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?
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.
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?
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).
Those are not trivial numbers.
Quote from: Robotbeat on 02/14/2012 05:54 pmKeep 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.
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!).
Quote from: Robotbeat on 02/14/2012 06:59 pmFalcon 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 aluminum and is claimed (by Elon) to be lighter than competing ones.
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.
Quote from: Robotbeat on 02/14/2012 07:09 pmTo 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.
Quote from: Ben the Space Brit on 02/14/2012 04:22 pm JWST has also demonstrated just how problematic and elaborate folding TPS can be.No, it hasn't. Point out one problem.
JWST has also demonstrated just how problematic and elaborate folding TPS can be.
Quote from: Jim on 02/14/2012 04:39 pmQuote from: Ben the Space Brit on 02/14/2012 04:22 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?
Quote from: baldusi on 02/15/2012 05:19 pmDo 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.