To go up to 13200kg to Mars seems to require something more than just cross-feed, as does 21,200kg to GTO.
My only thought is that perhaps the Methane stage is further along then we think, to the point where they won't put in the effort to make a 2-engine kerolox upper stage since they know they'll debut the methane engine on the US, say within 2 years, and the current US is good enough for the time being.
I just don't believe the 21 and 53 ton figures are based on anything that's not as described.They must believe they can achieve that performance with the system as advertised, and at the advertised price.
Quote from: MikeAtkinson on 08/04/2013 08:15 pmTo go up to 13200kg to Mars seems to require something more than just cross-feed, as does 21,200kg to GTO.I was surprised by that too. The ~21mT had been bandied around before, but I thought it had been superseded. As for explanations for the increased performance, so far I've seen a tank stretch, higher chamber pressure, higher expansion ratio and cross-feed. It kind of worries me that they're changing so much all at once before we've had even a single F9 flight to GTO. What's driving all this? Previously I thought it was performance shortfalls to GTO, but if the 21mT is real, that can't be the case.
It also all makes sense with an eye on reusability. If they really can pull that off, it will be first stage only, at least for quite a while. That could (_if_ it also works from a business POV) make using FH less of a cost driver and in that scenario it actually makes sense to have the expendable second stage as simple as possible. If, of course, they can really recover the FH center core, too, which I still don't see how and they seem to hint at that they don't really have a plan, either.
Quote from: MikeAtkinson on 08/05/2013 08:24 am"I don't understand what is driving this either. Getting 53 tonnes to LEO and 21.1 tonnes to GTO both seem on the edge of what is possible, doing both with the same upper stage is in my opinion impossible. The GTO/TMI stage would need about 30 tonnes extra propellant for GTO and 40 tonnes extra for TMI. A tank stretch makes sense. They already do the same bodies and tanks at three or four different lengths. What's the problem with five or six?
"I don't understand what is driving this either. Getting 53 tonnes to LEO and 21.1 tonnes to GTO both seem on the edge of what is possible, doing both with the same upper stage is in my opinion impossible. The GTO/TMI stage would need about 30 tonnes extra propellant for GTO and 40 tonnes extra for TMI.
From KSC it would be difficult to recover the core booster stage, but from Brownsville I think they could pick a convenient island down range, Bahamas to Puerto Rico to land the FH core.
Quote from: pippin on 08/04/2013 09:47 pmIt also all makes sense with an eye on reusability. If they really can pull that off, it will be first stage only, at least for quite a while. That could (_if_ it also works from a business POV) make using FH less of a cost driver and in that scenario it actually makes sense to have the expendable second stage as simple as possible. If, of course, they can really recover the FH center core, too, which I still don't see how and they seem to hint at that they don't really have a plan, either.From KSC it would be difficult to recover the core booster stage, but from Brownsville I think they could pick a convenient island down range, Bahamas to Puerto Rico to land the FH core.
Quote from: Roy_H on 08/05/2013 02:51 pmQuote from: pippin on 08/04/2013 09:47 pmIt also all makes sense with an eye on reusability. If they really can pull that off, it will be first stage only, at least for quite a while. That could (_if_ it also works from a business POV) make using FH less of a cost driver and in that scenario it actually makes sense to have the expendable second stage as simple as possible. If, of course, they can really recover the FH center core, too, which I still don't see how and they seem to hint at that they don't really have a plan, either.From KSC it would be difficult to recover the core booster stage, but from Brownsville I think they could pick a convenient island down range, Bahamas to Puerto Rico to land the FH core.Why would anyone wants to have a flight path between Cuba and Florida. There are just too many populated areas along the flight path.It would be better have a flight path between the Yucatan peninsula and Cuba mostly over water.It will probably be an oceanic landing platform of some sort for core recovery. Think most if not all the governments on small Caribbean Islands really wants to explain why a ballistic vehicle heading their way is a good thing.
. As the fairing gets large in diameter, the 53 tonne number will shrink due to increased drag.