Author Topic: SpaceX fairing  (Read 37414 times)

Offline go4mars

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Re: SpaceX fairing
« Reply #40 on: 02/14/2012 04:41 pm »
Additionally, has SpaceX ever claimed it wishes to do Ariane-5-style dual launches or is this just a forum assumption of what they will do with FH?
Yes.  IIRC, Shotwell mentioned it almost 2 years ago. 
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Offline baldusi

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Re: SpaceX fairing
« Reply #41 on: 02/14/2012 05:42 pm »
The real issue is cost.  If you can really only afford one fairing size right now, a 5m-class one is the one you want because you can handle wider payloads, should any come your way.  Also building a 4m-class PLF would be an extra cost that isn't really a necessity.  Not all companies have pockets as deep as ULA.
I seriously doubt that developing a smaller fairing is very expensive. In fact, it might well be the cheapest part of the rocket. And it is quite commercial. Ariane 5, Vega, and Atlas V all use Ruag and Antares uses  fairings, I know Delta IV offered the SYLDA, so it seems to be a COTS piece of equipment. Please note that the separation mechanism, sound suppression inlay, connectors, etc. are mostly the same.
In any case, it might well be the cheapest upgrade available for the money. Remember that a 4m fairing has 38% less drag losses. That's a lot. So, in every 5.2m launch that would fit a 4m they are paying that cost. That also translates into strain on the thrust structure. Less strain allows for more aggressive ascent profiles. And since Falcon can fly with 3.6m Dragon, and 5.2m fairing, flying with 4m should be easy. An there's weight issues. In the case of the Atlas V, the 5m medium fairing is 1700kg heavier than the 4m. And the F9 separates the fairing while the US is firing, so it does adds an extra weight.
What's more, I think very few commercial satellites need 5m. If you need that you can only use Arian 5 (120M), Atlas V(180M) or H-IIA (I don't know how much). If you can use 4m, then you can use Proton (80M), Sea Launch (around 70M?), Soyuz-ST, LM-3BE. What do you think satellite operators usually chose? In particular, Atlas V and H-IIA/b have zero share in the commercial market. And only five satellites per year use the upper part of the Arian 5. So at most (and I guess is much less) there are five commercial satellites that might need 5m.
Look into the fairing sizes for DoD, too. Delta IV did 11 4m launches and 2 5m launches, plus the 5 heavies, of course. Atlas IV is 19 of 4m vs 9 of 5m. In just 3 (the two OTV plus one NROL) of the 11 launches (sans heavy) of 5m F9 could match the performance of the LV. So overall it would seem that they would rather get the extra performance
Quote
Regarding the PLF length, I read somewhere that SpaceX is claiming a variable-length PLF, should there be customer interest to justify its development.  Additionally, has SpaceX ever claimed it wishes to do Ariane-5-style dual launches or is this just a forum assumption of what they will do with FH?
I think it was proposed somewhere. But I'm stating that as an economist. The FH is too expensive unless you dual manifest for at least 80% of the GTO market (that's about 16 satellites/yr, btw). Without dual manifest it's too expensive. Will be dirty cheap if they do, though.

Online Robotbeat

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Re: SpaceX fairing
« Reply #42 on: 02/14/2012 05:54 pm »
Keep in mind drag losses are more significant for smaller rockets. Wouldn't make much of a difference for larger rockets (Falcon Heavy in particular).
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Offline baldusi

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Re: SpaceX fairing
« Reply #43 on: 02/14/2012 06:47 pm »
Keep in mind drag losses are more significant for smaller rockets. Wouldn't make much of a difference for larger rockets (Falcon Heavy in particular).
The Atlas V guide says that the GTO (1800m/s deficit) difference between a 400 and a 500 is almost 950kg. A 401 to a 501 is 700kg. Between a Delta IV (4,2) and a (5,2) is 1,076kg. I couldn't get the numbers on any other LV (the H-IIA didn't shows for same configuration, and the Ariane 5 doesn't offers 4m). Those are not trivial numbers. And going from 3.5tonnes to 4.5tonnes means reaching 35% vs 50% of the market.

Offline ugordan

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Re: SpaceX fairing
« Reply #44 on: 02/14/2012 06:53 pm »
Those are not trivial numbers.

Nor are they solely due to higher drag. A bigger fairing weighs more, there's also additional hardware for Atlas in the 5xx variant like the CFLR.

Online Robotbeat

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Re: SpaceX fairing
« Reply #45 on: 02/14/2012 06:59 pm »
Keep in mind drag losses are more significant for smaller rockets. Wouldn't make much of a difference for larger rockets (Falcon Heavy in particular).
The Atlas V guide says that the GTO (1800m/s deficit) difference between a 400 and a 500 is almost 950kg. A 401 to a 501 is 700kg. Between a Delta IV (4,2) and a (5,2) is 1,076kg. I couldn't get the numbers on any other LV (the H-IIA didn't shows for same configuration, and the Ariane 5 doesn't offers 4m). Those are not trivial numbers. And going from 3.5tonnes to 4.5tonnes means reaching 35% vs 50% of the market.
The larger fairings are also pretty heavy. In the case of Atlas V, the larger fairing covers the entire second stage as well. 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!).

My statement about how drag losses are less significant for larger rockets is supposed to be a general statement, anyway. Falcon 1 has far higher drag losses than Saturn V, for instance. Gravity losses tend to be a much bigger concern for larger rockets. In some ways, gravity losses and drag losses trade against each other... if your rocket has a relatively low T/W through the lower atmosphere, it will have lower drag losses but higher gravity losses. If it's a small solid-rocket-based launcher, you'll have high drag losses but low gravity losses.

At the large end of the spectrum for mostly-cylindrical rockets, the taller your rocket (for the same propellant and chamber pressure), the larger your chamber throat must be in relation to your rocket's diameter, thus it's harder to get as much T/W (so will tend to have higher gravity losses), but a taller rocket also has a smaller frontal-area-to-total-mass ratio so its drag losses are less than for a shorter rocket. That's the general picture for largish rockets, at least.
« Last Edit: 02/14/2012 07:06 pm by Robotbeat »
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Offline pippin

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Re: SpaceX fairing
« Reply #46 on: 02/14/2012 07:07 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.

Online Robotbeat

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Re: SpaceX fairing
« Reply #47 on: 02/14/2012 07:09 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.
« Last Edit: 02/14/2012 08:30 pm by Robotbeat »
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Offline pippin

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Re: SpaceX fairing
« Reply #48 on: 02/14/2012 07:13 pm »
To be honest, I'm not entirely sure whether Falcon 9's fairing is carbon fiber or carbon composite, just that it isn't aluminum and is claimed (by Elon) to be lighter than competing ones.

Well, the question is whether it's already in existence so one could tell at all :)
Ariane 5 and Atlas 5 use carbon composite, though, and RUAG (the maker of these fairings) has quite a position in the market and they didn't get it for their overly heavy designs.

Might well be that SpaceX has a prototype that's the lightest one around but then the next question is whether it meets the same requirements as the more heavy competing ones.
« Last Edit: 02/14/2012 07:15 pm by pippin »

Offline kevin-rf

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Re: SpaceX fairing
« Reply #49 on: 02/14/2012 07:16 pm »
Light, but strong enough to handle the loads at maxQ. That is the danger for any new light weight fairing design.
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Offline pippin

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Re: SpaceX fairing
« Reply #50 on: 02/14/2012 07:18 pm »
Plus all the vibration modes. Which might as well be an advantage for SpaceX since they don't use solids.

Offline baldusi

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Re: SpaceX fairing
« Reply #51 on: 02/14/2012 07:20 pm »
Originally I had stated that they could earn some extra 100kg to 200kg from a smaller fairing. Looking into those numbers, even if not so critical, I'm inclined to think that it's going to be more than that.
And let's remember that the F9 is supposed to have a T/W of 1.45, so the drag losses should have an impact. Of course, if the new F9 block II has a T/W of 1.19, as it briefly appeared on their site after the FH presentation, then it might be less critical. But it sure should weight less, that should give some saving.

Offline oldAtlas_Eguy

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Re: SpaceX fairing
« Reply #52 on: 02/14/2012 08:27 pm »
The interstage seems to be a carbon fiber aluminum core composite. So the faring would probably be somthing similar.

Offline Antares

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Re: SpaceX fairing
« Reply #53 on: 02/15/2012 01:57 am »
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.

I'd bet a steak dinner that SpaceX isn't entirely sure what it's made of either. ;)
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Offline Kabloona

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Re: SpaceX fairing
« Reply #54 on: 02/15/2012 09:21 am »
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.

I'd bet a steak dinner that SpaceX isn't entirely sure what it's made of either. ;)

LOL. And after the Taurus debacle, one wonders if Orbital is sure what the Antares fairing is made of.

Offline go4mars

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Re: SpaceX fairing
« Reply #55 on: 02/15/2012 05:00 pm »
  JWST has also demonstrated just how problematic and elaborate folding TPS can be.
No, it hasn't.  Point out one problem.
Relative Price. 
http://forum.nasaspaceflight.com/index.php?topic=23637.msg677193#msg677193

Now that it's $8.5 billion instead of $6.5, it's an even bigger problem. 
« Last Edit: 02/15/2012 05:01 pm by go4mars »
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Offline baldusi

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Re: SpaceX fairing
« Reply #56 on: 02/15/2012 05:19 pm »
  JWST has also demonstrated just how problematic and elaborate folding TPS can be.
No, it hasn't.  Point out one problem.
Relative Price. 
http://forum.nasaspaceflight.com/index.php?topic=23637.msg677193#msg677193

Now that it's $8.5 billion instead of $6.5, it's an even bigger problem. 
Do you think that it went out of budget because of the opening system?
I really doubt it. They could have stated that they needed a bigger fairing. I'm sure Raug and Arianespace would gladly make a bigger fairing for less than 200M. Of course ULA could have pitched a Delta IV plus a bigger fairing. Both LV have 5m bodies, so they could go to 8.4m relatively easy. Again, somewhere between 100M to 500M extra cost.
But that was not the point. The JWST has specification so out of what's currently available, that they had to use small mirrors and active optics. They had to qualify everything for 20K working temperature (including sensors). They had to develop the shade.
When you look at all, the opening system wasn't that much extra complication, since they needed to be able to adjust all the mirrors due to thermal expansion. And as I said, going monolithic could have meant at most 500M in vehicle development. So it was not the cause. The problem was that every single piece was a couple of technology generation ahead of the state of the art. The folding mechanism was simply never done, not ahead of the technology curve. In fact, I would ask you how do they fit comm sats and spy sats within current fairings.

Offline go4mars

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Re: SpaceX fairing
« Reply #57 on: 02/15/2012 06:02 pm »
Do you think that it went out of budget because of the opening system?
NASA claim.  Not mine.   

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090043018_2009044057.pdf

"Ares V would enable the launch of a simpler 6-meter monolithic mirror with the same or better light-gathering power while producing a 30 per cent savings in overall mission development cost by reducing the need for stowage and deployment hardware and testing. "
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Offline baldusi

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Re: SpaceX fairing
« Reply #58 on: 02/15/2012 06:14 pm »
Do you think that it went out of budget because of the opening system?
NASA claim.  Not mine.   

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090043018_2009044057.pdf

"Ares V would enable the launch of a simpler 6-meter monolithic mirror with the same or better light-gathering power while producing a 30 per cent savings in overall mission development cost by reducing the need for stowage and deployment hardware and testing. "
NASA is big. That is the claim of the ones trying to save the sinking ship that was Ares V when it was clear it was going to be cancelled. Ask the actual engineers and scientist doing telescopes.

Offline go4mars

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Re: SpaceX fairing
« Reply #59 on: 02/15/2012 06:32 pm »
NASA is big. That is the claim of the ones trying to save the sinking ship that was Ares V when it was clear it was going to be cancelled. Ask the actual engineers and scientist doing telescopes.
Are you proposing that they made up the 30% number?   
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