Recovering SpaceX’s Falcon 9 Ocean Landing Video | Hacker News Reader

Recovering SpaceX’s Falcon 9 Ocean Landing Video

nasaspaceflight.com

248 pointskilroy12332 comments

Raw video: https://www.youtube.com/watch?v=7m8H8OlJ3o8

Recovered video: https://www.youtube.com/watch?v=CjZ33C9JZTM

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

"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.

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

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

Even better, it wasn't a satellite dish. It was a pizza dish.

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

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.

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)

And don't use interlaced video!

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

It's available, but as said, the bitflips are a manual process.

https://github.com/michaelni/FFmpeg/commits/spacexdebug1

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)

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?

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

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?

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.

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

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):

> 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.

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?

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.

> But the article was talking about early blocks messing up the encoding on following blocks.

More accurate to say that it was messing up the decoding of following blocks.

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

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

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

http://www.bbc.com/news/science-environment-27166780

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.

Some nice info about FFmpeg compression

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

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

so no more MPEG?

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

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

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

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