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

[The Amazing Catstronaut]

So is this now a return-to-flight from the return-to-flight thread now? Return-to-hop? Return-to-fire?

[Naito]

After looking at Elon's photo of "used" F9 where there is lots of chipped and bubbled painted surfaces which is only superficial. 

The Space Shuttle saved 600 lbs after stopping painting the white latex paint on the 3rd exterior tank. So why not no more white paint on F9 and it might save 200 to 300 lbs plus no more chipped paints to check out for loose flakes....

ET paint was carried almost all the way to orbit, which means 1 pound saved there was almost directly 1 pound of payload.  Falcon 9 is only the first stage, there would be savings but not nearly as efficiently as it did on the shuttle.

[rpapo]

So is this now a return-to-flight from the return-to-flight thread now? Return-to-hop? Return-to-fire?

At the rate it's going, there will wind up being a discussion, update and party thread for each rocket core, just like when we had only five different space shuttles to keep track of.

[dodo]

They should really start giving names to the cores, then...

Edit: oh, sorry, I didn't notice that there was a new thread on this precise subject in the Reusable Rockets section.

[Jcc]

What are these cracks/peels on the grid fins?

May be imperfections originally in the surface that are highlighted by the soot. How would these fins be made, die cast or 3D printed?

[llanitedave]

What are these cracks/peels on the grid fins?

Character marks.

[Kabloona]

How would these fins be made, die cast or 3D printed?

I'm guessing waterjet. That's how they did the grid fins for MOAB. See pic in this link (the green bomb with the guy standing beside the grid fins).

http://www.ormondllc.com

[Herb Schaltegger]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

[meekGee]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

Isn't re-entry plasma much hotter than the exhaust plume?  And the plume might be ionized right near the engine bell, but then it mixes with cold air, then gets back-blown past the body.  I do wonder if it is still ionized at that point.

[the_other_Doug]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

This kind of thing doesn't seem to be a huge problem to me in re the economics of reuse.  My bet is that they will have modular interstage units that can be pulled off and replaced quickly.  The used interstage is taken off to a refurb site, the nitrogen thrusters are cleaned and checked, and grid-fin submodules are cleaned when possible, pulled and replaced with new or refurbed grid-fin submodules when needed.

The whole process could take as little as a week.  When done, you have a newly refurbed interstage that you send off to the launch site to be attached to a newly landed rocket, and its freshly-used interstage gets sent off to the refurb building.  And so on.

This can be quite the efficient assembly line kind of refurb process, and I can see such a thing happening when they need to get into really high flight rates.

Until then, I'm sure they'll do all necessary clean-up and refurbishment in the integration buildings and won't even need to take the interstage off of the first stage to refurb it.  But, again, make these things modular, and you can just pull a grid-fin assembly or a nitrogen thruster assembly and replace it with a new or newly refurbed one.

Either way, the refurb cycle doesn't appear to pose an extreme technical or managerial challenge to me...

[leaflion]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

Isn't re-entry plasma much hotter than the exhaust plume?  And the plume might be ionized right near the engine bell, but then it mixes with cold air, then gets back-blown past the body.  I do wonder if it is still ionized at that point.

There is no "re-entry plasma".  They are not reentering fast enough for that.  The deceleration burn means that they are coming in at a lazy mach 2-3.  You're probably imagining an orbital reentry, which is going mach 20+.  Then ionized air is a big deal. At mach 2-3, you get a little warm, but nothing is being ionized.

[Stan-1967]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

How much of a plasma environment is the returning S1 exposed to?  I thought the boostback, whether RTLS or barge landing, nulled a significant amount of the re-entry velocity.   The re-entry speed is under Mach 5, yes?  Still not friendly to metals, but it's not an orbital re-entry.  It seems more comparable to SR-71 type speeds and material needs.

The supersonic retropropulsion portion of the flight seems the most challenging to the surfaces.   You not only have the shock front around the engine bells, but the introduction of very hot exhaust gasses into a potentially stagnant shock bubble & shock impingements on the surface of the vehicle.   Paint applied direct over the Al-Li alloy is not optimum for this condition I would think. 

When I see the condition of the grid fin assembly, I also wondered if the open loop hydraulic system was allowing the working fluid purge from the vehicle and streak across/contaminate the exterior surfaces of the stage.  I also think those hydraulic fluids are a potential source for corrosion mechanism to affect structure. 

Ideally, SpaceX would have surface coatings that protect the integrity of the base functional metal, and provide the ability to visually inspect for damage without removing the coating.  It needs to be able to stick on for perhaps dozens of launches, and from the pictures we are seeing of the returned stage, paint alone does not seem to be up to that demand.   If the refurbishment philosophy is a gas n' go type of turnaround, I think we can potentially expect to see the exterior undergo the needed changes to protect the vehicle against the hazards of the return, as well as facilitate the rapid inspection and return to flight status needed to minimize the refurbishment cost.

[Herb Schaltegger]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

Isn't re-entry plasma much hotter than the exhaust plume?  And the plume might be ionized right near the engine bell, but then it mixes with cold air, then gets back-blown past the body.  I do wonder if it is still ionized at that point.

There is no "re-entry plasma".  They are not reentering fast enough for that.  The deceleration burn means that they are coming in at a lazy mach 2-3.  You're probably imagining an orbital reentry, which is going mach 20+.  Then ionized air is a big deal. At mach 2-3, you get a little warm, but nothing is being ionized.

Plasma isn't the only thing I referred to in my post. Please read carefully.

[Kabloona]

When I see the condition of the grid fin assembly, I also wondered if the open loop hydraulic system was allowing the working fluid purge from the vehicle and streak across/contaminate the exterior surfaces of the stage.

Seems to me they'd be smart enough to run the vent line up to the top of the interstage for that very reason.

[meekGee]

What are these cracks/peels on the grid fins?

Character marks.

Plasma can erode metal very easily, as can localized hotspots created by shockwave impingements (see your handy copy of the CAIB Report, fellow space geeks)

No doubt, this kind of thing will be among the topics SpaceX will be studying extensively on this and future recovered stages as they determine the true economics of refurbishment/reusability.

Isn't re-entry plasma much hotter than the exhaust plume?  And the plume might be ionized right near the engine bell, but then it mixes with cold air, then gets back-blown past the body.  I do wonder if it is still ionized at that point.

There is no "re-entry plasma".  They are not reentering fast enough for that.  The deceleration burn means that they are coming in at a lazy mach 2-3.  You're probably imagining an orbital reentry, which is going mach 20+.  Then ionized air is a big deal. At mach 2-3, you get a little warm, but nothing is being ionized.

Plasma isn't the only thing I referred to in my post. Please read carefully.

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

[Herb Schaltegger]

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 )

[Rhyshaelkan]

Possibly mentioned before, but 99 pages is a bit too much to sift through.

I hope they use the returned core to test

1. Reusability.

2. Launch Abort System.

This is the perfect vehicle to kill two launches with one.

[Kabloona]

Possibly mentioned before, but 99 pages is a bit too much to sift through.

I hope they use the returned core to test

1. Reusability.

2. Launch Abort System.

This is the perfect vehicle to kill two launches with one.

Reusing a stage for launch abort has been discussed and would seem ideal since the stage need only survive until max drag, or about 60 seconds, but a flight failure of the stage would not only sabotage a critical milestone test for crewed flight, it would pour cold water on the whole reusability idea.

Killing two birds with one stone, and not in a good way.

So I expect Elon to be very cautious about reflying the first few recovered stages.

[llanitedave]

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

Except even we out-of-the-loop nerds have far more data than we did 365 days ago!  And which makes it a Happy New Year!

[rickl]

Reusing a stage for launch abort has been discussed and would seem ideal since the stage need only survive until max drag, or about 60 seconds, but a flight failure of the stage would not only sabotage a critical milestone test for crewed flight, it would pour cold water on the whole reusability idea.

Killing two birds with one stone, and not in a good way.

That is an excellent point, and one which I had not considered.