Author Topic: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video  (Read 160582 times)

Offline cscott

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #180 on: 07/25/2014 04:53 AM »
On the video this is titled "landing burn".
I don't believe the wording in the video, at least not precisely.  Obviously an engine is burning.  But there is a big difference in the flame size at +11:12 vs +11:33 , and the earlier one has a pulsating pattern.
Also, time to decelerate from terminal velocity to hover is T = V * a where a = m / (F-W) = 1/(F/m - g) => T = V/(F/m - g) .   Guesses of V=100m/s, F = 600 kN, m = 18000 kg yields deceleration of 30g and firing time of 3 seconds, which is consistent with my parsing of the video.  However, the video label "landing burn" occurs 24 seconds before splashdown.

I think you are seeing the exhaust begin to interact with the water, and confusing this with a throttle up.  If you look at the F9R and Grasshopper flights, it is obvious the 'landing burn' is longer than 3 seconds.  And a 30g deceleration would be brutal.  See the CRS-3 video discussion.

Offline AJA

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #181 on: 07/25/2014 06:04 AM »
I don't think you need a quadcopter when you have Elon's personal jet in the area.

I doubt Elon's personal jet would be allowed to get as close. One, or even two precision landings aren't exactly a comprehensive base for predicting the performance of the subsequent attempt. It's not trivial to track a fast-moving object from another fast moving object. Hence the "convoluted" submarine idea.

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We don't know what other free variables were specified on this landing attempt.
...
These landing attempts are about supersonic retropropulsion and reentry heating on the structure, which is the flight regime F9R can't easily test.  (Propellant quantities can be computed, they don't need a test flight for that.)

But we do know the variables that need to be specified, in order for something to meet the pin-point criterion. Wasn't this landing different enough from what would be required for RTLS, that it's insufficient to demonstrate future landing accuracy in itself?

Yeah, but the mass distribution would affect retropropulsion, control and re-entry heating. Something with more propellant, and sloshing around to boot, would have different dynamic (and perhaps even static stability), or need more control inputs to follow a programmed trajectory. I don't know. Sure, you can simulate it, but then, you can simulate most things.

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Crazy talk.  The progression between cassiope, CRS-3 and ORBCOMM flight has been landing closer to shore each time.

I did look at a map. I was suggesting somewhere up/down the East coast itself (or in the Carribean). But I may be grossly over-stimating how far the first stage travels in assuming it has the legs to attempt going feet dry over an area more desolate and cordoned off than the Cape.

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That would defeat the point.  FH is a three-stage rocket.  The two boosters are the first stage.  Getting rid of a stage has a large negative impact on performance; study the rocket equation.

I get the concept of staging. But it's not like SpaceX are pursuing maximum performance everywhere. The hit in performance could be compensated by being able to get all three cores to RTLS. I was only offering a counter to the argument that losing all three first stages would rip S2 to shreds.

Lastly, I'd considered all the reasons you mentioned that go against an off-shore base, but to it's only an assumption that the pros don't weigh up to the cons.

[Greater overheads + increased turn-around time (immaterial if it's not on the critical path)] vs [increased payload margins + maybe decreased complexity + ability to retrieve core stages on FH class launches + redundancy + catering to sub-orbital research payload market]. The Cape isn't too far from the coast, and they already operate in the "salt air" (admittedly they can have huge facilities and climate controlled rooms and all that when based on a land, and connected to a grid).

Economics is pretty pliable. It hasn't been too long ago since the days when discussions of cheap re-usability itself was heresy; yet here SpaceX are... making the economics work.

Offline douglas100

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #182 on: 07/25/2014 09:30 AM »

...Economics is pretty pliable. It hasn't been too long ago since the days when discussions of cheap re-usability itself was heresy; yet here SpaceX are... making attempting to make the economics work.

Fixed that for ya. And even SpaceX can't defy the financial law of gravity: it must keep costs down and get the revenue stream up or go bust. Spending on complicated offshore infrastructure does not seem to me a good way to do either.
Douglas Clark

Offline mvpel

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #183 on: 07/25/2014 11:04 AM »
On the video this is titled "landing burn".
I don't believe the wording in the video, at least not precisely.  Obviously an engine is burning.  But there is a big difference in the flame size at +11:12 vs +11:33 , and the earlier one has a pulsating pattern.

The orange flames you see at +11:12 are not "RCS", they're the fuel-rich turbine exhaust. The pulsating you see is that exhaust flapping in the wind of the descent.

The RCS is cold nitrogen in any case - you can see it in action, as a little white plume on the right side of the stage, in the OG-2 launch video just after stage sep, as the stiffener ring falls away from the M1-D nozzle extension.

If you look at at the 1km F9R-Dev flight with the cows, you'll see the flapping orange flame quite clearly about a minute and a half in. The actual exhaust plume of the engine is never visible to the camera, as it's being directed straight down in a supersonic pillar.

The +11:33 white circle is not flame, it's a huge splash of water being hurled outward by 140,000 pounds of thrust in the moments before landing. We've seen what Merlin engines can do with water on the CRS-3 launch.
« Last Edit: 07/25/2014 11:07 AM by mvpel »
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Offline Mader Levap

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #184 on: 07/25/2014 12:00 PM »
It hasn't been too long ago since the days when discussions of cheap re-usability itself was heresy; yet here SpaceX are... making the economics work.
Nope. They are in progress of making it work technically.

It remains to be seen if it will be economic. I think it will be, but it is not proven at this point and we are at least decade away from that.
Be successful.  Then tell the haters to (BLEEP) off. - deruch
...and if you have failure, tell it anyway.

Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #185 on: 07/26/2014 12:16 AM »
Quote from: SpaceX
At this point, we are highly confident of being able to land successfully [..] and refly the rocket with no required refurbishment.

I don't know how they can make any claims about refurbishment if they haven't recovered a stage yet.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline cscott

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #186 on: 07/26/2014 03:14 AM »
Quote from: SpaceX
At this point, we are highly confident of being able to land successfully [..] and refly the rocket with no required refurbishment.

I don't know how they can make any claims about refurbishment if they haven't recovered a stage yet.

They haven't recovered an intact stage.  They *have* recovered parts from the water.  (And five complete dragons, of course.) That may be enough to give them confidence that they have not made any major mistakes in their understanding of the reentry environment.  There are four engine relights & burns (with full telemetry) *after* supersonic reentry, so they know that the reentry isn't significantly harming the engines.  And, of course, they've fired the engines *many* times, recycled propellant, etc, so they have a pretty good handle on the service life of the components.

"Feeling confident" that they are "able" doesn't exactly mean that they *plan* to do so immediately.  I strongly suspect the first landed stage will be fully torn down and every part examined before it's reflown.

And note that they only said "refly the rocket", not "refly the rocket 50 times" without refurbishment.  So the claim is not quite as bold as it may initially seem.

Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #187 on: 07/26/2014 03:19 AM »
There's more than just the engines to consider. I just think it was an overly bold statement. (From SpaceX? Never!)
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Robotbeat

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #188 on: 07/26/2014 03:26 AM »
They've flown F9R-dev1 at least 20 times (they don't release video of every time). That's probably where such a statement comes from.
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Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #189 on: 07/26/2014 03:28 AM »
What's that got to do with anything? It's the reentry that does the damage currently unknown wear (if any).
« Last Edit: 07/26/2014 03:28 AM by QuantumG »
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Robotbeat

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #190 on: 07/26/2014 03:30 AM »
What's that got to do with anything? It's the reentry that does the damage (if any).
On the contrary, launch and landing are probably harder on the vehicle than a few Mach reentry. Or at least, SpaceX likely believe so.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #191 on: 07/26/2014 03:32 AM »
What's that got to do with anything? It's the reentry that does the damage (if any).
On the contrary, launch and landing are probably harder on the vehicle than a few Mach reentry. Or at least, SpaceX likely believe so.

I'm not arguing that. The point is they can't possibly know that yet. Until they recover a stage, they won't know how beaten up it is.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Robotbeat

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #192 on: 07/26/2014 03:39 AM »
What's that got to do with anything? It's the reentry that does the damage (if any).
On the contrary, launch and landing are probably harder on the vehicle than a few Mach reentry. Or at least, SpaceX likely believe so.

I'm not arguing that. The point is they can't possibly know that yet. Until they recover a stage, they won't know how beaten up it is.
We're talking about SpaceX, here. BFR, Mars Colony of a million people who pay just $500,000 SpaceX. They know it doesn't blow up until it topples over. That's better proof of not being beat up than anything they have about a Mars colony.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Robotbeat

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #193 on: 07/26/2014 03:41 AM »
Also, the stages are instrumented with strain gauges and such and they've gotten telemetry all the way down to the water. They know what kind of beating the stage has taken from that right there.
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Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #194 on: 07/26/2014 03:42 AM »
That's certainly better than nothing, but I don't think it's sufficient for the claim they've made here. They need to recover the stage.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline sojourner

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #195 on: 07/26/2014 03:48 AM »
Hey, just had a thought and wasn't sure what the best thread to put this in was.

Is it possible that the fact that SpaceX hasn't done the boost back phase on any flight contributing to the stage "kabooming" when it falls over in the ocean? By that I mean, could it have extra weight from the unused fuel (particularly the oxygen in the upper part of the stage) contributing with how hard it hits?  Might including the boost back before the water landing increase the chance of recovering an intact stage?

Online mme

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #196 on: 07/26/2014 03:57 AM »
Quote from: SpaceX
At this point, we are highly confident of being able to land successfully [..] and refly the rocket with no required refurbishment.

I don't know how they can make any claims about refurbishment if they haven't recovered a stage yet.
They are claiming they are confident, not that they know it for a fact.  They don't have the stage but they have the telemetry and whatever simulations they've run.  They have a fair idea the stresses the stage encountered on reentry and they know everything was functioning as they expected.

When they recover one, especially if they land one, then they'll know for a fact.  Maybe it will turn out they are wrong, but I can't see the problem with them saying they are confident at this point.

Edit: I really need a proof reader.
« Last Edit: 07/26/2014 05:10 AM by mme »
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Offline QuantumG

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #197 on: 07/26/2014 04:06 AM »
Quote from: SpaceX
At this point, we are highly confident of being able to land successfully [..] and refly the rocket with no required refurbishment.

I don't know how they can make any claims about refurbishment if they haven't recovered a stage yet.
They are claiming they are confident, not that they know it for a fact.  They don't have the stage but they have the telemetry and whatever simulations they've run.  They have a fair idea the stresses stage encountered on reentry and they know everything was functioning as they expected.

When they recover one, especially if they land one, then they'll know for a fact.  Maybe it will turn out they are wrong, but I can't see the problem with being them saying they are confident at this point.

Fair enough. Point taken.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline deruch

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #198 on: 07/26/2014 04:37 AM »
When's the last time SpaceX wasn't highly confident about something?  That's sort of their defining trait isn't it? :)
« Last Edit: 07/26/2014 04:37 AM by deruch »
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Online docmordrid

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Re: Falcon 9 v1.1 ORBCOMM - First Stage Ocean Landing Video
« Reply #199 on: 07/26/2014 04:43 AM »
When's the last time SpaceX wasn't highly confident about something?  That's sort of their defining trait isn't it? :)

The times they've said a stage only had a small chance of making it down intact? Saying they'd crater a Grasshopper? Etc.
DM

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