Author Topic: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION  (Read 220063 times)

Offline LouScheffer

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #460 on: 05/01/2017 02:02 PM »
  Terminal velocity looked like about 300 m/s.  This is about as expected from something of that size, shape, and mass.
Interesting. That terminal velocity is 2x the 150 m/sec terminal velocity observed on the first F9 landing at the Cape. F9 has bulked up since then...
http://forum.nasaspaceflight.com/index.php?topic=39100.msg1465116#msg1465116
I'm very suspicious of that 150 m/s number.  If we plug in what we know of the booster (mass = 30t, from Hans), cross sectional area of 10 m^2 (known), coefficient of drag of a cylinder end on (0.8), density of air at 4000m (0.8 kg/m^3), we get a terminal velocity of about 300 m/s.  None of these figures seems uncertain enough to get the terminal velocity down to 150 m/s.

Offline alang

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #461 on: 05/01/2017 02:10 PM »
"...the execution of 100s of people at SpaceX "

I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well.  Still, these days, who knows?

Haha, I lol'ed...  :-)

Amazing footage indeed. Would have loved a closer ground-to-booster view on landing but that's my only quibble.

Congrats to the NRO on being able to snoop even more on all of us
Elon just posted a nice view on Instagram.

Something like six seconds from start of leg deployment to landing. How does that compare with previous landings?

Offline laika_fr

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #462 on: 05/01/2017 02:20 PM »
Massive bow shock on three engines.
some studies have shown that a large bow is easier to maintain, and probably more efficient on multiple engines
on one engine you may "pierce" the arc more easily, it's a balance between thrust and air pressure, takes time to fine tune it.

a shrubbery on Mars

Offline envy887

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #463 on: 05/01/2017 02:24 PM »
Massive bow shock on three engines.
some studies have shown that a large bow is easier to maintain, and probably more efficient on multiple engines
on one engine you may "pierce" the arc more easily, it's a balance between thrust and air pressure, takes time to fine tune it.

Yes, the eye of Sauron - we've seen this on previous entries. This was definitely the best footage of it so far, though.

Offline deruch

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #464 on: 05/01/2017 02:26 PM »
Because we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.

Separation: 1.68 km/s at 69.6 km altitude, T+2:23
Apogee: 0.293 km/s at 166 km altitude, T+4:46
Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc.  So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone.  Plus it may change on a launch by launch basis.  Or, since he made those statements quite a while ago, they may no longer be doing this.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Kabloona

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #465 on: 05/01/2017 02:26 PM »
  Terminal velocity looked like about 300 m/s.  This is about as expected from something of that size, shape, and mass.
Interesting. That terminal velocity is 2x the 150 m/sec terminal velocity observed on the first F9 landing at the Cape. F9 has bulked up since then...
http://forum.nasaspaceflight.com/index.php?topic=39100.msg1465116#msg1465116
I'm very suspicious of that 150 m/s number.  If we plug in what we know of the booster (mass = 30t, from Hans), cross sectional area of 10 m^2 (known), coefficient of drag of a cylinder end on (0.8), density of air at 4000m (0.8 kg/m^3), we get a terminal velocity of about 300 m/s.  None of these figures seems uncertain enough to get the terminal velocity down to 150 m/s.

I'm looking at hrissan's video analysis and trying to find why his number was so much lower. I don't see any obvious errors, but it was a night landing, so maybe the darkness of the video threw his analysis off somehow.

Offline StuffOfInterest

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #466 on: 05/01/2017 02:34 PM »
Where is the tracking camera that followed the entire launch/landing flight?  It was definitely up the coast a ways from the landing site as there was always some side view of the rocket.  It would be an interesting perspective to have a camera near the landing site to look up the throat as the rocket is coming back in.

Offline Helodriver

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #467 on: 05/01/2017 02:35 PM »
The extreme closeups the vehicle at terminal velocity falling toward LZ-1 were most likely by a 45th Space Wing range tracking camera, not a dedicated SpaceX asset.

Was anticipating the quality of those images starting a few years ago. Nice to predict the future once again.  8)

Hope that becomes a regular part of coverage at some point.

http://forum.nasaspaceflight.com/index.php?topic=36558.msg1330568#msg1330568

Offline Kabloona

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #468 on: 05/01/2017 02:35 PM »
Because we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.

Separation: 1.68 km/s at 69.6 km altitude, T+2:23
Apogee: 0.293 km/s at 166 km altitude, T+4:46
Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc.  So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone.  Plus it may change on a launch by launch basis.  Or, since he made those statements quite a while ago, they may no longer be doing this.

Welsh Dragon's altitude vs. time plot upthread shows nicely that the boostback burn was entirely horizontal, because the altitude vs. time curve during the boostback burn has the same shape as the corresponding period during the "free fall" period on the other side of the curve...ie, going up with (horizontal) boostback is the same as going down under gravity alone, as far as altitude vs. time is concerned.

Which makes sense, now that they've recovered several stages and proven that the stage can survive "falling" from apogee with an entry burn of reasonable duration.
« Last Edit: 05/01/2017 02:49 PM by Kabloona »

Offline alang

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #469 on: 05/01/2017 02:39 PM »
"...the execution of 100s of people at SpaceX "

I had heard that this approach was used in North Korea to encourage hard work among the survivors, but I didn't expect it to be used in the USA as well.  Still, these days, who knows?

Haha, I lol'ed...  :-)

Amazing footage indeed. Would have loved a closer ground-to-booster view on landing but that's my only quibble.

Congrats to the NRO on being able to snoop even more on all of us
Elon just posted a nice view on Instagram.

Something like six seconds from start of leg deployment to landing. How does that compare with previous landings?

Seems about about a second earlier during CRS-10:

Offline sevenperforce

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #470 on: 05/01/2017 02:49 PM »
Because we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.

Separation: 1.68 km/s at 69.6 km altitude, T+2:23
Apogee: 0.293 km/s at 166 km altitude, T+4:46
Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc.  So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone.  Plus it may change on a launch by launch basis.  Or, since he made those statements quite a while ago, they may no longer be doing this.

Welsh Dragon's altitude vs. time plot upthread shows nicely that the boostback burn was entirely horizontal, because the altitude vs. time curve during the boostback burn has the same shape as the corresponding period during the "free fall" period on the other side of the curve...ie, going up with (horizontal) boostback is the same as going down under gravity alone, as far as altitude vs. time is concerned.
With this wealth of data, we should be able to derive near-exact propellant loading numbers for the entire flight.

Offline mme

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #471 on: 05/01/2017 02:52 PM »
A few observations from this wonderful footage:

There is a "heartbeat" like glow (not the nitrogen thrusters) at the base of the rocket every few seconds.  My guess is that they are releasing pressure through the engines so (as opposed to the vents) so they don't upset the attitude.

The jets are navigating in 3d,not just two.  You can see them thrusting fore and aft as well as sideways.
I suspect that some of the "heartbeat" is for ullage.  The stage is essentially in freefall and they'll want to keep the propellent at the bottom of the tanks.
Space is not Highlander.  There can, and will, be more than one.

Offline Welsh Dragon

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #472 on: 05/01/2017 02:53 PM »
I am currently doing the burns with a 1 second resolution. So that should give better data if you want to do something with it. EDIT: In reply to sevenperforce
« Last Edit: 05/01/2017 02:53 PM by Welsh Dragon »

Offline deruch

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #473 on: 05/01/2017 03:04 PM »
Because we know that the boostback burn is always going to be just about perfectly horizontal (as anything off-horizontal is going to waste propellant), we can now determine for the first time with reasonably good accuracy exactly what the trajectory was at MECO, based on separation altitude vs apogee.

Separation: 1.68 km/s at 69.6 km altitude, T+2:23
Apogee: 0.293 km/s at 166 km altitude, T+4:46
Hans Koenniggsman has talked before about using the boostback burn to lower the apogee by aiming below the horizon and thereby reducing upward velocity, etc.  So, while it may be fine as a rule of thumb, I wouldn't necessarily rely on that as 100% set in stone.  Plus it may change on a launch by launch basis.  Or, since he made those statements quite a while ago, they may no longer be doing this.

Welsh Dragon's altitude vs. time plot upthread shows nicely that the boostback burn was entirely horizontal, because the altitude vs. time curve during the boostback burn has the same shape as the corresponding period during the "free fall" period on the other side of the curve...ie, going up with (horizontal) boostback is the same as going down under gravity alone, as far as altitude vs. time is concerned.

Which makes sense, now that they've recovered several stages and proven that the stage can survive "falling" from apogee with an entry burn of reasonable duration.
My caution wasn't about any one particular launch but more because sevenperforce was saying that it was a given for all launches.  That may turn out to be the case moving forward as SpaceX has improved their hardware and their recovery knowledge, but it isn't automatically so based solely on a logical assumption.  Especially not given Hans' previous comments.  Though, since this is the NROL-76 thread, and it did in fact use a purely horizontal burn, this is a bit of moot point. 
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline mn

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #474 on: 05/01/2017 03:06 PM »
Both yesterday and again today, the presenter of the webcast stated that the Falcon 9 is 12m in diameter. I am right that he is confusing the F9 - which I thought is 3.6m in diameter - with the Falcon Heavy, correct?

The presenter said 12ft (at about 15:50 into the webcast replay) which is close enough with rounding.

Edit: I went back and listened to the full webcast and the presenter said 12m in the pre launch chatter, and said 12ft later in the broadcast after launch.
« Last Edit: 05/04/2017 06:09 PM by mn »

Offline edkyle99

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #475 on: 05/01/2017 03:11 PM »
Both yesterday and again today, the presenter of the webcast stated that the Falcon 9 is 12m in diameter. I am right that he is confusing the F9 - which I thought is 3.6m in diameter - with the Falcon Heavy, correct?

The presenter said 12ft (at about 15:50 into the webcast replay) which is close enough with rounding.

The diameter is 12 feet - 144 inches.  That is 3.6576 meters exactly.

 - Ed Kyle
« Last Edit: 05/01/2017 03:11 PM by edkyle99 »

Offline mn

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #476 on: 05/01/2017 03:12 PM »
Looks like aerodynamic braking is pretty strong, as expected.  After the entry burn, it accelerated for a while in the thin air, then decelerated at about 2G.   Terminal velocity looked like about 300 m/s.  This is about as expected from something of that size, shape, and mass.

The announcer said 1000 km/h ( = 277 m/s ), (but he may have been rounding).

Offline Star One

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #477 on: 05/01/2017 03:14 PM »
It's been noted elsewhere that this mission like USA-193 features a brown raptor bird in its patch.

https://m.facebook.com/photo.php?fbid=116648047531&l=169616826b
« Last Edit: 05/01/2017 03:16 PM by Star One »

Offline RonM

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #478 on: 05/01/2017 03:15 PM »
Both yesterday and again today, the presenter of the webcast stated that the Falcon 9 is 12m in diameter. I am right that he is confusing the F9 - which I thought is 3.6m in diameter - with the Falcon Heavy, correct?

The presenter said 12ft (at about 15:50 into the webcast replay) which is close enough with rounding.

Since he said it two days in a row, it was an error in his script (meters instead of feet). He got it right later, or should I say the script was correct.

Offline edkyle99

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #479 on: 05/01/2017 03:25 PM »
With this launch, LC 39 Pad A has handled more launches this year than any other launch center, let alone launch pad.   Likely temporary, but shows how hard SpaceX is pushing to recover from AMOS 6.

This was the tenth successful first stage landing and the fourth at LZ-1.  Nine first stages have now flown to recovery (one twice).  Something like four of those have apparently been retired.

Among v1.2 variants, this had the shortest first stage burn (137 seconds) and the second longest boost-back burn (40 seconds).

F9-34 performed the 98th LC 39A liftoff.

 - Ed Kyle
« Last Edit: 05/01/2017 03:28 PM by edkyle99 »

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