Author Topic: SpaceX Falcon 9 : Iridium NEXT Flight 4 : December 22/23, 2017 : Discussion  (Read 81696 times)

Online ugordan

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One more airborne video, just for the commentary's sake.


Offline su27k

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Telephoto video taken by a SpaceX employee, some nice outreach:
« Last Edit: 12/23/2017 11:31 AM by su27k »

Offline nacnud

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Hey considering he had no idea what it was to start with he worked it out fairly quickly, had me  ;D ;D ;D at the beginning!
« Last Edit: 12/23/2017 11:36 AM by nacnud »

Offline nisse

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Did SpaceX perform some experimental landing manoeuvre since they didn't want to risk the drone ship? Maybe some high speed energy saving scheme?

Offline clongton

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What was the purpose of a boostback and entry burn for a vehicle that was intended to be disposed of?
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Offline ZachS09

What was the purpose of a boostback and entry burn for a vehicle that was intended to be disposed of?

Just to simulate a first stage landing profile. Might as well do more testing.
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Offline Herb Schaltegger

Did SpaceX perform some experimental landing manoeuvre since they didn't want to risk the drone ship? Maybe some high speed energy saving scheme?

Read L2 if you have it. If you don't have it, it's worth it. Disposing of the core wasn't about "not risking" the drone ship; after all, this very core was landed on the drone ship some months back, wasn't it?

What was the purpose of a boostback and entry burn for a vehicle that was intended to be disposed of?

SpaceX was either: #1) testing flight parameters of the entering/landing stage; #2) ensuring that the stage didn't interfere with fairing recovery attempts by guiding it as if it were a standard entry/landing; #3) just performing an exercise for control personnel and software procedures - "Test as you fly!" and all that; or #4) some combination of the above factors.
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Offline Kaputnik

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In this age of recycle and environment considerations, and Blue Planet II, I find dumping a rocket that can be recovered leaving me conflicted.

OTOH think of all the diesel they saved by not steaming out there with an ASDS...
But yeah I kind of agree with you. Single-use launch vehicles are starting to look like how we used to do this...
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Offline LouScheffer

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One more airborne video, just for the commentary's sake.


This guy did a great job of reporting, in my view.   He did not jump to conclusions (What is that?  I've never seen anything like it?), then he worked out it was likely a rocket launch, then why it looked the way it did (launched in the dark, rose into the sun).   He stated what he was sure of (North to South) and what he could not tell (east to west or west to east).   Excellent real-time reporting of an unusual event.

Offline aero

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How far away from Vandenburg was the farthest confirmed viewing of the launch. We saw it very clearly here in San Diego, it was spectacular. But San Diego is not that far from the ground track, there is video from Phoenix. Anything farther away?
« Last Edit: 12/23/2017 02:20 PM by aero »
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Offline sevenperforce

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In this age of recycle and environment considerations, and Blue Planet II, I find dumping a rocket that can be recovered leaving me conflicted.

OTOH think of all the diesel they saved by not steaming out there with an ASDS...
But yeah I kind of agree with you. Single-use launch vehicles are starting to look like how we used to do this...
In a strange way, the idea of dumping a reused booster actually validates the economics of reuse.

Recalling the days when people said "They'll never be able to recover them" which quickly turned into "They can recover them, but they won't be able to refly them." Now, they're so successful at recovery that they can actually make a business decision about expending a booster after one reflight.

Those kinds of economic profit-and-loss decisions are what you'd expect if reuse was actually about profitability and not just one charismatic rich guy's obsession.

Offline RDoc

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There appeared to be things separating from what I assume to be the returning booster, does anyone have any thoughts on what they are?

Online deruch

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How far away from Vandenburg was the farthest confirmed viewing of the launch. We saw it very clearly here in San Diego, it was spectacular. But San Diego is not that far from the ground track, there is video from Phoenix. Anything farther away?

South Africa! 

Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Online deruch

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There appeared to be things separating from what I assume to be the returning booster, does anyone have any thoughts on what they are?

Thruster firings.  So, plumes of cold nitrogen gas.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline king1999

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There appeared to be things separating from what I assume to be the returning booster, does anyone have any thoughts on what they are?

Thruster firings.  So, plumes of cold nitrogen gas.
The angry fume from S1 when it realized that no droneship was awaiting. ;D

Offline cscott

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2) the fairing demonstrating the RCS bursts appears to fall much slower than the one that does not suggesting a slowed descent from chutes. It could just be perspective that creates that illusion, though.

I think you're right about slower descent, although you're right it could be greater/less distance from the viewer or other trick of perspective.  I don't think it's a parachute responsible at that altitude, though; I'm pretty sure the different profile is solely to due the fact that the active half is actively attitude-controlled.  Instead of tumbling and diving nose first like the passive half, the active half is in a controlled glide, round side down, like a flying bathtub.  That accounts for its greater altitude, or greater horizontal distance (if it's a perspective effect)---or both.

Parachute deployment would wait until the fairing is back in the sensible atmosphere, and maybe later, depending on the tradeoffs between cold gas control authority and parafoil control authority.  The parafoil needs at least enough atmosphere present to deploy properly, even if the first deployment is just a hypersonic drogue.

Offline SLC

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As for what the first-stage water-landing experiment might have been ... 

Looking ahead to the landing-back-on-your-launch-mounts thing, could it have been some kind of simulation of landing an F9 back on its mounts?  Or at least positioning it with centimetre accuracy relative to some specified target, rather than the metre accuracy now routine with the ASDS?

I know there are no plans to physically land an F9 back on its hold-down clamps, but this kind of simulation might validate some of the BFR control routines, and retire at least some of the risk before they have to do it for real with the prototype BFR.  They traded landing legs for extra landing fuel, and that might have allowed some precision sideways positioning.

Offline cscott

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I strongly suspect the first cradle landing experiments will take place on land, in the middle of a big empty field. (LZ-1 at the Cape might count; as would McGregor.)

It's hard to measure sub-meter positioning in the middle of a moving ocean.

Online Johnnyhinbos

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it's a moot point regardless - as SpaceX has specifically said that without bottom mounted RCS they don't have enough control authority for that level of precision. I wouldn't anticipate that they will put any development into cradle landing on the Falcon family. They are already gearing up for the BFR family development and will engineer in that type of fine control from the outset.

 
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Offline SLC

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<snip>
It's hard to measure sub-meter positioning in the middle of a moving ocean.
I was thinking more of relative movement; sort of "slide 5 m North - now 4 m East - now 3 m South - now 2 m West and ... fall into the sea".  Like rocket dressage.  I think acceleration sensors might be able to track the rocket's responses to the centimetre.

I also take the point about bottom-mounted RCS.  But I thought they might want to explore the outer limits of control authority possible with just nozzle-gimballing and top-mounted RCS (with hardware that's just experienced a re-entry).  At least this would tell them how forceful the bottom-mounted BFR RCS will need to be.

Of course they've modelled all this already.  But data points are always reassuring.
« Last Edit: 12/23/2017 07:27 PM by SLC »

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