Author Topic: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION  (Read 219061 times)

Offline Proponent

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #520 on: 05/01/2017 08:25 PM »
Do we know which core flew today?

Offline stcks

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #521 on: 05/01/2017 08:30 PM »
Do we know which core flew today?

B1032. Check the number painted just above the octaweb.

Offline georgegassaway

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #522 on: 05/01/2017 11:28 PM »
I have the longest boostback, at 45 seconds or longer, taking place during the CRS-9 flight, during which the first stage returned to LZ 1.  For some reason, a shorter 33 second burn was used for CRS-10, which also returned to LZ 1.  Both of these flights had a 141 second first stage MECO.

Didn't CRS-10 have a much higher lofted trajectory than CRS-9? If so,  less horizontal velocity and shorter distance to fly back. 2nd stage has to work a bit harder but as long as it has enough fuel, then that allows for a shorter burn for the boostback.

May require a longer re-entry burn due to heating issues (falling at a steeper angle, from higher altitude) if the heating level is a concern for multiple re-use or minimal refurbishment/parts replacement.

Took a quick look at Flight Club videos, MECO for CRS-9 seemed to be at about 58-58.5 km, CRS-10 at about 64 km.  I'm sure much better detailed info is available, but that seems to confirm a higher lofted trajectory

Offline rockettrey

Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #523 on: 05/02/2017 12:56 AM »
I also eagerly await all the smart and informed answers to these questions!  Gravity losses and basic orbital mechanics are something I somehow missed out on my space "career"!  Thanks everyone!

Offline Herb Schaltegger

Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #524 on: 05/02/2017 01:10 AM »
I also eagerly await all the smart and informed answers to these questions!  Gravity losses and basic orbital mechanics are something I somehow missed out on my space "career"!  Thanks everyone!

I'll catch hell but, whatever ...

Just like all NSF-based discussions of spaceflight eventually gravitate toward SpaceX, most SpaceX discussions among uneducated (*) fans eventually turns to Kerbal Space Program. But aside from the snark, if you spend a few weeks with that game and really try to learn it, you'll get a better intuitive grasp of the physics involved than you can get without a multi-year college education.

(*) Not an insult; just shorthand to describe those who may lack at least a Bachelor's level degree in aerospace engineering, physics, or something similar.
Ad astra per aspirin ...

Offline bunker9603

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #525 on: 05/02/2017 01:36 AM »
Great Youtube footage with nice close-ups of the landing (Not my video)


33 seconds in is my favorite


https://www.youtube.com/watch?v=GoRKhH8J1YQ#t=75.629688
« Last Edit: 05/02/2017 01:38 AM by bunker9603 »

Offline IanThePineapple

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #526 on: 05/02/2017 01:46 AM »
I also eagerly await all the smart and informed answers to these questions!  Gravity losses and basic orbital mechanics are something I somehow missed out on my space "career"!  Thanks everyone!

I'll catch hell but, whatever ...

Just like all NSF-based discussions of spaceflight eventually gravitate toward SpaceX, most SpaceX discussions among uneducated (*) fans eventually turns to Kerbal Space Program. But aside from the snark, if you spend a few weeks with that game and really try to learn it, you'll get a better intuitive grasp of the physics involved than you can get without a multi-year college education.

(*) Not an insult; just shorthand to describe those who may lack at least a Bachelor's level degree in aerospace engineering, physics, or something similar.

Oof, I've played about 1500 hours of KSP, I must have at least a mediocre grasp on physics
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Offline Robotbeat

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #527 on: 05/02/2017 01:59 AM »
  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.
The shape of the engine bells gives you something more like an inverted cone, about 1.3 drag coefficient. Also, the grid find are pretty big and generate quite a lot of drag plus some lift, allowing the vehicle to fly at an angle of attack, further decreasing terminal velocity.
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Offline macpacheco

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #528 on: 05/02/2017 02:24 AM »
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.
Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē) but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.
Imagine if the stage were going at orbital velocity horizontally, that speed would be enough to cancel out gravity and keep it in orbit.
Half orbital speed would cancel quarter gravity.
1/4 orbital speed would cancel 1/16 gravity.
A typical GTO mission staging speeds, F9 boosters are flying at something like 1/3 of orbital speed, which cancels 1/9 of gravity.
In LEO with RTLS missions, F9 boosters are flying something between 1/4 and 1/5 of orbital speed.

Edit: Thanks for the correction, Mr LouScheffer !
« Last Edit: 05/02/2017 03:22 AM by macpacheco »
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Offline LouScheffer

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #529 on: 05/02/2017 02:39 AM »
Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē) but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.
Imagine if the stage were going at orbital velocity horizontally, that speed would be enough to cancel out gravity and keep it in orbit.
Half orbital speed would cancel half gravity.
1/4 orbital speed would cancel 1/4 gravity.
Centripetal acceleration goes like v^2/r, so half orbital speed cancels 1/4 gravity.  1/4 orbit speed cancels 1/16 gravity.

So for the speeds reached by the first stage, gravity cancellation is quite a minor effect.

Offline baldusi

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #530 on: 05/02/2017 02:40 AM »
The fact that Ball contracted the flight might not mean much. They could be building the while thing, they could be building the bus and integrating a payload from a different manufacturer, they could be just integrators, or they might have the option because the lost some contract and were approached by the main contractor to sell the launch service.
What I wonder, is if they could do this only because they have the USAF certification.

Offline JMS

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #531 on: 05/02/2017 03:10 AM »
Wow, there sure were some great close-ups of the returning booster - anybody notice that?

Yes... multiple times in both the UPDATES and DISCUSSION threads. And, yes, they are fantastic images.

Offline Pete

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #532 on: 05/02/2017 04:15 AM »
Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē) but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.
Imagine if the stage were going at orbital velocity horizontally, that speed would be enough to cancel out gravity and keep it in orbit.
Half orbital speed would cancel half gravity.
1/4 orbital speed would cancel 1/4 gravity.
Centripetal acceleration goes like v^2/r, so half orbital speed cancels 1/4 gravity.  1/4 orbit speed cancels 1/16 gravity.

So for the speeds reached by the first stage, gravity cancellation is quite a minor effect.

Interesting.
Due to Centripetal/centrifugal effect, the rocket "weighs" about 9% less, at start of boostback burn.
Due to altitude, the rocket "weighs" about 6% less, at apogee.

Offline Lars-J

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #533 on: 05/02/2017 04:28 AM »
Great Youtube footage with nice close-ups of the landing (Not my video)


33 seconds in is my favorite


https://www.youtube.com/watch?v=GoRKhH8J1YQ#t=75.629688

The best footage is from this new Instagram video posted by Elon:
https://www.instagram.com/p/BTjVdLVB1bO/

Offline kevinof

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #534 on: 05/02/2017 08:31 AM »
I watched this "live"  (aka youbube), have watched the video maybe 30 times since then and my jaw still drops.

This video from Elon is even better and you can see the flip and almost instant re-start of the S1 to get back home - It doesn't hang around. Then the falling S1 coming back in is just crazy. Anyone else yell out "legs,legs.." when watching it come into land live or is that just me. They seem to leave it very late (too late for my ticker anyway).

Wonderful stuff. Will never get old and never be the same again.


Great Youtube footage with nice close-ups of the landing (Not my video)


33 seconds in is my favorite


https://www.youtube.com/watch?v=GoRKhH8J1YQ#t=75.629688

The best footage is from this new Instagram video posted by Elon:
https://www.instagram.com/p/BTjVdLVB1bO/

Online Steven Pietrobon

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #535 on: 05/02/2017 10:59 AM »
The best footage is from this new Instagram video posted by Elon:
https://www.instagram.com/p/BTjVdLVB1bO/

Here are the Instagram videos on Youtube.



« Last Edit: 05/02/2017 11:00 AM by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline kevinof

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #536 on: 05/02/2017 12:18 PM »
Nice gimbal movement on the first video. Working hard.

Offline AncientU

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #537 on: 05/02/2017 01:04 PM »
We've come a long way from reconstructing the landing footage of CRS-3, haven't we? :)

Congratulations to SpaceX on their first DoD flight and for a spectacular depiction of how our robot overlords will soon invade us. I, for one, welcome more simulations.

Nice reminder... CRS-3 was April 18, 2014. 
Three years to go from seemingly impossible to routine!
First half (1y8m) got us to first land landing -- now (1y4m later) a core has been reflown, a handful are scheduled this year, and landing is routine -- though not boring.  Final upgrade of F9 is being fab'd to incorporate lessons learned.
Brilliant test program. 

Naysayers... any last words?
(other than ULA's 'wet blanket/lost performance' comment yesterday at #ulcats)
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Les Kovacs, ULA: want to throw a wet blanket on concept of reusability. Additional systems needed to land stages comes at cost of payload.

Edit: added Kovacs quote
« Last Edit: 05/02/2017 03:15 PM by AncientU »
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Offline gospacex

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #538 on: 05/02/2017 01:27 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.
Once the engine shuts down, gravity would be slowing the stage down 10m/s per second downward (10m/sē)

After MECO and boostback, whatever slowdown gravity induces on the way up, will be again imparted by the same gravity on the way down. Essentially, if boostback thrust vector is strictly horizontal, the vertical component of velocity does not change, and when the stage arches up and then falls back and when it is at the same altitude as where boostback was done, the vertical component of velocity will be exactly the same, only now pointing down. (Since boostback is done at the altitude of 70km, air resistance is negligible).

Quote
but since the stage is flying horizontally at some good speed, that speed produces a centripetal force with fights gravity on its own.

In this flight, horizontal velocity component after boostback was only 290m/s. It's too low to induce significant centripetal force. (see 16:44 on the "NROL-76 Launch Webcast" youtube vid, when S1 reached the top of the return parabola).
« Last Edit: 05/02/2017 01:38 PM by gospacex »

Offline su27k

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Re: SpaceX Falcon 9 - NROL-76 - May 1, 2017 - DISCUSSION
« Reply #539 on: 05/02/2017 01:31 PM »
We've come a long way from reconstructing the landing footage of CRS-3, haven't we? :)

Congratulations to SpaceX on their first DoD flight and for a spectacular depiction of how our robot overlords will soon invade us. I, for one, welcome more simulations.

Nice reminder... CRS-3 was April 18, 2014. 
Three years to go from seemingly impossible to routine!
First half (1y8m) got us to first land landing -- now (1y4m later) a core has been reflown, a handful are scheduled this year, and landing is routine -- though not boring.  Final upgrade of F9 is being fab'd to incorporate lessons learned.
Brilliant test program. 

Naysayers... any last words?
(other than ULA's 'wet blanket/lost performance' comment yesterday at #ulcats)

All good except for the Elon TimeTM factor, if you look back at the interview after CRS-3, the plan was successful landing in 2014 and refly in 2015, so it took them twice as long to accomplish what they set out to do.

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