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

[ugordan]

This guy was pretty close to both the launch and landing pad. So close, in fact, that it's the only video I've seen where the sonic booms arrived 13 seconds before landing.

[modemeagle]

This guy was pretty close to both the launch and landing pad. So close, in fact, that it's the only video I've seen where the sonic booms arrived 13 seconds before landing.

Using the video it appears to be from here.
2.28 Miles from the launch pad
4.4 Miles from the landing pad

The SpaceX launch center is 6 miles from the landing pad.

[Rocket Science]

More "grid-fin" goodness for all you fans!

http://www.aerospaceweb.org/question/weapons/q0261.shtml

[edkyle99]

Reading about the lattice (grid) fins, I see that high pressure hydraulic fluid is vented when they are operating.  Could some of the "soot" covering the stage be this fluid accumulating after being vented during reentry?

 - Ed Kyle

[Kabloona]

Reading about the lattice (grid) fins, I see that high pressure hydraulic fluid is vented when they are operating.  Could some of the "soot" covering the stage be this fluid accumulating after being vented during reentry?

 - Ed Kyle

What happens to the spent hydraulic fluid was debated extensively in the link below. Some people believe it's vented out of the interstage, others argued it's captured in a waste tank.

So whether or not you believe any of the fluid may be now visible on the skin of the stage depends on your opinion as to whether or not the spent fluid is recaptured.

http://forum.nasaspaceflight.com/index.php?topic=36536.0

My own guess is that they dump the fluid in order to avoid the extra weight and cost of a catchment tank and plumbing.

OTOH, one argument against that view is that no one has been able to see evidence of hydraulic fluid on the skin of Grasshopper in photos or videos of its hops in TX.

[CyndyC]

Reading about the lattice (grid) fins, I see that high pressure hydraulic fluid is vented when they are operating.  Could some of the "soot" covering the stage be this fluid accumulating after being vented during reentry?

 - Ed Kyle

What happens to the spent hydraulic fluid was debated extensively in the link below. Some people believe it's vented out of the interstage, others argued it's captured in a waste tank.

So whether or not you believe any of the fluid may be now visible on the skin of the stage depends on your opinion as to whether or not the spent fluid is recaptured.

http://forum.nasaspaceflight.com/index.php?topic=36536.0

My own guess is that they dump the fluid in order to avoid the extra weight and cost of a catchment tank and plumbing.

OTOH, one argument against that view is that no one has been able to see evidence of hydraulic fluid on the skin of Grasshopper in photos or videos of its hops in TX.

Kabloona, your guess is exactly right. Interesting to know of that older thread you found and the same debate. There was the following within my long quote yesterday from Spaceflight101, and now I understand it more clearly myself. I thought they were saying the whole tank for hydraulic fluid was dumped overboard.

"The four fins are rotated and tilted independently by an open hydraulic system using pressurized hydraulic fluid supplied from a pressurized tank that is dumped overboard after flowing through the hydraulic actuators of the fin system. The design was also driven by overall mass considerations."

[mheney]

Reading about the lattice (grid) fins, I see that high pressure hydraulic fluid is vented when they are operating.  Could some of the "soot" covering the stage be this fluid accumulating after being vented during reentry?

 - Ed Kyle

Given that the fluid is vented from near the top of the stage (where the grid fins are) into an airstream
that is moving up relative to the stage, I don't think it's going to end up being deposited in the area
where you see soot.  Vented fluid would be blown away past the top of the stage, instead.

[Kabloona]

Kabloona, your guess is exactly right. Interesting to know of that older thread you found and the same debate. There was the following within my long quote yesterday from Spaceflight101, and now I understand it more clearly myself. I thought they were saying the whole tank for hydraulic fluid was dumped overboard.

"The four fins are rotated and tilted independently by an open hydraulic system using pressurized hydraulic fluid supplied from a pressurized tank that is dumped overboard after flowing through the hydraulic actuators of the fin system. The design was also driven by overall mass considerations."

Thanks for that reference from SF101, Cyndy. I hadn't seen that before.

[Jcc]

Reading about the lattice (grid) fins, I see that high pressure hydraulic fluid is vented when they are operating.  Could some of the "soot" covering the stage be this fluid accumulating after being vented during reentry?

 - Ed Kyle

What happens to the spent hydraulic fluid was debated extensively in the link below. Some people believe it's vented out of the interstage, others argued it's captured in a waste tank.

So whether or not you believe any of the fluid may be now visible on the skin of the stage depends on your opinion as to whether or not the spent fluid is recaptured.

http://forum.nasaspaceflight.com/index.php?topic=36536.0

My own guess is that they dump the fluid in order to avoid the extra weight and cost of a catchment tank and plumbing.

OTOH, one argument against that view is that no one has been able to see evidence of hydraulic fluid on the skin of Grasshopper in photos or videos of its hops in TX.

They may have included hydraulic fluid recovery in Grasshopper. F9R-Dev did not have the tight margins of an orbital vehicle.

[cscott]

Again, look at the shadows in the deposits at the top of the stage. It is clear that the top soot is coming from *above*.  S2 ignition is a logical source given the direction.

[Ohsin]

One more pic from LZ-1.

https://mobile.twitter.com/SpaceXTrip/status/679933830493540353/photo/1

Did the recovery team had its own patches?(From that hard hat)

[Mongo62]

So the recovered first stage will be erected at 39A and static fired. Was there ever any serious consideration given to launching it again with a mass simulator replacing the second stage and payload? The stage has been paid for already, so it would be essentially "free" flight testing. Maybe even keep sending it uphill until it finally fails, with inspections between each flight. The hardware costs would be minimal, mainly the cost of a mass simulator for each flight, plus the cost of propellant.

If that was too much, how about dropping a nose cone on it and launching it straight up, like New Shepard but a lot higher? Instead of reaching a measly 100.5 km, it might reach 500 km or more. Or would that be too "In your face, Bezos!" for SpaceX?

[Zed_Noir]

So the recovered first stage will be erected at 39A and static fired. Was there ever any serious consideration given to launching it again with a mass simulator replacing the second stage and payload? The stage has been paid for already, so it would be essentially "free" flight testing. Maybe even keep sending it uphill until it finally fails, with inspections between each flight. The hardware costs would be minimal, mainly the cost of a mass simulator for each flight, plus the cost of propellant.

If that was too much, how about dropping a nose cone on it and launching it straight up, like New Shepard but a lot higher? Instead of reaching a measly 100.5 km, it might reach 500 km or more. Or would that be too "In your face, Bezos!" for SpaceX?

Think Musk wants a shiny trophy on display somewhere.

[Mader Levap]

The stage has been paid for already, so it would be essentially "free" flight testing.

It would not be free for two reasons.

First is obvious: ops, permissions and all of that means a lot of workhours for a lot of people.

Second is opportunity cost. It is possible to have better use of stage than something that amounts to stunt.

[MarsInMyLifetime]

Before the memory of the crane-supported stage fades from mind, I had this question: How do you suppose they attached the lifting apparatus to the top of the stage prior to the crane applying tension to it? Was it a ring that just dangled and docked into place, or would there have been some worker assistance with the fittings? (and if so, how the heck did they get up there?)

[Dante80]

Before the memory of the crane-supported stage fades from mind, I had this question: How do you suppose they attached the lifting apparatus to the top of the stage prior to the crane applying tension to it? Was it a ring that just dangled and docked into place, or would there have been some worker assistance with the fittings? (and if so, how the heck did they get up there?)

I would love to hear the answer to this too. What I do know is that SpaceX has designed the interstage with crane movement after landing in mind.

[Mongo62]

The stage has been paid for already, so it would be essentially "free" flight testing.

It would not be free for two reasons.

First is obvious: ops, permissions and all of that means a lot of workhours for a lot of people.

Second is opportunity cost. It is possible to have better use of stage than something that amounts to stunt.

I would not call it a stunt. Multiple flights using a mass simulator, replicating the first stage flight profile, but avoiding risk to expensive customer cargoes, seems like a fine way to gain experience in first stage reflight operations, as well as (if the test series goes well) build customer confidence in the use of previously flown first stages. The hardware costs would be minimal, albeit the paperwork costs and payroll costs would still exist.

[meekGee]

Before the memory of the crane-supported stage fades from mind, I had this question: How do you suppose they attached the lifting apparatus to the top of the stage prior to the crane applying tension to it? Was it a ring that just dangled and docked into place, or would there have been some worker assistance with the fittings? (and if so, how the heck did they get up there?)

Like you climb a coconut tree...  Two ropes and don't forget the shackles or you'll have to go up twice.

That, or a man lift.

[MarsInMyLifetime]

I see that boom lifts can get up to 185 feet, so that does seem like a possibility. But in that case, after the worker returns to ground, why not use that same system as the support, rather than bring in a separate crane? I suppose the crane could lift a platform into place and then take over station-keeping. We missed something in the wee hours!

[CorvusCorax]

Regarding the scorch marks on the F9 core - I found an extremely educative video about flame protection and its effects on the 1969 Apollo 11 Saturb V launch - and the systems applied to the launch pad hold down clamps and service structures to protect them from the exhaust



The top of the Falcon 9 1st stage would face very similar conditions on 2nd stage ignition - and so does the tail end during reentry.

For traditional "Sooting" to occur, you would need a fuel rich combustion with unburnt carbon in it to condense on the target surface (much like in diesel engines when under high load)
Is Merlin using such a fuel rich mixture?

I don't think so:
Fuel rich kerosene burns yellow. That can be seen for example after stage landing. The first stage exhaust however has an extremely blue white tint to it, much brighter I think than in previous falcon 9 launches -  maybe attributed to the denser, super cooled oxygen. That would indicate a balanced or even oxygen rich combustion, and that would hardly leave any sooting.

Unless the burnt surface had a protective paint like these Saturn V structures, that would char them black