Author Topic: Fairing reuse  (Read 550911 times)

Offline sevenperforce

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Re: Fairing reuse
« Reply #240 on: 03/26/2016 11:54 AM »
C'mon folks, this is all a bit ridiculous.  ??? You're forgetting a major issue: MASS
 
If you keep the fairing attached to the second stage you are having to accelerate a lot more mass up to your final velocity - plus carry it around for any maneuvering and de-orbit burns. And on top of that, having it hinged open or cantilevered out means your center of thrust may no longer be going through your center of mass - have fun with that! All of these things are tremendously wasteful and makes all of your operations harder. The best thing to do is keep the fairings as light as possible and jettison them as early as possible. The slower the rocket is going when you ditch them, the lower your re-entry energy is going to be (coming in from slower or a lower altitude, or both).
 
The suggestion of hingeing the fairing was to allow it to be jettisoned in one piece, not with the intent of carrying it to orbit.

Offline Jim

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Re: Fairing reuse
« Reply #241 on: 03/26/2016 01:07 PM »
Hingeing would take too long to come off

Offline OxCartMark

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Re: Fairing reuse
« Reply #242 on: 03/27/2016 12:35 AM »
Before we get too deep into designing this (which I think began a dozen or so pages back) can someone provide some numbers for pitot static pressure at that altitude and speed?  Maybe then with that we can do some slightly more educated guessmongering.

Online Arb

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Re: Fairing reuse
« Reply #243 on: 03/27/2016 02:03 PM »
Before we get too deep into designing this (which I think began a dozen or so pages back) can someone provide some numbers for pitot static pressure at that altitude and speed?  Maybe then with that we can do some slightly more educated guessmongering.

And if this is going to become a design thread it should be so renamed and a separate updates thread created for any news (official or otherwise) about what SpaceX are really doing...

Mods, please.

Offline rickyramjet

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Re: Fairing reuse
« Reply #244 on: 03/27/2016 03:42 PM »
Before we get too deep into designing this (which I think began a dozen or so pages back) can someone provide some numbers for pitot static pressure at that altitude and speed?  Maybe then with that we can do some slightly more educated guessmongering.

And if this is going to become a design thread it should be so renamed and a separate updates thread created for any news (official or otherwise) about what SpaceX are really doing...

Mods, please.
How is this thread any different than the hundreds of others where NSFers make design suggestions in the absence of info from SpaceX?  Or, even in the absence of scientific knowledge? I say leave it as is!

Offline cscott

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Re: Fairing reuse
« Reply #245 on: 03/27/2016 05:54 PM »
For the same reason many other threads on this site are split into "update" and "discussion" threads---some of us have much less patience for rube goldberg guesswork or (on other threads) concern trolling than others.

Offline iamlucky13

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Re: Fairing reuse
« Reply #246 on: 04/01/2016 02:01 AM »
You know, if it would be possible to hinge the damn thing, why not simply hinge it along one long edge? Then it could open along that edge and tumble away still connected.

That radically changes the separation dynamics, and not in a good way. As Orbital Sciences can attest, making a fairing separate reliably under thrust loads is not a trivial problem.

Sorry, when I posted, I was thinking about the interstage between first and second stage, not the nose fairing.  What is wrong with dumping the fairings?  You can't save everything yet.
The fairings are hella expensive.

I don't know if they're "hella" expensive, but they are significantly more expensive than I think most people realize. Apparently Ariane 5 fairings are around $6 million, and that's a similar size composite fairing. SpaceX might be doing theirs for cheaper, but even half that is still no small pile of pennies.
http://spacenews.com/41132ruag-books-order-for-18-ariane-5-fairings/

The fairing is certainly a lot less expensive than a first stage, but I suspect SpaceX is hoping it will prove one of the easiest parts to retrieve, so even if the value of the savings is not in the same ballpark as re-using a 1st stage, it might have a high return relative to the amount they have to invest developing the recovery technique.

Offline JamesH65

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Re: Fairing reuse
« Reply #247 on: 04/01/2016 10:04 AM »
 It does beg the questions of WHY they are so expensive. Anyone know?

Offline rpapo

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Re: Fairing reuse
« Reply #248 on: 04/01/2016 10:14 AM »
It does beg the questions of WHY they are so expensive. Anyone know?
They're big, and they're composite.  The cost of making composite structures goes up rapidly with size, for a variety of reasons (material, tooling, processes required, difficulty in avoiding flaws, etc).
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Offline JamesH65

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Re: Fairing reuse
« Reply #249 on: 04/01/2016 01:24 PM »
It does beg the questions of WHY they are so expensive. Anyone know?
They're big, and they're composite.  The cost of making composite structures goes up rapidly with size, for a variety of reasons (material, tooling, processes required, difficulty in avoiding flaws, etc).

Still, $6M seems a lot. Once you have the tooling in place, and have sorted the process and the QA, I would expect the price to drop fairly rapidly.

Offline sevenperforce

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Re: Fairing reuse
« Reply #250 on: 04/01/2016 02:26 PM »
You know, if it would be possible to hinge the damn thing, why not simply hinge it along one long edge? Then it could open along that edge and tumble away still connected.

That radically changes the separation dynamics, and not in a good way. As Orbital Sciences can attest, making a fairing separate reliably under thrust loads is not a trivial problem.
What about something like this?



One seam, two hinges. Each hinge only needs 45 degrees of movement to provide full clearance; the imbalanced thrust loading immediately pulls the entire fairing off to the side opposite the seam. Spring-loading the hinges ought to provide a smooth enough and rapid enough deployment to clear the payload, and would be lighter than using a pneumatic system. You might need a puff of RCS to correct for the millisecond of imbalanced thrust on the rocket but given the mass of the rocket, fuel, and payload in comparison to the mass of the fairing the misalignment would be minuscule.

Assuming that the springs push the hinge into a locked position, the fairing would present a high surface area for re-entry and naturally align itself along an aerodynamic plane which protects the inside.

Offline Jim

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Re: Fairing reuse
« Reply #251 on: 04/01/2016 03:20 PM »
1.  Spring-loading the hinges ought to provide a smooth enough and rapid enough deployment to clear the payload,

2. and would be lighter than using a pneumatic system.

3. You might need a puff of RCS to correct for the millisecond of imbalanced thrust on the rocket but given the mass of the rocket, fuel, and payload in comparison to the mass of the fairing the misalignment would be minuscule.


1.  What type of springs?  And how do you know they "ought" to?

2.  Based on what?  If no pneumatics, what pushes the fairing away?

3.  What RCS?

Do you know that the fairing separates while the vehicle is under thrust and still accelerating.

Also, the bottom of the fairing is disconnected at the same time as the seam splits.
« Last Edit: 04/01/2016 03:21 PM by Jim »

Offline Joffan

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Re: Fairing reuse
« Reply #252 on: 04/01/2016 04:29 PM »
Question - would it be possible to open the fairing between stage 1 MECO and stage 2 engine start, or is that still too low in the atmosphere for a typical payload? Would there be any issues with shedding the fairing either under no thrust or with the engine start-up thrust?

My expectation is that one of these issues is a deal-breaker for slightly earlier jettison of the fairing, but I don't know for sure...
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Offline Senex

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Re: Fairing reuse
« Reply #253 on: 04/01/2016 04:47 PM »
I just re-read the thread — leads me to the following points:

The fairing must be jettisoned.  Carrying the mass to orbit kills your payload capacity.  Not debatable.

The fairing has a large surface area and a low mass.  "Fluffy" recovery — less heating.  A whole different recovery mode from the second stage.  A paper airplane "dropped" from orbit will survive.  (See Japanese origami experiment - the problem is finding it!)

The shape of the half-fairings is a good approximation of a lifting body.  If you can organize the fairing's mass to put the centre of gravity in the right place it will "fly."  The trick may be initially stabilizing it in the correct attitude — which may be what SpaceX is working on.

They may be trying to figure out how much damage is from wave action.  Minor flotation bags and a beacon could help in recovering the fairing before it is damaged.

This should be doable — after some trial and error.  And they get a trial for "free" on every launch.

Offline sevenperforce

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Re: Fairing reuse
« Reply #254 on: 04/01/2016 05:35 PM »
1.  Spring-loading the hinges ought to provide a smooth enough and rapid enough deployment to clear the payload,

2. and would be lighter than using a pneumatic system.

3. You might need a puff of RCS to correct for the millisecond of imbalanced thrust on the rocket but given the mass of the rocket, fuel, and payload in comparison to the mass of the fairing the misalignment would be minuscule.


1.  What type of springs?  And how do you know they "ought" to?

2.  Based on what?  If no pneumatics, what pushes the fairing away?

3.  What RCS?

Do you know that the fairing separates while the vehicle is under thrust and still accelerating.

Also, the bottom of the fairing is disconnected at the same time as the seam splits.
Outward-opening hinges mounted on the inside. Steel springs, I assume. I'm saying they could be designed to open smoothly and rapidly enough.

The fairing would be pushed away by the continued acceleration of the vehicle; as soon as the springs opened, the center of mass would shift and cause differential force on the fairing. You would need only one pneumatic clip holding the two doors together and fixed to the second stage body; once that clip retracts, the doors swing open and acceleration takes care of the rest.

I was talking about the RCS on the upper stage being used to correct the stage misalignment due to the momentary COM shift.

Offline RDoc

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Re: Fairing reuse
« Reply #255 on: 04/01/2016 05:46 PM »
I just re-read the thread — leads me to the following points:

The fairing must be jettisoned.  Carrying the mass to orbit kills your payload capacity.  Not debatable.

The fairing has a large surface area and a low mass.  "Fluffy" recovery — less heating.  A whole different recovery mode from the second stage.  A paper airplane "dropped" from orbit will survive.  (See Japanese origami experiment - the problem is finding it!)

The shape of the half-fairings is a good approximation of a lifting body.  If you can organize the fairing's mass to put the centre of gravity in the right place it will "fly."  The trick may be initially stabilizing it in the correct attitude — which may be what SpaceX is working on.

They may be trying to figure out how much damage is from wave action.  Minor flotation bags and a beacon could help in recovering the fairing before it is damaged.

This should be doable — after some trial and error.  And they get a trial for "free" on every launch.

This is my view as well, but with the addition of some control surfaces and flight computers.

Offline cambrianera

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Re: Fairing reuse
« Reply #256 on: 04/01/2016 05:54 PM »
@sevenperforce,
once your “doors“ open, the center of mass of the system follow the movement of the doors.
Moreover the doors are loosing their stand on the second stage.
The result is the fairing collapsing on the payload.
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Offline The Amazing Catstronaut

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Re: Fairing reuse
« Reply #257 on: 04/01/2016 06:20 PM »
You can reuse a fairing with a normal fairing separation, indeed, you should be. Fairings ain't broke and are a fairly rare failure mode if your quality assurance is indeed assured. It works, it's optimal, we should focus our attention on what the fairing is doing once detached from the structure of the rocket.

I've always been of the opinion giving the fairing a few thrusters to orient itself, a (light) parafoil, a GPS, and then scooting the the fairing out of the air SMART reuse/CORONA style is the right idea. You can do shebang without adding a ridiculous amount of mass, although you are going to have to accept a certain minor amount of performance loss.

I don't know if they're actually doing that. To me the idea seems sensible enough I have the feeling I've heard it somewhere before. Unsure. I didn't read the whole thread nor have I read too deeply into it.

Edit: And after looking back in the thread it seems that idea has been suggested before and I even replied to it. Doh!
« Last Edit: 04/01/2016 06:23 PM by The Amazing Catstronaut »
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Offline sevenperforce

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Re: Fairing reuse
« Reply #258 on: 04/01/2016 07:34 PM »
@sevenperforce,
once your “doors“ open, the center of mass of the system follow the movement of the doors.
Moreover the doors are loosing their stand on the second stage.
The result is the fairing collapsing on the payload.
Then add a vertical bearing arm to the inside of the upper stage coupler to hold the fairing in place until the COM shifts far enough out.

Offline Jim

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Re: Fairing reuse
« Reply #259 on: 04/01/2016 09:09 PM »

The fairing would be pushed away by the continued acceleration of the vehicle;

Fairings aren't pushed away by the vehicle.  They are detached at the base at the same time as the seams open and are pushed away by a pneumatic system or ordnance.

You would need only one pneumatic clip holding the two doors together and fixed to the second stage body;

Fairings use many bolts or devices (more than 5 and some in the tens) to hold them together.

Outward-opening hinges mounted on the inside. Steel springs, I assume. I'm saying they could be designed to open smoothly and rapidly enough.


To generate the forces and the acceleration required, they would have to huge and hence heavy

This is how fast a fairing comes off

« Last Edit: 04/01/2016 09:16 PM by Jim »

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