Author Topic: SpaceX's Fairing Catchers (GO Ms Tree, GO Ms Chief)  (Read 251456 times)

Offline niwax

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It is falling from over 100 km up and is ‘floppy’. A 50km dispersion doesn’t sound crazy to me given upper altitude winds and such.

Or some deviation from the first point they have aerodynamic control. A 50km approach on a target of a defined size. Like cruise missiles whose orientation integrators have to be stable enough for x% deviation on their range to hit the target.
« Last Edit: 06/08/2018 07:59 am by niwax »
Which booster has the most soot? SpaceX booster launch history! (discussion)

Offline edzieba

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As far as I am aware the cold-gas thrusters on the fairing halves are solely for orienting for re-entry, and the fairings cannot 'navigate' themselves outside the atmosphere (and with only the limited-reservoir thrusters and no real motors, any translation capability would be minuscule even if exo-atmospheric GNC were added). Thus, from the moment of separation until the moment the parachutes deploy the position error can only ever increase, not decrease.

Offline rsdavis9

As far as I am aware the cold-gas thrusters on the fairing halves are solely for orienting for re-entry, and the fairings cannot 'navigate' themselves outside the atmosphere (and with only the limited-reservoir thrusters and no real motors, any translation capability would be minuscule even if exo-atmospheric GNC were added). Thus, from the moment of separation until the moment the parachutes deploy the position error can only ever increase, not decrease.

Entering the atmosphere at a angle oriented correctly could get you some translation. So if one end is heavier than the other end it will come in at an angle and positioning that correctly with the trhusters could make a difference.
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Offline edzieba

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Because it is falling passively, it is going to be stable in only one orientation*. The RCS thrusters will put it in that orientation, and might be able to aim the 'nose' in a compass direction (an 'Earth down' camera would enable correct orientation, tracking the Sun or Moon if visible may give 'free' orientation). Any flex, any buffeting, any error in initial entry angle, any crosswinds, etc will result in a non-straight track during descent before chute deployment.


* According to the Ariane study technically there are 3 possible stable re-entry orientations, but concave-down results in fairing-destroying sideloads on the edges (same reason large supersonic ring-slot parachutes are so hard), and edge-down results in extreme heating, so convex-down remains he only stable configuration of actual use.

Offline ejb749

Why don't they just use a helicopter to grab it?  The net seemed silly at first, and now it seems 4X sillier.

Take a helicopter out on the ship. 
Take off from the ship when the rocket is launched.   
Hook the parasail.  If it misses, just try again until it's hooked.
Lower the fairing onto the ship. 
Land the helicopter, and head for the port.

No silly net needed.  You don't even need a fast ship.
You might wreck the parasail, but it's probably not reusable anyway.

Offline speedevil

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You might wreck the parasail, but it's probably not reusable anyway.
You may also due to the large, un-aerodynamic poorly balanced load crash the helicopter.

Offline Wolfram66

You might wreck the parasail, but it's probably not reusable anyway.
You may also due to the large, un-aerodynamic poorly balanced load crash the helicopter.

This is not new tech. they've been doing it since the 60's

Offline docmordrid

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You might wreck the parasail, but it's probably not reusable anyway.
You may also due to the large, un-aerodynamic poorly balanced load crash the helicopter.

 This is not new tech. they've been doing it since the 60's

With long, floppy, composite structures which are intended to be re-launched?
« Last Edit: 06/22/2018 12:44 am by docmordrid »
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Offline deruch

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Why don't they just use a helicopter to grab it?  The net seemed silly at first, and now it seems 4X sillier.

Take a helicopter out on the ship. 
Take off from the ship when the rocket is launched.   
Hook the parasail.  If it misses, just try again until it's hooked.
Lower the fairing onto the ship. 
Land the helicopter, and head for the port.

No silly net needed.  You don't even need a fast ship.
You might wreck the parasail, but it's probably not reusable anyway.

I'm 100% sure that, at least initially, when they were thinking about recovering the fairings, SpaceX considered Mid-Air Retrieval (MAR) with helicopters and had it as an option in their trade space.  I don't know exactly why they chose ships over that option, but I feel confident in assuming it wasn't due to frivolousness or lack of reason.  Maybe it will turn out that their underlying thinking/assumptions which supported choosing fast ships over helicopter-based MAR are unfounded and they eventually switch to that method.  I don't know.  But even after seeing that their first set-up was proving insufficient, they chose to go with 4x bigger net area on the ships instead of pivoting to the helicopters.  To me, that indicated that whatever reasoning they had for going that direction initially is likely still in effect.
« Last Edit: 06/22/2018 06:41 am by deruch »
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Online meekGee

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Why don't they just use a helicopter to grab it?  The net seemed silly at first, and now it seems 4X sillier.

Take a helicopter out on the ship. 
Take off from the ship when the rocket is launched.   
Hook the parasail.  If it misses, just try again until it's hooked.
Lower the fairing onto the ship. 
Land the helicopter, and head for the port.

No silly net needed.  You don't even need a fast ship.
You might wreck the parasail, but it's probably not reusable anyway.

I'm 100% sure that, at least initially, when they were thinking about recovering the fairings, SpaceX considered Mid-Air Retrieval (MAR) with helicopters and had it as an option in their trade space.  I don't know exactly why they chose ships over that option, but I feel confident in assuming it wasn't due to frivolousness or lack of reason.  Maybe it will turn out that their underlying thinking/assumptions which supported choosing fast ships over helicopter-based MAR are unfounded and they eventually switch to that method.  I don't know.  But even after seeing that their first set-up was proving insufficient, they chose to go with 4x bigger net area on the ships instead of pivoting to the helicopters.  To me, that indicated that whatever reasoning they had for going that direction initially is likely still in effect.

I'd guess helicopters are a "last resort" option.

In the video, two relatively light helicopters are capturing a very light load in perfect weather over land.

For SpaceX, very large helicopters have to perform these operations with a heavy payload, off of a deck of a ship/barge, and in random weather.  It's a big step up in terms of complexity, cost, and risk to lives.

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Offline biosehnsucht

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Even if the fairing stayed perfectly still in relation to the helicopter and didn't serve as a kite dragging it around by the regular winds of nature, I imagine the down wash from the helicopter itself would make things "interesting".

Online Johnnyhinbos

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Why don't they just use a helicopter to grab it?  The net seemed silly at first, and now it seems 4X sillier.

Take a helicopter out on the ship. 
Take off from the ship when the rocket is launched.   
Hook the parasail.  If it misses, just try again until it's hooked.
Lower the fairing onto the ship. 
Land the helicopter, and head for the port.

No silly net needed.  You don't even need a fast ship.
You might wreck the parasail, but it's probably not reusable anyway.
There’s that “just” word again.

As has been already said, there’s no doubt SpaceX has considered more traditional methods before leasing a large vessel, designing massive outrigger arms, fitting a massive and ungainly net structure to said arms, and hiring a parafoil GNC company to provide precise steering to a fairing half.

Of course my guess is if they started these attempts using a helicopter we’d be reading...

“Why don’t they just put a net on a boat and catch it as it comes down?”

:-)
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Offline edzieba

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You might wreck the parasail, but it's probably not reusable anyway.
You may also due to the large, un-aerodynamic poorly balanced load crash the helicopter.

This is not new tech. they've been doing it since the 60's
Here's the presentation on a study associated with this research.

I suspect the reason for the net-on-a-ship is just cost: if the fairings re-enter far enough from the shore to be out of range of a land-based helicopter avoiding the NOTAM area, then you need to ship-base your helicopter already. Capturing with the ship rather than the helicopter means eliminating the helicopter the ship would otherwise need to carry.

Offline cscott

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The helicopter option seems to add considerable risk to operations, as well.  If you plan to be launching every week, that's a lot of helicopter flight hours and skilled crews you are putting at risk.  The boat option seems almost entirely automated, doesn't rely on pilot availability and skill, and doesn't endanger lives.

Offline Lar

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let's not get into "they could do it this way" ... that is more suited for the fairing recovery thread. Keep this focused on the specific topic of Mr. Steven.
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Offline Michael Baylor

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SpaceX appear to have done some sort of test with Mr. Steven involving an aircraft on June 28th. Unlikely that Mr. Steven's new net is finished, but maybe they just let there to monitor the test. NRC Quest was also sent out.

Two NOTAM's were filed with one on the 28th and one on the 29th. Mr. Steven did not head out on the 29th and the second NOTAM was taken down, so the 29th may have been a backup day.

Video of Mr. Steven's movements: https://twitter.com/CowboyDanPaasch/status/1012478077446782977

I've attached a screenshot of Mr. Steven's position and the NOTAMs.

Offline Nydoc

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SpaceX appear to have done some sort of test with Mr. Steven involving an aircraft on June 28th. Unlikely that Mr. Steven's new net is finished, but maybe they just let there to monitor the test. NRC Quest was also sent out.

Two NOTAM's were filed with one on the 28th and one on the 29th. Mr. Steven did not head out on the 29th and the second NOTAM was taken down, so the 29th may have been a backup day.

Video of Mr. Steven's movements: https://twitter.com/CowboyDanPaasch/status/1012478077446782977

I've attached a screenshot of Mr. Steven's position and the NOTAMs.
Mr. Steven was in the East Channel prior to this excursion and has now returned to berth 240. One or more fairing halves are being kept at the BFR factory site in the Historic District and presumably are being modified at this location. My guess is that a modified fairing half is currently being offloaded for inspection and possible further modifications. Once it is offloaded at berth 240 Mr. Steven will return to its normal berth in the East Channel.

*edit: Also Elsbeth III is currently in Morgan City. This might be an indication of SpaceX expanding their drone fleet. Who knows...
« Last Edit: 06/29/2018 08:40 pm by Nydoc »

Offline jpo234

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Offline speedevil

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Article by Eric Ralph/vaporcobra:

SpaceX’s Mr Steven gains upgraded arms to catch its first Falcon 9 fairings

And is the ring entirely unrelated.
Could this be the much famed 'bouncy castle' ?
- it is smaller even than the existing net though, which doesn't make a lot of sense.

Could it perhaps be a recovery aid, to be dropped around a floating object?

Offline ClayJar

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And is the ring entirely unrelated.
Could this be the much famed 'bouncy castle' ?
- it is smaller even than the existing net though, which doesn't make a lot of sense.

Could it perhaps be a recovery aid, to be dropped around a floating object?

My uninformed guess (based on the "bouncy castle" concept) is that perhaps the ring is a second target for fairing recovery experimentation.  Mr Steven would be going after one half with the "boat and net" concept, while the other fairing half would be aiming at the "life raft".  If you've got two actively-controlled fairing halves per launch, you may as well run experiments in parallel, eh?  Would it be two separate experiments, or would the life raft more closely associated with Mr Steven?  Can't wait for more clues.

(Also, clicking on the life raft image in the article and getting a "jiggle-3D" view was a treat. ;D)

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