Author Topic: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION  (Read 220020 times)

Offline envy887

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #500 on: 05/01/2017 04:56 PM »
...
It does give me the sense that SpaceX is experimenting with fly-back trajectory shaping to minimize damage to the stage.  Note that none of the LZ 1 stages has re-flown to date.

 - Ed Kyle

We know GTO/ASDS boosters (e.g. Thaicom) are in queue to be reused, and we know they get far more damage on entry than RTLS boosters.

However, they still certainly could be trying to shape the trajectory to get an easier entry. That would be wise.

Online abaddon

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #501 on: 05/01/2017 05:08 PM »
From the Update thread:
I have confirmation that one-half of the fairing was recovered via parachute. My message said it was recovered from the water, intact.
That's SpaceX for you, always doing things in half measure...

More seriously... I would expect we would start seeing recovery hardware on both fairing halves sooner or later.  I know they want to land them on "bouncy castles", wonder if there is anything salvageable from a water recovery though.

Online abaddon

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #502 on: 05/01/2017 05:12 PM »
Note that none of the LZ 1 stages has re-flown to date.
That's not really saying much, since only one stage has re-flown so far.  Obviously the Orbcomm2 booster is out, but we don't know anything about reflight plans (or not) for the other two previous successful LZ-1 landings (CRS-9 & CRS-10).

Online rockets4life97

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #503 on: 05/01/2017 05:18 PM »
So, to the speculation about whether this booster had upgraded fuller thrust: can't Chris or someone simply ask SpaceX for us? Doesn't seem like the kind of thing they are intentionally hiding. 

Online Lars-J

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #504 on: 05/01/2017 05:20 PM »
Amazing flight... Amazing footage. Woo hoo!  ;D


Do people recall this ad from a couple of years ago by PWR? (Now part of AeroJet rocketdyne?) :D
So far this year... 9 US orbital launches:
 - 5 by SpaceX
 - 4 by ULA (1 Delta IV, 3 Atlas V)

If counting by engines:
 - 50 engines by SpaceX
 - 5 engines by AJR
« Last Edit: 05/01/2017 05:22 PM by Lars-J »

Offline sevenperforce

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #505 on: 05/01/2017 05:21 PM »
...
It does give me the sense that SpaceX is experimenting with fly-back trajectory shaping to minimize damage to the stage.  Note that none of the LZ 1 stages has re-flown to date.

 - Ed Kyle

We know GTO/ASDS boosters (e.g. Thaicom) are in queue to be reused, and we know they get far more damage on entry than RTLS boosters.

However, they still certainly could be trying to shape the trajectory to get an easier entry. That would be wise.
Peak heating on GTO entries is higher, but maybe there are other considerations we aren't able to see. A big lofted trajectory with boostback, like today's, will have lower peak heating but might have higher gee forces because it slams into the atmosphere going a lot faster.
So, to the speculation about whether this booster had upgraded fuller thrust: can't Chris or someone simply ask SpaceX for us? Doesn't seem like the kind of thing they are intentionally hiding. 
Evidently not, based on the acceleration off the pad. Acceleration was pretty much identical to CRS-10.

Offline M.E.T.

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #506 on: 05/01/2017 05:26 PM »
Well, I learnt something today.

I was surprised that even though the main engine cut out at around 65km altitude, the booster gained more altitude AFTER main engine cut out than it had gained for the entire time that the engine was actually burning. This is obviously old news to you experts on the forum, but to me as a layman I just intuitively expected that altitude gains would stop pretty soon after the booster's engine cut out.

As it turns out, the booster engine cut out at 65km, but the 1st stage continued up to attain an altitude of 165km or so before it started falling back to Earth.

In hindsight it makes sense, as basic physics tells me that vertical speed would only decrease by 10m/s once the thrust disappeared, but it was interesting to see nevertheless. Normally we just see the 2nd stage altitude after MECO.

Offline hans_ober

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #507 on: 05/01/2017 05:34 PM »
...
It does give me the sense that SpaceX is experimenting with fly-back trajectory shaping to minimize damage to the stage.  Note that none of the LZ 1 stages has re-flown to date.

 - Ed Kyle

We know GTO/ASDS boosters (e.g. Thaicom) are in queue to be reused, and we know they get far more damage on entry than RTLS boosters.

However, they still certainly could be trying to shape the trajectory to get an easier entry. That would be wise.
Peak heating on GTO entries is higher, but maybe there are other considerations we aren't able to see. A big lofted trajectory with boostback, like today's, will have lower peak heating but might have higher gee forces because it slams into the atmosphere going a lot faster.
So, to the speculation about whether this booster had upgraded fuller thrust: can't Chris or someone simply ask SpaceX for us? Doesn't seem like the kind of thing they are intentionally hiding. 
Evidently not, based on the acceleration off the pad. Acceleration was pretty much identical to CRS-10.

I second this. While the post-reentry velocity of S1 is ~800m/s for RTLS and ~1300m/s (I suspect that it was a bit higher for SES-10), RTLS boosters have a lot of vertical velocity, which is why I'm guessing that in certain cases, they slam through the atmosphere so quickly that they might not even hit terminal velocity (since it's time for the landing burn before they have time to slow down.

On the other hand, GTO S1s have mostly horizontal velocity. The re-entry burn might be to reduce the vertical velocity (since S1 will hit the dense atmosphere before it slows down enough). Slower vertical velocity means that they can bleed off more horizontal velocity slowly, by flying at a high angle of attack and 'lifting' the booster.

We've got official confirmation from Elon that they plan on doing this. This will be very important for FH. The core will be doing around 3-3.5kmps in some cases, and will need to slow down to around 1.5kms before it hits the atmosphere (using the entry burn). Again, this will be mainly to bleed off vertical velocity. Now, if the booster is falling slow enough, but travelling horizontally fast enough, they can bleed a LOT of this speed off by flying at high angles of attack (which is why they need bigger grid fins). (Will they try complete horizontal? :o A lot to gain if they can somehow pitch the engines higher than the interstage to generate more lift  ::)

tldr: RTLS has mostly vertical velocity, slams into the atmosphere very quickly, and in some cases does not reach terminal velocity.
GTO has horizontal velocity, probably speeds close to half a minute at terminal velocity (although the re-entry is hotter).

Offline hans_ober

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #508 on: 05/01/2017 05:38 PM »
Well, I learnt something today.

I was surprised that even though the main engine cut out at around 65km altitude, the booster gained more altitude AFTER main engine cut out than it had gained for the entire time that the engine was actually burning. This is obviously old news to you experts on the forum, but to me as a layman I just intuitively expected that altitude gains would stop pretty soon after the booster's engine cut out.

As it turns out, the booster engine cut out at 65km, but the 1st stage continued up to attain an altitude of 165km or so before it started falling back to Earth.

In hindsight it makes sense, as basic physics tells me that vertical speed would only decrease by 10m/s once the thrust disappeared, but it was interesting to see nevertheless. Normally we just see the 2nd stage altitude after MECO.

This happens on S2 too. The vertical velocity imparted by S1 on GTO flights takes S1 and s2 to ~135km. S2 pitches up a little and increases this to ~170km. If you look closely, you'll notice that S2 flies to around ~170km, and then actually falls in altitude to ~160km before completing it's burn.

This effect is more apparent on rockets with low thrust S2. Look at Ariane 5, Atlas or Delta. Centaur is so low thrust that it barely finishes circularizing before it starts falling back, which is why Atlas booster has to fly lofted.

Offline .Scott

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #509 on: 05/01/2017 05:46 PM »
Odd that I didn't spot any military bods in mission control for an NRO launch. Did Space X keep them out the way somewhere to keep the cool image going.
I'm sure the "military bods" were monitoring from a SCIF.  Too bad, they were probably focused on their payload during that amazing 1st-stage recovery video.

Offline edkyle99

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #510 on: 05/01/2017 05:49 PM »
Stage 2 should have reentered an hour or two or four ago, correct?

 - Ed Kyle
« Last Edit: 05/01/2017 05:53 PM by edkyle99 »

Offline spacekid

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #511 on: 05/01/2017 05:52 PM »
Well, I learnt something today.

I was surprised that even though the main engine cut out at around 65km altitude, the booster gained more altitude AFTER main engine cut out than it had gained for the entire time that the engine was actually burning. This is obviously old news to you experts on the forum, but to me as a layman I just intuitively expected that altitude gains would stop pretty soon after the booster's engine cut out.

As it turns out, the booster engine cut out at 65km, but the 1st stage continued up to attain an altitude of 165km or so before it started falling back to Earth.

In hindsight it makes sense, as basic physics tells me that vertical speed would only decrease by 10m/s once the thrust disappeared, but it was interesting to see nevertheless. Normally we just see the 2nd stage altitude after MECO.
I think on this flight, it was flying more up than normal.

Offline Herb Schaltegger

Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #512 on: 05/01/2017 06:07 PM »
Stage 2 should have reentered an hour or two or four ago, correct?

 - Ed Kyle
Have you seen L2 re S2 on this flight?
Ad astra per aspirin ...

Offline edkyle99

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #513 on: 05/01/2017 06:23 PM »
Stage 2 should have reentered an hour or two or four ago, correct?

 - Ed Kyle
Have you seen L2 re S2 on this flight?
Yes.  I still expect reentry was to take place within three hours of liftoff based on NOTAMs.

 - Ed Kyle

Offline sanman

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #514 on: 05/01/2017 06:57 PM »
Wow, there sure were some great close-ups of the returning booster - anybody notice that? I've never seen such great close-ups like that before.

Offline LouScheffer

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #515 on: 05/01/2017 07:10 PM »
I was wondering why we can see the nitrogen jets.  After all, nitrogen is pretty transparent (we look through kilometers of it every day).  And it can't be that it's cold enough to condense water out of the air, since there is almost no atmosphere until it returns to much lower altitudes.

The only thing I can think of is that the free expansion cools the jet so much that droplets of liquid nitrogen condense, and scattering from these drops is what we see. 

No it doesn't turn to liquid , we see like you can see any gas venting into a vacuum.  Just like the other engines.
Not saying that it's different from other gasses - just wondering from a physics perspective why we can see it at all.

I finally found a good reference on this.  It's CONDENSATION OF NITROGEN IN A HYPERSONIC NOZZLE FLOW FIELD .  It covers this exact topic (visibility of plumes from nitrogen cold-gas thrusters) in detail, in an attempt to understand the effect of attitude control thrusters on observations.  They conclude the visible properties of the plume are due to Raleigh scattering from small particles of condensed gas.
Quote
It is well known that nozzle gas sources, such as those employed as attitude control system thrusters, produce a hypersonic flow which condenses when the gas source pressure is sufficiently high for a given gas source temperature. [...]  the formation of such species results in enhanced scattering of optical radiation incident upon the plume.
Quote
Based upon the electron beam and Raman density data (Fig. 25), approximately 10 to 20 percent of the total flow molecules were in the condensed phase.

Offline pb2000

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #516 on: 05/01/2017 07:49 PM »
The latest spaceX flickr photo from the update thread, has a bizzare trick of the light/angle that make it appear that a few merlins are missing. Weird.
Launches attended: Worldview-4 (Atlas V 401), Iridium NEXT Flight 1 (Falcon 9 FT)

Offline Senex

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #517 on: 05/01/2017 07:51 PM »
And Lou wins an official NSF "I corrected Jim!" T-shirt.

Jim, with his amazing knowledge, sets such a high bar that the T-shirts will always be rare.

Congratulations, Lou!

(Chris, we really need to get those T-shirts printed)
« Last Edit: 05/01/2017 07:55 PM by Senex »

Offline stcks

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #518 on: 05/01/2017 07:57 PM »
And Lou wins an official NSF "I corrected Jim!" T-shirt.

Jim, with his amazing knowledge, sets such a high bar that the T-shirts will always be rare.

Congratulations, Lou!

(Chris, we really need to get those T-shirts printed)

Both are assets on this forum. Two of the handful of reasons I signed up.

Online abaddon

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #519 on: 05/01/2017 08:16 PM »
Jim wasn't wrong, so it is dubious to claim he was corrected.

Thanks to Lou for looking up the details on what is going on.  Fascinating stuff.

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