Author Topic: CRS-3 Falcon 9 first stage to sport legs and attempt soft splashdown  (Read 219937 times)

Offline Dudely

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Was that footage recorded onboard as well? If so it's somewhat amusing to think there is a good quality video lying at the bottom of the ocean somewhere.

It's unlikely that it would have been saved to some sort of solid state storage before everything shut down, but perhaps.

Offline ugordan

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including the chip that records the video.

If there's anything that records it currently. My guess is no as that would be additional hardware with little to gain at this point.

Offline mmeijeri

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There we go with solutions in search of a problem again. Why would they do that? Increase bandwidth requirements massively and the box that encodes the video possibly doesn't even support MJPEG.

Well, here we have so much packet loss that it makes more sense to have a lower frame rate and resolution and less compression. It's not as if the higher resolution is doing us any good right now.

Quote
The objective is not to get better video of it via live telemetry, it's to recover a flight stage. Once a stage is recoverable, all bandwidth limitations can go out the door if you don't want immediate video (and for telemetry availability reasons this wasn't real-time, either). Stick a full HD camera with a solid state recorder onto the stage. Recover the stage and you have video that's order of magnitude better than 15fps interlaced NTSC video.

Shuttle SRBs didn't use live video, but recorders, too.

Sure. But in the meantime using different video encoding sounds like a very easy fix. Unless the box doesn't support it, as you say.
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Offline ugordan

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But in the meantime using different video encoding sounds like a very easy fix. Unless the box doesn't support it, as you say.

As you already know, MJPEG is basically similar to MPEG with all frames being key frames. From the stream we *did* get, there's something like 2-3 keyframes that are to any degree useful/complete.  MJPEG would not change that, it would just increase bandwidth required for video as it's not making use of similarity between subsequent frames.

Now, I have a suspicion that starting with CRS-1 SpaceX changed the way they transmit live video from a dedicated NTSC analog feed and dedicated frequency to an MPEG-4 stream carried over the main telemetry link. This made for a noticeable drop in video quality and lower resiliency to errors. This additional MJPEG bandwidth would then be bandwidth that needs to be shared with other, more important vehicle telemetry, unless you dropped the frame rate significantly - in which case you again end up having basically just a couple of frames of any action.

IMHO it's just not worth the effort to switch codecs and lower framerate even more down to a slideshow all for the sake of last couple of seconds of booster flight, a booster that's supposed to be recoverable in the end. Since the next flight is supposed to end up closer to the shore and boosters after that eventually be brought back to land, current downlink methods are sufficient, as much as I dislike how the current video implementation is very intolerant of packet loss. The video system Orbital flew on the first two Antares flights had much more graceful video degradation, but it may have also been a dedicated frequency.

Offline mmeijeri

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That makes sense. I wonder if they do record the video feed on the way up, I don't think they've ever released footage without visible packet loss. Could they relay the feed to a recording device on the Dragon?
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Offline ugordan

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I wonder if they do record the video feed on the way up, I don't think they've ever released footage without visible packet loss. Could they relay the feed to a recording device on the Dragon?

I'd categorize that under "anything's possible, but is it worth the hassle ?" department. I don't think they record the feed for later playback on Dragon, but they might be reconstructing ground telemetry afterwards if several sources are available.

A curious thing regarding CRS-3 launch, I saw more glitches in the SpaceX webcast during MVac ignition than I did on the NASA feed - which I though was being fed the *same* decoded onboard stream passing through Hangar AE!
« Last Edit: 04/30/2014 01:13 pm by ugordan »

Offline AncientU

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Pretty garbled footage, but it's enough to give a taste of what happened. It would certainly have been something to actually have been in that bit of the ocean watching that thing land, what a sight it must have been.
wait a couple weeks
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Offline nat.vincent

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If a GoPro, with a 64gb card in it, can store more than 8 hours of video, at minimal cost, I'm sure the system that they have would be totally able to store video on board.

Online woods170

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If a GoPro, with a 64gb card in it, can store more than 8 hours of video, at minimal cost, I'm sure the system that they have would be totally able to store video on board.
That still won't do you any good if the GoPro and the 64gb card end up on the bottom of the ocean.

Offline mmeijeri

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That still won't do you any good if the GoPro and the 64gb card end up on the bottom of the ocean.

Maybe that was in response to my suggestion to do the recording on the Dragon? I've never heard of comsats storing and later replaying feeds from onboard cameras on the launch vehicle, but that sounds potentially useful too. I can't think of a fundamental reason this wouldn't work, but that doesn't mean much. What's the typical bandwidth that's available between a spacecraft and its launch vehicle? Would it be difficult to increase that if necessary? Is this worth the hassle? I don't know, but it doesn't sound difficult. Are there difficulties I'm overlooking?
« Last Edit: 04/30/2014 02:59 pm by mmeijeri »
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Offline Jim

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What's the typical bandwidth that's available between a spacecraft and its launch vehicle?

Usually, zero.  Typically there is no communication between the LV and SC.  When there is, it is only a few discretes or a subset of the spacecraft telemetry that is interleaved with the LV telemetry.

Offline mmeijeri

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We're getting off-topic here, and I'd be happy to take it to a new thread if we go on much longer. What about Apollo though? Couldn't the whole stack be controlled from the spacecraft? I think I've read it was a requirement for Orion too. Is it still the plan to do that eventually, even if it's not in the first versions? Is it difficult to add communication? I'm sure it's more involved than just adding a cable / wifi, but I can't think of much else myself.
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Offline ugordan

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Couldn't the whole stack be controlled from the spacecraft?

Don't confuse a man-rated system and manned spacecraft with a generic term of spacecraft meaning comsat, NASA science mission, etc. There's no requirement for the latter to know anything about the LV.

In this particular case, SpaceX might have some other interface between its own Dragon and its own F9 than what a typical payload would use. Doesn't mean the LV should expose that interface to other payloads. There are standard electrical interfaces for payloads, IIRC, these are outlined in the respective LV User Guide.

As for controlling a manned stack from the spacecraft, I'm not sure if that's still relevant today. LVs like Atlas, Ariane, F9 have multiple avionics strings for redundancy. The only relevant signals toward the spacecraft that would be of interest are some basic LV health data and EDS abort signal.
« Last Edit: 04/30/2014 03:05 pm by ugordan »

Offline aceshigh

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SpaceX is not just communicating with diehard space nuts as us: SpaceX is heavily engaged in convincing international customers, the US public, US government and US military in betting on them for space launches in the future. Of course they want to release a pretty video of this momentous occasion! As I understand it, the reworking will just be filling out the blanks in a choppy transmission. What's the big deal? They are a private company in a tough competitive environment, it isn't as if they are obliged to release raw data to anybody.

isnīt telemetry data more important than the video?


when SpaceX is trying to sell their products, do they present the technical data to customers, or they present a bunch of nice video footage?

ok, maybe a bit of both, but still, if SpaceX has the data showing the rocket was completely stabilized, what was itīs final velocity before turning off and splashing down, etc... itīs fine by me, and better than a video in which you probably wouldnt really be able to tell much from the onboard footage, no matter how good the video was.

Offline mmeijeri

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There are standard electrical interfaces for payloads, IIRC, these are outlined in the respective LV User Guide.

Good point. Looking forward to an updated User Guide for v1.1.
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Offline ugordan

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Looking forward to an updated User Guide for v1.1.

It's been long overdue, IMHO, but this is really, really getting OT.

Edit/Lar: yes, it is.
« Last Edit: 04/30/2014 09:47 pm by Lar »

Offline AJW

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I spent a day in Nevada with a video crew using an RC helicopter to capture video of a car race.  The camera operator was able to view a lower resolution in-flight video feed in real-time, but the onboard camera stored an HD video that was used for final production.

If the stages will be lost, this doesn't make sense, but as soon as stages are expected to be recovered, I suspect that both systems will be employed.

Offline Lars_J

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I spent a day in Nevada with a video crew using an RC helicopter to capture video of a car race.  The camera operator was able to view a lower resolution in-flight video feed in real-time, but the onboard camera stored an HD video that was used for final production.

If the stages will be lost, this doesn't make sense, but as soon as stages are expected to be recovered, I suspect that both systems will be employed.

Yes, I would expect the same. Seeing beautiful full HD footage of the entire 1st stage flight would be incredible.

Online Dave G

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If a GoPro, with a 64gb card in it, can store more than 8 hours of video, at minimal cost, I'm sure the system that they have would be totally able to store video on board.
That still won't do you any good if the GoPro and the 64gb card end up on the bottom of the ocean.

Depends on how far down the bottom is.  There are companies that retrieve that kind of stuff. 

The CRS-3 ocean landing spot was very deep.  Salvage in shallower water is a lot more practical. 

Elon specifically mentioned the next first stage will land in shallower water.
« Last Edit: 04/30/2014 09:50 pm by Dave G »

Online meekGee

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I just noticed - maybe I'm behind everyone else and missed it, but:

Didn't SpaceX say that on this flight, they'll fire the engine first, and only then deploy the legs?

In the video, I think Frame 8 shows deployed legs and no plume, and Frame 9 shows a plume.

Or is it that an undisturbed, throttled down, 1-engine plume is invisible to the camera, and only upon contact with the water does the plume become visible.

Ah.  Might have answered my own question there.  Maybe.

EDIT:  Yeah, looking closer at frame 7 and 8 (and maybe even 2, but not sure), there's a disturbance on the water, which can only be caused by the exhaust - it's just too cold to show.

Need to look at down-pointing footage from F9R-dev1 to compare - but IIRC there wasn't any on the last test flight.
« Last Edit: 05/07/2014 02:42 am by meekGee »
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