Author Topic: The Laser Spot noticed above the Grid Fins  (Read 12751 times)

Offline Ohsin

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The Laser Spot noticed above the Grid Fins
« on: 03/23/2016 07:36 am »
Is the patch over grid fins some kind of reflector? I see what seems like a red laser spot over it in one of the launch photographs. First image has it but second one doesn't.

https://c2.staticflickr.com/2/1623/25395662282_942fd68ba3_o.jpg

https://c2.staticflickr.com/2/1505/25218536590_3a9666357e_o.jpg

What could it be used for?
« Last Edit: 03/23/2016 07:38 am by Ohsin »
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Offline tleski

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Re: The Laser Spot noticed above the Grid Fins
« Reply #1 on: 03/23/2016 11:21 am »
After going over the launch photos on their Flickr I found another example of the illumination of the same spot on the CRS-5 launch. Does not look as pretty and red as in the SES-9 launch photo, but it is the same location and a pretty obvious spot of light:

https://c1.staticflickr.com/9/8638/16512101410_83763eb9ea_o.jpg
« Last Edit: 03/23/2016 11:22 am by tleski »

Offline ugordan

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Re: The Laser Spot noticed above the Grid Fins
« Reply #2 on: 03/23/2016 11:44 am »
That laser spot has been there for a while. My guess is it has some alignment purpose.

Offline OxCartMark

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Re: The Laser Spot noticed above the Grid Fins
« Reply #3 on: 03/23/2016 02:11 pm »
High rate data transmission?  Implemented since CRS-7?  Guesses.
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Offline PerW

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Re: The Laser Spot noticed above the Grid Fins
« Reply #4 on: 03/23/2016 02:19 pm »
measuring movements maybe?

Offline Kabloona

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Re: The Laser Spot noticed above the Grid Fins
« Reply #5 on: 03/23/2016 02:20 pm »
That laser spot has been there for a while. My guess is it has some alignment purpose.

I'd take a WAG that it's from a ground-based source aimed at the vehicle to help assess how much sway they're seeing in the rocket from wind when the rocket is on the pad, after strongback retraction. The rocket is so tall and slender, they may be having some concerns about wind loads being placed on the base of the rocket while it's held down.

From observed motion of the (ground fixed) laser beam relative to the size of the reflector pad, they should be able to calculate a maximum deflection, plug it into a structural model, and derive the structural loads being placed on the vehicle and the hold-down clamps.

Just a guess, of course.

Offline dorkmo

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Re: The Laser Spot noticed above the Grid Fins
« Reply #6 on: 03/23/2016 02:42 pm »
im leaning twords the sway measurement

but ill add laser power for fun
https://en.wikipedia.org/wiki/Wireless_power_transfer#Lasers

Offline goretexguy

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Re: The Laser Spot noticed above the Grid Fins
« Reply #7 on: 03/23/2016 02:46 pm »

Offline Jim

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Re: The Laser Spot noticed above the Grid Fins
« Reply #8 on: 03/23/2016 03:10 pm »
Possibly the presumptive laser light is for a theodolite to align the guidance platform?
 

Not done that way any more.

Offline The Roadie

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Re: The Laser Spot noticed above the Grid Fins
« Reply #9 on: 03/23/2016 11:19 pm »
I'd take a WAG that it's from a ground-based source aimed at the vehicle to help assess how much sway they're seeing in the rocket from wind when the rocket is on the pad,
I have that confirmed by a "ground-based source."  ;)
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Offline cscott

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Re: The Laser Spot noticed above the Grid Fins
« Reply #10 on: 03/23/2016 11:51 pm »
I'd take a WAG that it's from a ground-based source aimed at the vehicle to help assess how much sway they're seeing in the rocket from wind when the rocket is on the pad,
I have that confirmed by a "ground-based source."  ;)
I wonder if the grey box is actually the limit they'd like to maintain.  IE if the laser spot leaves the box, winds are too high, bring back the strongback.  Easy for a console operator to monitor that way.

Offline CyndyC

Re: The Laser Spot noticed above the Grid Fins
« Reply #11 on: 03/24/2016 04:01 am »
From observed motion of the (ground fixed) laser beam relative to the size of the reflector pad, they should be able to calculate a maximum deflection, plug it into a structural model, and derive the structural loads being placed on the vehicle and the hold-down clamps.

I wonder if the grey box is actually the limit they'd like to maintain.  IE if the laser spot leaves the box, winds are too high, bring back the strongback.  Easy for a console operator to monitor that way.

Either way, if the light is making a new star on the flag, someone probably needs to worry.
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Offline mvpel

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Re: The Laser Spot noticed above the Grid Fins
« Reply #12 on: 03/25/2016 06:17 pm »
I would suspect the grey box is a grid like an old Sun mousepad which allows automatic measurement of the sway angle.



(I think I'm showing my age by admitting that I've actually used one of these mousepads before. :D )
« Last Edit: 03/25/2016 06:30 pm by mvpel »
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Offline rocketguy101

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Re: The Laser Spot noticed above the Grid Fins
« Reply #13 on: 03/25/2016 06:51 pm »
I would suspect the grey box is a grid like an old Sun mousepad which allows automatic measurement of the sway angle.



(I think I'm showing my age by admitting that I've actually used one of these mousepads before. :D )
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Online AJW

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Re: The Laser Spot noticed above the Grid Fins
« Reply #14 on: 03/25/2016 11:22 pm »
I would suspect the grey box is a grid like an old Sun mousepad which allows automatic measurement of the sway angle.

I'm not disagreeing with your conjecture, but I believe that laser mice may only indicate change in position, not absolute position.  If this is indeed the case, the question would be how to decide your start or zero position in order to decide the sway angle.   You might select your zero before the TE retracts, but there is always some movement at that point as the stage settles.

Now I'll show my age... When I was a kid, Doug Engelbart would stop by the house to home-brew with my dad.   I don't remember him bringing any early mice by, but I remember that he called his home-brew 'Dougweiser'.
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Online Comga

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Re: The Laser Spot noticed above the Grid Fins
« Reply #15 on: 03/26/2016 12:13 am »
I have designed, among other things, an optical metrology system for a space system somewhat like this, measuring sway, but on smaller object with more resolution than one would think would be needed for a rocket body.  There are many options on how to do this and opinions vary.  My system uses an option unlike, and more accurate than, one for an identical purpose flown by a well respected and well known organization.  None of the methods I have seen or thought about would look like this.

It isn't obvious how a large target (~500 mm scaling from the 3.8 meter stage diameter) would be useful.  A large target probably wouldn't work with an interferometric system, which would probably have too much resolution anyways.  Comparing the location of the spot to the edges of the reflector is a pretty crude way to make that measurement, although it could be used as a go/no-go indicator.  The spot moves off the target, or rather the target sways off of the spot, then it has passed some limit.  Seems awfully crude to me.

Maybe there is an underlying pattern to the target we just can't see in the resolution of the photo.   That would still be crude.  And it would probably have been seen in some previous photos of the stage before it is erected. 

In one of the images the dot is near the centerline. That suggests that it's not a positional metrology system, where they are just looking for the spot to move across the target.   Maybe the target has some unobvious properties, and can be observed from places that allow for perspective and parallax.  It's still not clear why that would be easier or more accurate then straight forward imaging.

I admit to being puzzled by this dot. 
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Offline MikeAtkinson

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Re: The Laser Spot noticed above the Grid Fins
« Reply #16 on: 03/26/2016 07:28 am »
Possibly not side to side but back and forth using distance to the reflector. A large reflector is then needed so that the side to side sway does not lead to the beam missing the reflector.

Offline Kabloona

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Re: The Laser Spot noticed above the Grid Fins
« Reply #17 on: 03/26/2016 09:29 am »
Possibly not side to side but back and forth using distance to the reflector. A large reflector is then needed so that the side to side sway does not lead to the beam missing the reflector.

That's better because automated and doesn't require someone eyeballing the vehicle.

Offline belegor

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Re: The Laser Spot noticed above the Grid Fins
« Reply #18 on: 03/26/2016 12:01 pm »
Possibly not side to side but back and forth using distance to the reflector. A large reflector is then needed so that the side to side sway does not lead to the beam missing the reflector.

That's better because automated and doesn't require someone eyeballing the vehicle.

Possibly even both combined, i.e. back and forth measured via distance (e.g. time-of-flight, or other schemes) and side to side using the position of the beam on the target? Or is only one dimension of interest?

Offline sewebster

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Re: The Laser Spot noticed above the Grid Fins
« Reply #19 on: 03/26/2016 05:01 pm »
I guess the patch isn't some sort of retroreflective sticker?

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