That's for the airframe. They were and probably are not yet sure how many reflights they can do with that. But there is the statement of Elon Musk about the engines. 40 cycles, which was assumed to be ignitions between refurbishments. But the engines have no meaningful limit of use. After 40 cycles some highly stressed components need to be replaced.
Quote from: sanman on 01/03/2016 09:07 pmSo on the one hand there's the idea that across multiple reflights, you keep the same engines in the same spots, using them in exactly the same way again and again. This means that the 3 engines used for multiple burns within a flight are a bit more suped up - particularly that central engine that gets used for landing.Then on the other hand, there's the idea that you "rotate the tires" across multiple reflights - swapping the less used engines in place of the more used ones, so that they all get their fair share of wear and tear.Which way is the better way out of those 2 approaches - and why? Are there any other approaches that might be better still? Why?Early on SpaceX may be taking engines off at a much higher rate to validate empirically how they're doing, so let's ignore that for right now.Once they have validated engine reliability, I'm not familiar with how airlines handle this but I would imagine that you would not remove an engine unless there is a reason you don't want it to fly on the next flight.Over time you're going to end up with a mix of used engines, including the potential for some to be flown on new stages, so "rotating" them is not going to add much value, especially the eight outboard engines.
So on the one hand there's the idea that across multiple reflights, you keep the same engines in the same spots, using them in exactly the same way again and again. This means that the 3 engines used for multiple burns within a flight are a bit more suped up - particularly that central engine that gets used for landing.Then on the other hand, there's the idea that you "rotate the tires" across multiple reflights - swapping the less used engines in place of the more used ones, so that they all get their fair share of wear and tear.Which way is the better way out of those 2 approaches - and why? Are there any other approaches that might be better still? Why?
Quote from: Lars-J on 01/03/2016 06:31 pmThe center engine is used in all burns. And as far as why you would use the same other two engines for multiple burns - we don't know - but it has been assumed, since when each engine has a its own supply of ignition fluids (TEA/TEB) it makes more sense to just give 3 engines more of it instead of giving all engines the same restart capability. (It is nasty dangerous stuff) But I could be wrong on the last point.I am assuming something else. All engines are ground started from an external supply. So why would they not be air started by a common supply? It would be a pure software command, which engine restarts. That would make it possible to use the outer engines in turn. Only the center engine would need to be replaced/refurbished sooner. Unless there are other reasons in the geometry of the stage to always use the same engines.
The center engine is used in all burns. And as far as why you would use the same other two engines for multiple burns - we don't know - but it has been assumed, since when each engine has a its own supply of ignition fluids (TEA/TEB) it makes more sense to just give 3 engines more of it instead of giving all engines the same restart capability. (It is nasty dangerous stuff) But I could be wrong on the last point.
Though I've not seen any mention of it, from a reusable /refurb perspective, I wonder if it would make sense to get away from high pressure gas, and He altogether by going in some IVF path? Then you can drop the COPV He bottles and associated struts
Umm, right now I doubt that structural issues will be the limiting factor for the number of reuses. Right now a significant number of their payloads need to use the margin they have for landing the stage so it can't be reused. Judging by their manifest that makes it unlikely they're going to get more than two or three reflights out of a core so the discussion is quite moot for F9.I know, those here who haven't really done the maths on how much reuse saves (but that's another thread) think those payloads will go on a heavy but given the cost associated with that this is unlikely.So... Nice theory exercise for MCT and BFR but not really relevant for F9...
I know, those here who haven't really done the maths on how much reuse saves (but that's another thread) think those payloads will go on a heavy but given the cost associated with that this is unlikely.
Their manifest says otherwise.And no, it's not their concept to use heavy for everything. They have stated that they might eventually do that but everything beyond that is amazing people fantasy.
Right now a significant number of their payloads need to use the margin they have for landing the stage so it can't be reused.
Quote from: pippin on 01/04/2016 03:37 amRight now a significant number of their payloads need to use the margin they have for landing the stage so it can't be reused.... It has yet to be established just how heavy a payload the F9FT can throw to GTO and still carry legs and reserve propellant for a downrange landing. A barge landing is estimated to require a ~15% performance margin. I am guessing we won't really know for sure immediately as the next GTO payload (SES-9) is quite heavy.According to Wiki the heaviest bird F9 has thrown to GTO was TurkmenAlem52E/MonacoSAT: https://en.wikipedia.org/wiki/TurkmenAlem52E/MonacoSAT at 4707kg. According to Gunter's, SES-9 is 5330kg, so it will be the heaviest payload to GTO for F9 to date.
From back-of-the-envelope calculations of the four improvements (cooled fuel, full thrust, bigger second stage, better ISP of second stage), and Musk's comments about staging velocity, ( https://forum.nasaspaceflight.com/index.php?topic=34077.msg1463298#msg1463298 ) it's possible SES-9 could be recoverable, particularly if they are willing to accept an 1800 m/s deficit to GEO (apogee at GEO, no inclination reduction).
Total work days from recovery is at 14 days so far with 6 days (weekends + holidays) as probably no work = 8 work days of single shift crew.Question becomes how many average crew over the period 10,20,50 100? My guess is at 20 only so far
That would be a current balance for refurbishment cost at 8 days X $740 per day X 20 workers + $50,000 in equipment charges and other charges = $168,400 so far.Refurbishment labor costs (1 to 2 months of 50 crew)+misc costs $.5-1MReplacement parts? $0-10M [largest ticket item are engines]3 engines swapped out is only a charge of $3-4.5M plus $1M in other parts brings a probable refurbishment cost to a range of $1.5M to $6.5M.
Falcon 9/Heavy is probably not going to change since that would take significant engineering resources for a product/system that is already "good enough".
Of course that assumes that the He pressurization system doesn't continue to be their Achilles Heal...
Quote from: guckyfan on 01/03/2016 07:24 pmQuote from: Lars-J on 01/03/2016 06:31 pmThe center engine is used in all burns. And as far as why you would use the same other two engines for multiple burns - we don't know - but it has been assumed, since when each engine has a its own supply of ignition fluids (TEA/TEB) it makes more sense to just give 3 engines more of it instead of giving all engines the same restart capability. (It is nasty dangerous stuff) But I could be wrong on the last point.I am assuming something else. All engines are ground started from an external supply. So why would they not be air started by a common supply? It would be a pure software command, which engine restarts. That would make it possible to use the outer engines in turn. Only the center engine would need to be replaced/refurbished sooner. Unless there are other reasons in the geometry of the stage to always use the same engines.You might be right. We don't know if there is a central source of TEA-TEB, or if the engines have their own supply.