~~~
codezero
Wow, looking at the original, that recovery is pretty amazing!

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TrainedMonkey
"SpaceX improvised, sending CEO Elon Musk’s private jet out to the landing
area with a small satellite dish affixed behind a window. The plane kept a
safe distance from the re-entering stage, but managed to retrieve telemetry
confirming that the landing had been completed successfully.

...

On April 28, SpaceX published both the original and the partially repaired
video stream on their web site, and asked the world for help.

...

The main response came from the NASASpaceFlight.com forum, with several
skilled programmers and computer experts willing to take up the challenge. The
first results came surprisingly quickly."

So, it would be more accurate to say that people from NASA forums figured it
out. In particular special version of FFMPEG decoder was written for the task.

~~~
Narishma
It's NASASpaceFlight.com forums, not NASA forums. AFAIK, they're not
associated with NASA.

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NamTaf
I love these post mortem write-ups. Also, the idea of Elon sending out his
private jet with a satellite dish pointing out the window is duct-tape-fixes-
everything Engineer-solution as hell. I love it :D

~~~
nardi
Even better, it wasn't a satellite dish. It was a _pizza dish._

Source: [http://youtu.be/F3Hoz7_s6pQ](http://youtu.be/F3Hoz7_s6pQ) (about
2:40)

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XorNot
God damn. The recovered video is an _amazing_ improvement. I hope the special
FFMpeg version finds some more use in the future - that seems like a massively
beneficial spin off tool.

~~~
rasz_pl
Sadly recovery was mostly manual guess work. There was some talk of modelling
distortions, but manual process was too advanced at that point.

Most of this could of been avoided if SpaceX used SDR to receive that video
signal. Its vastly easier to recover when you have original distorted I/Q than
trying to guess what went wrong in hardware black box receiver. Original Video
transport stream is encapsulated, encoded and modulated using one of the DVB-
something schemes. Those provide robust FEC (error correction).

SpaceX provided file was a result of radio stream badly interpreted inside
some black box receiver, there was no FEC any more to help automated recovery.

Lets hope SpaceX learned a lesson and will use SDR in the future (and bump up
FEC rate to 1/2 in bad weather)

~~~
wolf550e
And don't use interlaced video!

~~~
Already__Taken
I think they've learnt that one the latest F9R-dev flight looked like it
wasn't interlaced.

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trhway
just an observation to put Musk's achievements in perspective - Russia failed
today to perform maiden launch of its new Angara rocket design. The design is
the first new design since USSR times, has been 20+ years in development and
its main feature is the Unified Module architecture. Basically the same module
approach as Falcon 9/Heavy. Musk took half the time to successfully develop
and put his system to use and has very real and plausible chance of getting it
into man-rated flights (this may be very-very far plans for Angara, well after
[and if] Russia makes unmanned Angara flights successful)

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mrfusion
I'm curious what happened to damage the video in the first place? Did the
vehicle record a normal quality video, and then it got corrupted over
transmission? Wouldn't corruption like that be random though, and not within
the encoding?

~~~
smackfu
The vehicle transmitted MPEG4 video, that then had byte level corruption due
to transmission issues. MPEG4 really doesn't like corruption.

~~~
mrfusion
Ok so it was fine before transmission? But the article was talking about early
blocks messing up the encoding on following blocks. I'm thinking if there are
transmission errors it would be more like incorrect or flipped bits? Why would
that affect encoding?

Or is the transmission streaming, or is the receiver re-encoding it?

~~~
jreimers
The earlier blocks being corrupted would affect later blocks because the later
blocks are encoded as the difference from the previous block, hence the error
of the previous block propagates even if the later blocks are correct.

~~~
mrfusion
Ok, I get it now. Thanks jreimers and smackfu!

~~~
TheLoneWolfling
Jumping on this comment because HN won't allow me to respond to a prior
comment of yours (link:
[https://news.ycombinator.com/item?id=7878923](https://news.ycombinator.com/item?id=7878923)):

> how can you have a current in a single wire without a loop?

There are ions always wandering around in the ionosphere - the ionosphere is
partly-ionized plasma. Low-density, but there. When you have a generator that
produces an electric potential bias across the top/bottom of the craft, you
end up with electrons being emitted into space from and positive ions being
attracted to the side biased negative, and electrons in the ionosphere being
attracted to the side biased positive. Effectively: the plasma completes the
circuit. There are bunches of additional optimizations (electron guns, etc)
but that's the basic idea.

~~~
mrfusion
Wow that makes sense. I thought the spacecraft would be above the atmosphere
but maybes there are still a few ions in LEO?

Also how could such a generator work? That makes a potential on the two ends?

~~~
TheLoneWolfling
There's a surprising amount of atmosphere up where we would consider it to be
at orbital heights. People think of the atmosphere as suddenly ending, but it
doesn't.

For example, one of the major considerations for how the ISS orients its solar
panels is minimizing drag.

And that's what an electrical generator does. It produces an electric
potential difference between its two terminals.

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danielweber
People on /r/spacex were posting a bunch of progressions of the video as it
was being reconstructed. Very interesting all the way.

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dm2
There was also video written to on-board storage that has yet to be extracted
yet, isn't there? If not, why?

~~~
bradyd
Due to rough seas the rocket stage sank before they were able to recover it.

[http://www.bbc.com/news/science-
environment-27166780](http://www.bbc.com/news/science-environment-27166780)

~~~
dm2
That article is about the previous landing.

The recent vertical landing should have been much closer to shore and was
planned to have a much better chance of recovery.

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pfraze
Some nice info about FFmpeg compression

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eps
Damn, that's very nice. I guess they won't be using MPEG anymore though :)

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fuddle
Awesome, great effort by the folks at NASASpaceflight.com.

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mellisarob
so no more MPEG?

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sitharus
Slight correction - it wasn't NASA that recovered the video, rather
NASASpaceflight.com, an independent community of spaceflight fans.

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jccooper
Incorrect title. It was the NASA Space Flight forum (or rather some members
thereof). NASA had nothing to do with it.

~~~
dang
Thanks. We reverted the title. (Submitted title was "How NASA recovered
SpaceX’s Falcon 9 Ocean Landing Video".)

