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Off Topic => General Discussion => Topic started by: bknight on May 04, 2021, 04:01:20 PM

Title: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: bknight on May 04, 2021, 04:01:20 PM
I have watched many of the SpaceX videos of the second stage igniting.  I noticed again today that when the engine ignites there are rolling horizontal line in the first stage video of the event.  Why does this occur?
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: JayUtah on May 04, 2021, 06:24:49 PM
My first thought was that it's a standing(ish) wave effect produced when the second stage plume interacts with the open top of the first stage.  That kind of effect will be highly sensitive to plume density.

But then the effect does seem suspiciously aligned with the video frame, making me think it could also be some kind of video artifact.
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: cjameshuff on May 04, 2021, 07:24:43 PM
My first thought was that it's a standing(ish) wave effect produced when the second stage plume interacts with the open top of the first stage.  That kind of effect will be highly sensitive to plume density.

But then the effect does seem suspiciously aligned with the video frame, making me think it could also be some kind of video artifact.

It might be both, exhaust resonating in the open top of the booster with some visible effect to its brightness/opacity at a frequency close to the frame rate.
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: Zakalwe on May 05, 2021, 05:17:05 AM
Its probably vibration from the exhaust plume impinging on the first stage uppers. The frequency probably matches the frame rate of the rolling shutter in the camera sensor. I suspect that it's similar to the rolling shutter effect you get with fast moving objects such as propellers.

https://youtu.be/dNVtMmLlnoE
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: bknight on May 05, 2021, 03:07:57 PM
To all, thanks for the info.
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: Peter B on May 08, 2021, 03:32:28 AM
Rocket exhaust contains ionised gases doesn't it? Would that affect the signals in some way?
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: smartcooky on May 08, 2021, 06:12:03 AM
Rocket exhaust contains ionised gases doesn't it? Would that affect the signals in some way?

Yes, but I can't see how it would affect the cameras inside the hole. If you've ever see one of those beautiful videos of taken from inside a Falcon 9 payload fairing as it re-enters the earth's atmosphere, you would see that the ionization doesn't affect the video.

I am also pretty sure the downlink antennae are exterior.   


ETA: Here you go.... enjoy
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: Peter B on May 09, 2021, 01:39:18 AM
Rocket exhaust contains ionised gases doesn't it? Would that affect the signals in some way?

Yes, but I can't see how it would affect the cameras inside the hole. If you've ever see one of those beautiful videos of taken from inside a Falcon 9 payload fairing as it re-enters the earth's atmosphere, you would see that the ionization doesn't affect the video.

I am also pretty sure the downlink antennae are exterior.   


ETA: Here you go.... enjoy


Wow! What spectacular images!

Do you mind me asking, though: were those images broadcast, or recovered from the Go-Pro once the fairing was picked up?
Title: Re: Rolling horizontal lines in SpaceX first stage viewing the second ignition
Post by: smartcooky on May 11, 2021, 09:40:44 PM
Rocket exhaust contains ionised gases doesn't it? Would that affect the signals in some way?

Yes, but I can't see how it would affect the cameras inside the hole. If you've ever see one of those beautiful videos of taken from inside a Falcon 9 payload fairing as it re-enters the earth's atmosphere, you would see that the ionization doesn't affect the video.

I am also pretty sure the downlink antennae are exterior.   


ETA: Here you go.... enjoy


Wow! What spectacular images!

Do you mind me asking, though: were those images broadcast, or recovered from the Go-Pro once the fairing was picked up?

That I don't know

I doubt they were broadcast intentionally but they could have been downlinked via telemetry.

This Scott Manley video tells about some clever people tapping into SpaceX's downlinks and grabbing video from the engineering cameras, video that doesn't appear on the live youtube channel during launches, for example, the cameras inside the fuel tanks.