Author Topic: SpaceX fairing  (Read 37420 times)

Offline spacejulien

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Re: SpaceX fairing
« Reply #60 on: 02/15/2012 06:34 pm »
I share baldusi’s point here.

First, the cost saving given in the paper referenced by go4mars [1] is not justified at all, no sources, no cost breakdown whatsoever. Also, this paper has been published by an ARES projects planning manager in October 2009, just when the Augustine commission recommended to toss it.

Second, a 6 m monolithic mirror is not just driving fairing size. If you want to avoid adaptive optics to have the cost benefit you need a very sturdy monolithic mirror. That has its weight. For comparison, the SOFIA telescope has a diameter of 2.7m and weighs 15.4 metric tons [2]. Scale that up gives you 15.4*(6/2.7)^2=76mT. Even if you divide by factor two (space-, not aircraft-HW) you’ll end up with 38 mT. Other reference, the largest monolithic mirror without adaptive optics has 4.2m diameter and weighs 16.5 mT [3], so factor two for 6 m diameter plus spacecraft and sunshield. Acc. to [1], fig. 6 this would have been within the P/L capability of ARES V to Sun-Earth-L2, but is definitely outside Ariane 5 and Falcon Heavy capabilities. So stop arguing about the fairing diameter as limiting factor using JWST as an example, esp. in a Falcon thread.
Folding mechanisms are state of the art, the telescope’s allowed mass is the limiting factor. This made the active mirror alignment necessary, even if it were monolithic, and that drove (drives) the cost.

[1] http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090043018_2009044057.pdf
[2] http://www.nasa.gov/pdf/503322main_SOFIA%20_QuickFacts2.pdf
[3] http://en.wikipedia.org/wiki/William_Herschel_Telescope
« Last Edit: 02/15/2012 06:43 pm by spacejulien »
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Offline go4mars

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Re: SpaceX fairing
« Reply #61 on: 02/15/2012 06:47 pm »
a 6 m monolithic mirror is not just driving fairing size. If you want to avoid adaptive optics to have the cost benefit you need a very sturdy monolithic mirror. That has its weight. For comparison, the SOFIA telescope has a diameter of 2.7m and weighs 15.4 metric tons [2]. Scale that up gives you 15.4*(6/2.7)^2=76mT. Even if you divide by factor two (space-, not aircraft-HW) you’ll end up with 38 mT. Other reference, the largest monolithic mirror without adaptive optics has 4.2m diameter and weighs 16.5 mT [3], so factor two for 6 m diameter plus spacecraft and sunshield. Acc. to [1], fig. 6 this would have been within the P/L capability of ARES V to EML2, but is definitely outside Ariane 5 and Falcon Heavy capabilities. So stop arguing about the fairing diameter as limiting factor using JWST as an example, esp. in a Falcon thread.  Folding mechanisms are state of the art, the telescope’s allowed mass is the limiting factor. This made the active mirror alignment necessary, even if it were monolithic, and that drove (drives) the cost.
Thank you spacejulien.  That returns us to the point on the linked thread: That the savings on a monolith JWST could have been used to develop something like F-XX (Elon's guaranteed $2.5 billion 150 tonne launcher) for an equal or better, lower-risk telescope (because it would have the mass capacity while hammerhead EELV's presumably do not).   That assumes that 30% is in the ball-park.  We will probably never know for sure if 30% is exactly accurate, but it's the only number we have been given. 
« Last Edit: 02/15/2012 06:48 pm by go4mars »
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Offline Jim

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Re: SpaceX fairing
« Reply #62 on: 02/15/2012 06:55 pm »
  That returns us to the point on the linked thread: That the savings on a monolith JWST could have been used to develop something like F-XX (Elon's guaranteed $2.5 billion 150 tonne launcher) for an equal or better, lower-risk telescope (because it would have the mass capacity while hammerhead EELV's presumably do not).   That assumes that 30% is in the ball-park.  We will probably never know for sure if 30% is exactly accurate, but it's the only number we have been given. 

Wrong, that is just fantasy, there are no savings.  No one would take that offer.  Elon's guarantee is meaningless.   



Offline spacejulien

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Re: SpaceX fairing
« Reply #63 on: 02/15/2012 07:03 pm »
go4mars, there are a lot of ifs implied in your statement:
If Elon could develop a Falcon XX incl. Merlin 2 for 2.5 B$ (which I severely doubt),
if he could accomplish that until 2018 (which I doubt),
if one would have known at the outset of JWST that the launch would slip to 2018+,
if it would have been known at the beginning that the cost would be 8.5 B$,
if the political environment at that time would NOT have permitted to embark on such a large-scale commercial development (remember FY2011 rollout),
if it is really 30% of the JWST total (which I doubt, reasons given in post #60),
if you can really be sure you can definitely avoit adaptive optics (which I doubt, as the mirror is used under completely different environmental conditions than it was manufactured).

Three ifs are retroactive and unchangeable, you can't do anything about them, the other ifs are numerous enough not to go down that track. Too risky project management, more so than JWST itself.

But now, back to F9 and FH fairings...
« Last Edit: 02/15/2012 07:13 pm by spacejulien »
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Offline kevin-rf

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Re: SpaceX fairing
« Reply #64 on: 02/15/2012 09:12 pm »
Elon's guarantee is meaningless.   

I don't know, I put them a little more credible than Boeing management on 787 deliveries ;)
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Offline krytek

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Re: SpaceX fairing
« Reply #65 on: 02/15/2012 09:20 pm »
Falcon 9 uses a carbon-fiber fairing which supposedly is very, very light (compared to the fairings on competing rockets... of course, the Falcon 9 hasn't flown, yet!).
Plus the "competing rockets" also use fairing that are mainly made from carbon. If you do it right, a carbon-composite structure can be just as light or even lighter than a purely carbon one, carbon fiber is good for tensile loads, need lots of filler for compression loads.
To be honest, I'm not entirely sure whether Falcon 9's fairing is carbon fiber or carbon composite, just that it isn't plain aluminum alloy and is claimed (by Elon) to be lighter than competing ones.

this is from RUAG's official site
Quote
The fairings are built in composite technology based on aluminum honeycomb cores with carbon fiber reinforced plastic face sheets

Can you please explain the difference between "carbon fiber" and "carbon composite", not sure I understand the terminology.


Offline peter-b

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Re: SpaceX fairing
« Reply #66 on: 02/15/2012 09:26 pm »
Quote
The fairings are built in composite technology based on aluminum honeycomb cores with carbon fiber reinforced plastic face sheets

Can you please explain the difference between "carbon fiber" and "carbon composite", not sure I understand the terminology.

As I understand it, "carbon fibre" is a term usually used as shorthand for "carbon fibre reinforced polymer", which is most commonly a composite material made by binding layers of graphite fibres into a matrix of epoxy resin.

"Carbon composite" is an even vaguer term, which basically just indicates some composite material that uses "carbon" (probably in the form of graphite fibres).  I suspect that in this case it indicates some sort of composite material combining graphite fibres, polymers, and lightweight metal elements.
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Offline spacejulien

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Re: SpaceX fairing
« Reply #67 on: 02/15/2012 09:37 pm »
Quote
The fairings are built in composite technology based on aluminum honeycomb cores with carbon fiber reinforced plastic face sheets

Can you please explain the difference between "carbon fiber" and "carbon composite", not sure I understand the terminology.

As I understand it, "carbon fibre" is a term usually used as shorthand for "carbon fibre reinforced polymer", which is most commonly a composite material made by binding layers of graphite fibres into a matrix of epoxy resin.

"Carbon composite" is an even vaguer term, which basically just indicates some composite material that uses "carbon" (probably in the form of graphite fibres).  I suspect that in this case it indicates some sort of composite material combining graphite fibres, polymers, and lightweight metal elements.

For the latter (usually) some sort of core material is used, honeycomb cores are very popular in aerospace [1]. Then the two surfaces are covered by some sort of CFRP lay-up [2], then called face-sheets. Gives very light structures with good buckling performance. As launchers are usually under compression loads between drag, inertia and the trust of the engine and thus susceptible to buckling such "sandwich" is very popular for interstages, fairings, skirts, intertank structures, thrust frames, payload adapters, etc.

[1] http://en.wikipedia.org/wiki/Honeycomb_structure
[2] http://en.wikipedia.org/wiki/Carbon_fiber-reinforced_polymer
« Last Edit: 02/15/2012 09:38 pm by spacejulien »
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Offline beancounter

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Re: SpaceX fairing
« Reply #68 on: 02/16/2012 02:09 am »
Quote
The fairings are built in composite technology based on aluminum honeycomb cores with carbon fiber reinforced plastic face sheets

Can you please explain the difference between "carbon fiber" and "carbon composite", not sure I understand the terminology.

As I understand it, "carbon fibre" is a term usually used as shorthand for "carbon fibre reinforced polymer", which is most commonly a composite material made by binding layers of graphite fibres into a matrix of epoxy resin.

"Carbon composite" is an even vaguer term, which basically just indicates some composite material that uses "carbon" (probably in the form of graphite fibres).  I suspect that in this case it indicates some sort of composite material combining graphite fibres, polymers, and lightweight metal elements.

For the latter (usually) some sort of core material is used, honeycomb cores are very popular in aerospace [1]. Then the two surfaces are covered by some sort of CFRP lay-up [2], then called face-sheets. Gives very light structures with good buckling performance. As launchers are usually under compression loads between drag, inertia and the trust of the engine and thus susceptible to buckling such "sandwich" is very popular for interstages, fairings, skirts, intertank structures, thrust frames, payload adapters, etc.

[1] http://en.wikipedia.org/wiki/Honeycomb_structure
[2] http://en.wikipedia.org/wiki/Carbon_fiber-reinforced_polymer


Carbon fibre and expoxy composite's have been used in boat building for at least a decade probably several.  Commonly together with foam of various densities for different structures but also with timber.  Carbon fibre on it's own has been used for masts, booms, etc.  It's hardly a new material and it's properties are well understood.

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Offline krytek

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Re: SpaceX fairing
« Reply #69 on: 02/16/2012 09:36 am »
Again that what's confusing, I've played around some with carbon fiber and epoxy, which isn't all too difficult to work with.
Can't imagine what carbon fiber "on it's own" would make though, unless it's compressed or made into some sort of complex weave.

Offline Crispy

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Re: SpaceX fairing
« Reply #70 on: 02/16/2012 10:17 am »
The shuttle component max size may have been set by rail tunnel size, but that's a pretty generous 'standard.'
Not to mention that USA tunnel clearances are much larger than British ones. There are no double-decker passenger trains in the UK for this reason.

Hang on this isn't the railways forum... :D

Offline corrodedNut

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Re: SpaceX fairing
« Reply #71 on: 03/14/2012 04:19 pm »
Looks like confirmation the fairing's inagural flight will be out of Vandenberg.

From SFN:

"The upgraded Falcon 9 launcher should arrive at the Vandenberg launch site in late 2012, according to Shotwell...The new version of the Falcon 9 rocket will also feature modified propellant tanks and a 5.2-meter, or 17-foot, diameter payload fairing."


Offline go4mars

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Re: SpaceX fairing
« Reply #72 on: 03/14/2012 04:23 pm »
"The new version of the Falcon 9 rocket will also feature modified propellant tanks"
Does that imply stretched tanks?  Is this the tall version?
« Last Edit: 03/14/2012 04:23 pm by go4mars »
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Offline corrodedNut

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Re: SpaceX fairing
« Reply #73 on: 03/14/2012 04:33 pm »
"The new version of the Falcon 9 rocket will also feature modified propellant tanks"
Does that imply stretched tanks?  Is this the tall version?

Conventional wisdom says yes.

Offline oldAtlas_Eguy

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Re: SpaceX fairing
« Reply #74 on: 03/14/2012 04:38 pm »
"The new version of the Falcon 9 rocket will also feature modified propellant tanks"
Does that imply stretched tanks?  Is this the tall version?

Makes sense. The less supported configurations the less GSE and the costs associated with it. If VAFB is set to launch only stretched vehicles (as opposed to the F9's current length) then they only need one set of F9 support equipment (strongback).

Even if this is overkill for some of the VAFB payloads there will not be much of a cost difference between the manufacture of the stretched vehicle and the non-stretched. Plus it gives then the capability to prove out the stretched F9 prior to its use at the cape and the pad mods there as well to support it.

Offline ugordan

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Re: SpaceX fairing
« Reply #75 on: 03/14/2012 04:44 pm »
Playing devil's advocate for a second, but couldn't "modified propellant tanks" mean simply structural changes to handle the significantly higher thrust of M1d?

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Re: SpaceX fairing
« Reply #76 on: 03/14/2012 10:08 pm »
Playing devil's advocate for a second, but couldn't "modified propellant tanks" mean simply structural changes to handle the significantly higher thrust of M1d?
Could be, but if you're going to do that why wouldn't you do the stretch at the same time?  As OAE said, the fewer configurations you're working with, the simpler your operations become.

Now given that they're talking about the first flight with these changes being with CASSIOPE, I suppose there's an argument to be made for making as few changes as possible in order to mitigate risk, but I figure as long as you're doing it you might as well go all the way.  Unless there's something I'm missing about the amount of risk introduced by the core stretch?

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