Author Topic: Fairing reuse  (Read 560533 times)

Offline cambrianera

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Re: Fairing reuse
« Reply #320 on: 04/09/2016 07:50 PM »

The point would be to close clamshell again after separation to have the same aerodynamic shape reenter that went up. And then do trailing ballute, streamer or parachute or whatnot to survive the splash

The shape that went up is not optimal for reentry.
It probably has a stable attitude, but the two half fairing have half mass/surface, therefore more chances to survive reentry (if stabilized).
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Offline Space Ghost 1962

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Re: Fairing reuse
« Reply #321 on: 04/09/2016 07:54 PM »

The point would be to close clamshell again after separation to have the same aerodynamic shape reenter that went up. And then do trailing ballute, streamer or parachute or whatnot to survive the splash

The shape that went up is not optimal for reentry.
It probably has a stable attitude, but the two half fairing have half mass/surface, therefore more chances to survive reentry (if stabilized).

Yes, and the mass distribution will be all wrong as well for return/recovery "flight".

What you'd be after is some kind of "nested" (or recursive) design, where the offsets in one are balanced by the others. Not an easy design challenge.

The cost of jettison isn't cheap here. Remember, you could lose a mission in saving a buck.

Offline Joel

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Re: Fairing reuse
« Reply #322 on: 04/09/2016 08:51 PM »
Is it out of the question to have the fairing separation event coincide with MECO and let the fairings attach to the first stage? From my understanding, MECO now happens at around 80 km (correct me if I'm wrong) which is not that far from space.

Doesn't the desire to eventually reuse the entire rocket suggest that the first stage needs to stage later in order to give more margin to the second stage?

Offline cambrianera

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Re: Fairing reuse
« Reply #323 on: 04/09/2016 09:05 PM »
Is it out of the question to have the fairing separation event coincide with MECO and let the fairings attach to the first stage? From my understanding, MECO now happens at around 80 km (correct me if I'm wrong) which is not that far from space.

Doesn't the desire to eventually reuse the entire rocket suggest that the first stage needs to stage later in order to give more margin to the second stage?

Look at page 11 (all page, but specially this post http://forum.nasaspaceflight.com/index.php?topic=37727.msg1507081#msg1507081 )
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Offline savuporo

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Re: Fairing reuse
« Reply #324 on: 04/09/2016 09:11 PM »
The cost of jettison isn't cheap here. Remember, you could lose a mission in saving a buck.
Yeah but that somewhat of a weak argument for a rocket that already sprouted legs and grid fins. And yes, these are on first stage, but losing the payload with the first stage pays just as little as screwing up fairings or something else later.
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Offline robert_d

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Re: Fairing reuse
« Reply #325 on: 04/10/2016 12:28 AM »
So Here is a (just notional) picture based on the fact that E. Musk is really trying to find a way to reuse the fairings.
It assumes 1) that no possible set of equipment could be mounted within the fairing that would guarantee reuse. 2) No possible means will be found to rejoin the halves; and 3) the deceleration/reentry must include added energy and not just rely on a passive system. I understand the weight penalty such an idea entails. But in theory that could be offset a bit by firing the outer engines starting just before MECO and until fairing separation. Still to be determined would be final landing method. Dropping it directly into the ocean seems counter to the whole idea of reuse.
« Last Edit: 04/10/2016 12:34 AM by robert_d »

Online meekGee

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Re: Fairing reuse
« Reply #326 on: 04/10/2016 12:33 AM »
There's another idea that was batted around a long time ago.

Have fairing retract, as a whole cylinder, onto the first stage, and return with it.

What's left around the pilot is a light cover that's sufficient to protect the payload against the residual atmosphere at 100 km.

(I believe that this damage is from the speed of the flow, but that the actual force on the payload is very low)

The clear negative is that you need to separate this secondary cover as well.

The positives are that A) you carry the heavy payload to a lower altitude, and B) that they come back with the first stage and so don't need an additional recovery mechanisms, helicopters, etc.

EDIT:  To clarify - this is just blue sky thinking.   The plan right now is clearly to parachute the two individual halves, and then recover mid-air.
« Last Edit: 04/10/2016 01:10 AM by meekGee »
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Offline robert_d

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Re: Fairing reuse
« Reply #327 on: 04/10/2016 01:04 AM »
Just had another thought. Make second stage 5 meters like the original fairing but then mount the payload BEHIND the second stage propellant tanks. Interstage would then be just really long.  Engine bell would swing away on a hing just before the payload deploys behind the tanks. How's THAT for the crazy meter?
« Last Edit: 04/10/2016 01:04 AM by robert_d »

Offline CJ

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Re: Fairing reuse
« Reply #328 on: 04/10/2016 01:07 AM »
I'll take a stab at reading the tea leaves here, based on what's known plus some wild theorizing on my part as to what SpaceX might have in mind.

Okay, what's known? I'm taking it as a given that they want to recover and reuse fairings. I'm also taking it as a given that one of the fairing halfs had a cold gas thruster of some sort on SES9.

So here's my wild guesswork; the eventual plan is to, via very tiny clod gas thrusters, stabilize the fairing halfs so that they are enter outside-first (sort of like a boat floating) relative to the velocity vector. To damp out oscillation and impart a little stability, spin them at a few RPM (with the rotational axis aligned with the velocity vector). Based on what we've seen washed up, that might (I'm guessing) get them past the reentry.

After reentry, deploy a small drogue chute on a strong line. Assuming the fairings can't be immersed in salt water (?) this line and drogue could be snagged by a helicopter with the correct gear.

It would be far easier if the fairings could be immersed in salt water, assuming their terminal velocity (perhaps aided by a small drogue) would make water impact survivable, but I don't know whether that's feasible.

For location and tracking in either case, a small GPS-based transponder could be used. 

 

Offline Radical_Ignorant

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Re: Fairing reuse
« Reply #329 on: 04/10/2016 07:22 AM »

And how to keep them connected? Well, I see on the video were they test separation mechanism that both parts are connected, so it seems possible. And in old days there were those rockets controlled by cables, so there are things which can survive and do the job.


not true on either point.  The cables would put loads on the fairings and there is no way to bring them together in a controlled matter without them slamming together.

Which rockets were controlled by cables?

Of course that they would put loads, and so? This load would be symetric, fairings would be tiny bit heavier.
No way to bring them together? You mean that it's impossible to control  force required to pull the cable? Or you say that using force in only one way it's not possible to gently stop momentum? Like for example on rocket falling from the sky? Or you claim that TOWs (thanks tyrred - I was lazy) weren't working because there is no cable which could easily withstand rocket exhaust?

It's always super easy to claim "no it's impossible". But that's rarely true. That would be too hard, or that would not be cost effective, or that could be dangerous/not reliable because of... that I could believe.


How about "it's simply unnecessary."

Could you then please explain me what is necessary? I could believe that all is really required it's to reduce speed of impact with water. Pieces found are already quite large, so it would be believable.
Can you then help me and explain what for are those tests with controlling them? What could it help?

Offline Radical_Ignorant

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Re: Fairing reuse
« Reply #330 on: 04/10/2016 07:54 AM »
{....}

I'll try offer my criticism, and not just dismissal.  Although I would add that "dismissal", when it comes from many veteran sources pretty clued into real world experience with space hardware, is a good hint that an idea may not be great.   
{....}
This is wrong. I'm not disrespecting his opinion, I'm not even saying he is wrong and I'm right. All I was saying is that he provided nothing more than an opinion. And if something is valid because senior engineer said that - that is argument from person, from authority, not from fact. It's no educational value or no value at all. It's more an order than an answer "I'm senior here, be quiet and listen". And there is infinite amount of examples where senior (old, experienced) space guys were wrong :p

Sure I understand that lot of you folks are tired of our ignorance and dumb ideas. But then patience and politeness are things thanks to which we could admire your knowledge and learn from this forum even more.

So back to the topic of cables....

I don't think the cables seen in the SpaceX fairing test video from the Plum Brook facility indicate in any way that cables would work like this in a freefall/zero-g environment.   It's nice to imagine in our gravitationally conditioned minds {....}
It's accelerating, not free falling, so you are wrong here. However force is probably not 1g so it would behave differently, but I don't know why much differently.

It's too easy to think of this problem like a household vacuum cord automatically winding itself back inside the appliance housing, but it just won't work like that.  Each pull of the cord/cable on attached fairing halves will accelerate the halves in the direction of the pull.   Unless the vector of that acceleration exactly moves the halves to a rendezvous, they will impact obliquely, & spin apart from each other from an in-elastic collision, and not rendezvous.   Furthermore, once they are accelerating towards each other, cables cant slow them down.   Ever try making compression forces with a string?  That means RCS and sensors, and you may as well eliminate the cables entirely.   I see a a big tangled mass of cable and fairing resulting after a few collisions together.

1) They won't spin apart because they will be hold together by the very cable we talk about. That's the reason why IMO it could make sense - there I s no docking mechanism.

2) "Each pull will..." Sure it will. So you have 8 points to attach force. Quite a control system. It's not complicated to simulate it in software. Of course much harder to make it working in this simulation. But I believe it's software problem how to bring them back together gently.

3) "Can't slow them down." That's why you do it gently. Like shuttle landing. Once it was over airfield you could not move it up and try again. I don't see it as no go.


Offline Ohsin

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Re: Fairing reuse
« Reply #331 on: 04/10/2016 11:08 AM »
So at the moment they are looking to recover one half if I am right. But lets say in future after all experience gained they are recovering both halves, if recovery of one half goes wonky would that make other piece useless? Or these halves are designed to be swap-able?
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Offline cambrianera

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Re: Fairing reuse
« Reply #332 on: 04/10/2016 12:11 PM »
So at the moment they are looking to recover one half if I am right. But lets say in future after all experience gained they are recovering both halves, if recovery of one half goes wonky would that make other piece useless? Or these halves are designed to be swap-able?
Halves are manufactured separately (not single piece fairing cut in half) on computer controlled machinery.
Likely swappable.
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Offline Jim

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Re: Fairing reuse
« Reply #333 on: 04/10/2016 12:23 PM »
It's always super easy to claim "no it's impossible". But that's rarely true. That would be too hard, or that would not be cost effective, or that could be dangerous/not reliable because of... that I could believe.

"too hard, or that would not be cost effective, or that could be dangerous/not reliable because of." equates to "it's impossible"

Offline Jim

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Re: Fairing reuse
« Reply #334 on: 04/10/2016 12:29 PM »

2) "Each pull will..." Sure it will. So you have 8 points to attach force. Quite a control system. It's not complicated to simulate it in software. Of course much harder to make it working in this simulation. But I believe it's software problem how to bring them back together gently.

3) "Can't slow them down." That's why you do it gently. Like shuttle landing. Once it was over airfield you could not move it up and try again. I don't see it as no go.


No, it is not a software problem. Cables are inadequate in that they can not provide 6 DOF control, since the only other anchor is the other fairing..   They will not prevent the fairing from twisting or hitting each other. There still are aero loads at separation.

Offline Jim

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Re: Fairing reuse
« Reply #335 on: 04/10/2016 12:32 PM »
 
Or you claim that TOWs (thanks tyrred - I was lazy) weren't working because there is no cable which could easily withstand rocket exhaust?

Not relevant example.  Those cables weren't hundreds of miles long.  Also, the two TOW exhausts are angled way from the center line

Offline Kaputnik

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Re: Fairing reuse
« Reply #336 on: 04/10/2016 12:48 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.
If you push a long edge hinged fairing over the other long edge, you get an inward movement of the hinge.
You can add a reaction beam to keep the hinge clear from the payload, but this would increase the mass of the fairing.



Is it just me or does that looks rather Rogallo-esque? Hmmm...
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Offline llanitedave

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Re: Fairing reuse
« Reply #337 on: 04/10/2016 03:23 PM »

And how to keep them connected? Well, I see on the video were they test separation mechanism that both parts are connected, so it seems possible. And in old days there were those rockets controlled by cables, so there are things which can survive and do the job.


not true on either point.  The cables would put loads on the fairings and there is no way to bring them together in a controlled matter without them slamming together.

Which rockets were controlled by cables?

Of course that they would put loads, and so? This load would be symetric, fairings would be tiny bit heavier.
No way to bring them together? You mean that it's impossible to control  force required to pull the cable? Or you say that using force in only one way it's not possible to gently stop momentum? Like for example on rocket falling from the sky? Or you claim that TOWs (thanks tyrred - I was lazy) weren't working because there is no cable which could easily withstand rocket exhaust?

It's always super easy to claim "no it's impossible". But that's rarely true. That would be too hard, or that would not be cost effective, or that could be dangerous/not reliable because of... that I could believe.


How about "it's simply unnecessary."

Could you then please explain me what is necessary? I could believe that all is really required it's to reduce speed of impact with water. Pieces found are already quite large, so it would be believable.
Can you then help me and explain what for are those tests with controlling them? What could it help?


I've suggested a small parachute.  That and maybe a couple of small aerodynamic surfaces to add a bit of stability.  Don't see the need for much else.
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Offline Radical_Ignorant

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Re: Fairing reuse
« Reply #338 on: 04/10/2016 06:00 PM »

2) "Each pull will..." Sure it will. So you have 8 points to attach force. Quite a control system. It's not complicated to simulate it in software. Of course much harder to make it working in this simulation. But I believe it's software problem how to bring them back together gently.

3) "Can't slow them down." That's why you do it gently. Like shuttle landing. Once it was over airfield you could not move it up and try again. I don't see it as no go.


No, it is not a software problem. Cables are inadequate in that they can not provide 6 DOF control, since the only other anchor is the other fairing..   They will not prevent the fairing from twisting or hitting each other. There still are aero loads at separation.

Since there are four points of attachments on each fairing half it's easy to control twisting. You know how long is each cable. As well as it's easy to measure pressure on the cable. If one is longer that means it should be pulled little bit faster than other ones.

No 6DOF control? Why you need that?

I doubt now we talk about the same they thing? Why should they prevent fairing halves from hitting each other? It's all about hitting each other in controlled manner to reconnect and make shape which is safe in atmospheric heat and can be easily make floatable.

Sorry for lacking animation skill.

I see there two problems, which no one mentioned.
1) cables can touch payload or rocket in initial phase
2) it makes no difference really - it's all just about making it hit water little slower, atmospheric part makes no harm for them in current state or half fairing are good and stable enough lifting body and it's just enough to attach small parachutes to them and stabilize their rotation for a moment of launching it?

Offline S.Paulissen

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Re: Fairing reuse
« Reply #339 on: 04/10/2016 08:15 PM »
It just seems the simplest solution would be to put a 'light' TPS on the outer surface of the fairing and stabilize the reentry orientation with an inflatable drag augmentation device (al la NASA's low density supersonic decelerator)  and eat the mass penalty by throwing performance at it. 

I seriously doubt they'll go much further down the fairing recovery road until they have enough excess performance to make the more error resistant plan work (i.e. keep sep nearly identical to current practice, then add steps later to reduce risk).
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