SpaceX Falcon 9 FT - ORBCOMM-2 - Dec. 21, 2015 (Return To Flight) DISCUSSION

[meekGee]

Of course - but I only had something to contribute wrt the plasma...

Right. And your comments were interesting and more in line with what I was getting at with my comment, which is why I didn't quote you directly. I quoted the NEXT person who took a single word out of the content of the post and started running with it (yes, I've been watching football all day so expect more metaphors).

At any rate, SOMETHING is going on at the surface of those grid fins and to cause what looks like obvious localized physical damage to the interstage surface. It almost looks like a few spots of localized delamination - maybe that spot on the interstage was caused when the S2 Mvac ignited? Don't know but I bet SpaceX is interested and will be investigating thoroughly.

Which - I know you understand - was the point of my post.

(Welcome to the New Year, NSF - same as the last year - more nerds arguing about minutiae in the absence of real data )

I blame tap-a-talk.  Too much information, too small a screen.  and the iWatch keyboard is so hard to type on.

No - that wasn't serious.   Not totally.

As for damage mechanisms - yes - there could be plenty.  Rarefied supersonic flow - I don't have any intuition about what it does to surfaces.

Hey - maybe that was part of the reason they were chasing fairings.  Maybe they had test patches on them.

[Rocket Science]

The X-15 program with 199 flights showed that re-usability was possible. SpaceX proved that they could make a pinpoint vertical powered landing. After the stage is examined and material upgrades are made if/where necessary next will be to re-fly and recover the stage again and prove the economics. I really don't see any technical show-stoppers at this point... Lather-rinse-repeat...

[Mike_1179]

From my hazy memory of grad school, boundary layer transitions in supersonic flow are rather nasty things to simulate with CFD. Remember the Boundary Layer Transition DTO on Discovery all those years back; that was to provide data to compare against CFD models.

We have a basic idea that that supersonic retro burn pushed the boundary layer away from the structure; these little bumpy fins hanging off the side of the stage might see some heating that's difficult to model. Combine that with strange shockwaves through the grid fins and you've got the possibility for localized heating that might be challenging to predict ahead of time. Use these returned stages to validate your CFD and go from there.

[AJW]

From my hazy memory of grad school, boundary layer transitions in supersonic flow are rather nasty things to simulate with CFD. Remember the Boundary Layer Transition DTO on Discovery all those years back; that was to provide data to compare against CFD models.

We have a basic idea that that supersonic retro burn pushed the boundary layer away from the structure; these little bumpy fins hanging off the side of the stage might see some heating that's difficult to model. Combine that with strange shockwaves through the grid fins and you've got the possibility for localized heating that might be challenging to predict ahead of time. Use these returned stages to validate your CFD and go from there.

If that's a camera pod between the two grid fins, there should be some interesting footage of just what the grid fins go through.

[Comga]

If that's a camera pod between the two grid fins, there should be some interesting footage of just what the grid fins go through.

I believe that the protrusion with the dark holes is a cold gas N2 thruster.

[cscott]

On r*ddit there is a side-by-side comparison image with the pre-launch rocket.  There is some asymmetry, which makes it clear we're looking at the "back" side here; that is, the side which is usually hidden by the transporter/erector.

It's worth noting that the F9FT is not radially symmetric; it's a front/back mirror symmetry which will come in handy since the F9FT cores are basically identical to the FH side boosters.  So there are some fittings which are on the "near to the center core" side both front and back. (Or "far from the center core"; we don't know which yet.)

[OxCartMark]

Orville Wright @orvillewright Dec 19
Flyer back in barn at Kitty Hawk. No
damage found, ready to fly again.

Notice how the man himself said "no damage found".  That's enough for me to not be concerned about peeling paint (or whatever it is) on the grid fins.

[Coastal Ron]

But without good info otherwise, I take him at his word on it, no damage.

Maybe not "damage", which would imply unexpected wear and tear.

But what if what we're seeing is expected wear and tear?

Need more info...

[The Amazing Catstronaut]

I doubt Elon would release that statement without something more than a quick look over. They've certainly analysed the contents of all of these pictures far before we did and are likely to still be doing so.

This is something that they likely modeled before the launch itself. If reality didn't match with their simulations I can imagine Elon would have been more guarded in his tweeting. It's not good PR to lie and they don't have a precedent of it.

[guckyfan]

I doubt Elon would release that statement without something more than a quick look over. They've certainly analysed the contents of all of these pictures far before we did and are likely to still be doing so.

I am sure not only the pictures. They must have scanned tons of sensor data stored during the flight for anomalies too.

[gadgetmind]

I bet the COPVs and struts have all been checked *very* carefully!

I'm trying to think of what other parts would suffer more in flight than during a static fire. Of course, now that SpaceX have a pre-flown rocket, I guess that's what they are going to find out.

[clongton]

I don't believe some of you guys. Some of your statements are beyond belief. Elon said there was "no damage". So:

1. There was no damage beyond what was expected to be dealt with during refurb
2. He just made a rash statement without examining the vehicle and reading the reports and was wrong -or-
3. He flat out lied.

There are no other options.

Now I will grant that he is given to making statements that often prove to be too short on time span but to my knowledge he has *NEVER* done #'s 2 or 3 - never. So for all you who are questioning the honesty or the integrity of his statement, you're either saying he just makes stuff up to sound good or he's a liar. Good grief. Are you really so desperate to see your name in print that you will actually get on that bandwagon?

Now obviously there is some superficial/skin-deep damage due to the return environment the vehicle came thru to make its way back to LZ-1, but I have seen nothing beyond searing or chipping of paint or loss of some potentially ablative material which is supposed to burn away anyway. I see no dings or bends in the airframe or any of its appendages, in other words "no damage". SpaceX has reported that the tanks are fine and engines are fine and able to be fired again. The only thing we have not seen is the landing legs, which are reported to be in good condition.

In all the years we have been following this man's adventures he has never lied to any of us. He has also never made a rash and uninformed statement. He has made predictions that were shortsighted wrt time frame, but he has never been untruthful nor rash. So why now? What are you guys thinking?

He said "no damage" and based on his history of truthfulness and informed statements I believe him. There was no "damage".

[Rocket Science]

This was the X-15 after her hyper-sonic flight, compared to her the Falcon looks pristine. BTW this X-15 was repaired but she never flew again sine the program met its objectives. She still sits pretty in Dayton.   Falcon appears to need cosmetic and not structural attention...

[OxCartMark]

This is not a space shuttle.
It doesn't need refurbishment.
Its missing paint, not missing tile.
With more launches there will be more lost paint.
The people that evaluated it had more information than the one picture y'all have to go on.

[RonM]

The grid fins are not a problem. They can easily be swapped out for freshly coated ones and refurbished later. Why are people making a big deal about this?

[Kabloona]

The grid fins are not a problem. They can easily be swapped out for freshly coated ones and refurbished later. Why are people making a big deal about this?

Because in the absence of any real damage, space nerds gotta find something to obsess over, so chipped paint becomes the problem du jour. 

[OxCartMark]

The grid fins are not a problem. They can easily be swapped out for freshly coated ones and refurbished later. Why are people making a big deal about this?

Because we were shown a small subsection of a larger something that was stated by a reputable source as being undamaged and some people are so intent in being able to see what they want to see that they are claiming that the undamaged part needs to be repainted or refurbished before it is undamaged.  Wait, that makes no sense.

[Dave G]

The grid fins are not a problem. They can easily be swapped out for freshly coated ones and refurbished later. Why are people making a big deal about this?

For me, the main question is: How much effort will it take to refurbish the stage for reuse.

Yes, various parts can be replaced, and the used parts can be refurbished and reused.  Someone on this thread even suggested replacing and refurbishing the entire interstage.  But all of this costs money, and reuse is all about saving money.  So the success or failure of reusability boils down to details about how much stuff needs to be refurbished or replaced.

In the end, I'm confident that SpaceX will figure out how to make reuse extremely cost effective.  Musk has outlined a long-term vision where the stage will just be refueled and flown again, like a commercial airliner, and knowing how SpaceX works, I'm pretty sure they'll get there, or very close to it.

But the question now is: How far away from this long-term vision are they today?  And that leads to detailed discussion of things like paint chips on grid fins.

[Zpoxy]

I don't see anything earth shaking here. The gridfins have a little chipped paint. A little sandpaper, some alodyne (if they are aluminum) and some touch-up paint, done. You guys are making mountains out of molehills. Quite frankly I don't even see any molehills.

[Comga]

(snip)
He said "no damage" and based on his history of truthfulness and informed statements I believe him. There was no "damage".

I agree with you.
What was the source of the first of the two images in the comparison?
There are odd differences, including an obvious element that seems to have switched sides of the N2 thruster cluster, which is in the red circles below.
They are definitely both FT interstages, with the lowered N2 thrusters and no cowlings over the grid fin pivots.
Could they be of opposite sides of the rocket?  Is there a logo on the "back" side?